Importance of grating orientation when monitoring contrast sensitivity before and after refractive surgery.

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.