On the vertical caloric nystagmus.

Eye movements in response to caloric stimuli are recorded traditionally in the horizontal plane only. Twin channel electronystagmographic traces of 124 patients undergoing evaluation of vertigo were reviewed. Thirty traces (24%) were found to include a "true" vertical component to the evoked nystagmus. There was no correlation between the existence and the nature of any vestibular pathology and the presence of the vertical nystagmus. Thus, a vertical component to the caloric nystagmus (the so-called "perverted" caloric nystagmus) is not necessarily a pathological sign, and can be a normal variant, caused by excitation of the vertical semicircular canal - most probably the posterior one. The mechanisms of heat transfer in the temporal bone and the source of this vertical caloric nystagmus are discussed in the context of the published literature.