Good advice and something to think about Frank. Skydive centers and mail order services can sell you a pair of skydiver goggles that fit over glasses. They come in tinted and clear...if you bail out without your glasses secured they are going to depart your face pronto. These should help keep them on your face during a crash/rapid deceleration. Here is a link but there are others..

http://www.gogglesandglasses.com/etbblkwo_240.html

Walt