title: Three multizone photorefractive keratectomy algorithms for myopia. The Melbourne Excimer Laser Group.
abstract: OBJECTIVE
  To compare the efficacy and complications of three different excimer laser algorithms for multizone photorefractive and photoastigmatic keratectomy.
  
  
  METHODS
  Three different software algorithms were applied to treat myopia and myopic astigmatism with the VISX 20/20 excimer laser. Each algorithm had a maximum ablation zone of 6 mm but differed in the number of zones employed, the proportion of the total treatment allocated to each ablation zone, and the treatment of astigmatism. The Melbourne multizone technique equally divided myopia correction into a maximum of three ablation zones. The Pop multizone technique biased myopia treatment into the smaller diameter zones to a maximum of six ablation zones, with one central island pretreatment. The Alpins multizone technique equally divided myopia treatment through all zones up to a maximum of six, with one central island pretreatment.
  
  
  RESULTS
  A total of 585 patients (780 eyes) were treated and 625 eyes (80%) were followed for more than 6 months. The mean baseline spherical equivalent refractive error was -5.63 D (-1.00 to -19.50 D). Between 71 and 79% of eyes were treated for astigmatism. There was no statistically significant differences in baseline refractive error or other characteristics among the three groups. At 6 months, the Alpins multizone algorithm had more eyes with a refractive error within +/- 1.00 D of emmetropia (p = 0.01) and more within +/- 2.00 D of emmetropia (p < 0.01). This new algorithm produced more eyes with an uncorrected visual acuity of 20/20 or better at 6 months (p < 0.01). When multiple logistic regression was used to correct for any differences in baseline myopia among the three groups, this algorithm also had a higher odds ratio for achieving 20/20 or better uncorrected visual acuity (OR = 1.58).
  
  
  CONCLUSIONS
  At 6 months, all three algorithms were effective in the reduction of myopia. Significantly better visual acuity and refractive results were achieved with the Alpins multizone algorithm that spread the total treatment over a larger number of ablation zones, with an equal number of diopters of treatment in each zone.
authors.affiliation: Melbourne Excimer Laser Group, Australia.
authors.forename: N A
authors.initials: NA
authors.lastname: Alpins
authors.forename: H R
authors.initials: HR
authors.lastname: Taylor
authors.forename: D G
authors.initials: DG
authors.lastname: Kent
authors.forename: Y
authors.initials: Y
authors.lastname: Lu
authors.forename: M
authors.initials: M
authors.lastname: Liew
authors.forename: T
authors.initials: T
authors.lastname: Couper
authors.forename: V
authors.initials: V
authors.lastname: McGough
mesh_terms: D000293:Adolescent; D000465:Algorithms; D001251:Astigmatism / Q000601:surgery; D003315:Cornea / Q000601:surgery*; D005500:Follow-Up Studies; D006801:Humans; D054018:Lasers, Excimer; D009216:Myopia / Q000601:surgery*; D018903:Photorefractive Keratectomy; D012029:Refraction, Ocular; D012044:Regression Analysis; D012189:Retrospective Studies; D016896:Treatment Outcome; D014792:Visual Acuity