title: Corneal astigmatic change after photorefractive keratectomy and photoastigmatic refractive keratectomy.
abstract: OBJECTIVE
  To evaluate and compare the efficacy, safety, predictability, and surgically induced astigmatism (SIA) of photorefractive keratectomy (PRK) and photoastigmatic refractive keratectomy (PARK).
  
  
  METHODS
  Department of Ophthalmology, National Taiwan University Hospital, Taipei, Taiwan.
  
  
  METHODS
  In this retrospective study, 70 eyes were treated for myopia and 70 eyes were treated for myopic astigmatism. Refraction, corneal topography, slitlamp findings, and visual acuity in the 2 groups at 1, 3, and 6 months were evaluated and compared. Vector analysis was performed to determine the SIA in both groups.
  
  
  RESULTS
  The mean preoperative spherical equivalent at the glasses plane in the PRK and PARK groups was -6.06 diopters (D) and -7.18 D, respectively. At 6 months, the mean reduction in astigmatism in the PARK group was 61.0%. Predictability was within +/-1.0 D in 85.2% of eyes in the PRK group and 62.5% in the PARK group. An uncorrected visual acuity of 20/40 or better was achieved in 91.8% and 83.9% of eyes, respectively. The mean SIA was 0.64 D in the PRK group, with a general with-the-rule axis shift. The results of vector analysis were more favorable when calculated from refractive values than from Sim-K corneal topography values. The mean astigmatism correction index and index of success calculated from refractive data were 0.75 and 0.38 in the PARK group. The mean magnitude and angle of error were 0.22 +/- 0.52 D and -2.13 +/- 24.41 degrees, respectively.
  
  
  CONCLUSIONS
  Photorefractive keratectomy and PARK were effective and safe procedures for the correction of myopia and myopic astigmatism. However, SIA occurred with spherical myopic treatments. This small SIA may be a confounding factor in low astigmatic treatments.
authors.affiliation: Department of Ophthalmology, National Taiwan University Hospital, Taipei, Taiwan.
authors.forename: Elizabeth P
authors.initials: EP
authors.lastname: Shen
authors.forename: Chia-Ning
authors.initials: CN
authors.lastname: Yang
authors.forename: Fung-Rong
authors.initials: FR
authors.lastname: Hu
mesh_terms: D000328:Adult; D001251:Astigmatism / Q000209:etiology* / Q000503:physiopathology / Q000601:surgery*; D003315:Cornea / Q000473:pathology*; D005260:Female; D006801:Humans; D054018:Lasers, Excimer; D008297:Male; D008875:Middle Aged; D009216:Myopia / Q000601:surgery*; D018903:Photorefractive Keratectomy / Q000009:adverse effects* / Q000379:methods; D012029:Refraction, Ocular; D012189:Retrospective Studies; D012449:Safety; D014792:Visual Acuity