title: The vestibulo-ocular reflex during active head motion in Chiari II malformation.
abstract: BACKGROUND
  Chiari type II malformation (CII) is a developmental anomaly of the cerebellum and brainstem, which are important structures for processing the vestibulo-ocular reflex (VOR). We investigated the effects of the deformity of CII on the angular VOR during active head motion.
  
  
  METHODS
  Eye and head movements were recorded using an infrared eye tracker and magnetic head tracker in 20 participants with CII [11 males, age range 8-19 years, mean (SD) 14.4 (3.2) years]. Thirty-eight age-matched healthy children and adolescents (21 males) constituted the control group. Participants were instructed to 'look' in darkness at the position of their thumb, placed 25 cm away, while they made horizontal and vertical sinusoidal head rotations at frequencies of about 0.5 Hz and 2 Hz. Parametric and non-parametric tests were used to compare the two groups.
  
  
  RESULTS
  The VOR gains, the ratio of eye to head velocities, were abnormally low in two participants with CII and abnormally high in one participant with CII.
  
  
  CONCLUSIONS
  The majority of participants with CII had normal VOR performance in this investigation. However, the deformity of CII can impair the active angular VOR in some patients with CII. Low gain is attributed to brainstem damage and high gain to cerebellar dysfunction.
authors.affiliation: Section of Pediatric Neurology, Children's Hospital, University of Manitoba, Winnipeg, Manitoba, Canada.
authors.forename: Michael S
authors.initials: MS
authors.lastname: Salman
authors.forename: James A
authors.initials: JA
authors.lastname: Sharpe
authors.forename: Linda
authors.initials: L
authors.lastname: Lillakas
authors.forename: Maureen
authors.initials: M
authors.lastname: Dennis
authors.forename: Martin J
authors.initials: MJ
authors.lastname: Steinbach
mesh_terms: D000293:Adolescent; D000328:Adult; D001139:Arnold-Chiari Malformation / Q000473:pathology / Q000503:physiopathology; D002648:Child; D005133:Eye Movements / Q000502:physiology*; D019416:Head Movements / Q000502:physiology*; D006801:Humans; D008297:Male; D012027:Reflex, Vestibulo-Ocular / Q000502:physiology*