Paul has to wear extremely thick glasses because his vision is so poor. No, you don't understand: these things are crazy thick. As Paul says, "My glasses are so thick…" (Prologue.1.9)
Our friendly Shmoop audience yells, "How thick are they, Paul?
Oh, we just kill ourselves.
But oddly enough, with those thickeroo glasses, he is the only one able to see things others can't—or won't. His glasses symbolize his ability to see the truth better than most people. They also remind us of the event that gave him this insight into the behavior of those around him.
And we bet they slip down his nose a lot, too.