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Choosing your sunglasses

The ozone layer protects any form of life existing on earth against excessive exposure to ultraviolet sunrays (UVR). The thinning of the ozone layer has increased the UV rays reaching the earth's surface. It is then very important to protect yourself from the dangerous sunlight rays whether you are in a working environment or having fun outside, and this is very easy to do.

The best protection is to stay away from sunlight and wear protective clothing and a wide brim hat. Also, apply a sunscreen of skin protection factor (SPF) 15 or higher to all areas of exposed skin. This applies to adults as well as children, whose skin is more sensitive.

Your eyes also need protection against UV and intense light.

Why wear sunglasses?

A good choice of sunglasses will help your vision by reducing sun glare, improving contrasts, and allow you to better tolerate the sunlight. Sunglasses which reduce blue light will improve the contrasts. Wearing this type of sunglasses increases your safety when driving or when doing sports.

Sunglasses also help prevent eye damage caused by direct sunlight. Those which absorb at least 75 percent of visible light -- most of them being models -- guarantee a sufficient protection against blue light without distorting the vision. If you spend lots of time in a glaring place, in the sea or snow, for example, wearing protective blue light sunglasses is advised. Amber colored lenses block blue light and make objects viewed from far mist more precise (in mountains). However, they do not always reduce sufficiently the sunlight and make it bearable.

Several years ago, studies demonstrated that many brands of sunglasses did not block UV rays well enough. The question then was if people were better without sunglasses. This fear came from the fact that, when protecting the eyes, sunglasses caused pupil dilatation. We then thought that pupil dilatation allowed a greater number of UV rays to penetrate the eyes. It seems today that this fear was groundless. The pupils are just slightly dilated, even when wearing very dark sunglasses. According to research, current sunglasses block a lot more UV rays than necessary to counterbalance the pupil dilatation.

Do not look at the sun, even if you are wearing sunglasses!! In fact, only welding masks of intensity factor 14 can protect. You should never stare at the sun, as 10 to 15 seconds are enough to burn your eyes, which would normally cause permanent blindness.

Which sunglasses?

Choose comfortable sunglasses, that is, glasses which are dark enough to protect from intense, but not too dark, as it could reduce your visibility. The more intense the light (for example, on high altitude ski slopes or on the sea), the darker the glasses. However, most sunglasses are suitable for a vast range of light intensity.

Types of lenses: Ordinary sunglasses lenses almost uniformly reduce all light intensities. Polarized lenses are specially conceived to reduce reflected glare -- that is the sunlight reflecting on gliding surfaces, like water or snow. Polarized sunglasses are thus particularly intended for driving. They can also be useful for fishing, as they provide a better vision of water. Moreover they block the major part of the light reflecting in water at certain angles.

Photochromic lenses react to UV intensity - they darken when outside and lighten when inside. In general, the darkening happens within 30 seconds, whereas it takes about 5 minutes to lighten. These lenses are also sensitive to temperature; they darken in low temperature. Photochromic lenses have uniform or graduated tints. If you are thinking of wearing them for driving, choose quite dark lenses, because the roof and windows of the car already block a major part of the UV rays, so, the lenses will not darken too much.

"Mirror" lenses reflect all or part of the useless light rather than absorbing it as ordinary sunglasses do. They do not offer any particular benefit. Metallic surfaces get easily scratched; it is thus better to choose scratch resistant lens surfaces.

Nowadays, most lenses are plastic lenses. Thin lenses always remain, as plastic is more resistant than glass and, as a result, is less easily broken. Very thin glasses would not resist high impact trials. Polycarbonate plastic, used in the production of sport sunglasses, is particularly resistant, does not break at the slightest impact, and due to an adequate surface, can overcome scratches. Glass lenses do not get scratched that much, but are heavier. If you buy polycarbonate plastic lenses, be sure to buy those which have a scratch resistant coating.

Before buying sunglasses, be sure that they do not distort your vision. Try them by looking at a rectangular object, for example, at floor tiles. If the lines remain straight, distortion is insignificant.

If you will be exposed to direct sunlight for long periods of time, it is better for you to wear panoramic sunglasses or glasses with lateral screens.

Light and UV rays

Light is a form of energy called electromagnetic energy. It travels through space like a wave. The electromagnetic spectrum is made up of wavelengths. Only one part of the spectrum is visible. It is perceived by our eyes as a gradation of colors ranging from purple to red, via blue, green, yellow and orange.

The sun is the earth's most important source of luminosity. It is also a powerful source of electromagnetic energy, outside the visible range of the spectrum. Only forty-five percent of the solar energy reaches the earth as visible light; the rest are invisible rays.

There are two types of invisible sunlight rays - the infrared rays (IR) and the ultraviolet rays (UVR). These rays are also absorbed by the eyes. The luminous infrared rays have broader wavelengths than visible light; these are thermal rays, that is, they are sources of heat. Half of the solar energy reaches the earth in the form of heat or infrared rays. The infrared rays carry less energy than visible light.

