First, try them on! I was coveting a pair of the Oakley Enduring (women's model) glasses. Then I tried them on--it was instantly apparent they were not for me. In this case, the glasses were just too small and flat-out uncomfortable.

I find most unisex glasses to be too big. And I also remember (granted this is a ways back they may be better now) that photochromatic lenses are not dark enough when it's sunny and too dark when it's not--the worst of both worlds.

If you do a lot of riding in a aggressive position or in the aerobars, you may want a frameless pair. I have a pair of Rudy Project Maskerynas that I like for riding.