CATARACT

in medicine, opacity of the crystalline lens of the eye. If the opaque areas are minute, scattered dots (a condition known as blue dot cataract, or punctate cataract) or if only the periphery of the lens is affected (this type, called coronary cataract, is said to affect 25 percent of the population), there may be no appreciable diminution of vision. In instances of cataracts that do seriously impair vision, the standard treatment is surgical removal of the lens. Cataracts that seriously affect vision may be present at birth. Congenital cataract may number among the defects that originate in a mother's infection with German measles (rubella) during the first three months of pregnancy. Cataracts may form in infants that have galactosemia, a hereditary metabolic disease in which there is inability to utilize galactose, a derivative of milk sugar. Babies with rickets may have cataracts, as may those with Down's syndrome or hypothyroidism. Cataracts in infants are in most cases not progressive. If the opacity is severe, these cataracts are known as white eye, in reference to the appearance of the pupil. Diabetes mellitus, particularly in young persons whose diabetes is not well controlled, may cause cataracts. The disease may also impair vision by its effect upon the retina. Cataracts may result from prolonged exposure to heat, as in glassblowing or iron puddling, to X rays, or to bombardment with subatomic particles, especially neutrons. The best-known form of cataract is the type that develops with advancing age. Such cataracts result from the continuing growth of the lens throughout life and its concomitant increase in density. If the opaque area is in the central area of the lens, the eventual loss of vision is greater than that produced by peripheral cataracts. In the early stages of the growth of the cataract, near vision may temporarily improve to the point that the affected person finds it possible to read without glasses. a waterfall (q.v.), especially one containing great volumes of water rushing over a precipice.