In reply to Mick Borroff:
While climibing Mera about two years back I just took along some oversized ski goggles that fitted right over my prescription frames. Seemed to work pretty well and I wore them all the time I was above the snowline.
They didn't seem to fog more than than normal glacier glasses (which I sometimes wear with contact lenses) - but are a bit hot to wear all day if the sun is belting down.
I can't remember the make I used (one of the big names) and it set me back about 30 or so quid - a lot less than the quotes I got to grind custom lenses to fit goggles or glacier specs
chrs