The Influence of Convergence on Downbeat Nystagmus

This is a patient presenting with progressive imbalance and oscillopsia over the course of approximately 1 year. On examination, he had cerebellar ataxia in addition to spontaneous downbeat nystagmus (DBN). His downbeat nystagmus increased in lateral and downgaze, which are characteristic features, but also increased with convergence. This is contrary to infantile nystagmus, where (horizontal) spontaneous nystagmus damps with convergence. Convergence will often provoke or accentuate acquired vertical nystagmus, perhaps due to involvement of the otolith pathways, which are responsible for linear translation, and dependent on orbital position and viewing distance. In addition to his downbeat nystagmus increasing with convergence, when an accommodative target is brought slowly toward the right eye (right eye remains in the center of the orbit rather than in adduction, which occurs during convergence), it has the same effect in increasing his downbeat nystagmus.