Do you have an anti-fog coating on your glasses, and does your helmet support Pinlock insert? A friend of mine wore glasses with a coating and they stayed clear. This was 30 years ago, so presumably the technology has gotten better. We used to play paintball in the winter every weekend, and he never complained about his glasses. The goggles we used were dual-pane and never fogged either - Pinlock works on the same concept. Even better if your helmet is compatible with a heated or dial-pane visor, but those are usually reserved for off-road only/non-certified snowmobiling helmets.
I personally don't usually have a problem with my standard single-layer visor fogging. I keep the inside spotless by washing with dish soap and never touch it with my fingers. It will fog when not moving, so I open it all the way at stops. I find that once you let it fog the first time, it gets harder and harder for just the airflow to keep it clear.