mexicant

Actually, it's more about duration than anything. A good rule of thumb is turn the volume up no higher than 50 or 60% and limit your use time to one hour. Some people recommend a period of "auditory rest" of up to two hours before going back to the headphones again but I haven't heard the official word on that. Certainly couldn't hurt.
It's always weird to tell people that 100 decibels of a symphony orchestra is just as damaging as 100 decibels of electric guitar. Some people seem to think that classical music is easier on your ears than rock or jazz. Unfortunately, your ears don't discriminate and loud is loud no matter what. I always feel like such a kill-joy when I have to talk in practicalities like that.

Ummm, I hope your referring doc was only kidding about the glass eye thing. Maybe he was just trying to be humorous...in a lame, twisted sort of way

but glasses are soooo hot