A cataract is a clouding of the eye's natural lens, causing vision loss. A cataract can occur in either or both eyes. If left untreated, the clouding can eventually lead to legal blindness or even total blindness.
Most cataracts are related to aging, but cataracts can also be present at birth or develop later in life caused by physical injury or trauma.
The lens lies behind the iris and the pupil. In a normal eye, light passes through the transparent lens. The lens is made of mostly water and protein. As we age, some of the protein may clump together and start to cloud a small area of the lens. This is a cataract. Over time, the cataract may grow larger and cloud more of the lens, making it harder to see.