I'm really worried about my genes. I don't want to have a child that could potentially go blind at the age 20.
Yeah that would be tough, but is there any particular reason to be concerned?
It's a hereditary disease that runs through our family so I don't want to spend money on something I could prevent now.
Your fear is justifiable. It's ok not to have children if your family has some genetic condition.
I'm not ready to be a parent to a kid with blindness.
Choosing not to have biological children to prevent passing on a genetic issue is okay. You could always adopt. Just make sure you discuss the issue openly with potential spouses.