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Blindness is a lack of vision. It may also refer to a loss of vision that cannot be corrected with glasses or contact lenses.

• Partial blindness means you have very limited vision.
• Complete blindness means you cannot see anything and do not see light. (Most people who use the term "blindness" mean complete blindness.)

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.

Loss of vision; No light perception (NLP); Low vision; Vision loss and blindness

Blindness has many causes. In the United States, the leading causes are:

• Accidents or injuries to the surface of the eye (such as chemical burns or sports injuries)
• Diabetes
• Glaucoma
• Macular degeneration

The type of partial vision loss may differ, depending on the cause:

• With cataracts, vision may be cloudy or fuzzy, and bright light may cause glare
• With diabetes, vision may be blurred, there may be shadows or missing areas of vision, and difficulty seeing at night
• With glaucoma, there may be tunnel vision and missing areas of vision
• With macular degeneration, the side vision is normal but the central vision is slowly lost

Other causes of vision loss include:

• Blocked blood vessels
• Complications of premature birth (retrolental fibroplasia)
• Complications of eye surgery
• Lazy eye
• Optic neuritis
• Stroke
• Retinitis pigmentosa
• Tumors such as retinoblastoma and optic glioma

When you have low vision, you may have trouble driving, reading, or doing small tasks such as sewing or making crafts. You can make changes in your home and routines that help you stay safe and independent. Many services will provide you with the training and support you need to live independently.

Sudden vision loss is always an emergency, even if 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 will depend on the cause of the vision loss.

For long-term vision loss, see a low-vision specialist, who can help you learn to care for yourself and live a full life.

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Olitsky SE, Hug D, Smith LP. Disorders of Vision. In: Kliegman RM, Behrman RE, Jenson HB, Stanton BF, eds. Nelson Textbook of Pediatrics. 19th ed. Philadelphia, Pa: Saunders Elsevier;2011:chap 613.

Yanoff M, Cameron D. Diseases of the visual system. In: Goldman L, Schafer AI, eds. Cecil Medicine. 24th ed. Philadelphia, Pa: Saunders Elsevier; 2011:chap 431.