Fogging is devilish to solve.
As a skier I realized back in high school that eyeglasses just weren't going to cut it, but going to contact lenses isn't the total solution. Anyone that has skied someplace like. . .say whistler where there is a lot of vertical and a lot of temperature gradient between top and bottom, has experienced mid-mountain fog. This is pretty much what cyclists put up with, they make their own mid-mountain fog and haul it around with them. Ventilation schemes on ski goggle designs are only effective if you are moving fast enough to keep fresh air circulating, the first time you come to a stop at something like one of those inconvenient-intersection-things its all over.
The situation is actually compounded by really really cold temps. I wear contacts and after about -10F I have no choice but to wear some sort of eye-protection (not that there aren't many good reasons to wear eye protection both on the road and trail) any speed at all at -15F on down and my eyelashes are freezing and yes. . .contact lenses start freezing. If I come to a stop at cold temperatures, often one breath and my eyewear instantly have a bullet proof layer of ice on them. I've tried some venting tactics-ski masks with strategically placed bits of duct tape that are intended to direct my breath downward and away from the glasses but sooner or later I'm squinting through a slit. Visibility is the single biggest obstacle I encounter riding in sub-zero weather.
Not all glasses are created equal. I've gone through several styles of eyewear and some were definitely more effective. I had pretty much settled on Smith Bazooka sliders with the yellow lens, they seemed to have the balance between air space and protection and were reasonably durable but an unanticipated trip through the washing machine last spring reduced their service-life. I found some photochromatic Julbo "Instincts" on clearance last summer and so far so good. I also bought some crap called "FOGTECH" advanced one-step-anti-fog-solution at REI last week. We shall see.
I think Machka claims to wear eyeglasses no matter what the weather but I suspect she has developed some sort of bat-like sonar with all that night-riding she does.