1430, from L. cataracta "waterfall," from Gk. katarhaktes "swooping, rushing down," from kata "down" + arhattein "to strike hard." Its alternative sense in L. of "portcullis" was probably passed through M.Fr. to form the Eng. meaning "eye disease" (1547), on the notion of "obstruction."
A loss in the transparency of the lens of the eye, which reduces a person's ability to see. The condition can be treated by surgically removing the lens and replacing it with an artificial one, or with corrective eyeglasses or contact lenses.