Blindness - partial or complete loss of sight. Blindness may be caused by injury, by lesions of the brain or optic nerve, by disease of the cornea or retina, by pathological changes originating in systemic disorders (e.g., diabetes) and by cataract, glaucoma, or retinal detachment. Blindness caused by infectious diseases, such as trachoma, and by dietary deficiencies is common in underdeveloped countries where medical care is inadequate. River blindness, caused by a parasitic worm transmitted by black flies, results in severe itching and disfiguring lesions. Infection of the eye area can destroy vision. An estimated 18 million people in Africa, Latin America, South America, and Yemen are infected with the parasite; 1 million of those infected are expected to become blind or severely impaired. Until recently, pesticides have been used to eradicate the flies. Two new drugs, ivermectin and amocarzine, have proved effective when used together. Most infectious diseases of the eye can be prevented or cured.

A major cause of congenital blindness in the United States, ophthalmia neonatorum, which is caused by gonorrhea organisms in the maternal birth canal, is now prevented by placing silver nitrate solution in all newborn infants' eyes. Retinitis pigmentosis, a hereditary and degenerative eye disease, affects 100,000 people in the United States. An early sign is night blindness which progresses to total blindness. Color blindness, an hereditary problem, is an inability to distinguish colors, most commonly red and green. Snow blindness is a temporary condition resulting from a burn of the cornea caused by the reflection of sunlight on snow. Night blindness results from a deficiency of vitamin A. See eye.

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