Seesaw nystagmus associated with involuntary torsional head oscillations

Objective: To assess the diagnostic value of eye-head coupling in seesaw nystagmus (SSN). Background: SSN is a rare binocular disorder characterized by alternating skew deviation and conjugate ocular torsion. Methods: We examined a patient with a congenital nystagmus that switched to a pendular SSN on near viewing and was associated with involuntary torsional head oscillations. Results: The binocular torsional eye movements were in phase with the clinically visible head oscillations (i.e., head movements were not compensatory for the torsional eye movements). Conclusion: This finding suggests that torsional eye-head coupling in pendular SSN has a common pathologic origin. We suggest that alternating vertical disparity of both eyes in pendular SSN is compatible with an oscillating signal acting on an intact vestibular system. The absence of brainstem lesions on high-resolution MRI supports this assumption.