Replying to Cleaning your INSIDE goggle lens?

I've heard various opinions on proper cleaning procedures for goggle lens's. I have an Oakley Grey Polarized lens. When cleaning the outside I always use the Oakley storage lens, and that works great, plus that's what Oakley recommends. The real question I have is how to clean the inside of your lens. I've heard that if you don't clean it properly, you ruin the anti-fog film that's coating the inside lens, which I believe has happened to me with past pairs. I have some marks and smudges from dirty snow, water, and dust coating the inside of my lens. How do I properly clean that off without ruining the goggles?