The themes of blindness and sight are key throughout this entire play, and of course feed into the dramatic irony, not only in the inevitable ending where Oedipus blinds himself but also in the way that the audience knows that he is the killer of the former king of Thebes who he is so desperately trying to find. This is something that is evident in the initial declaration of Oedipus when he determines to find the killer:
I'll start again--I'll bring it all to light myself!
Apollo is right, and so are you, Creon,
to turn our attention back to the murdered man.
Oedipus himself uses imagery of being able to see the past and what happened, "bringing it to light." The dramatic irony is of course that what he will "bring to light" is his own involvement in the murder in a way that will shock and horrify him and everybody else around him.
Seeing is another key motif when Oedipus asks Jocasta about the precise nature of how his father died. Before this, Tiresias, the blind seer, has delivered his prophecy which has been mocked and disregarded by Jocasta. Yet when Jocasta tells Oedipus about the appearance of her first husband, Oedipus says he has a "terrible fear the blind seer can see." When Jocasta provides further details, Oedipus says:
Now I can see it all, clear as day.
The dramatic irony in these lines lies in the way that Oedipus is finally able to "see" the truth that he has ignored, either consciously or unconsciously for so long, as what Jocasta tells him reminds him about his own role in his father's death. This section is significant as it infers that Tiresias, as blind as he is, actually has better "sight" than Oedipus.