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CLINICAL INVESTIGATIONS ON SQUINT

A MONOGRAPH

BY

DR. C. SCHWEIGGER,

PROFESSOR OF OPHTHALMOLOGY AT THE UNIVERSITY OF BERLIN

TRANSLATED FROM THE GERMAN

BY

EMILY J. ROBINSON

EDITED BY

GUSTAVUS HARTRIDGE, F.R.C.S.

LONDON
J. & A. CHURCHILL
11, NEW BURLINGTON STREET
1887




TRANSLATOR'S PREFACE


The subject of Squint is so interesting that we venture to think an
English rendering of this exhaustive monograph will be acceptable to
many ophthalmic surgeons and students.

While adhering as far as possible to the spirit and style of the
original we have not hesitated here and there to give a somewhat free
translation. This has been partly necessitated by the difficulty of
finding an exact equivalent in English for all the terms used in the
original text.

In the German Edition the old system of inches is used. We have (with
the consent of the author) altered these to the dioptric system.

                                        E. J. R.
                                        G. H.




PREFACE


_Amicus Plato, amicus Socrates, magis amica veritas._ May my friends and
colleagues, whose views differ from mine, read the following
observations without prejudice. A fact, which does not agree with the
system, is generally worth more than theory, still it is very difficult
for even the most important fact to find recognition if it contradicts
received opinion. For theories and dogmas are narcotics, which are
necessary to men; some flatter themselves by composing them, while
others content themselves by satisfying their own craving for a creed.
Reasonably applied, they may be useful, but the boundary line is only
too easily over-stepped. It is the task of science to observe also
whether theories correspond with the progress of facts. The present
reigning theory on strabismus will have to submit to various
limitations; on the other hand, we are ready to leave to the scholastic
science of medicine and its followers certain dogmas which remain
unproved and which have nothing but the fact of their existence to
recommend them.

The small compass of the following treatise proves that it was not
intended to exhaust the rich literature on the subject; I have only
referred to the same where it appeared to me necessary for the interest
of the work in hand.

Above all, it has been my endeavour to treat the subject of this
treatise (which occurs so frequently in practice) in a way intelligible
to every physician, at the same time, however, to bring sufficiently
into notice those facts and views which are of value to my special
colleagues.

                                  C. SCHWEIGGER.

                                  BERLIN.




INDEX TO CONTENTS.


INTRODUCTION.                                                    PAGES

Ordinary use of the word squint and its meaning. Apparent
squint. Paralytic and typical squint. Law of association.
Squint angle and linear measure of the deviation.
Permanent, periodic, latent, monolateral, and alternating
squint                                                             1-8

CONVERGENT SQUINT.

Donders' theory and the test of it by statistics. Limits
of error in the subjective and objective determination of
hypermetropia. Statistics of convergent squint. Hypermetropia
and favouring circumstances. Participation
of the accommodation. Preponderance of the interni
and insufficiency of the externi. Nebulae of the cornea.           9-26

PERIODIC CONVERGENT SQUINT.

In myopia, emmetropia, and hypermetropia. Intermittent
squint. Accommodative squint                                     27-35

CONVERGENT SQUINT IN MYOPIA                                      36-38

SQUINT FROM PARALYSIS OF THE ABDUCENS                            39-40

HYSTERICAL SQUINT                                                41-43

DIVERGENT SQUINT.

Absolute and relative divergence. Statistics of divergent
squint. Causes                                                   44-49

DYNAMIC SQUINT, INSUFFICIENCY OF THE INTERNI AND
MUSCULAR ASTHENOPIA.

Diplopia and power of overcoming prisms. Facultative
divergence. Dynamic absolute divergence. Parallel
strabismus. Relative divergence in myopia. Muscular
asthenopia. Dynamic relative divergence. Treatment
of muscular asthenopia                                           50-63

BINOCULAR VISION IN SQUINT.

Single vision in squint. Theory of exclusion. Forms of
binocular vision in squint                                       64-74

VISUAL ACUTENESS OF THE SQUINTING EYE.

The trial of vision and its results. Appearance, diagnosis.
Peculiarities and statistics of congenital defective vision.
Relation of the same to defective vision in squint               75-104

CURE OF SQUINT.

Spontaneous cure. Voluntary loss of the habit. Cure of
convergent squint by means of convex glasses. Strabotomy.
Tenotomy. Advancement. Result of the
operation and choice of methods. After-treatment by
means of influence on the ocular muscles and on the
accommodation. Aim of more extended results of the
operation. Artificial strabismus. Operation for periodic
convergent squint. Strabotomy in homonymous diplopia.
Operation for squint after paralysis of the abducens.
Operation for divergent squint and for periodic divergence.
Degree of the result of the operation. Determination
on the age best suited for operation                           105-141




SQUINT

INTRODUCTION


By squinting, in the German vocabulary, is understood every oblique
direction of the visual axes. We prefer that the eyes which turn towards
us should do so in a straight line, and feel it to be something ugly and
out of harmony, if anyone squints at us. AEsthetic feeling is, however,
too individual and uncertain a guide to be laid down as a foundation for
the decision of questions of medicine. Parents have repeatedly brought
to me children said to squint, when frequent and careful examination of
them showed normal position of the eyes and perfect binocular vision;
the over-anxious parents had taken mere physiological convergence or
side glances for squinting.

On the other hand, cases appear in which such a strong semblance of
squinting is present, that at the first glance one cannot say whether
absolute fixation takes place or not. A very simple examination suffices
to determine these doubts:--Cause the patient to gaze at a certain point
on the horizon and cover first one eye and then the other. If the
covered eye remains stationary, no squint exists, but if it is observed
that when giving one eye its freedom and covering the other, the first
must make a movement in order to fix the object to be looked at, it is
only a question of discovering whether the squint does not simply ensue
from the covering up of the eye. We will return to these cases at
greater length, in order to occupy ourselves now with the fact, that the
examination above referred to proves the non-existence of strabismus,
while appearance still allows us to suspect its existence.

This apparent contradiction finds its explanation in the fact that the
scientific notion of squinting is determined by the direction of the
visual axes. Strabismus is present when one eye only is directed to the
fixed point, while the visual line of the other eye deviates from it.

But we cannot see the direction of the visual line, we can only judge of
it from the position of the cornea. It is exactly that line which joins
the point fixed with the centre of the fovea centralis. We can determine
the position of the cornea by a perpendicular line passing through the
centre of the cornea; this does not coincide with the visual line but
deviates from it about 5 deg. outwards. In the case of parallel lines of
vision the corneae are directed slightly outwards, a position which we
are accustomed to consider as the normal one. If the angle formed by the
above-mentioned perpendicular and the visual line is larger than usual,
_i. e._ if the corneae move further outwards than usual, the unusual
appearance strikes us, and gives us the impression of a divergent
squint. The enlargement of this angle, which is usually indicated as
Angle a, is a peculiarity of the hypermetropic eye; and where we have an
apparent divergent squint we may expect to find also hypermetropia,
while an apparent convergent squint occurs occasionally in myopia of
high degree.

If we turn now to those cases in which a real deviation of the visual
line occurs, we must first consider the cause, and afterwards
distinguish it from paralysis of the ocular muscles. The faulty position
may be constantly present or it may only occur when the paralysed muscle
is called into action. It is almost invariably combined with double
vision; sometimes the latter is the prevailing symptom, whilst the
faulty position of the eye is in no way obtrusive, and can only be
proved by careful investigation.

In contrast to paralysis of the ocular muscles stands the typical
concomitant squint, in which the squinting eye normally accompanies the
movements of the other. Transitional forms may thus be brought about, in
some of which the paralysis recovers, with complete or almost complete
restoration of movement, but with continuance of the squint. On the
other hand, in concomitant strabismus, restriction of movement towards
the opposite side not unfrequently develops itself.

This impairment of movement has its origin generally in a want of use.
Those who squint have less need for movement, since one of their eyes is
already directed obliquely. In divergent strabismus this is apparent,
but in convergent strabismus the squinting eye governs the field of
vision on the side to which it turns. When the fixing eye is turned
towards the side of the squinting eye in convergent strabismus, the
latter, it is true, makes a concomitant movement, which does not,
however, bring it by a long way to the limit of the movement of which it
is capable. The defect of motion is therefore generally present in both
eyes, and is usually most marked in the squinting eye. Often, indeed,
there is present at the same time a congenital or acquired insufficiency
of the antagonistic muscle, but that want of use has also much to do
with it, is shown by the improvement of mobility that often follows even
short practice.

From the law of equal innervation, which governs the movements of the
eyes, it follows that the fixing eye lapses into the associated
deviation as soon as the squinting eye is directed straight forwards.
If, for example, a convergent squinting eye is put into fixation, an
innervation of the external rectus, with which just as strong an
associated contraction of the internal rectus of the other eye, is
called forth; the direction of the squint then, as well as the degree of
deviation, is transferred from one eye to the other. It is naturally the
same with divergent squint.

Squinting upwards or downwards seldom occurs as a symptom by itself;
more frequently it is associated with convergent or divergent squint.

According to the law of associated movements, when an eye squinting
upwards is put into fixation, the other eye should make a movement
downwards, as normally both eyes move together up and down, yet this is
not always the case. For example, when an upward deviation is present in
convergent squint, it not uncommonly follows that the secondary
deviation of the eye which usually fixes is also inwards and upwards;
only exceptionally in cases of deviation in height of the squinting eye
does the sympathetic movement take place without change of height.
Sometimes with deviation of height, I found combined a distinct rotation
of the eye, generally thus, that together with the movement upwards was
combined a rotation of the vertical meridian outwards and _vice versa_;
in fixing the eye a rolling inwards was combined with the movement
downwards. The other eye then usually showed a similar rotation (thus
the meridian of both eyes rotated simultaneously to the right or left),
but the deviation in height was not always the same.

The law of equal innervation requires in alternate fixation, first with
one eye, then with the other, that the same degree of deviation be
transferred to the non-fixing eye. When exceptions appear, and the
deviation in the two eyes is unequal, it is (provided the inequality has
not been caused by attempted operation, or is the result of paralysis),
usually to be explained by the fact, that an accommodative movement
takes place when we are expecting an associated one. For example, if
there is convergent squint and hypermetropia in both eyes, but more
hypermetropia in one than the other, in alternate fixation it will be
found that the least hypermetropic eye always undergoes the greatest
deviation, because in fixation with the more hypermetropic eye a
stronger effort of accommodation unites itself with a corresponding
innervation of the internal rectus, which is transferred equally to the
other and non-fixing eye. Thus it happens frequently in divergent
strabismus, when one eye is myopic, the other emmetropic. If the latter
fixes an object stationed near the "far point" of the myopic eye, the
internal recti and the accommodation act simultaneously; on the other
hand if the myopic eye fixes, it wants no accommodation and the
emmetropic eye sinks into divergence.

With regard to the immutability of the squint; it must not be understood
that the squint angle always remains the same with the same individual;
in most cases the amount of deviation varies, the squint is now less,
now greater; it is desirable however, to know the bounds within which it
fluctuates.

To determine the degree of the squint one can either ascertain the angle
of the squint, or use v. Graefe's so-called linear measure of deviation.

The squint angle is that angle, which the visual line of the squinting
eye encloses with the direction it ought normally to take--it may be
measured with the aid of a perimeter. The patient's head is so placed by
means of a chin rest, that the axis of the squinting eye is in the
centre of the arc of the perimeter; a distant point in the centre of the
field of vision is fixed. Behind the patient is a candle, the reflection
of which is thrown into the squinting eye by means of a plane mirror;
now slide the mirror along the arc of the perimeter, till the reflection
on the cornea stands in the centre of the pupil of the eye which is
under observation. The point which the mirror occupies on the arc of the
perimeter, indicates the squint angle. In deviation in height of the
squinting eye, bring the arc of the perimeter into the corresponding
direction and so measure at the same time the degree of deviation in
height. Were the method more exact than it is, one would be able to
measure the angle formed by the visual line and the axis of the cornea.

To find the linear measure of the deviation, cover the fixing eye and
allow the squinting eye to fix. Hold a millimetre measure close to the
under lid, so that a chosen portion of it stands under the centre of the
pupil; uncover the other eye and when the squinting eye returns to its
deviation, it can be seen over which point the centre of the pupil
stands, and the linear measure of the deviation is thus obtained. The
secondary deviation of the other eye is measured of course in the same
way. If, in consequence of amblyopia, the squinting eye possesses no
certain fixation, the measure may be so held that the _nil_ point of the
division coincides with the lower punctum, and then in unchanged
fixation the portion lying under the centre of the pupil is determined,
first in the sound and then in the squinting eye.

The execution of one or other of these forms of measurement is in every
case to be recommended, and if their exactness is not as perfect as can
be desired, still, on the other hand it should be remembered, that for
surgical treatment, an exact measurement of the deviation does not
possess the importance sometimes assigned to it, as in most cases the
squint angle shows considerable variations.

In a large number of cases these variations are so great, that a correct
position of the eyes alternates with a more or less considerable squint,
which as the case may be, appears seldom or often, sometimes only under
certain conditions, and sometimes quite unexpectedly (periodic squint).
In some cases stationary or permanent squint begins with the periodic
form, however, one must not conclude that periodic squint is invariably
the precursor of the permanent form. In by far the greater number of
cases periodic squint continues unchanged without ever becoming
permanent.

The transition from squint to the normal condition is formed by those
cases, in which the proper position of the eyes is maintained by a
desire for binocular single vision, while the elastic tensions of the
muscles are such, that squinting sets in as soon as binocular single
vision is rendered impossible (latent squint).

The squint is generally one sided (monolateral), for the eyes in this
case are usually of unequal value, and the best is always preferred for
use. The eye which has the acuter vision is always made use of when
something has to be carefully observed. But when the acuteness of vision
is equal, and one eye is emmetropic and the other hypermetropic, or if
both are hypermetropic but in varying degree, the most hypermetropic eye
is always the squinting one; for with a greater power of accommodation
it does not accomplish more than the emmetropic or less hypermetropic
one with slighter expenditure of strength. Why should a man strain his
accommodation when no advantage is thereby gained?

In most cases the squinting eye has also an available power of vision
and is on that account used for fixing objects which lie in the
direction of its visual axis; it can also be made to fix objects in
front, this occurs as soon as the other eye is covered; it remains as
the fixing eye till the next blinking of the lids, or movement to
another object for fixation, or till both eyes are closed for a short
time, when it returns to its former deviation.

A true alternating strabismus, _i. e._ alternate use of first one eye
and then the other to fix objects straight ahead, only occurs when both
eyes are of equal value as regards weakness and acuteness of vision, or
when one is more conveniently used for near, and the other for distant
vision. In these circumstances one eye is always short-sighted and is
used for near objects, while the other is emmetropic (or in less degree
near-sighted or long-sighted) and is preferred for distant things. The
reason for the alternation lies in the necessity for the act of vision
itself; it begins regularly whenever distant and near objects are
alternately fixed. Alternating squint is usually divergent, with short
sight on one side, still convergent strabismus may occur under these
conditions.




CONVERGENT SQUINT


To Donders belongs the merit of having pointed out the presence of
hypermetropia in about two thirds of all cases of convergent strabismus.
The fact is undeniable, the theories built upon it are doubtful. Donders
declares no other conclusion to be possible, than this, that the
hypermetropia is the cause of the squint. "To see clearly, the
hypermetrope must accommodate vigorously for each distance. In looking
even at distant objects he must overcome his hypermetropia by exerting
his accommodation, and in proportion as the object approaches him, he
must add to it as much accommodation as the normal emmetropic eye would
use. The inspection of near objects requires then a special amount of
exertion. There exists, however, a certain connection between
accommodation and convergence of the visual lines. The stronger one
converges the more one has to put into action the accommodation. A
certain tendency to convergence cannot then be absent during any effort
of the faculty of accommodation."

Right as these conclusions may appear, and as they really are, as far as
emmetropia is concerned, they leave out of sight the fact, that the
connection between accommodation and convergence is an individual and
acquired one. The weak side of the theory lies in the fact, that that
relation between accommodation and convergence which is developed in
emmetropia in consequence of daily practice, is given as being in itself
normal and the one for all conditions of refraction. The relation
between accommodation and convergence depends on the state of
refraction, and alters with any of its changes in the course of life. In
proportion as myopia is gradually developed in originally existing
emmetropia, myopes learn to converge to the neighbourhood of their far
point without allowing their accommodation to come into action. With
hypermetropia it is just the contrary. By far the greater number of
hypermetropes learn to use their accommodation without difficulty, even
with parallel lines of vision, for they see distant objects clearly,
while they neutralise their hypermetropia by accommodation, without
sacrificing the parallelism of the visual lines.

It is important to notice that Donders' theory makes convergent squint
appear as almost a necessary consequence of hypermetropia. According to
Donders, hypermetropes have to choose between the advantages of
binocular vision with an effort of accommodation corresponding to the
hypermetropia, and relief to the accommodation by too strong convergence
with the sacrifice of binocular fixation; and the decision will tend to
the latter condition, if circumstances exist which deprecate the value
of binocular vision.

The demand for binocular fusion of the retinal images will be greater if
both eyes are of equal value; on the contrary it will be less, if the
retinal image or the visual acuteness of one eye is less perfect than
that of the other. Varieties of weakness; when one eye always receives a
clear retinal image, the other an indistinct one; lowering of the visual
acuteness of one eye by nebulae, astigmatism or any other cause.
According to Donders all these furnish a reason why, in existing
hypermetropia, binocular fixation should be abandoned and convergent
strabismus developed.

It cannot be denied that the relation existing between convergent
strabismus and hypermetropia may be as Donders represents it; the only
question is, whether it really is so. A theory may appear very
acceptable, and may rest on a firm physiological basis; it will,
however, be more perfect if it answers to facts. Physiological
possibility is not always pathological reality, for other unusual causes
besides physiological ones acquire value, and so things become
pathological. If Donders' theory is right, convergent strabismus must
really begin, as soon as double hypermetropia meets with causes which
depreciate the value of binocular vision. The theory may be tested then
by statistics, which confront the cases of hypermetropia and convergent
strabismus with those cases in which hypermetropia meets with Donders'
conditions and normal binocular vision still remains.

The statistics, which I have collected, relate to all the cases which
have appeared in my private practice during the last ten years. The
number would be much more considerable if I had included the patients of
the University Clinic; however, the reliability of the single elements
of which the statistics are composed was to me more important than the
number. In my private practice I have myself examined every case with
reference to these statistics for at least five years.

In a large clinic, where more than 5000 new patients annually come under
treatment, one must frequently content oneself by satisfying the demands
of the moment; thus the sources of inaccuracy in the statistics would be
augmented.

Included in the statistics were not merely the cases which came under
treatment for squint, but all in which squinting was present or those in
which it could be objectively proved (for example, by scars left by
previous operations for squint), that squint had formerly existed.

Further, in the following statistics, only those cases were included,
where an exact determination of the amount of error was possible; in
most cases this was also verified objectively with the ophthalmoscope.
In many cases, especially in children, the objective determination of
refraction alone is possible, and is practicable only with the greatest
difficulty and by the use of atropine.

Those cases deserve particular mention, in which it remained doubtful
whether hypermetropia of slight degree or emmetropia was present. Even
in full visual acuteness it is not unusual that with weak convex glasses
(of less than a dioptre) binocular vision is just as clear as with the
naked eyes, while in monocular investigation convex glasses cause a
slight indistinctness of vision. Are we to recognise hypermetropia here
or not? Opposed to the objection that in covering one eye the
hypermetropia is more easily neutralised by accommodation, stands the
observation that binocular is, as a rule, clearer than monocular vision,
wherefore, in the usual method for testing the sight, unless special
precautions are taken, full binocular visual acuteness does not prove
the presence of absolutely distinct retinal images. These doubts arise
much oftener in lowered visual acuteness. All conclusions which we
derive from visual acuteness become very inexact as soon as it is
lowered. In such cases, in determining anomalies of refraction we are
accustomed to consider the strongest convex--relatively, the weakest
concave glass, with which the visual acuteness individually present is
reached, as the most correct expression of the hypermetropia or myopia,
and with good reason if it is a case of ordering spectacles, as all
sources of error in the method of examination are then avoided as far as
possible; but it is quite another question if in such cases an exact
measurement of the amount of error is required solely for diagnostic
purposes; investigation with the ophthalmoscope is then alone decisive
and furnishes proof at the same time of how unreliable the determination
of the error by testing the vision is, in cases of short sight. One can
realise this most readily in cases of myopia with congenital amblyopia;
one gets frequently with the most exact correction possible of the
objectively determined myopia no better visual acuteness than with a
very imperfect one. In one case, for instance, which I have repeatedly
examined in the course of years, the degree of myopia determinable by
means of the ophthalmoscope amounted to at least 6.5 D., while the
weakest concave glass with which the full visual acuteness of 5/24 was
attainable was 2.5 D. Under these circumstances, if one relies merely on
the trial of vision, the degree of myopia appears too small, that of the
hypermetropia, on the contrary, just as much too great.

But even the ophthalmoscopic diagnosis of refraction has its limits of
error. It is a question of determining the conditions under which the
image of the fundus of the eye still appears distinct. We will except
those circumstances which prevent our obtaining a clear erect image of
the fundus of the eye, as, for example, high degrees of astigmatism,
nebulae, &c.--even under normal circumstances the fundus of the eye does
not always present such sharply-defined lines, that one could form a
perfectly safe opinion from the clearness of the image.

When we call the ophthalmoscopic diagnosis of refraction objective, we
only mean to say that we count the subjective opinion of the patient to
be of less value, than that of the physician who examines him. The
determination of the glass even, with which we believe we are able
distinctly to see the fundus of the eye, is also an objective one.
Whoever, for instance, is firmly convinced that convergent strabismus
depends on hypermetropia, will, in doubtful cases, very easily carry his
subjective conviction into the objective examination, and will still see
clearly the fundus of even an emmetropic eye with a weak convex
glass--the objective signs for the clearness of the image have no
absolutely defined limits. But apart from this, other sources of error
are possible. A person using the ophthalmoscope, for instance, who,
without knowing it--and such a thing may happen--possesses a slight
degree of latent hypermetropia, will find his own hypermetropia
everywhere, just also as a myope, who deceives himself slightly about
the degree of his myopia in the calculation of the ophthalmoscopic
diagnosis of refraction, lays rather too high a value on his own myopia.

Finally it must be added, that if the ophthalmoscopic estimation of
refraction is to be exact, mydriasis by atropine is required, when, as
is known, even emmetropic eyes may show a slight degree of
hypermetropia. Enough, we must not over-rate the value of the objective
determination of the error of refraction, and I would estimate the limit
of error at half a dioptre at least. If the examination is rendered more
difficult, as is frequently the case with children, by a restless and
impatient demeanour of the patient, even the objective diagnosis may
afford very doubtful results; such cases were, of course, excluded from
the statistics. Moreover, ophthalmoscopic determination of the error in
convergent strabismus is specially difficult, for one cannot advise the
patient as to a suitable direction for the eye not under investigation.
It is generally best to keep the eye not under investigation closed.

In practice it is immaterial whether emmetropia or a minimum degree of
hypermetropia is present; for statistics essentially devoted to
theoretical questions it seemed more suitable to unite these cases in a
separate group.

Accurately taken, the statistics should give the condition of refraction
at the age at which the squint begins. But, if there is a thankless
task, it is that of examining the erect image in children from two to
three years of age. To furnish accurate results this method requires a
certain tractability on the patient's side, which is never present at
this age, and not always in adults. A number of the cases surveyed in
the following table also came under observation long after the squint
commenced, and in some short-sighted persons in particular, the degree
of myopia at the time when squinting began, may have been less than it
was at the time of the examination.

Further, it seemed to me desirable to keep periodic, separate from
permanent squint; this, however, could not be accomplished with
exactness. It may easily happen that children with periodic squint
always squint just when one sees them, and in those cases which had
already been operated on when they came to be examined, it was quite
impossible to determine whether periodic or permanent squint had
formerly been present. Therefore I have represented separately in each
particular group the number of those previously operated on.

In the following table the refraction of the fixing eye and the visual
acuteness of the squinting eye are given. In alternating squint the
refraction of the emmetropic eye was taken, as determining it for
insertion in the lower division of the statistics.

A. Convergent squint with myopia:
   1. Slight myopia to M. = 1.75 D.
        (_a_) Permanent squint 11 cases (3 previously operated
      on). Anisometropia in 2 cases (one with M.
      1.25 D. of the fixing, M. 4 D. of the squinting eye;
      the other with M. 1.25 D. of the fixing, H. 4 D. and
      V. = 1 of the squinting eye). The examination of
      the visual acuteness of the squinting eye showed:
    V. more than 1/7              4 cases.
    V. 1/12 - 1/18                1 case.
    V. 1/24 - 1/36                1 case.
    V. Less than 1/36             4 cases (among them
                                    one with H. 2 D.
                                    in the squinting eye.)
    V. indeterminable             1 case.

        (_b_) Periodic squint 2 cases with very slight anisometropia
      and good vision.
  2. M. 2 D. to M. 3 D. 11 cases, all permanent (6 cases
          previously operated on), anisometropia with
          good vision in both eyes in 2 cases (in both, the
          less myopic eye squints). V. of the squinting
          eye more than 1/7 in 6 cases.
    V. 1/12 - 1/18                1 case.
    V. 1/24 - 1/36                2 cases.
    V. less than 1/36             2 cases (one with H = 5 D).
  3. M. 3.5 D. to 6 D.
           (_a_) Permanent 11 cases (one previously operated
         on). Anisometropia in 2 cases, of which one consisted
         of alternating squint, while the other possessed
         in the fixing eye M. 4 D., in the squinting one M. 7.5
         D. with good vision on both sides.
    V. more than 1/7              7 cases.
    V. 1/24                       1 case.
    V. 1/36                       1 case (in fixation with this
        eye; the visual axis shows a linear deviation of 2 mm.
        The presence of emmetropia is detected with the ophthalmoscope).
          Two cases were excluded from the statistics of vision, one on
        account of congenital capsular cataract, covering almost the
        whole pupil area, the other on account of choroiditis of the
        macula lutea.
        (_b_) Periodic squint 4 cases with good vision,
      anisometropia in 2 cases.
  4. M. 6.5 D. and more.
      (_a_) Permanent 11 cases, among them 9 with V.
    more than 1/7, 2 excluded from the statistics, one on
    account of complication with corneal nebulae, cataract,
    &c., the other possessed in the fixing eye M. 6.5 D.
    V. = 10/70 and slight nystagmus, in the squinting eye
    a smaller amount of sight not accurately noted, and
    strong nystagmus in fixing with this eye.
      (_b_) Periodic squint in 4 cases with good vision.
  5. Myopia with nystagmus and congenital amblyopia
         on both sides, 2 cases (not included in the
         statistics of vision). Altogether 56 cases, among
         them 10 with periodic squint.

B. Convergent squint in emmetropia, including simple
    myopic astigmatism, 98 cases.
        (_a_) Permanent 81 cases (13 previously operated
      on). Visual acuteness more than 1/7 in 44 cases. V.
      less than 1/7 to V. = 1/12 6 cases; V. less than 1/12 to
      V. = 1/36 20 cases; V. less than 1/36 7. Excluded from
      statistics of vision 4 (3 on account of complications,
      1 on account of lack of accurate information).
        (_b_) Alternating convergent squint with emmetropia
      in one, myopia in the other eye, 4 cases. The degree
      of the myopia was 3.75 D., 5 D., 6 D., 12 D.
      Vision good on both sides.
        (_c_) Periodic squint 13 cases (in 6 of them the
      refraction was objectively and subjectively determined
      in mydriasis by atropine). No anisometropia worth
      mentioning was present in any of these cases. Visual
      acuteness more than 1/7 9 cases. V. < 1/7 to V. = 1/12
      2. V. < 1/12 to V. = 1/36 1; one case with choroiditis
      excluded.

C. Convergent squint with doubtful hypermetropia to
    H. = 1 D., including simple hypermetropic astigmatism,
    38 cases.
         (_a_) Permanent 30 cases (5 previously operated on).
      Visual acuteness more than 1/7 7 cases. V < 1/7 to
      V. = 1/12 2. V. < 1/12 to V. = 1/36 5. V. < 1/36 2 cases.
      4 excluded (3 complicated with cataract, one on
      account of impossibility of a trial of vision).
        (_b_) Periodic squint 8 cases. V. more than 1/7 7.
      V. < 1/7 to V. = 1/12 1 case.

