Considering that the eyes are wet and exposed all the time and one would think that in contact with cold winter temperatures they might freeze, eyeballs are actually always warm even though unprotected. Unlike other bodily extremities, the eyes are constantly pumped with a strong supply of warm blood—even in the coldest situations. Furthermore, our eyes are nestled rather deeply in our heads where bone, tissue, and fat also help keep them warm. Essentially, it’s virtually impossible for the eyes to freeze as long as they are inside a warm, functioning body.

The primary blood source to the eye is the ophthalmic artery, which is a branch of the same deep artery that supplies the brain. When in cold surroundings, the body diverts even more blood to the brain which, in turn, helps keep eyes even warmer.

Because tears are saltwater, they are also resistant to freezing; however, they can solidify in extreme cold and possibly “gum up” the eyelids. Even so, the eye itself will be unaffected. Basically, our eyes will only naturally freeze after our bodies are dead and cold. Saltwater freezes at much colder temperatures than normal water, which is why our eyes can stay moist in sub-zero temperatures with our salty tear drops.

Even though eyeballs do not get cold in winter, additional brightness from the snow can ‘burn’ your eyes. Too much UV exposure can cause inflammation of the cornea, a condition called keratitis, which makes your eyes red, sore and sensitive to light.

More Info: thebrainmaze.com