The following is sort of reposted from this thread which you might want to page through since it has some good information.

While it's relatively easy to produce prescription lens for non-wrap sunglasses, those that have a lot of wrap-around that's recommended for activities such as cycling are more difficult to create in prescription format... especially if the wraps use a rimless design. Many brands of high-end sunglasses allow for prescription via clip-on/in inserts. These are typically subframes that can accept a prescription ground lens.




They work fine but there are several things I don't like about them.

1. If you adjust them to sit close to the face without the inserts then when the inserts are used, they can be touching which might be annoying
   
2. Heavier but after a bit the feeling of the extra weight goes away. You can get plastic lenses which help bring down the weight but they might not be of the best optical quality which might cause other problems (see below).
   
3. Multiple optical surfaces can cause distortion due to differences in index of refraction although if you use really good quality prescription glass lenses this should not be too bad. The downside is that glass can be heavier than polycarb plastic.
   
4. They fog up easier in cold humid weather and are hard to clear when that happens. The Rudy Project Kerosenes I use have a "vent control" feature which helps keep things from fogging.
   
5. Sweat can run between the two optical surfaces and be hard to wipe away. Other things can get trapped between the wrap and lens such as bugs and dirt.
   
6. Makes you look even more goofy

In general, I only use my inserts for when I'm MTBing and wear my contacts when I'm RBing. I do carry the inserts with me just in case my contacts foul up and I have to ditch them.

Oakley has the ability to embed a prescription lens right into the main wrap lens itself. It's pricey though. For certain models of Rudy Project, Adidas and Smith, there's an outfit called Sports Optical that will handle custom-grounding of lens that will fit into certain wrap frames but they're very expensive (prices start at $250 I believe). And if like me, you need to have interchangable lenses to match different lighting conditions then you have to get all your different lenses ground with prescription. This can get pretty costly but is the ultimate solution aside from contacts or surgery.