Ultraviolet Rays and Your Eyes

Fashion aside, sunglasses serve an important purpose: protecting eyes from the harmful rays produced by the sun. You're probably well aware of the need to protect your skin from the sun, but it's equally important to protect your eyes.

Ultraviolet (UV) radiation consists of invisible rays from the sun. The three bands of UV light are: UVA, UVB and UVC. UVC rays are of little concern as they are absorbed by the upper atmosphere and do not reach the earth's surface.

UVB rays are the ones that burn the skin and can damage the eyes. Combined with cold wind and snow, UVB has the potential to cause snow blindness (photokeratitis), a temporary (lasting 12 to 48 hours) but painful problem in the cornea of the eye.

Although not all scientists agree, there is some research that suggests that daily exposure to UVB in very bright sunlight over a period of many years may cause cataracts, a gradual clouding of the lens of the eye.

Experts also suspect that the primary cause of eye growths such as pingueculae or pterygia is exposure to UVB rays. [Read more about pingueculae and pterygia.]

UVA rays are primarily absorbed within the lens of the human eye, though there are no documented disorders of the human eye from UVA. This, however, remains a much debated and researched topic, says the Sunglass Association of America (SAA).

A globally used index measures the amount of solar ultraviolet rays that are reaching the surface of the earth. Scientists use a scale of 1 to 11 to indicate how much threat exists at a particular time and place from sun exposure, and to permit the news media to warn people when UV levels are high. Usually such warnings include advice to wear hats and other protective clothing, sunglasses, and sunscreen. Avoiding the sun around midday is also important.

Sunglass standards for lenses place limits solely on UVB and UVA rays, but bear in mind that both the standards and labeling are voluntary, not mandatory. According to these standards, sunglasses must block at least 70 percent of UVB and at least 60 percent of UVA.

To best protect your eyes, look for sunglasses that provide at least 98 percent protection from both UVA and UVB rays. UVC rays are blocked automatically since they are absorbed in the atmosphere and do not reach the earth. Some of the higher-priced products with polycarbonate, glass or plastic (CR-39) lenses can claim to block 100 percent of the UV rays.

One question people ask frequently is whether pupil dilation from wearing sunglasses can cause problems for the eyes.

The answer to this is that there is a very minimal dilation of the eyes when wearing sun protection and that the protection received from wearing sunglasses is greater even than simply standing in the shade.

According to the SAA, sunglasses "reduce the UV more than if you were to stand in the shade, since the shade more or less evenly attenuates all wavelengths, visible and UV, while sunglasses preferentially attenuate shorter wavelengths (i.e., UV wavelengths)." Thus, sunglasses provide more protection than shade alone.
 

Another question people ask is whether it's necessary to wear sunglasses in the winter. While the sun's rays feel less intense during wintertime, they are still strong enough to worry about eye damage, including the snow blindness mentioned above. New snow can reflect up to 80 percent of ultraviolet rays, according to the World Health Organization, while normal ground surfaces and bodies of water tend to reflect less than 10 percent. (The numbers for beach sand and sea foam are estimated at 15 percent and 25 percent.) [Read more about winter sunglasses and ski goggles.]

Finally, what if you're wearing contact lenses that have UV protection? This is a good idea, because such lenses can decrease the amount of UV rays that enter the cornea and affect the eye structures beneath. But you still need to wear sunglasses over the contact lenses, because UV rays will affect the eye tissue that is not covered by the contacts. Your eyes will be more comfortable, too, with the light and glare reduction that sunglasses provide.