A cataract is a clouding of the lens of the eye. The lens of the eye functions like a camera lens—it focuses the image on the retina at the back of the eye. When the lens is cloudy from a cataract, the image on the retina appears blurred. Age is the biggest risk factor for cataracts; by age 80 more than half of Americans will either have a cataract or cataract surgery. Cataracts can occur in one or both eyes.

The lens is made up mostly of protein and water. The protein is arranged precisely to be clear and let light through. With age, the proteins may clump together to cause clouding. When a cataract is small, it only affects a small area of the lens and does not affect vision. Cataracts tend to grow slowly over time so that vision worsens. In addition the lens slowly changes from clear to a yellowish or brownish tint, which can tint vision without affecting the sharpness of the image. This tint may make it difficult to see blues and purples. The term "age-related" can be misleading, as cataracts can form as early as age 40 or 50 but usually do not affect vision till after age 60.

Other risk factors include diabetes, smoking, alcohol use, and prolonged exposure to ultraviolet light. Prevention measures include wearing UV-blocking sunglasses and brimmed hats to reduce exposure to sunlight, stop smoking, and eat a diet rich in anti-oxidants from fruits and vegetables. Eye protective vitamin supplements may also help. Everyone at age 60 should have a dilated eye exam at least every 2 years. In addition to cataracts, this exam will check for age-related macular degeneration, glaucoma, and other vision problems.

The symptoms of cataracts include blurred vision, colors appear faded, glare or halos from lights, poor night vision, double vision, and frequent prescription changes for eyeglasses or contact lenses. The early symptoms of cataracts may be improved with sunglasses, better lighting, and new eyeglasses. However, surgery is often the only effective treatment. Cataract surgery involves removing the cloudy lens and replacing it with an artificial lens called an intraocular lens (IOL). A lens is only replaced if clouding affects daily activities such as driving, reading, or watching TV. Sometimes the lens will be removed even if it does not affect vision; for example, if it prevents eye examination or treatment of other vision problems.

Reference: http://www.nei.nih.gov/health/cataract/cataract_facts.asp.

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