Consider frame materials. Aluminum and titanium frames are very durable and offer custom fitting options. Plastic frames are light and durable but usually can't be bent to offer a custom fit.

Assess overall weight. Glasses need to be comfortable. Large lenses and thick frames add up to heavy glasses, something most people find uncomfortable. If you need thick lenses, get the smallest diameter lens that looks good on you.

Understand lens materials. Glass lenses resist scratching but are heavy and have lower shatter resistance. Polycarbonate (plastic) lenses are light and shatter resistant but demand care to prevent scratches. Custom options for lenses include an antireflective coating to cut glare, enhanced thinness for light weight and good looks, and photoreactive tinting that gets darker in bright light. Beware: These options can easily double your total cost.

Shop for metal frames that can withstand vigorous bending without damage. Opt for a separate set of specialized sports glasses with an impact-resistant frame and lenses secured by a strap.

Read the label carefully. You want 100 percent UV (ultraviolet light) protection from both UVA and UVB rays. Some lenses are labeled as UV400, which means the same thing.

Own several pair of sunglasses since one pair can't do everything. Leave a pair in the car for driving--cheap ones if you tend to sit on them. A slim stylish pair will not protect your eyes from debris while riding your bike. Expensive, sporty wrap-arounds will make you look like a yahoo at work.

Look for shatter-resistant polycarbonate lenses for water and snow sports, which require protection against strong reflected rays. Glass lenses, with their increased scratch resistance and fine optical quality, are a good choice for pricey, dress-up glasses. Polarized lenses, which reduce glare, are always a good idea.

Choose lens color carefully. Sensitive eyes need dark lenses. Gray or gray-green are good for general use. Brown works well for daytime driving or golf. Yellow and amber provide depth perception in low-light conditions. Avoid light blue and pink for driving or sports as they distort color. Some models have interchangeable lenses.