title: Effects of earth-fixed vs head-fixed targets on static ocular counterroll.
abstract: OBJECTIVE
  To investigate whether static ocular counterroll (OCR) gain is reduced during viewing of an earth-fixed vs a head-fixed target.
  
  
  METHODS
  Twelve healthy individuals were recruited. The target consisted of a red fixation cross against a grid pattern at a viewing distance of 33 cm. The target was mounted on a wall (earth fixed) or was coupled to the head (head fixed). Changes in mean torsional eye position were plotted as a function of head position steps (0 degrees +/- 25 degrees in 5 degrees steps), and sigmoidal fits were performed. Mean static OCR gain was calculated by taking the derivative of the fitted functions.
  
  
  RESULTS
  Mean static OCR gain was 40% lower with a head-fixed target (-0.084) than with an earth-fixed target (-0.141) (P < .001).
  
  
  CONCLUSIONS
  The reduction in static OCR gain during viewing of a head-fixed target indicates that static OCR is partially negated when a target moves with the head.
authors.affiliation: Department of Ophthalmology and Vision Sciences, University of Toronto, Toronto, Ontario, Canada.
authors.forename: Manokaraananthan
authors.initials: M
authors.lastname: Chandrakumar
authors.forename: Zahra
authors.initials: Z
authors.lastname: Hirji
authors.forename: Herbert C
authors.initials: HC
authors.lastname: Goltz
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Mirabella
authors.forename: Alan W
authors.initials: AW
authors.lastname: Blakeman
authors.forename: Linda
authors.initials: L
authors.lastname: Colpa
authors.forename: Agnes M F
authors.initials: AM
authors.lastname: Wong
mesh_terms: D000293:Adolescent; D000328:Adult; D003290:Convergence, Ocular / Q000502:physiology*; D005133:Eye Movements / Q000502:physiology*; D005260:Female; D005403:Fixation, Ocular / Q000502:physiology*; D019416:Head Movements / Q000502:physiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D014102:Torsion Abnormality / Q000503:physiopathology*; D020432:Trochlear Nerve Diseases / Q000175:diagnosis / Q000503:physiopathology; D014741:Video Recording; D015348:Vision, Binocular / Q000502:physiology; D055815:Young Adult
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