Tobacco-induced primary-position upbeat nystagmus.

The effects of tobacco smoking on the eye movements of normal human subjects were studied using direct current electrooculography and the magnetic search coil technique. Tobacco induced a transient primary-position upbeat nystagmus in the dark, which was suppressed by visual fixation. It obeyed Alexander's law and was associated with oblique upward fast phases that alternated from side to side. Tobacco-induced nystagmus exhibited a latency of onset at 40 to 90 seconds, a duration of 10 to 20 minutes, and maximum slow-phase velocities at 2 to 3 minutes. We suggest that tobacco induces primary-position upbeat nystagmus through the excitatory effects of nicotine on the central vestibular pathways.