What causes blindness?
The many causes of blindness differ according to the socioeconomic condition of the nation being studied. In developed nations, the leading causes of blindness include ocular complications of diabetes, macular degeneration, glaucoma, and traumatic injuries. In third-world nations where 90% of the world's visually impaired population lives, the principal causes are infections, cataracts, glaucoma, injury, and inability to obtain any glasses. In developed nations, the term blindness is not used to describe those people whose vision is correctable with glasses.
Infectious causes in underdeveloped areas of the world include trachoma, onchocerciasis (river blindness), and leprosy. The most common infectious cause of blindness in developed nations is herpes simplex. Other causes of blindness include vitamin A deficiency, retinopathy of prematurity, blood vessel diseases involving the retina or optic nerve including stroke, infectious diseases of the cornea or retina, ocular inflammatory disease, retinitis pigmentosa, primary or secondary malignancies of the eye, congenital abnormalities, hereditary diseases of the eye, and chemical poisoning from toxic agents such as methanol.