There's a similar thread on here somewhere that I'm too lazy to find for you.

But my astigmatism is bad enough (particularly in combination with my normal prescription) that I can't get prescription athletic sunglasses. The size of the lenses would be too big (compared to normal sunglasses). Contacts bother my eyes but I prefer to wear them on rides anyway. It's a little too unnerving for me to have any peripheral vision that isn't corrected. But...I also won't ride without some kind of glasses protecting my eyes.