I went to my optometrist to find a pair. He didn't have anything on the shelf but had many catalogs with frames of all styles. I looked through the catalogs and picked out a number of frames which he got in for me to try on. As mentioned above, for riding, they need to be big enough to block the wind and sit high enough so I'm not looking over the tops of them when I'm in the drops. Being curved around the face helps too. The prescription may limit the amount of curvature you can get.