Sophocles certainly wasn't shy about the motif of sight vs. blindness. If you've got way too much time on your hands, go through the play and highlight words like "see," "sight," "vision," "eyes," and "blind." Since this motif is symbolic of the pursuit of "knowledge," you can go ahead add that word, along with terms like "oracle," "truth," "prophecy," and "Apollo," since he's the god that represents all these ideas. The Oracle of Shmoop predicts that your highlighter will run out of ink, and your script will end up looking like a neon patchwork quilt.
Though this motif of seeing and not seeing is laced throughout the beginning of the play, it first becomes crystal clear when the prophet Teiresias hobbles on stage. If one of Sophocles's ancient audience members missed the irony in this episode, he must've visited the wine stand a few to many times. Teiresias is literally blind, but he can see clearly the horror that is Oedipus's past, present, and future. Oedipus's eyes work just fine, but unfortunately he's completely blind to the dreadful fate the gods have placed upon him. The doomed king's ignorance on this key matter is made even more ironic by the fact that he was made famous for his keen insight, by solving the riddle of the Sphinx.
When Oedipus finally sees the terrible truth of his life, Sophocles hammers home his metaphor by having the king stab out his own eyes. Oedipus says he does this because he can no longer look on the horrors that his unwitting actions have created. With this most famous of gougings, Oedipus literally becomes the thing he's always metaphorically been: blind. At the end of the play, Oedipus becomes symbolic of all of humanity, stumbling forward through a dark and unknowable universe.