In the United States, people are legally blind if their best eye has 20/200 vision or less with the help of glasses or contact lenses. Having 20/200 vision means that a person cannot be more than 20 ft (6.1 m) away to see what a person with normal vision can see from 200 ft (60.96 m) away.

The United States also considers people legally blind if their visual field is 20 degrees or less, even with the help of glasses or contact lenses. Having a visual field of 20 degrees means that people have trouble seeing to the side (peripheral vision) when looking straight ahead. A vision test is used to measure a person's visual field.

Legal blindness does not mean that a person cannot see at all. People who are legally blind often have some vision, but their field of vision may be very narrow or blurry. Or they may have blind spots that glasses cannot correct.

Being diagnosed as legally blind restricts a person's ability to obtain a driver's license. But a legally blind person is usually eligible for low visibility aids and other benefits to help improve daily functioning.