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?
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.
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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.
Ultraviolet (UV) rays are higher in energy and do not fall within the realm of visible light, as shown here. In the electromagnetic spectrum, radio waves have the lowest energy, and gamma rays have the highest energy.
- 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.
|UV Index||Risk Level||Recommendations|
|2 or less||Low||1. Wear sunglasses.
2. If you burn easily, use sunscreen with an SPF* of 15+.
|3 - 5||Moderate||1. Wear sunglasses.
2. Cover up and use sunscreen.
3. Stay in the shade near midday, when the sun is strongest.
|6 - 7||High||1. Wear a hat and sunglasses.
2. Cover up and use sunscreen.
3. Reduce time in the sun between 10 a.m. and 4 p.m.
|8 - 10||Very high||1. Wear a hat and sunglasses.
2. Cover up and use sunscreen.
3. Minimize sun exposure between 10 a.m. and 4 p.m.
|11+||Extreme||1. Wear a hat and sunglasses.
2. Apply sunscreen (SPF 15+) liberally every two hours.
3. Try to avoid sun exposure between 10 a.m. and 4 p.m.
|*SPF = sun protection factor |
Information based on U.S. Environmental Protection Agency standards.
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.
Kids Need UV Protection Even More Than Adults
The risk of damage to our eyes and skin from solar UV radiation is cumulative, meaning the danger continues to grow as we spend time in the sun throughout our lifetime.
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With this in mind, it's especially important for kids to protect their eyes from the sun. Children generally spend much more time outdoors than adults.
In fact, some experts say that because children tend to spend significantly more time outdoors than most adults, up to half of a person's lifetime exposure to UV radiation can occur by age 18. (Other research cited by The Skin Cancer Foundation says slightly less than 25 percent of our lifetime exposure to UV radiation is sustained during childhood.)
Also, children are more susceptible to retinal damage from UV rays because the lens inside a child's eye is clearer than an adult lens, enabling more UV to penetrate deep into the eye.
Therefore, make sure your kids' eyes are protected from the sun with good quality sunglasses. Also, encourage your child to wear a hat on sunny days to further reduce UV exposure.
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. Your optician 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.
The amount of UV protection sunglasses provide is unrelated to the color and darkness of the lenses.
For example, a light amber-colored lens can provide the same UV protection as a dark gray lens. Your optician can verify that the lenses you choose provide 100 percent UV protection.
But for HEV protection, color does matter. Most sunglass lenses that block a significant amount of blue light will be bronze, copper or reddish-brown (see lens tint guide).
Again, your optician can help you choose the best "blue-blocking" lenses.
In addition to sunglasses, wearing a wide-brimmed hat on sunny days can reduce your eyes' exposure to UV and HEV rays by up to 50 percent.
More Tips About Sunglasses and UV Exposure
Many misconceptions exist about the right sun protection for your eyes. Keep these tips in mind:
This UV Index devised by the Environmental Protection Agency and National Weather Service provides a color-coded warning system to alert people to the dangers of being outdoors on certain days.
- Not all sunglasses block 100 percent of UV rays. If you're unsure about the level of UV protection your sunglasses provide, take them to your eye doctor or optician for an evaluation. Many eye care professionals have instruments such as spectrophotometers that can measure the amount of visible light and UV radiation your lenses block.
Almost all sunglasses block a portion of HEV rays, but some tints block more blue light than others. Blue-blocking sunglass lenses usually are bronze, copper or reddish-brown in color.
- Remember to wear sunglasses even when you're in the shade. Although shade reduces your UV and HEV exposure to some degree, your eyes still will be exposed to UV rays reflected from buildings, roadways and other surfaces.
- Sunglasses are important especially in winter, because fresh snow can reflect 80 percent of UV rays, nearly doubling your overall exposure to solar UV radiation. If you ski or snowboard, choosing the right ski goggles is essential for adequate UV protection on the slopes.
- Even if your contact lenses block UV rays, you still need sunglasses. UV-blocking contacts shield only the part of your eye under the lens. UV rays still can damage your conjunctiva and other tissues not covered by the lens.
Wearing sunglasses protects these delicate tissues and the skin around your eyes from UV damage.
- If you have dark skin and eyes, you still need to wear sunglasses.
Although your dark skin may give you a lower risk of skin cancer from UV radiation, your risk of eye damage from UV and HEV rays is the same as that of someone with fair skin.
You need not fear the outdoors and sunny days, as long as you are equipped with the right eye and skin protection to reduce your UV exposure.
Proportion of lifetime UV dose received by age 18: what Stern et al actually said in 1986. Journal of Investigative Dermatology. May 2005.
UV doses of young adults. Photochemistry and Photobiology. April 2003.
Risk reduction for nonmelanoma skin cancer with childhood sunscreen use. Archives of Dermatology. May 1986.
About the Author: Gary Heiting, OD, is senior editor of AllAboutVision.com. Dr. Heiting has more than 25 years of experience as an eye care provider, health educator and consultant to the eyewear industry. His special interests include contact lenses, nutrition and preventive vision care. Connect with Dr. Heiting via Google+.
[Page updated June 2014]
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