In Sophocles' Ajax, why does the playwright focus so much on vision, perception, and eyes?

Sophocles seems to have been drawn to the theme of literal versus spiritual vision. As many students have discovered, Sophocles' Oedipus the King deals with this theme as when, for example, the blind Teiresias knows that Oedipus killed his father and married his mother. Once Oedipus learns the truth about his past, he blinds himself and thus becomes like Teiresias.

At least 15 years before Oedipus the King, Sophocles brought the Ajax to the Athenian theater. In this play, Sophocles offers another study in a character who experiences distorted sight. In the Ajax, however, the goddess Athene causes Ajax's sight to become altered. Ajax has attempted to kill Agamemnon, Menelaus, and Odysseus, but Athene causes Ajax to kill cattle instead:

I stopped him. I threw down into his eyes
an overwhelming sense of murderous joy
and turned his rage against the sheep and cattle
and those protecting them—the common herd
which so far has not been divided up. (Ian Johnston translation)

When Ajax realizes that his eyes deceived him, he feels that the only way to regain his honor is to kill himself with his enemy Hector's sword. Ajax, however, gives a deceptive speech in which he fools his comrades into thinking that he is not going to kill himself. Earlier in the play, Ajax's sight was distorted. After hearing Ajax's deception speech, the Chorus is overjoyed and although they think that they "see" things clearly, they have actually been blinded in metaphorical sense to Ajax's true purpose:

From our eyes Ares has removed
those terrifying agonies.

Following Ajax's suicide, his half-brother Teucer's eyes also have become affected. He declares,

O this is surely the most painful sight
of anything my eyes have ever seen.

Teucer, in turn, calls Agamemnon's sight into question.

You miserable man,

where are your eyes when you go on like this?

After Agamemnon criticizes Teucer for not having two Greek parents, Teucer reminds Agamemnon that he, too, came from a heritage in which Greek and barbarian had intermingled.

Thus, in Sophocles' play, most of the major characters in the play experience some sort of distortion of their eyesight. Why Sophocles unifies this play with the vision motif is a matter of interpretation. Perhaps he is trying to teach his audience that everyone is susceptible to their vision being distorted in regard to different things: people, situations, the divine, etc.