Sunglasses (eyeglasses with tinted lenses) have three purposes: increasing comfort,
improving visibility and protecting the eyes.
reduce glare and brightness, whether from the sun directly or from water,
snow, sand or reflective surfaces. Bright flashes off water or shiny
surfaces can subject the eye to 10 times more light than needed to see.
Glare can be painful and dangerously distracting while driving or playing
To be sure
that sunglasses will block glare, select lenses that are dark enough
to hide your eyes. For comfortable vision on sunny days, sunglasses
should block 75 to 90 percent of visible light. If dark enough, sunglasses
will eliminate eye strain and squinting when in bright light.
improve vision by enhancing contrast in hazy or overcast conditions.
protect the eyes by blocking harmful light. Although the eye depends
on light to see, wavelengths below the color blue (ultraviolet light
or UV) on the color spectrum can harm the unprotected eye. These rays
are invisible to the human eye. UV light is potentially harmful to the
eye and is strongly linked to cataracts and macular degeneration. It
can "sunburn" the eyes, causing temporary blindness (photokeratitis).
The cornea, lens and retina are all vulnerable.
two types of ultraviolet light. UVA are the light rays that "age"
eye tissues and skin. They contribute to wrinkling and cataracts. They
are closer to visible light than UVB. UVB rays are the "burning"
rays that cause skin cancer, degenerate the macula, burn the cornea,
and cause photokeratitis.
Glasses can be treated to filter out both types of UV rays. Sunglasses that
are not treated for UV light may actually be detrimental to the eyes. Dark lenses
reduce light entering the eye, causing the pupil to dilate and exposing the
inside of the eye to more UV radiation than without the sunglasses.
is constant throughout the year, while UVB light increases intensity
in the summer. UV light passes through glass, water, clouds and some
clothing. Up to 85 percent of UV light shining on sand and snow is reflected
back off these surfaces. UVB light is greater at high altitudes.
Ozone depletion in the upper atmosphere has increased the amount of UV radiation
that reaches earth. For every 1 percent of ozone depletion, UVB rays reaching
the earth increase by 2 percent.
effects of exposure accumulate over time, throughout our entire lives.
For this reason, parents should start protect their children's eyes
very early in life with UV-blocking sunglasses. Anyone who spends a
lot of time outdoors should be extra cautious about UV radiation.
when evaluating sunglasses. Inexpensive sunglasses from discount or
department stores may not provide the protection or quality you really
need. Whether purchasing sunglasses from an optical store or not, look
for specific characteristics that provide proper fit and function.
High quality, well fitting sunglasses provide comfort, sharp vision and the
best protection possible. Sunglasses should fit according to the same guidelines
as regular eyeglasses.
Wraparound or side-screen models block UV light and glare that would otherwise
reach the eyes from over, under and around the sides of the frames.
styles may cause vision distortion. To test the quality of the lenses,
put on the sunglasses and look at a vertical edge or line (a door frame,
floor tiles, etc.). Move your head back and forth, sweeping your eyes
across the width of the lenses. If you notice any wiggle in the line,
the lenses may be defective and could distort your vision. Your eye doctor can also test the optical quality of your sunglass lenses.
best protection, choose sunglasses that block UVA and UVB rays between
290 and 400 nanometers. You can select from shades and tints that meet
your personal needs, and special treatments like polarization and photochromic
lenses. The shade and color of sunglass lenses has no effect on their
ability to block UV light - UV coating is a separate treatment.
medium shades are good for daily wear. For extra bright conditions and
outdoor sports, darker shades will be more comfortable. It is wise to
have multiple pair to choose from for different occasions.
tinting refers to lenses that are darker at the top and lighter at the
bottom. It protects the eyes from glare when looking up but allows clear
vision when looking down. Double-gradient tinting is also available,
in which the upper and lower parts of the lens are dark and the center
is light. These are comfortable in situations where light is reflected
up from snow or water.
tints filter different wavelengths of light. Some may enhance or distort
colors and affect contrast. Select your tint based on your lifestyle
and personal needs.
- Gray - Allows true color perception, but does not enhance contrast.
Good for golf, cycling, or running.
- Green - Allows true color perception and good contrast in bright
light. Reduces eye strain in bright light.
- Good in hazy sun, enhances contrast. Good for high-glare sports
such as skiing, fishing or sailing.
- Brightens cloudy, hazy, or foggy skies. Excellent for contrast.
Minimizes eye strain. Good for hunters, pilots and snow skiers. Distorts
color (images look yellow orange).
- Improves contrast and depth perception in low light. Good for
snow skiing and trap shooting, especially on overcast days.
- Excellent depth perception in low light. Contrasts objects against
blue or green backgrounds. Good for skiing and hunting.
- Reflect high-intensity light to reduce glare. Available in a
variety of colors.
lenses are the ultimate sun lenses, blocking glare by absorbing light from scattered angles. Polarized
filters are added to the lenses during the manufacturing process. Golfers,
fishermen and outdoors enthusiasts prefer these lenses. They are also
recommended for driving. Polarization is a separate feature from shade
or tint; various colors filter out different light. Polarized filters
also do not block UV light, although the lenses may be treated
for this too.
lenses are sensitive to light. They automatically darken within 30 seconds
of exposure to bright light. Once out of the sun, they lighten in about
five minutes. They provide freedom from switching between prescription
glasses and sunglasses, or from removing and replacing non-prescription
sunglasses when going in and out of the sun.
issues, the impact of ultraviolet light on eye health is a worldwide
concern. Several countries have set voluntary standards for sunglass
manufacturers in order to protect their citizens'eyes. In Australia,
these standards are mandatory.
and labeling regulations cover characteristics such as refractive properties
like distortion and blur, impact resistance, UV protection, color transmission
and appropriateness for driving. Check labels when purchasing sunglasses
and contact regulatory organizations for more information.
widely recognized regulatory agencies are:
National Standards Institute
must be impact resistant, but they are not shatterproof. They are not
tough enough to protect the eyes for high-impact sports or industrial
safety purposes. Sunglasses cannot provide protection against intense
light sources such as sunlamps, lasers, welding torches or solar eclipses.
F.M. "Does the ANSI Z80.3 Nonprescription Sunglass and Fashion
Eyewear Go Far Enough?" Optometry and Vision Science, 1990,
vol. 6, no. 6, pp. 431-4.
J.K., Cranton, D., Chou B.R. "Tinted Lenses and the ANSI Standards
for Traffic Signal Transmittances," Optometry and Vision Science,
1991, vol. 68, no. 9, pp. 750-5.