what is the significance of earl of Gloucester blindness?

Real blindness is often, in literature, used to symbolize blindness of the thoughts or of the thinking. The Earl of Gloucester is blind to the characteristics of his children (both legitimate and illegitimate), and he is not aware of their character until later in the play.

Gloucester's blinding in the play represents his emotional blindness towards his two sons, Edgar and Edmund. The running irony in Lear is that men only see the truth after they have been physically blinded. It is only after Gloucester's blindness that he really sees the true nature of his sons and which son actually loved him.