Rain-X (for car windshields) has an anti-fog product. A bottle (~$5.00) will last a 30 y.o. the rest of his/her life. I use it on the inside of the $3.00 un-vented safety goggles I got from Home Depot. Home Depot also has safety glasses that fit over prescription glasses. They don't need venting because they don't close in around your eyes. They can still fog and the Rain-X will work. You can just about perceive some blurring after a time in the cold and wet but nothing like the total whiteout condition that you get without any kind of anti-fog on your lenses.

H