Like [MENTION=151366]BobbyG[/MENTION], I haven't found anything that works really well on any kind of glasses in precipitation heavier than a light mist.

Three things that have helped in heavier rain:
1. Cycling cap with the bill flipped down.
2. MTB helmet with a visor.
3. Flip-up cycling glasses with a prescription lens underneath.

All three of those sort of work, and the mechanism in all three cases is obviously keeping rain off the glasses.