is clouding of the normally clear and transparent lens inside the eye. When cataract develops, the lens becomes cloudy as if light transmission to the retina is obstructed by a frosted window. Cataract develops gradually over the years and it may affect one or both of your eyes, but the rate of progression varies among individuals. If the cataract only covers a small part of the lens, your eyesight may not be affected. If a large portion of the lens becomes cloudy, your eyesight can be partially or completely lost.