There are lens cleaners and anti-foggers that the scuba folks use on their masks. One is called Aquaseal Sea Drops. I used a scuba mask when I was practicing rolling and this stuff works pretty well. It keeps glass and plastic clean and prevents it from fogging. I would be careful in putting it on your $400 eyeglasses until you're sure it won't harm the plastc lens. You can get it at any scuba shop.