title: Vertical fusional vergence: the key to dissociated vertical deviation.
abstract: OBJECTIVE
  To test the previous findings of Enright that disparity-induced vertical vergence is mediated primarily by the oblique muscles, and to relate this normal eye movement pattern to the eye movement pattern seen in subjects with dissociated vertical deviation.
  
  
  METHODS
  Sixteen normal volunteers underwent 55 measurements of the cycloversion associated with prism-induced vertical vergence using an afterimage apparatus. A Vernier scale measured the direction and magnitude of the torsional shift that occurred with recovery of fusion on removal of a 3- or 4-prism diopter prism.
  
  
  RESULTS
  Of the 55 trials, the directions of torsional shift were consistent with the oblique muscles being the primary mediators of vertical fusional vergence in 51 (93%) (P = .03 using a binomial distribution). The mean +/- SD value of torsional shift was 1.15 degrees+/-0.76 degrees in the expected direction.
  
  
  CONCLUSIONS
  Vertical fusional vergences in this study were produced primarily by the oblique extraocular muscles. The eye movement patterns of these vertical vergences in normal subjects are qualitatively similar to those seen in recordings of patients with dissociated vertical deviation. Dissociated vertical deviation thus seems to be an exaggeration of a normally occurring eye movement pattern. The cyclovertical component of dissociated vertical deviation may help stabilize the fixing eye by damping vertical nystagmus, while the accompanying hypertropia is an incidental and undesirable side effect.
authors.affiliation: Wilmer Ophthalmological Institute, The Johns Hopkins University School of Medicine, Baltimore, MD, USA.
authors.forename: E W
authors.initials: EW
authors.lastname: Cheeseman
authors.forename: D L
authors.initials: DL
authors.lastname: Guyton
mesh_terms: D000293:Adolescent; D000328:Adult; D000360:Afterimage; D003290:Convergence, Ocular / Q000502:physiology; D005133:Eye Movements / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D015835:Ocular Motility Disorders / Q000503:physiopathology*; D009801:Oculomotor Muscles / Q000503:physiopathology*; D015357:Vision Disparity / Q000502:physiology*; D014787:Vision Tests