title: The effects of ablation diameter on the outcome of excimer laser photorefractive keratectomy. A prospective, randomized, double-blind study.
abstract: OBJECTIVE
  To determine the effects of the ablation diameter on the outcome of excimer laser photorefractive keratectomy.
  
  
  METHODS
  Eighty patients were randomized to either a 5.00-mm or a 6.00-mm treatment group and within these groups underwent either a -3.00-diopter (D) or a -6.00-D correction based on their preoperative refraction. A Summit Omnimed excimer laser was used throughout the study.
  
  
  RESULTS
  In eyes treated with a 6.00-mm-diameter ablation, the initial hyperopic shift was reduced, with significant differences at 1 week with -3.00-D corrections and at 1 and 4 weeks with -6.00-D corrections (P < .01). At 6 months, the refractive changes were greater and closer to that intended with 6.00-mm-diameter ablations. The predictability of photorefractive keratectomy was significantly improved with 6.00-mm zones, with a reduction in variance of the refractive changes at all stages postoperatively (P < .05 to P < .001). With -3.00-D corrections, objective measurements showed significantly less anterior stromal haze in eyes treated with 6.00-mm zones at 6 months (P < .05). With -6.00-D corrections, haze was significantly reduced at 1, 3, and 6 months in the eyes treated with 6.00-mm zones (P < .05). Five eyes treated with 5.00-mm zones experienced severe regression of the correction, with marked corneal haze and a reduction of 3 or more lines of best corrected Snellen visual acuity at 6 months. No eyes treated with 6.00-mm zones were similarly affected. Computerized measurements of "night" halo were significantly lower in the 6.00-mm treatment groups at 1 week and at 1 and 6 months in the eyes with -3.00-D corrections and at 1 week and at 1 month in the eyes with -6.00-D corrections (P < .05). At 6 months, seven patients treated with 5.00-mm zones complained of severe disturbances of night vision. No eyes in the 6.00-mm group were similarly affected.
  
  
  CONCLUSIONS
  Treatment with 6.00-mm ablation diameters precipitated less initial overcorrection, greatly improved the predictability of photorefractive keratectomy, and was associated with a reduction in complications impairing postoperative visual performance.
authors.affiliation: Department of Ophthalmology, St Thomas' Hospital, London, England.
authors.forename: D P
authors.initials: DP
authors.lastname: O'Brart
authors.forename: M C
authors.initials: MC
authors.lastname: Corbett
authors.forename: C P
authors.initials: CP
authors.lastname: Lohmann
authors.forename: M G
authors.initials: MG
authors.lastname: Kerr Muir
authors.forename: J
authors.initials: J
authors.lastname: Marshall
mesh_terms: D000328:Adult; D003315:Cornea / Q000502:physiology / Q000601:surgery*; D003318:Corneal Opacity / Q000503:physiopathology; D004311:Double-Blind Method; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted; D053685:Laser Therapy / Q000379:methods; D008297:Male; D008875:Middle Aged; D009216:Myopia / Q000503:physiopathology / Q000601:surgery*; D011183:Postoperative Complications; D011446:Prospective Studies; D012029:Refraction, Ocular; D016896:Treatment Outcome; D014785:Vision, Ocular / Q000502:physiology