I wear prescription glasses, and you'd think that they would
suffice as eye protection. However, there have been several
occasions while shooting pistols with erratic ejection patterns (my
Steyr M40 comes to mind) when the spent case would eject
straight up, ricochet off
the shooting stall crossmember and end up wedged between my eyelid
and glasses. This can be somewhat annoying, not to mention
painful.
For this reason, I now pack a baseball cap in my range bag.