D. Hypermetropia 1 D. to 1.5 D. 37 cases.
        (_a_) Permanent 23 (4 cases previously operated on).
      V. more than 1/7 13, V. < 1/7 to V. = 1/12 3. V. < 1/12
      to V. = 1/36 3. V. < 1/36 3. One case excluded
      (choroiditis of the macula lutea).
        (_b_) Periodic squint 14 cases. V. more than 1/7 12.
      V. < 1/12 to V. = 1/36 1 case. One excluded on account
      of choroiditis.

E. Hypermetropia 1.5 D. to 2 D. 61 cases.
        (_a_) Permanent 41 (3 previously operated on). V.
      more than 1/7 26 cases. V. < 1/7 to V. = 1/12 3;
      V. < 1/12 to V. = 1/36 3; V. < 1/36 2; (7 cases excluded,
      2 as complicated, 5 on account of the impossibility of
      testing the vision).
        (_b_) Periodic 20 cases. V. more than 1/7 16; V.
      < 1/7 to V. = 1/12 2; V. < 1/12 to 1/36 1; V. < 1/36 1
      case.

F. Hypermetropia 2 D. to 3 D. 88 cases.
        (_a_) Permanent 58 cases. V. more than 1/7 26 cases;
      V. < 1/7 to V. = 1/12 5 cases (among them one with V.
      = 1/12 in both eyes); V. < 1/12 to V. = 1/36 17; V.
      < 1/36 4 cases. Six cases excluded as indeterminable.
        (_b_) Periodic 30 cases. V. to 1/7 24; V < 1/7 to V.
      = 1/12 3; V. < 1/12 to V. = 1/36 1; V < 1/36 1. One case
      excluded as indeterminable.

G. Hypermetropia 3 D. to 4.5 D. 54 cases.
        (_a_) Permanent 35 cases (9 previously operated on).
      V. more than 1/7 18 cases; V. < 1/7 to V. = 1/12 1 case;
      V. < 1/12 to 1/36 9; 7 cases excluded.
         (_b_) Periodic 19 cases. V. more than 1/7 14; V.
         < 1/7 to V. = 1/12 1; V. < 1/12 to V. = 1/36 3; V. < 1/36
         1 case.

H. H. 5 D. and more, 16 cases.
        (_a_) Permanent 9; V. to 1/7 3; V. < 1/7 to V. = 1/12
      3; V. < 1/12 to V. = 1/36 2; V. < 1/36 1 case.
        (_b_) Periodic 7; V. to 1/7 4; V. < 1/7 to V. = 1/12 3
      cases.


_Table of Refraction and Acuity of Vision in Convergent Strabismus._

[Transcriber's note: Key created to make table fit page]

KEY:
A: Permanent
B: V. to 1/7.
C: V. < 1/7 to V 1/12.
D: V. < 1/12 to V. 1/36.
E: V. < 1/36.
F: Excluded.
G: Periodic.
H: V. to 1/7.
I: V. < 1/7 to V. 1/12.
J: V. < 1/12. to V. 1/36.
K: V. < 1/36.
L: Excluded.

--------------------+---+----+---+----+----+----+----+----+----+----+----+----
    Convergent      |   |    |   |    |    |    |    |    |    |    |    |
    strabismus.     | A | B  | C | D  | E  | F  | G  | H  | I  | J  |K   | L
--------------------+---+----+---+----+----+----+----+----+----+----+----+----
Myopia              | 44| 26 |  2|  4 |  7 |  5 | 10 | 10 | -- | -- | -- | --
Emmetropia          | 85| 48 |  6| 20 |  7 |  4 | 13 |  9 |  2 |  1 | -- |  1
H ? to H. 1 D.      | 30| 17 |  2|  5 |  2 |  4 |  8 |  7 |  1 | -- | -- | --
H. 1 D. to H. 1.5 D.| 23| 13 |  3|  3 |  3 |  1 | 14 | 12 | -- |  1 | -- |  1
H. 1.5 D. to H. 2 D.| 41| 26 |  3|  3 |  2 |  7 | 20 | 16 |  2 |  1 |  1 | --
H. 2 D. to H. 3 D.  | 58| 26 |  5| 17 |  4 |  6 | 30 | 24 |  3 |  1 |  1 |  1
H. 3 D. to H. 4.5 D.| 35| 18 |  1|  9 | -- |  7 | 19 | 14 |  1 |  3 |  1 | --
H. 5 D. and more    |  9|  3 |  3|  2 |  1 | -- |  7 |  4 |  3 | -- | -- | --
--------------------+---+----+---+----+----+----+----+----+----+----+----+----
                    |325|177 | 25| 63 | 26 | 34 |121 | 96 | 12 |  7 |  3 |  3
--------------------+---+----+---+----+----+----+----+----+----+----+----+----

According to this the percentage of the hypermetropia (including
doubtful cases) amounts to 66 per cent. Dr. Isler in his dissertation,
'The Dependence of Strabismus on Refraction,' gives the percentage of
hypermetropia in convergent squint as 88 per cent.--a great difference,
which can, however, be partly accounted for. Isler found in
hypermetropia of 2 to 10 dioptres squinting in 75 per cent.; in my
statistics H. 1.5 D. to the highest degrees of hypermetropia are
likewise represented by 75 per cent. As the difference between H. 2 D.
and H. 1.5 D. amounts to only half a dioptre, the results of the
statistics agree perfectly within these limits; the difference lies only
in the slighter degrees of hypermetropia, for the diagnosis of which
refer to pp. 12 to 14.

The influence of hypermetropia is very apparent in the percentage of
periodic squint. While in myopia, emmetropia, and slight hypermetropia,
the sum total of permanent as compared to periodic squint is as 100:
19.5, this number mounts in hypermetropia of 1 D. to H. = 3 D. to 52.5
and in the higher degrees to 59 per cent. Despite the small number of
cases it is probably no mere accident that in the highest degrees (of H.
= 5 D. and more) this percentage is calculated at 77.7.

But just this undoubted favouring of periodic squint by hypermetropia,
helps to show that this condition is one of the causes of squint, but
not the only one, for in periodic squint just those conditions are
wanting which induce a permanent deviation.

It is further proved by the table that in convergent strabismus, myopia
appears just about as frequently as the higher degrees of hypermetropia
(of 3 dioptres and more). The fact that these are not so strongly
represented in convergent strabismus, as one would have expected
according to his theory, had also struck Donders. "This cannot be
wondered at," he continues, "the power of accommodation, even with
increased convergence, does not here suffice to produce clear images.
One gains much better ideas by practice from imperfect retinal images
than by correcting, as far as possible, the retinal images by a maximum
of accommodation." I can concede neither to the facts on which the
theory is based nor to the theoretical structure itself.

An additional statistic which I drew up of the cases of hypermetropia
which occurred during one year in my private practice, showed that the
higher degrees are rare in the same proportion as cases of convergent
strabismus are, with the corresponding degrees of hypermetropia.
Further, however, I maintain that as a rule, at the age when squint
usually begins, the accommodation really suffices to overcome even high
degrees of hypermetropia. In all cases where we find full acuity of
vision without correction of extreme hypermetropia--and this is
frequently the case in young persons who do not squint--we may assume
that the accommodation perfectly suffices to produce clear retinal
images, without excessive convergence. In full acuity of vision even
high degrees of hypermetropia are no trouble to children. Asthenopia,
which occurs in children in connection with hypermetropia, is nearly
always accompanied by defective vision. Were the increased demand on the
accommodation really the cause of convergent strabismus, asthenopia
would be far more common than it is among hypermetropic children who do
not squint.

One can assert, with far greater right, that a sufficient ground for
squint is not given by slight degrees of hypermetropia, for the latter
are accommodatively overcome and binocular fixation retained by youthful
persons without any difficulty, even when the additional motives
enumerated by Donders are present. I have endeavoured to obtain a
foundation for the depreciating influence of these circumstances
favorable to squint, for I counted in my private practice, at the same
time with the cases of squint, those cases also in which, despite those
conditions which lessen the value of binocular vision, squinting was not
present. Taking notice then of those cases in which the hypermetropia of
the better or less hypermetropic eye amounted to at least 1.5 D., in
order to allow the influence of the hypermetropia to be more
conspicuous. The patients from which the above-cited 219 cases of
convergent strabismus with a hypermetropia of at least 1.5 D. are drawn,
comprised also 117 cases in which, with the same degree of hypermetropia
and simultaneous difference of refraction or monocular amblyopia, no
convergent squint was present; of these cases 101 had acuity of vision
to 1/7; less than 1/7 to V. = 1/12 7, and V. less than 1/12 to V. 1/36 9
cases. The percentage 219: 117 = 100: 53, which is yielded for the
middle and higher degrees of hypermetropia, is not exactly convincing
for the accommodative theory of squint; it would be placed still less
favorably if we were to include the lowest degrees of hypermetropia in
the statistics.

In face of these facts I do not consider it a happy question, that of
seeking after "reasons for the prevention of squint." We do not want to
quarrel with Donders over the question why all hypermetropes do not
squint. Here, of course, I quite agree with Ulrich that squint does not
occur if the necessary muscular conditions are absent. The identity of
the fields of vision, on the other hand, seems to me to be of no
importance for the age at which squint usually commences. This identity
presupposes the habit of binocular fusion; but convergent squint arises,
as a rule, before this habit is acquired. But even if binocular fusion
were already learnt, it is given up with astonishing rapidity by
children as soon as squint develops itself (see Case 16). The fixed
habit of binocular fusion and the identity of the fields of vision
dependent on it, is contracted only when squint does not occur,
notwithstanding the presence of conditions favorable to it.

However, the number of cases is so considerable in which, despite the
presence of the causative motives suggested by Donders, no convergent
strabismus is present, that the co-operation of other causes is
necessary for the production of squint, and the first thing we do is to
think of those causes which lead to squint even without hypermetropia.

The attempt has really been made to attribute the commencement of
convergent strabismus to the accommodation even in emmetropia, and
offers fresh proof how easily facts are overwhelmed by theories. Donders
originally gave it as his opinion, that loss of power or paresis of the
accommodation produces strabismus just as little as the decrease in the
amount of accommodation which comes with increase of years; a year
later, because he could not agree with Donders' theory, Javal declared
the principal cause to be due to weakening of the accommodation and not
the refraction, but without producing any other ground for the assertion
than that of his own good pleasure. Afterwards, Donders sought to
explain the occurrence of convergent strabismus in emmetropia by paresis
of accommodation, which must indeed, according to his theory, produce
the same result as hypermetropia.

I content myself by reminding my readers, that at the age when
convergent strabismus usually arises, between the second and third year
of life, a determination of the near point is utterly impossible; a
foundation in fact is therefore wanting to the theory. But, further, if
paresis of accommodation really had the significance assigned to it,
atropine, which is so frequently used in the ophthalmic treatment of
children, would be followed by convergent strabismus. This is still more
the case with diphtheritic paralysis of accommodation, which is present
more frequently than we are aware of, for it is only a trouble to
children in the schoolroom, in younger children it passes through its
natural uninterrupted course of recovery unobserved, in hypermetropia as
well as in emmetropia. If the accommodation were really of great
importance in the occurrence of squint, convergent strabismus would
frequently be an after symptom of diphtheria, which, as is known, is not
the case. The few cases of squint which I have seen after diphtheria,
had their origin in paresis of the external rectus, which was proved by
the objective defect in movement, as well as by the disappearance of the
squint, with the recovery of the paralysis of the abducens.

That the accommodation can play a part, is shown by the rarity of
periodic accommodative squint, but for the great majority we must seek
the chief cause of squint in emmetropia and myopia, in elastic
preponderance of the internal recti and insufficiency of the externi,
and it is apparent that the same causes will also be influential in
hypermetropia.

In hypermetropia, if one causes fixation at about 30 cm. and then covers
the eye with the hand, it frequently deviates inwards. Donders infers
from this, that most hypermetropes prefer to sacrifice comfortable and
clear vision in order to retain binocular vision. Now, it is easy to
convince oneself that youthful hypermetropes see distinctly even without
correction of their hypermetropia, and we may assume that they see
comfortably if they do not complain of asthenopia; but that is by no
means always the case, for the appearance of asthenopia is conditional
on the relation of the degree of the hypermetropia to the amount of the
accommodation, which, apart from a few other causes, depends chiefly on
the age of the patient.

Just as we refer the deviation outwards of the covered eye to
insufficiency of the interni or preponderance of the externi, we may
conclude an inward deviation of the covered eye to be due to
insufficiency of the externi or preponderance of the interni, and this
all the more, as in hypermetropia the covered eye very frequently
remains in fixation, and falls away exceptionally into relative
divergence.

Just as in myopia even in the lesser degrees, insufficiency of the
interni or preponderance of the externi is not rare, so in hypermetropia
insufficiency of the externi or preponderance of the interni appears to
be frequent; and if this disturbance of the muscular balance be followed
even in myopia or emmetropia by convergent strabismus, this will of
course happen still more easily if at the same time hypermetropia, or
even without hypermetropia, the remaining favouring conditions mentioned
by Donders are present. Of course I do not deny the effect of the
hypermetropia and of those other favouring conditions, but only wish to
draw attention to the fact with reference to them, that as a rule they
do not of themselves suffice to produce convergent strabismus.

Nebulae have always been regarded as one of the causes of squint; here I
quite agree with Donders that they may operate, firstly, as general
causes of weak sight; secondly, through this, that the irritated
condition, combined with the keratitis, may produce a spasmodic,
afterwards a trophic shortening of the muscles; but this seldom happens.

Whether nebulae are found rarely or often in squint, depends in great
measure on the statistic materials which are worked out. In my
statistics they do not occur in any quantity worth mentioning, because
in private practice purulent ophthalmia keratitis, and in short, the
whole army of external inflammations of the eye is much rarer, than in
that portion of the populace which fills public clinics. Further, it is
to be observed that the mere occurrence of nebulae in squint proves
nothing--even squinting eyes may develop keratitis. We must at least
require to be assured that the squint began after the keratitis.

Among the causes which promote the occurrence of squint, Donders
mentions also conditions which diminish convergence. We have ascribed a
very important _role_ to the muscles, and have only to occupy ourselves
here with the relation between the visual line and the axis of the
cornea, which we have already mentioned on page 2. Donders has measured
the angle _a_ in ten cases of hypermetropia with convergent strabismus,
and from the comparison with hypermetropic non-squinting eyes draws the
conclusion, that in similar degrees of hypermetropia a higher amount of
_a_ specially disposes to strabismus. I will not repeat here the witty
deduction by which Donders seeks to point out that a higher value of a
must be followed by insufficiency of the externi and preponderance of
the interni; the concession is enough that these circumstances exist and
are the cause of the squint.




PERIODIC CONVERGENT SQUINT.


The opinion is prevalent that convergent strabismus usually begins in
the form of periodic squint, and that a permanent deviation is developed
in this way only. In many cases it may be so; on the other hand I have
sometimes seen convergent strabismus arise suddenly, without a
preliminary stage of periodic squint. This question, however, is of no
special interest. It is more important to note that periodic squint
frequently continues to exist unchanged, without ever becoming
permanent.

Like the whole doctrine of strabismus, opinions on periodic squint have
been governed by Donders' theory, regardless of facts, but as the
accommodation frequently exercises a perceptible influence, it is
judicious to consider first of all the cases in which this does not
happen.

Convergent squint in myopia begins as a rule with periodic squint, and
may continue to exist in this form: some patients who would not be
operated upon have been under my observation for years; sometimes a
correct position was retained for a long time, and sometimes strong
convergent squint was present, proving that accommodation had nothing
whatever to do with it. In myopia of higher degree the accommodation is
scarcely used--unless concave glasses are worn; still periodic squint
occurs under these circumstances. For example:

CASE 1. Miss B--, aet. 22, possesses in both eyes myopia of 6.5 D. with
full visual acuteness and without posterior staphyloma. A concave
eyeglass of 4.5 D. is used off and on for distance, and the eyes have
never been over-exerted in looking at near objects. For a long time
tendency to convergent squint, which is combined with diplopia, has
existed on the left side. The eyes generally have a perfectly normal
position, but occasionally convergent squint occurs, remains in
existence a few hours, perhaps for a whole day even, and disappears
again. The deviation here amounts to 4 or 5 mm. As the patient did not
wish for an operation, I have been able to observe the condition for
years without any change in it or without the squint becoming permanent.
The cause of periodic squint is certainly not to be sought for here, in
the accommodation.

Many cases of convergent strabismus with myopia constantly offer such a
peculiar phase of the defect, that one has accepted the statements which
ascribe to short-sightedness a determining influence on this form of
squint, without asking for further proof. It may, therefore, be useful
for our purpose to cite a few cases of periodic convergent strabismus
with emmetropia. For instance:

CASE 2. Louise S--, aet. 6-1/2, came under treatment for follicular
conjunctivitis, convergent strabismus appearing simultaneously on the
right side; the investigation showed the acuity of vision of left eye =
5/12, right V. = 5/36, the ophthalmoscope, and also mydriasis by
atropine, proved the presence of emmetropia. The squint had first been
observed when the child was about two years old, then it disappeared
spontaneously and returned again three or four months ago.

In the course of treatment, which extended over about six months, the
child came repeatedly into my consulting room, sometimes with squint,
sometimes without, in the periods during which correct fixation existed,
no squint occurred even when working. Examination with the stereoscope
showed no normal binocular fusion even during normal position of the
eyes.

CASE 3. Vera von K--, aet. 6; tendency to convergent strabismus, mostly
on right side, has existed one and a half years. Normal position as a
rule, on covering the eye immediate convergence, with a deviation of 5
mm.; with additional aid of a red glass and weak prisms deviating in a
vertical direction, homonymous diplopia is very easily provoked. Visual
acuteness on both sides 5/12, the left slightly better than the right;
emmetropia in mydriasis by atropine. A year later a repeated examination
gave the same result.

The cause of periodic squint in these cases can only be sought in the
bearing of the ocular muscles; an elastic preponderance of the interni
existed, which ceased, as a rule, on using the externi. A special
influence of the accommodation was not traceable, which does not of
course prevent this from acting differently in other cases. But in
periodic squint it may frequently be observed that the deviation
commences under influences which have nothing to do with the
accommodation, but, on the contrary, under those which weaken the
muscular energy generally, for example, fatigue, anxiety, &c.

Like convergent squint generally, the periodic form is also more
frequent in hypermetropia than in emmetropia or myopia, and we admit
that in hypermetropia the strain on the accommodation has more influence
in producing the deviation. But as the appearance of periodic squint in
emmetropia or myopia is proved without participation of the
accommodation, solely on the ground of the muscular forces--so the
presence of the same forces in hypermetropia ought not to be ignored.

It happens, indeed, that in considerable degrees of hypermetropia a
slight convergent deviation occurs only from time to time, the cause of
which, on closer investigation, can only be sought in the ocular
muscles. For example:

CASE 4. Paul F--, was first introduced to me in 1872 as a child of three
years and two months, with a tendency to convergent strabismus on the
right side of two months' standing, which was sometimes greater,
sometimes less, and sometimes was not present at all. In 1877 I saw him
again suffering from conjunctivitis, without perceiving any squint; no
examination respecting it was made. In 1880 his elder brother came under
treatment for apparent myopia, which with the ophthalmoscope proved to
be hypermetropia, and my attention, being again drawn to the eyes of the
family, I requested the younger brother to come for examination. At
first sight the position of the eyes appeared to be quite normal, on
more careful inspection slight convergent squint of the right eye showed
itself occasionally. On both sides apparent emmetropia or very slight
hypermetropia, acuity of vision on left side 5/9, on the right 5/18,
ophthalmoscopic diagnosis of refraction was impossible on account of
restless fixation.

With the addition of a red glass diplopia cannot be produced, the left
field of vision is observed in the stereoscope, then the right one on
covering the left eye; never both together. In mydriasis by atropine
hypermetropia of high degree (about 4 dioptres) is ophthalmoscopically
detected on both sides, with convex 4.5 D., V. = 5/9 with slight
convergent deviation of the right eye.

What has here prevented the transition to permanent squint with a
deviation corresponding to the great strain on the accommodation? That
the accommodation was really in action is proved simply by the apparent
emmetropia and the school-work, that no retention of binocular single
vision took place is shown by the proved incapacity for binocular fusion
of the retinal images. Nothing then remains but to accept the fact that
in the ocular muscles inducement was only given for a slight periodic
squint, not for a permanent one answering to the amount of accommodation
used.

As further proof that periodic squint may occur even in hypermetropia
quite independently of the accommodation, I should like to cite a case
of intermittent convergent strabismus which a number of other oculists
have seen besides myself.

CASE 5. Sophie S--, aet. 7-3/4, has suffered for two years from a strong
convergent squint on the left side, occurring every other day. The
deviation amounts to 7 mm. (the same deviation is transferred to the
left eye, when the right is put into fixation). On the intervening days
the position of the eyes is quite normal, on covering one only a slight
deviation takes place. The visual acuteness amounts to 5/12 on the left,
5/24 on the right, ophthalmoscopically with atropine hypermetropia of
two dioptres. Quinine has been given without avail, a convex glass of 2
D. also, which has been worn for the last half year, has not affected
the deviation.

Diplopia was not present--on the intervening days free from squint, with
the aid of a red glass, homonymous diplopia could be detected without
perceptible deviation, still it was impossible to bring about a union of
the double images by prisms. In the stereoscope the left field of vision
was first inspected, then both, still fusion of the fields of vision was
not traceable. The statements, moreover, as indeed could not be expected
otherwise in a child of such tender age, were not free from
contradictions, but the existence of normal binocular vision was very
doubtful. I therefore performed tenotomy of the left internal rectus,
after which normal position continued to exist on the following squint
days. After three quarters of a year I saw the child again; the squint
was perfectly cured, even on looking down, convergence was no longer
present. Whether a permanent cure was thus obtained, seems to me
doubtful, owing to the rare peculiarities of this case.

Mannhardt also describes a similar case of intermittent squint; that of
a girl aged eight years, in whom periodic convergent strabismus had
begun four years previously, and for two years had occurred regularly
every other day. On undecided vision the eyes were normally placed, but
as soon as a near or distant object was fixed, a considerable deviation
inwards of the left eye occurred. Under the covering hand both eyes
deviated inwards equally. On the non-squinting days strabismus could in
no way be produced even by fixation of the nearest objects, only under
the covering hand a deviation inwards ensued. The squint could not be
removed by quinine, but only by correction of the hypermetropia of 3 D.
In any case, then, hypermetropia was one of the causes of the squint,
but not the only one, as it cannot operate on alternate days only.

Javal, who tries to make this case coincide with his theory, accepting
an intermitting paresis of accommodation as the cause of squint, is
manifestly in error, as Mannhardt particularly mentions that acuity of
vision, refraction and accommodation remained perfectly equal on both
days.

If it is thus proved, that also in periodic inward squint the deviation
may occur quite independently of the accommodation, on the other hand it
is apparent, that if once a tendency to squint exists, a
disproportionately strong convergence may very easily unite itself with
the accommodation. Particularly of course in hypermetropes, who are able
to fix nothing without using their accommodation, a remarkable
fluctuation of the squint angle very frequently takes place. Sometimes
the deviation is exceedingly strong, sometimes so slight that it seems
to be absent. It is usually impossible to determine if it is really
absent, for as soon as we single out a point for fixation to make the
investigation feasible, strong deviation sets in. If in such cases we
perfectly atropise both eyes, restore the attainable acuity of vision by
neutralisation of the hypermetropia with convex glasses, and yet,
nevertheless, as is generally the case, the customary strong convergence
takes place on fixation of a distant object, there can be no talk of a
strain on the accommodation; at most we can say, that the impulse for
accommodation, habitually united with the intention to see distinctly,
and the too strong convergence combined with it, also takes place,
though by paralysis of the accommodation the participation of the same
has become impossible. As accommodative squint those cases are chiefly
indicated in which the deviation only takes place when there is a claim
on the accommodation. In most cases of this kind hypermetropia is
present. I have occasionally seen periodic accommodative squint with
emmetropia of the fixing eye.

CASE 6 may serve as an example: H. B--, aet. 15, shows a considerable and
very varying periodic inward squint. Sometimes correct position is
present, sometimes strong deviation, indeed the latter only occurs on
looking at distant objects, while for near ones correct position of the
eyes generally takes place. The examination showed for the right eye
hypermetropia 1.5, for the left myopia 3.5 D.; full acuity of vision on
both sides. The squint occurring in the left eye on looking at distant
objects was therefore accommodative; the effort of the accommodation
necessary for correcting the hypermetropia united itself to an
excessively strong innervation of the interni, as the interests of
binocular vision came but slightly into consideration on account of the
myopia in the left eye. For near objects the myopic eye is used without
accommodation and therefore also without convergent strabismus of the
right. But if one caused a point about 25 cm. distant to be fixed first
with the right (hypermetropic) eye while the left was covered and then
caused fixation to be transferred to the left, the accommodative
convergent strabismus induced was alternately transferred to the left
eye and continued, although the left eye fixed without any effort of the
accommodation on account of its myopia. Double tenotomy of the interni
and correction of the hypermetropia effected the cure of the squint.

The clearest cases of accommodative strabismus are those in which
usually a correct position and sometimes even binocular fusion is
present, while squint occurs only during the strain on the accommodation
necessary for distinct vision.

CASE 7. Miss Bertha v. Pr--, aet. 27, shows strong accommodative squint
of the right eye, said to have been observed by her parents when she was
fifteen months old. Correct position of the eyes is generally present
with indistinct vision; the endeavours to see clearly immediately causes
striking convergence of the right eye. On the left hypermetropia 3.5 D.,
vision normal; on the right the same degree of hypermetropia, vision not
more than 1/12 of the normal, no ophthalmoscopic report. On correction
of the hypermetropia and with aid of a red glass crossed diplopia
immediately appears, which is corrected by a prism of 5 deg. base inwards;
prisms of 12 deg. with the bases inwards are overcome on fixation of an
object about 12 ft. distant by divergence. The elastic tension of the
ocular muscles necessitates then a preponderance of the externi, and an
effort of the accommodation necessary to overcome the hypermetropia,
which on account of the congenital amblyopia of the right eye unites
itself with excessive convergence. Had the elastic tension of the ocular
muscles made a preponderance of the interni a condition, permanent
convergent squint would have been the result, and one would have called
the weak sight of the right eye amblyopia from want of use.

Typical accommodative squint occurs quite independently of the will on
each effort of the accommodation, and is not combined with diplopia. It
is otherwise in those cases of hypermetropia of high degree in which
patients voluntarily call forth convergent squint, and retain it for a
short time for the purpose of distinct vision. They are then perfectly
conscious of the squint, and perceive also as a rule the double images
which occur at the same time; I have seen such cases in adults who could
only produce the accommodation necessary for distinct vision by the aid
of a too strong convergence; they, however, only now and then made use
of this help. Although differing much from the typical form, these cases
of voluntary accommodative squint were also included in the statistics.

In involuntary periodic (even if not accommodative) squint, the patient
as a rule is not conscious of the occurrence of the false position; that
exceptions to this occur Case 1 has given us an instance.




CONVERGENT SQUINT IN MYOPIA.


For the aetiology of convergent strabismus it is of interest to ascertain
the age at which it is developed, and one of the first results we obtain
is the exceptional position which the union of myopia with convergent
strabismus takes in this category. Of the 56 cases contained in the
above statistics I possess reliable information of the time of
commencement in 11 cases; the squint was twice observed before the
fourth year of life, once between four and ten years of age, eight times
between the tenth and thirty-third years of life.

I must first state prominently with regard to the connection of myopia
with convergent squint that I see no reason for holding short sight to
be the cause of the squint, as v. Graefe does.

A specially severe strain of the eyes, as v. Graefe assumes, was not
traceable in the cases observed by me. Excessive convergence and strain
on the accommodation is often enough present in weak sight, for example,
in astigmatism without the existence of squint; were short sight in
general an inducement to convergent squint these cases would appear much
oftener than they actually do, owing to the frequency of myopia. In my
opinion the cause of their rarity lies in the fact that myopia is
frequently combined with insufficiency of the interni and preponderance
of the externi, but only rarely with the reverse condition of the
muscles. If, however, a preponderance of the interni develops itself
together with the myopia, convergent strabismus is easily produced, for
without correction of the myopia by spectacles, the desire for retaining
binocular single vision for everything beyond the far point is lessened
by the indistinctness of the retinal images. Within the range of their
field of distinct vision these squinting myopes frequently retain
binocular vision, while the capacity for accepting parallel rays or
retaining them for long, is lost.

