I have been wearing glasses since the third grade. I don't even remember not being able to see but my mom says she took me because I told her I could not clearly see what was written on the board at school.
I read this interesting article about a little girl who was thought to be delayed and it turned out she only needed glasses! She is even a member of Mensa now as a toddler!
http://today.msnbc.msn.com/id/47233631/ns/today-good_news/t/meet-mensas-youngest-us-member-she-joined-age/

& this article states: Even if no signs of an eye problem are evident, the recommended first eye exam should be at 6 months of age and again at age 3, according to the American Optometric Association
http://www.victoriaadvocate.com/news/2012/aug/09/yl_guest_column_081212_184267/

Im planning on having my DD eyes checked soon even if she doesn't show major signs of vision problems. She is only 7 months. It will be interesting to see how they check them at that early of an age.