We have developed a new technique for analyzing the rotation vector of eye movement with an infrared CCD camera [Imai et al.: Acta Otolaryngol 1999;119:24-28]. We used this technique to analyze the eye rotation axis of benign paroxysmal positioning nystagmus (BPPN) that was induced by the Dix-Hallpike maneuver in 14 patients with benign paroxysmal positioning vertigo (BPPV). Eye rotation axes of BPPN in 8 patients were closely perpendicular to the posterior canal of the undermost ear in the provocative head position. Under the hypothesis that BPPN is due to a mechanical stimulation of the posterior canal by canalolithiasis, this finding suggested that the posterior canal of the undermost ear is the lesion. On the other hand, eye rotation axes of BPPN in the other 6 patients were closely aligned with the naso-occipital axis. It is suggested that canalolithiasis induces endolymphatic flow in both posterior and anterior canals via the common crus and the summation of the eye movements induced by stimulation of both the posterior and anterior canals rotates the eye along the naso-occipital axis.
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