macular degeneration
dystrophy of the macula lutea, which affects both eyes and causes progressive loss of central vision. Macular degeneration occurs at various ages from birth to old age. Age-related macular degeneration is among the most common causes of visual impairment in older people, with an incidence of about 5% in those ages 55 to 64 and up to about 45% in those ages 75 to 84. There are two types: exudative (or wet) macular degeneration, in which blood vessels grow under the retina and hemorrhage in the area of the macula; and atrophic (or dry) macular degeneration, in which one of the retinal layers degenerates or atrophies. Apart from age, other risk factors for the disease include exposure to ultraviolet light, smoking, hypertension, and possibly zinc deficiency in the diet.