Strictly speaking, the periodic squint present in these cases is of a
peculiar kind, for the binocular single vision present within range of
the convergence excludes the notion of squint; the latter only occurs
when an object lying outside the point of convergence is fixed.
Moreover, according to the common use of language, I have only used the
expression periodic convergent squint for the change between a parallel
direction of the visual axes and pathological convergence.

As squint in myopia usually commences at an age when binocular fusion
has already become a fixed habit, diplopia regularly takes place with
it, but patients become more easily accustomed to this than in paralysis
of the ocular muscles, because the retinal images are indistinct and the
double images in the field of vision always keep at about the same
distance, while in paralysis of the ocular muscles the distance is
constantly changing.

The myopia, in these cases, is not the cause of the squint, but only a
favouring circumstance. If the same preponderance of the interni is
developed at the same age in emmetropia, squint is not so easily caused,
as the distinct retinal images present in the whole field of vision
render it easy to retain binocular single vision. Therefore we see the
same form of squint arise less often in emmetropia (see Case 45) when
childhood is past, than in myopia. As a rule preponderance of the
interni in hypermetropia leads eventually to convergent squint even in
childhood.

In emmetropia and hypermetropia convergent strabismus seldom arises
after the tenth year (paresis of the abducens of course excepted),
therefore in my investigations as to the time of commencement of typical
squint I have only considered those patients who came under my treatment
before their tenth year. We must rely for the most part on the vague
statements of the parents, which lose in exactness in proportion as the
origin of the squint is of distant date; moreover, I have myself seen a
great many of the children before they were four years old. In this way
I have collected reliable information respecting the origin of the
squint in 193 cases, and of these (_a_) 88 cases occurred in children
one to three years old, (_b_) 53 in children three to four years old,
(_c_) 35 cases in children of over four years of age. It is thus at once
seen that in the great majority of cases, convergent strabismus
commences in children under four years of age, who have not yet begun to
read and write, and have no inducement to use their accommodation
severely, and still less continuously.




SQUINT FROM PARALYSIS OF THE ABDUCENS.


Convergent squint as a result of paralysis of the abducens is not very
often seen. It is first to be observed that a convergent squint,
including the whole field of vision, occurs by no means in all cases; in
about half the cases binocular fusion is retained towards the healthy
side, diplopia then only occurs when the weak abducens is exerted beyond
its strength. In those cases in which convergent squint is present in
the whole field of vision paralysis of the abducens cannot be the sole
cause, but some other cause than the most apparent one must co-operate.
An insufficiency of the externi of previous existence, or an elastic
preponderence of the interni may be considered. I have not been able to
persuade myself of the fact that hypermetropia can play any part
therein.

In by far the greater number of cases paralytic convergent squint
recovers together with the paralysis of the abducens, the field of
single vision transfers itself gradually from the healthy side to the
side of the weak abducens, and at length governs the whole field of
vision. In proportion as the muscle again fulfils its normal functions,
the habit of binocular fixation regains its power, and it seldom happens
that the elastic tension of the muscles has so changed during paralysis
that the desire for binocular single vision does not suffice to overcome
it. Case 48 furnishes an example of the fact that although the squint
occurred as a consequence of paralysis of the abducens, it certainly
remained in existence after healing of the paralysis on account of
previously existing insufficiency of the externi.

Congenital paralysis of the abducens seems more frequently to have
convergent squint as a result. If, for example, convergent squint is
observed in the first year of life, and we find a complete defect of
motion on the part of one abducens when the children become old enough
to be examined, we may certainly assume that the case is one of
congenital paralysis of this muscle, or at least that the paralysis
originated soon after birth. Doubtless, however, cases appear, of
congenital paralysis of the abducens without squint, and as these cases
are so rare I will describe two which I observed in adults.

CASE 8. Miss H--, aet. 17, has nominally since her birth a considerable
defect in the outward movement of the left eye. On looking to the left
homonymous diplopia is present, on looking to the front and the right
binocular single vision and no squint; on both sides emmetropia and full
acuity of vision.

CASE 9. Mr. V. W--, aet. 24, has likewise congenital paralysis of the
left abducens. No squint, but as soon as the left eye is used for
fixation in the left direction there occurs in the right one a strong
secondary movement inwards.




HYSTERICAL SQUINT.


In the hysterical form we see rather a rare variety of convergent
squint, which is conditional on contraction of the interni through
restriction of movement of the externi. Hysterical symptoms may at the
same time appear in the eyes or elsewhere, still this does not always
happen. As these cases are rare I will relate a few of those I have
observed. (These cases are not included in the above statistics.)

CASE 10. Anna R--, aet. 20, came under treatment in February, 1878,
stating that on the previous day she perceived blindness of the right
eye on waking; in the afternoon she felt particularly weary, and after
she had slept about an hour woke with blindness in both eyes. No
perception of light, good pupillary reaction, ophthalmoscopic report
normal. Patient was treated with copious enemata and dismissed on the
fifth day cured.

In February, 1880, she again came under treatment with blindness of both
eyes, also perceived the previous day on waking. Convergent strabismus
was present at the same time, of such a degree that the eyes converged
to a point 10 to 20 cm. distant. The outward movement was suspended in
both eyes. The attempt to turn the eye outwards is accompanied by short
convulsive movements, and followed by an immediate rebound to the
convergent position. She asserts her inability to see the movements of a
hand before her eyes, is able, however, to move about in a strange room,
unsteadily certainly, but with avoidance of obstacles; she sits down on
a chair indicated to her, &c. The position of the eyes proves that there
was no simulation in all this; it would be impossible for any person to
simulate a strong convergent squint continuously for four to five days.
Eight days after her admission the patient was dismissed with normal
movement of the eyes and good vision.

CASE 11. Miss Antonie E--, aet. 15, who has been treated by her family
physician for various hysterical disturbances, suffered since the middle
of December, 1879, from convergent strabismus with permanent but very
varying deviation, which is at times very slight, and sometimes amounted
to more than 7 mm. The movement outwards is in both eyes rendered
difficult, still the outer edge of the cornea is brought to the outer
angle of the lids with trouble and twitching movements. Homonymous
double images are present, their mutual distance is alike in the whole
field of vision, but is (six or eight weeks after the commencement of
the squint) signified as being slight; at the same time a difference in
height is present, the image of the left eye stands lower, prism 30 deg.,
base outwards, places the images just above one another. Nystagmus
occasionally occurs in monocular fixation (with exclusion of the other
eye). In due course a gradual improvement set in, the deviation and the
distance apart of the double images became slighter, the outward
movement better, and in the middle of April, 1880, four months after the
trouble began, no squint and no diplopia were present, the outward
movement normal, facultative divergence = 0.

The hysterical character of the visual disturbance showed itself when
the vision was tested. I will first observe that repeated investigations
with atropine showed emmetropia, while in the first investigation on the
left side, No. 36 at 5 m. was not recognised with the naked eye, but
only with weak concave glasses (with - .5 D. V. = 5/18). With the right
eye No. 0.8 was read fluently, from 0.75 she asserted she was unable to
recognise a word, with - 2 D. V. = 5/36. It would be wrong to conclude
from this myopia or spasm of the accommodation, for here, as in most
cases of hysterical weak sight, it could be shown that whatever glass
one chose to hold before the patient's eyes, was followed by an
improvement in the statements. The same improvement in visual acuteness
was repeatedly obtained in this case by a weak prism (3 deg.), held before
the fixing eye during monocular examination, and in the end, V. 5/12 was
obtained for the right eye, as against 5/6 with a prism of 3 deg.

Finally, on May 1st, full visual acuteness was present on both sides.
Field of vision and sense of colour normal.

CASE 12. Mrs. B--, aet. 30, previously treated for various hysterical
disturbances, has complained for about eight days of disordered vision,
the binocular nature of which was proved as patient had herself observed
that on closing one eye she could at once see clearly. Near objects to
15 cm. are seen distinctly. With all this, at the first examination it
was impossible to produce diplopia, either with the aid of a red glass
or prisms, &c., the images of first one eye, then the other were always
seen by turns. A few days later, on repeating the examination, double
images were perceived, they were homonymous with slight difference in
height (image of the right eye lower), the lateral displacement is
corrected by a prism of 28 deg. Micropsia of one image was also perceived.
On both sides the outward movement is rather difficult. Full visual
acuity on both sides--in the first examination slight myopia - .75 D. is
specified, afterwards emmetropia. The visual disturbance was removed by
goggles with faintly ground glass on the right side--preparations of
iron, bromide salts, shampooing with cold water and electricity were
used. In six weeks' time binocular single vision was again restored; the
facultative divergence = 0. With red glass and vertically deviating
prisms homonymous diplopia corrected by prism 3 deg. Field of vision and
sense of colour remained normal throughout.




DIVERGENT SQUINT.


If we want to draw a comparison between convergent and divergent squint,
we must consider only absolute divergent strabismus, for convergent
strabismus does not offer a parallel to relative divergent squint. In
absolute divergent squint the direction of the visual axes is such that
they would meet behind the patient's head; in the relative divergent
squint the axes of vision are parallel or slightly convergent, but they
do not cross at the point fixed by the one eye, but at a greater
distance off.

If we then only compare that which admits of comparison, we first find
out that divergent squint is rarer than the convergent form, and the
cause contained in the ocular muscles is here brought to light still
more clearly than there.

We must next distinguish between permanent and periodic squint, and we
see the latter so frequently continue as such, that we must not consider
the transition from this variety to the permanent one to be the rule.

In 183 cases of absolute divergent strabismus which appeared in my
private practice in the same space of time as the cases of convergent
squint above discussed I have been able to obtain exact determinations
of the refraction and visual acuteness. The weakness of the fixing eye
was the test for classing them among the statistics, and in patients who
had been long under observation, the first certain determination of
refraction, which was necessary, as several children are included who
came under treatment with divergent strabismus and emmetropia whilst
myopia developed itself later.


A. Divergent squint with hypermetropia.

(_a_) Permanent 4 cases. Visual acuteness of the squinting eye more than
1/7 1 case, V. less than 1/36 1 case, 2 excluded, one on account of
complication with detachment of retina, the other on account of
impossibility of testing vision.

(_b_) Periodic squint 5 cases. Among them 3 with double hypermetropia, 2
with emmetropia in one, and hypermetropia in the other eye. Visual
acuteness of more than 1/7 in 3 cases; V. = 1/9 1 case; V. = 1/36 1
case.


B. Divergent squint in emmetropia.

(_a_) Permanent 32 cases. Among them 10 with alternating strabismus and
anisometropia of at least 2 D. And in 9 cases emmetropia in one, myopia
in the other eye; once simple hypermetropic astigmatism in one, with
myopic astigmatism in the other eye. Visual acuteness of both eyes in
these 10 cases more than 1/7. In the 22 cases of monocular squint the
visual acuteness of the squinting eye amounted 8 times to more than 1/7
-, 10 times 1/12 to 1/36 (in 1 case V. = 1/36 with nystagmus of the
squinting eye when put into fixation). V. less than 1/36 in 3 cases; 6
cases excluded on account of complications.

(_b_) Periodic squint 28 cases. Among them 5 with anisometropia of at
least 2 D. (emmetropia in one, myopia in the other eye). Visual
acuteness of the squinting eye more than 1/7 in 27 cases, less than 1/7
to V. = 1/12 in 1 case.


C. Divergent squint in myopia to M. = 2 D.

(_a_) Permanent 24 cases (among them 6 with anisometropia of at least 2
D.). Visual acuteness of the squinting eye more than 1/7 in 15 cases. V.
less than 1/7 to V. = 1/12 2; V. less than 1/12 to V. = 1/36 3; V. less
than 1/36 2 cases; 2 cases excluded on account of complications (one on
account of atrophy of the optic nerve, the other on account of posterior
polar cataract).

(_b_) Periodic squint 23 cases. Among them 10 cases with anisometropia
of at least 2 D. Visual acuteness more than 1/7 in all 23 cases.


D. Divergent squint in myopia 2 D. to M. = 4 D.

(_a_) Permanent 17 cases. Among them 2 with anisometropia of more than 2
D. V. to 1/7 9 cases. V. < 1/7 to V. = 1/12 1 case. V. < 1/12 to V. =
1/36 2 cases. V. < 1/36 1 case. Four cases excluded (2 with choroiditis,
1 with congenital cataract, 1 with traumatic cataract).

(_b_) Periodic 8 cases. Among them 4 with anisometropia of at least 2 D.
V. to 1/7 7 cases. V. 1/36 1 case.


E. Divergent squint in myopia 4 D. to M. 6.5 D.

(_a_) Permanent 10 cases. V. more than 1/7 in 5; V. less than 1/36 in 3
cases, 2 excluded (one on account of large anterior synechia, one on
account of choroiditis of the macula lutea).

(_b_) Periodic 9 cases. Among them one with anisometropia of more than 2
D. V. more than 1/7 5 cases. V. = 1/9 1 case; 3 cases excluded on
account of complications.


F. Divergent squint in myopia more than 6.5 D.

(_a_) Permanent 8 cases. V. more than 1/7 4 cases, 4 excluded on account
of choroiditis of the macula lutea.

(_b_) Periodic 10 cases. V. to 1/7 9 cases; V. = 1/12 in one case.


_Table of Refraction and Visual Acuteness in Divergent Squint._

[Transcriber's note: Key created to make table fit page]

KEY:
A: Permanent.
B: V. to 1/7.
C: V. < 1/7 to V. = 1/12.
D: V. < 1/12 to V. = 1/36.
E: V. < 1/36.
F: Excluded.
G: Periodic.
H: V. to 1/7.
I: V. < 1/7 to V. = 1/12.
J: V. < 1/12 to V. = 1/36.
K: V. < 1/36.
L: Excluded.

-------------------+---+----+----+----+----+----+----+----+----+----+----+---
                   | A | B  | C  | D  | E  | F  | G  | H  | I  | J  | K  | L
-------------------+----+----+----+----+----+----+----+----+----+----+----+--
Hypermetropia      |  4|  1 | -- | -- |  1 |  2 |  5 |  3 |  1 |  1 | -- | --
Emmetropia         | 37| 18 | -- | 10 |  3 |  6 | 28 | 27 |  1 | -- | -- | --
Myopia to M. 2 D.  | 24| 15 |  2 |  3 |  2 |  2 | 23 | 23 | -- | -- | -- | --
M. 2 D. to 4 D.    | 17|  9 |  1 |  2 |  1 |  4 |  8 |  7 | -- |  1 | -- | --
M. 4 D. to 6.5 D.  | 10|  5 | -- | -- |  3 |  2 |  9 |  5 |  1 | -- | -- |  3
M. more than 6.5 D.|  8|  4 | -- | -- | -- |  4 | 10 |  9 |  1 | -- | -- | --
-------------------+---+----+----+----+----+----+----+----+----+----+----+---
                   |100| 52 |  3 | 15 | 10 | 20 | 83 | 74 |  4 |  2 | -- |  3
-------------------+---+----+----+----+----+----+----+----+----+----+----+---

It follows then from this, that periodic absolute divergent squint is
just about as frequent as the permanent form and that both become more
rare as the degrees of myopia increase. As, however, in spite of this,
myopia is present in about 60 per cent. of all cases, the connection can
be no other than this, that myopia frequently unites itself with
insufficiency of the interni and preponderance of the externi; in this
respect, as in every other, myopia and hypermetropia are directly
opposed.

The setting up of a "hypermetropic divergent strabismus," dependent on
hypermetropia, seems to me only to show how much people have been
carried away by the idea that the cause of the squint must be given by
the state of refraction. Isler claims 17 to 29 per cent. of the cases
for hypermetropic divergent strabismus; of these, however, the half
possess only slight hypermetropia of 2 D. or less, which perfectly
agrees with the fact that the same observer has also found in convergent
squint a remarkably high percentage of the lower degrees of
hypermetropia.

Whether squint originates in the permanent or periodic form depends
chiefly on whether the movement of convergence is retained or lost.
There are cases of considerable divergent squint, in which the near
point of the convergence is scarcely removed, while on the other hand,
the physiological innervation for convergence may be lost, without
absolute divergence ever being brought about. In a number of emmetropic
or slightly myopic cases with absolute preponderance of the externi, the
physiological connection between accommodation and convergence is
maintained in a relaxed way; thus, for example, it is impossible to
converge voluntarily to a large object, as, for instance, a pencil held
in the vertical line, while accurate convergence immediately follows on
reading at the same distance; in other cases accommodation can be
exerted to the near point, without inducing the slightest impulse to
convergence. This circumstance is worthy of consideration for the
prognosis of the operation. A mere relaxing of the tie between
accommodation and convergence may be strengthened by practice, but if
the impulse to innervation is completely lost, it will scarcely be
possible to restore it again; as after complete laying aside of absolute
divergence the relative form still continues to exist.

Those cases deserve special consideration in which emmetropia is present
in one eye, in the other myopia. Slight degrees of one-sided myopia
reconcile themselves with the continuance of a normal binocular act of
vision. If the far point of the myopic eye lies at an inconvenient
proximity even for reading, then, as a rule, the emmetropic eye is used
for near as well as distant objects; if, on the contrary, the degree of
myopia answers to a range of vision convenient for working, and visual
acuteness is normal, then the temptation to use the emmetropic eye only
for distance and the myopic one only for near objects is so
overpowering, and the advantages on the other hand which would be
offered by clinging to binocular vision so slight, that a convenient
monocular vision is generally preferred. Even for objects which lie
nearer the eye than the far point of the myopic, and at the same time
farther than the near point of the emmetropic eye, for which, therefore,
both eyes could secure clear retinal images, binocular vision is not
used. In cases in which the patient can read with proper binocular
fixation, if one covers all but one line and then makes with prisms
double images standing one above another, it is the myopic eye alone
which almost invariably shows a clear retinal image.

The usual result of this is, first a relaxing of binocular vision, and
as together with this the motive for convergence, namely, the effort of
the accommodation ceases, the conditions for the commencement of
divergence are produced. Still the elastic tension of the ocular muscles
decides even here; if the interni preponderate, convergent squint
results, when the myopic eye is used for near objects, the emmetropic
for distant ones. If the externi preponderate, then permanent or
periodic divergent strabismus is caused. Nevertheless, in a remarkable
minority of cases the elastic tension of the ocular muscles is so
regulated that, despite relaxation of binocular fusion, neither
convergent squint nor absolute divergence occurs, but simple relative
divergence remains with employment of the myopic eye for near objects.




DYNAMIC SQUINT, INSUFFICIENCY OF THE INTERNI AND MUSCULAR ASTHENOPIA.


The habit of binocular single vision, when it has once reached its
normal development, governs the movements of our eyes to a great degree;
the desire to avoid double images makes itself continually felt; and
where this is not possible, an uncomfortable feeling of uncertainty
arises at every movement of the body. Double images are prevented as far
as possible by movements of the eyes, which we must designate as
voluntary when we are conscious of their occurrence.

If we follow a moving object with the eyes, the latter make
corresponding movements in order to keep the image in the centre of both
retinae. For example, if we look at a distant object which approaches in
the direction of one visual axis, this eye will necessarily remain
still, while the other will be put into convergence in proportion as the
object advances. If this did not happen, if this eye remained also
immovable, the retinal image would deviate outwards more and more from
the macula lutea and diplopia would arise. In order then to avoid
diplopia the macula lutea moves to where the retinal image is formed. We
can, however, move the images on the retina by the aid of prisms without
movement of the object. If, for example, we hold a prism before the eye
so that the base lies towards the temporal side, the retinal image will
be displaced towards the base of the prism, outwards then from the
macula, and double images will occur, which are at once removed by a
distinctly perceptible inward movement of the eye. In this way, by means
of a prism applied with the base inwards, outward deviation may be
produced, and even in a modified way deviations in height of the visual
axes by means of prisms with the base upwards or downwards. Here the
force of habit is apparent, for in the daily use of our eyes we
continually practise the inward movement of the visual axes; we can also
easily restore the customary degree of convergence by means of prisms
with the bases outwards; physiologically indeed, it is quite immaterial
whether an object is in a proximity to our eyes attainable by
convergence, which causes double images until it is binocularly fixed,
or whether by the aid of prisms we bring the retinal images of a distant
object to parts of the retinae which do not correspond. If we look at a
distant object fixed with parallel visual axes, under normal
circumstances, prisms of 6 deg. to 8 deg. with the base inwards can be overcome,
that is to say, as in weak prisms the deviation is equal to about half
of the prism, an absolute divergence of the visual axes of 3 deg. to 4 deg. may
be produced by which the double images are blended. It is immaterial
whether we apply a prism of, say 8 deg. to one eye, or prisms of 4 deg. with the
bases inwards to both. The facultative divergence thus attainable
remains the same, which speaks for the fact, that this monolateral
movement attainable by prisms is also combined with double innervation;
and of course in the eye remaining in unmoved fixation, with impulses to
innervation which are reciprocally abolished.

In the physiological use of our eyes we certainly never have occasion to
practise absolute divergence, but we constantly practise the transition
from the inward to the outward movement of the eyes, and experiments
with prisms teach us, that the innervation of the externi therewith
connected may even be carried somewhat beyond the physiological limits
of parallelism. Moreover, the extent of the "facultative" divergence
attainable by prisms shows a considerable latitude.

The case is similar with deviation in height of the visual axes. In
looking upwards or downwards the innervation of both eyes is usually
precisely the same, but on looking at any point when holding the head
obliquely, the difference in height of the eyes then present must be
balanced by a corresponding difference in the direction of the visual
axes. The same thing happens, if we hold a vertically deviating prism in
front of one eye in binocular vision; prisms of 2 deg. to 3 deg. may then be
overcome by difference in height of the eyes; rarely is a much greater
difference in height of the visual axes attainable. I have seen this
particularly in those cases where facultative divergence also was
greater than usual.

It happens especially in myopia that prisms of considerably more than 6 deg.
to 8 deg. are overcome by divergence, and certainly without causing any
inconvenience. Among the cases presented for examination, those, of
course, are most numerous where the patients have some complaint to
make, even if this have quite a different cause. In any case a divergent
position of the axes of vision corresponds to the balance of the
muscles, and this does not generally occur, for this reason, because
retaining binocular single vision necessitates a parallel or convergent
position of the eyes. Frequently, however, even a slight impediment to
binocular fusion, such as the application of a red glass to one eye,
suffices to procure preponderance in the elastic tensions of the
muscles, and to cause the fixed point to appear double. We can put a
stop to binocular single vision still more surely by applying to one eye
a prism with the base upwards or downwards. If the double images of a
point 4 to 5 meters distant show a crossed lateral position besides the
difference in height caused by the prism, we may assume that an
absolute divergent position of the eyes corresponds to the elastic
tension of the muscles; and the measure of the deviation will be given
by those prisms which, placed with the bases inwards before one or both
eyes, bring the double images perpendicularly over one another. As a
rule, in these cases the degree of divergence which occurs on cessation
of binocular single vision, is almost as great as the facultative
divergence, which may be reached in the interest of binocular single
vision.

V. Graefe designates as "dynamic squint" that condition in which the
position of divergence corresponding to the state of tension of the
muscles does not occur because binocular vision is retained. Without
clearly defined limits these conditions pass on into periodic squint,
when either diplopia occurs together with the divergence, or the habit
of binocular fusion becomes less frequent or is quite forgotten, while,
however, according to the varying state of the muscles sometimes normal
position, sometimes divergence, is present. A correct position of the
eyes is quite possible even without binocular fusion, then only the
regulator is wanting, which, in the varying play of the muscular forces,
ensures the balance of position and movement.

The older ophthalmologists had a parallel strabismus and probably
understood by that, what we now designate as relative divergence. The
connection between relative divergence and myopia, pointed out by
Donders, is universally admitted; on the other hand, in more modern
literature we scarcely find any intimation of the fact that a parallel
squint occurs, which is quite independent of myopia, and rests solely on
the fact that the impulse of innervation for convergence is lost. A few
examples may explain this condition.

CASE 13.--Auguste T--, aet. 28. On the left emmetropia, V. 12/20. On the
right the visual acuteness is variously given, but certainly does not
amount to more than 1/5 nor less than 1/10 of the normal.
Ophthalmoscopic report normal. The left eye is naturally the fixing one,
the right always remains parallel--for near objects double images are
present. A convergent movement is not attained, either for near objects,
or by means of prisms with bases outwards for distant ones. Prisms with
the bases inwards are not overcome; with vertically deviating prisms the
double images of distant objects stand perpendicularly above one
another.

CASE 14.--Ludwig v. K--, aet 32, has complained of diplopia repeatedly
for fifteen years. Statement in August, 1877: Convergence to a pencil
held before patient on the median line is only retained to about 50 cm.,
nearer, crossed diplopia occurs. In reading, binocular fixation is
possible with an effort at a nearer point. The facultative divergence
does not amount to more than 3 deg.; even by convergence to a distance of 4
mtr. prisms of 3 deg. only are overcome. Emmetropia and full visual acuity
on both sides. In Sept., 1880, three years after, the statement remained
unaltered. Patient has only used the prismatic spectacles then
prescribed off and on, as the symptoms are sometimes more troublesome,
sometimes less so, and he exerts his eyes but little on the whole.

A restriction of movement of the internal recti did not exist in these
cases; the absence of the convergent movement is not then to be set down
to the interni not possessing the proper power for acting, but only to
the fact that the impulse for their simultaneous innervation was
wanting. We frequently find this absence of innervation in divergent
squint, and then generally consider it to be a consequence of the
squint, which, however, as the above cases show, need not necessarily be
the case. If preponderance of the externi is at the same time present,
absolute divergence is the result, but not always permanent squint,
frequently only the periodic form. The anomaly of innervation may also
usually be proved in such cases, in that after the removal by operation
of the absolute divergence it continues to exist in the relative form;
it can indeed happen that for a few days after the operation convergent
squint is present for distance, together with relative divergence for
near objects.

The highest phases of this anomaly, as represented in Cases 13 and 14,
are seldom seen. Slighter degrees, which, like so many other things, are
usually designated as "insufficiency of the interni," are more
frequently met with and are combined with asthenopia. On the one hand,
in looking at near objects a tendency exists to the formation of double
images, which are removed by the action of the interni; on the other
hand, however, the habit of binocular single vision is relinquished on
account of the frequent diplopia. In all forms of squint we see that
binocular fusion is forgotten; still it seems more natural to assume
this to be the result, and not the cause of the squint, as Krenchel
does.

Another form of relative divergence is that which is brought about in
consequence of extreme myopia. The change in form of the myopic eye
diminishes its mobility, associated movements of the eyes may be
replaced by turning the head, but this is not possible for the movement
of convergence. Further, in extreme myopia the far point is generally
used for reading, &c., and sometimes even a somewhat greater distance,
because on account of the close proximity of the objects the retinal
images are so large that they are sufficiently clearly recognised even
if they are not quite distinct. At all events accommodation certainly
does not take place, hence one motive favouring convergence is removed.

Finally, however, such considerable convergence as clear vision demands
in high degrees of myopia, would be difficult even for a normally
movable eye. Reasons enough therefore exist for giving up binocular
fixation and using only the more convenient eye for reading, without
effort to the accommodation and convergence. In myopia of high degree
patients almost always read with relative divergence, and these myopes
do just what we must advise them to do, they avoid strain of the
accommodation and convergence of the visual axes and thus keep well.

Notwithstanding that this condition necessarily results from the nature
of extreme myopia, it is frequently held to be pathological, which it
certainly is not in itself. At most, the short-sightedness and change in
form of the eye are pathological; the relative divergence on the other
hand is simply a harmless result of the above conditions.

No doubts whatever exist about this relative divergence. The theory that
the demands on the working eye must be very much increased is quite
unfounded. If any harmful influence were to be feared for the fixing
eye, one would observe the same in convergent squint, when, as a rule,
one eye only is used for fixation even after operation.

In convergent strabismus, however, no one, at least no ophthalmologist,
thinks of entertaining such fears for the eye used in fixation, and
where is the physiological basis of this whole idea to be found? Is the
visual purple more active in monocular than in binocular vision, or what
physiological activity is thereby taxed in increased degree?

I have found no confirmation of Alfred Graefe's theory that in myopia
the eye chiefly used in fixation is frequently affected with choroiditis
of the macula lutea, &c., but have only observed that patients to whom
this happens seek the advice of a physician more eagerly than when the
same intra-ocular troubles befall the other usually neglected eye in
connection with myopia.

