Blindness is a lack of vision. It may also refer to a loss of vision that cannot be corrected with glasses or contact lenses.
People with vision worse than 20/200 are considered legally blind in most states in the United States.
Blindness has many causes. In the United States, the leading causes are diabetes, glaucoma, macular degeneration, and accidents (such as chemical burns or sports injuries).
Worldwide, the leading causes of blindness are cataracts, onchocerciasis (river blindness), trachoma, leprosy, and vitamin A deficiency.
Other causes include: