Pathophysiology of Cataract - Arma

The term cataract is derived from the Greek word cataractos, which describes rapidly running water. When water is turbulent, it is transformed from a clear medium to white and cloudy. Keen Greek observers noticed similar-appearing changes in the eye and attributed visual loss from "cataracts" as an accumulation of this turbulent fluid, having no knowledge of the anatomy of the eye or the status or importance of the lens.

The lens is a clear part of the eye that helps to focus light, or 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. The lens must be clear for the retina to receive a sharp image.
The lens is made mostly of water and protein. Specific proteins within the lens are responsible for maintaining its clarity. Over many years, the structures of these lens proteins are altered, ultimately leading to a gradual clouding of the lens. Beside that, the clear lens can also changes slowly to a yellowish/brownish color, adding a brownish tint to vision.

Cataracts are very common in older people. A cataract can occur in either or both eyes. It cannot spread from one eye to the other. The clouding may become severe enough to cause blurred vision. Most age-related cataracts develop from protein clumping. When a cataract is small, the cloudiness affects only a small part of the lens. You may not notice any changes in your vision. Cataracts tend to grow slowly, so vision gets worse gradually. Over time, the cloudy area in the lens may get larger, and the cataract may increase in size. Seeing may become more difficult. Your vision may get duller or blurrier.

Cataracts also cause the lens to change to a yellowish/brownish color. As the clear lens slowly colors with age, your vision gradually may acquire a brownish shade. At first, the amount of tinting may be small and may not cause a vision problem. Over time, increased tinting may make it more difficult to read and perform other routine activities. This gradual change in the amount of tinting does not affect the sharpness of the image transmitted to the retina. If you have advanced lens discoloration, you may not be able to identify blues and purples. You may be wearing what you believe to be a pair of black socks, only to find out from friends that you are wearing purple socks. The risk of cataract increases as you get older. Other risk factors for cataract include
• certain diseases like diabetes
• personal behavior like smoking or alcohol use
• environmental factors such as prolonged exposure to ultraviolet sunlight.

References:
http://www.emedicinehealth.com/cataracts/article_em.htm
http://www.nlm.nih.gov/medlineplus/ency/article/001001.htm
http://nihseniorhealth.gov/cataract/whatisacataract/01.html