To know what a Cataract is, it may be helpful to learn some basic facts about the structure of the eye. Light from the object you are looking at passes through the window of the eye, the clear transparent cornea. Then it passes through the pupil, the black opening in the center of the colored part of the eye, which is called the iris.

The lens, normally a crystal clear structure located behind the pupil and iris, focuses light on the retina, much as the lens in a camera focuses light.

The retina acts as the film in a camera and forms the image. The image is transmitted by the optic nerve to the brain, where the actual process of "seeing" takes place.

The term "cataract" refers to a clouding or loss of transparency of the lens. As clouding progresses, light has difficulty passing through the lens. This results in dim, distorted or blurred images on the retina and decreased vision. It's like looking through a dirty window.

Cataracts do not "grow." A cataract is not skin over the eye, nor is it a tumor. A cataract progresses as a result of increasing cloudiness of the lens. There is no way of predicting how rapidly a cataract will progress. Some develop slowly over a period of many years, while others progress rapidly. At the present time, there is no known treatment that will slow or stop the progression of a cataract.

The cause of most cataracts is unknown. They probably are a result of the aging process. However, a cataract may be caused or accelerated by conditions such as injury, inflammation inside the eye, certain disorders of blood chemistry and some drugs.