Keep them clean for one. A wash before taking the field is good enough. I use Opsdrops, but catcrap might do the same thing.I know this is by now an old thread but does anyone have a really good way of anti-fogging glasses?:shrug:
My military friend swears by spitting in them and rubbing it around.
I have also hear of people putting bandaides in them, tucking into the frame. Apparently the vapours from the adhesive do something helpful.