Blindness in Oedipus the King

I believe that the reoccurring notion of blindness plays an important role throughout the play. Tiresias is the 'seer' that is blind, yet knows the truth. Oedipus can see and does not know the truth till the end of the tragedy. However those that can see, namely Oedipus at the beginning of the tragedy don't really see all that is going on, and the truth behind his life. Tiresias responds to Oedipus' reproach by saying "So, you mock my blindness? let me tell you this. You with your precious eyes you're blind to the corruption of your life, to the house you live in, those you live with (468-473)." It was not till the end of the play that Oedipus literally blinds himself, does he realize the truth. Of all the intricate layers of meaning and lessons that this play conjures, I think that the lesson that nothing is always what it seems, appears to be the most important one.