Final answer:
Oedipus refers to the blind prophet Tiresias' awareness of Thebes' plight from the plague, highlighting dramatic irony as Tiresias sees the truth of Oedipus' situation clearer than Oedipus does who is metaphorically blind to his own life's realities.
Step-by-step explanation:
When Oedipus says, "blind though you are, you know our city lies Sick with plague," he is addressing the blind prophet Tiresias, acknowledging his physical blindness but also the prophet's awareness of Thebes' suffering due to the plague.
The irony here is that Tiresias, despite his lack of physical sight, sees the truth about Oedipus' situation more clearly than Oedipus himself, who is metaphorically blind to the realities of his life and the prophecies that have been fulfilled.
Oedipus is pushing Tiresias to reveal his knowledge about the cause of the plague – the unresolved murder of the former king, Laius – not yet realizing that the investigation will lead to his own downfall.
The dramatic tension escalates as Tiresias, initially reticent, eventually hints at the grim truth: Oedipus is himself the cause of the plague as he has unwittingly fulfilled the Oracle of Delphi's prophecy, having killed his father and married his mother.
This revelation leads to disastrous consequences, as prophesied by Tiresias and confirmed by later events in the play. Oedipus, upon discovering the terrible truth, blinds himself, thus embodying the prophecy that he would be blind to the truth until he can literally see no more.