A cataract is formed when the natural lens of the eye, responsible for focusing light and producing sharp images, becomes cloudy and hardens, resulting in a loss of visual acuity. The lens of the eye is normally clear at birth but is one of the first parts of the body to show the effects of aging. It usually develops gradually over several months or years. Normally, the onset of a cataract in one or both eyes may cause decreased night vision, impaired depth perception, and increased color distortion.