title: Dissociated vertical deviation: head and body orientation affect the amplitude and velocity of the vertical drift.
abstract: OBJECTIVE
  Five subjects with dissociated vertical deviation (DVD) were studied to determine if the amplitude or velocity of the vertical components of the DVD were affected by head/body orientation with respect to gravity.
  
  
  METHODS
  Deviations were measured in head upright, head supine, and supine positions, with head hanging postures using a binocular CCD video-based infrared eye tracker. Subjects were required to fixate a target presented in the primary position during alternate or cover/uncover tests.
  
  
  RESULTS
  Amplitude and velocity of DVD both in onset and recovery were affected by head/body orientation with respect to gravity. In four of five subjects, the amplitude of the DVD was asymmetric between the two eyes when the head was upright. When the head/body was moved from an upright to a supine with head hanging backward condition, the amplitude of the DVD in the two eyes inverted. The eye with the larger DVD in the upright position had a smaller DVD in the head-hanging orientation. A similar relationship existed between velocity and head/body orientation. We found that DVD velocity increased with amplitude.
  
  
  CONCLUSIONS
  Passive effects of gravity on the eye-inorbit do not influence DVD magnitude or frequency of occurrence. The data suggest, however, that otolithic and possibly neck afferent inputs play a role in DVD magnitude and may be a part of the etiology of the condition.
authors.affiliation: Department of Psychology, York University, Ontario, Canada.
authors.forename: H C
authors.initials: HC
authors.lastname: Goltz
authors.forename: E L
authors.initials: EL
authors.lastname: Irving
authors.forename: J A
authors.initials: JA
authors.lastname: Hill
authors.forename: S P
authors.initials: SP
authors.lastname: Kraft
authors.forename: M J
authors.initials: MJ
authors.lastname: Steinbach
mesh_terms: D000328:Adult; D004585:Electrooculography; D005133:Eye Movements / Q000502:physiology*; D005260:Female; D006112:Gravitation; D006257:Head; D006801:Humans; D008297:Male; D008875:Middle Aged; D015835:Ocular Motility Disorders / Q000209:etiology / Q000503:physiopathology*; D009949:Orientation / Q000502:physiology*; D011187:Posture / Q000502:physiology*