From the beginning of Othello, the audience recognizes a deceit in Iago, not apparent to the Venetians, when he admits that "I am not what I am," (I.i.66). On the other hand, the audience is introduced to the ever trusting Othello,a well-respected member of the Duke's court. He is held in high esteem; the Duke calling him "Valiant Othello," (I.iii.48); and is trusted to protect the citizens of Venice most admirably. Desdemona has seen something in him and has married him because she, "saw Othello's visage in my mind," (I.iii.252). She has no concerns about him.
Ironically,many of the events that take place and the disastrous consequences are based on things that are not seen. Othello's misplaced trust in "honest, honest Iago," who claims to have seen Cassio using Desdemona's handkerchief, sews the seed of doubt in the jealous Othello's mind. This leads him to make poor decisions, based purely on the "ocular proof" (III.iii.364) that Iago purports to present in the form of Desdemona's handkerchief. The discrepancy between what is seen and what can be believed is therefore very strong in Othello, reinforcing the use of the "sight" motif and the theme of appearance versus reality.
Othello is about misunderstandings and misinterpretations. People are so easily deceived by appearances- that is, what you see is not always what you get- and they are manipulated because of their own human weaknesses - such as Othello's jealousy which, when aroused and "perplexed in the extreme," (V.ii.349) leads to irrational behavior. Honor and reputation are vitally important to Othello, and the very thought of infidelity on Desdemona's part shames, or so Othello believes, not only him, but, Desdemona herself, even to the point of thinking that killing her will allow him to "again thy former light restore,"(V.ii.9) meaning that he can effectively save her from herself and restore her dignity. He is concerned about how society will view her.
At the end of Othello, Lodovico remarks to Iago, whom he calls a "Spartan dog,... The object poisons sight; let it be hid," (365-367)clearly indicating how Iago uses his power of manipulation to make others believe what they think that they see even without true consideration.
The references to animals, such as "The Barbary horse" (I.i.112) used derogatorily to describe Othello and the "old black ram" (89) should also be addressed when discussing Othello and issues of potential racism. The handkerchief itself is also an important symbol as it is the "proof" that Othello demanded and upon which all the events turned.