Open your vents, and if it's really bad open the visor that little crack to let some air in. I see lots going around with it fully open all the time... if a piece of debris from a knackered road surface gives a chip or dent on your car imagine what it will do to your eye!
If your visor fogs up inside (especially in the rain) then invest in some antifog spray. I got some Bob Heath stuff and it's worked well all through winter.
Besides, everyone knows the biggest problem is getting an itchy nose
