As is virtually always the case in art and literature, blindness as the absence of the physical sense of sight is a symbol (we could say a Jungian universal symbol) of the absence of spiritual, social, etc. ignorance of the truth; in Oedipus Rex, the "blindness" of Oedipus to the consequences of his deeds is iterated in the blindness he inflicts on himself in the play's climax. Also universal is the physical blindness of the prophet or "seer" who brings messages from the all-seeing oracles. What makes this play so universally recognized as the epitome of the blindness/"blindness" metaphor is the implication that all human actions bear unknown consequences, and therefore we must/should rely on a higher "all-seeing" power to guide us, and that out own sight (understanding) is always imperfect.
Seeing and blindness are both literal and figurative in Oedipus Rex. The literal sense is that what people believe is what they see. Jocasta and her husband had a child and took it to the mountain to die in order to prevent their son (Oedipus) from killing his father as foretold by the prophet Teiresias. Jocasta marries Oedipus after her husband is killed by robbers. Her belief about her husband’s death is based on what others saw. However, the blind prophet Teiresias is the only who truly sees. He speaks the truth of what will come and what has transpired, but Jocasta and Oedipus discard his words. As the play unravels, Jocasta and Oedipus finally see what transpired. After “seeing” the truth, Jocasta kills herself and Oedipus blinds himself. Thereafter, Oedipus’ family carries a curse.