SEESAW NYSTAGMUS ASSOCIATED WITH INVOLUNTARY TORSIONAL HEAD OSCILLATIONS

Objective: To assess the diagnostic value of eye-head coupling in sees aw nystagmus (SSN). Background: SSN is a rare binocular disorder chara cterized by alternating skew deviation and conjugate ocular torsion. M ethods: We examined a patient with a congenital nystagmus that switche d to a pendular SSN on near viewing and was associated with involuntar y torsional head oscillations. Results: The binocular torsional eye mo vements were in phase with the clinically visible head oscillations (i .e., head movements were not compensatory for the torsional eye moveme nts). Conclusion: This finding suggests that torsional eye-head coupli ng in pendular SSN has a common pathologic origin. We suggest that alt ernating 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 ass umption.