Muscular asthenopia undoubtedly occurs; it is only a question whether it
is as frequent as it is diagnosed. It has its foundation in that the
convergence necessary for reading, writing, &c., can only be sustained
by an effort of the internal recti, which exceeds their strength, and
finally results in painful fatigue of the muscles, just as accommodative
asthenopia depends on painful fatigue of the muscles of accommodation.
The similarity reaches still further. We occasionally find that despite
considerable degrees of hypermetropia no asthenopia occurs even in
persons who strain their eyes; while, on the other hand, asthenopic
troubles appear in hypermetropia which are not removed by correction of
the refraction and must consequently have some other motive. Yet still
more is this the case with those disorders, of which muscular asthenopia
may be supposed to be the cause. Notwithstanding the existence of a
considerable preponderance of the externi, muscular asthenopia may be
entirely absent. If we find, for example, that as soon as we do away
with binocular single vision absolute divergence occurs even on looking
at a distant fixed point, and that prisms of 12 deg. to 30 deg. are overcome by
divergence, we may safely assume that the elastic preponderance of the
externi must be overcome in reading, &c., in the interest of binocular,
single vision by a stronger muscular effort of the interni, which is,
however, very frequently accomplished without fatigue. Asthenopic
disorders are also frequently present together with preponderance of the
externi, which continue to exist despite the removal of the same by
operation, and must consequently have some other cause. The diagnosis of
accommodative asthenopia is as a rule confirmed _ex juvantibus_; this
cannot be asserted for the muscular form.

For example, Case 15.--Mathilde F--, aet. 21, has suffered from
asthenopic disorders for three years. The investigation at the beginning
of January, 1880, shows: On the left, myopia 4 D., V. = 5/18, No. 0.3 is
read at 10 cm.; on the right, myopia 6 D., V. 5/24, 0.3 is read with
difficulty, cylindrical glasses cause no improvement. Patient converges
to about 8 cm., on exclusion absolute divergence of 3 to 4 mm. follows,
with slight upward deviation of the right eye.

On correction of the myopia the facultative divergence amounts to = 26 deg.
Here one might easily have concluded the asthenopia to be a result of
fatigue of the interni, but this opinion was refuted by the effect of
the treatment. The double tenotomy of the externi performed on January
2nd was first followed by convergent squint with homonymous double
images, which were united by a prism of 12 deg. with the base inwards. In
the course of a few days single vision was again restored. A fortnight
after the operation, on correction of the myopia, patient could see
singly to 3 mtr.: towards both sides homonymous double images were still
present, and in fixation to 30 cm. relative divergence on exclusion of
one eye. Six months after the operation, on correction of the myopia and
application of red glass to one eye, crossed double images occur close
together, which become homonymous by means of a prism of 3 deg. with the
base inwards. Patient sees double images always, without being much
disturbed by them, yet they cannot be united by means of prisms. The
habit of binocular single vision has also gradually been lost. In
reading (without correction) a movement of convergence takes place (it
cannot be determined whether this answers exactly to the distance of the
object). If, on the other hand, one asks the patient to fix binocularly
larger objects, such as a pencil close to her, she is unable to do it,
relative divergence occurs then, as well as on exclusion of one eye. The
asthenopic disorders remain unchanged and are not removed even by
prismatic spectacles. Despite all reasons then for the supposition the
asthenopia was certainly not of a muscular nature.

The uncertainty as to diagnosis is still greater in those cases which,
according to v. Graefe, were to be designated as dynamic relative
divergence; cases in which with parallel visual axes a disturbed
balance is not present but occurs on convergence in such a way that the
interni only perform their destined work with difficulty, and are
nevertheless urged on in the interest of binocular single vision, till
they give way in painful fatigue.

According to v. Graefe the diagnosis of this condition must be carried
out in the following way. First of all the convergence must be fixed on
a near object in the median line; if one eye remains behind in the
movement it may be accounted for in various ways, for example, the
impediment of movement caused by the change in form of the eye in myopia
or the faulty innervation of the interni mentioned on p. 54. In both
cases for the most part no dynamic, but manifest relative divergence is
present in viewing near objects. It may also happen that the patient
does not converge sufficiently, merely because accommodation is absent.
This experiment does not then prove the presence of dynamic relative
convergence, and v. Graefe came to the conclusion, therefore, that a
normal position of the eyes obtained only by the habit of binocular
single vision must be relinquished so soon as we cause binocular single
vision to cease. Just as under these circumstances dynamic absolute
divergence is manifested in the observance of distant objects, so must
this be the case in dynamic relative divergence in the observance of
near objects. One eye is first excluded while looking at an object about
25 cm. distant, to determine whether it still remains in a proper
position for fixation. We have reason to believe that the position which
occurs in the excluded eye answers to the given conditions of tension of
the muscles. Still it is not necessary to cause binocular vision quite
to cease, it is sufficient and even more advantageous, simply to make
binocular single vision impossible, which we are able to do by means of
prisms. If, for example, a point be fixed lying at the usual distance
for work of 25 to 30 cm., or, according to v. Graefe, a large spot
intersected by a vertical line, and one then applies a vertically
deviating prism to one eye, the influence of binocular single vision on
the ocular muscles is removed, as the fusion of the double images
standing above one another is impossible; and nothing prevents the
assumption of a relative position of divergence instead of a proper
convergent one; as a result of this the double images show a crossed
lateral position as well as the difference in height produced by the
prism. The extent of this lateral deviation may be measured by means of
prisms, which being applied to the eyes with the bases inwards place the
double images again perpendicularly above one another. Von Graefe holds
it to be of importance to determine the strongest prisms which can be
overcome for the given distance by means of convergence and by the
outward movement of the eyes.

On the strength of this method of inquiry there is a prevalence of
opinion that the asthenopic disorders common in myopia are caused by
over-exertion of the ocular muscles; indeed people believe this so
strongly that they assume the presence of muscular asthenopia even in
individuals in whom the habit of working with relative divergence is
already firmly rooted. Relative divergence may perchance cause annoyance
through double images, though this really seldom happens, but it can
never cause muscular asthenopia, for the internal recti muscles protect
themselves by means of relative divergence from any stronger exertion.

Asthenopic disturbances are certainly frequent in myopia, but the above
method of inquiry does not at all prove that their cause lies in the
ocular muscles, for those appearances from which one concludes dynamic
relative divergence and muscular asthenopia, are found in almost all
myopes, even when the latter have no asthenopic troubles, for they owe
their origin to the nature of the myopia. Myopes learn to converge to
the distance of their far point, without exerting the accommodation; if
we now cause a point at this distance to be fixed and then exclude one
eye, or make binocular fusion impossible by means of vertical prisms,
what imaginable reason is there for the excluded eye to remain in proper
fixation? In emmetropia the habitual relation between accommodation and
convergence will be able to ensure that the excluded eye also remains
covering the fixed object, convergently as well as accommodatively; in
myopia, every discretionary relative divergence up to parallelism of the
lines of vision is perfectly justified, because no effort of the
accommodation takes place. How in the world can it be held to be
pathological that a movement of convergence does not occur, when one has
just artificially removed all those physiological conditions which could
possibly have brought it about? If one now likes, as v. Graefe proposes,
to determine the prisms, which can be overcome by means of the outward
movement, there is no doubt about the fact, that with the aid of prisms
the lines of vision may be made parallel or even divergent, the retinal
images indeed, always retaining the same distinctness, in so far as they
are not injured by the prismatic diffusion of colours. There is just as
little reason why the convergence usually attainable should not also be
restored by the aid of prisms with the bases outwards, the retinal
images are not only impaired by the prisms, but the accommodation united
with the convergence, no longer corresponds to the real distance of the
fixed point.

Enough, all these incidents, which are to prove the presence of muscular
asthenopia in myopia, occur when the investigation is carried out as
usual in the region of the far point, entirely on a physiological basis,
and must not therefore be held to be pathological without further proof.

The proof of muscular asthenopia in slight degrees of myopia,
emmetropia, or hypermetropia, is somewhat more certain; a deviation from
physiological laws is certainly present, if we find that the
corresponding convergence does not unite itself with the accommodation
for a near object, we must be quite sure that an exact accommodation for
the fixed point is also really present. It by no means follows because
one causes a large black spot to be observed at a distance of 25 to 30
cm., that an exact accommodation takes place; one can see these things
even with circles of diffusion, the retinal images are already dimmed by
means of the prisms, and one can easily convince one's self that, on the
renunciation of clear retinal images, normal eyes can reach every
attainable convergence or relative divergence by means of prisms.
Insufficient accommodation and defective convergence are, however,
easily caused by all painful sensations situated near the eye, which
make the accommodation uncomfortable and fatiguing. This applies to
every common head- or tooth-ache, and in the same manner to disturbances
arising in the conjunctiva, or which depend on the stretching of the
collective tunics of the eye in myopia, or which allow any other
so-called "nervous" origin to be suspected.

We must place the same claims to the diagnosis of muscular asthenopia as
to that of the accommodative form. Just as the latter is only detected
if convex glasses really give the expected relief, so the proof of
muscular asthenopia is only furnished when relief to the interni is
brought about by means of the appropriate remedies. For myopes, who do
not fall back on the aid of relative divergence, notwithstanding that
they possess a clear field of vision only attainable with difficulty
through convergence, it is the simplest plan to remove the far point to
about 25 to 30 cm. by specially adapted concave glasses. If only slight
myopia or none at all is present, but the relation between accommodation
and convergence is disturbed, the latter can be corrected by means of
prisms with the bases inwards--to be sure, only in a slight degree, as
prisms of more than 4 deg. are scarcely suited for spectacles, partly on
account of their weight and partly on account of the diffusion of
colours. Prisms may be ground with concave or convex surfaces, according
to the requirements of refraction or accommodation.

Finally, if an elastic preponderance of the externi can be proved by
means of considerable facultative divergence, the same may be lessened
by tenotomy of one or both externi; still after my own experience I
cannot advise the performance of this operation unless prisms of at
least 16 deg. are overcome by absolute divergence, for I have seen many
patients in other practices who have acquired convergent squint and
diplopia for distance as the sole result of the operation, while the
asthenopic troubles for near objects continue. The proof that it is not
a case of muscular asthenopia is sometimes only obtained by the
operation.




BINOCULAR VISION IN SQUINT.


The fact that those who squint do not as a rule have diplopia, while
squints depending on paralysis of the ocular muscles are combined with
diplopia, was difficult to explain as long as the view was adhered to of
identical retinal areas founded on anatomical construction. The first
explanation hit upon was that a false identity became established, an
inequality of the retinae; were this the case diplopia must of necessity
occur on correction of the squint by tenotomy.

Commencing with the assumption of a congenital identity which led under
all circumstances to the occurrence of diplopia as soon as the images of
the same object fell in both eyes upon non-identical points of the
retinae, the hypothesis was next advanced that the image of the squinting
eye was not perceived, that a constant suppression of the sensations in
the squinting eye took place. Suppression of sense-impressions does take
place; as soon as our attention is entirely engrossed upon anything, we
are in a position to disregard the impressions upon all other organs of
sense; they do not reach our consciousness. That visual sensations are
easily disregarded may be proved by experiments. Hold a small plane
mirror obliquely before one eye, with the brim pressed into the angle of
the nose so that the objects lying at the side and behind are seen in
the mirror. If the other eye is now used to read with, it is quite easy
to disregard the objects seen in the mirror provided that our attention
is not attracted to places by a particularly bright light. No doubt
those who squint also possess this physiological power, and it is
therefore certain that they make use of it under certain circumstances;
but the suppression theory necessitates that they should constantly and
always do so, since diplopia is bound to occur directly they do not do
it.

The absence of double vision is in fact the only evidence that can be
adduced in favour of the exclusion theory; this negative fact, however,
proves nothing, and is, moreover, capable of other explanations, as soon
as one abandons the theory of congenital retinal identity. The
examination of those who squint demonstrates the untenability of this
theory. People who squint seldom complain of diplopia, but double images
can be rendered apparent in a comparatively large proportion of cases,
usually with the greatest ease, by covering the best eye with a red
glass and squinting with a vertically deviating prism. Many squinters
now admit the presence of double images, but their position by no means
corresponds to the identity theory, their lateral displacement is far
too slight, or patients find themselves unable to localise the position
of the image. It sometimes happens that alternating vision with both
eyes is mistaken for diplopia, the images are then invariably specified
as homonymous; however, with attention it is easy to distinguish this
alternating vision from the simultaneous perception of two images of one
and the same object.

There can be no doubt that in most cases the position of the double
images does not correspond to the principle of identity, and just as
little doubt that one to whom double images are easily made apparent
cannot possess the confirmed habit of always suppressing the image of
the squinting eye. A certain number of cases remain in which it is
impossible to produce diplopia; that these, however, do not constantly
suppress the image of the squinting eye may be proved in the very simple
way I have indicated. An object of fixation is placed in a darkened
room, on one side of and behind the squinting eye is placed a small
flame, the reflection of which, by means of a plane mirror before the
squinting eye is thrown upon its retina. The reflection of the flame is
seen on the cornea of the squinting eye, by slight rotation of the glass
it can be brought into the area of the pupil, and at the same instant
the patient sees the light, the reflection of which can easily be made
to coincide with the image of the fixation object seen by the other eye.
The experiment has then an entirely objective basis, it always succeeds,
a fact on which I lay special stress, even in eyes whose vision is very
defective; therefore here also the habit of suppression of the retinal
images of the squinting eye is not present.

That the squinting eye really possesses its full share of the visual
field can easily be proved (especially in divergent squint) by the aid
of a perimeter. The best eye is covered with a red glass, so that the
objects projected from the fixation point, as well as the excentric
field of vision of this eye, appear red. As soon as the test object
moves towards the side of the squinting eye and enters the visual area
covered by the latter, it appears in its natural white colour, and this
in most cases before it has reached the centre of the retina of this
eye.

Another proof that the squinting eye is really used for vision appears
to me to lie in the fact that persons who squint, provided of course
that the vision of the eye concerned is not very defective, do not show
that uncertainty in the estimation of distance, which is apt to prove so
troublesome to those who have only monocular vision.

[Illustration: FIG. 1.]

If, then, the view of the constant suppression of the retinal images of
the squinting eye is untenable, how is it to be explained that squint as
the result of paralysis of the ocular muscles causes diplopia, while
concomitant squint does not? The answer to this question is clear as
soon as we abandon the supposition of a congenital retinal identity, and
look instead upon the relation of the eyes to each other as harmonious;
identity, or co-ordination as something acquired. Central fixation is
congenital and depends upon anatomical conditions, for as the macula
lutea is anatomically the most perfect part of the retina, it is natural
that the new-born child soon learns to place this part of the retina
opposite objects which attract its attention, and therefore those
relations of the eyes to each other are naturally developed. For
instance, if both eyes (Fig. 1) are directed to the distant point _a_,
the image of point _b_, situated at the same distance, will fall on the
inner half of the retina of the left eye; the left eye will now learn by
experience to refer inner retinal images to objects lying to the left of
the fixation point; at the same time, however, with binocular fixation,
the right eye learns to seek the images of the temporal half of its
retina in the left field of vision, and _vice versa_. From this it is
easy to trace the laws of binocular diplopia. For example, let _a_ in
Fig. 2 be the fixation point, while at the same time the image of _b_
belongs in both eyes to the temporal half of the retina. Now, as we have
already seen, the right eye has learnt to refer temporal retinal images,
to objects lying to the left of the fixation point, while for the same
reasons the left eye projects temporal images to the right. While then
point _a_ is seen binocularly singly, point _b_ appears double, and
certainly the image of the right eye is projected to the left of the
fixation point, and that of the left eye to the right of it, in other
words, crossed diplopia is present. But the eyes are divergent relative
to point _b_; double images then which occur as a result of divergence
(whether relative or absolute) must appear crossed, and one will easily
be able to infer that for the same reasons those double images which
occur in consequence of convergence, must be homonymous. All this,
however, only with the presupposition, that the habit of binocular
fixation is already fully developed; any disturbance of the same, in
whatever way (by prisms, mechanical displacement of the eyes, paralyses
of the ocular muscles, or by those forms of squint which arise after
childhood is past) causes the double images to illustrate the law above
explained. Certainly diplopia may be absent even then, but only in very
rare instances. Now and then this happens in objectively proved ailments
of the ocular muscles, where the patients complain of disturbed vision,
which disappears immediately on the exclusion of one eye (see Case 12),
a method of relief they usually discover for themselves; thus the
indistinct vision is seen at once to be a disturbance of binocular
vision. Many such patients learn to see the double images which formerly
escaped them, after they have been instructed how to do so during the
examination. With others, all efforts are in vain, it is impossible to
render them conscious of the double images, notwithstanding that the
presence of the binocular disturbance of vision proves that the habit of
binocular fixation exists. This apparent contradiction is explained, if
one reflects that the physiological basis of vision rests on a series of
conclusions. The first thing which strikes us as a result of binocular
fixation is, that the images of the centres of the retinae may be
referred to one and the same region of the room, and this experience
will be retained, even if the images on the centres of the retinae
represent different objects in consequence of paralysis of the ocular
muscles; the images are notwithstanding referred to one and the same
part of the room, all objects are thrown together promiscuously, and the
consequent embarrassment is of course removed directly one eye is shut.
The experience of those patients whom it is impossible to render
conscious of double images, despite the habit of binocular fixation,
reaches up to this point. A second conclusion belongs to diplopia, and
for that it is necessary to seek out from the confusion of objects, the
two retinal images belonging to one and the same object, and the
majority of people, though not all, take this second step also. It is
seen at the same time that the opinion held by Donders, that diplopia is
absent in squint, does not suffice, for this reason, because the image
in the deviating eye is too excentric. What becomes then of the image
lying in the centre of the retina?

[Illustration: FIG. 2.]

The absence of diplopia in squint may be explained quite simply by the
fact that the habit of binocular fixation has not been learnt or has
been forgotten; one can learn nothing that cannot be again forgotten.
The normal fusion of the visual fields can only develop in consequence
of binocular fixation, and diplopia is only possible when some kind of
binocular fusion exists. If no binocular fusion exists, then all
possibility of diplopia is excluded. And why should those who squint
from their earliest childhood not see well with both eyes, but yet with
each separately, just as is the case with animals with laterally placed
eyes? For example, in Fig. 3 there is convergent squint of the left eye,
the right eye fixes the point a, whose retinal image is cast at _a_' in
the left eye; the direction outwards in which these images are projected
is discovered by drawing a straight line from _a_ to _c_ (the optical
centre of the eye); suffice it to say that point _a_ is seen by each eye
in the direction in which it really stands.

[Illustration: FIG. 3.]

But although both eyes see at the same time, yet the close relation
which in binocular fixation develops between the centres of the retinae
does not occur in squint; firstly, because the retinal area in the
squinting eye which corresponds to the fixation point is too excentric,
and secondly, because the angle of the squint often changes. In
binocular fixation, the fixation point of one retina answers to the
corresponding point of the other; in squint, on account of the varying
size of the squint angle, if a like relation develops between the eyes,
the fixation point of one retina must correspond to a larger area of the
other. Possibly this explains a fact that is often to be observed. In
those cases of squint where diplopia can easily be caused by covering
one eye with a red glass and the other with a vertically deviating
prism, the double images disappear on rotation of the prism round the
axis of vision, as soon as the angle of the prism reaches an angle of
about 45 deg. The occurrence of double images shows that there exists for
the upper and lower parts of the retinae a community of vision by no
means coinciding with the identity principle. The disappearance of the
diplopia can be explained by the fact that the variations of the squint
angle take place chiefly in the horizontal direction. Therefore the area
in the squinting eye that corresponds to the fovea centralis of the
fixing eye must be more extensive in the horizontal than in the vertical
direction. Alfred Graefe has designated this phenomenon as "regional
exclusion." Whilst then a sort of community of vision exists for the
upper and lower parts of the retinae, the sensations of the retinal area
lying in the horizontal plane of the macula lutea of the squinting eye
must be suppressed. The physiological occurrence of a suppression of the
retinal images, as far as we are able to investigate it, always refers
to the whole retina; however, the possibility of a "regional exclusion"
should not be excluded to begin with; but in the inductive sciences it
is for us to ask first, whether an incident really happens, and not
whether it is possible. The fact from which Alfred Graefe draws his
inference is not, as we have just seen, to be explained in any other
way, and the ophthalmoscopic test described on p. 65 proves that also in
these cases of "regional exclusion" both eyes are used for vision.

In many cases of periodic squint the condition of binocular vision is
very interesting. Binocular fusion may be quite absent even in normal
position of the eyes; on the other hand the non-occurrence of diplopia
in squint does not prevent the occurrence of perfect binocular fusion
with a normal position. In periodic outward squint I have sometimes seen
binocular fixation without the existence of binocular fusion; the
excluded eye deviates outwards, but as soon as it is free it puts itself
into fixation, whilst neither with prisms nor stereoscope can anything
other than alternating vision be proved, _i. e._ neither binocular
diplopia nor fusion.

If squint arises when the habit of binocular single vision has become
confirmed, diplopia is always present, at least at first; even children
of six to seven years old make this statement uninvited, but they soon
get accustomed to the new relations, and after a short time it is
impossible to make them see double images (see Case 42). Habits cling
more closely in adults, therefore that form of convergent squint in
particular, which usually develops quickly in myopia of average degree,
causes annoying diplopia to last for a longer time. For just when these
patients want to employ binocular vision in order to estimate distance
correctly, diplopia occurs to hinder and confuse them.

It is otherwise with the relative divergence which is developed in
consequence of myopia. At first diplopia is present here for a short
time; in this case circumstances are specially favorable to a temporary
suppression of the deviating eye; the fixing eye receives large distinct
images to which the attention is directed. Meanwhile the relatively
divergent eye is usually turned to other more distant objects that
furnish indistinct retinal images, from which the attention is easily
diverted. The habit of suppression may become so dominant that binocular
fixation continues to exist for distant objects and the presence of
binocular fusion is easily traceable, while for near objects, which are
monocularly fixed with relative divergence, it is impossible to render
the patient conscious of the images of the deviating eye.

Considerable squint is by no means necessary for the cessation of normal
binocular single vision; slight, frequently recurring deviations are
quite sufficient, as in those cases where want of control renders
physiological innervation for convergence more difficult. Double images
are present here, although not in a troublesome way, as is usual in
relative divergence, but binocular single vision does not exist even for
distance. The reason for this does not lie in the impossibility of
fixing the same object simultaneously with both eyes, for the
objectively proved deviation may be extremely slight. A union cannot be
obtained even by prisms. If crossed double images are present close
together, a prism of a few degrees base inwards suffices to make them
homonymous. The habit of binocular single vision is lost, in consequence
of that disturbance to the innervation of the interni which is
designated as insufficiency of the same.

The stereoscope, as well as the prism, is useful for testing binocular
single vision, especially when it is suitably modified for the purpose.
The prismatic glasses usually attached to stereoscopes are here quite
superfluous. The advantage of the prismatic deviation consists solely in
the fact that the centres of the images fixed for the macula lutea on
each side can be removed farther from one another than the distance
apart of the eyes amounts to, so that a greater extension of the visual
area is rendered possible. Ordinary stereoscopic pictures are quite
useless for testing binocular vision; it is a question here of employing
diagrams, which contain on the one hand very prominent identical figures
stimulating binocular fusion but which, on the other hand, offer for
each eye special attractions not present in the visual field of the
other. Further, it is desirable to regulate the stereoscope so that the
glasses are not firmly inserted, but that glasses from the trial case
may be applied according to the condition of refraction of the patient
and the distance of the stereoscopic images.

The stereoscope is generally used with the greatest advantage in those
cases where there is no conspicuous deviation, and by testing binocular
vision conclusions may be drawn as to whether normal binocular fusion
exists or has disappeared in consequence of the squint.

It is desirable to use both methods of investigation, that with the
stereoscope as well as prisms, as each test has its own value. One who
at once combines the stereoscopic fields of vision certainly has
binocular single vision; in other cases this is only so far lost that
the stereoscopic combination does not take place at once but only after
some trouble. Care must be taken, especially when one eye has defective
vision, that the corresponding visual field contains objects
sufficiently large and easily recognisable, as very small objects which
do not correspond to the lowered visual acuity are easily overlooked. It
sometimes happens that both fields are seen at the same time, but that
there is no fusion; finally it happens frequently that there is complete
suppression of one visual field. In testing with prisms it may appear
doubtful as to whether binocular fusion or suppression of one eye
exists; however, the stereoscope at once gives us certain information.
It must not be forgotten that the altered relations between the eyes,
which are always possible in squint, also appear at the same time; he
who sees double with prisms, may yet be able completely to suppress the
stereoscopic visual field of one eye. Binocular fusion, suppression of
the squinting eye and simultaneous vision with both eyes without
binocular fusion can alternate in the same individual. Von Kries has
come to the same conclusion, and if our colleague is unable to explain
all the phenomena of binocular vision that he could observe in his own
case, we need not be astonished if we sometimes hear from our patients
statements that appear incomprehensible and unphysiological.

At any rate it is evident that the absence of diplopia in squint can
easily be understood, without adopting the arbitrary idea of a constant,
habitual suppression of the image of the squinting eye.




VISUAL ACUTENESS OF THE SQUINTING EYE.


Whether the state of refraction or the condition of the muscular
equilibrium is held to be the chief cause of squint, defective vision of
one eye will always have to be acknowledged as one of the most important
favouring circumstances; in order to cure squint it is important to have
regard to the visual acuity of both eyes, and not only to the defective
condition. But this is no easy matter.

First it is to be observed, that most cases arise at an age when an
objective determination of refraction is possible, but when the visual
acuteness cannot be determined. Even in children who have received
slight instruction, it is frequently difficult to distinguish whether
imperfect knowledge of the letters or faulty visual acuteness is the
cause of the non-recognition of the test-letters; when testing the
vision of children it is often better to use figures than letters.

Further, in these cases it is much to be desired that the habit of
determining the refraction and visual acuteness at the same time should
be discontinued, particularly in reduced visual acuteness, as the
test-tables only contain a few letters, which have to be recognised at a
distance of 5 to 6 metres. If they have once been read with one eye it
may easily happen that in testing the second eye they are repeated from
memory, without being clearly recognised; even a child soon learns the
few letters by heart. Therefore, when it has been a case of determining
the visual acuteness I have always conducted the examination at a
distance of one metre, as the choice of letters or figures which can be
employed at this distance is much larger than for greater distances. In
every case the reading of test-letters must be used as an additional
means of examination. We must never forget that the test of vision is a
perfectly subjective examination, and that we are obliged first of all
to accept the statements of patients as they are given without knowing
what they are worth. I have met with patients in the most highly
educated classes of society who, in intra-ocular troubles, for example,
haemorrhage of the retinal artery in the macula lutea, could not
distinguish the largest type in the first examination, and the next day
(perhaps with slight difficulty) could read small print.

Such inaccuracies may continue to exist during repeated examinations and
for long periods. One of my patients, for instance, who first came under
treatment in the year 1873, had extreme myopia in the left eye with good
visual acuity; with the right eye, which was also myopic, and had
suffered for several years from choroiditis of the macula lutea he could
read only No. 20 Snellen, and a year later 7-1/2 was read with
difficulty, word by word. Choroiditis of the macula lutea gradually
developed in the left eye, and in the same proportion the statements as
to visual acuteness of the right eye improved, so that finally at the
end of 1881, 0.5 was read with difficulty with this eye, while the left
still sufficed to read 0.4 (at about 5 cm.). As I tried to comfort the
patient, who was very anxious about his left eye, with the fact that the
right eye had considerably improved in the course of the year, he
replied that he might previously have seen just as well with the right
eye if he had only taken the trouble, this was certainly my own opinion.

The attention and intelligence shown by patients during examination
materially influences its results, and one should never hold the first
trial of vision to be conclusive. We must always remember, however, that
all conclusions drawn from visual acuteness become more unreliable in
proportion as the latter is slight. We must attend to some peculiar
difficulties in testing the vision of those who squint or we shall be
liable to make great mistakes. When testing the squinting eye,
particularly in children, it is not sufficient merely to cover the other
or to hold the hand over it, for they know how to bring the usual eye
into fixation by holding the head on one side or peeping between the
fingers; we must keep it carefully closed with a bandage.

