Most people know that the sun's rays are bad for the skin. Far fewer know that it can be harmful to the eyes. To lessen the risk, companies are selling contact lenses with a special ultraviolet-blocking ingredient that they say can keep out as much as 90 percent to 99 percent of ultraviolet rays.

Two types of ultraviolet radiation from the sun reach the eyes — A and B. The most known negative effects are from ultraviolet B radiation, which causes small damage that builds over time, said Gregory Good, assistant dean at Ohio State University College of Optometry. The cumulative damage can contribute to the formation of cataracts and pterigia, raised wedge-shaped growths on the eye that can cause irritation and even obstructed vision.

While the sun feels hottest at midday, the exposure to the eyes is often worst during early morning and late afternoon, according to a published study. The reason is most likely that eyebrows shield the eyes when the sun is high in the sky, scientists say. Wearing a hat can help, but it doesn't block all rays. Sunglasses with UV block also help, but ultraviolet rays still slip in over the rims and through the sides.

UV-blocking contact lenses protect the inner structures of the eye — including the cornea, the iris, the lens and the retina.

"All other things being equal, I would want the best UV protection in a lens," said Jeffrey L. Weaver, executive director of the American Board of Optometry in St. Louis, Mo., which certifies optometrists.

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Contact lenses with UV blocking are completely clear, and there are no downsides — except limited choice, said Stephen M. Cohen, past president of the Arizona Optometric Association.

UV-blocking contact lenses have been around for more than a decade, but have gained in popularity in recent years. Only a limited number meet Food and Drug Administration standards for "Class 1" protection, in which 90 percent of UV-A radiation is blocked and 99 percent of UV-B radiation is blocked. The American Optometric Association (AOA), a doctors' group, offers a "seal of acceptance" for Class I lenses, and so far only six products — all from Johnson & Johnson's Vistakon unit's Acuvue line — have gotten the seal.

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