ACCOMMODATION CONVERGENCE RELATIONSHIPS AND AGE

Purpose. The objective of this study was to determine if there are dif ferences in accommodative-convergence/accommodation (AC/A) and converg ence-accommodation/convergence (CA/C) ratios in subjects with increasi ng age. The authors aimed to relate the findings to the present theori es of the development of presbyopia. Methods. Using a Canon AutoRef R- 1 to measure accommodation and an IRIS eye movement monitor to measure eye movements, the authors determined objective AC/A and CA/C ratios for 23 subjects between 17 and 42 years of age with normal binocular v ision. Changes in accommodation and convergence responses were stimula ted by lenses (-1.00 DS and -2.00 DS) and prisms (4 and 8 prism diopte rs), respectively. Measures were made at two visits on consecutive day s. Results. A moderate linear relationship was found between AC/A rati o and age (P <.002), and a strong linear relationship was found betwee n CA/C ratio and age (P < .0001). The decrease in CA/C ratio with age was due to a decreased accommodative response to prisms (P = .0001). M easurements were reliable, with 95% confidence intervals at +/-1.28 De lta/D and +/-0.02 D/Delta for AC/A and CA/C ratios, respectively. A re ciprocal relationship existed between the AC/A and CA/C ratios. Conclu sion. The AC/A ratio increases, and the CA/C ratio decreases, in perso ns between 20 and 40 years of age. This may be because increasing cili ary muscle contraction is required to produce a given change in accomm odation with increasing age or because of changes in the adaptability of the tonic accommodation and vergence systems with age.