title: Non-linearity of the response accommodative convergence to accommodation ratio.
abstract: OBJECTIVE
  Previous studies have reported variation in stimulus accommodative convergence to accommodation (AC/A) ratio across differing accommodative stimuli. Response AC/A ratio was assessed across 4 accommodative demands to determine if these differences could be due to accommodative inaccuracies to stimuli.
  
  
  METHODS
  Twenty-three student participants aged 18 to 26 years (mean age 20.3 ± 1.7 years) successfully completed all testing conditions. The modified Thorington technique was used at 4 m to measure heterophoria. The Shin Nippon SRW 5000 infrared autorefractor was used to determine accommodative change to -1.50, -3.00, -4.50, and -6.00D lens stimuli.
  
  
  RESULTS
  Significant differences were found in response AC/A ratio between different minus lens stimulated accommodative demands (p < 0.001). Mean AC/A ratio values were 3.11 ± 1.29 with the -1.50D lens stimulus; 4.03 ± 2.11 with -3.00D; 4.14 ± 1.40 with -4.50D; and 4.48 ± 1.56 with -6.00D. No differences in linearity were noted between myopes and non-myopic participants, but myopes tended to have higher response AC/A ratios than non-myopes, mean 4.88 ± 1.89 for myopes vs 3.61 ± 1.47 for non-myopes (p = 0.045).
  
  
  CONCLUSIONS
  Response AC/A ratio did not display linearity across 4 minus lens accommodative stimuli, but tended to increase with accommodative demand. Significant variability in response AC/A ratio was found, both within individuals to different accommodative demands, and between individuals across the data set.
authors: Academic Unit of Ophthalmology and Orthoptics, The Medical School, University of Sheffield, Sheffield, UK. miriamsjohnston@gmail.com
authors: Miriam S
authors: MS
authors: Johnston
authors: Alison Y
authors: AY
authors: Firth
mesh_terms: D000065:Accommodation, Ocular / Q000502:physiology*; D000293:Adolescent; D000328:Adult; D002648:Child; D003290:Convergence, Ocular / Q000502:physiology*; D005139:Eyeglasses; D005260:Female; D006801:Humans; D008297:Male; D009216:Myopia / Q000503:physiopathology* / Q000628:therapy; D012029:Refraction, Ocular; D013285:Strabismus / Q000503:physiopathology*; D055815:Young Adult