what are the use irony in this play

One example of dramatic irony comes when the old soothsayer visits the King. Oedipus ridicules the man because he's blind, and Tiresias in a fit of anger tells the king that though he can see he is "blind" to the truth. When Oedipus becomes blind, he finally realizes the truth of the man's words. Irony is also to be found in the fact that it is the blind man who truly sees.

We also know from the outset that Oedipus is going to kill his father and marry his mother.