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THROUGH A LENS, DARKLY

Bright sunshine is one of the best things about summer, but as far as your health is concerned, it's also one of the most dangerous. Excessive exposure to sunlight not only damages your skin, it can injure your eyes as well.

The ultraviolet (UV) rays of the sun are responsible for wreaking havoc with your eyes, especially UV-A and UV-B rays. Long-term exposure to both types of radiation can dramatically increase your risk for developing eye disease, and ultimately, loss of vision.

One of the most serious consequences of excessive sun exposure is the development of cataracts, a clouding of the eyes' natural lenses. In a study of more than 800 Chesapeake Bay fishermen, researchers found that the men who neglected to shade their eyes over the years had three times the number of cataracts as their counterparts who routinely wore sunglasses or hats.

Ultraviolet radiation also contributes to age-related macular degeneration, a condition responsible for most cases of blindness in American adults over the age of 55. Although the exact cause of the disease is unknown, UV rays are thought to play a role by damaging the retina, leading to blurred vision and "holes" in the visual field.

You're at higher-than-average risk for eye damage from UV radiation if you spend a lot of time in the great outdoors, live in the mountains or a sunny locale, or take certain medications. Drugs used to treat gout, high blood pressure and psoriasis, and the antibiotic tetracycline can increase not only your skin's sensitivity to the sun, but also your eyes' sensitivity. Folks with light-colored eyes are more vulnerable to the damaging effects of UV rays, and need to be especially diligent about protecting their peepers.

When it comes to keeping your eyes safe from sun-related injury, investing in a good pair of sunglasses is your best bet. With hundreds of styles and brands to choose from, selecting the right shades can be a challenge.

The pair that you end up wearing should block out 99 to 100 percent of UV-A and UV-B radiation. These sunglasses bear UV light protection statements on their labels, including "100 percent UV-A and UV-B filtering," or "UV absorption to 400 nanometers."

Wearing sunglasses that don't adequately filter out UV light may actually result in more eye damage than wearing no sunglasses at all. Dark lenses can cause the pupils to dilate, allowing more UV rays to enter and injure the eyes.

You can spend a fortune on shades, but that doesn't guarantee that they'll protect your eyes adequately. Ultraviolet protection is instilled in sunglasses when certain chemicals are added to the lens mixture or when they're applied directly to the lens surface.

Dark-colored lenses are better at screening out visible light, and the sunglasses that you choose should be dark enough to block 75 to 90 percent of visible light. Lenses that are gray, green or brown in color are generally considered best.

Shades with mirror finishes have a thin metallic coating on their lenses, and they can help minimize the amount of light entering your eyes. They also make you look super cool, but don't assume that they offer full UV protection unless the labels say they do.

Polarized lenses are a plus: They reduce the glare from reflective surfaces like water, concrete and sand. They're usually a little more expensive than other types of sunglasses, but they're well worth the price if you spend a lot of time working or playing in high-glare conditions.

Blue-blocking shades do just what their name implies -- they shield your eyes from blue light, which is thought to contribute to cataracts and macular degeneration. These amber-colored specs are designed to make distant objects appear more distinct, and they're especially popular with hunters, fishermen, pilots and other folks who strive for Superman vision.

This year, fashion dictates that you wear sunglasses with small frames and dime-sized lenses. If you opt for the trendy John Lennon look, you'll be missing out on the greater protection offered by larger frames and lenses.

Wrap-around frames, like the kind you get from your eye doctor, are generally better for shielding your eyes. Wearing them might land you a citation from the fashion police, but they'll help save your sight by screening out UV rays that sneak in around the tops and sides of smaller glasses.

Buying a good pair of sunglasses is the first step toward protecting your eyes from the summer sun. Now all you have to do is remember to wear them.

Dr. Rallie McAllister is a family physician in Kingsport, Tenn. Her column appears every other week on this page. Her Web site is www.rallieonhealth.com.

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