Patterns of Nonlinearity in the Ratio of Stimulus Accommodative Convergence to Accommodation

Background: This study disputes the assumption that the stimulus accommodative convergence to accommodation (AC/A) ratio is linear. Subjects and Methods: Accommodative convergence induced by minus lenses of varying power (-1.50 to -6.00DS, at intervals of 1.50DS) is measured on the Synoptophore in a group of 96 non-strabismic children aged 6 years 3 months to 11 years 2 months (mean 8.81 ± 1.43 years). Results: The mean AC/A ratios obtained with a stimulus to accommodation of 1.5D; 3.00D; 4.5D; 6.00D are 2.25 ± 1.47; 2.88 ± 1.15; 3.28 ± 1.02; 3.49 ± 0.85 respectively. Five patterns of change in AC/A ratio with stiumulus are described. Conclusion: Further studies in all age groups are necessary to investigate the non-linearity of the AC/A ratio over repeated measurements and the repeatability of the testing method.