Sunglasses have a function more valuable than just fashion statements or to shield eyes from the sun’s glare.  They protect your eyes from damage and disease caused by overexposure to Ultraviolet (UV) rays!  We’ll take the mystery out of sungl¬asses and help you understand what to look for when you buy a pair.

Damage to Your Eyes

Acute eye damage may be caused from single outings on very bright days.  Excessive exposure to ultraviolet light reflected off sand, snow, water or pavement can damage the eye’s surface.  Similar to a sunburn, eye surface damage usually disappears within a couple of days, but may lead to further complications.

Long-term exposure to UV radiation (“sunburn rays”) may contribute to the development of various eye disorders, such as macular degeneration, the leading cause of vision loss among older Americans, and cataracts, a major cause of visual impairment and blindness around the world.

There are four things that a good pair of sunglasses should do for you:

1. Provide protection from ultraviolet rays in sunlight.  Ultraviolet (UV) light damages the cornea and the retina.  Good sunglasses can eliminate UV rays completely.  A visible light wave is electromagnetic energy with wavelengths of 400 to 700 nm.  The shorter the wavelengths, the higher the energy.  Just above the visible light spectrum is ultraviolet (UV) light, and it turns out that natural sunlight is rich in UV light.  Because of its high energy, UV light can damage both your cornea and your retina.

2. Provide protection from intense light.  When the eye receives too much light, it naturally closes the iris.  Once it has closed the iris as far as it can, the next step is squinting.  If there is still too much light, as there can be when sunlight is reflecting off of snow, the result is damage to the retina.  Good sunglasses can block light entering the eyes by as much as 97 percent to avoid damage.

3. Provide protection from glare.  Certain surfaces, such as water, can reflect a great deal of light, and the bright spots can be distracting or can hide objects.  Good sunglasses can completely eliminate this kind of glare using polarization (we’ll discuss polarization later).  Most artificial light is around 400 to 600 lumens.  A sunny day is about 1,000 lumens in the shade to more than 6,000 lumens on concrete.  Our eyes are comfortable until we get to around 3,500 lumens, then our eyes begin to have difficulty absorbing the light.  These brighter areas are flashes of white called glare. Squinting is to try to reduce the discomfort caused by the amount of light entering our eyes.  Prolonged exposure to light of such intensity can cause damage resulting in temporary or even permanent blindness.

4. Eliminate specific frequencies of light.  Certain frequencies of light can blur vision, and others can enhance contrast.  Choosing the right color for your sunglasses lets them work better in specific situations.

When we talk about light in reference to sunglasses, three types of light are important.

Direct light – Direct light is light that goes straight from the light source (like the sun) to your eyes.  Too much direct light can wash out the details of your surroundings and make it almost painful to try to focus your vision on anything.

Reflected light – Reflected light is usually in the form of glare.  It is light that has bounced off a reflective object to enter your eyes.  Just like direct light, strong reflected light can make it difficult to perceive the details or directly view an object.  Snow, water, glass and white sand are all good reflectors.

Ambient light – Ambient light is light that has bounced and scattered in many directions so that it is does not seem to have a specific source.  A good example of ambient light is the glow in the sky around a major city.  It would be very hard to identify a single source of light for that glow.  Ambient light is how you are able to see when there is no direct source of light.

Good sunglasses can eliminate the ultraviolet part of the spectrum, cut down on direct light to the point where it is comfortable and eliminate or decrease reflected light (depending on the reflecting surface).

What to Look for in Sunglasses

There are thousands of sunglasses available today.  Below are some of the features sunglasses have.  We try to note the features that are more important to look for to ensure your eyes are protected.

UV Coating

Several of the most serious eye problems can be linked to one cause: UV light. UV is often separated into two categories based on the frequency and wavelength of the light: UV-A and UV-B.

As a natural protection mechanism, the cornea of your eye absorbs some UV rays.  But some of the UV-A light, in particular, reaches the lens of the eye.  Over time this absorption can lead to cataracts or macular degeneration.  Plastic and glass lenses also absorb some UV light, however, it can be improved by adding a special coating to the lenses.  Polycarbonate lenses offer 99 percent UV protection.  Some labels read “UV protection up to 400nm” – this means 100 percent UV absorption.  Be careful of purchasing sunglasses that state they “block UV” – without saying how much!  They need to block 99 to 100 percent of UV rays.

Mirror Coating

Mirror finishes are just thin layers of various metallic coatings on ordinary lenses.  They are not necessary to reduce light since other things can do that, although that is one of the qualities they have.  Poor quality ones will scratch easily.  Do not assume they will protect your eyes from UV radiation.  Check the label to ensure the sunglasses block 99 to 100 percent of UV rays.

Tint Color and Darkness

Darkness can help limit light coming in to reduce squinting.  However, the color and degree of darkness do not tell you anything about the lenses ability to block UV rays. UV coating itself is colorless.  Color choice is a personal decision based on your needs and wants.  Each color has different qualities to consider:

• Gray:  reduce the overall amount of brightness with no contrast or color distortion.  Gray lenses offer good protection against glare, making them a good choice for driving and general use.

• Yellow or gold:  reduce the amount of blue.  Since blue light can create a kind of glare known as blue haze.  The yellow tint virtually eliminates the blue part of the spectrum and has the effect of making everything bright and sharp.  That’s why snow glasses are usually yellow or blue.  This tint really distorts color perception and creates a harsh visible light, which makes it inappropriate for any activity that relies on accurate color.

