Ultraviolet (UV) Radiation and Your Eyes

The UV Index developed by the U.S. Environmental Protection Agency (EPA) and the National Weather Service (NWS) has made many Americans more aware of the risks of sunburn and skin cancer from the sun’s ultraviolet (UV) radiation.

But did you know UV and other radiation from the sun also can harm your eyes?

Extended exposure to the sun’s UV rays has been linked to eye damage, including cataracts, macular degeneration, pingueculae, pterygia and photokeratitis that can cause temporary vision loss.

And new research suggests the sun’s high-energy visible (HEV) radiation (also called “blue light”) may increase your long-term risk of macular degeneration. People with low blood plasma levels of vitamin C and other antioxidants especially appear at risk of retinal damage from HEV radiation.

Dangers of Ultraviolet Radiation to Your Eyes

To protect your eyes from harmful solar radiation, sunglasses should block 100 percent of UV rays and also absorb most HEV rays. Frames with a close-fitting wraparound style provide the best protection because they limit how much stray sunlight reaches your eyes from above and beyond the periphery of your sunglass lenses.

While many people refer to ultraviolet radiation as UV light, the term technically is incorrect because you cannot see UV rays.

The three categories of invisible high-energy UV rays are:

UVC rays. These are the highest-energy UV rays and potentially could be the most harmful to your eyes and skin. Fortunately, the atmosphere’s ozone layer blocks virtually all UVC rays.

But this also means depletion of the ozone layer potentially could allow high-energy UVC rays to reach the earth’s surface and cause serious UV-related health problems. UVC rays have wavelengths of 100 -280 nanometer (nm).

UVB rays. These have slightly longer wavelengths (280-315 nm) and lower energy than UVC rays. These rays are filtered partially by the ozone layer, but some still reach the earth’s surface.

In low doses, UVB radiation stimulates the production of melanin (a skin pigment), causing the skin to darken, creating a suntan.

But in higher doses, UVB rays cause sunburn that increases the risk of skin cancer. UVB rays also cause skin discolorations, wrinkles and other signs of premature aging of the skin.

UVA rays. These are closer to visible light rays and have lower energy than UVB and UVC rays. But UVA rays can pass through the cornea and reach the lens and retina inside the eye.

Overexposure to UVA radiation has been linked to the development of certain types of cataracts, and research suggests UVA rays may play a role in development of macular degeneration.

Various eye problems have been associated with overexposure to UV radiation.

As an example, UVB rays are thought to help cause pingueculae and pterygia. These growths on the eye’s surface can become unsightly and cause corneal problems as well as distorted vision.

In high short-term doses, UVB rays also can cause photokeratitis, a painful inflammation of the cornea. “Snow Blindness” is the common term for severe photokeratitis, which causes temporary vision loss usually lasting 24-48 hours.

The risk for snow blindness is greatest at high altitudes, but it can occur anywhere there is snow if you don’t protect your eyes with UV-blocking sunglasses.

Because the cornea appears to absorb 100 percent of UVB rays, this type of UV radiation is unlikely to cause cataracts and macular degeneration, which instead are linked to UVA exposure.

HEV Radiation Risks

As the name suggests, high-energy visible (HEV) radiation, or blue light, is visible. Although HEV rays have longer wavelengths (400-500 nm) and lower energy than UV rays, they penetrate deeply into the eye and can cause retinal damage.

According to a European study published in the October 2008 issue of Archives of Ophthalmology, HEV radiation — especially when combined with low blood plasma levels of vitamin C and other antioxidants — is associated with the development of macular degeneration.

Outdoor Risk Factors

Anyone who spends time outdoors is at risk for eye problems from UV radiation. Risks of eye damage from UV and HEV exposure change from day to day and depend on a number of factors, including:

• Geographic location. UV levels are greater in tropical areas near the earth’s equator. The farther you are from the equator, the smaller your risk.
• Altitude. UV levels are greater at higher altitudes.
• Time of day. UV and HEV levels are greater when the sun is high in the sky, typically from 10 a.m. to 2 p.m.
• Setting. UV and HEV levels are greater in wide open spaces, especially when highly reflective surfaces are present, like snow and sand. 
In fact, UV exposure can nearly double when UV rays are reflected from the snow. UV exposure is less likely in urban settings, where tall buildings shade the streets.
• Medications. Certain medications, such as tetracycline, sulfa drugs, birth control pills, diuretics and tranquilizers, can increase your body’s sensitivity to UV and HEV radiation.

Surprisingly, cloud cover doesn’t affect UV levels significantly. Your risk of UV exposure can be quite high even on hazy or overcast days. This is because UV is invisible radiation, not visible light, and can penetrate clouds.

Measuring Ultraviolet Rays

In the United States, the risk for UV exposure is measured using the UV Index.

Developed by the NWS and EPA, the UV Index predicts each day’s ultraviolet radiation levels on a simple 1 to 11+ scale.

In addition to publishing the UV Index daily, the EPA also issues a UV Alert when the level of solar UV radiation that day is expected to be unusually high.

Sunglasses That Protect Your Eyes From UV and HEV Rays

To best protect your eyes from the sun’s harmful UV and HEV rays, always wear good quality sunglasses when you are outdoors.

Look for sunglasses that block 100 percent of UV rays and that also absorb most HEV rays. We can help you choose the best sunglass lenses for your needs.

To protect as much of the delicate skin around your eyes as possible, try at least one pair of sunglasses with large lenses or a close-fitting wraparound style.

UV PROTECTION RECOMMENDATIONS

If you’re wondering how high today’s UV light levels are where you live, here’s a handy UV index map for the United States.