It is still more frequently the case that visual acuteness is stated to
be less than it is in reality. The result of always using the better eye
for fixation is, that fixation is not learnt with the weaker one. Even
where there is no squint we see very frequently that in one-sided
hypermetropia the accommodation is only used in that proportion which
has become habitual to the emmetropic eye and does not therefore suffice
to produce clear retinal images, while good visual acuteness is obtained
by means of the correcting convex glasses. In the case of squinters
(even without difference of refraction) it happens very frequently that
the first statements as to the visual power are considerably below the
truth. Patients who assert that they can only read the largest print
with difficulty, frequently read smaller, and even the smallest type
without more trouble, and we must be careful to ascertain this at first.
Accurate reports are usually obtained more quickly by means of convex
glasses or eserine. In any case insufficient accommodation is, according
to this, one of the difficulties, but not the only one, which has to be
overcome before the squinting eye can be put into fixation. We can
understand that the innervation necessary for distinct vision can be set
aside even without loss of visual acuteness, just as we see the movement
of convergence disappear without the interni losing their capacity for
contraction.

In order to explain the relation between squint and defective vision,
we must first consider the question hitherto neglected, or what is
worse, answered with preconceived opinion, as to whether the same form
of defective sight which is so common in squint also occurs without
squint. No one doubts the existence of congenital amblyopia,
nevertheless it has received but little attention in the handbooks on
ophthalmology. Leber, for instance (in the well-known compilation, vol.
v), does not mention it at all.

A more or less considerable reduction of visual acuteness, with good
field of vision, normal sense of colour and normal ophthalmoscopic
condition, are characteristic of congenital amblyopia. Colour-blindness
may of course be present at the same time. I also hold as probable the
very rare occurrence of congenital defects of the visual field in good
central vision, but I will reserve for the present the few observations
I possess on the subject.

Together with congenital defective vision we must consider the
depreciation in visual acuteness usually present in nystagmus, although
it might be asserted that it can neither be the cause nor the result of
the nystagmus, for we find very considerable degrees of congenital
defective sight in both eyes without nystagmus, as well as nystagmus
with remarkably good visual acuteness. Not to complicate the question,
however, I have excluded all cases of nystagmus from the following
investigation. All cases of myopia of higher degree (_i. e._ of more
than 6 D.) have also been excluded, as in such cases for various
well-known reasons the full visual acuteness is never present. In the
case of individual patients who remained for years under my observation
I have been able to convince myself that visual acuteness decreased in
accordance with the increase of myopia; on the other hand, however, it
appeared to me very probable that just those cases of myopia, which from
the beginning do not possess full visual acuteness, have a special
tendency to increase quickly.

For instance, if the examination of a hypermetropic eye, whose defect
can be exactly determined by means of the ophthalmoscope, shows very
faulty visual acuteness which is but slightly or not at all improved on
correction of the hypermetropia, it is clear that the cause of defective
sight is not to be sought in the hypermetropia. It is just the same with
astigmatism. In defective vision with astigmatism proved by means of the
ophthalmoscope, how frequently it is the case that not even the
slightest improvement can be obtained with cylindrical glasses. This is
usually attributed to the presence of an irregular astigmatism situated
near the asymmetric meridian. If we illuminate the eye by means of a
plane mirror, and observe one spot on the pupillary area which looks
sometimes bright, sometimes dark, during slight rotations of the glass,
this appearance can only be caused by the above-mentioned irregularity
of the refraction of light, and it will be easy to determine whether the
same takes place in the cornea or in the lens. But if this appearance is
not present then irregular astigmatism cannot be proved. It is purely
intentional, or a play upon words, if we refer an existing defective
sight to an optic cause which cannot be proved. For instance, if
haziness of the cornea exists, it is not difficult to learn to estimate
by practical experience whether the amount of visual disturbance
corresponds to the optic irregularities caused by the opacities and
irregular refraction of the cornea. Slightly nebulous corneae with
disproportionately bad vision were therefore included in the following
statistics; however, they do not influence the result as there are only
ten cases in all. On the other hand, considerable opacity of the corneae
or cases which were complicated with anterior synechia, &c., were
excluded from the statistics.

If then we find defective vision, the development of which has not been
noticed by the patient, together with normal ophthalmoscopic condition
and full visual field, and if it is further seen that the condition
remains unchanged for years, we have every reason for considering the
defective sight to be congenital. The statements of patients must of
course be received with caution. If congenital amblyopia of moderate
degree exists in both eyes, patients do not usually know that it is
possible for anyone to see better; if the congenital defect is one
sided, it is generally only casually noticed on closing the better eye.
We can scarcely doubt that it is a case of congenital amblyopia if it
happens in children. Acquired defective sight without ophthalmoscopic
cause seldom occurs among children. I have seen a few cases as a result
of severe cerebral disease (hydrocephalus, for example); so-called
anaesthesia retinae, or amblyopia marked by contraction of the visual
field is not quite so rare. It is easy to avoid confounding both these
cases with congenital amblyopia.

One must be more careful about drawing conclusions with regard to
adults, for on the one hand it happens that gradually developed
monocular visual disturbances are only accidentally observed by patients
after they have reached a high degree, and it is very difficult then to
persuade these attentive observers that it is not a case of sudden
blindness of one eye. (Only a few people seem to be really aware that
they have two eyes, and still fewer appear to suspect the existence of a
visual field.)

In all these cases opportunity is hardly given for mistakes with
reference to the diagnosis of congenital amblyopia, as slowly developed
monocular defect scarcely occurs without ophthalmoscopic cause. On the
other hand, ophthalmoscopic symptoms (such as haemorrhage of the retinal
artery in the macula lutea) may disappear without leaving a trace, while
defective vision remains. The law of habit, however, usually helps us
here. In congenital monocular defect patients are generally accustomed
to this condition, and only notice it when special claim is made on the
visual faculty of this eye,--he, on the other hand, who is accustomed
to see with two equally good eyes, may not observe a gradually occurring
blindness of one eye, if his talent of observation be faulty, but I have
never had reason to suppose that a rapid depreciation of the central
visual acuteness of one eye is also overlooked. Rapidly occurring
monocular visual disturbances are noticed, whether detected with or
without the ophthalmoscope.

Two peculiarities appear in isolated cases of congenital amblyopia,
which may render the testing of vision difficult: rapid fatigue of the
retina, and depreciation of the central visual acuteness in such a way,
that an adjoining part of the retina possesses a better visual faculty
than the centre.

Rapid fatigue of the retina occurs in comparatively good visual
acuteness. For example:

CASE 16.--Mr. W--, aet. 35, came under treatment for conjunctivitis. In
testing the vision, emmetropia (or doubtful hypermetropia) was found on
the left, V. = 5/6. Refraction of right eye similar to that of left, V.
= 5/18 to 5/12, but with rapidly occurring fatigue of the retina.
Patient had observed this fifteen years before, when shooting during his
period of army service. Position and movements of the eyes are normal.

This peculiarity occurs more often in higher degrees of defective
vision. For example:

CASE 17.--Mrs. von G--, aet. 60, has always seen badly with the left eye.
On the right H. 1.25 D., V. 5/12. On the left with + 2 D., V. 1/12 with
+ 5 D. words of No. 1.75 were recognised; but the visual acuteness above
stated is only present at the first moment; after a few seconds
everything disappears in a fog. The left eye has a slightly conical
nebulous cornea, detected only on focal illumination, which does not,
however, cause the slightest irregular astigmatism, and cannot,
therefore, serve as explanation of the defective sight.

This rapid fatigue, which only permits the visual acuity present to be
estimated for a short period at a time, may easily result in the visual
acuity being supposed to be worse than it is.

The other phenomenon above mentioned, which occurs in defective vision
without being actually a necessary symptom, is the depreciation of the
central visual acuity, which we designate as central scotoma in acquired
amblyopia. It should be remembered that the visual acuteness which we
determine under these conditions is something different from what we are
usually accustomed to designate by this idea. When we simply talk of
visual acuity we always imply the central visual acuity; however, in
cases where the centre of the retina is so injured in its function, that
the peripheral parts lying near are too often called into requisition,
we do not determine the central visual acuity at all, but that of the
nearest and at the same time best, excentric part. We cannot prevent
patients from using that part of the retina which seems best to them for
recognising the test objects. In such cases (just as in acquired central
scotoma) continuous print is read badly, and with more trouble than one
would expect from the visual acuteness which is specified in the
recognition of single letters. Of course spelling and reading are two
different things; the excentric visual acuity may perfectly suffice for
the recognition of single letters, central and also excentric visual
acuity is necessary for reading. There are patients who, despite full
visual acuteness, are unable to read continuously, as soon as a defect
in the right half of the visual field extends close to the fixation
point. To read fluently, the excentric vision must work on in advance
for the width of several letters, but if the first letter is seen
excentrically, the excentric visual acuteness rapidly sinking in a
physiological way, does not suffice for the following ones.

When testing the vision these circumstances should be carefully
regarded. The apparent contradiction between the visual acuteness
specified with test-letters, and the uncertainty in reading continuous
print, may be taken for simulation (I have seen some sad examples of
this in acquired central scotoma), and, on the other hand, if in the
form of defective vision now under discussion we content ourselves by
merely employing reading tests, we take the visual acuteness to be worse
than it is, or than we find it later when single test-letters are used,
for even though excentric, it is yet always visual acuteness. The
excentricity of that part of the retina put into fixation is usually so
slight, that the oblique direction of the visual axis cannot be seen
with the naked eye; if considerable and extensive defect of the centre
of the retina is present, either varying fixation occurs, sometimes
parts lying to the nasal and sometimes to the temporal side are put into
fixation; or excentric fixation exists; an inner retinal area but
sometimes also a temporal then usually has comparatively the best visual
acuteness.

A third peculiarity which sometimes occurs in extreme degrees of
congenital amblyopia, is monocular nystagmus of the weak eye. This
trembling may be so slight that it is only observable during
investigation with the ophthalmoscope; in other cases it is most marked
as soon as the weak eye is put into fixation by exclusion of the sound
one.

Cases of congenital amblyopia in both eyes, where no explanatory cause
can be traced, and no nystagmus is present, are rare, but all the more
interesting. For instance:

CASE 18.--Mr. F--, aet. 56, has seen badly from childhood; the visual
acuteness of each eye singly examined amounts to 1/18 to 1/12, binocular
1/12. No. 0.75 is read with difficulty at 8 cm. Ophthalmoscopic
condition is normal. In mydriasis by atropine hypermetropia of 3 to 4
dioptres results. With convex 3. 5 D. on the right V. 1/18 to 1/12, on
the left V. 1/12, binocular V. 1/12 to 1/9, with convex 6 D. still only
0.75 can be read, but more fluently than with the naked eyes.

Normal binocular fusion may continue to exist even in extreme degrees of
monocular weak sight; I have observed it up to a visual acuteness of
1/24. The stereoscope is well adapted to prove binocular fusion in these
cases; only we must then take care that sufficiently large letters are
present in the visual field of the defective eye, so that they may
easily be recognised with the existing visual acuteness. Binocular
fusion is naturally rendered still more difficult if the weak-sighted
eye is at the same time hypermetropic to a high degree, as it then
receives simultaneously indistinct retinal images on account of the
difference of refraction; and yet in the above table there are 117 cases
with hypermetropia of at least 2 D. in the better eye, and faulty visual
acuteness in the other, 7 with visual acuteness of less than 1/7 to V.
1/12, and 9 with less than 1/12 to V. 1/36.

In the highest degrees of congenital defective vision, binocular fusion
cannot as a rule be proved; partly because the methods of investigation
by which we are able to prove binocular fusion presuppose the existence
of a sufficient visual acuteness. On the other hand, it cannot be
expected that normal binocular vision can be learnt with such a large
amount of monocular defective vision. If the relative strength of the
muscles is normal, so also are the position and movements of the eyes,
if elastic preponderance on the part of the muscles is present, which in
monocular defective vision of considerable degree is no longer governed
by binocular fusion, and this is frequently the case, squint is
developed.

Sometimes other congenital anomalies are present at the same time with
congenital defective vision (for example, congenital dermoid growths on
the edge of the cornea), and undoubtedly hereditary influences play a
considerable role therein.

In order to determine the relation of congenital defective vision
without squint, to defective vision with squint, I have taken those
cases where congenital defective vision without squint was observed,
together with the cases of squint, from the diaries of my private
practice for the last ten years. I have personally investigated every
case, and the observations on each were carefully examined before being
included in the statistics; all cases with myopia of six or more
dioptres, all cases of double nystagmus, and, finally, all those cases
where the previous existence of squint might be suspected, were
excluded, as above stated. I must also remark that before the last ten
years I had not begun to collect these cases. In order to find monocular
congenital defective vision one must seek for it, as patients usually
come under treatment for quite different disorders, and in the
consulting-room there is not always time carefully to investigate what
possesses interest for us but none for the patient. In cases of squint
the opportunity for investigating the power of vision does not escape us
so easily, and yet the same list, which contains among 629 patients 177
cases of squint with a visual acuteness of 1/8 to less than 1/36,
furnished at the same time 98 cases with undoubted congenital defective
vision of the same high degree without squint, which I place together in
the following review.

Cases of congenital amblyopia with visual acuteness of 1/7 are so
frequent, that I have not drawn up special statistics of them. I was not
anxious to collect a large number of cases but only material for
evidence. I have therefore divided the 98 cases I observed into 3
groups. (1) Cases with visual acuteness of less than 1/7 to V. 1/12; (2)
V. less than 1/12 to V. 1/36; (3) visual acuteness less than 1/36. The
limits between these groups are of course not very sharply defined, for
what is designated as "measurement" of visual acuteness contains, even
if we accept the statements of patients as trustworthy, not an
inconsiderable number of sources of error; and we often find a
remarkable absence of conformity in the analysed causes of congenital
amblyopia, according as we seek to determine the visual acuteness by
means of single test-letters or by reading printed matter. In a case of
visual acuteness of 1/12 No. 0.75 with convex 6 was the smallest type
that could be read, and that with difficulty, larger type was usually
required; and in one case where at first only single words of No. 2.25
were read with difficulty--this test was on that account repeated in
myosis by eserine--No. 1.75 was finally the smallest print which could
with the same difficulty be deciphered. In the division of the groups
here arranged the best visual acuteness ascertained in the various
examinations was always used as the basis.

A. Vision less than 1/7 to V. 1/12 38 cases. The examination of the
better eye showed:


     (_a_) Emmetropia in 18 cases. A determination of refraction,
     mostly ophthalmoscopic, of the weaker eye is submitted in 11
     cases, which divide themselves into, 4 with emmetropia, 3
     with hypermetropia (of H. 2 D. and 2.25 D.), 3 with
     hypermetropic astigmatism, I with myopic astigmatism.

     (_b_) Myopia in 5 cases (3 of M. 1 D. to 1.5 D., 2 of M. 4.5
     D. and 4 D.), the condition of the defective eye was
     determined in 3 cases, and was twice hypermetropic, once
     astigmatic.

     (_c_) Hypermetropia in 8 cases, hypermetropic astigmatism in
     3. In 4 cases an exact determination of refraction even of
     the better eye was for some reason impracticable.

There are 4 cases in this group where the visual acuteness in both eyes
did not exceed the above-stated small amount, and one which was
interesting from another point of view.

CASE 19.--Max L--, aet. 8-1/2, recognises No. 24, and a few letters of 18
at 5 metres with the better eye with convex 6 D.; at 1 metre V. 1/4 to
1/3, the left eye recognises only No. 60 at 5 m. with + 6 D. at 1 m. No.
0.75 is read with difficulty. If we exclude one eye it lapses into now
less, now greater convergence, and still no squint is present, but
diplopia as well as binocular fusion can be proved by the aid of prisms.
The theory of Donders that squint is less frequent in hypermetropia of
high degree because too strong convergence would not suffice to furnish
clear retinal images, is scarcely tenable in the face of such cases. If
indistinct retinal images are added to a visual acuteness of only 1/3 to
1/4 still, even with faulty accommodation, it is difficult to believe
how a child could learn to read if it did not hold the book close to its
eyes, which was not the case here, and indeed seldom happens. Therefore,
in spite of defective vision the accommodation must have sufficed,
without sacrificing binocular fusion, whilst in all probability
accommodative convergence followed on exclusion of one eye.

B. 48 cases had visual acuteness from 1/12 to 1/36. The better eye was--

     (_a_) Emmetropic in 16 cases; in 6 of them the refraction of
     the defective eye was determined, which showed in one case
     emmetropia, 3 hypermetropia, 2 astigmatism.

     (_b_) Myopia of the better eye was present in 7 cases (in 3
     myopia of 1 D., in 4 M. 3 D. to 6 D.).

     (_c_) Hypermetropia in 18, astigmatism in 4 cases. In 3
     cases the condition of the better eye was, for some reason
     or other, indeterminable.

In this group I should like to point out the following cases as worthy
of attention:

CASE 20.--Margarethe T--, aet. 16, has hypermetropia 2 D. in the right
eye, V. 5/6, in the left the ophthalmoscope shows with an otherwise
normal condition a higher degree of hypermetropia, with + 6.5 D., V.
1/18, with + 10 D. No. 3.0 is read. No spectacles have been used until
now; for the past few years school tasks have been performed with a
certain effort, only during the last year the asthenopia has increased.
Squint is not present, and with prisms as well as with the stereoscope
(by the use of objects, whose size corresponds to the defective sight on
the left side) binocular fusion can be proved.

The case is the same as regards divergent strabismus.

CASE 21.--Mr. H--, aet. 28, has myopia 6 D., V. 6/9 in the right eye; the
left eye has always been weak sighted, emmetropia is detected with the
ophthalmoscope, with normal fundus, V. 1/18. No squint, binocular fusion
can be proved with prisms.

CASE 22.--Mr. B--, aet. 47, has hypermetropia 5 D., V. 5/9 in the right
eye. Left eye with + 5 D., V. 1/18 (a few letters of 12 also were
recognised at 1 m.). It seems, however, that the patient is not able
exactly to indicate the position of the retinal images of his left eye,
he does not know, as he expresses himself, "whether the letters stand
here or there." Patient observed the defective sight long ago; the
ophthalmoscopic condition is normal. Patient really comes on account of
his son, aged 7-1/2, in whom hypermetropia of 3.5 dioptres is detected
with the ophthalmoscope, right eye with + 3.5 V. 5/9. Left eye has
convergent squint, V. 1/36, No. 3.0 is read with + 6.5 D.

The hereditary tendency is seen also in the following case:

CASE 23.--Mrs. S--, aet. about 46, on the left H. 4 D., V. 5/18 to 5/12,
has used no spectacles until now, and reads No. 0.75 without glasses at
about 15 cm. R. with + 4 D., V. 1/18, with + 6.5 D. large letters of No.
5.0 are recognised.

Two sons, present at the same time, are hypermetropic. One has in either
eye V. 1/4, the other a slighter degree of congenital amblyopia.

CASE 24.--Johanna L--, aet. 4, came under treatment for a congenital
fibroma covered with hair, about the size of a cherry-stone, situated on
the outer corneal margin of the left eye, which was removed. Three years
later, when the child had learnt to read, emmetropia and full visual
acuteness was observed in the right eye, with the left No. 4.0 only is
read with difficulty. The ophthalmoscope shows a slight degree of
irregular astigmatism of the cornea, which in no way explains the
defective vision; the image of the fundus is perfectly clear and quite
normal.

CASE 25 afforded me a not altogether pleasant surprise. Martin M--, aet.
58, has matured cataract in the right eye, with perfectly satisfactory
light reflex, proper projection, &c. On the left progressive cloudiness
of the lens has begun. The course of operation and cure were regular in
every respect, but the power of vision finally was so small that with a
clear pupillary area, and otherwise normal condition, only single words
of No. 3.0 were recognised with difficulty at 10 to 15 cm. with convex
20 D. For the first time the patient remembers that he noticed the
defective sight in his right eye at the age of sixteen, and was for this
exempt from army service. The operation performed later on the left eye
procured satisfactory vision.


C. Visual acuteness of less than 1/36 12 cases.

Determination of refraction of the better eye is given in 6 cases, and
showed twice emmetropia, twice slight myopia, twice hypermetropia. I
only possess an exact ophthalmoscopic determination of the condition of
the defective-sighted eye in one instance with H. 2.5 D.

This group is of special interest in that it represents the extreme
degrees of congenital amblyopia, and, on the other hand, because it
contains 5 cases of children under 10 years of age.

CASE 26.--Constanze von M--, aet. 9-1/2. Defective vision on the left
side had been noticed long before by the child's parents. On May 1,
1879, emmetropia was observed in right eye, V. 5/12 to 5/9. No. 0.4 is
read at 15 cm. On the left, only movements of the hand are seen, fingers
cannot be counted even when close to the eye; the visual field is good,
that is, on moving the hand in the periphery of the visual field the
child sees "something" without being able to state what it is. Reaction
of the pupils as rapid and equal as usual. The ophthalmoscopic condition
(even with dilated pupils) is perfectly normal. All tests for simulation
were of course applied.

On account of the importance of the case, I suggested another
examination a year and a half later, on the 22nd December, 1880, which
showed precisely the same result as the former one--optic disc, macula
lutea, &c., perfectly normal, the ophthalmoscopic determination of the
refraction shows H. 2.5 D.

The child's father also possesses in the left eye a slight degree of
congenital defective sight, observed for many years, with normal
ophthalmoscopic condition; No. 0.5 is read with + 6.5 D. at 10 cm.

CASE 27.--Tina S--, aet. 6. The defective sight of the left eye had been
remarked some months previously; report on July 16th, 1878: R. full
visual acuteness, L. movements of the hand are scarcely visible. The
child cannot count fingers. Normal ophthalmoscopic condition. Eserine
and separate use were prescribed. On September 9th, 1878, fingers were
counted with the left eye at 1.5 m., single words of No. 4.0 were
recognised, No. 3.5 with convex 6.5 D., but always with oscillating
fixation. The improvement in the child's statements may be referred to
the fact that she had meanwhile learnt to form right conclusions from
the very imperfect sensual impressions of her left eye.

CASE 28.--Frank J--, aet. 10. Left eye. V. 10/50 to 10/40, No. 1-1/2
Snellen is read at 4 inches. On the right, nystagmus on fixation,
fingers are counted at 5-6 feet. The ophthalmoscopic condition is
normal. A sister of the boy squints.

CASE 29.--Ernest G--, aet. 8, has slight nebulae on both corneae. On the
left V. 15/40. On the right, fingers are counted at 4 inches with visual
axis deviating inwards.

CASE 30.--I operated on Moritz L-- for congenital cataract before he was
a year old in 1869 by means of a needle operation. In June, 1877, a thin
ophthalmoscopically transparent secondary cataract appeared in both
eyes; on the left, with convex 12 D. V. 3/24 to 3/18, with convex 16 D.
No. 0.4 is read at 10 cm. On the right, with convex 12 D., fingers are
counted with difficulty at about 1 m., with inward deviation of visual
axis.

CASE 31 is also worthy of note. Carl H--, aet. 22, shows quite a number
of congenital anomalies on the left side of the face, harelip, deformed
nostril and a skin defect on the inner corner of the eyelid. There is a
congenital dermoid growth of the size of half a pea situated on the
inner lower corneal margin. A slight irregularity in the curve of the
cornea near the dermoid is detected with the ophthalmoscope; the fundus
of the eye is perfectly normal. Fingers are not counted further off than
a metre with visual axis deviating inwards. The right eye is emmetropic
(perhaps slightly hypermetropic), and has full visual acuteness. There
is no squint.

It is customary to "explain" these cases of monocular amblyopia by
previously existing squint, and one is quite satisfied if by the
examination of patients it is only possible to prove that they have
occasionally squinted, although the advocates of the amblyopia ex
anopsia disallow the presence of the same under these conditions, that
is, in periodic squint. Of course a theory which cannot exist without
the assertion that occasional alternation suffices to hinder the
development of defective vision caused by disuse, cannot possibly hold
periodic squint to be the cause of it. Certainly permanent squint may
also disappear, but this much I have been able to determine, that this
seldom happens before the twelfth year of life, and one may surely
reckon that children in whom permanent squint is developed at the usual
early period of life, still squint at the age of ten years. Cases 24 and
26 to 30 can under no circumstances be explained by previous squint,
notwithstanding that they represent the extremest degrees of amblyopia,
but the question is undoubtedly that of congenital defective vision;
moreover I have excluded from the statistics of congenital amblyopia all
cases in which the previous presence of squint could even be supposed.

A table of the cases above described with reference to the defective
condition is interesting; when a determination of refraction existed for
the weak eye I have given it, and when this was not the case I have
stated that of the better eye, thus it is seen that among 85 cases in
which the refraction was determined, hypermetropia (including
hypermetropic astigmatism) was present in 39. Hypermetropia was found
then in 47 per cent of all the cases. The percentage would probably be
higher, if all weak-sighted eyes had been examined from the beginning as
to their state of refraction, but as I only learnt to know the relation
between hypermetropia and the higher degrees of congenital amblyopia
from my statistics, I did not take notice of this relation when
investigating individual cases.

How does congenital amblyopia now stand in relation to that disturbance
of vision which we observe in squint? I see no difference; whether
squint is present or not, the form of defective vision is precisely the
same, and nothing happens in the combination with squint which could not
also be proved without it. The relation to hypermetropia, which is
proved with congenital amblyopia, also appears in squint.

A collective table of cases of convergent and divergent squint included
in the statistics (pp. 19 and 47) shows:

  (_a_) In myopia, emmetropia, and doubtful hypermetropia,
        with convergent and divergent squint together
        329 cases. Among them:
          Visual acuteness to 1/7                     239
                 "         less than 1/7 to V. 1/12    19
                 "             "    1/12 to V. 1/36    46
                 "             "    1/36               25
        Defective sight of higher degree than 1/7, 27.3 per
          cent.

  (_b_) In hypermetropia 1 to 3 D., including the few cases
        of hypermetropia with divergent squint, 177 cases.
        Among them:
          Visual acuteness to 1/7                     121
                "          less than 1/7 to V. 1/12    17
                "              "    1/12 to V. 1/36    27
                "              "    1/36               12
        Defective sight then, 31.6 per cent.

  (_c_) In hypermetropia 3 D. and more, 70 cases with convergent
        squint, with:
          Vision to 1/7                                39
          V. < 1/7 to V. 1/12                           8
          V. < 1/12 to V. 1/36                         14
          V. < 1/36                                     9
        Defective sight then, 44.2 per cent.

This regular increase of defective sight with the increase of the
hypermetropia can be no mere accident, and speaks strongly for the
identity of defective vision in squint with congenital amblyopia. Were
defective vision caused by the squint the various states of refraction
would show no difference in the percentage of defective vision.

Further, the circumstance is worthy of remark that among 198 cases of
periodic squint (convergent and divergent) which are applicable for the
statistics of visual acuteness--

         170 possess V. to 1/7.
          16    "    V. < 1/7 to V. 1/12.
           9    "    V. < 1/12 to V. 1/36.
           3    "    V. < 1/36.
    14.2 per cent. then of defective vision of considerable degree.

That defective sight on the whole plays an influential part as a cause
of squint is doubted by no one, indeed we see blind eyes lapse into
squint as soon as the conditions necessary to it are supplied by the
muscles. Of all the prevailing causes present defective vision will be
the more decisive in proportion as it is of high degree; for the motive
which despite the presence of favouring circumstances can prevent the
real occurrence of squint, binocular vision, becomes less efficacious as
the defective vision becomes more considerable. As binocular fusion
takes place frequently in periodic squint, for a time at least, that is
as long as proper fixation lasts, one can understand that periodic
squint exists chiefly in cases where the visual faculty of both eyes is
good. Even the highest degrees of congenital amblyopia are not excluded,
for periodic squint appears where the faculty of binocular fusion has
been completely lost. Further, that considerable congenital defective
sight is more frequent with than without squint, may be accounted for
quite simply by the fact that, in extreme degrees of it, binocular
fusion cannot be learnt at all, while in the lesser degrees it is more
easily forgotten again.

If defective vision is undoubtedly one of the causes of squint, we must
seek for the grounds upon which it has been taken to be a consequence of
squint, and described as amblyopia ex anopsia. I will not inquire to
whom the honour of this invention belongs. I do not want to write a
history of mistakes but only to examine the basis of the views now
current. The most complete record of the same may be found in the
well-known journal on the 'Cure of Eye Diseases,' vol. v, p. 1011.
Leber, who does not seem to recognise the existence of congenital
amblyopia, has shown quite a special predilection for amblyopia ex
anopsia.

