title: A novel haploscopic viewing apparatus with a three-axis eye tracker.
abstract: OBJECTIVE
  To validate the accuracy and precision of a novel haploscope for use in investigating the mechanisms underlying normal eye control as well as the mechanisms of cyclovertical strabismus in pediatric and adult subjects. The accuracy and precision represent the device's ability to reproducibly measure true eye positions.
  
  
  METHODS
  A novel haploscope was developed that allows the measurement of eye positions and movements under specified conditions of vergence, head tilting, and cover testing. Equipped with video oculography, the haploscope can aid in the objective assessment of binocular and adaptive mechanisms that maintain oculomotor alignment. The device's accuracy and precision were assessed using a model eye with 3 axes of rotation. The device was then used to measure ocular torsion during the well-documented phenomenon of ocular counter-roll with head tilt. The eye movements of 6 normal subjects were measured as each subject fixated binocularly on the center of radially symmetric targets during head tilting.
  
  
  RESULTS
  The device yielded Pearson correlations with the model eye of R = 1.0, with residual error (re), a measure of accuracy, about all 3 ocular axes peaking at re = 19 +/- 5 arcmin. For human subjects, average positional error was re = 21 +/- 9 arcmin. Ocular counter-roll averaged 5.7 +/- 0.9 degrees for left and right eyes.
  
  
  CONCLUSIONS
  These results validate the accuracy and precision of this novel haploscope. They support its use in future investigations of the mechanisms of oculomotor control and alignment.
authors.affiliation: The Krieger Children's Eye Center at The Wilmer Institute The Johns Hopkins University School of Medicine, Baltimore, Maryland 21287-9028, USA. nramey1@gmail.com
authors.forename: Nicholas A
authors.initials: NA
authors.lastname: Ramey
authors.forename: Howard S
authors.initials: HS
authors.lastname: Ying
authors.forename: Kristina
authors.initials: K
authors.lastname: Irsch
authors.forename: Marie C
authors.initials: MC
authors.lastname: Müllenbroich
authors.forename: Reena
authors.initials: R
authors.lastname: Vaswani
authors.forename: David L
authors.initials: DL
authors.lastname: Guyton
mesh_terms: D000328:Adult; D016477:Artifacts; D003290:Convergence, Ocular; D004867:Equipment Design; D053483:Eye Movement Measurements / Q000295:instrumentation*; D005133:Eye Movements; D005403:Fixation, Ocular; D006257:Head / Q000502:physiology; D006801:Humans; D008875:Middle Aged; D008954:Models, Biological; D009799:Ocular Physiological Phenomena; D011187:Posture; D012016:Reference Values; D015203:Reproducibility of Results; D012399:Rotation; D054159:Torsion, Mechanical; D014741:Video Recording; D015348:Vision, Binocular