A cataract is a cloudiness that develops in the normally clear lens of the eye. A natural lens is referred to as a cataract when it has turned cloudy.
A cataract is not a growth or a film on the surface of the eye, but rather is defined as any opacity in the normally clear human lens.
The human lens is a transparent finely focusing element suspended behind the pupil of the eye. It is about the size of an ordinary pill and consists of a strong, transparent outer capsule filled with a transparent flexible gel. As the lens varies its thickness, it enables the eye to focus on both near and far objects.
When light enters the eye, it passes through the cornea (the eye’s clear front window) and then through the pupil and the lens to focus the light rays onto the retina at the back of the eye. The retina changes the light images into electrical impulses and sends them to the brain via the optic nerve. When the lens develops a cataract, light becomes distorted, scattered, and redirected, and is not focused clearly on the retina. Vision is reduced, and blindness can eventually result.
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. Some cataracts mature slowly over a period of years, whereas others can form rapidly within a few months..