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

Gratton , L.C. and Firth, A.Y. (2010) Stimulus and response AC/A ratios in an orthoptic student population. British and Irish Orthoptic Journal, 7. pp. 41-44. ISSN 1743-9868

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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 3.8m) was measured with an alternate prism cover test using a Gulden prism bar with and without -3.00DS lenses. A Shin-Nippon SRW-5000 auto-refractor [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). 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 3.8m was found to be higher than the stimulus AC/A ratio in a group of normal participants who were Orthoptic students. This is due the accommodative lag which normally occurs when viewing through minus lenses.

Item Type: Article
Copyright, Publisher and Additional Information: British and Irish Orthoptic Society
Keywords: Accommodative convergence / convergence (AC/A) ratio, lag of accommodation
Institution: The University of Sheffield
Academic Units: The University of Sheffield > Faculty of Medicine, Dentistry and Health (Sheffield) > School of Medicine (Sheffield) > Clinical Sciences Division North (Sheffield) > Department of Medicine (Sheffield)
Depositing User: Miss Alison Y Firth
Date Deposited: 06 Apr 2011 17:10
Last Modified: 19 Sep 2014 03:35
Status: Published
Publisher: British and Irish Orthoptic Society
Refereed: Yes
URI: http://eprints.whiterose.ac.uk/id/eprint/42926

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