Given natural selection is true, why do we still have genetic eye sight issues? Because I would think bad eye sight would get you killed (or at least the inability to eat) in a hunter gatherer society.
Our eyes are incredibly precise things. It does not take much to disrupt their function. Evolution is full of little tweaks and changes. If we wiped out everyone with bad eyesight, more would just be born. Fewer, but we can’t expect to get that number close to zero.
However, there is another issue. Modern eyesight issues, even with a genetic factor, are largely caused by the environment. These “bad” genes are only bad in a modern world and did not cause bad eyesight earlier in humanity.
Who’s to say that ancient eyesight was really horrendous relative to today and that natural selection has been improving eyesight for eons.
Also note that eye issue would impact people differently. A craftsman will suffer greatly from farsightedness. A hunter would have few if any serious issues from not being able to see close up.
Bad eyesight and bad enough eyesight to get you killed are two very different things. Humans have also been able to care for their sick for a very long time, leading to and increase in those who would have been too sick to pass on their genes.
Humans are social animals, so if one has bad eyesight, all of the others who see the hungry lion are warn and protect the one who didn’t see it.
I personally do not like the phrase, “Survival of the fittest” ‘cause it’s too easy to misunderstand. It should be replaced by something like, “Survival of the just barely adequate.”
A rabbit that can outrun a fox by a mile has no greater evolutionary advantage than one that outruns by an inch.
Our eyes are good enough so this is evidence that improving it provides no benefit in offspring.
A population that has an improvement here is no better off.
Bad eyesight wouldn’t get you killed nor stop you from eating. You’d need to have _really_ bad eyesight (as in, pretty much blindness), _and_ not live in any kind of society for bad eyesight to be lethal.