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Ultraviolet Rays and Your
Eyes:
Fashion aside, sunglasses
serve an important purpose:
protecting eyes from the
harmful rays produced by the
sun. You're probably well
aware of the need to protect
your skin from the sun, but
it's equally important to
protect your eyes.
Ultraviolet Light's Dangers
Ultraviolet (UV) radiation
consists of invisible rays
from the sun. The three
bands of UV light are: UVA,
UVB and UVC. UVC rays are of
little concern as they are
absorbed by the upper
atmosphere and do not reach
the earth's surface.
UVB rays are the ones that
burn the skin and can damage
the eyes. Combined with cold
wind and snow, UVB has the
potential to cause snow
blindness (photokeratitis),
a temporary (lasting 12 to
48 hours) but painful
problem in the cornea of the
eye.
Although not all scientists
agree, there is some
research that suggests that
daily exposure to UVB in
very bright sunlight over a
period of many years may
cause cataracts, a gradual
clouding of the lens of the
eye.
Experts also suspect that
the primary cause of eye
growths such as pingueculae
or pterygia is exposure to
UVB rays. UVA rays are
primarily absorbed within
the lens of the human eye,
though there are no
documented disorders of the
human eye from UVA. This,
however, remains a much
debated and researched
topic, says the Sunglass
Association of America
(SAA).
Measuring Ultraviolet Rays
A globally used index
measures the amount of solar
ultraviolet rays that are
reaching the surface of the
earth. Scientists use a
scale of 1 to 11 to indicate
how much threat exists at a
particular time and place
from sun exposure, and to
permit the news media to
warn people when UV levels
are high. Usually such
warnings include advice to
wear hats and other
protective clothing,
sunglasses, and sunscreen.
Avoiding the sun around
midday is also important.
Sunglass standards for
lenses place limits solely
on UVB and UVA rays, butbear
in mind that both the
standards and labeling are
voluntary, not mandatory.
According to these
standards, sunglasses must
block at least 70 percent of
UVB and at least 60 percent
of UVA.
To best protect your eyes,
look for sunglasses that
provide at least 98 percent
protection from both UVA and
UVB rays. UVC rays are
blocked automatically since
they are absorbed in the
atmosphere and do not reach
the earth. Some of the
higher-priced products with
polycarbonate, glass or
plastic (CR-39) lenses can
claim to block 100 percent
of the UV rays.
One question people ask
frequently is whether pupil
dilation from wearing
sunglasses can cause
problems for the eyes.
The answer to this is that
there is a very minimal
dilation of the eyes when
wearing sun protection and
that the protection received
from wearing sunglasses is
greater even than simply
standing in the shade.
According to the SAA,
sunglasses "reduce the UV
more than if you were to
stand in the shade, since
the shade more or less
evenly attenuates all
wavelengths, visible and UV,
while sunglasses
preferentially attenuate
shorter wavelengths (i.e.,
UV wavelengths)." Thus,
sunglasses provide more
protection than shade alone.
Another question people ask
is whether it's necessary to
wear sunglasses in the
winter. While the sun's rays
feel less intense during
wintertime, they are still
strong enough to worry about
eye damage, including the
snow blindness mentioned
above. New snow can reflect
up to 80 percent of
ultraviolet rays, according
to the World Health
Organization, while normal
ground surfaces and bodies
of water tend to reflect
less than 10 percent
Finally, what if you're
wearing contact lenses that
have UV protection? This is
a good idea, because such
lenses can decrease the
amount of UV rays that enter
the cornea and affect the
eye structures beneath. But
you still need to wear
sunglasses over the contact
lenses, because UV rays will
affect the eye tissue that
is not covered by the
contacts. Your eyes will be
more comfortable, too, with
the light and glare
reduction that sunglasses
provide.
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