Give your eyes a break with polarized sunglasses. They reduce glare off reflective surfaces like water and snow, enhancing your vision and reducing eyestrain. This makes polarized lenses ideal for activities on the water like fishing and boating, or snowsports like skiing and snowboarding. They're also great for driving.
Photochromic lenses change tint in response to available light, allowing more or less visible light transmission as you need it. So no matter where you are or what the weather's doing, your shades are just right. Highly versatile and convenient, photochromic sunglasses may be more expensive, but they'll be the only pair you'll need.
Interchangeable sunglasses allow you to quickly switch out lenses when lighting conditions change, when a lens is damaged, or simply when you feel like going for a different look. Most come with two sets of lenses, one for sunny days and another for lower-light conditions; additional replacement lenses are often available.