title: Disparity-driven vs blur-driven models of accommodation and convergence in binocular vision and intermittent strabismus.
abstract: OBJECTIVE
  To propose an alternative and practical model to conceptualize clinical patterns of concomitant intermittent strabismus, heterophoria, and convergence and accommodation anomalies.
  
  
  METHODS
  Despite identical ratios, there can be a disparity- or blur-biased "style" in three hypothetical scenarios: normal; high ratio of accommodative convergence to accommodation (AC/A) and low ratio of convergence accommodation to convergence (CA/C); low AC/A and high CA/C. We calculated disparity bias indices (DBI) to reflect these biases and provide early objective data from small illustrative clinical groups that fit these styles.
  
  
  RESULTS
  Normal adults (n = 56) and children (n = 24) showed disparity bias (adult DBI 0.43 [95% CI, 0.50-0.36], child DBI 0.20 [95% CI, 0.31-0.07]; P = 0.001). Accommodative esotropia (n = 3) showed less disparity-bias (DBI 0.03). In the high AC/A-low CA/C scenario, early presbyopia (n = 22) showed mean DBI of 0.17 (95% CI, 0.28-0.06), compared to DBI of -0.31 in convergence excess esotropia (n=8). In the low AC/A-high CA/C scenario near exotropia (n = 17) showed mean DBI of 0.27. DBI ranged between 1.25 and -1.67.
  
  
  CONCLUSIONS
  Establishing disparity or blur bias adds to AC/A and CA/C ratios to explain clinical patterns. Excessive bias or inflexibility in near-cue use increases risk of clinical problems.
authors.affiliation: Infant Vision Laboratory, School of Psychology & Clinical Language Sciences, University of Reading, United Kingdom; Orthoptic Department, Royal Berkshire Hospital, Reading, United Kingdom. Electronic address: a.m.horwood@reading.ac.uk.
authors.forename: Anna M
authors.initials: AM
authors.lastname: Horwood
authors.affiliation: Infant Vision Laboratory, School of Psychology & Clinical Language Sciences, University of Reading, United Kingdom.
authors.forename: Patricia M
authors.initials: PM
authors.lastname: Riddell
mesh_terms: D000065:Accommodation, Ocular / Q000502:physiology*; D000293:Adolescent; D000328:Adult; D002648:Child; D002675:Child, Preschool; D003290:Convergence, Ocular / Q000502:physiology*; D003463:Cues; D005260:Female; D006801:Humans; D008297:Male; D008962:Models, Theoretical; D012030:Refractive Errors / Q000503:physiopathology*; D013285:Strabismus / Q000503:physiopathology*; D015357:Vision Disparity / Q000502:physiology*; D015348:Vision, Binocular / Q000502:physiology*