title: Astigmatic change 1 year after excimer laser treatment of myopia and myopic astigmatism. Melbourne Excimer Laser Group.
abstract: OBJECTIVE
  To evaluate the surgically induced astigmatism (SIA) 1 year after excimer laser photorefractive astigmatic keratectomy (PARK) and photorefractive keratectomy (PRK).
  
  
  METHODS
  Royal Victorian Ear and Eye Hospital, Melbourne, Australia.
  
  
  METHODS
  This study comprised 333 PARK patients and 155 PRK patients treated with a VISX 20/20 excimer laser and followed prospectively for 12 months. Vector analysis of the change in astigmatism was used to calculate the SIA in the PRK group and the percentage of astigmatism corrected in the PARK group.
  
  
  RESULTS
  Among patients with low cylinders astigmatic correction varied greatly, particularly in those treated for large amounts of myopia. The spherical PRK treatments yielded a mean induced postoperative astigmatism of 0.47 diopter. There was a linear relationship between this inadvertent SIA and increasing myopia.
  
  
  CONCLUSIONS
  Excimer laser surgery for myopia creates a low degree of random, unpredictable SIA that may be the result of irregular epithelial thickening during postoperative healing. This creates a background noise of astigmatic change upon which the targeted astigmatic correction is superimposed.
authors.affiliation: Department of Ophthalmology, University of Melbourne, Australia.
authors.forename: G C
authors.initials: GC
authors.lastname: Tabin
authors.forename: N
authors.initials: N
authors.lastname: Alpins
authors.forename: G F
authors.initials: GF
authors.lastname: Aldred
authors.forename: C A
authors.initials: CA
authors.lastname: McCarty
authors.forename: H R
authors.initials: HR
authors.lastname: Taylor
mesh_terms: D000328:Adult; D000368:Aged; D001251:Astigmatism / Q000503:physiopathology* / Q000601:surgery*; D003315:Cornea / Q000503:physiopathology / Q000601:surgery*; D005260:Female; D006801:Humans; D054018:Lasers, Excimer; D008297:Male; D008875:Middle Aged; D009216:Myopia / Q000503:physiopathology / Q000601:surgery*; D018903:Photorefractive Keratectomy; D011446:Prospective Studies; D012029:Refraction, Ocular; D016896:Treatment Outcome; D014792:Visual Acuity