Blindness is the lack of vision, or a loss of vision that cannot be corrected with glasses or contact lenses. Blindness may be partial, with very limited vision, or complete, with no perception of light. People with vision worse than 20/200, or a field of vision of less than 20 degrees in the better eye, are considered legally blind in most states in the U.S.

Blindness has many causes. In the United States, the leading causes are diabetes, glaucoma, macular degeneration, and accidents (such as chemical burns or injuries from bungie cords, fishing hooks, fireworks, racket balls, and similar objects).

Worldwide, the leading causes of blindness are cataracts, onchocerciasis (river blindness), trachoma, leprosy, and vitamin A deficiency.

Other causes include:

• Blocked blood vessels
• Complications of premature birth (retrolental fibroplasia )
• Complications of eye surgery
• Lazy eye
• Optic neuritis
• Stroke
• Tay-Sachs disease
• Retinitis pigmentosa
• Retinoblastoma
• Lead poisoning
• Optic glioma

It is important for a blind person to be able to dress, eat, function independently, and stay safe. Many services are available that provide the training and support that allow blind people to function independently.

Sudden vision loss is always an emergency, even you have not completely lost all vision. You should never ignore loss of vision, thinking it will get better.

Contact an ophthalmologist or go to the emergency room immediately. Most serious forms of vision loss are painless, and the absence of pain in no way diminishes the urgent need to get medical care. Many forms of vision loss only give you a short amount of time to be successfully treated.

A complete and thorough eye examination will be performed. The treatment plan will depend on the cause.