Visual Performance After Photorefractive KeratectomyA Prospective Study
Wayne Verdon, OD, PhD;
Mark Bullimore, OD, PhD;
Robert K. Maloney, MD, MA (Oxon)
Arch Ophthalmol. 1996;114(12):1465-1472.
Abstract
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Objective
To prospectively examine the effect of excimer laser photorefractive keratectomy (PRK) on best-corrected visual performance using psychophysical tests that were likely to be more sensitive to image degradation than high-contrast Snellen visual acuity.
Design
Prospective cases series.
Patients
A cohort of 18 subjects with an average of -5.08 diopters (D) of myopia (SD=±1.63 D) was tested before PRK and at 3, 6, and 12 months after PRK.
Intervention
Photorefractive keratectomy was performed using a laser (Excimed UV200, Summit Technology, Waltham, Mass) and a polymethylmethacrylate mask; a 5-mm ablation zone was used.
Main Outcome Measures
Best-corrected highcontrast visual acuity, best-corrected low-contrast visual acuity (18% Weber contrast), and best-corrected letter-contrast sensitivity. Measurements were repeated with dilated pupils and in the presence of a glare source.
Results
One year after PRK, the mean best-corrected high-contrast visual acuity was reduced by half a line (P=.01), and the mean best-corrected low-contrast visual acuity was reduced by 11/2 lines (P=.002). The losses were somewhat greater when the subject's pupils were dilated and a glare source was used. The reduction in dilated low-contrast visual acuity was positively correlated with the decentration of the ablation zone (r=0.47), providing evidence of an association between corneal topography and the functional outcome of PRK.
Conclusion
Low-contrast visual acuity losses after PRK are notably greater than high-contrast visual acuity losses for best-corrected vision. Low-contrast visual acuity is a sensitive measure for gauging the outcome success and safety of refractive surgery.
Author Affiliations
From the Jules Stein Eye Institute and the Department of Ophthalmology, University of California, Los Angeles (Drs Verdon and Maloney); and the School of Optometry, University of California, Berkeley (Dr Bullimore).; Dr Verdon is now with the School of Optometry, University of California, Berkeley. Dr Bullimore is now with the College of Optometry, The Ohio State University, Columbus. Dr Verdon has no proprietary interest in the research. Drs Maloney and Bullimore have received occasional honoraria from Summit Technology.
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