Seesaw nystagmus (SSN) is characterized by conjugate torsional nystagmus with opposite vertical components in the two eyes. The waveform may be pendular or jerk (hemi-seesaw nystagmus, HSSN), in which the slow phase corresponds to one half-cycle and the quick phase to the other. Pendular SSN and HSSN have distinct clinical presentations and underlying causes. The pathophysiology of pendular SSN may be instability of visuovestibular interactions, while the underlying mechanism for HSSN may be related to the ocular tilt reaction or an imbalance in vestibular pathways. We report a patient with HSSN due to unilateral mesodiencephalic infarction that becomes apparent during visual fixation only.
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Midbrain lesion-induced disconjugate gaze: a unifying circuit mechanism of ocular alignment? Maximilian U. Friedrich, Laurin Schappe, Sashank Prasad, Helen Friedrich, Michael D. Fox, Andreas Zwergal, David S. Zee, Klaus Faßbender, Klaus-Ulrich Dillmann Journal of Neurology.2024;[Epub] CrossRef
Vertical gaze palsy is usually associated with lesions of the rostral midbrain and thalamo-mesencephalic junction. The rostral interstitial nucleus of the medial longitudinal fasciculus (riMLF), the interstitial nucleus of Cajal, and the posterior commissure located in the midbrain are the critical area in supranuclear control of vertical eye movements. We describe a case of vertical one-and-a-half syndrome accompanying contralateral abduction and incomplete depression palsy due to thalamo-mesencephalic infarction. These vertical eye movement abnormalities are presumed to be caused by damage to the ipsilateral riMLF, interstitial nucleus of Cajal, and oculomotor fascicles.