[See-saw nystagmus. Clinical aspects, diagnosis, pathophysiology: observations in 2 patients].

See-saw nystagmus is an uncommon but characteristic kind of nystagmus. Typically there is intorsion and elevation of one eye and simultaneous extorsion and depression of the other eye. The nystagmus can be of pendular-waveform or jerk-waveform. The pendular-waveform see-saw nystagmus is commonly due to a midline meso-diencephalic, bilaterally compressing mass. The jerk-waveform see-saw nystagmus is mostly due to a unilateral lesion in the meso-diencephalic junction. For explanation, a current theory assumes a unilateral lesion of the interstitial nucleus of Cajal sparing the rostral interstitial nucleus of the medial longitudinal fascicle. Another concept suggests a lesion of the vertical vestibulo-ocular-reflex. We report two patients with jerk-waveform see-saw nystagmus. In both patients an internuclear ophthalmoplegia was found additionally. The origin was a unilateral brainstem infarction in both cases. We explain the symptomatology of see-saw nystagmus and discuss the actual theories of its origin.