title: Posterior semicircular canal nystagmus is conjugate and its axis is parallel to that of the canal.
abstract: A patient with a postoperative fistula of the left posterior semicircular canal is presented. Negative pressure in the external ear canal produced upbeat-torsional nystagmus, which was recorded in three dimensions using binocular scleral search coils. The nystagmus was conjugate, without skew deviation, and its trajectory corresponded to the anatomic axis of the left posterior canal. The current study helps validate Ewald's first law in humans: the axis of nystagmus should match the anatomic axis of the semicircular canal that generated it. This law is clinically useful in diagnosing pathology of the vestibular end-organ, such as benign paroxysmal positional vertigo or the superior semicircular canal dehiscence syndrome.
authors.affiliation: Eye and Ear Research Unit and the Institute of Clinical Neurosciences, Royal Prince Alfred Hospital, and the University of Sydney, Australia.
authors.forename: P D
authors.initials: PD
authors.lastname: Cremer
authors.forename: A A
authors.initials: AA
authors.lastname: Migliaccio
authors.forename: D V
authors.initials: DV
authors.lastname: Pohl
authors.forename: I S
authors.initials: IS
authors.lastname: Curthoys
authors.forename: L
authors.initials: L
authors.lastname: Davies
authors.forename: R A
authors.initials: RA
authors.lastname: Yavor
authors.forename: G M
authors.initials: GM
authors.lastname: Halmagyi
mesh_terms: D000368:Aged; D004584:Electronystagmography; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging; D008575:Meniere Disease / Q000175:diagnosis / Q000503:physiopathology; D009759:Nystagmus, Pathologic / Q000175:diagnosis / Q000503:physiopathology*; D012665:Semicircular Canals / Q000503:physiopathology*; D014057:Tomography, X-Ray Computed; D014722:Vestibule, Labyrinth / Q000503:physiopathology