I can't believe I didn't respond sooner. Actually I have used Rain-X with great success on my plastic lensed 'glasses' to bead up rain. The same company also offers an anti-fog solution that also works well. Even though it has worked for me I'd like to point out that you may want to first try these treatments on an old pair of similar glasses to what you wear now or just treat a very small corner of your present prescriptions to ensure that there aren't any adverse affects like clouding of the lens.

If you need a quick anti-fog solution, wiping your lenses dry with dish detergent works in a pinch... worked for my diving masks, ski goggles and plastic motorcycle face shields.