eyewear ?

I know that there is some spray that they make for paint ball mask thats an anti-fog.  I have never used it personaly but i have seen people use it when i was into playing paintball, so i am not for sure if it works or how well it works.  i hope is helps.

I think some of the anti-misting sprays used by motorcyclists work as well, but I've never actually tried them.

I wear glasses inside my fursuit head. I tried the anti-fog wipes. They didn't work. The only thing that seems to work is my mate installed small fans on either side of my face that blow in. They de-fog my glasses beautifully. ANd they weren't part of the original design. He added them after the head was finished, so it is possible to install them even though your head is completed.

To my knowledge, there is not a fool proof product that will work in all instances.  Air flow around the lenses is the only thing I know of that keeps my glasses from fogging up.

Stop emitting body heat!

No seriously, you need to install vents around the head with fans in them. It's cheaper to buy contacts, though.

also if you have a higher glasses prescription, it may be abad idea to use the sprays. They can actually make the outer layer peel off the lenses, which is very bad! Be careful when spraying things on the lenses!