Last year I got some prescriptioin goggles from Riders Eyeware. There is an issue with them fogging up, unless you are moving. I bought some anti-fog spray, which didn't work. Well, I have found an anti-fog wipe that is fantastic. I used to have to put my goggles on at the last minute because they would fog up so quickly, and at a stop light, I would have to lift them off a little to stop them fogging up. Now I can put them on and not worry at all. I also bought the "Rain Coat" treatment from the same place. It's specifically made for MC windshields and helmet shields. I put a coating on, but only drove in misting, so wasn't able to give it a good try. You can check it out at the following link.
http://motosolutions.com/

