Eye twitching is a sequence of rapid and painless involuntary muscle spasms in the eyelids. This disease, known as blepharospasm, can be unilateral or bilateral, although it is generally caused by the upper eyelid. This could be a one-off or occasional phenomenon. Generally, a small twitch is brief, lasting no more than a few seconds. The eyelid motions may be so slight that they could be invisible to an observer, and even before it has passed, the person witnessing it will not become completely conscious of the twitching.
This can be discomfiting and irritating, and typically does not trigger any huge concern. When this disorder continues and worsens to the point that any time it twitches, the eyelid is forced to close, medical advice should be obtained because this is likely to be a symptom of a more severe underlying issue.