Jaw winking, also known as the Marcus Gunn phenomenon, is widening of a congenital ptosis when a patient is chewing, swallowing, or opening the jaw (i.e., a trigemino-oculomotor synkinesis). It is believed to result from aberrant innervation of the pterygoid muscles and levator palpebrae superioris.
Eyelid closure on jaw movement or opening of the mouth, inverse Marcus Gunn phenomenon, is also described, as the Marin-Amat syndrome, thought to be due to aberrant facial (VII) nerve regeneration.
Rana PVS, Wadia RS. The Marin-Amat syndrome: an unusual facial synkinesia. Journal of Neurology, Neurosurgery and Psychiatry 1985; 48: 939-941