Visual acuity with astigmatic blur

Atchison, David A. & Mathur, Ankit (2011) Visual acuity with astigmatic blur. Optometry and Vision Science, 88(7), E798-E805.

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Abstract Purpose: To determine how high and low contrast visual acuities are affected by blur caused by crossed-cylinder lenses.

Method: Crossed-cylinder lenses of power zero (no added lens), +0.12 DS/-0.25 DC, +0.25 DS/-0.50 DC and +0.37/-0.75 DC were placed over the correcting lenses of the right eyes of eight subjects. Negative cylinder axes used were 15-180 degrees in 15 degree step for the two higher crossed-cylinders and 30-180 degrees in 30 degree steps for the lowest crossed cylinder. Targets were single lines of letters based on the Bailey-Lovie chart. Successively smaller lines were read until the subject could not read any of the letters correctly. Two contrasts were used: high (100%) and low (10%). The screen luminance of 100 cd/m2, together with the room lighting, gave pupil sizes of 4.5 to 6 mm.

Results: High contrast visual acuities were better than low contrast visual acuities by 0.1 to 0.2 log unit (1 to 2 chart lines) for the no added lens condition. Based on comparing the average of visual acuities for the 0.75 D crossed-cylinder with the best visual acuity for a given contrast and subject, the rates of change of visual acuity per unit blur strength were similar for high contrast (0.34± 0.05 logMAR/D) and low contrast (0.37± 0.09 logMAR/D). There were considerable asymmetry effects, with the average loss in visual acuity across the two contrasts and the 0.50D/0.75 D crossed-cylinders doubling between the 165± and 60± negative cylinder axes. The loss of visual acuity with 0.75 D crossed-cylinders was approximately twice times that occurring for defocus of the same blur strength.

Conclusion: Small levels of crossed-cylinder blur (≤0.75D) produce losses in visual acuity that are dependent on the cylinder axis. 0.75 D crossed-cylinders produce losses in visual acuity that are twice those produced by defocus of the same blur strength.

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14 citations in Scopus
13 citations in Web of Science®
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ID Code: 49202
Item Type: Journal Article
Refereed: Yes
Keywords: contrast, visual acuity, crossed-cylinder astigmatism
DOI: 10.1097/OPX.0b013e3182186bc4
ISSN: 1040-5488
Subjects: Australian and New Zealand Standard Research Classification > MEDICAL AND HEALTH SCIENCES (110000)
Divisions: Current > QUT Faculties and Divisions > Faculty of Health
Current > Institutes > Institute of Health and Biomedical Innovation
Current > Schools > School of Optometry & Vision Science
Copyright Owner: Copyright 2011
Deposited On: 19 Mar 2012 23:11
Last Modified: 01 Aug 2014 11:07

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