A cataract is a clouding of the natural lens of the eye. A cataract is not a growth, or a film across the eye. When light enters the eye, it passes through the cornea (the eye’s clear front window), and then through the pupil. Behind the pupil is the lens of the eye. The lens focuses the light rays onto the retina at the back of the eye. The retina is responsible for the signal that is sent from the eye to the brain. The eye generally functions like a camera with a system of lenses (cornea and lens), aperture (pupil) and film (retina). When the lens becomes clouded with the development of a cataract, light is distorted and is not focused clearly on the retina. Vision is reduced and blindness can eventually result. Almost everyone who lives a long life will develop cataracts. The cloudiness does not spread from one eye to the other but cataracts will usually develop in both eyes at some time. Most cataracts mature slowly over several years however some cataracts may develop rapidly within a few months.