One of the most basic feature for all sunglasses is complete protection against the potentially damaging effects of the sun's ultraviolet-A and ultraviolet-B rays. You should never purchase dark tinted sunglasses that do not offer 100 percent UV protection. Why? Because sun glasses make the pupil of the eye dilate and open up to allow more light in which, in turn, allows UV rays to easily enter the eye. If your sunglasses lack complete UV protection, they can result in damage to your eyes.

Polarized sunglasses reduce bothersome glare from flat surfaces like snow, water, roads and other reflective surfaces. By removing the glare, polarized sunglass wearers see better and have less eye fatigue as they need to squint less. These advantages are critical to drivers, airline pilots, heavy-equipment operators, outdoor enthusiasts like hunters and fishermen and many athletes like skiers, golfers and ball players.

Glasses tend to fall or rub up against objects so it’s important to consider the material used for the lens. Consider impact-resistant sunglasses as they resist breakage when dropped or mishandled. Lenses made of a trade-name plastic called CR-39 are lighter than glass and even more resistant to breakage. Glasses made of high-index plastic are even lighter than CR-39 glasses and have a coating that protects them against scratching.

Photo-cromic sunglasses have lenses that are designed to brighten or darken in response to the intensity of sunlight. When outdoors the lens are dark providing the maximum protection. But when you go indoors, where the lighting is lower, the optics lighten allowing the sunglass wearer to see better in low light conditions.

When sunglass wearers get rain, mist, or fog on the lenses it becomes near impossible to see clearly. However, water sheeting is a feature that helps preserve visual acuity even when the lens are exposed to water and get wet.

Water-sheeting allows the water to form in a see-through sheet on the lens rather then in individual droplets that block or distort vision. Water sheeting lens are essential for fishermen out on the water in the early morning mist.