When choosing sunglasses, it is important to choose quality lenses. The first thing you should do is make sure the lenses are dark enough to keep your eyes comfortable, but not too dark that they reduce your vision. Also, if you spend a lot of time outdoors in intense glare from sunlight bouncing off snow or water, you should wear sunglasses that block blue light. Medium to dark lenses with a grey, or a slightly brown or green tint, will filter out most blue light.

Glass lenses have the best optical clarity and scratch resistance, but are heavier than plastic lenses and can break on impact. Most sunglasses have plastic lenses, since they are tougher than glass and less likely to shatter. If you buy plastic lenses, look for a pair with a scratch-resistant coating.

You also want to make sure that there is very little distortion in the lenses. You can check for distortion by putting the sunglasses on and looking at a repeating pattern such as floor or ceiling tiles. If the lines stay straight when you move your head up and down and side-to-side, then the amount of distortion in the lenses is acceptable. However, if you notice that the lines begin to bend as you move, then you should try to avoid these sunglasses.

Sunglasses are made with different kinds of lenses to meet different needs:

• Regular lenses reduce the brightness of everything evenly.
• Polarizing lenses are designed to cut glare due to reflection. This means they are good for driving and outdoor activities in the snow or on water.
• Photochromic lenses change with the intensity of UV light by turning darker when outdoors and lighter when indoors. If you wear these for driving, choose sunglasses that are fairly dark.
• Flash or mirror lenses reflect all or part of the light instead of absorbing it. They offer no performance advantage as they scratch easily. You should choose a pair with a scratch-resistant coating.