Choosing Sunglasses

CONSIDERATIONS

Sunglasses aren't just fashion anymore! You used to buy them at the corner drugstore because you liked the way they looked, and they did make things darker. Since they only cost a couple of dollars, and really weren't that important, you proceeded to abuse them. But all of that has changed. Try on a pair of quality sunglasses and you will not believe what a difference they make.

Sunglasses are now designed to fill different vision needs and life-styles. The variety of choices are endless, and misinformation abounds about how to choose suitable glasses for different conditions. Before you choose, consider the following.

Where will you wear them? High altitudes? Around water or snow?
What will the weather be like? Sunny? Overcast? Changing Conditions?
What activities will you be using them for? Cycling? Driving? Skiing? Fishing?

Unless you never venture outdoors in daylight, you need sunglasses to protect your eyes. Even when the sun is not shining brightly, enough UV rays can get to your eyes to cause trouble. So, even on days that are hazy, cloudy or foggy, sunglasses will protect your eyes, and can improve your visual clarity.

LET THERE BE LIGHT

Without light, we don't see, but too much is harmful. In fact, intense light can damage the eye. The light spectrum includes the invisible (ultraviolet or UV), visible (includes blue), and infrared (IR) light rays.

ULTRAVIOLET (UV) is the most dangerous solar radiation. The greatest concern for sunglasses performance is to filter out UV light, since it is absorbed by the eye tissue and the damaging effects are both immediate and cumulative. These rays are 300 times more intense at an altitude of 10,000 feet because of the thin atmosphere, and reflections off sand and water make UV rays 180 times stronger at the beach than in your own backyard. The ozone absorbs a good deal of these harmful rays, so areas where the ozone layer is deteriorating, such as major cities, are particularly dangerous.

There are three types of utraviolet light: A, B, and C.

A is considered less harmful, but is still potentially damaging to the eye, and is important to screen. It causes wrinkles, and squinting without the aid of sunglasses will contribute to the process.
B is considered the most harmful to the eye. It consists of the shortest wavelengths of light reaching the earth. In addition to causing sunburn and cancer, these rays can contribute to the formation of cataracts and cause keratitis, something like a painful sunburn on the front of the eye. Snowblindness is a severe case of keratitis.
C is absorbed by the ozone layer, and presents minimal danger to eyes because the exposure is nil.

BLUE light is closest to UV in the spectrum and the eye has the most difficulty focusing these rays. Its short rays also scatter more than other light, sometimes producing a light haze that partially obscures vision. Totally blocking blue light is unnecessary, and actually undesirable, because you lose color recognition. The extent of harm caused by these rays is still not known.

INFRARED (IR) is simply heat. Nothing more. Normal solar infrared is almost completely and harmlessly absorbed by the atmosphere and the eye. Normal doses don't even harm the retina. Your eyes may feel a bit warm or dried out with over exposure, but IR isn't the main source of eye fatigue, as some people claim.

UV PROTECTION Both clear and tinted lenses can be specially treated to block 100 percent of these eye-damaging rays. Look for sunglasses labeled "absorbs UV up to 400 NM" (completely absorbs UVA and UVB). This is especially important for people who have had cataracts removed since they have lost the eye's natural lens that protects the retina from UV radiation. Sunglasses are governed by the FDA which sets requirements for impact-resistance only. If the label conforms to the policy of the Sunglass Association of America, it will also name one of the following sunglass categories.

COSMETIC OR FASHION glasses can pass as much as 30% UVB and 40% UVA (labeled 60-70% protection). These glasses are bought mainly for the image they invoke for the wearer.

GENERAL-USE glasses must have less than 5% UVB and 8% UVA light transmission (labeled 92-95% protection). These higher quality glasses protect your eyes against harmful rays.

SPECIAL PURPOSE glasses must pass no more than 1% of the UVB (labeled 99-100% protection) and have equal screenings of visible light and UVA.

LIGHT TRANSMISSION This rating on sunglasses indicates the amount of visible light that the lens allows to reach your eye. Look for glasses listing a transmission value of 10 to 25 percent. If you're going to use the glasses in very bright conditions, such as climbing on glaciers, pick a very dark lens with about 3 to 10% visible light transmission. For other activities, a lighter lens may be preferable to allow for variable light conditions. If no value is listed, look in a mirror; if you can see your eyes through the lenses, they are not dark enough, but they shouldn't be so dark that your vision is impaired. Personal preference will also be a factor and some people, such as those with blue eyes, can be more light sensitive than others.

