Well, as a fellow glasses wearer, here's my advice: Check your local airsoft provider (or look online) and try to find a wire-mesh airsoft (full face) mask. the reason I advise this is because while fogged up goggles certainly aren't fun for any player, having both the goggles and your glasses fogged up at the same time can be most frustrating. This is what I plan to switch to as soon as UPS visits me again.
Alternately, I would advise talking to your optometrist about it, they'll likely be able to provide some fit-over glasses for what you need. (or if you have the money, you could get prescription safety goggles, though if you can't afford contacts, prescription goggles are probably out of the picture.)
Third option: (This is what I've been using recently) some chemistry style goggles fit over most glasses frames rather well, just check to make sure they meet the proper ANSI standards for eye protection (most are made to protect from chemicals rather than kinetic impact) it seems to work rather well ('cept for the double-fogging I mentioned earlier, a sweatband can help prevent this, as do anti-fog wipes)
Fourth option: most of the paintball masks I've used fit over glasses, and they work fine for airsoft. (but still, be wary of fog)
If you live in a dry area, the fogging should be less of a problem, where I live it's pretty humid, so it tends to bother me. your mileage may vary.