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.