I saw some film adaptation of shakespeare many years ago - Macbeth perhaps? - and there was this genius thing in it: a character had to read a letter, and he held it at arms' length and tilted his head to the side to try to read it ... because he didn't have reading glasses. When I saw that I had the same revelation as you did - in the past, literate people lost their ability to read when their eyesight failed.

Also, I had the exact experience you had with the glasses, except I was in the first grade. I got my eyes tested and they said, "How do you read what the teacher writes on the balckboard?" and I said, "You are supposed to be able to read the blackboard?" I thought it was part of the mystery of school that you weren't supposed to know what the teacher was writing.