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BLINDNESS

People who are blind rely on their other senses-smell, touch, hearing, taste-to help them manage in the world. Blind people have to memorize identifying features, like sounds and smells, of the places that they often go. They also have to pay close attention to where things are located in their homes in order to get around safely, always putting objects in the same places after use so that they can be found again.

Some blind people use canes or guide dogs to get around. A white cane indicates that the person using it is visually impaired. Blind people tap their canes on sidewalks, floors, and streets. They learn to identify the locations of things-like steps, walls, or doors-simply by the different sounds that their cane taps make. Various high-tech devices have been invented, including laser canes, that use sound or light waves that bounce off objects and send signals to the user about where these objects are located, what they might be made of, and how big they are. Guide dogs, or seeing-eye dogs, are specially trained to lead blind people about. The dog and the person work as a team, with the dog following commands that help the blind person go about her day. The dog, in turn, signals the person when she is approaching a curb or when it is safe to cross a street.

Blindness is complete loss of sight. It can happen when certain parts of the eyeballs, the optic nerves (which carry visual signals from the eyes to the brain), or the sight centers of the brain are damaged. Such damage can occur as a result of injuries or diseases. A person can also be born with eye or brain abnormalities that cause blindness. In many cases, particularly in very poor countries, infectious diseases and poor diets can also cause blindness. A lack of vitamin A, in fact, is the leading cause of blindness worldwide. With basic medicines and proper nutrition, such cases could be prevented.

For every one person in the United States who is totally blind, there are four others who are visually impaired or "legally blind." These people have some ability to see, but they see so poorly-even with eyeglasses-that they cannot do things that require good vision, like driving a car.