See-saw nystagmus is an uncommon but highly characteristic eye movement disorder made up of cyclic movements: intorsion and elevation of one eye, with synchronous extorsion and depression of the other for one half-cycle; the movements reverse in each eye for the next half cycle¹. It generally has a pendular waveform, but may also be a jerk nystagmus². 

Looking at the bridge of the patient’s nose may help to appreciate the seesaw nature of the oscillation³.  Jerk see-saw nystagmus can be clinically indistinguishable from pendular see-saw nystagmus, and from the torsional-vertical nystagmus which occurs with medullary lesions. It may be associated with a paroxysmal or tonic OTR.

Jerk see-saw nystagmus has fast (of saccadic origin) and slow phases.  The nystagmus has synchronous torsional, vertical and sometimes horizontal components.  The slow phases ot the torsional and the vertical components show an exponentially decrementing velocity waveform, suggesting that the slow phases are due to loss of the neural integration of torsional and vertical eye velocity signals to eye position signals².

• The torsional component of jerk see-saw nystagmus is conjugate.
• The vertical component of jerk see-saw nystagmus is disjunctive, so that the eye with the extorting fast phases beats downward, while the eye with the intorting fast phases beats upward.

Pathogenesis

Jerk see-saw nystagmus is due to unilateral inactivation of the torsional eye-velocity integrator, the interstitial nucleus of Cajal, and with sparing of the torsional fast phase generator, in the adjacent rostral interstitial nucleus of the medial longitudinal fasciculus.

Causes

The pendular form usually arises from a midline, extrinsic, suprasellar mass lesion compressing or invading the brainstem bilaterally at the junction of the midbrain and diencephalon².

The jerk form is due to a unilateral midbrain or lateral medullary lesion¹.

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From: Hari Kumar KVS, Singh P. Seesaw Nystagmus. N Engl J Med. 2017;376(24):e51. doi:10.1056/NEJMicm1613244
 

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