title: 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.
  
  
  OBJECTIVE
  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).
authors.affiliation: Ichijo Ear, Nose and Throat Clinic, Ekimae, Hirosaki, Japan. hiro3387@mvj.biglobe.ne.jp
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Ichijo
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D003937:Diagnosis, Differential; D004584:Electronystagmography; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009759:Nystagmus, Pathologic / Q000175:diagnosis / Q000209:etiology* / Q000503:physiopathology; D009760:Nystagmus, Physiologic / Q000502:physiology*; D056888:Patient Positioning; D011187:Posture / Q000502:physiology*; D012189:Retrospective Studies; D012665:Semicircular Canals / Q000503:physiopathology*; D014717:Vertigo / Q000150:complications* / Q000175:diagnosis / Q000503:physiopathology; D055815:Young Adult