title: Capturing the Moment of Fusion Loss in Intermittent Exotropia.
abstract: To characterize eye movements made by patients with intermittent exotropia when fusion loss occurs spontaneously and to compare them with those induced by covering 1 eye and with strategies used to recover fusion.
  
  
  
  Prospective study of a patient cohort referred to our laboratory.
  
  
  
  Thirteen patients with typical findings of intermittent exotropia who experienced frequent spontaneous loss of fusion.
  
  
  
  The position of each eye was recorded with a video eye tracker under infrared illumination while fixating on a small central near target.
  
  
  
  Eye position and peak velocity measured during spontaneous loss of fusion, shutter-induced loss of fusion, and recovery of fusion.
  
  
  
  In 10 of 13 subjects, the eye movement made after spontaneous loss of fusion was indistinguishable from that induced by covering 1 eye. It reached 90% of full amplitude in a mean of 1.75 seconds. Peak velocity of the deviating eye's movement was highly correlated for spontaneous and shutter-induced events. Peak velocity was also proportional to exotropia amplitude. Recovery of fusion was more rapid than loss of fusion, and often was accompanied by interjection of a disconjugate saccade.
  
  
  
  Loss of fusion in intermittent exotropia is not influenced by visual feedback. Excessive divergence tone may be responsible, but breakdown of alignment occurs via a unique, pathological type of eye movement that differs from a normal, physiological divergence eye movement.
authors.affiliation: Department of Ophthalmology, University of California, San Francisco, San Francisco, California.
authors.forename: John R
authors.initials: JR
authors.lastname: Economides
authors.affiliation: Department of Ophthalmology, University of California, San Francisco, San Francisco, California; Center for Mind/Brain Sciences, The University of Trento, Trento, Italy.
authors.forename: Daniel L
authors.initials: DL
authors.lastname: Adams
authors.affiliation: Department of Ophthalmology, University of California, San Francisco, San Francisco, California. Electronic address: hortonj@vision.ucsf.edu.
authors.forename: Jonathan C
authors.initials: JC
authors.lastname: Horton
mesh_terms: D000293:Adolescent; D000328:Adult; D002648:Child; D005099:Exotropia / Q000503:physiopathology* / Q000601:surgery; D053483:Eye Movement Measurements; D005260:Female; D005403:Fixation, Ocular; D006801:Humans; D008297:Male; D008875:Middle Aged; D009801:Oculomotor Muscles / Q000601:surgery; D013508:Ophthalmologic Surgical Procedures; D011446:Prospective Studies; D012438:Saccades / Q000502:physiology*; D015348:Vision, Binocular / Q000502:physiology*