I was just thinking about Kim Peek, and how his "brilliance" is all for naught. He remembers everything he ever sees, but his brain doesn't provide a sort of filter to allow him to usefully process that information. He can't make sense of anything, so the result is useless to him.
You and I have a sort of filter. We walk into a room, and don't notice every single detail, since a lot of those details are completely useless to us. We don't waste our minds contemplating that the blue carpet is exactly the same as it was last time, and only end up noting the things that look out of place. Good eyes allow us to see that, but in general the brain acts as the filter for us. If we have bad eyes, we get glasses and put the burden on our brains. We'd rather see everything and let the brain operate.
My idea is that bad eyesight is a sort of alternate solution for this processing problem. It could essentially be viewed as an external filter to take that initial processing load off of the brain. I'm not arguing that it's better than seeing things well and letting the brain work it out - this is obviously not the case. It's better to see everything and ignore it than to not see things at all, obviously.
But assume that Kim Peek had to live his whole life with bad eyes. Would he be able to process information better than he can now? Would his brain have adapted in a way so as to be able to reason about the limited data that he could observe? Would he be as able as a typical person when it came to figuring the world out?
I don't know the answers, but just wanted to get the idea written down. In a nutshell, I'm viewing eyesight as a way to move that internal filter to a more external location, to achieve a similar benefit. The benefit is being able to work with a smaller amount of information and make some sense of it.