There's no episode where Homer goes to the future and finds everyone blind, but what you're talking about sounds like "Bart to the Future". The episode shows the future of the whole family in a vision that Bart experiences. One thing that happens is that Bart goes to ask Ned Flanders for money, and when Ned answers the door, it turns out that he's blind. Ned says, ruefully, "I never should have had that trendy laser surgery. It was great at first but, you know, at the ten-year mark your eyes fall out."
