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.
Prospective cases series.
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.
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.
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.
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.
Verdon W, Bullimore M, Maloney RK. Visual Performance After Photorefractive Keratectomy: A Prospective Study. Arch Ophthalmol. 1996;114(12):1465–1472. doi:10.1001/archopht.1996.01100140663003
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