Visual and Positional Modulation of Pendular Seesaw Nystagmus: Implications for the Mechanism.

BACKGROUND

The mechanisms of pendular seesaw nystagmus (SSN) remain unknown.

METHODS

We evaluated modulation of pendular SSN by removal of visual fixation, convergence, and positional changes in 2 patients, one with bitemporal hemianopia due to a traumatic damage of the optic chiasm and the other with platybasia compressing the medulla and lower cerebellum.

RESULTS

In both patients, the pendular SSN markedly decreased or disappeared with convergence, without visual fixation in darkness, during static head tilt toward each shoulder while sitting and while supine.

CONCLUSIONS

The similar patterns of nystagmus modulation observed in our patients with a different etiology indicate a common role of both visual and otolithic inputs in generating pendular SSN.