title: Variation of binocular-vertical fusion amplitude with convergence.
abstract: OBJECTIVE
  The maximum binocular vertical disparity that can be fused with disparity vergence (vertical-fusion amplitude or VFA), varies with convergence angle. VFA is larger for convergence responses to near than to far viewing distances; however, the clinical norms for changes in VFA with convergence have not been established. VFA at several convergence angles was measured to obtain a quantitative description of the changes in VFA with convergence.
  
  
  METHODS
  Fifty-six adults took part in the study. Horizontal and vertical disparity stimuli were presented on a computer monitor by using the red-green anaglyphic technique. Stimulus to convergence was altered either by changing horizontal disparity on the computer monitor (experiment I: nine horizontal disparities: 1.2-22.5 PD [Delta]) or by changing the binocular viewing distance (experiment II: five viewing distances: 25-300 cm). Convergence was held constant during an experimental session, while vertical disparity was incremented in steps of 0.05 Delta after a subjective report of fusion, until the subject reported diplopia. The maximum vertical disparity that could be fused was defined as the VFA.
  
  
  RESULTS
  VFA increased linearly over the range of convergence stimuli (y = 0.10x + 1.62) and intersubject variability of VFA increased marginally with the amount of convergence. Linear regression equations with similar slopes and y-intercepts were observed in experiments I and II.
  
  
  CONCLUSIONS
  The results of the experiments provide a quantitative description of a linear relationship between VFA and convergence. The linear regression equation could be used in a clinical setting to establish norms and to screen for vertical vergence abnormalities.
authors: School of Optometry, University of California at Berkeley, Berkeley, CA, USA. srbharad@indiana.edu
authors: Shrikant R
authors: SR
authors: Bharadwaj
authors: M Pia
authors: MP
authors: Hoenig
authors: Viswanathan C
authors: VC
authors: Sivaramakrishnan
authors: Baskaran
authors: B
authors: Karthikeyan
authors: Donna
authors: D
authors: Simonian
authors: Katie
authors: K
authors: Mau
authors: Sally
authors: S
authors: Rastani
authors: Clifton M
authors: CM
authors: Schor
mesh_terms: D000293:Adolescent; D000328:Adult; D003290:Convergence, Ocular / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D015357:Vision Disparity / Q000502:physiology; D014787:Vision Tests; D015348:Vision, Binocular / Q000502:physiology*; D014796:Visual Perception / Q000502:physiology