I took off my steamy glasses to be able to see and this question came up to my mind. Which is the physical reason for our eyes not fogging up like glasses do?
You can fog up the surface of the cornea.
But in order to condense water on a surface the surface temperature has to at least reach the dew point temperature for a particular barometric pressure and relative humidity.
Typically if you are inside a building for example with air conditioning and walk out into warmer, humid air, glasses can fog since they can be of lower temperature, un-warmed by the body.
But since your body generally keeps the surface temperature of the cornea warm (I would guess between 30 to 35 degC), you would have to have very warm temperatures and highly humid conditions for that to happen. But the physics say it can happen. Good thing we have built in windshield wipers (eyelids).
Eyes do fog up, if the environmental conditions are right.
But since you can clear the fogging by blinking, and blinking is a reflex action, you don't often notice that it is happening.