This was not a major problem when I simply wore my regular prescription (non-shaded) glasses. Maybe a little problem. But I finally decided that it was time to get real cycling shades, with the justification that all that riding without sun glasses was going to lead to cataracts (I'm old enough to worry about such things). So I sprang for a pair of Rudy Project shades with prescription inserts, and now issues with sweat/fogging are much worse! Frustrating. I may have to start wearing something on my forehead. Wearing the glasses further down my nose is not an option - the corrective lenses will be in the wrong position.