Convergence induced upbeat nystagmus

Abstract

Upbeat nystagmus occurred on voluntary convergence in a patient with the dorsal midbrain syndrome. Upward pursuit eye movements were also impaired. The clinical findings implicate a defect in the upward pursuit pathways in the region of the posterior commisure. This defect presumably caused a bias in vertical pursuit tone and resulted in downward drift of the eyes with upward corrective saccades. The act of convergence increased or unmasked this subtle bias in downward pursuit tone. The authors report the observation and review the literature on convergence evoked nystagmus.

Key Words:

• dorsal midbrain syndrome
• upbeat nystagmus
• convergence induced nystagmus