Ultra-Violet (UV) Radiation and Sunlight
What You Should Know and How to Protect Yourself


The Bottom Line

Without proper ultra-violet (UV) protection, you increase your risk of skin cancer, cataracts, and macular degeneration.

Background

Sunlight is composed of 3 types of UV radiation:  UV-A and UV-B (which are both dangerous), and UV-C (which is absorbed by the ozone layer).  UV-B can cause sunburn and lead to cancer.  The cornea (front surface of the eye) and the lens inside the eye absorb more than 99% of this form of radiation to protect (as much as possible) the retina in the back of the eye.  UV-A radiation penetrates deeper into the eye and can cause damage to the retina.

Other Facts

*UV radiation can attack from any angle... from the air, reflected off water, snow, and sand... boaters and skiers beware.
*UV rays are strongest during the mid-day hours between 10 a.m. to 3 p.m.
*Residents living closer to the equator are more likely to be exposed to UV.
*UV radiation increases 4% for every 1000 feet above sea level.
*On cloudy days, up to 80% of UV light can still reach the eye.
*Some medications can make you more susceptible to UV damage.  Among those drugs: the acne medications tetracycline hydrocholoride (Achromycin) and minocycline hydrochloride (Minocin), the allergy medication Claritin, and even the pain killer ibuprofen.
*Genetic factors, such as fair skin, light hair, and light eyes can cause greater absorption of UV.

Damage to the Eyes

Photokeratitis - Occurs after overexposure to UV radiation over a short period of time.  The front surface of the cornea absorbs UV-B radiation and the cells melt together.  This "sunburn of the eye" can cause foreign body sensation, light sensitivity and excessive tearing.  Effects are usually temporary with no long-term effects.

Cataracts - Occur after cumulative long-term exposure (over a lifetime) to UV radiation.  Cataracts occur in the lens, which is located just behind the pupil.  The lens helps focus light onto the retina to give you a clear image.  The center of the lens absorbs UV-B radiation, which causes an opacity or cloudiness.  Thus, when a cataract forms,  you see a blurry image that cannot be improved with glasses.  Though cataracts can be surgically removed and replaced with a prosthetic lens, why not prevent them if you can?

Age-Related Macular Degeneration (AMD) - Some clinicians have projected that extended exposure to UV radiation can contribute to the aging process of the retina which can lead to AMD.  Laboratory studies show that both UV and deep blue light cause retinal damage.  As well, chronic exposure to short-wavelength visible light (blue light) can cause damage to the macula.

Pterygium - This is an overgrowth of blood vessels and fibrous tissue that starts on the white of the eye (as a pinguecula) and grows onto the cornea, possibly causing vision loss.  It is prevalent in people who work outdoors in the sun and wind.  Pterygia can be surgically removed, but recurrence can occur.

Skin Cancer - Most people know about this risk and apply sun block accordingly.  But not many think about the risk to eyelids and the skin around the eyes that could be covered by sunglasses.

Protection

A chemical UV protective coating on the lens surface of sunglasses should block 99-100% of both UV-A and UV-B radiation.  The American Optometric Association offers a Seal of Acceptance to sunglasses that meet these standards.  You should be aware that some sunglasses may have a label that declare an amount of UV protection, but these labels may be misleading or lack any guarantee. 

The sunglasses must also filter out 75-90% of visible light.  Though color is not a factor in protection, gray lenses decrease glare and squinting (and wrinkles), and they do not affect the way colors appear.  As well, darker-tinted sunglasses don't block out more UV rays than lighter-tinted lenses.

Do blue-blocking sunglasses provide more protection?  Scientists disagree on whether blue light even causes any damage to the eyes.  But, this isn't a big concern during the summer months (or those locations where the sun shines most of the time), since the highest exposure to blue light comes from snow reflection.

One misconception about sunglasses is that they actually cause more damage to the eyes because they cause the pupil to dilate, thus letting more damaging light into the eyes.  At least one study has shown that this is not true.

Wraparound designs are the most effective style of sunglasses.  They prevent peripheral rays of light from entering your eyes.  Wide-brimmed hats also help, reducing UV exposure by about half.  If you are one who spends a lot of time on or around the water, mirror and polarizing lenses will reduce glare and basically make you more comfortable.

Children need protection as well, and are actually more susceptible to UV damage, because the tissues in their eyes are more translucent.  Eye experts recommend keeping children out of the sun between 10 a.m. and 4 p.m., when UV rays are most dangerous.  Cumulatively, by age 18, a person can acquire 50% of the total lifetime dosage of UV radiation, so they recommend wearing sunglasses year-round.

(Review of Optometry, July 15, 2000)


Links

Prevent Blindness America - www.preventblindness.org
The Environmental Protection Agency - www.epa.gov/ozone
The American Optometric Association -
www.aoanet.org