Original article
Convergence accommodation to convergence (CA/C) ratio: stability with different levels of convergence demand
Authors:
Komal J. Hirani ,
Academic Unit of Ophthalmology and Orthoptics, University of Sheffield, Sheffield
About Komal J.
BMedSci (Hons)
Alison Y. Firth
Academic Unit of Ophthalmology and Orthoptics, University of Sheffield, Sheffield
About Alison Y.
MSc DBO(T)
Abstract
Aim: To measure the convergence accommodation to convergence (CA/C) ratio over a range of levels of convergence demand.
Methods: Convergence accommodation was measured in 26 subjects with normal binocular single vision. The CA/C ratio was calculated by measuring the accommodative changes induced with base-out prisms of 5Δ to 20Δ in 5 Δ steps whilst the participant maintained binocular fixation on a pseudo-Gaussian target at 40 cm. Accommodative change was measured using the open-field view Shin-Nippon SRW-5000 autorefractometer [Grand Seiko Company, Fukuyama, Japan].
Results: The mean age of the participants was 20 ± 2.5 years (range 18–29 years). The mean (± SD) CA/C ratio for the 5 Δ, 10 Δ, 15 Δ and 20 Δ prisms was 0.13 (±0.07) D/PD, 0.12 (±0.05) D/PD, 0.13 (±0.05) D/PD and 0.13 (±0.05) D/PD, respectively. The overall mean (±SD) CA/C ratio was 0.13 (±0.04) D/PD (range 0.04–0.20 D/PD). One-factor repeated measures ANOVA found that the CA/C ratio did not change significantly with an increase in convergence (F = 0.202, d.f. = 3, 69, p = 0.8947).
Conclusion: The CA/C ratio did not change significantly with increasing induced vergence. The data suggest that some degree of non-linearity/variation should be expected in the normal, healthy population of the same age group.
How to Cite:
Hirani, K.J. and Firth, A.Y., 2009. Convergence accommodation to convergence (CA/C) ratio: stability with different levels of convergence demand. British and Irish Orthoptic Journal, 6, pp.60–64. DOI: http://doi.org/10.22599/bioj.11
Published on
01 Aug 2009.
Peer Reviewed
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