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