Originally Posted by Black Bud
Protective glasses are also a good idea if you can find a way to keep them from fogging (I haven't yet!!).
Five possible options (none of which I have tried on cycling glasses, BTW):
1.) Glasses anti-fog spray, available at eye-care specialists, drug stores, etc
2.) Spray a bit of ammonia, wipe off
3.) Paintball goggle anti fog - I'm not sure if it's really any different from 1.), but it works decent on plastic lenses
4.) Dive mask anti fog
The fifth is the cheapest, if not a bit rude; divers will hork onto the lenses, rub, and give a rinse (or in the case of cycle goggles, I imagine a gentle wipe). It works quite well - I know some divers who swear by it over any artificial means.