SUNGLASSES

WHY DO WE NEED SUNGLASSES?

Sunglasses enhance the normal light filtering capabilities of our eyes and are helpful in protecting against the sun's damaging rays. A good pair of sunglasses can reduce glare, filter out the majority of ultraviolet (UV) light, provide visual protection as well as comfort and minimize color distortion.

THE SUN'S RAYS

The sun transmits visible blue and visible violet rays, as well as UV rays which are undetected by the naked eye. All of these rays can be harmful to your eyes. The UV rays, however, pose the most potential damage.

Bright sunlight can damage the cornea (the outer transparent part of the eye that transmits light to the retina), the lens (the part of the eye responsible for focusing), and the retina (the innermost layer of the eye that transmits an image to the brain.)

ALL ABOUT UV LIGHT

An important consideration when purchasing sunglasses is the light transmission factor - the amount of visible light that reaches the eye through the sunglass lens.

It is recommended that sunglass lenses should not transmit more than 30 percent of visible light. This, however can vary with the situation. In areas where light is intense, such as at the beach (especially white sand) or on snow, as little as 10 to 15 percent transmission is preferred.

Sometimes, people are more sensitive to UV rays including those who have had cataract surgery or who take certain medications. Good sunglasses that block out most or all UV light and ones that wrap around the face are important to help minimize the light entering the eyes.

Manufacturers frequently attach a tag to sunglasses stating the transmission factor or that the product conforms to the American National Standard (ANSI) Requirements for Non-Prescription Sunglasses and Fashion Eyewear, Z80.3. The standard specifies different "type of use" levels for sunglass transmittance, and the tag declares which level the particular pair of glasses meets.

TYPES OF LENSES

Clip-On Lenses

Clip-on lenses are used over glasses with prescription lenses, instead of using sunglasses with prescriptions. They are convenient, but may not fully cover the lens, and coupled with the lens surfaces of the regular glasses, can produce annoying reflections. In addition, they may scratch prescription lenses or fall off.

Gradient

Sunglasses can be of gradient density (dark on the top, tapering to light at the bottom, lighter in the center). The latter are useful for skiing or boating, where sunlight can come from overhead or be reflected into the eyes from below.

Mirrored

Lenses can also be coated with a thin metallic film, which looks like a mirror and reflects light rays, thereby further reducing the amount of harmful rays that can reach the eye.

Photochromatic

This type of lens changes according to the amount of light; they automatically darken in bright light and lighten in low light situations. These lenses are helpful under a wide variety of light conditions. The amount of light, lens thickness and temperature all affect how dark the lenses will get. One difficulty with photochromatic lenses is that they may not change rapidly enough to adjust to new light situations. Photochromatic lenses come in several baseline shades of darkness.

Polarizing

These lenses, which reduce glare and "bounce-up" reflections from flat surfaces, are useful for driving, boating, fishing, and other activities involving high intensity light.

Color Of Lenses

Neutral gray or "smoke" lenses provide the best color perception. Other good choices are green or brown tints. Dark lenses may be preferred by those whose eyes are especially sensitive to light. Tints such as red, orange, blue or purple are less suitable because they may interfere with color perception and tend to let in too much light compared to other color lenses.

Blue Blockers

These lenses which have a cosmetically less acceptable bright yellow tint are also known as "sharp shooter" glasses. By blocking out the blue light they interfere with true color perception but they may help you see a little better under certain lighting conditions. A popular type of blue blockers is made by Corning Glass and is called CPF 511.

Quality Of Lenses And Safety

Lenses should be inspected for such flaws as scratches, bubbles and distortions. The Federal Food and Drug Administration requires that all lenses are impact-resistant and be made of optical quality glass or plastic, both of which can be purchased with or without a corrective prescription. This does not mean the lenses are shatterproof or unbreakable, but that they can withstand moderate impact.

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