The term cataract refers to any cloudiness or opacity of the normally transparent crystalline lens of the eye. A cataract may or may not cause a loss of vision, depending on the size of the opacity, its density, and its location. Severe cataracts are a major cause of treatable blindness throughout the world. In medical practice the term cataract designates those opacities which impair vision.
Small opacities of the lens are common, and cataracts can be present from birth. They can be caused by trauma to the eye, inflammation, infection, and exposure to radiation (including sunlight), and are associated with genetic diseases and conditions such as diabetes. In most people the lens gradually becomes cloudy as a result of aging. During the early stages vision can be corrected with prescription glasses. As the cloudiness increases, surgery may be necessary to remove the crystalline lens and implant a replacement plastic lens. Prior to the advent of lens implants, after cataract surgery patients had to wear either very thick "cataract" glasses or contact lenses. The hard nucleus of the crystalline lens can be removed in one piece through a surgical incision, or a tiny ultrasonic probe can be used to break the cataract into small pieces, which are rinsed from the eye through a small incision. The small incision method is increasingly popular, because it allows for a more rapid recovery.