What diseases can it reflect?
When the facial nerve, which controls the eye muscles, is stimulated or compressed, it will contract and cause the eyelid to beat.
There are two kinds of muscles in the human eyelid. One is called orbicularis oculi muscle, which is shaped like a wheel and encircles the eye. When it contracts, the eyelid will close. This kind of orbicularis oculi muscle is controlled by the facial nerve. Another kind of eyelid muscle is called levator palpebrae superioris. When it contracts, the eyelid will open. This kind of muscle is controlled by the oculomotor nerve.
In these two kinds of muscle tissues of eyelid, orbicularis oculi muscle plays an important role in protecting the eyeball. It can lubricate and clean the cornea through continuous closure, and make protective response to any external stimulation.
Under normal circumstances, these activities of opening and closing eyes are controlled by brain nerves. However, once the facial nerve that controls orbicularis oculi muscle is stimulated by some external factors, it may act autonomously without the command of brain, causing the orbicularis oculi muscle to contract repeatedly, even spasm or vibration, and people will obviously feel that the eyelid is beating involuntarily, which is called eyelid jump.
Most people are limited to the upper or lower eyelid beat, but some people will gradually develop into the upper and lower eyelid twitch. When the facial nerve that controls the eyelid muscle is stimulated in any part of the conduction pathway, it can lead to the eyelid beating. Different parts of the nerve are stimulated, and the parts, range and degree of the eyelid beating are also different.
If the stimulus is limited to the nerve endings that control the orbicularis oculi muscle, i.e. near the eyelid, the symptoms are simple upper eyelid or lower eyelid jump. If the stimulated part is in the main part of the facial nerve in the brain cavity, the whole upper and lower eyelids will be involved in the beating range. The most intuitive performance is that the eyes can't help blinking, which is called 'blepharospasm' in medicine.