title: Photoastigmatic refractive keratectomy in myopes. Nidek US Investigators Group.
abstract: OBJECTIVE
  Photoastigmatic refractive keratectomy (PARK) was studied in a multi-center clinical trial. The Nidek EC-5000 excimer laser was evaluated for its effect on refraction, visual acuity, and safety measures as part of a U.S. Food and Drug Administration (FDA) regulated study.
  
  
  METHODS
  Eight U.S. centers enrolled adults with eyes having refractive astigmatism up to 4.00 D and a myopic spherical equivalent refraction up to -8.00 D. Results are reported for 749 eyes of 486 patients with at least 6 months follow-up. The rectangular beam scanning Nidek EC-5000 used a 5.5-mm-diameter treatment zone, a 7.0-mm-diameter peripheral blend zone, and a 40 Hz pulse rate for surface treatment of myopic astigmatism. Nomogram corrections to machine settings were required to achieve the desired results.
  
  
  RESULTS
  Preoperative average spherical equivalent refraction of -4.90+/-1.74 D was reduced to -0.02+/-0.79 D at 6 months. Refractive stability was established at 3 months. Over 62% of eyes were within +/-0.50 D of desired correction at 6 months, with over 86% within +/-1.00 D. Uncorrected visual acuity improved by an average of 10 Snellen lines; over 64% of eyes saw 20/20 or better uncorrected and over 93% saw 20/40 or better uncorrected at 6 and 12 months. PARK treatment effectively reduced astigmatism with little average axis error or magnitude error. Corneal haze and safety concerns were minimal.
  
  
  CONCLUSIONS
  Photoastigmatic refractive keratectomy using the Nidek EC-5000 excimer laser provided significant reduction of myopia and astigmatism, with minimal complications.
authors.affiliation: Casey Eye Institute, Oregon Health Sciences University, Portland 97201-4197, USA. macraes@ohsu.edu
authors.forename: S M
authors.initials: SM
authors.lastname: MacRae
authors.forename: J S
authors.initials: JS
authors.lastname: Peterson
authors.forename: D D
authors.initials: DD
authors.lastname: Koch
authors.forename: L F
authors.initials: LF
authors.lastname: Rich
authors.forename: D S
authors.initials: DS
authors.lastname: Durrie
mesh_terms: D000328:Adult; D000368:Aged; D001251:Astigmatism / Q000503:physiopathology / Q000601:surgery*; D003315:Cornea / Q000503:physiopathology / Q000601:surgery*; D005260:Female; D006801:Humans; D054018:Lasers, Excimer; D008297:Male; D008875:Middle Aged; D009216:Myopia / Q000503:physiopathology / Q000601:surgery*; D017060:Patient Satisfaction; D018903:Photorefractive Keratectomy; D012029:Refraction, Ocular; D012449:Safety; D016896:Treatment Outcome; D014792:Visual Acuity