title: Twenty-year follow-up of a randomized prospective clinical trial of excimer laser photorefractive keratectomy.
abstract: OBJECTIVE
  To investigate the 20-year efficacy and safety of photorefractive keratectomy (PRK).
  
  
  METHODS
  Long-term observational case series.
  
  
  METHODS
  In the setting of a university hospital, a study population of 42 patients (42 eyes) who had, as part of a randomized prospective trial, undergone PRK 20 years previously were studied. All had received -3.0 or -6.0 diopter (D) corrections with either 5.0 or 6.0 mm optical zones or a multizone treatment. The mean preoperative spherical equivalent refractive error (SEQ) was -5.13 D (range, -2.75 to -8.0 D). The outcome measures included visual acuity, refractive error, corneal topography and axial length.
  
  
  RESULTS
  Between 1 and 20 years there was an increase in mean myopic SEQ of -0.54 D (P < 0.02). In patients younger than 40 years of age at time of correction, this increase was -0.92 D (P < 0.002) with an accompanying increase in variance (P < 0.02), whereas in those older than 40 it was -0.08D (P = 0.8). In female patients the change was -0.69D (P < 0.01), while in males it was -0.26D (P = 0.6). The efficacy index at 20 years was 0.49, and the safety index was 0.97. Corrected distance visual acuity improved between 1 and 20 years (P < 0.01); 93% of corneas were clear at 20 years; 3 eyes had trace haze. There was an improvement in haze scores between 1 and 20 years (P < 0.02). Cornea power remained unchanged between 6 months and 20 years (P = 0.4). Axial length increased by a mean of 0.84 mm (P < 0.0001). There was no ectasia.
  
  
  CONCLUSIONS
  There was a slight but significant increase in myopic SEQ after PRK between 1 and 20 years, particularly in those under 40 at the time of treatment and in female patients. Corneal power remained unchanged, but axial length increased. The procedure was safe, with no long-term sight-threatening complications and with improvements in corrected distance visual acuity and corneal transparency with time.
authors: Keratoconus Research Institute, Department of Ophthalmology, St. Thomas' Hospital, London, United Kingdom. Electronic address: davidobrart@aol.com.
authors: David P S
authors: DP
authors: O'Brart
authors: Keratoconus Research Institute, Department of Ophthalmology, St. Thomas' Hospital, London, United Kingdom.
authors: Zaid
authors: Z
authors: Shalchi
authors: Keratoconus Research Institute, Department of Ophthalmology, St. Thomas' Hospital, London, United Kingdom.
authors: Robert J
authors: RJ
authors: McDonald
authors: Keratoconus Research Institute, Department of Ophthalmology, St. Thomas' Hospital, London, United Kingdom.
authors: Parul
authors: P
authors: Patel
authors: London Vision Clinic, London, United Kingdom.
authors: Timothy J
authors: TJ
authors: Archer
authors: Moorfields Biomedical Research Centre, University College, London Institute of Ophthalmology, London, United Kingdom.
authors: John
authors: J
authors: Marshall
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D058452:Axial Length, Eye / Q000503:physiopathology; D003315:Cornea / Q000503:physiopathology / Q000601:surgery; D019781:Corneal Topography; D004311:Double-Blind Method; D005500:Follow-Up Studies; D054018:Lasers, Excimer / Q000627:therapeutic use; D009216:Myopia / Q000503:physiopathology / Q000601:surgery; D018903:Photorefractive Keratectomy / Q000379:methods; D011183:Postoperative Complications; D011446:Prospective Studies; D012030:Refractive Errors / Q000503:physiopathology; D016896:Treatment Outcome; D014792:Visual Acuity / Q000502:physiology