Amblyopia from want of use, which formerly included all possible
disturbances to vision, great and small, is now only accepted in two
cases, for squint and congenital cataract, if the latter is not operated
on very early in the first or second year of life.

The fact is simply this, that in congenital cataract even the most
successful operation is frequently deceiving as to its issue without
ophthalmoscopic report; this is the more disagreeable as the most exact
reflection test before the operation fails to prove the existence of
this defective sight. But does it follow from this, that congenital
cataract has induced defective sight from want of use? We find the same
defective vision also in congenital defective development of the
transparent lenses (so-called luxation of the lens). On the whole, we
often find several congenital defects in the same individual. The very
circumstance that the cataract is congenital makes it probable that the
defective sight is so also, or are we to take congenital cataract as
being a guarantee against congenital amblyopia?

Von Graefe, who first considered this defective sight to be congenital,
designated it in his later lectures as originating from want of use,
probably in order to advise the earliest possible performance of an
operation. There is no mention of his having brought forward evidence
for this assertion; that the great master himself said it was enough,
and the host of believers felt themselves to be the happy possessors of
a new dogma.

A number of children appeared in my practice, in whom congenital
cataract was needled by von Graefe in the first or second year of life
with recovery of transparent media, who showed, however, the extremest
degrees of defective vision when they were sufficiently intelligent to
have their vision tested. Whoever is interested in this can find a
number of such cases in the Royal Institution for the Blind at Steglitz,
which I am accustomed to visit several times a year by request of the
committee. On p. 91 I have related a case of monocular congenital
defective sight in congenital cataract of both eyes.

Everywhere then the principle holds good, that whoever makes an
assertion must be prepared to verify it; amblyopia from non-use is
denoted as an inherited trouble, and still not a single observation
exists which furnishes proof that an eye of previously ascertained good
visual acuteness has become amblyopic in consequence of disuse, a fact I
drew attention to ten years ago. Leber replies to this, he remembers "to
have seen patients with complete amblyopia in the squinting eye, who
stated that its visual faculty had been found to be good during an
examination instituted years before." Is this intended as an
observation? By that I mean is it a proof of facts, for the
trustworthiness of which he holds himself responsible: in the handling
of scientific questions I do not place the least reliance on the dim
recollections of unnamed individuals. Even in personally conducted
examinations we must be on our guard to avoid mistakes, and now we are
confronted with mere recollections of tests of vision!

By means of the above observations the theory that "the peculiar variety
of monocular amblyopia which is so frequent in monocular squint is
hardly observed without squint" is sufficiently disproved.

Leber seeks to enfeeble Alfred Graefe's statement that the presence of
extremely defective vision may sometimes be proved at a very early age,
in children who have only squinted a short time (the rapid development
of amblyopia in consequence of the squint really appears incredible), by
the assertion "that just at the earliest age, when the activity of the
optic nerve is not yet sufficiently strengthened by use, the conditions
for producing amblyopia from non-use are most favorable with complete
exclusion of one eye," but complete exclusion of the squinting eye does
not take place even in extremely defective sight, as can easily be seen
by the mirror test (p. 66) I described fourteen years ago. Which
activities of the optic nerve apparatus are strengthened then by use?
Perhaps visual acuteness? The physiological conditions of this are only
to be sought in the anatomical structure, and the physiological
arrangements of the retina or the visual organs, which cannot be changed
much by use. What we can learn from the visual act relates solely to the
conclusions which we are able to draw from sensual impressions; but
visual acuteness, _i. e._ the faculty for the recognition of distinct
points, is an anatomical, physiological gift, and not a thing to be
acquired.

The opposing observation, that squint, even of monolateral character
dating from earliest childhood, continued to the middle and later years
of life, can still exist with very good visual faculty, may easily be
explained by alternation from time to time. If that is so indeed, if
squint begins during the presence of good visual acuteness, and nothing
further is necessary to its maintenance than alternation from time to
time, why should defective vision from non-use ever be developed? With
good visual faculty on both sides alternations also occur from time to
time.

Still more convincing are those cases which are numerous where the
visual acuteness of the squinting eye only amounts to about 1/7 to 1/12,
and where, on this account, there is no alternation. Were this defective
sight acquired through non-use it must of necessity be progressive; it
must exist in proportion to the duration of the squint. A moderate
experience will suffice to show that this is not the case. And further,
defective sight must continue progressive even after removal of the
squint by operation, for by the operation nothing is changed in the
relations of the binocular vision present in squint, which are dismissed
with the one word, "suppression," by the advocates of defective vision
from non-use.

Moreover, suppression may exist for years without the slightest
disadvantage to the visual faculty.

CASE 32.--In November, 1873, I operated on Fritz F-- for a slight
divergent squint of the left eye. Slight hypermetropia was present on
both sides, and nearly full visual acuteness. In October, 1880,
perfectly normal position of the eyes showed itself with the same visual
acuity and emmetropia in both eyes; at the same time, however, the boy
affirmed that when reading he could never see with his left eye but only
with the right; in reality only the right visual field was perceived in
the stereoscope.

The second reason brought forward is, that the variety of amblyopia from
non-use is quite a peculiar one; "it consists of a functional
disturbance of those parts of the retina whose images belong to the
common V. F., and are suppressed in squint in order to render vision
distinct--the macula and the temporal and only a part of the nasal
halves of the retina." Does this hold good for all cases of amblyopia in
squint, or do those cases only belong to amblyopia from non-use where
excentric fixation takes place with an inward deviating visual axis? It
would be difficult to draw the line. I have seen a case in which the
squinting eye possessed a visual acuteness of 5/36 together with
excentric fixation and nystagmus; however, I attach no value to isolated
cases. We frequently find excentric fixation with a visual acuteness of
1/12 to 1/36. Further, those cases cannot possibly be regarded as
results of squint, which possess unsteady oscillating fixation or
rapidly trembling nystagmus, which occurs as soon as the squinting eye
fixes. But this conclusion is false, even for the excentric fixation
with visual axis deviating inwards; if it were right the angle at which
the eye deviates inwards on fixation in convergent squint would always
be greater than the squint angle. Those cases are, of course, more
remarkable where this is not the case; however, on close investigation
those cases are more frequent where the angle of deviation is about the
same size or smaller than the squint angle, and is fixed with a part of
the retina which undoubtedly belongs to the common visual field.

On p. 91 I have described two cases of excentric fixation in children
who had never squinted, and it is only necessary to take a little
trouble to repeat the mirror test which I described, to be convinced
that squinting eyes have not lost the power "of using those parts of the
retina," even if they are amblyopic to an extreme degree; without the
slightest doubt the reflection is perceived as soon as it falls on the
retina.

Value is attached to the improvement produced by the separate use of the
squinting eye. According to my experience no higher visual acuity can be
attained by use of the amblyopic eye, than that which is best detected
by the aid of eserine in the first examination, if it is only carried
out thoroughly enough. No doubt if we proceed otherwise, and rest
content with whatever statements the patient likes to make, without
giving ourselves any more trouble, we may expect the most superficial
diagnoses to show the most astonishing therapeutic results, as, indeed,
often happens. And now, talking of strychnine injections! When two
celebrated ophthalmologists occupy themselves simultaneously with the
therapeutics of strychnine, one of whom obtains the most astonishing
results in atrophic troubles of the optic nerves, but, on the other
hand, obtains no real improvement in "amblyopia from non-use," while the
other can show brilliant success in the last-named form of defective
vision, and, on the other hand, none in atrophy of the optic nerves, we
may perhaps conclude that both are right, if even really on the negative
side, and that the circumstances are the same in the tests of vision.
Again, we must examine more closely some of the cases, in which
strychnine injections showed a brilliant result. (Anyone interested in
the original work can read up the 'Vienna Weekly Medical News' for the
year 1873.)

"1. Wilhelm H--, a strong healthy boy, aet. 12, complains of defective
vision. Right eye has nothing abnormal in its outward appearance, and
just as little in the fundus. V. 16/100, H. 2.5 D., Snellen IV-I/II; is
the smallest type he reads at 3 to 7 inches. With + 10, I-I/II is read
at 4 to 6 inches. Left eye V. 16/70. H. 2.75 D. II-I smallest type
legible at 3 to 12 inches. With + 4 D. I-I/II is read at 4 to 6 inches.
On March 14th, 1872, first injection of strychnine with 0.002 gr. in the
temples. An hour later V. of right eye 16/70, left unchanged. On March
23rd, 1872, after one injection daily, V. of each eye is 16/50."

Patient shows then in the right eye visual acuity 16/100, with manifest
hypermetropia 2.5 D.; in all probability the total hypermetropia really
present was higher, and was scarcely corrected by means of convex 4 D.
If the patient now reads No. I-I/II Snellen with + 4 D. at 6 inches,
this proves a visual acuity of 1/3 during the first investigation before
the strychnine injection, and shows that the estimate of 16/100 was
inaccurate. At the close of the treatment, only a visual acuity of 16/50
(almost exactly 1/3) is specified for distance. The result seems to me,
then, to be this, that the patient during repeated examinations has
gradually learned to make more accurate statements, indeed, with a boy
twelve years old one can scarcely expect it to be otherwise.

"4. Paul A--, aet. 18, was operated on ten years ago for internal squint
of the right eye, and dismissed with + 2 D. for distance, and + 6.6 D.
for near use. He now complains of decrease of his visual acuity. The
eyes are normal externally and internally. Hyperopic formation in a high
degree. Right eye V. 1/20, with and without convex glasses, without
glass only VIII-I/II with difficulty, with + 6 V-I/II the smallest. Left
eye appears emmetropic, but is decidedly hyperopic. V. 5/4. Glasses are
rejected; I-I/II is read fluently at 6 to 12 inches. After one injection
the right eye recognises III-I/II with + 6, after the second II-I/II,
after the eighteenth I-I/II with difficulty. The visual acuity, however,
remains at 1/20, and is not changed after six months, although latterly
patient daily practised with + 3 D."

Visual acuity of 1/20 suffices to read III-I/II at 2.5 inches, II-I/II
at 1.5 inches, and I-I/II at about 1 inch; clear, retinal images are
then scarcely obtainable, but we know what hypermetropes can do in that
case; besides this, if the patient is examined for weeks by Snellen's
method, he may get so far as to realise fairly well "the strange fate of
that man" of I-I/II, despite larger diffusion circles; in any case
vision remained at 1/20, despite strychnine and separate use.

In extremely defective vision little importance should be paid to the
fact of slight diversity in the statements, as where visual acuity
amounts only to about 1/36, or where fingers are counted at a distance
of 1 to 2 metres, it is quite immaterial, as far as the usefulness of
the eyes is concerned, whether fingers are counted at a half or a whole
metre, and we ought never to forget that all conclusions which we draw
from the state of the visual acuity, are unreliable in proportion as the
latter is lowered. Indeed, on repeated examination of such cases we
frequently find considerable fluctuation in the statements of the
patients, therefore we ought not to expect accurate statements for very
inexact sensual impressions.

By separate use, even in extremely defective vision, no improvement in
visual acuteness is developed, but only a more complete acquirement of
the power of deducing right conclusions from imperfect sensual
impressions. That which has been most unscientifically designated as
"suppression of diffusion circles," depends solely on this method of
use. As with indistinct retinal images so with facial impressions which
are insufficient, one can never learn to recognise larger objects
aright.

We must never forget that vision is a conclusive act acquired by
practice; whoever sees well with one eye, and is weak sighted with the
other, acquires this end only for the sensual impressions of the better
eye, and must first collect experience for the defective eye, before he
can use it.

Leber has recently joined those cases which are described as blindness
through blepharospasm, to amblyopia from disuse. First, I wish to
observe that blepharospasm is not a necessary cause; I have seen the
same disturbance of vision follow severe double blenorrhoea, which
destroyed one eye but left the other uninjured. These children are
always of an age which renders any trial of vision impossible, and we
are therefore obliged to draw conclusions as to visual power from the
movements of the body. If children move as though they were blind, it
need not necessarily follow that they are so in the common meaning of
the word. The art of vision is a difficult one, the acquisition of which
begins with the earliest days of life; we do not call every person blind
who does not see what is before his eyes, because he does not understand
how to see it. A child who has only imperfectly learnt the conclusive
act of vision, and forgotten it again during a continued disuse of both
eyes, will not know how to use perfect visual acuity, and will move like
a blind person till he again learns to estimate the relations between
his retinal images and the things of the material world, which happens
in a very short time.

After this digression let us turn again to amblyopia from disuse, and to
the last trump which is played for it. "Those cases are very remarkable
where an immediate improvement occurs after tenotomy in amblyopia of
high degree, which according to this is certainly produced and
maintained by the squint." As proof a case is cited by Knapp, who
describes it in the following words:--"The improvement in visual power
varied very much. In many cases it was indefinable, in others very
pronounced; for example, in one case, where it was very great before the
operation, only No. 16 Jaeger could be read at 1 inch, while after it
No. 2 was read at 8 to 9 inches."

And we are to believe wonders on the strength of this scanty
communication! It is an every-day experience that a person who squints,
who has just asserted his inability to read the largest type,
immediately afterwards reads smaller and the smallest type, and it would
at least first have to be determined that all endeavours to produce a
better visual result before tenotomy were unsuccessful; but as the
communication stands, the conclusion as to the effect of tenotomy is
quite a superficial _post hoc ergo propter hoc_. Moreover, I had this
case in view when I spoke on this matter in the first edition of my
'Handbook:'--"The frequently repeated assertion that a considerable
improvement of vision may occur as a direct result of tenotomy, is so
little in accordance with all the laws of physiology, that inquiries
must be instituted _ad hoc_, and carried out with the most perfect
exactitude. Only trials of vision which are carefully carried out and
repeated several times before the operation, and which have regard to
visual acuteness for distance as well as for near objects, the latter
indeed by the aid of convex glasses or Calabar extract, can be
recognised as proving anything in face of such a perfectly improbable
assertion. In the course of examinations so instituted I have not myself
found that tenotomy exercises any direct influence on visual acuity."

I would not have given so much space to this explanation had not a
principle been in question. The occurrence of amblyopia as a result of
non-use has been deductively constructed and is not inductively proved
by observation. It is just an article of faith, and in science we cannot
rely on such things; we must not depart from the inductive method.




ON THE CURE OF SQUINT.


Therapeutic investigations have their safest and most instructive basis
in observation of the course of a disease as it appears without
complications, and with no unusual symptoms; we can only arrive at a
certain decision as to the extent of our therapeutics when we know
exactly what will happen without skilled assistance. When squint is once
present it is seldom complicated by fresh symptoms; on the other hand,
spontaneous cures unquestionably take place. We must certainly not rely
simply on the statements of patients themselves. On p. 1 we have seen
what mistakes occur, even when it is a question of whether squint is
present or not. How little such vague statements are worth is seen by
the fact, that the question as to the direction of the previous squint
very seldom finds a satisfactory answer; as a rule it is impossible to
determine whether periodic or permanent squint has been present.

If we undertake the task of converting the statements of patients as to
previous squint into observations, in order to confirm the statements
from the objective material, we must first prove whether the squint
cannot by some means be still produced (by excluding the eye or by
raising or lowering the eyes). Thus the condition of binocular vision
offers us valuable guides. If we find that binocular fusion does not
exist with available power of vision on both sides, but that the same
conditions of sight appear in the eyes as we have learnt to attribute to
squint, there is no reason for doubting the statements about a
previously existing squint. It is otherwise in those cases of extreme
amblyopia where normal binocular vision is never expected, or at least
cannot be proved on account of the enormous difference between the two
eyes.

If we discover the existence of normal binocular fusion, squint may
nevertheless have been present at a former time, for in many cases, of
periodic squint particularly, the habit of binocular fusion is never
quite lost.

That squint can disappear of itself is unquestionable; how often this
happens it is difficult to say. The fact that in ophthalmic practice we
see many more squinting children than adults is best explained by
this,--that squinting children are brought to us by their parents, while
adults who still squint have usually given up any desire for a cosmetic
improvement, and only come under treatment accidentally or on account of
other ailments; lastly, a considerable number of cases are cured by
operation. If the squint has disappeared we only discover by accident
that it was ever present. The fact of its previous existence may usually
be determined by other signs more positive than mere statements from
memory; with reference, however, to the age at which the spontaneous
cure takes place we are left to depend almost entirely on the patient's
statement. As far as I have been able to determine, the period from the
ninth or tenth up to the sixteenth year seems to offer the most
favorable conditions.

We rarely have an opportunity of watching the disappearance of squint,
still I have observed two cases in which a permanent convergent squint
disappeared after about a year. In both cases the squint had arisen in
young people (of eight and nineteen years of age) in the course of
irido-choroiditis which terminated in blindness, and disappeared with
the sight. The fixing eye was emmetropic in one case, in the other the
condition of error could not be determined owing to nebulae of the
cornea.

We more frequently see periodic squint disappear.

CASE 33.--M--, a boy aet. 10, was first examined by me in April, 1873;
the right eye has hypermetropia 4.5 D., and almost full visual
acuteness, the left has convergent squint, and recognises No. 6-1/2
(Snellen) with convex 10 D.; V. = 1/18 at 1 metre. (The boy's father
also squints with the left eye, which is amblyopic to a high degree (V.
= 1/36), right eye has emmetropia, and full visual acuteness). The
prescribed spectacles (convex, 4.5 D.) were used for working, but not
continually; still three years later, in 1877, the deviation was
considerably less and only occurred occasionally. In March, 1880,
nothing more was seen of the squint, only slight convergence still
recurred on excluding the left eye. Patient now wears convex 4.5 D.
constantly.

On account of the importance which the disappearance of squint possesses
in hypermetropia I will describe a few more cases which belong here.

CASE 34.--Mrs. B--, aet. 32, has on the left H. 1.5 D., V. 5/9; on the
right H. 1.5 D., V. 5/12, binocular vision (H. =.75 D., V. = 5/6 to
5/9). Asthenopic troubles are the cause of her present complaint. She
says she squinted with the right eye as a child till her eighth or ninth
year; the present position of the eyes is quite normal; ordinary type is
read at the usual distance with normal fixation without glasses.
Particularly keen fixation is rarely followed by squint, which may be
produced by excluding the right eye; the latter then deviates about 5
mm. inwards and slightly upwards; the secondary deviation of the left
eye is rather less. Only the left visual field is seen in the
stereoscope.

CASE 35.--Mrs. W--, aet. 31, has on the right H. 3.5 D., V. 5/9, on the
left V. = 1/16 with + 4 D., single words of No. 0.8 are read (mother and
aunt have also congenital weak sight in this eye). Position and movement
of the eyes are perfectly normal, exclusion of the left eye is followed
by slight relative divergence. In answer to my question whether she had
not previously squinted, patient replied that she did not know, it had
always been a matter of dispute in her family; as, however, only the
right visual field was seen in the stereoscope, we may be sure that
squint had been present and that binocular fusion had been lost in
consequence.

CASE 36.--Mrs. G--, aet. 49, report in March, 1876: On the right H. 3 D.,
V. 10/10, on the left H. 4 D., V. 10/40; a previously existing squint
had disappeared of itself; the position of the eyes appears perfectly
normal, but binocular fusion is not present; with red glass before one
eye and a prism deviating in a vertical direction before the other,
patient does not see double, but first with one eye and then with the
other. The squint as well as its disappearance occurred however, at a
time when it would have been regarded as an error to allow children to
use convex glasses.

CASE 37.--Miss H--, governess, aet. about 30, came under treatment for
asthenopic disorders; on both sides hypermetropia 2.5 D., visual
acuteness 5/18. She owns to have squinted as a child,--it had often been
remarked when she was at school. The squint gradually disappeared, but
still occurred sometimes on keen fixation. The usual position of the
eyes appears perfectly normal, and gives no suspicion of squint;
convergence occurs on exclusion, sometimes with downward deviation of
the right eye. With the aid of a red glass changing fixation is easily
produced even without prisms, but never diplopia. At first only the left
visual field was seen with the stereoscope; then the right on exclusion
of the left eye; never both at the same time. According to this the
condition of binocular vision speaks entirely for the fact, that squint
had existed long enough to prevent the development of a normal binocular
visual act, and the squint had disappeared without the help of convex
glasses in spite of the hypermetropia.

CASE 38.--Bertha W--, aet. 18, reads with the naked eye on the right No.
0.75 at 10 cm., on the left only 1.75 at the same distance;
hypermetropia of 6 D. is detected with the ophthalmoscope, with + 5.5
the visual acuteness of the right eye amounts at 1 metre to 1/9 (if the
test-letters had contained No. 8 or 7.5, that would probably have been
recognised also), on the left with + 5.5 D., V. = 1/12, with + 6 D. No.
0.8 is read with difficulty. Patient admits to have squinted as a child;
no squint is present now; binocular fusion can be detected with prisms
and she only squints now and then on the left side to assist vision,
with which, patient states without being questioned, diplopia is
combined. Spectacles have not been used till now.

I could cite several more such cases, but they would prove no more than
these. At any rate the fact is settled that squint can disappear
spontaneously, and without the aid of convex glasses even in high
degrees of hypermetropia.

Wecker's announcement that "this spontaneous cure goes hand in hand with
the progressive decrease of the accommodation, and depends on the fact
that the squinter, on the strength of this progressive decrease,
renounces more and more the aid which he finds in the increased
convergence during the act of accommodation," only proves to how great
an extent one may be prejudiced by theories. A limitation of the
accommodation must necessarily increase the claims which are made on it,
and can only afford inducement for calling forth all the help possible
to support the accommodation.

The fact that squint spontaneously disappears after normal binocular
fusion is completely and permanently lost, and in individuals who
accommodate without the occurrence of a too strong convergence,
notwithstanding their hypermetropia and without the help of the
controlling influence of binocular single vision, seems to me quite
irreconcilable with Donders' theory. Every motive for the same,
hypermetropia, difference of refraction, monocular defective vision,
&c., may not only be present without the occurrence of squint, they do
not even prevent the spontaneous recurrence of a squint already cured.
Of course I will not affirm that the causes made so prominent by Donders
exercise no influence on the origin of squint, but will only emphasize
the fact, that other causes exist which possess a greater influence, and
which we can find only in the ocular muscles.

We have no experience as to whether this spontaneous cure occurs in
myopia with divergent squint. This is not to be wondered at, as
hypermetropia is present in the great majority of cases of squint, and
the observations as to spontaneous cure are also rare in these. But I
can vouch for one case where a slight absolute divergent squint, with
crossed diplopia, which I treated shortly after its origin in a youthful
myope, with prismatic spectacles, soon disappeared, and remained
permanently cured.

The inclination to preponderance of the interni appears to be peculiar
to youth, while later on circumstances change in favour of the externi,
and that seems to me the chief ground for the spontaneous cure of
convergent squint. The cure is not always complete; deviation still
occurs on exclusion, or on particularly keen fixation; sometimes,
however, also under conditions which can only be put down to a change in
the elastic tensions of the muscles. The following is an interesting
illustration of this:

CASE 39.--Miss S--, aet. 20, states that she squinted frequently as a
child from her fifth to her tenth year; the squint gradually
disappeared, but returned again from time to time during the last half
year without apparent cause. The examination showed normal position of
the eyes, slight convergence only on exclusion. Visual acuteness on the
right 5/6, with atropine ophthalmoscopic and functional emmetropia, the
visual acuteness is lowered to 5/12 by convex 1 D.; on the left
hypermetropia 7 D., visual acuteness 5/18; the same degree of
hypermetropia is found with the ophthalmoscope.

Crossed diplopia with a difference in height is distinguished with the
aid of a red glass, the difference being corrected by a prism of 4 deg.,
with the base downwards before the right eye; a prism of 4 deg. with the
base inwards suffices to place the double images immediately above one
another. Spontaneous diplopia does not take place; only the right visual
field is seen in the stereoscope. As patient lived in Brandenburg and
only came to consult me occasionally I never had an opportunity of
seeing the squint till she decided to stay here for some time. It was
then seen that a peculiar oscillating deviation of the left eye of about
4 mm. inwards often occurred. As the previous spontaneous disappearance
of the squint and the crossed diplopia made one fear that tenotomy of
the internus might be followed by divergence, instillations were used in
order to make a more exact measurement of the deviation,--by this means
the condition was so improved in the course of a few weeks, that
deviation no longer occurred even on exclusion of the right eye.

The spontaneous cure of squint may, however, be quite complete; indeed I
have seen one case where convergent squint became divergent.

CASE 40.--A young lady, slightly over twenty years of age, showed on the
right M. .75 D., V = 10/10, on the left H. 1.5 D., V. 10/40 to 10/30,
and slight divergent squint on the left side. Crossed diplopia could be
produced with a red glass, tenotomy of the left abducens sufficed to
correct it. I had not concealed my doubts as to her statement that she
had previously squinted inwards, but they were quite dispelled by a
photograph taken about twelve years before, in which decided right
convergent squint could not be mistaken. There is something to be said
for the fact that it may have been a periodic squint, which occurred
during the taking of the picture, as the photographer would have taken
pains to hide a permanent squint in some way.

Conscious suppression of squint happens now and then, although very
rarely.

CASE 41.--Miss A. L--, aet. 27, is stated to have commenced to squint in
her first year, until at the age of eighteen she took pains to cure the
habit, and with perfect success as far as regards the position of the
eyes; the only disagreeable symptom was that she could no longer read
with the naked eye. Spectacles were therefore prescribed for her, convex
5 D., but even they did not quite remove the trouble in reading; it was
now a disagreeable, painful sensation to have recourse to squint in
order to see more clearly. It was easiest to read with greatly lowered
field of vision and with the help of a convex eyeglass as well as the
spectacles. During the examination I found on the right hypermetropia
5.5 D., visual acuteness 5/12 to 5/9, on the left with + 5.5 D., V =
1/12. With convex 6 D. No. 0.5 was read at 12 inches from the glass, but
not nearer, with normal fixation on both sides. The binocular near point
(if we may employ this expression in the absence of normal binocular
fusion) was considerably removed without the existence of paresis of the
accommodation, despite the over-correction of the hypermetropia. It was
rather a question of the same disposition of the relative amplitude of
accommodation as I have previously described in a similar case. By
methodical practice of binocular vision, I had taught an intelligent boy
to fix binocularly, not only for distance, but also for near objects,
but here again the relative amplitude for accommodation was diminished,
so that with correct binocular fixation he could only read with convex
glasses, which greatly over-corrected the hypermetropia. Finally, the
normal amplitude of accommodation was restored by tenotomy of the left
internal rectus, and when I saw the patient twelve years later I was
able to satisfy myself that both were perfectly preserved. In the case
of Miss L--, I believed I ought to give up all thoughts of an operation;
the position of the eyes could not be improved, convex 5.5 D. eyeglass
perfectly sufficed for distance, and convex 7 D. spectacles for reading.
It seemed to me senseless to perform tenotomy merely to enable her to
use the same glass for distance and for near objects, without any
possibility of a cosmetic improvement. Moreover the condition of
binocular vision quite confirmed the statements as to the previous
squint. Diplopia could only be produced now and then with the help of
prisms and red glass, at first the right visual field only was seen in
the stereoscope, on closer observation also the left, but without
binocular fusion.

Besides, the proved decrease of the relative power of accommodation in
both these cases, marked by a voluntary suppression of the squint, does
not appear in those cases where squint disappears of itself, the state
of the accommodation, therefore, shows nothing unusual.

The spontaneous cure of squint teaches us two important facts, firstly,
that the conditions of tension of the ocular muscles may change in the
course of time, and secondly, that normal binocular fusion of the
retinal images is not necessary for a correct position of the eyes;
neither the spontaneous nor the operative cure of squint presupposes the
presence or the restoration of a normal binocular fusion. If this were
the case the operation for squint would not be of much use.

Observation of these cases further teaches, that treatment with convex
glasses has prospects of success, particularly in periodic squint with
hypermetropia, if squint can disappear spontaneously even without
correction of the hypermetropia. At the same time, however, it appears
that we need not form hasty conclusions about it. Periodic squint
frequently arises during the earliest years of life, and everyone
(perhaps with the exception of a few ophthalmologists) will at once
reject the idea of allowing children of two to three years old to wear
spectacles; constant wearing of spectacles even by older children seems
to me not to be without risk as long as there is any chance of their
falling when running, playing, &c., in which case the eyes as well as
the spectacles would be in danger. As a rule I only order children to
wear convex spectacles when they are distinctly indicated, and then only
during sedentary occupations, when working and eating. Of course,
exceptions may be made according to the individuality of the child, and
the care with which it is looked after at home.

