Click on the image if you don't have Netscape version 3 or later. Cataracts are a cloudiness that form in the lens of the eye. The lens normally is clear. Poor vision results because the cloudiness interferes with light entering the eye. Cataracts are due to a change in the lens material.
Most cataracts are a result of ageing and long-term exposure to ultraviolet light.
Some are caused by injury and certain diseases and in rare cases by exposure to toxic materials and radiation. Occasionally cataracts are present at birth, due to baby's mother having had rubella during the pregnancy, or genetic defects. The clouded areas become larger and denser and cause the patient's sight to become worse. The time taken for this to happen varies from a few months to many years. Usually cataracts affect both eyes but often develop at different rates in each eye.