Accommodation-convergence relationships and age.
OBJECTIVE
The objective of this study was to determine if there are differences in accommodative-convergence/accommodation (AC/A) and convergence-accommodation/convergence (CA/C) ratios in subjects with increasing age. The authors aimed to relate the findings to the present theories 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 vision. Changes in accommodation and convergence responses were stimulated by lenses (-1.00 DS and -2.00 DS) and prisms (4 and 8 prism diopters), respectively. Measures were made at two visits on consecutive days.


RESULTS
A moderate linear relationship was found between AC/A ratio and age (P < .002), and a strong linear relationship was found between 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). Measurements were reliable, with 95% confidence intervals at +/- 1.28 delta/D and +/- 0.02 D/delta for AC/A and CA/C ratios, respectively. A reciprocal relationship existed between the AC/A and CA/C ratios.


CONCLUSIONS
The AC/A ratio increases, and the CA/C ratio decreases, in persons between 20 and 40 years of age. This may be because increasing ciliary muscle contraction is required to produce a given change in accommodation with increasing age or because of changes in the adaptability of the tonic accommodation and vergence systems with age.
Bruce
A S
AS
Centre for Eye Research, School of Optometry, Queensland University of Technology, Brisbane, Australia.
Atchison
D A
DA
Bhoola
H
H
D000065:Accommodation, Ocular / Q000502:physiology*; D000293:Adolescent; D000328:Adult; D000375:Aging / Q000502:physiology*; D003290:Convergence, Ocular / Q000502:physiology*; D005133:Eye Movements; D006801:Humans; D011305:Presbyopia / Q000503:physiopathology