Ultraviolet Radiation
The sun is a welcome sight for most people. It makes us feel good.
But too much is dangerous. It can cause painful blistering sunburns
and long term problems like skin cancer and cataracts.
Ultraviolet (UV) radiation is invisible. It is the high-energy rays
from the sun beyond the violet/blue end of the visible spectrum. Ultraviolet
radiation is divided into two major bands, UV-A and UV-B. UV-A is longer
wavelength radiation, close to blue in the visible light spectrum. It
tans the skin and has been implicated in skin aging. UV-B is more active,
shorter wavelength radiation that causes blistering sunburn and is associated
with skin cancer. Most UV radiation is absorbed by the anterior structures
of the eye, although some of it does reach the light-sensitive retina.
UV absorption by the eye may be a causative factor in a number of serious
eye diseases. Protection is simple, safe, and inexpensive.
Sunlight-related eye diseases
Cataracts are a cloudiness of the lens
inside the eye, which occurs over a period of many years. UV radiation
can be a factor in cataract development.
Macular degeneration is a serious age-related
eye disease and a major cause of legal blindness among Americans over
age 50. Exposure to UV and intense violet/blue visible radiation may
contribute to aging processes in the retina.
Pterygia are growths on the white of the eye that extend onto
the cornea. It is seen most commonly in people who work outdoors in
the sun and wind and is related to the amount of UV exposure. It can
be removed surgically, but often recurs. They can cause cosmetic concerns
and visual loss if untreated.
Skin Cancer can be caused by excessive UV exposure.
What situations increase UV exposure?
Individuals whose work or recreation involves lengthy exposure to sunlight are
at greatest risk.
UV is reflected off surfaces just like visible light, so skiing, boating
and beach-going will increase UV exposure. UV intensity is greatest
during the midday hours and during summer months. Ultraviolet
radiation levels increase nearer the equator, so residents in the
southern U.S. are at greater risk. UV levels are also greater at high altitudes.
Are children at risk?
Yes. They typically spend more time outdoors in the sunlight than
adults do. Solar radiation damage to the eye may be cumulative and
may increase the risk of developing an ocular disorder later in life.
Protect the eyes of children against UV radiation by wearing a brimmed
hat or cap and sunglasses. Sunglasses for children should have lenses
made of plastic rather than glass for added impact protection.
Are sunglasses enough?
A brimmed hat
blocks roughly 50% of the UV radiation and reduces UV radiation that
may enter above or around the sunglasses. Ultraviolet-absorbing
eyewear provides the greatest measure of UV protection, particularly
if it has a wraparound design to limit the entry of peripheral rays.
UV absorption can be incorporated into nearly all optical materials currently in
use and does not interfere with vision. Lenses do not have to be dark
to provide UV protection. Polarized lenses and lenses that change
tint with light level are additional sunglass features that are
useful, but do not, by themselves, provide UV protection.
For outdoor use in the bright sun, sunglasses that absorb 99-100% of the full UV
spectrum to 400 nm are recommended.
Currently there is 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% of both UV-B
and UV-A. Consumers are advised to be wary of claims that sunglasses
"block harmful UV" without saying how much.
Opticians at Harvard Vanguard Medical Associates Optical
Shops can test your lenses for the amount of UV protection.
