I don't have any personal experience, but I recall a similar thread on one of the bulletin borads within the past month or two.

In that thread, a couple of different posters indicated the ones that use a separate lense holder put the prescription lenses too close to your face so that they tend to fog up. As a result, I decided to go with a pair of prescription sun glasses. My eyeglass guy retro fitted a pair of bows that curve behind my ears. There is no way these are going to slide down my nose or fall off.