title: Visual performance after photorefractive keratectomy. A prospective study.
abstract: 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.
  
  
  METHODS
  Prospective cases series.
  
  
  METHODS
  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.
  
  
  METHODS
  Photorefractive keratectomy was performed using a laser (Excimed UV200, Summit Technology, Waltham, Mass) and a polymethylmethacrylate mask; a 5-mm ablation zone was used.
  
  
  METHODS
  Best-corrected high-contrast 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 1 1/2 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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Jules Stein Eye Institute, University of California, Los Angeles, USA.
authors.forename: W
authors.initials: W
authors.lastname: Verdon
authors.forename: M
authors.initials: M
authors.lastname: Bullimore
authors.forename: R K
authors.initials: RK
authors.lastname: Maloney
mesh_terms: D000328:Adult; D001251:Astigmatism / Q000503:physiopathology* / Q000601:surgery; D015331:Cohort Studies; D015350:Contrast Sensitivity / Q000502:physiology; D003315:Cornea / Q000503:physiopathology* / Q000601:surgery; D003318:Corneal Opacity / Q000209:etiology / Q000503:physiopathology; D005260:Female; D019466:Glare; D006801:Humans; D054018:Lasers, Excimer; D008297:Male; D008875:Middle Aged; D009216:Myopia / Q000503:physiopathology* / Q000601:surgery; D018903:Photorefractive Keratectomy; D011183:Postoperative Complications; D011446:Prospective Studies; D011601:Psychophysics; D014792:Visual Acuity / Q000502:physiology*