• Amber and brow:  are good general purpose tints.  They have the added benefit of reducing glare and have molecules that absorb higher frequency colors, such as blue and UV rays.  They may help prevent cataracts over time.  They can distort some colors similar to the yellow lenses, but increase contrast and clarity.   They offer very high contrast and depth perception. optimum for object definition

• Green:  reduce glare and offer the highest color contrast with little color distortion, they are very popular for multi-use.

• Rose and pink:  causes color distortion but offers the best contrast of objects against a green or blue background.  They make a good choice for hunting or water skiing.  Also the best for computer eyestrain.

• Blue:  also good in snow because it counteracts the white, but distorts other colors.

• Vermillion:  also good on water to define water from other objects, but has the worst color distortion.

A medium tinted lens is good for day-to-day wear.  However, if you use the glasses for very bright conditions, select darker tinted lenses.  But, don’t be fooled into thinking darker lenses offer more protection.  The degree of darkness does not represent the lenses’ ability to block UV light, so be sure to check the label.

AR Coating

A common problem with sunglasses is called back-glare.  This is light that hits the back of the lenses and bounces into the eyes.  The purpose of an anti-reflective (AR) coating is to reduce these reflections off the lenses.

Gradient Tint

Gradient lenses are permanently shaded from top to bottom or from top and bottom toward the middle.  There are single gradient lenses (dark on top and lighter on the bottom) and double gradient lenses (dark on top and bottom and lighter in the middle).  The single gradient lenses are useful for driving because they reduce glare while allowing you to see clearly, but are not good for sports.  Double gradient lenses are the opposite – they are better for sports where light reflects up off the water or snow, but not for driving, because they make the dashboard appear dim.  Tinting has little to no effect on UV protection!

Polarized

Polarized lenses are the best way to reduce reflected glare, such as sunlight that bounces off of smooth surfaces like snow or water.  These lenses are useful for skiing, fishing and driving.  Polarization does not have any relation to UV light absorption, but many lenses are now combined with a UV coating.  Be sure to check the label before making your purchase.  A lot of sunglasses advertised as polarizing actually are not. There’s a simple test you can perform before you buy them to make sure. Find a reflective surface, and hold the glasses so that you are viewing the surface through one of the lenses. Now slowly rotate the glasses to a 90-degree angle, and see if the reflective glare diminishes or increases. If the sunglasses are polarized, you will see a significant diminishing of the glare.

Blue Blocking

Whether blue light is harmful to the eye is still being debated; however, there is some scientific evidence the retina may be more sensitive to blue visible light.  Lenses that block all blue light are tinted amber.  This tint allegedly makes distant objects appear more distinct, especially in snow or haze.  These lenses are popular with skiers, hunters, boaters and pilots.

Wraparound

Wraparound sunglasses are designed to keep light from shining around the frames and into your eyes, protecting your eyes from all angles.

Photochromic

Depending on the amount of UV rays exposed to, photochromic lens will change from light to dark.  Although some photochromic lenses may be good UV-absorbent sunglasses, it takes time for them to adjust to different light conditions.  The majority of the darkening takes place in about thirty-seconds; however, the lightening takes about five minutes.

Choosing the Perfect Features for You

The key to finding the perfect pair of sunglasses is to pick the right features for your situation. Here are some of the most important features to compare when you buy a pair of sunglasses:

• Lens material – CR-39 is a plastic made from hard resin that meets optical quality standards.
Polycarbonate is a synthetic plastic material that has great strength and is very lightweight. These lenses tend to be lighter and are more impact-resistant. Glass lenses are heavier but are much more resistant to scratches.

• Lens quality – Optical-quality polycarbonate and glass lenses are free of distortions, such as blemishes or waves, and have evenly distributed color across each lens. Here’s an easy way to tell if the lenses in a pair of sunglasses are of good quality. Find a surface with repeating lines, like a tiled floor. Hold the sunglasses a short distance away from your face and cover one eye. Look through one of the lenses at the lines while moving the sunglasses slowly from left to right and then up and down. The lines should stay straight as you look at them. If they wiggle or waver in any way, then the lenses are not optical quality and will distort your vision. Distortion is extremely common in cheap sunglasses.

• Lens darkness – For outdoor sports such as mountain climbing and snow-skiing, you want a tint that blocks most light. (to 97 percent of light!) For most purposes, like going to the beach or driving, look for a tint that absorbs or blocks 70 percent to 90 percent of light. Tints that offer less than 60-percent blockage are mainly good for fashion since they offer only mild protection.

• Special coatings or features – Anti-reflective, waterproof, mirror and scratch-resistant coatings, polarization and tinting improve the functionality of the sunglasses but also add cost.

• Frame and lens design – Normal frames similar to prescription eyeglass frames offer no protection from ambient light, direct light and glare from other angles.  Wrap-around frames, larger lenses and special sidereal attachments can keep this extra light from your eyes it you can accept the looks.

• Frame material – Most inexpensive sunglasses use simple plastic or wire frames, while higher cost sunglasses use high-strength, light-weight composite or metal frames.  Also, the better sunglasses usually have features like tension springs that connect the arms to the face instead of just screws.

• Brand recognition – The simple truth is that a brand name does add cost.  Just like shoes and suits, people associate certain brands with quality and extravagance.  Some companies spend huge amounts of money to advertise a brand and create an identity.  That cost is often passed on to the consumer in the product’s price.  However, it is possible to find high-quality sunglasses that don’t have a brand-name price.

A good eyeglass maker unbiased review place is Eyeglass.