Importance of grating orientation when monitoring contrast sensitivity before and after refractive surgery
Accepted 14 November 2007.
Purpose
To measure losses in contrast sensitivity at different orientations of grating stimuli in refractive surgery patients and show the importance of orientation when higher-order aberrations (HOAs) are altered.
Setting
Manchester Centre for Vision, Manchester Royal Eye Hospital, Manchester, United Kingdom.
Methods
Contrast sensitivity for sine-wave gratings of 12 cycles per degree was measured in 12 patients before and after different types of refractive surgery. Measurements were taken at 4 orientations with small (3.0 mm) and large (dilated) pupils using a binary search procedure. Higher-order aberrations were also measured.
Results
Changes in contrast sensitivity at different orientations were seen in patients before and after the surgery. All patients had significantly higher aberrations after surgery. Patients with increased amounts of postoperative HOAs were more likely to exhibit orientation effects.
Conclusions
When contrast sensitivity is tested with gratings, it is advisable to measure more than 1 orientation. This particularly applies when root-mean-square error values are unusually high, such as in refractive surgery patients.
From the Faculty of Life Sciences (Murray, Ritchie, Bremner, Tahir), University of Manchester, and the Vision Centre (Parry) and Manchester Centre for Vision (Brahma, Ikram), Manchester Royal Eye Hospital, Manchester, United Kingdom
Corresponding author: H.J. Tahir, University of Manchester, Faculty of Life Sciences, Moffat Building, PO Box 88, Sackville Street, Manchester, M60 1QD, United Kingdom.
No author has a financial or proprietary interest in any material or method mentioned.
Mr. Tahir was funded by the British College of Optometrists.
WaveLight Technologie AG provided advice in accessing the raw data from their instrument. Aris Pallikaris provided input into the development of the ideas linking contrast sensitivity to orientation selectivity.
ABSTRACT