We are more rarely able to remove permanent convergent squint by means
of convex glasses than the periodic form; that it is possible, however,
I should like to show by an account of a patient, who offers, besides,
other interesting peculiarities.

CASE 42.--Marie S--, aet. 6, came under treatment on November 28th, 1878,
for recent superficial marginal keratitis of the left eye, which was
treated first with atropine; a few days later slight blepharitis
appeared also. On December 9th, atropine was discontinued; on the 14th,
the position of the eyes was still quite normal; on the 19th, permanent
convergent squint of the left eye was present. Squint had never been
observed in the child before. Double images were voluntarily announced
without my having inquired for them, they were homonymous and moved
further apart at both sides of the visual field. On December 28th, the
squint still remained the same, the double images were, however,
scarcely noticed by the child, so quickly do the relations of the
corresponding points of the retina change even in the sixth year. Both
eyes were atropinised for the better determination of the error, when a
slight degree of hypermetropia was shown by the ophthalmoscope, at most
1.5 D.; certainly a higher degree was specified when the vision was
tested, namely, on the right H. 2.5 D., V. = 5/12 to 5/9, on the left H.
1.75 D., V. = 5/18, probably, however, the objective determination was
more exact than the child's statements. If a child of six knows its
letters and figures sufficiently well to undergo a visual test, that is
as much as we can expect; in any case, however, the forms of the
letters and figures which we use for the visual test are not easy to
children, and the more objective the way in which the child comprehends
the examination, the less it perplexes itself by guesses, but only names
the letters which it really distinctly recognises, the less deficient
are the reports as to the visual acuteness; the proportionately larger
retinal images are still recognised, even if they are no longer quite
distinct, but consist of diffusion circles as a result of
over-correction of the hypermetropia. That these observations were right
for the case in point, is seen by the fact that eight days later, after
the effects of the atropine had passed off, the child could see better
with the naked eyes than with convex glasses, and that finally, when it
had become accustomed to the forms of the letters and figures employed,
V. = 5/9 was announced on the right, and V. = 5/12 on the left.

Mydriasis by atropine had no influence whatever on the squint,
therefore, on December 31st, convex spectacles 2 D. were prescribed for
permanent use. On January 4th, the linear deviation still amounted to 4
mm.; on January 15th, convergence was no longer discernible for
distance, with red glass double images occurred at once; on January
21st, no squint was present, and binocular fusion was again restored;
prisms immediately caused double images, the facultative divergence was
= 0. I thought it prudent to order the spectacles to be worn till the
middle of March, when they were discontinued; squint has not appeared
since then.

In this case it is impossible to determine what really induced the
squint, certainly not the slight hypermetropia, for the child had
already learnt to read without squinting, and was spared any exertion at
the time when the squint arose. Neither can we look for the cause in the
inflammatory condition for which the child first came under treatment,
this was as good as removed before the squint began and no exciting
condition worth naming was present. Moreover, most cases of squint
arise without directly assignable causes. It seems to me unquestionable
that the permanent use of convex glasses made the pathological relation
between accommodation and convergence normal, before it had firmly
established itself, and before the muscular relations were definitely
changed, and that the squint was really thus cured. But if the child had
not been under treatment I should scarcely have seen the squint so soon
after its first occurrence, and most cases of squint arise at an age
which forbids the permanent wearing of spectacles.

If permanent squint has already existed for a long time, nothing can be
hoped for from the use of convex glasses; for the conditions of the
muscles are then so much changed, that they are no longer influenced by
such weak physiological powers. I have been able to convince myself in
the case of several squinting persons, who conscientiously wore the
spectacles prescribed for them elsewhere, that the squint was concealed
by this means; that may suffice in some cases, but if it is a question
of young girls we may well ask, which is to be preferred for appearance
sake, squint or spectacles.

Tenotomy effects essentially a cosmetic improvement--its object is to
restore the correct position of the eyes by equalising the elastic
muscular tensions. The means at our disposal are, the simple separation
of the tendon of the too-tense muscle from the sclerotic, the
distribution of the operation between both eyes, and finally, increasing
the strength of the antagonist by moving forwards its insertion.

The method of tenotomy as I carry it out is as follows: The conjunctiva
is seized with fine forceps exactly over the insertion of the muscle to
be divided, and the fold thus raised cut into with the smallest possible
wound. Provided we operate on the right spot we enter this opening with
the forceps and immediately seize the tendon close to its insertion on
the sclerotic, which is drawn forwards, as was the conjunctiva, and
loosened with flat, curved scissors, the points of which must be rounded
off. The incision must only be large enough to allow a small hook with a
knob to be inserted through it and behind the insertion of the tendon,
which is now lifted up and divided with fine pointed scissors close to
its insertion into the sclerotic. It is important to make sure that a
few threads coming off from the tendon at the ends of the insertion do
not remain uncut; we can only consider the operation to be complete when
the hook, carried behind the edge of the insertion made clearly visible
by the foregoing proceeding, slides up to the margin of the cornea
without any interruption.

The method of performing advancement is as follows: An incision is made
in the conjunctiva over the tendon of the muscle to be brought forward
and just at the outer bend of the latter, then loosened together with
the subconjunctival tissue to the corneal margin; it is desirable to
carry out this loosening close to the sclerotic, as the flap of the
conjunctiva thus formed must afford sufficient support to the muscle to
be brought forward. Then the capsule of Tenon is cut into at one edge of
the insertion, a flat, curved, blunt hook without a knob is carried
between muscle and sclerotic, and out again at the other edge of the
insertion. We must be careful to get the muscle as clean as possible on
the hook in the whole width of its insertion, that is without the
capsule of Tenon, for the suture put in ought only to enclose the
muscle, without at the same time dragging the capsule of Tenon. For the
suture I always use fine catgut which is provided at both ends with
curved needles; needles of slightly different form may be chosen in
order that the threads may be easily distinguished from one another. A
needle is carried behind the hook from each thread, one through the
upper, the other through the lower edge of the muscle, between it and
the sclerotic, then the thread is tied in a knot on the muscle to make
sure that it does not slip back through the loop of the thread after
its separation from the sclerotic. Then the threads are knotted on the
muscle, and the insertion is separated from the sclerotic. As the edge
of the insertion is now exposed we can see how the land lies, and can
carry the threads exactly in the direction of the muscle under the
conjunctiva to the corneal margin, where they are passed through, and
ends tied in a knot. By this means the muscle is drawn forwards
precisely in its normal direction and stretched tighter. The wound in
the conjunctiva is closed by a suture.

It is desirable to slightly stretch the muscle that is to be brought
forward in both the above operations while the eye is rolled towards the
opposite side with forceps. Further, as I always operate under
chloroform, I dispense with the usual test of the immediate effect of
the operation; such tests have no value before the effects of the
narcotic have completely disappeared, and one must be sure in the way
above described that no single fibres are left undivided. I lay special
stress on the fact that the operation is so performed, that it is able
to bring about the desired mechanical effect.

The immediate mechanical effects of simple tenotomy may be easily
deduced; the divided muscle retracts as far as its elasticity and its
relations with the surrounding tissues permit. With reference to the
internal and external rectus with which strabotomy specially has to do,
those relations come principally under observation which the front part
of the muscle enters into with the conjunctival tissues; the greater the
extent to which we loosen these relations, the farther the muscle can
retract. If it is a question of obtaining a greater effect, I am
accustomed to loosen the subconjunctival tissue at the front part of the
muscle behind the lachrymal caruncle to a greater extent--this offers
the additional advantage that the distorting sinking in of the caruncle
is avoided.

By dividing one rectus its antagonist gains in proportion and rolls the
eye towards it as far as its own elastic tension and the powers still
present on the other side permit. The improvement in position which we
strive to obtain is brought about by the elastic power of the
antagonist, and not by the tenotomy itself, and it is seen by this then,
that the term strabotomy simply, does not quite express the
circumstances of the case. Tenotomy is nothing more than the means for
procuring a preponderance of the elastic power of the antagonist,
therefore the effect attainable on the position of the eye does not
depend solely on the division of the muscle, but to a great extent on
the elasticity of the antagonist, and may be nullified at once, if the
antagonist does not perform what we expect from it, and that may happen
without our being able to foresee it. For example:

CASE 43.--Julie B--, aet. 21, is stated to have squinted inwards since
her third year, principally with the right eye, but with occasional
alternation. The deviation amounts to 5 mm., the outward movement of
both eyes is perfectly normal. Hypermetropia 2 D., visual acuteness 5/18
on both sides. Ophthalmoscopically with atropine the same degree of
hypermetropia. Tenotomy of both interni on March 7th, 1879. On March
14th, deviation 5 mm., just as before. Then renewed division of the
internal rectus and shortening of the external rectus of the right eye;
but still the result was insufficient. Therefore, on March 21st, the
left eye was dealt with in the same way. By this means a normal position
of the eye was obtained, which was perfectly preserved when I saw the
patient again a year and a half later. Everything led me to suppose
beforehand that simple tenotomy of both internal recti would perfectly
suffice to remove the squint, yet it was of no use, but had to be
supplemented by shortening both external recti. In such cases I would
not advise repeated tenotomies, but for the correction of the
insufficient result as soon as possible by advancement of the
antagonist.

Advancement very frequently gives us an opportunity of seeing with our
own eyes the insufficiency of the antagonist and its faulty anatomical
development. We may suppose this to be the case if the mobility towards
the side of the antagonist is faulty, however that is no proof;
considerable insufficiency may co-exist with perfectly normal mobility.
If limitation of movement is present, to which insufficiency of the
antagonist may be assigned as the cause, or if it is desirable to obtain
the greatest possible result by means of an operation on the squinting
eye, we must combine tenotomy of the deviating muscle with advancement
of the antagonist. The same is stretched tighter, and rolls the eye more
strongly to its side, and we can regulate the degree of shortening of
the muscle, by the distance behind the insertion at which we place the
threads in the muscle, also by the distance from the corneal margin at
which we place our anterior sutures, although the rapidly increasing
ductility of the conjunctiva makes it desirable that we should not go
far from the corneal margin.

The exact rules for the application of the methods of operation differ
according to the nature of the case under consideration. If we
contemplate first the largest group, that of the ordinary permanent
convergent squint, the choice of the method is principally determined by
the average degree of deviation, the condition of error, and the visual
power, lastly by the mobility, particularly the outward movement of the
eyes. If the visual power of both eyes is nearly the same, or if the
squinting eye possesses such a visual acuteness that it can be used in
fixation, it is advisable as a rule to arrange the relations of the
muscles as equally as possible in both eyes--simple division of the
internal recti is therefore, as a rule, to be performed in both eyes.
If, on the other hand, the vision of the squinting eye is in a high
degree defective, so that only the better one is used, it is generally
advisable to confine the operation as far as possible to the squinting
eye; in that case, tenotomy of the internal rectus and advancement of
the external rectus is usually indicated in the squinting eye, and
frequently suffices.

Deviations which are so slight, that the careful division of both
interni without loosening the conjunctiva at the front part of the
muscle makes us fear an excessive result, are seldom the subject of
operative treatment; if the deviation is slight but still a
disfigurement, if it amounts to 3 to 4 mm., distribution between both
eyes is suitable, because, when the squinting eye possesses requisite
visual acuteness it is put into fixation more frequently after the
operation than before. Under these circumstances, if the operation is
confined to the squinting eye, and a sufficient result is thereby
obtained, as soon as this eye is used for fixation a remarkable
secondary deviation of the other eye occurs, which is not the case if
the tensions of the muscles have been balanced by an operation on both
sides.

A deviation of 5 to 6 mm. may usually be balanced by means of simple
double tenotomy if the conjunctiva is considerably loosened behind the
caruncle; not unfrequently, however, we must be careful to strengthen
the result by means of the after-treatment. Commonly, during the first
twenty-four hours, the result appears to be quite satisfactory, whilst
on the second or third day troublesome convergence again sets in. By
practice of the outward movement we then usually obtain at once a
perceptible improvement of the position. Both eyes are repeatedly turned
as far as possible to the right and left, by which means is obtained on
the one hand, exercise of the external recti, on the other, increase of
the effect of the tenotomy of the internal recti. I order these
exercises to be begun on the day after the operation.

Besides this, however, in the relation between accommodation and
convergence of the visual axes there is a very essential cause which is
able to lessen the immediate effect of the operation. Persons who squint
inwards, even if emmetropic, have the habit of combining accommodation
for near objects with excessive convergence of the visual axes, thus
the immediate effect of the operation is diminished as soon as they
begin to use their eyes again. This happens, not by a lessening of the
effect of the tenotomy, which could, indeed, only be increased by
exertion of the internal recti, but in that sufficient time is not given
for the external rectus to regain its normal elastic tension. Nothing is
changed at first by the operation in the customary relation between
accommodation and innervation of the internal recti--it is a question,
then, of avoiding every exertion of the accommodation for some time, in
order that no inducement for strong convergence should be given. I am
accustomed, therefore, even in the case of emmetropes, to paralyse the
accommodation by means of atropine twenty-four hours after the
operation, and to remove the far-point by convex glasses to about 0.70
m.; the spectacles must, of course, be worn constantly, for only by that
means can we be sure that they are always used for near objects. After a
few weeks the spectacles are discontinued, first for distance, then for
near objects also. This after-treatment is not necessary under all
circumstances; but I have repeatedly assured myself that an originally
sufficient result which perceptibly diminished after a few days, could
by this means be restored and permanently maintained even in emmetropes.

In the case of hypermetropes, we more often meet with the same
experience; in permanent convergent squint it is by no means necessary
to neutralise the hypermetropia permanently after the operation, but it
happens here more often than in emmetropia, that a perfectly good
immediate effect is lost within the first week after the operation, and
can be restored again by permanently wearing the correcting convex
glasses. In such cases also, I am accustomed after a few months to
discontinue the spectacles for distance as an experiment, while they are
still used for working.

Simple tenotomy of both internal recti does not, as a rule, suffice for
deviations of more than 7 mm.; therefore, even if both eyes possess good
visual power, we must still decide on tenotomy of both internal recti
together with advancement of the external rectus of the squinting eye,
or anticipate repeated tenotomies of the internal recti, or seek to
obtain the greatest possible effect by means of slight modification of
the method of procedure.

Provided that the muscle was completely divided, and sufficiently
loosened from the conjunctiva during the first operation, a repetition
of the tenotomy can only aim at an increase of the effect if the elastic
tension of the antagonist has improved in the meantime. I very rarely
therefore carry out repeated tenotomies; it seems to me much more
desirable to obtain a sufficient result at one operation whenever that
is possible.

In some cases where there is a deviation of 7 to 9 mm., the effect of
the tenotomy may be increased by inducing a strong divergence
immediately after the tenotomy of the internal recti, which is
maintained for 6 to 8 hours. For this a thread is passed through the
conjunctiva at the outer edge of the cornea about 4 mm. above the
horizontal meridian, and out again about 2 mm. below the horizontal
meridian, then from below upwards in the same way, so that the
conjunctiva is contained in a loop. The needle is then passed through
the external canthus from the conjunctival surface and fastened by tying
it over a roll of paper. This procedure is only to be recommended in
exceptional cases; a greater effect on the internal recti is thus
obtained, while with reference to the position the result depends on the
elastic tension of the external rectus just as in simple tenotomy.

If the squinting eye has only an unavailable visual acuteness, a
combination of tenotomy of the internal rectus with shortening of the
external rectus is the best procedure. As a rule, simple tenotomy of the
internal rectus of the squinting eye is of very little use in such
cases, as the abducens, weakened by continual extension and wanting
practice, places too slight an opposing power in the balance. The chief
effect of the operation then devolves on the other solely available eye,
which is not a desirable circumstance, and is also frequently
insufficient. On the other hand, the combination of tenotomy of the
internal rectus with advancement of the external rectus enables us
successfully to change the opposing muscular tensions. As a rule, the
operation may be confined to the squinting, weak-sighted eye, as that
suffices to obtain a correction of 5 to 6 mm.

If the result is seen to be insufficient, it may be supplemented by
tenotomy of the internal rectus of the other eye; in the case of
deviations of more than 7 mm. it is advisable to divide the operation
between the eyes in this way.

The suture has a special use in so-called artificial strabismus; that
is, in those cases where convergent is converted into divergent squint
through unskilful treatment, or where tenotomy of the abducens,
performed on account of "insufficiency of the internal recti," is
followed by convergent strabismus. I have not found confirmation of the
fear expressed by Arlt, that the method proposed by me could be scarcely
practicable if it is a case of the advancement of a muscle too far
forward, and I have corrected a large number of such cases in other
practices. It is seldom profitable to take up things in which others
have been unsuccessful, but it bring its own reward in the case of
artificial squint.

Periodic convergent squint offers a less certain ground for the
operation. The change between normal position and a very considerable
squint gives rise to the fear that an operation which would be able to
remove the convergence might finally induce divergent strabismus. This
fear is certainly not groundless, but at the same time it must be
remembered that, with the exception perhaps of a few cases of clearly
accommodative deviation, elastic preponderance of the internal recti or
insufficiency of the external recti is generally the cause of periodic
squint also. I have frequently, in periodic squint, performed double
tenotomy of the internal recti with the slightest possible loosening of
the conjunctiva. I have also attempted to confine the operation to the
shortening of the external rectus without loosening the internal recti
and with success, but not frequently enough to be able to deliver a
certain opinion upon it.

In periodic squint, the first care must always be to determine the
condition of refraction, if possible with atropine, and to neutralise or
over-correct hypermetropia if present. If squint is absent during the
use of convex glasses, which happens frequently under these
circumstances, the operation offers no further advantages, as the
constant use of convex glasses afterwards can hardly be avoided. If the
periodic deviation continues to exist, the operation can be carried out
according to the above rules and so as to cause a slight effect.

The final result is usually attained after two to three weeks in
convergent squint; it is better to allow a slight degree of convergence
to exist, as divergence, however slight, existing at this time, brings
with it the fear of a gradual increase. It happens occasionally, that
after years, convergence asserts itself again; I have observed it in
spontaneous (see Case 39) as well as in operative cure of squint; still,
this is so unusual, that I should like to give an illustration of the
latter observation on account of its rarity.

CASE 44.--Hedw. von L--, aet 10, came under treatment in April, 1874, for
convergent squint on the left side which arose in her seventh year, with
occasional alternation. Emmetropia, determined with atropine on both
sides and good visual acuteness. Diplopia was present at the
commencement of the squint. Patient can only be rendered conscious of
double images by the help of a red glass and vertically deviating
prisms. Double tenotomy of the internal recti effected a normal
position, and at the end of December, 1874, the continuance of the same
could be proved as well as binocular fusion with prisms. At the
beginning of 1880, I was informed that from time to time periodic squint
had occurred with diplopia. In the middle of March, I had an opportunity
of seeing the young lady. Myopia 2 D. had meanwhile developed on both
sides, visual acuteness almost = 1. The position of the eyes was
perfectly good, slight convergence occurred during covering, homonymous
double images with a red glass which, at a distance of 5 m., were joined
by a prism of 8 deg.; stereoscopic fusion was not perfectly certain. A true
squint could not be proved. On April 3rd, as patient stopped for a few
hours on her journey through, a striking convergent squint of the left
eye was seen. The deviation amounted to 4 to 5 mm. Single vision existed
at a distance of 15 to 20 cm., then homonymous double images appeared,
which did not correspond to the objective deviation; the double images
were however corrected by a prism of 6 deg. (base outwards) for an object 5
m. distant.

We cannot conclude the consideration of the operative treatment of
convergent squint without once more returning to the relation between
the line of vision and the position of the cornea. The angle [Greek: a]
still deserves mention in a few thankful words--_hic mihi angulus
praeter omnes ridet_--it is a very useful guide in tenotomy. In tenotomy
we may count as gain the apparent divergence which it causes in
hypermetropes who do not squint. We obtain a perfect cosmetic result,
while a convergence, objectively determinable, but not otherwise easily
visible, continues to exist. It would be folly to exceed this; and for
cases where binocular fusion does not exist, and where diplopia is not
present, to wish to remove this covered convergence due to the angle
[Greek: a], the cosmetic result would be impaired by it.

Those cases where it is a question of uniting homonymous double images
are very instructive when considering tenotomy. Only when squint arises
after childhood (after the fifteenth year) does it cause troublesome
diplopia, this accords naturally with the laws of normal binocular
fusion learnt meanwhile. (On the other hand those cases, which sometimes
occur after tenotomy, with the double images in a position which does
not correspond to the normal physiological laws and which cannot
therefore be united by prisms, are naturally unsuitable for the
operative removal of diplopia.) Cases in which convergent squint is
followed by troublesome double images, appear, with the exception of the
hysterical form mentioned on p. 41, chiefly in myopia, more seldom in
emmetropia, and very rarely in hypermetropia; for if the conditions
contained in the ocular muscles are coincident with hypermetropia,
squint usually arises in the course of childhood, before normal
binocular vision has become a fixed habit.

As the cases here under consideration are not very common, I will relate
a few from which conclusions may be derived as to the effect of
tenotomy.

CASE 45.--Miss von B--, aet. 14, came under treatment on May 1st, 1875,
for diplopia, which made its appearance about a year previously.
Emmetropia and full visual acuteness exist on both sides. The double
images are homonymous and further apart on both sides of the visual
field. At first single vision existed only to about 0.75 m.; gradually,
however, the area of single vision was extended by practice of the
outward movement, supported by the use of prismatic spectacles, so that
after a year patient could see singly to a great distance. This
improvement was not maintained. At the beginning of 1879, diplopia was
again present to a troublesome degree, particularly on looking
downwards; on looking straight forwards the left eye showed a slight
convergent deviation, amounting at most to 2 mm. During various
examinations the distance of the double images was stated to be now
less, now greater, a prism of at least 5 deg., at most of 9 deg., was requisite
for correction. Diplopia was at once removed by tenotomy of the left
internal rectus, with very slight loosening of the conjunctiva, and has
not appeared since.

CASE 46.--Miss A--, aet. 17, suffered from diplopia for a few weeks, a
year and a half ago; for the last half year the diplopia is continuous,
and striking squint is stated to be sometimes present. Myopia 2 D. on
both sides, visual acuteness = 5/9. On fixation of an object about 4 m.
distant, the left eye deviates inwards at most 2 mm.; homonymous double
images, with a red glass and on correction of the myopia, which were
united by means of prism 14 deg. at a distance of 5 m., without red glass
(with retinal images alike on both sides) prism 8 deg. sufficed to unite
them. If a vertically deviating prism is held before one eye, the double
images stand just above one another when looking at an object 20 cm.
off, on nearer approach they are crossed. On May 3rd, 1879, tenotomy of
the left internal rectus with small conjunctival wound without loosening
of the conjunctiva, and union of the conjunctival wound by a suture. On
May 8th, single vision, also with correction of the myopia and with red
glass. Facultative divergence = 2 deg. On May 14th, with correction of the
myopia, there was still single vision for distance; however, with red
glass double images occurred again; and at the end of May the condition
of the double images was just the same as before the operation. On
vertical shifting of one visual field by a weak prism the double images
are brought into a vertical line by means of prism 16 deg., with the base
outwards. Therefore, on July 1st, the right internal rectus was also
divided, with small conjunctival wound without loosening of the
conjunctiva and without suture. The evening after the operation slight
divergence on covering. On July 24th, binocular single vision is
present; with red glass homonymous double images at 5 m., corrected by
prism 4 deg. This time the result was final; for in the middle of October,
three months after the operation, the report was exactly like the one of
July 24th above stated.

CASE 47.--Mrs. A--, aet. 33, has suffered for six months from alternating
convergent squint with diplopia, for a short time even a parallel
position is still possible. On the right myopia 4 D., V. = 6/12. On the
left myopia 4 D., V. 6/9. Single vision occurs to 22 cm., at a greater
distance homonymous double images, whose mutual distance remains the
same when looking to one side. On correction of the myopia a prism of at
least 32 deg. is necessary for the union of the double images for an object
at 4 m. Two days after tenotomy of the internal recti on both sides, the
facultative divergence amounted to 7 deg. (at 4 m.) on correction of the
myopia. Single vision was also present when looking strongly to one
side, and with differentiation of one retinal image by a red glass.

CASE 48.--Mr. B--, aet. 32, first observed the occurrence of diplopia at
the beginning of April, 1877. Myopia 6 D. is present in both eyes,
visual acuteness on the right 1/2, on the left rather more than 1/2
(5/9). The double images are homonymous and sometimes (not always) move
farther apart at the limits of the visual field. Patient could only
decide after two years, in July, 1879, on the operative treatment then
proposed. Diplopia continued to exist; single vision was only now and
then possible for a short time. On correction of the myopia (if one eye
is provided with a red glass) prism 12 deg. suffices for union of the double
images. If one visual field is moved in a vertical direction by a prism
of 5 deg. during the trial of convergence, prism 38 deg. is necessary in order
to equalize the lateral deviation of the double images, and to place
them perpendicularly above one another for an object 5 m. distant. On
July 14th, tenotomy of the internal rectus of the left eye; single
vision next day on correction of the myopia, prism 6 deg. is overcome by
divergence; if, however, double images are produced by a vertically
deviating prism of 5 deg. they immediately show homonymous lateral
deviation, which is corrected by prism 18 deg. at a distance of 5 m.

Two months after the operation the diplopia was certainly better, but by
no means removed; squint occurred periodically as before, so that
sometimes single vision was possible at 3 to 4 m., sometimes troublesome
diplopia was present.

During the test of convergence with prisms deviating in a vertical
direction, a prism of 38 deg. was necessary for the equalization of the
lateral deviation just as before the operation. Therefore in the middle
of October the internal rectus of the right eye was divided, and the
conjunctiva loosened as far as the caruncle. Three days afterwards
single vision, facultative divergence = prism 5 deg.; in the trial of
convergence, equalization by means of prism 8 deg. In the middle of
October, two months after the operation, diplopia had not appeared
again; facultative divergence = 0; homonymous double images are produced
by a red glass before one eye, slight convergent deviation on covering
it, which in the trial of convergence is equalized by prism 20 deg. The
preponderance of the interni was now so far lessened for the ordinary
use of the eyes, that permanent binocular single vision was possible.

Notwithstanding the small number of these cases we may conclude from
them, that homonymous diplopia in typical convergent squint (not
paralytic) can only be corrected occasionally by one-sided tenotomy when
the deviation is slight. As a rule it is necessary to distribute the
operation between the eyes. A result seems attainable by means of simple
tenotomy on both sides, which is expressed by prism 20 deg. in the trial of
convergence. In future cases it would be desirable to determine during
correction of the anomalies of refraction (1) the weakest prism which is
able to unite the double images at about 5 m. distant (without red
glass); (2) the distance at which the double images stand apart from one
another during the trial of convergence with prisms deviating in a
vertical direction; and (3) the prism which brings the double images
immediately above one another in the case of objects about 5 m. off.

Next to the cases above discussed stand those where convergent squint
remains after paralysis of the abducens; at the same time slightly
defective mobility and a distinct moving apart of the double images
towards the affected side can usually be detected. In a few such cases I
could restrict myself to tenotomy of the internal rectus of the affected
eye, but in those cases which I was able to attend to more particularly,
double tenotomy was necessary, and did not always suffice. Here also the
advancement of the external rectus is suitably applied, which I should
like to illustrate by means of a few examples.

CASE 49.--Mr. B--, aet. 20, was seized by paralysis of the abducens of
the right eye in November, 1877. In April, 1878, convergent squint was
still present, and as it continued patient decided on an operation in
February, 1879. Both eyes are emmetropic and possess full visual
acuteness.

Immediately before the operation the double images were united at 4 to 5
m. in the horizontal plane by a prism of 39 deg.; towards the right their
deviation rather increased. The measurable deviation amounted to 4 mm.
in the right eye, the secondary deviation of the left to 5 mm. In order
to proceed carefully, I confined myself at first to tenotomy of the
internal rectus of the right eye. After the space of a week single
vision was present at the distance of 1 metre in the middle line and at
the height of the eyes; at about 5 m. homonymous double images corrected
by prism 12 deg., together with slight difference in height (= prism 4 deg.,
base upwards before the right eye). The area of double vision extended
from the limit of the right visual field to about 20 deg. the other side of
the middle line.

