title: Excimer laser photorefractive keratectomy for high myopia: four-year experience with a multiple zone technique.
abstract: OBJECTIVE
  The purpose of the study is to evaluate the results of the authors' 4-year experience with excimer laser photorefractive keratectomy (PRK) and multiple optical zone corneal ablation in highly myopic eyes.
  
  
  METHODS
  The authors retrospectively evaluated 56 eyes of 44 patients (mean refraction, -11.3 diopters [D]; range, -5.75 to -24.5 D) who underwent PRK with a Visx Model 20/20 laser (Visx, Santa Clara, CA). Preoperative visual acuity of 20/40 or better was present in 46 eyes. Corneal ablation was divided into concentric optical zones (4, 5, and 6 mm), allowing corrections of up to 18 D, with a refractive goal of within -1 D from emmetropia in 49 eyes. A hand-held fixation system was always used, and a nitrogen-blowing system (NBS) was used in the first 21 eyes only.
  
  
  RESULTS
  Before retreatment, the range of final cycloplegic refraction from emmetropia in eyes treated with NBS versus not was within +/-1 D in 6 (28.6%) and 15 eyes (44.1%), between -1.25 and -3 D in 5 (23.8%) and 14 eyes (41.1%), and more than -3 D in 10 (47.6%) and 5 eyes (14.7%), respectively. No lines of visual acuity were lost in 37 eyes (80.4%) with 20/40 or better visual acuity before surgery. Three eyes showed vision loss due to worsening of myopic maculopathy and one due to corneal haze. Correction stabilized within 9 months, and at a mean time of 25.6 months, the correction attained was of -8.5 +/- 3.6 D, achieving 90.3% of attempted correction. Eyes with preoperative myopia less than -10 D (n = 27) showed regression less than -1 D in 8 eyes (29.6%), between -1.25 and -3.00 D in 5 eyes (18.5%), and greater than -3.00 D in 1 eye (3.7%); eyes with more than -10 D (n = 29) regressed in 3 (10.3%), 6 (20.7%), and 1 eye (3.4%), respectively. Severe haze was observed in 11 eyes (19.6%) 3 months after surgery. Two eyes showed decentration greater than 1.5 mm. At last examination, night driving problems were reported by 12 (41.4%) of 29 patients evaluated who drive.
  
  
  CONCLUSIONS
  After the NBS was eliminated, the multiple-zone technique achieved a long-term, stable 83.1% reduction of preoperative myopia. Patients with severe myopia appreciated reduction of most of the refractive defect, although perception of halos was noted by 16 patients.
authors.affiliation: Centro di Microchirurgia Ambulatoriale, Monza, Italy.
authors.forename: M
authors.initials: M
authors.lastname: Piovella
authors.forename: F I
authors.initials: FI
authors.lastname: Camesasca
authors.forename: C
authors.initials: C
authors.lastname: Fattori
mesh_terms: D000328:Adult; D003315:Cornea / Q000503:physiopathology / Q000601:surgery*; D003318:Corneal Opacity / Q000503:physiopathology; D005260:Female; D006801:Humans; D054018:Lasers, Excimer; D008297:Male; D008875:Middle Aged; D009216:Myopia / Q000503:physiopathology / Q000601:surgery*; D009584:Nitrogen / Q000008:administration & dosage; D017060:Patient Satisfaction; D018903:Photorefractive Keratectomy / Q000379:methods*; D012029:Refraction, Ocular; D012086:Reoperation; D012189:Retrospective Studies; D016896:Treatment Outcome; D014792:Visual Acuity / Q000502:physiology
chemical_list: D009584:Nitrogen