Denouement and Discussion
Marcus Gunn Phenomenon
Marcus Gunn phenomenon consists of unilateral ptosis at rest with elevation of the eyelid when the mouth is open. This condition is classified under the general heading of "synkinetic ptosis," and the most common type is trigemino-oculomotor synkinesis, or the jaw-winking phenomenon. It is most noticeable during infancy, at which time rapid up and down movements of the eyelid are apparent when the infant is nursing. If the jaw is deviated to the affected side, the ptosis increases but if it is deviated to the unaffected side or if the jaw is projected forward, elevation of the eyelid occurs. It is usually present on the left side and is almost always unilateral. Although there are various theories concerning the etiology of this phenomenon, most believe that during embryogenesis the fifth cranial nerve (trigeminal) fibers were misdirected into the third cranial nerve (oculomotor). As a result of this, when the mouth
Gellis SS, Feingold M, Eckerd JM, Howard LJ. Picture of the Month. Am J Dis Child. 1980;134(8):783–784. doi:https://doi.org/10.1001/archpedi.1980.02130200051016
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