title: Vertical vergence adaptation produces an objective vertical deviation that changes with head tilt.
abstract: OBJECTIVE
  To document the cyclovertical ocular motor mechanism used for vertical fusion in healthy subjects, and to explore whether vertical vergence training in healthy individuals can produce objectively confirmed vertical deviations that change with head tilt, revealing a basic mechanism that can produce a pattern of misalignment in an otherwise normal ocular motor system that is similar to superior oblique muscle paresis (SOP).
  
  
  METHODS
  Seven subjects with normal orthoptic examinations were adapted to vertical image disparities using our tilting haploscopic eye-tracking apparatus presenting concentric circle targets without torsional cues. Static eye positions were recorded with head straight and when tilted 45 degrees to the left and right, during both binocular and monocular viewing.
  
  
  RESULTS
  Vertical fusional vergence was accompanied by a cycloversion, with the downward-moving eye intorting and the upward-moving eye extorting, implicating primary involvement of the oblique extraocular muscles. After adaptation to the slowly increasing vertical target separation, all subjects developed a temporary vertical deviation in the straight ahead position that increased with head tilt to one side and decreased with head tilt to the other side.
  
  
  CONCLUSIONS
  These results not only show that head-tilt-dependent changes in vertical deviation are not necessarily pathognomonic for SOP, but also, and more importantly, suggest mechanisms that can mimic SOP and suggest a possible role for vertical vergence training in reducing deviations and thus the amount of head tilt required for fusion. Ultimately, vertical vergence training may provide an adjunct or alternative to extraocular muscle surgery in selected cases.
authors.affiliation: Wilmer Eye Institute, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21287-9028, USA. kirsch1@jhmi.edu
authors.forename: Kristina
authors.initials: K
authors.lastname: Irsch
authors.forename: David L
authors.initials: DL
authors.lastname: Guyton
authors.forename: Nicholas A
authors.initials: NA
authors.lastname: Ramey
authors.forename: Rohit S
authors.initials: RS
authors.lastname: Adyanthaya
authors.forename: Howard S
authors.initials: HS
authors.lastname: Ying
mesh_terms: D000222:Adaptation, Physiological; D000293:Adolescent; D000328:Adult; D005133:Eye Movements / Q000502:physiology*; D005260:Female; D019416:Head Movements / Q000502:physiology*; D006801:Humans; D008297:Male; D009801:Oculomotor Muscles / Q000502:physiology*; D014741:Video Recording; D015348:Vision, Binocular / Q000502:physiology*; D014792:Visual Acuity / Q000502:physiology; D055815:Young Adult
keywords: Bielschowsky head tilt test; basic cyclovertical deviation; superior oblique paresis; vertical vergence adaptation; video-oculography