Marcus Gunn phenomenon is a rare condition characterized by movement of the upper eyelid in a rapid rising motion (a "wink") each time the jaw moves. The wink phenomenon may be elicited by opening the mouth, thrusting the jaw to the side, jaw protrusion, chewing, smiling, or sucking. It is usually present at birth and may occur with other eye abnormalities (such as strabismus) or vision problems. Although it usually affects one eye, it can affect both eyes in rare cases.The exact cause is not known. Marcus Gunn phenomenon is generally sporadic, but familial cases have been reported. Treatment is not always needed but may include surgery in more severe cases. (https://rarediseases.info.nih.gov/diseases/6972/marcus-gunn-phenomenon)