While Anne Sullivan's smoked glasses literally protect her sensitive eyes that have undergone several operations as a result of her childhood experience with trachoma--

And now she has opened her eyes; they are inflamed, vague, slightly crossed, clouded by the granular growth of trachoma, and she often keeps them closed to shut out the pain of light.

--they evoke, for one thing, the image created by the passage from St. Paul's Letter to the Corinthians: 

For now we see through a glass, darkly; but then face to face: now I know in part; but then shall I know even as also I am known                                                                        1 Corinthians: 12

When Anne Sullivan first arrives at the Kellers' home in Tuscumbia, Alabama, she sees through her smoked glasses rather darkly because she is in a strange place and is yet haunted by memories of her brother Jimmie, whom she feels that she neglected. Further, because of inexperience, she does not yet clearly perceive how to help Helen. So, she pursues what seems to be an impossible task, partly because society is very much in the dark about how to work with the visually and hearing impaired. However, it is with great determination that Miss Sullivan persists in teaching Helen first to behave, and then to learn letters and words that she spells out into the girl's hand. Finally, Helen connects this finger game with the objects that have been spelled out when Anne makes Helen refill the pitcher whose water the girl has rudely poured upon Miss Sullivan's head.

And, with this success, Miss Sullivan now "knows in part" that she has proven herself to be a competent teacher when there were those at the Perkins Institute who doubted her. Nevertheless, she yet struggles with the loss of her brother and her inability to fully reach Helen. In some time "then shall I know" occurs with Anne as she succeeds in getting control of Helen and breaking through to her, teaching her "to know," as well as being victorious over her own inner demons along with the forces of Captain Keller's disapproval. She now sees more clearly as she has attained self-esteem in her success.

Anne's smoked glasses can also symbolize the marred perspective that the Kellers have of Anne at first as they do not understand Miss Sullivan's perspective with regard to the discipline that Helen needs, and the importance of her control over Helen so that she can learn.