The earth's atmosphere absorbs a major part of the sun's ultraviolet rays. Only five percent of the solar energy reaches the earth in the form of UVR. Comparatively to visible light, these rays have a shorter wavelength but are a bigger source of energy. The UV band is divided in UVC, UVB and UVA. The atmospheric ozone layer absorbs the UVC rays, which thus cannot reach the earth's surface.

Eyes and UV rays

UVB rays cause suntan, but can also cause skin cancer. They can encourage or accelerate eye damage and its complications. The UVA rays are dangerous as well for the eye. The thinning of the ozone layer, and the fact that people live longer, increase the risks of short term high intensity exposures as well as long term low intensity exposures. Most of the damaging effects of UVB and UVA absorbed by the eyes are cumulative. As a result, the damages increase progressively and are not reversible. Also, some people are more sensitive than others to UV rays.

The absorption of light creates heat or chemical reactions. These reactions can be damaging to the eyes when the degree of light absorbed is bigger than the eye's capacity for repair. As the UV rays contain more energy than the visible light, their absorption is more dangerous. The external eye membrane, that is the cornea and the conjunctiva, absorbs the UVB rays. The crystalline lens mostly absorbs the UVA. The retina, that is, the opaque tissues situated at the back of the eye, absorbs the visible light. If there are too many UV rays in the atmosphere, the frontal parts of the eyes can be damaged, and the visible light is too intense, the retina can suffer permanent damage, and can even suffer permanent blindness. This is what happens when looking directly at the sun for more than a few seconds.

The effect of the UV rays, together with the wind and eye dryness, can cause snow blindness (keratitis lagophtalmos and conjunctivitis), a temporary but very unpleasant disorder. Some studies show that the risk of cataract (the eye crystalline becoming gradually opaque) increases with everyday exposure to intense sunlight, more precisely to UV, for several years, mostly when light reflects on large surfaces - like the sea for example. However, some scientists do not agree on this fact. Some people are more prone to develop cataracts than others, and this might have nothing to do with UV exposure.

Blue light, that is the visible light situated in the blue spectrum, constitutes another potential danger. The eye cannot concentrate on the blue waves as well as it does for other colors. However, the brain adjusts the visual perception when the vision is slightly blurred. It has never been able to demonstrate that the blurry effect caused by the blue light could damage the eye. Studies revealed, however, that the retina can suffer photochemical damages caused by shorter wavelengths of visible light -- the blue end of the spectrum. At present, some scientists think that regular outside exposure to blue light, for several years, can age the retina and accelerate macula degeneration for sensitive people. This retina disorder is the main cause of blindness in people over 60 years of age. On the opposite, other scientists think that these fears are groundless.

UV protection

It is not necessary to buy expensive fashion sunglasses in order to have an adequate protection against UV rays. Most of the sunglasses currently on the market block a large proportion of UV rays, but not the same amount. Moreover, it is not always possible to establish how much UV rays are blocked by the sunglasses on the basis of lens color or degree of opacity.

A large number of the sunglasses manufacturers comply voluntarily to labeling standards established by the industry. Three of these standards are: the ANSI Z80.3 Standard, published by the par American National Standards Institute, the UV Labeling Program of the Sunglass Association of America, as well as the CSA Z94.5-95 Standard of the Canadian Association as regards the direct selling of sunglasses. Sunglasses which abide to these standards carry a label or sticker indicating the category -- cosmetic, general purpose, specific purpose. Standards set the protection requirements against UV rays for each category.

Cosmetic sunglasses normally have slightly tinted lenses and are advised for places where the sun is not very strong; they block between 0 and 60 percent of visible light and UVA. They must also block between 87.5 and 95 percent of UVB. Cosmetic lenses are not recommended for day driving, unless the precisely indicated by the manufacturer.

General purpose sunglasses must block between 60 and 92 percent of visible light and UVA. They must also block between 95 and 99 percent of UVB. Wearing general purpose sunglasses is intended for situations where brutal sunlight would force to screw up one's eyes. These lenses are suitable for driving.

Specific purpose sunglasses can block as much as 97 percent of visible light. They must also block at least twice more UVA rays than the visible light till a maximum of 98.5 percent. They must block at least 99 percent of UVB. Specific purpose sunglasses are not intended for driving. It may be indicated on the label that they are suitable for long term exposure to direct sunlight.

Advice

Your sunglasses need not be high-tech to be comfortable and practical. Polarized lenses, which reduce the glare caused by reflection, are particularly useful when driving. Neutral and uniform tints are always a good choice. Grey lenses, darkish or greenish, from medium to dark intensity, will filter the major part of the blue light without causing any notable color distortion. All these characteristics are found in a large number of affordable sunglasses.

Good sense commands to wear sunglasses when it is sunny -- as much for personal comfort as to reduce the risks caused by UV rays and blue light.

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