LENS COLOR The lens color you choose can affect what, and how well you see. The shades of amber, rose, gold, or brown reduce scattered blue light, and give the best definition in flat light conditions like skiing or sailing. Neutral gray or green lenses distort colors the least, and provide the truest view. Always determine the color of the lens from the inside, as the outside may have a different coating.

GRAY is the traditional aviator's choice, as dictated by the military specification for pilots, because it offers the least color distortion.

BROWN filters out some of the blue portion of the spectrum but makes greens and reds appear brighter. Tests show that brown is also good for increasing contrast sensitivity while leaving colors true.

GREEN is said to have characteristics similar to that of the natural color sensitivity of the eye. They maintain contrast and supply clarity, reducing visible light but not interfering with color vision.

YELLOW is too light for sunny conditions, but will make things seem brighter and clearer and increase depth perception when it's overcast. They are often used for "shooters glasses" for this increased depth perception.

RED / ROSE provides glare reduction, eliminating blue light haze while brightening and enhancing vision.

GLARE Not only does glare make you squint, it makes your eyes work harder, and your pupils contract. Studies have shown that glare is the real cause of most eye fatigue. Most people expect sunglasses to take care of this, but there are different types of glare. Some lenses do a better job of absorbing them than others.

DIRECT glare happens when overall light levels are high, typically a sunny day. * REFLECTED glare occurs when light bounces off water or snow.

DISCOMFORT glare hurts your eyes to look at it, but you can still see what you're looking at. It affects performance and makes you squint, causing eye strain and headaches. Eye fatigue slows your reaction time, decreases your ability to track objects, and alters depth perception.

VEILING glare is blinding. It also causes headaches and eye strain, but it can be even more dangerous than discomfort glare because it actually blocks your vision.

SPECIAL COATINGS/FILTERS

POLARIZED lenses have a special filter that absorbs and eliminates glare reflected at certain angles, usually off flat surfaces such as water or glass (not metal). This is especially helpful to drivers, water-skiers, or boaters.

MIRRORED lenses provide even better glare protection, reflecting all or part of the unwanted light instead of absorbing it as regular lenses do. They are sometimes recommended for snow and water, but they scratch easily and some produce annoying reflections.

GRADIENT lenses, darker at top than at bottom, are often preferred by drivers and cyclists. They block light from above without dimming your direct view.

DOUBLE GRADIENT lenses are darker on top and bottom than in the center. On water, sand, snow or ice, they can reduce glare from above and below while keeping central vision clear.

PHOTOCHROMIC or Photosensitive lenses react to the amount of UV light to which they are exposed, darkening or lightening depending on the conditions. Temperature affects the rate of change in these lenses and lower temperatures mean increased darkening. They are good for variable light and weather conditions.

MATERIALS

OPTICAL GLASS is distortion free, and naturally hard so it can be precisely polished and formed. The tint in glass is permanent, heat will not affect it (up to 1500deg;F), and it resists scratches, but it's much heavier than plastics.

POLYCARBONATE lenses don't withstand heat well, or hold tints and coatings as well as glass, and are prone to scratching, but they inherently block all UV light. They are lighter and impact resistant which is good for active sports.

PLASTIC ACRYLIC lenses are inexpensive, scratch easily, and the dyed on tint will fade.

OPTICAL QUALITY Cost does not always reflect quality. More likely, you are paying for fashion, not eye protection. Avoid annoying and fatiguing image distortion with quality optics. Lenses should be impact resistant to help protect against eye injuries. Look for clarity with no distortion.

CLARITY can be determined by holding the lens under a light (fluorescent tubes are excellent), and moving it back and forth. If the light appears wavy, the lens is optically flawed. This method works for both plastic and glass lenses.

DISTORTION is an unwanted, and potentially dangerous distraction. To check for this, hold the glasses at arm's length, and look through them to a distant object with straight horizontal and vertical lines. Move the glasses up, down, and around. If the lines you are looking at seem curved or wavy, the lenses are distorted.

STYLE AND FIT Glasses should be comfortable, stay in place, and not block too much of your visual field. The frames should fit snugly but not press on your nose, temples, or the bone or cartilage around your ears. Put the glasses on, bend your head forward, and see if they stay in place. Frames are an important part of sunglasses, and often a major part of the cost. They should be sturdy, especially if you will be involved in action sports. Large or wrap around frames provide the best total coverage for the eye. Side shields are recommended for glacier climbing, to prevent snow blindness. They should never be worn while driving, or during other activities where your peripheral vision is important.

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RULES OF THE TRAIL:

Carry out all garbage.
Hike on marked trails, not across fragile alpine growth.
Use existing campsites or sites away from water and trails.
Respect and protect the wilderness.
Tread lightly and only carry home photographs and memories.