In The Miracle Worker by William Gibson, Annie Sullivan wears dark glasses to protect her eyes from bright lights. Annie was almost blind when she was a child and attended Perkins Institute for the Blind. An operation helped her regain her sight, but her eyes are still extremely sensitive to light. Hence, she wears dark glasses.
Annie is hired by the Keller family as a teacher for Helen, who is both blind and deaf. Because of Annie's previous experiences with blindness, she knows how to handle Helen, although there is an extra challenge because of Helen's deafness. Still, Annie has a plan about how to teach Helen. She spells words into Helen's hand and teaches her simple sign language.
Annie also realizes that Helen needs discipline more than just about anything else. Helen's family has a tendency to coddle her because of her disabilities, and they actually reward Helen for her bad behavior. They don't mean to, but they give her things she wants just to calm her down, and this reinforces those acts. Annie cuts off this habit and disciplines Helen as needed.
Eventually, thanks to Annie Sullivan, Helen Keller learns how to behave and how to communicate. Inspired by Annie, she becomes an inspiration to the world.