[The Marcus Gunn phenomenon]

Ten cases of the Marcus Gunn phenomenon are reported. This synkinesis presents as an involuntary raising of the upper eyelid, often exhibiting ptosis at rest, when the lower jaw drops or deducts towards the opposite side. Hypotheses proposed to explain its mechanisms are reviewed, and the differential diagnosis is discussed in relation to the Marin Amat syndrome, the significance of which is considered. In addition, a case of rarely reported faciopalpebral synkinesis is also reported, the patient presenting involuntary raising of an upper eyelid during spontaneous or voluntary smiles.