To expand on this, how would people with poor eyesight know or find out that their sight was worse than the majority of the population? Are there any famous examples of people with poor eyesight?
Usually fairly well, from what little I've read. There's a history of saints caring for and healing the blind, and the Catholic Church and pious wealthy people emulated that. For an example in 1256 King Louis IX of France opened the Hospice des Quinze-Vingts to offer basic care to poor blind people and that still exists today.
Though there is also a history of some pretty grotesque satire and blind people getting paid to fight each other as a sort of entertainment, but neither of those things were ever entirely socially acceptable. Blind people were very often forced to be beggars because they couldn't get a source of income with their disability as well.
Enrico Dandolo, the Doge of Venice during the Fourth Crusade, and King John of Bohemia were both blind for part of their lives and held important positions without raising as far as I know any controversy.
OP, by "poor eyesight," do you mean mild myopia (that today would be treated with corrective lenses) or near-blindness?