Further, the fact it relates, if common in the ancient world, would not deserve such strong wording to people who were familiar with such things as blind oracles. Rather, even were blind oracles commonplace in the ancient world, this one is special because he is not just a conveyor of bad news to Oedipus, but a kind of archetype, symbol, or personification of the message Sophocles is sending us that vision and blindness are not actually dichotomous, but intrinsically entangled.

Oepidus is another archetype of the same thing: sight and blindness coexisting, not sequentially, but simultaneously.

Another important way in which Oedipus was both blind and yet possessed of light becomes clear when we think about the steps he has taken to avoid killing his father. When we read Oedipus Rex, we like to think that finding ourselves in his shoes we could have done better. Were the oracle of Delphi still in business today and were he to give us the kind of news he gave to Oedipus that we were destined to kill father and marry mother, would we act any more wisely than did Oedipus? The mistake Oedipus makes is in assuming that the oracle was referring to his foster-father, Polybus. So, when he first hears the words of the oracle that he was destined to murder his father and raise children with his own mother, the first thing he does is get out of Corinth, putting as much distance between himself and those whom he thought his parents as he can, and we know what happened on the way to Thebes.

Now we read this and we think, "Ah, if only he had gone straight back and told his mother and father what the Delphic oracle had told him, they would have shown him the light, and, living happily ever after...

for, once he had been made to understand that the people who raised him were not his actual parents, he could then have chosen never to kill or marry anyone his senior, and been doubly sure by never killing or marrying anyone, period."
It seems like a plausible course of action for one with such a heavy "weird" upon him, like someone having a premonition they will die in an airplane crash and thereafter refusing to travel by air. But it was not to be.

Sophocles wants to convey something here, and is using the vision/blindness theme to add mystique and import to a larger issue still; we can never thwart fate. The very actions we take to do so somehow ensure that our fate catches up to us.

This is the biggest kind of blindness in Oedipus; the absolute inability of human beings to see all the myriad ways in which things work to bring us to our fates. Had Oedipus done what we flatter ourselves to think we would have done, namely consult the assumed parents with the new information before doing anything, and then sitting on our hands to make sure the prophecy didn't come to pass, it wouldn't have made any difference in the end. Had he become king of Corinth, at some point he would have had to go to war with Thebes, ended up killing Laius in open battle, and been forced by some obscure custom to marry the vanquished king's widow to retain the crown. In another sense, we are all Oedipus, trying to understand and outwit fate. Somehow, some way, fate would get Oedipus in the end, and have Oedipus working hard to help it.

In a sense both figurative and real, Oedipus was blind before his enlightenment, and blinded later by enlightenment.