These glasses are quite good and fit nicely over my prescription glasses.

I bought them to use while I go on bicycle riding, but I found them to be very inconvenient for that purpose. The frame is so thick all around that it creates a lot of blind spots. For example, when I am riding in bent position, I can not see a significant portion of the path ahead of me because the top of the frame is blocking it.

Again, I would like to emphasize that there is nothing wrong with the glasses for normal use if you are sitting or standing in upright position. Bicyclists have to look for something else. May be&nbsp;<a data-hook="product-link-linked" class="a-link-normal" href="/Polarized-Clip-on-Flip-up-Plastic-Sunglasses-Wrap-Style-Polarized-Brown-65mm-Wide-X-55mm-High-140mm-Wide/dp/B003LZYT3A/ref=cm_cr_arp_d_rvw_txt?ie=UTF8">Polarized Clip-on Flip-up Plastic Sunglasses - Wrap Style - Polarized Brown - 65mm Wide X 55mm High (140mm Wide)</a>.

Update 11/29/2011:
I bought two (one clear and one shaded) bifocal safety glasses and I couldn't be happier with what I got. I highly recommend for bicyclists to consider this option. I did not order from Amazon, but they seem to be available here.
<a data-hook="product-link-linked" class="a-link-normal" href="/AO-Safety-3M-Tekk-11374-Bx-Reader-1-5-Diopter-Safety-Glasses-Silver-Black-Frame-Clear-Lens/dp/B0013WIILW/ref=cm_cr_arp_d_rvw_txt?ie=UTF8">AO Safety/3M Tekk 11374 Bx Reader +1.5 Diopter Safety Glasses, Silver/Black Frame, Clear Lens</a>
<a data-hook="product-link-linked" class="a-link-normal" href="/Dewalt-DPG59-215C-Reinforcer-Rx-Bifocal-1-5-Smoke-Lens-High-Performance-Protective-Safety-Glasses-with-Rubber-Temples-and-Protective-Eyeglass-Sleeve/dp/B000646VGC/ref=cm_cr_arp_d_rvw_txt?ie=UTF8">Dewalt DPG59-215C Reinforcer Rx-Bifocal 1.5 Smoke Lens High Performance Protective Safety Glasses with Rubber Temples and Protective Eyeglass Sleeve</a>