title: Excimer laser correction of astigmatism with multipass/multizone treatment. The Melbourne Excimer Laser Group.
abstract: OBJECTIVE
  To evaluate the accuracy of excimer laser correction of myopic astigmatism by multipass/multizone photoastigmatic refractive keratectomy (PARK).
  
  
  METHODS
  Tertiary referral ophthalmic hospital with an associated private laser facility.
  
  
  METHODS
  This study comprised a consecutive series of 332 eyes of 289 patients who were followed for 6 months. All patients were 18 years or older, had stable myopic astigmatism (up to a -19.0 diopters [D] spherical equivalent [SE] at the spectacle plane), and had a best corrected visual acuity of at least 20/60 in both eyes. All eyes were treated with a VISX Twenty-Twenty excimer laser. The correction was divided between ablation zones using a multipass/multizone treatment paradigm based on the amount of myopia and astigmatism. Patients were examined 1 week, and 1, 3, and 6 months after surgery.
  
  
  RESULTS
  Analysis of the mean percentage of spherical correction across the range of myopic preoperative SEs treated demonstrated 90% correction for most amounts of myopic astigmatism. Eyes with low myopia (mean preoperative SE < or = -5.0 D) treated with < or = -1.0 diopter cylinder (DC) of astigmatism achieved a mean percentage of spherical correction of 91% versus 93% in eyes with high myopia (> -5.0 D mean preoperative SE). Eyes with low myopia treated with > -1.0 DC of astigmatism achieved a mean percentage spherical correction of 90% versus 89% in eyes with high myopia. The differences between the two groups were not statistically significant. Patients with high relative cylinder (> 80% of total sphere treated) achieved comparable results. Analysis of the astigmatic component of the treatment, independent of the spherical result, showed a trend toward overcorrection in the high myopia group with less than -1.0 DC and a mean astigmatic correction of 89 and 98%, respectively, in the low and high myopic astigmatism groups. The mean angle of error was +2.0 degrees.
  
  
  CONCLUSIONS
  Multipass/multizone PARK for myopic astigmatism demonstrated a high degree of predictability and stability with desirable results for low and high levels of astigmatism across the range of myopic astigmatism treated by surface ablation.
authors.affiliation: Melbourne University Department of Ophthalmology, Royal Victorian Eye and Ear Hospital, Victoria, Australia.
authors.forename: S
authors.initials: S
authors.lastname: Brodovsky
authors.forename: T
authors.initials: T
authors.lastname: Couper
authors.forename: N A
authors.initials: NA
authors.lastname: Alpins
authors.forename: C A
authors.initials: CA
authors.lastname: McCarty
authors.forename: H R
authors.initials: HR
authors.lastname: Taylor
mesh_terms: D000328:Adult; D001251:Astigmatism / Q000601:surgery*; D003315:Cornea / Q000601:surgery*; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D054018:Lasers, Excimer; D008297:Male; D009216:Myopia / Q000601:surgery; D018903:Photorefractive Keratectomy / Q000379:methods*; D015203:Reproducibility of Results; D016896:Treatment Outcome; D014792:Visual Acuity