What Is a Cataract?
A cataract is a clouding of the lens in the eye that affects vision. The lens is a clear part of the eye that helps to focus an image on the retina. The retina is the light-sensitive tissue at the back of the eye. In a normal eye, light passes through the transparent lens to the retina. Once it reaches the retina, light is changed into nerve signals that are sent to the brain. A cataract can occur in either or both eyes. It cannot spread from one eye to the other. By age 80, more than half of all Americans either have a cataract or have had cataract surgery. Regular eye exams are important, and protecting eyes from the sun can help slow cataract development.
–Source: National Institutes of Health