title: Corneal optical irregularity after excimer laser photorefractive keratectomy. The Summit Photorefractive Keratectomy Topography Study Group.
abstract: OBJECTIVE
  To assess the influence of corneal surface microirregularities on objective and subjective visual performance after photorefractive keratectomy (PRK).
  
  
  METHODS
  Multicenter clinical trial.
  
  
  METHODS
  The alpha version of the Potential Corneal Acuity (PCA) computer program, currently under development, was used to qualitatively and quantitatively analyze the corneal surface of 176 eyes of 176 patients 1 year after PRK. Color maps of corneal surface irregularities were reviewed and quantitative values (PCA) predicting best spectacle-corrected visual acuity (BSCVA) as limited by the cornea were evaluated for associations with qualitative topography patterns, optical zone decentration, and clinical outcomes of BSCVA, uncorrected visual acuity (UCVA), subjective patient satisfaction, and a subjective glare/halo index.
  
  
  RESULTS
  Qualitatively, corneas after PRK were generally characterized by a ring of optical irregularity at the juncture of the ablation zone and untreated cornea. Standard corneal topography maps graded as irregular after PRK had a significantly higher PCA value than those graded as regular. There was a trend toward higher PCA values with greater optical zone decentration that was not statistically significant. Actual BSCVA was identical to that which the PCA value predicted in 32% of patients and was within one Snellen line in 71%, within two lines in 89%, and within three lines in 94%. The correlation between the PCA and the glare/halo index and with subjective patient satisfaction was statistically significant. The relationship between PCA and UCVA was not significant.
  
  
  CONCLUSIONS
  A ring of optical microirregularity of the corneal surface can appear at the juncture of the treated and untreated cornea after PRK, indicating that the optical zone edge might affect objective and subjective postoperative visual outcomes. Further understanding of corneal surface topography and refinement of the PCA program should help explain visual outcome after PRK.
authors.affiliation: Department of Ophthalmology, UMDNJ-New Jersey Medical School, Newark 07103, USA.
authors.forename: P S
authors.initials: PS
authors.lastname: Hersh
authors.forename: S I
authors.initials: SI
authors.lastname: Shah
authors.forename: D
authors.initials: D
authors.lastname: Geiger
authors.forename: J T
authors.initials: JT
authors.lastname: Holladay
mesh_terms: D000328:Adult; D003315:Cornea / Q000473:pathology / Q000601:surgery*; D003316:Corneal Diseases / Q000209:etiology* / Q000473:pathology; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted; D054018:Lasers, Excimer; D008027:Light; D008297:Male; D008875:Middle Aged; D009216:Myopia / Q000601:surgery*; D018903:Photorefractive Keratectomy / Q000009:adverse effects*; D011183:Postoperative Complications; D012542:Scattering, Radiation; D014786:Vision Disorders / Q000209:etiology* / Q000473:pathology; D014792:Visual Acuity