Choosing the right sunglasses

The easiest way to protect your eyes from the sun's hazardous radiation is to wear sunglasses, not only in the summer months, but year-round. Ultraviolet (UV) light can damage the iris, retina, lens, and cornea, leading to permanent vision loss. It's a good idea to request UV protection (an invisible coating) on all of your prescription glasses.

UV light has three wavelengths:

UVA is long, looks almost blue in the visible spectrum, and is responsible for skin tanning and aging. It may also contribute to skin cancer risk.

UVB is shorter and more energetic, and it's linked to sunburn and skin cancer. A large portion of UVB light is absorbed by the atmosphere's ozone layer.

UVC is short. It is completely absorbed by the ozone layer.

Sunglasses are labeled according to guidelines for UV protection established by the American National Standards Institute (ANSI). There are three categories:

Cosmetic. These lightly tinted lenses are good for daily wear. They block 70% of UVB rays, 20% of UVA, and 60% of visible light.

General purpose. These medium to dark lenses are fine for most outdoor recreation. They block 95% of UVB, 60% of UVA, and 60% to 90% of visible light. Most sunglasses fall into

this category.

Special purpose. These are extremely dark lenses with UV blockers, recommended for places with very bright conditions, such as beaches and ski slopes. They block 99% of UVB, 60% of UVA, and 97% of visible light.

Just because a lens is expensive or appears darker doesn't mean that its ability to block out UV radiation is any greater than that of a cheaper or lighter lens. Look for the ANSI label. Even inexpensive sunglasses can be protective.

There is some evidence that blue light from the sun may contribute to the development of age-related macular degeneration. Lenses with a red, amber, or orange tint may provide better protection against this light. You may find less distortion, however, with gray or green lenses.

If you aren't sure what kind of sunglasses to buy or think you may be at high risk for eye disease, ask an eye care professional for a recommendation.

For more information about keeping your eyes healthy, read The Aging Eye, a Special Health Report from Harvard Medical School.

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