Ever notice how many people need glasses to correct their vision?
There are a number of defects that human beings have scattered throughout the gene pool, of which less than perfect vision may be one of only minor importance. Eugenics would work on human beings just as well as it does on any other organism that that reproduces by recombining genetic material. The ones more highly adapted to the immediate environment, have a reproductive advantage over those less well adapted. But that means the less highly adapted die off before reproducing, thus eliminating ALL their genetic heritage, not just the poor adaptations.
“Ever notice how many people need glasses to correct their vision?
Poor eyesight does not inhibit reproduction. It may even assist it!