On humans, those with "poor" traits (for example, bad eyesight) would have been killed or died at a young age. Thus, only those with better genes (like those who could actually see well) would reproduce.
However, technology allows those with bad genes to have a higher chance of reproducing and passing those genes on to other humans. Needing glasses or contact lenses may not seem like a big deal, but we also allow things like diabetes, heart conditions, and the like to "spread" to more people.
Fortunately, we are now reaching the stage of being able to artificially improve ourselves genetically. Hopefully, people won't mess with stupid things like eye color and instead only touch important things like eyesight.
Please Note: I am not saying that people with any of the problems I listed are inferior, just genetically inferior.