title: [Corneal topography analysis before and after photorefractive keratectomy].
abstract: OBJECTIVE
  To study the change of corneal surface morphology before and after photorefractive keratectomy (PRK) and analyze the decentralization of the ablation.
  
  
  METHODS
  Corneal topography was examined on 122 eyes of 80 cases with myopia by computer-assisted photokeratography before and after PRK.
  
  
  RESULTS
  Before PRK, the corneal topography of most examined eyes (75.4%) was symmetric bow tie pattern or asymmetric bow tie pattern; after PRK, the corneal topography of the ablated regions was mainly round or approximately round (63.9%). There is no relationship between the distance of decentralization of the ablation site and preoperative refractive diopters. But the more is the distance of decentralization, the more is the increase of postoperative corneal astigmatism and also the more is the decrease of the best corrected visual acuity.
  
  
  CONCLUSIONS
  Examination and analysis on the corneal topography before and after PRK can clearly display the changes of the corneal surface morphology, and also can quantitatively evaluate the decentralization.
authors.affiliation: Department of Ophthalmology, Huanhu Hospital, Tianjin.
authors.forename: S
authors.initials: S
authors.lastname: Zhang
authors.forename: C
authors.initials: C
authors.lastname: Wang
authors.forename: H
authors.initials: H
authors.lastname: Yang
mesh_terms: D000328:Adult; D003315:Cornea / Q000473:pathology; D019781:Corneal Topography; D005500:Follow-Up Studies; D006801:Humans; D007430:Intraoperative Care; D054018:Lasers, Excimer; D008875:Middle Aged; D009216:Myopia / Q000473:pathology* / Q000601:surgery; D018903:Photorefractive Keratectomy