Non-linearity of the Response Accommodative Convergence to Accommodation Ratio

Abstract

Purpose: 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.