system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5 Before the invention of glasses, were people with bad vision just doomed to a miserable existence?
gpt
There's a bunch of bullshit answers in this thread.  The _truth_ is that while blindness or bad vision due to eye damage, parasites, cataracts, etc, was relatively more common in the past than it is today, on the whole people had better vision because _nearsightedness_ was very rare.  Because nearsightedness is mostly a disease of the modern world.  So most vision problems in the past couldn't have been fixed by glasses, and the main vision problem fixed by glasses in the modern world was vanishingly rare.

Nearsightedness results from spending time indoors a lot as a child.  The lack of strong illumination interferes with the mechanism controlling the growth of the eyes, resulting in eyes that are too long and as a result causing nearsightedness because the image focuses in front of the retina.  This has been demonstrated in animal models and the biochemical mechanism is understood.  This results in a very well documented pattern...in societies which are not industrialized, nearsightedness is rare to practically nonexistant.  Surveys of hunter-gatherers and other groups living in traditional ways find almost no one who is nearsighted.  As societies industrialize, nearsightedness skyrockets (there's a very good dataset from Singapore on this). 

Vision is important...all this nonsense about you not really needing to see more than a blur to spot predators and prey is baloney. Animals in the wild are camoflaged, hide effectively among the terrain, and are quite hard to spot without good vision to see them.  And that's not to mention foraging for plants, which are nearly impossible to identify at a distance without good vision.