Asymmetry of positioning nystagmus in posterior canalolithiasis

Abstract

Conclusions: Ewald's third law is correct in the posterior semicircular canal and the intensity of stimulatory nystagmus is 2.7 times as strong as that of inhibitory nystagmus. Objectives: Ewald's third law states that a flow of endolymph away from the ampulla causes more stimulation than a flow toward the ampulla in the posterior canal. The aims of this study were to quantify the asymmetry of positioning nystagmus in posterior canalolithiasis and to confirm the validity of Ewald's third law. Methods: Subjects were 20 patients who revealed typical vertical/torsional positioning nystagmus in the Dix–Hallpike test, 14 females and 6 males, with a mean age of 55.2 years. Nystagmus was recorded using an infrared camera and the findings were converted to digital data. Using ImageJ, we performed three-dimensional video-oculography and measured maximum slow-phase velocity of three components (horizontal, vertical, and torsional). Results: The mean value of maximum slow-phase velocity (sum of three components) in the head-hanging position was 42.3°/s and that in the sitting position was 15.6°/s. The former was significantly greater than the latter (p < 0.01).

Keywords::

• Vertical component
• torsional component
• Ewald's law
• Flourens' law
• video-oculography
• maximum slow-phase velocity

Acknowledgment

We thank Dr Kazunori Futai for preparing some of the figures.

Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.