Oedipus the King is a fabulous play, thought to be first played somewhere between<em> 430 - 426 BCE,</em> it is a famous classic tragedy by <em>Sophocles</em>. Oedipus the King is also known as <em>Oedipus Rex</em>, where<em> 'Rex' </em>stands for<em> 'King'</em> in latin.
In this tragedy, there is a point in the second chapter where Oedipus, the king of Thebes has a visit from an old soothsayer. Teiresias is the name of this old soothsayer, who is consulted regarding the plagues that torments the city of Thebes. Oedipus makes fun of Teiresias claims, and he replies that even though he can see, he still remains 'blind' to the truth.
Later on, King Oedipus loses his sight, and becomes blind. Here is where the irony becomes evident, because now King Oedipus realizes what the blind man was trying to say, and that the blind man was the one who truly saw the truth. This is an example of dramatic irony.
Hope this helps!