Stimulus and response AC/A ratios in an orthoptic student population

Authors

Lucy C. Gratton Academic Unit of Ophthalmology and Orthoptics, University of Sheffield, Sheffield
Alison Y. Firth Academic Unit of Ophthalmology and Orthoptics, University of Sheffield, Sheffield

DOI:

Keywords:

Accommodative convergence/convergence (AC/A) ratio, Lag of accommodation

Abstract

Aim: To measure the stimulus and response AC/A ratios using the distance prism cover test gradient method in young adults without strabismus or ocular abnormality.

Methods: AC/A ratios were measured in a group of orthoptic students. The distance deviation (at 3.8 m) was measured with an alternate prism cover test using a Gulden prism bar with and without -3.00DS lenses. A Shin-Nippon SRW-5000 autorefractor [Grand Seiko Company, Fukuyama, Japan] (open view) was used to measure the refractive state with and without a -3.00DS lens. The stimulus and response AC/A ratios were calculated.

Results: Data were analysed for 16 participants. The mean and standard deviations (SD) of the distance stimulus gradient AC/A ratio were 1.98:1 (1.30) and the mean (SD) distance response gradient AC/A ratio were 2.43:1 (1.60). A paired t-test found a significant difference between the distance response and stimulus gradient AC/A ratio values (t = 3.58, p = 0.003). A Bland-Altman plot suggested that the difference increased as the size of AC/A ratio increased.

Conclusion: The response gradient AC/A ratio when measured using the prism cover test at a distance of 3.8 m was found to be higher than the stimulus AC/A ratio in a group of normal participants who were orthoptic students. This is due to the accommodative lag which normally occurs when viewing through minus lenses.

Author Biographies

Lucy C. Gratton, Academic Unit of Ophthalmology and Orthoptics, University of Sheffield, Sheffield

BMedSci (Hons)
Alison Y. Firth, Academic Unit of Ophthalmology and Orthoptics, University of Sheffield, Sheffield

MSc DBO(T)

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Published

2010-08-01

Issue

Vol. 7 (2010)

Section

Original article

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