Exactly my point. Unless you experienced some barrier that made you sure that you had a problem, you wouldn't even know that you had a problem (unless we are t

Exactly my point. Unless you experienced some barrier that made you sure that you had a problem, you wouldn't even know that you had a problem (unless we are talking about advanced stage glaucoma or something like that- but these are mostly age-related ailments). And the more you go back in time, the less the number of people that would find out. Glasses were certainly an upper-class thing, as reading was an upper class thing. I did not even realize that I had a problem with my eyes until I found out that I could not see the blackboard from a distance that other kids could. Before that, I just thought that the blackboard couldn't be seen at all from that distance, and I found a nice zone from where I could read everything without risking the chalk-dust. Until I compared my reading ability at distance with several friends, I did not even know that I had a problem.