A cataract is a clouding of the lens of the eye, which is normally clear and transparent. When a cataract develops, the lens becomes foggy like a frosted window. There are many misconceptions about cataracts. They are not tumors, or a new growth of skin or tissue over the eye. They don't spread from eye to eye and they're not caused by using your eyes too much. In fact, no one knows what causes cataracts or how to prevent them. They usually develop gradually over a period of years and are considered a normal part of the aging process. Most of us, if we live long enough, will develop cataracts.