I have a pair of Wiley-X wrap-around glasses that accept a prescription insert. The ones that I have are the "Talon" model:

http://www.wileyx.com/EcommSuite/Pro...temCode=CHTAL1

Besides bicycling, I am a competitive shooter in Highpower Rifle/Service Rifle, and I purchased these for that sport, but found that they work well for cycling as well. I have a very strong prescription, and the Talons were recommended to me by the customer service people at Wiley-X. I originally purchased their "PT-3" glasses, but the PT-3's have much more curvature to the outer lens which prevented them from working well with my strength of prescription. The Talons are fine, though.

The prescription insert is similar to a regular pair of eyeglasses, but without the temple pieces. They have a set of clips that snap into the main glasses frame over the nose bridge. The glasses come with three outer lenses - clear, dark grey, and amber, for different light conditions.

As it turns out, I had no problem with them steaming up while cycling, but I did have issues with them steaming up in cold wet weather while shooting my rifle. It seems that my breath is deflected back and upwards by the stock/action of the rifle right on to the glasses.

There are several manufacturers of this type of eyeglass, Oakley included. You may have to do a web search for "tactical glasses" or some such.