The most common causes of blindness include cataracts, glaucoma, and age-related macular degeneration. Other causes include diabetic retinopathy, childhood blindness, and infectious diseases. The causes of blindness vary greatly between developed and developing countries. In developed countries, blindness occurs most often in conditions associated with aging. In developing countries, there is a much higher incidence of preventable blindness due to infection and cataracts.
In the United States, age-related glaucoma is one of the leading causes of blindness. Different types exist, but glaucoma results in damage to the retina and optic nerve, usually reducing the field of vision. Glaucoma causes about 15 percent of all blindness in the U.S. Screening for glaucoma after the age of 40 can prevent further loss of vision if the disease is detected. After cataracts, it is the second most common cause of blindness worldwide.
Age-related macular degeneration (AMD) is a progressive worsening of eyesight that can be part of the aging process. It doesn't usually cause total blindness but may make it difficult to read or see things sharply. AMD has no cure and is not well understood when no obvious cause is present.
Retinal neuropathy is a common complication of diabetes and another of the leading causes of blindness in the U.S. It occurs because of reduced circulation to the eyes, which can damage the retina. Retinal neuropathy can make vision worse and may result in complete blindness. Other causes in the U.S. include congenital blindness, accidents, and infection.
In the United States, the most common eye problem requiring medical treatment are cataracts, but it is not one of the common cause of blindness. Cataracts are a clouding of the lens of the eye, which impairs vision by making it more difficult for light to pass through. The majority of people more than age 50 have some clouding of the lens. Cataracts can be treated and vision restored by implanting an artificial lens. Cataracts go untreated in many developing countries, making it by far the leading cause of blindness worldwide.
Infectious causes of blindness are fairly rare in developed countries, but are much more common in developing countries. The resulting blindness is usually avoidable if the diseases are treated in their early stages. The most common infectious cause of blindness is trachoma, which can result in scarring of the cornea and total loss of vision. It has been estimated that up to 80 percent of global blindness can be prevented by nutritional, medicinal, and sanitation improvements.