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Cataracts

Description

An in-depth report on the causes, diagnosis, treatment, and prevention of cataracts.

Prevention

Although cataracts are not completely preventable, their occurrence can be delayed. Quitting smoking, avoiding overexposure to sunlight, drinking alcohol in moderation, and eating plenty of fresh fruits and vegetables can delay the formation of cataracts. No evidence exists that using eye drops or ointments or performing eye exercises will stem the onset of cataracts.

Avoiding Ultraviolet Radiation

The simplest and most effective way to protect against ultraviolet (UV) radiation is to stay out of the sun. A hat and cover-up should be worn outside, particularly when the sun is most intense (10 AM - 3 PM). A wide-brimmed hat can reduce eye exposure to UVB radiation by 30 - 50%. Because the sun's rays are highly reflective, sitting in the shade or under an umbrella by itself does not guarantee protection.

Note: Avoidance of the sun should not be taken to extremes. Some sunshine is desirable. Moderate sun exposure provides an important source of vitamin D, which is essential for healthy bones. There is a link between lack of sun exposure and depression (known as seasonal affective disorder, or SAD).

Sunglasses. Protective sunglasses do not have to be expensive. Sunglasses are classified into three categories based on UVA and UVB protection:

• Cosmetic purpose sunglasses block at least 70% UVB and up to 60% UVA. People should avoid these glasses if they have any risk for cataracts or eye problems.
• General purpose sunglasses block at least 95% UVB and a minimum of 60% UVA. At the very least, people should purchase general purpose sunglasses that are labeled "Meets ANSI Z80.3 General Purpose UV Requirements." Labels should indicate that sunglasses block UV radiation up to 400 nm.
• Special purpose sunglasses block at least 99% UVB and a minimum of 60% UVA rays. These are the optimal sunglasses for people at risk for cataracts. Ideally they should have the Skin Cancer Foundation's Seal of Recommendation for Sunglasses. Special purpose glasses should wrap around the head and block light coming from above, below, and both sides of the glasses. They should also fit snugly on the nose.
• Lenses that are simply dark but not coated with UV-absorbing material may actually increase the risk of cataracts because the pupil widens to compensate for the shaded glass. This may allow more harmful ultraviolet waves to enter. Polarized glasses cut glare but have no effect on UV radiation. Mirror finishes without additional processing for UV blockage are also not fully protective. There is some controversy over whether blue light is harmful to the eyes. Some people prefer amber lenses, which block out the blue spectrum.

Vitamins and Food

Antioxidant vitamins C and E. Because of the role oxidants may play in cataract formation, researchers are investigating the benefits of antioxidant vitamins and other food chemicals. Vitamins C, E, and riboflavin (a B vitamin), for example, are helpful in preserving glutathione levels, an enzyme that helps protect against oxidation in the eye. Low levels of vitamin C in the lens of the eye have been particularly strong predictors of cataracts. There is also some evidence that ultraviolet B radiation interacts with deficiencies in certain antioxidants, such as vitamin E and zinc, to increase damage in the corneas and lenses of the eye.

Evidence on the benefits of supplements of vitamin E or C, or vitamin-rich foods, is conflicting. For example, in two identically constructed trials in the US and Britain, the American group derived apparent benefits from vitamins E, C, and beta carotene while the British group reported very little cataract protection. A 2005 study suggested that long-term use of vitamin E supplements may slow cataract development. However, in a major on-going American study called the Age-Related Eye Disease Study (AREDS), researchers reported no difference in the incidence of cataracts after 7 years in people who took the antioxidant vitamins compared to those who took sham vitamins.

High doses of vitamins may have harmful effects. It is always wise, in any case, to pursue a healthy diet that is low in fats, high in complex carbohydrates, and rich in fruits and vegetables.

B vitamins. Some studies report some protection from a number of B vitamins, including vitamins B1 (thiamin) B2 (riboflavin), B3 (niacin) and B12 (folate). Riboflavin, for example, plays a critical role in the production of glutathione, an enzyme that helps protect against oxidation in the eye. All forms of vitamin B are widely available in dairy products, fortified grains, and meat.

Carotenoids. Carotenoids are a group of more than 700 fat soluble nutrients that produce the colors in foods such as carrots, pumpkins, sweet potatoes, tomatoes, and other deep green, yellow, orange, and red fruits and vegetables. Many are proving to be very important for health. Different carotenoids may be more beneficial then others. They include:

• Xanthophylls are compounds that form a particular category of carotenoids. The xanthophylls lutein and zeaxanthin are found in the lenses of the eye and may be of significant importance for people at risk for cataracts. Some evidence indicates supplements of xanthophyll-rich foods may help retard the aging process in the eye and protect against cataracts. In fact, some experts suggest that the higher risk of cataracts in women compared to men may be partly due to a lesser ability to transport these carotenoids from the blood into the eye. Xanthophylls can be obtained from dark green leafy vegetables (such as spinach), broccoli, and eggs.
• Lycopene is an important carotenoid that may also play an important role in eye health as a person ages. Tomatoes are the importance sources of lycopene.
• Beta carotene is the most widely studied carotenoid and is a powerful antioxidant. It has been specifically studied for cataract protection. Most studies, however, have found little or no benefits. A 2003 study did suggest that beta carotene may protect against cataracts in smokers, although it is important to note that other studies report a higher risk for lung cancer in smokers who take beta carotene.

Phytochemicals. Phytochemicals are substances in plants that have beneficial effects. Dark colored (green, red, purple, and yellow) fruits and vegetables usually have high levels of important plant chemicals and have been associated with a lower risk for cataracts. Tea contains certain plant chemicals called polyphenols that have been associated with protection against cataracts.

• Review Date: 3/1/2007
• Reviewed By: Harvey Simon, MD, Associate Professor of Medicine, Harvard Medical School; Physician, Massachusetts General Hospital

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