Possible Mechanism of Seesaw Nystagmus in Internuclear Ophthalmoplegia

ABSTRACT

The authors report jerky seesaw nystagmus, extorsional downbeating in the ipsilesional eye and intorsional upbeating in the contralesional eye, in a patient with internuclear ophthalmoplegia (INO) from focal pontine lesion. This pattern of nystagmus may occur by disrupting pathways from contralateral posterior and anterior semicircular canals by a lesion in the medial longitudinal fasciculus. Depending on the pathways involved, various patterns of dissociated torsional-vertical nystagmus may accompany INO.