Smith Optics has finally mastered the interchangeable sunglass concept. Manufacturers have tried to do it in the past, but the the Interlock is the first system I've seen that stands up to abuse and holds the lenses firmly in place. All you do is twist the ear stems, which opens the entire frame, and pop out the lenses. It's the perfect pair of glasses for ripping back across a flat near dusk or cruising home on a bug laden evening from your local stream or lake on a bike. You can also switch out the polarized lenses for a pair of clear ones. Smith offers a wide variety of styles and lenses. Check them out here.