What is the cause of eyelid twitching?

Irritability Nerve: The nerve sending signals to a particular muscle or part of that muscle is irritable for whatever reason. These "tics" are almost always benign, are self limited, and just an annoyance.

Myokymia: Random twitching of an eyelid, which happens in normal people, is called myokymia (an involuntary, spontaneous, quivering of a few muscle cell bundles within a muscle). Myokymia starts and stops spontaneously. In the eyelids, it can last a few minutes to a few days. It can be caused by stress, dry eyes, lack of sleep.