title: Effects of ablation diameter on long-term refractive stability and corneal transparency after photorefractive keratectomy.
abstract: OBJECTIVE
  To evaluate the effects of ablation diameter on long-term refractive stability and corneal transparency after photorefractive keratectomy (PRK).
  
  
  METHODS
  Long-term, prospective, follow-up study.
  
  
  METHODS
  One hundred twenty-three eyes treated between 1990 and 1993 at one institution as part of a number of ethical committee-approved clinical studies underwent long-term follow-up at 10 to 12 years after PRK.
  
  
  METHODS
  Photorefractive keratectomy was performed using the Summit Technology UV 200 and OmniMed Excimer lasers with either 4.0-mm (n = 36), 5.0-mm (n = 47), or 6.0-mm (n = 40) optical zones and either -3.0-diopters (D) or -6.0-D myopic spherical corrections, based on the original Munnerlyn algorithms.
  
  
  METHODS
  Refractive stability, refractive predictability, best spectacle-corrected visual acuity, and corneal haze.
  
  
  RESULTS
  Refractive outcome at 1 and 10 to 12 years of follow-up was better with 6.0-mm treatments, especially for -6.0-D corrections (P>0.001). The early hyperopic shift was significantly reduced with 6.0-mm zones, with less regression between 1 and 6 months, compared with 5.0- and 4.00-mm PRK, especially for -6.0-D corrections (P<0.001). The postoperative refraction remained stable between 1 and 10 to 12 years in all groups. Objective measurements of haze were less with 6.0-mm compared with 4.0- and 5.0-mm treatments (P<0.001). Night vision problems were significantly less with 6.0-mm PRK (P<0.01). There was no evidence of progressive hyperopic shift, corneal ectasia, or late onset of corneal haze in any of the eyes during the follow-up period.
  
  
  CONCLUSIONS
  Refractive stability was maintained between 1 year and 10 to 12 years after PRK with 4.0-, 5.0-, and 6.0-mm optical zones. A significant linear trend was observed in terms of refractive predictability, early hyperopic shift, regression, corneal transparency, and night haloes with better outcomes in PRK with a larger ablation zone. None of the eyes had sight-threatening complications such as ectasia or late-onset corneal haze during the follow-up.
authors.affiliation: Department of Academic Ophthalmology, St. Thomas' Hospital, London, United Kingdom. msrajan@tiscali.co.uk
authors.forename: Madhavan S
authors.initials: MS
authors.lastname: Rajan
authors.forename: David
authors.initials: D
authors.lastname: O'Brart
authors.forename: Philip
authors.initials: P
authors.lastname: Jaycock
authors.forename: John
authors.initials: J
authors.lastname: Marshall
mesh_terms: D003315:Cornea / Q000503:physiopathology / Q000601:surgery*; D019781:Corneal Topography; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D054018:Lasers, Excimer; D008297:Male; D008875:Middle Aged; D009216:Myopia / Q000503:physiopathology / Q000601:surgery*; D018903:Photorefractive Keratectomy / Q000379:methods*; D011446:Prospective Studies; D012029:Refraction, Ocular / Q000502:physiology*; D016896:Treatment Outcome; D014786:Vision Disorders / Q000503:physiopathology; D014792:Visual Acuity / Q000502:physiology*