In his own words, Ed is “blind as a bat” without his glasses because he has “terrible eyesight” and “can’t see anything” without them. He actually once went to get some new glasses, and when he told the girl who worked there his lens prescription, she said, “wow, really?!”
As is the case with a lot of people who have pretty bad eyesight, Ed’s glasses are actually the very first thing he reaches for when he wakes up in the morning.