In the cold winter, people often get their hands and feet frozen. At this time, they usually wear thick cotton padded jackets and trousers, cotton shoes, and cotton hats, but they often shiver. However, you will find that the eyes exposed to the outside are not afraid of the cold. Even if the eyebrows are frozen and there is frost on the eyelashes, the eyes can still look around freely. Why is that?
The answer to this question can be found in the structure of the eye. Because the front surface of the eyeball, including the cornea, conjunctiva, and sclera, although it is densely populated with tactile and pain nerve endings, there are very few nerve endings that sense temperature changes. Therefore, when the external temperature changes, there is little information reported to the brain, and the eye is relatively insensitive to cold and heat changes. Moreover, the cornea is a transparent structure without blood vessels, and there are very few blood vessels in the sclera, so the heat dissipation of these structures is very weak. On the other hand, because people often blink and the eyeball constantly moves, it can generate more heat. Coupled with the fact that the upper and lower eyelids, which are rich in blood vessels, can warm the eyeball, even in the coldest days of the winter, the surface temperature of the eyeball can still be above 10℃. Therefore, it's not surprising that the eyes are not afraid of the cold.