Ultraviolet (UV) radiation is the invisible high energy rays from the sun that are just beyond the violet/ blue end of the visible spectrum. More than 99 percent of UV radiation striking the eye is absorbed by the anterior structures of the eye, although some of it does reach the light-sensitive retina. This radiation is not useful for vision and there are good scientific reasons to be concerned that UV absorption by the eye may contribute to age-related changes in the eye and a number of serious eye diseases. Protection can be achieved by simple, safe and inexpensive methods such as wearing a brimmed hat, but the best protection is achieved by using eyewear that absorbs UV radiation.

What eye diseases are caused by or affected by sunlight?
Ultraviolet radiation can play a contributory role in the development of various ocular disorders including age-related cataract, pterygium, cancer of the skin around the eye, photokeratitis\keratitis and corneal degenerative changes, and may contribute to age-related macular degeneration.

Cataract is a major cause of visual impairment and blindness worldwide. Cataracts are a cloudiness of the lens which occurs over a period of many years. Laboratory studies have implicated UV radiation as a causal factor for cataract. Furthermore, epidemiological studies have shown that certain types of cataract are associated with a history of higher exposure to UV and especially UV-B radiation.

Age-related macular degeneration is the major cause of reduced vision in the United States among people over age 55. Exposure to UV and intense violet/blue visible radiation is damaging to retinal tissue in laboratory experiments, thus scientists have speculated that chronic UV or intense violet/blue light exposure may contribute to aging processes in the retina.

Pterygium is a growth of tissue on the white of the eye that may extend onto the clear cornea where it can block vision. It is seen most commonly in people who work outdoors in the sun and wind, and its prevalence is related to the amount of UV exposure. It can be removed surgically, but often recurs, and can cause cosmetic concerns and visual loss if untreated.

Cancer of the skin, including the eyelids and facial skin, is a well known consequence of excessive UV exposure.

Photokeratitis is essentially a reversible sunburn of the cornea resulting from excessive UV-B exposure. It follows from spending long hours on the beach or snow without eye protection. It can be extremely painful for 1-2 days and can result in temporary loss of vision. There is some indication that long term exposure to UV-B can result in corneal degenerative changes.

Am I at risk?
Everyone is at risk. No one is immune to sunlight-related eye disorders. Every person in every ethnic group in developed and developing nations alike is susceptible to ocular damage from UV radiation that can lead to impaired vision.

What factors increase the risk?
Any factor that increases the eyes sunlight exposure will increase the risk for ocular damage from UV radiation. Individuals whose work or recreation involves lengthy exposure to sunlight are at greatest risk.

Since UV radiation is reflected off surfaces such as snow, water and white sand, the risk is particularly high on the beach, while boating or at the ski slopes. The greatest during the mid-day hours, from 10 a.m. to 3 p.m. and during summer months. Ultraviolet radiation levels increase nearer the equator, so residents in the southern US are at greater risk. UV levels are also greater at high altitudes.

Since the human lens absorbs UV radiation, individuals who have had cataract surgery are at increased risk of retinal injury from sunlight unless a UV absorbing intraocular lens was inserted at the time of surgery. Individuals with retinal dystrophies or other chronic retinal diseases may be at greater risk since their retinas may be less resilient to normal exposure levels.

Are children at risk?
Children are not immune to the risk of ocular damage from UV radiation. They typically spend more time outdoors in the sunlight than adults. Solar radiation damage to the eye may be cumulative and may increase the risk of developing an ocular disorder later in life. It is prudent to protect the eyes of children against UV radiation by insisting they wear a brimmed hat or cap and sunglasses. Sunglasses for children should have lenses made of plastic rather than glass for added impact protection.

How can my eyes be protected from UV radiation?
Ultraviolet radiation reaches the eye not only from the sky above but also by reflection from the ground, especially from water, sand, snow and other bright surfaces. Protection from sun light can be obtained by using both a brimmed hat or cap and UVabsorbing eyewear. A wide-brimmed hat or cap will block roughly 50 percent of the UV radiation and reduces UV radiation that may enter above or around glasses. Ultraviolet absorbing eyewear provides the greatest measure of UV protection, particularly if it has a wraparound design to limit entry of peripheral rays.

Ideally, all types of eyewear, including prescription spectacles, contact lenses and intraocular lens implants, should absorb the entire UV spectrum (UV-B and UV-A). UV absorption can be incorporated into nearly all optical materials currently in use, and does not interfere with vision. Polarization or photosensitive darkening are additional sunglass features that are useful for certain visual situations, but do not, by themselves, provide UV protection.

For outdoor use in the bright sun, sunglasses that absorb 99-100 percent of the full UV spectrum to 400 nm are recommended. Additional protection for the retina can be provided by lenses that reduce the transmission of violet/blue light. Such lenses should not be so colored as to affect recognition of traffic signals. The visible spectrum should be reduced to a comfortable level to eliminate glare and squinting. Individuals who also wear clear prescription eye wear outdoors should consider using lenses which absorb 99-100 percent of the UV radiation to 380-400 nm.

What does the label on a pair of sunglasses tell me?
There is presently no uniform labeling of sunglasses that provides adequate information to the consumer. Labels should be examined carefully to insure that the lenses purchased absorb at least 99-100 percent of both UV-B and UV-A. Advise your clients to be wary of claims that sunglasses "block harmful UV" without saying how much they block.

Information in this article is based on "Ocular Ultraviolet Rdiation Hazards in Sunlight" statement by the National Society to Prevent Blindness Scientific Advisory Commtitee Task Force on Ultraviolet Light.