This result would have sufficed perfectly for a cosmetic tenotomy where
binocular fusion did not exist; the annoyance caused to patient by
diplopia, however, was only slightly relieved. I decided, therefore, on
a second operation, not without fearing an excessive result, and
performed tenotomy of the left internal rectus with a very small
conjunctival wound and by closing the wound by means of a suture. The
result was by no means excessive, for it was perfectly _nil_, apparently
even negative at first, for a few days after the operation the area of
single vision approached the eye to less than 0.5 m. and at 4 to 5 m. a
prism of 20 deg. was requisite for correction; however, eighteen days after
the tenotomy of the left internus everything was as before. Single
vision to 1 m. while prism 12 deg. corrected for a distance of 4 to 5 m. The
tenotomy then had no effect at all on the position of the eye; however,
the restriction of movement dependent on it, asserted itself in that the
double images were crossed on the limit of the right visual field (about
45 deg. towards the right). On the supposition that this insufficient result
might be caused by the suture of the conjunctival wound I decided to
repeat the separation of the internal rectus. The agglutination of the
muscle with the sclerotic is so slight for two to three weeks after the
operation that the strabismus hook perfectly suffices to sever the
connection; no suture was put in, but the result again was _nil_, and on
the day after the operation single vision was only present to 0.5 m. in
the middle line, just as after the previous tenotomy of the left
internal rectus. It was now clear that the result with respect to the
position of the eye was only unsuccessful because the antagonist did not
do its duty. I shortened the abducens (without touching the internus
again). The immediate effect, during the chloroform narcosis, was a
terrible divergence, but on the same evening it was less, and
twenty-four hours after the operation with a red glass, homonymous
double images were present close together at a distance of 4 m. Ten days
afterwards binocular single vision was insured, facultative divergence
= 3 deg. at 4 m., crossed double images towards the limits of both visual
fields, but only on moving the eyes in a lateral direction; no practical
use was made of this. If one could have diagnosed beforehand the
insufficiency of the externi assuredly present here, which was probably
the reason for the development of squint on the healing of the paralysis
of the abducens, one would have been able to combine shortening of the
right abducens with tenotomy of the internus in the first operation,
whereas the necessity for the advancement was only shown by the
abnormally slight effect of the tenotomy on the left side. According to
accounts received by letter the favorable result has continued.

We obtain a result more quickly by the immediate advancement of the
abducens. For example:

CASE 50.--Mr. K--, aet. 29, suffered from paresis of the right abducens
in the autumn of 1877. In December, 1878, convergent squint is present,
linear deviation 5 mm. (scarcely more on the left than on the right).
The defect of movement towards the side of the right abducens amounts to
about 2 or 3 mm. Diplopia is present in the whole visual field with
increase of the deviation towards the right. Emmetropia and full visual
acuteness on both sides. Tenotomy of the internal rectus and advancement
of the abducens of the right eye at the end of December. Three weeks
later single vision is present in the middle line; on the left limit of
the visual field crossed double images, on the right side homonymous
ones, beginning about 20 deg. from the middle line. The result was by no
means excessive.

In convergent squint with congenital paresis of the abducens, not much
can be attained without shortening the abducens. Of course only the
squint can be removed, not the paralysis, but if once a correct position
is attained for the middle line, cosmetic demands are satisfied; the
outward movement, which is absent, must be replaced by turning the
head.

The chief method for absolute divergent squint is the combination of
shortening with tenotomy of the externus. If the impulse for convergence
is once lost, so that an associated movement occurs in place of an
accommodative one on fixation of a point situated on the middle line, a
removal of the squint cannot be obtained by simple tenotomy of the
externi--another proof that a change of position of the eye is by no
means a necessary result of tenotomy.

Moreover, this slight aid given by tenotomy has its ground not solely in
the condition of the opposing recti muscles. In other practices I have
seen cases enough in which tenotomy of the externi, performed on account
of relative divergence, was followed by convergent squint, just as
injudicious division of the interni may induce divergent squint. It is
probable, therefore, that the faulty effect of simple tenotomy in
permanent absolute divergent squint depends on other causes, which, in
my opinion, are to be found in the obliques. The loop formed by the
obliques round the posterior circumference of the eye is most stretched,
when the visual line falls in with the muscular plane of the obliques in
a medial direction of the eyes. On the whole, then, it is proved that
the obliques are extended on turning the eyes inwards, but shortened on
turning the eyes outwards by means of their muscular action. In
divergent squint, if the movement inwards occurs but seldom or not at
all, the obliques consequently are not extended in a normal way--it
follows then that they lose in ductility, offer greater resistance to
the inward movement, and by means of their elastic tension continually
draw the posterior pole of the eye inwards and the cornea outwards. As
in strabotomy we cannot get at the obliques, it seems all the more
desirable to offer them stronger resistance by greater tension of the
internus by means of advancement. Certainly tenotomy of the external
rectus of the fixing eye is as a rule also necessary. A sufficient
result is usually thus obtained at once; if it is much lessened in the
course of one or two months there is nothing to prevent the repetition
of the tenotomy of one or the other external rectus.

The innervation for the movement of convergence is not always perfectly
lost; it withdraws itself from the influence of binocular fusion because
this is gradually forgotten while a convergence, even if an insufficient
one, unites itself with the effort of accommodation. If we ask such
patients to fix a large object lying near, a pencil, for example, they
cannot usually converge upon it, whilst if we ask them to read at the
same distance, a distinct convergent movement occurs; large objects are
sufficiently clearly recognised, even without distinct retinal images,
and the supposition that an effort of accommodation is present is only
justified if we employ sufficiently small objects at the examination, in
order to distinguish which, clear retinal images are necessary. Of
course we must have regard to the condition of refraction; myopes, who
use their far point for reading, want no accommodation, therefore no
convergent movement occurs, even if the impulse of innervation for it,
is not yet quite lost. However, the innervation for convergence may be
lost, without the internal recti losing in elastic tension. The
operative importance of this relation may be illustrated by an example.

CASE 51.--Bertha K--, aet. 10, has myopia 5 D. on both sides, visual
acuteness 12/20, and divergent strabismus. At 4 mm. the crossed diplopia
is corrected by prism 23 deg.; a convergent movement is no longer attained,
at most parallelism of the visual axes. Tenotomy of both interni on
October 2nd, 1873. The immediate result was convergent squint, with a
defect in movement outwards amounting to 4 to 5 mm. in both eyes. On
October 9th prism 37 deg. was still necessary to unite the homonymous double
images at a distance of 4 m.; single vision existed only to about 20 cm.
The area of single vision gradually extended itself; at the end of
October it was restored for distance also, facultative divergence
_nil_; however, relative divergence was present for near objects.
Naturally this was not the result of muscular weakness of the interni,
for they had proved their capabilities by a convergent squint,
fortunately only temporary, which made one anxious, but was solely the
result of a faulty innervation. The further course was also interesting.
After three years, in October, 1876, the myopia of the left eye amounted
to 8 D., that of the right 7 D., visual acuteness 1/2 on the right, on
the left 3/4 of the normal; a posterior staphyloma measuring about 1/3
of the diameter of the optic disc was present. The left eye was used for
near objects with relative divergence of the right and the occasional
occurrence of diplopia; there was convergence only to about 15 cm.
Facultative divergence _nil_.

We very frequently have the opportunity of seeing, that myopia increases
even after tenotomy of the externus, and if von Graefe's assertion that
the progress of myopia would be brought to a standstill by means of
tenotomy still finds believers, I should like to cite one example which
offers proof to the contrary.

In permanent divergent squint we shall have, as a rule, to combine
shortening of the internus of the squinting eye with tenotomy of both
externi, even if the convergent movement is still possible to a slight
degree. The result thus obtained differs somewhat; sometimes it suffices
at once, sometimes a repetition of the separation of the externi is
necessary later on. Two examples may illustrate this.

CASE 52.--Miss Marie M--, aet. 22, has squinted on the left side since
her third year, nominally after a keratitis, which left behind in the
left eye a nebula of the cornea of small circumference. The deviation
amounts to 8 mm. The visual power is much worse than the opacity of the
cornea leads us to suppose, with visual axes deviating inwards fingers
were only counted at a distance of about 1 m.

On the right myopia 1 D., V. = 4/5. A slight convergent movement is
still practicable. At the end of May, 1879, shortening of the left
internal rectus, tenotomy of both externi. The next day slight
convergence on viewing distant objects, correct position after four
days. In January, 1880, correct position of the eyes, convergence
possible to about 20 cm. While a correction of 8 mm. was immediately
obtained here, the same operation does not always permanently suffice
for slighter deviations.

CASE 53.--Ernest Sp--, aet. 11-1/2; divergent squint had been observed as
early as his second year. The deviation amounts to 5 or 6 mm., is
sometimes alternating, generally the left eye deviates. No convergent
movement on fixing a pencil about 25 cm. distant; the right eye is then
used for reading, the left one makes a distinct, but not a sufficient,
movement inwards. Emmetropia on both sides, visual acuteness nearly
perfect on the right, on the left 2/3 of the normal. Even with red glass
and prisms deviating in a vertical direction, double images not
perceived. On October 2nd, 1879, shortening of the left internal rectus,
tenotomy of both externi. A week later divergence was no longer present.
When reading, the left eye makes a distinct, perhaps rather too great,
movement of convergence, and yet six weeks after the operation, distinct
divergent squint was again present, even if to a slighter degree than
before; the left eye deviates 3 to 4 mm., the right 2 to 3 mm. outwards.
The result obtained amounted then to not more than about 3 mm. In the
middle of December the tenotomy of both externi was therefore repeated.
A week after the operation convergent squint of 2 mm. is present with
homonymous diplopia. A pencil made to approach on the middle line is
seen double to about 20 cm., on approaching nearer, double images are
not perceived in spite of distinct relative divergence. Double images at
a distance of 4 m. are corrected by prism 25 deg.; as, however, normal
binocular vision is not present, the value of this statement is very
questionable. Three weeks after the second operation the position of the
eyes was normal, and the slightest convergence was perceived only on
close investigation. Double images are no longer observed, however they
may still be brought to view.

In periodic divergent squint, if the deviation is considerable and
frequent, if at the same time the normal near point of convergence is
only attained with difficulty or not at all, we can hardly combine
shortening of the internus with tenotomy of the externus; more often
indeed, additional tenotomy of the externus of the other eye is
necessary in order to obtain a permanent cure. In exceptional cases
(when it seemed to me as if the squint depended more on insufficiency of
the internus than on preponderance of the externus) I have confined
myself to shortening the internus without separating the externus; I
will quote just one example of this.

CASE 54.--Ida K--, aet. 11. On the right, hypermetropia 3 D. with the
ophthalmoscope, visual acuteness 5/24. No. 0.3 is read with difficulty.
On the left, with the ophthalmoscope hypermetropia 4.5 D. with
asymmetric meridian. Single letters of 3.0 m. are recognised with convex
6.5 D. Fingers are counted at about 1-1/2 m. The choroid is slightly and
unequally pigmented, no ophthalmoscopically assignable reason exists for
the considerable visual defect. The left eye frequently deviates
outwards, convergence is attainable to 15 cm. On May 2nd, 1877,
shortening of the internus (without tenotomy of the externus). Two weeks
later slight convergent squint was present; in November, 1877, six
months after the operation, the position of the left eye was perfectly
normal.

Tenotomy of the externi suffices when the divergent deviation is
inconsiderable and does not occur often, if the normal near point of
convergence can still be reached, and binocular fusion is possible.

If we want to increase the effect of simple tenotomy of the externi,
this may be done just as well by practice of the associated movements of
the eyes as by practice of the convergence, of course for a short time
only after the operation. As long as the detached tendon of the external
rectus is not re-attached firmly with the sclerotic, all these movements
of the eyes help to strengthen the result of the tenotomy. In order to
practise convergence we can bring a suitable fixed point on to a mirror
and so make it possible for the patient himself to see the position of
his eyes, of course only in cases where binocular fusion is no longer
present. He who possesses a normal binocular vision is troubled in these
exercises by diplopia; but this is not the case in the suppression of
binocular fusion so frequent as a result of squint.

Periodic divergent squint is divided by no sharply defined limits from
those cases in which only a preponderance of the externi exists without
insufficiency of the interni. We frequently find very considerable
degrees of facultative divergence as a casual symptom, without the
occurrence of manifest divergence or the presence of asthenopic
troubles. If this is accompanied by weakness of the interni, absolute
divergence occurs on looking at near objects, sometimes for distance
also and certainly if we suppress binocular fusion by covering one eye
or render it difficult by colouring one visual field with a red glass.

In these cases the indications for the operation are given either by
asthenopia, by troublesome double images or by the disfigurement
inseparable from periodic squint; it will depend on the degree of the
facultative divergence, whether we confine the tenotomy of the externus
to one eye or whether we distribute it between both eyes.

Finally, it may be desirable to still say a few words as to the most
favorable period for the operation. The comprehension of the defective
sight often present in squint as caused by "non-use" has resulted in
the preposterous advice that tenotomy should be carried out as early as
possible. I can vouch for the fact that even the earliest tenotomy of
the ocular muscles is of no avail against congenital amblyopia. I have
repeatedly seen children on whom tenotomy had been performed in their
first year, usually with bad cosmetic result but with continuance of
defective sight of the squinting eye.

The final result of the operation is almost always very unsatisfactory
when performed on children before their fourth year. I can show a number
of good results in children on whom I operated between their fifth and
sixth year; however, the more I considered the subject, the more it
seemed to me advisable to raise the tests which must be imposed on the
patients. With children it is not so much a question of determining the
limit of age, but whether their intelligence is sufficiently developed
to render a reliable examination possible. A sufficient knowledge of
letters and the power of reading is necessary to an accurate trial of
vision; the entire bearing of the children must permit of the
ophthalmoscopic diagnosis of the weak condition and should raise no
scruples as to wearing spectacles which may be necessary after the
operation. Under any circumstances no harm is done by deferring the
operation until these conditions are fulfilled; the interval may be
filled up by practising the mobility of the eyes, which does more good
than the customary strabismus spectacles or even tying up the eye. If we
tie up the fixing eye, the squinting one is certainly put into fixation,
but the other squints instead, and of course it is just the same with
the plan, as childish as it is antiquated, of tying on a pierced walnut
shell before each eye.

Strabismus spectacles, _i. e._ those with a leather band to go round the
head, provided with leaden discs which cover one eye completely and
leave only a side aperture for the other, of course only induce a
transfer of the squint to the covered eye, together with practice of
the eye in a lateral direction; but apart from their unsightly
appearance they require a constant lateral direction of the eye, which
is followed even after a short time by fatigue of the muscles employed
and soon becomes unbearable. This is not the case if we cause the
mobility to be practised alternately and towards both sides; here we
must insist that the limits of the outward movement are really reached.
These exercises are at least rational and tend to increase the strength
of the antagonist, on which we must depend so much in the operation and
to diminish an insufficiency made worse by want of practice.


PRINTED BY ADLARD AND SON, BARTHOLOMEW CLOSE.

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Catalogue B]           _London, 11, New Burlington Street March, 1887_


_SELECTION_

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The Change of Life In Health and Disease: A Clinical Treatise on the
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Treatment of Pulmonary Consumption by Hygiene, Climate, and Medicine.
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Leprosy in British Guiana. By JOHN D. HILLIS, F.R.C.S., M.R.I.A.,
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Cancer of the Breast. By THOMAS W. NUNN, F.R.C.S., Consulting Surgeon to
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Clinical Notes on Cancer, Its Etiology and Treatment; with special
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The Suprapubic Operation of Opening the Bladder for the Stone and for
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The Surgery of the Rectum. By HENRY SMITH, Professor of Surgery in
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INDEX.


Abercrombie's Medical Jurisprudence, 4

Adams (W.) on Clubfoot, 11;
  on Contraction of the Fingers, 11;
  on Curvature of the Spine, 11

Alexander's Displacements of the Uterus, 6

Allan on Fever Nursing, 7;
  Outlines of Infectious Diseases, 7

Allingham on Diseases of the Rectum, 14

Anatomical Remembrancer, 3


Balfour's Diseases of the Heart and Aorta, 9

Balkwill's Mechanical Dentistry, 12

Barnes (R.) on Obstetric Operations, 5;
  on Diseases of Women, 5

Beale's Microscope in Medicine, 8;
  Slight Ailments, 8;
  Urinary and Renal Derangements, 14

Bellamy's Surgical Anatomy, 3

Bennet (J. H.) on the Mediterranean, 10;
  on Pulmonary Consumption, 10

Bentley and Trimen's Medicinal Plants, 7

Bentley's Manual of Botany, 7;
  Structural Botany, 7;
  Systematic Botany, 7

Braune's Topographical Anatomy, 3

Brodhurst's Anchylosis, 11;
  Curvatures, &c., of the Spine, 11;
  Orthopaedic Surgery, 11

Bryant's Acute Intestinal Strangulation, 9;
  Practice of Surgery, 11

Bucknill and Tuke's Psychological Medicine, 5

Bulkley's Acne, 13;
  Diseases of the Skin, 13

Burdett's Cottage Hospitals, 4;
  Pay Hospitals, 4

Burton's Midwifery for Midwives, 6

Butlin's Malignant Disease of the Larynx, 13;
  Sarcoma and Carcinoma, 13

Buzzard's Diseases of the Nervous System, 9;
  Peripheral Neuritis, 9


Carpenter's Human Physiology, 4

Cayley's Typhoid Fever, 8

Charteris on Health Resorts, 10;
  Practice of Medicine, 8

Chavers' Diseases of India, 8

Churchill's Face and Foot Deformities, 11

Clouston's Lectures on Mental Diseases, 5

Cobbold on Parasites, 13

Coles' Dental Mechanics, 13

Cooper's Syphilis and Pseudo-Syphilis, 14

Coulson on Diseases of the Bladder, 14

Courty's Diseases of the Uterus, Ovaries, &c., 6

Cripps' Diseases of the Rectum and Anus, 14

Cullingworth's Manual of Nursing, 6;
  Short Manual for Monthly Nurses, 6

Curling's Diseases of the Testis, 14


Dalby's Diseases and Injuries of the Ear, 12

Dalton's Human Physiology, 4

Day on Diseases of Children, 6;
  on Headaches, 10

Dobell's Lectures on Winter Cough, 8;
  Loss of Weight, &c., 8;
  Mont Dore Cure, 8

Domville's Manual for Nurses, 6

Draper's Text Book of Medical Physics, 4

Druitt's Surgeon's Vade-Mecum, 11

Duncan on Diseases of Women, 5;
  on Sterility in Woman, 5

Dunglison's Medical Dictionary, 14


East's Private Treatment of the Insane, 5

Ebstein on Regimen in Gout, 9

Ellis's Diseases of Children, 6

Emmet's Gynaecology, 6


Fagge's Principles and Practice of Medicine, 8

Fayrer's Climate and Fevers of India, 7

Fenwick's Chronic Atrophy of the Stomach, 8;
  Medical Diagnosis, 8;
  Outlines of Medical Treatment, 8

Flint on Clinical Medicine, 7;
  on Principles and Practice of Medicine, 7

Flower's Diagrams of the Nerves, 4

Fox's (C. B.) Examinations of Water, Air, and Food, 5

Fox's (T.) Atlas of Skin Diseases, 13

Freyer's Litholopaxy, 14

Frey's Histology and Histo-Chemistry, 4


Galabin's Diseases of Women, 6;
  Manual of Midwifery, 5

Gamgee's Treatment of Wounds and Fractures, 11

Godlee's Atlas of Human Anatomy, 3

Goodhart's Diseases of Children, 6

Gorgas' Dental Medicine, 13

Gowers' Diseases of the Brain, 9;
  Diseases of the Spinal Cord, 9;
  Manual of Diseases of Nervous System, 9;
  Medical Ophthalmoscopy, 9;
  Pseudo-Hypertrophic Muscular Paralysis, 9

Granville on Gout, 9;
  on Nerve Vibration and Excitation, 9

Guy's Hospital Formulae, 2;
  Reports, 2


Habershon's Diseases of the Abdomen, 9;
  Liver, 9;
  Stomach, 9;
  Pneumogastric Nerve, 9

Hambleton's What is Consumption?, 8

Hardwicke's Medical Education, 14

Harley on Diseases of the Liver, 9;
    Inflammations of the Liver, 9

Harris's Dentistry, 13

Harrison's Surgical Disorders of the Urinary Organs, 13

Hartridge's Refraction of the Eye, 12

Harvey's Manuscript Lectures, 3

Heath's Injuries and Diseases of the Jaws, 10;
  Minor Surgery and Bandaging, 10;
  Operative Surgery, 10;
  Practical Anatomy, 3;
  Surgical Diagnosis, 10

Helm on Short and Long Sight, &c., 11

Higgens' Ophthalmic Out-patient Practice, 11

Hills' Leprosy in British Guiana, 13

Holden's Dissections, 3;
  Human Osteology, 3;
  Landmarks, 3

Holmes' (G.) Guide to Use of Laryngoscope, 12;
  Vocal Physiology and Hygiene, 12

Hood's (D. C.) Diseases and their Commencement, 7

Hood (P.) on Gout, Rheumatism, &c., 9

Hooper's Physician's Vade-Mecum, 8

Hutchinson's Clinical Surgery, 11;
  Pedigree of Disease, 11;
  Rare Diseases of the Skin, 13

Hyde's Diseases of the Skin, 13


James (P.) on Sore Throat, 12

Jessett's Cancer of the Mouth, &c., 13

Jones (C. H.) and Sieveking's Pathological Anatomy, 4

Jones' (H. McN.) Aural Surgery, 12;
  Atlas of Diseases of Membrana Tympani, 12;
  Spinal Curvatures, 11

Jordan's Surgical Enquiries, 11

Journal of British Dental Association, 2;
  Mental Science, 2


King's Manual of Obstetrics, 6


Lancereaux's Atlas of Pathological Anatomy, 4

Lee (H.) on Syphilis, 14

Lewis (Bevan) on the Human Brain, 4

Liebreich's Atlas of Ophthalmoscopy, 12

Liveing's Megrim, Sick Headache, &c., 9

London Hospital Reports, 2

Lueckes' Hospital Sisters and their Duties, 7

Lund's Hunterian Lectures, 10


Macdonald's (J. D.) Examination of Water and Air, 4

Mackenzie on Diphtheria, 12;
  on Diseases of the Throat and Nose, 12

McLeod's Operative Surgery, 10

MacMunn's Spectroscope in Medicine, 8

Macnamara's Diseases of the Eye, 11;
  Bones and Joints, 11

Marcet's Southern and Swiss Health-Resorts, 10

Martin's Ambulance Lectures, 10

Mason on Hare-Lip and Cleft Palate, 12;
  on Surgery of the Face, 12

Mayne's Medical Vocabulary, 14

Middlesex Hospital Reports, 2

Mitchell's Diseases of the Nervous System, 9

Moore's Family Medicine for India, 7;
  Health-Resorts for Tropical Invalids, 7;
  Manual of the Diseases of India, 7

Morris' (H.) Anatomy of the Joints, 3

Mouat and Snell on Hospitals, 5


Nettleship's Diseases of the Eye, 12

Nunn's Cancer of the Breast, 13


Ogston's Medical Jurisprudence, 4

Ophthalmic (Royal London) Hospital Reports, 2

Ophthalmological Society's Transactions, 2

Oppert's Hospitals, Infirmaries, Dispensaries, &c., 5

Osborn on Diseases of the Testis, 13;
  on Hydrocele, 13

Owen's Materia Medica, 7


Page's Injuries of the Spine, 11

Parkes' Practical Hygiene, 5

Pavy on Diabetes, 10

Pavy on Food and Dietetics, 10

Pharmaceutical Journal, 2

Pharmacopoeia of the London Hospital, 7

Phillips' Materia Medica and Therapeutics, 7

Pollock's Histology of the Eye and Eyelids, 12

Porritt's Intra-Thoracic Effusion, 8

Purcell on Cancer, 13

Pye-Smith's Syllabus of Physiology, 4


Quinby's Notes on Dental Practice, 12


Raye's Ambulance Handbook, 10

Reynolds' (J. J.) Diseases of Women, 5;
  Notes on Midwifery, 5

Richardson's Mechanical Dentistry, 13

Roberts' (C.) Manual of Anthropometry, 5;
  Detection of Colour-Blindness, 5

Roberts' (D. Lloyd) Practice of Midwifery, 5

Robinson (Tom) on Syphilis, 14

Robinson (W.) on Endemic Goitre or Thyreocele, 12

Ross's Aphasia, 9;
  Diseases of the Nervous System, 9;
  Handbook of ditto, 9

Routh's Infant Feeding, 7

Royal College of Surgeons Museum Catalogues, 2

Royle and Harley's Materia Medica, 7


St. Bartholomew's Hospital Catalogue, 2

St. George's Hospital Reports, 2

St. Thomas's Hospital Reports, 2

Sansom's Valvular Disease of the Heart, 8

Savage on the Female Pelvic Organs, 6

Sewill's Dental Anatomy, 12

Sharkey's Spasm in Chronic Nerve Disease, 9

Shore's Elementary Practical Biology, 4

Sieveking's Life Assurance, 14

Smith's (E.) Clinical Studies, 6;
  Diseases in Children, 6;
  Wasting Diseases of Infants and Children, 6

Smith's (Henry) Surgery of the Rectum, 14

Smith's (Heywood) Dysmenorrhoea, 6

Smith (Priestley) on Glaucoma, 12

Snell's Electro-Magnet in Ophthalmic Surgery, 12

Snow's Clinical Notes on Cancer, 13

Southam's Regional Surgery, 11

Sparks on the Riviera, 10

Squire's Companion to the Pharmacopoeia, 7;
  Pharmacopoeias of London Hospitals

Starkweather on the Law of Sex, 4

Steavenson's Electricity, 11

Stille and Maisch's National Dispensatory, 7

Stocken's Dental Materia Medica and Therapeutics, 13

Sutton's General Pathology, 4

Swain's Surgical Emergencies, 10

Swayne's Obstetric Aphorisms, 6


Taylor's Medical Jurisprudence, 4

Taylor's Poisons in relation to Medical Jurisprudence, 4

Teale's Dangers to Health, 5

Thin's Cancerous Affections of the Skin, 13

Thomas's Diseases of Women, 6

Thompson's (Sir H.) Calculous Disease, 14;
  Diseases of the Prostate, 14;
  Diseases of the Urinary Organs, 14;
  Lithotomy and Lithotrity, 14;
  Stricture of the Urethra, 14;
  Suprapubic Operation, 14;
  Surgery of the Urinary Organs, 14;
  Tumours of the Bladder, 14

Thorowgood on Asthma, 8;
  on Materia Medica and Therapeutics, 7

Thudichum's Pathology of the Urine, 14

Tibbits' Medical and Surgical Electricity, 10;
  Map of Motor Points, 10;
  How to use a Galvanic Battery, 10;
  Electrical and Anatomical Demonstrations, 10

Tilt's Change of Life, 6;
  Uterine Therapeutics, 6

Tirard's Prescriber's Pharmacopoeia, 7

Tomes' (C. S.) Dental Anatomy, 12

Tomes' (J. and C. S.) Dental Surgery, 12

Tuke's Influence of the Mind upon the Body, 5;
  Sleep-Walking and Hypnotism, 5


Van Buren on the Genito-Urinary Organs, 14

Vintras on the Mineral Waters, &c., of France, 10

Virchow's Post-mortem Examinations, 4


Wagstaffe's Human Osteology, 3

Waring's Indian Bazaar Medicines, 8;
  Practical Therapeutics, 8

Warlomont's Animal Vaccination, 13

Warner's Guide to Medical Case-Taking, 8

Waters' (A. T. H.) Diseases of the Chest, 8

Weaver's Pulmonary Consumption, 8

Wells' (Spencer) Abdominal Tumours, 6;
  Ovarian and Uterine Tumours, 6

West and Duncan's Diseases of Women, 6

West's (S.) How to Examine the Chest, 8

Whistler's Syphilis of the Larynx, 12

Whittaker's Primer on the Urine, 14

Wilks' Diseases of the Nervous System, 8

Williams' (Roger) Influence of Sex, 4

Wilson's (Sir E.) Anatomists' Vade-Mecum, 3

Wilson's (G.) Handbook of Hygiene, 5;
  Healthy Life and Dwellings, 5

Wilson's (W. S.) Ocean as a Health-Resort, 10

Wolfe's Diseases and Injuries of the Eye, 11


Year Book of Pharmacy, 2

Yeo's (G. F.) Manual of Physiology, 4

Yeo's (J. B.) Contagiousness of Pulmonary Consumption, 8

       *       *       *       *       *

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