I have been wearing glasses for about twenty years. When I first started seeing an optometrist, probably in the second or third grade, I was told that I had an astigmatism, and that my eyes were showing signs of weakening, and it was inevitable that I would eventually require glasses. Within five years, her prognosis became a reality.
I had been warned by my parents to make sure I had sufficient light whenever I did any reading, lest I do damage to my eyes, and I received similar warnings about sitting too close to the television. (I found this article that explains how the dim-light-reading theory is a commonly-believed medical myth.) But according to the doctor, there was nothing to be done about my impending nearsightedness other than correcting for it once it became serious enough to be a hindrance. I was born with eyes that were set to deteriorate.
I eventually learned about evolution and natural selection in high school, and it struck me as odd that a condition such as nearsightedness would have survived in humans. It seems like it would be a distinct disadvantage for hunter-gatherer to lack the ability to make out objects at a distance. I didn’t pursue science very far in school, but this question lingered in my mind.
Later, upon studying in college, the answer occurred to me, though I make no claim to any kind of scholarly authority, and this is complete speculation on my part. For hunter-gatherers, vision was likely not nearly as important to their survival as hearing. Sure, early packs of hunters would need to spot their prey, but even without my corrective lenses, I’m able to tell whether an object at a distance is moving. I don’t need to be able to make out the details on its fur to tell what it’s doing.
It’s only in our modern life, with symbols and words posted everywhere, that making out details at a distance is a significant and necessary activity. It’s easy to forget that having a society where the majority of people are even literate is a relatively recent development. In those pre-literacy days, it wouldn’t have done much good to have signs posted everywhere.
Furthermore, it was only a few hundred years ago that a typical European resident travelling a few hundred miles would encounter several different languages and dialects on the way. More than that, it would be rare for someone a few hundred years ago to do much travelling beyond one’s own village. We didn’t need to have signs posted everywhere to direct masses of people, because there simply weren’t masses of people to direct! People who were more intensely involved in local, village affairs would understand things by social convention, and public directions wouldn’t be necessary.
Again, this is just pure spitballing on my part, but it makes sense to me. Thank goodness for glasses and contacts. Corrective lenses have been around for thousands of years, and only in recent times have they become a commonplace, mass-produced item. We invented them because we invented the need for them.