A cataract is the clouding of the natural lens inside the eye. As the natural lens of the eye becomes cloudy, it does not allow light to pass through it as well as it did when it was transparent. The natural lens is made of a strong, transparent outer covering or capsule filled with a clear gel material. When the gel starts to become cloudy, the incoming light rays are distorted or blocked before reaching the retina at the back of the eye. As the cataract develops, it becomes harder for a person to see.