Performance and Sport Sunglasses
The boom in outdoor sports activities like mountain biking, snowboarding, rock climbing, kayaking, skiing, golfing and in-line skating has also created a demand for sports- and performance-oriented sunglasses.
These special-purpose sunglasses are designed to be exceptionally light and comfortable, able to withstand extreme conditions and stay comfortably in place during any activity.
Perhaps the most important aspect of effective sports sunwear is the optical quality and visual enhancement properties of the lenses. In particular, sports and performance lenses are available in a wide variety of tints to modify light in certain ways to enhance contrast. This allows you to see certain objects (a tennis ball, for example) with greater clarity to enhance your reaction time.
Polycarbonate lenses are the lens of choice for most sport sunglasses because they are lightweight, super strong and more impact-resistant than lenses made of other materials.
Polarized lenses are also in demand, because they reduce glare from light reflecting off flat surfaces such as water or a field of snow. There is, however, some debate about the advisability of polarized lenses for sports like downhill and mogul skiing, since seeing sunlight reflecting from icy patches on the slopes is often beneficial.
Read more: http://www.allaboutvision.com/sunglasses/performance.htm