People with vision that is worse than 20/200 with glasses or contact lenses are considered legally blind in most states in the United States. Vision loss refers to the partial or complete loss of vision. This vision loss may happen suddenly or over a period of time. Some types of vision loss never lead to complete blindness. Blindness has many causes. In the United States, the leading causes are: Accidents or injuries to the surface of the eye (chemical burns or sports injuries)