If you ask your optometrist, you will be referred to the optometrist in your area that specializes in prescription sports glasses, including glasses for cycling. Take a printout of your prescription with you. The sports optometrist will have cases and cases of sports glasses so you can pick the frame that suits you the best, that fits well and the color of lens that is most appropriate for the light and glare conditions for your primary rides. You will be directed to the frame choices that are intended to be used by cyclists.

I purchased two Oakley frames with a gray lens and I am really happy with the comfort and fit.

If you purchase the glasses online, you risk the glasses not fitting your face correctly, and allowing light to come in at the sides and bounce around. Also, the optometrist will measure the distance between your eyes and may take other measurements that will result in you having a better pair of glasses.