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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.
Acknowledgements
The authors would like to thank Dr David Buckley for his help with statistical analysis. Also our thanks go to the participants from the University of Sheffield who gave up their time to take part in the study, and especially to Heather Nicholls for undergoing the testing regimen twice due to technical issues at her first visit, and for her assistance with setting up apparatus.