Why do we need to close our eyes when sleeping

When people are sleeping, only by closing their eyes can they sleep soundly and truly fall asleep. When people are not asleep, their eyes are controlled by the brain, and they have not really fallen asleep at this time. When they are truly asleep, the brain no longer controls the closing of the eyelids, and they will naturally fall asleep. This is why it is impossible to have a good sleep with your eyes open.

Why do we close our eyes when we sleep?

The main muscles responsible for opening and closing the eyes are the orbicularis oculi muscle and the levator palpebrae superioris muscle. The levator palpebrae superioris muscle is located above the superior rectus muscle and its function is to lift the upper eyelid, while the orbicularis oculi muscle surrounds the eyes, forms the eyelid, and is responsible for closing the eyes. The orbicularis oculi muscle contracts continuously and autonomously, which pulls the skin over it. Some people experience "eyelid twitching", which is caused by abnormal excitement of its nerves. In other words, some of the orbicularis oculi muscle fibers cannot contract continuously and autonomously in a short period of time.

So what are the "benefits" of closing your eyes? From an evolutionary perspective, every "instinctive function" of human beings is the result of natural optimization and is selected by the adaptation of organisms to the environment. When humans sleep, their protection against the external environment is limited, and their eyes need to directly feel the stimulation of light in order to see everything. The projection of light is generally in a straight line and cannot be blocked, so the eyeball needs to be exposed to the outside. However, such exposure is dangerous, so there is a protective barrier called eyelid. Moreover, when people sleep, the visual center is in a suppressed state, so even if the eyes are open and the image of the object is formed in the eyes, the brain still cannot perceive it. In other words, humans close their eyes when they sleep at night because their eyes are "useless" at that time, so they are folded up; and when they sleep during the day, they close their eyes to block out the light.