Yes, sunglasses look cool. And some would wear them in a dark subway for reasons other than eye protection. But, alas, the key benefit of wearing sunglasses is to protect the eyes from harmful exposure to sunlight. Sunlight contains certain types of light that can damage the delicate mechanism of the eyes. They can cause photokeratitis, which is a sunburning of the cornea resulting in impaired vision, or pinguecula, which is a damaging of the white parts of one's eyes and is exemplified by the formation of lesions on the eye surface.

Damage is caused by a particular wavelength of light generally referred to as ultraviolet light or UV rays. UV rays are not visible, and so may be present whether visible light surrounds us or not. In fact, UV light more easily penetrate cloud coverage than does visible light, so even in overcast conditions, there still may exist good reasons to protect the eyes from UV light.

Good sunglasses will block 99 to 100 percent of harmful UV rays. Sunglasses, such as the aviator glasses located on our site, specified as 'UV 400' (i.e., the lenses block out wavelengths up to 400 nanometers), will provide good protection from damaging light.

Some glasses are also designed to be 'blue blockers' which means they block out the blue part of the light spectrum. Some eye care experts believe blue light also is damaging to the eyes, hence the development of this technology. Blue-blocking sunglasses typically have amber-colored lenses.

Also, mirror-coated sunglasses ('flash coated') are especially good at limiting the amount of sunlight passing through to the eyes. In extremely bright sunlight, or if one has particularly sensitive eyes, these may be a good choice.

One thing to beware, make sure the glasses truly offer UV protection. Some cheaper sunglasses may not have effective UV blocking ability, and their use may result in INCREASED damage to the eyes compared to no use at all. This is because the shade will allow the pupils and eyes to open up more widely allowing even more UV rays to reach the sensitive parts of the eye. Tiny stickers saying the glasses offer UV protection should not be taken as a guarantee. It is safest to buy glasses of quality from a reputable manufacturer and from a reputable retail outlet. Knock-offs abound in the sunglass market, so buyer beware!