You have two options here. One, of course, is to swap out the “stock” lenses for prescription ones. A Colorado company called Opticus (www.opticus.com) specializes in adding prescription lenses to eyewear for mountaineering, ski, and general outdoor use.
For mountaineering, frames such as those on the Cebe Cecchinel ($160; www.cebe.com) are idealthey’re sturdy and comfortable, and come with side shields for complete eye protection. For all-around sport use, bicycling and the like, try Rudy Project’s Kerosene ($140; www.rudyprojectusa.com). Opticus probably can make lenses for the Kerosenes, depending on how heavy a prescription you need. I’ve also worn, and like, the Gargoyle Legend II ($110), which probably can take a prescription lens as well, and the Kaenon Kurb ($180; www.kaenon.com). Try some frames and find one that fits well and that stays put when you’re sweaty and on the move.
A second option is this: Rudy Project, Gargoyle, and several other eyewear makers offer prescription inserts that snap into the frame behind the “stock” lens. The advantage of this is that you can retain lens interchangeability, assuming the frames you choose allow that in the first place. I know I really like being able to swap out the lenses on my bicycling glasses, choosing yellow, clear, or smoke depending on light conditions. Cost is reasonable, about $40 to $50.