title: Variability of Ocular Deviation in Strabismus.
abstract: OBJECTIVE
  In strabismus, the fixating eye conveys the direction of gaze while the fellow eye points at a peripheral location in space. The stability of the eyes may be reduced by the absence of a common target.
  
  
  OBJECTIVE
  To quantify the stability of eye position in strabismus and to measure variability in the ocular deviation.
  
  
  METHODS
  From 2010 to 2014, a prospective comparative case study of 25 patients with alternating exotropia with normal visual acuity in each eye and 25 control individuals was conducted in a laboratory at a tertiary eye center. A video eye tracker was used to measure the position of each eye while participants alternated fixation on the center of a cross under dichoptic conditions or scanned pictures of natural scenes.
  
  
  METHODS
  Spatial and temporal variability in the position of the fixating eye and the nonfixating eye in patients with strabismus and control individuals, quantified by the log area of ellipses containing 95% of eye positions or mean SDs of eye position.
  
  
  RESULTS
  In the 25 patients with strabismus, the mean (SD) age was 28 (14) years (range, 8-55 years) and the mean (SD) ocular deviation was 14.2° (5.9°) (range, 4.4°-22.4°). In the patients with strabismus, the mean position variability (1.80 log units; 95% CI, 1.66-1.93) for the deviating eye was greater than for the fixating eye (1.26 log units; 95% CI, 1.17-1.35) (P < .001). The fixating eye of patients with strabismus was more variable in position than the fixating eye of individuals without strabismus (0.98 log units; 95% CI, 0.88-1.08) (P < .005).
  
  
  CONCLUSIONS
  In patients with strabismus, even without amblyopia, the deviated eye is more variable in position than the fixating eye. Both eyes are less stable in position than the eyes of control individuals, which indicates that strabismus impairs the ability to fixate targets steadily. Saccades contribute to variability of the deviation angle because they are less conjugate in patients with strabismus.
authors.affiliation: Department of Ophthalmology, University of California, San Francisco.
authors.forename: John R
authors.initials: JR
authors.lastname: Economides
authors.affiliation: Department of Ophthalmology, University of California, San Francisco2Center 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.
authors.forename: Jonathan C
authors.initials: JC
authors.lastname: Horton
mesh_terms: D000293:Adolescent; D000328:Adult; D002648:Child; D003941:Diagnostic Techniques, Ophthalmological; D004948:Esotropia / Q000503:physiopathology*; D005099:Exotropia / Q000503:physiopathology*; D005260:Female; D005403:Fixation, Ocular / Q000502:physiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D012438:Saccades / Q000502:physiology*; D014741:Video Recording; D015348:Vision, Binocular / Q000502:physiology