title: Determining corneal power using Pentacam after myopic photorefractive keratectomy.
abstract: OBJECTIVE
  To assess the accuracy of Pentacam Scheimpflug camera for corneal power measurement in eyes with previous photorefractive keratectomy for myopia.
  
  
  METHODS
  In this comparative interventional case series, 35 eyes of 35 patients who had myopic photorefractive keratectomy were studied. Corneal power was measured by conventional topography and Pentacam Scheimpflug camera, and equivalent keratometry readings (EKR) in different central corneal rings (0.5 to 4.5 mm), true net power and simulated keratometry (K) measurements as well as those obtained using Shammas no-history, Koch-Maloney and Haigis methods were compared with clinical history method.
  
  
  RESULTS
  All corneal power measurements except for the topography simulated K and true net power values were statistically similar to the clinical history values. Simulated keratometry and 4.5-mm EKR values were more closely correlated with clinical history method. Shammas formula, Pentacam simulated K and 3-, 4- and 4.5-mm EKR provided a 95% confidence interval within +/-0.50 D of the mean clinical history method value, among these, the width of the 95% limits of agreement (LoA) was narrower for Shammas and Pentacam simulated K and 4.5-mm EKR values; however, considerably large 95% LoA were found between each of these values and those obtained with the clinical history method. Estimated preoperative keratometry was statistically similar to the preoperative measurement; however, estimated refractive change was different from actual value.
  
  
  CONCLUSIONS
  The Pentacam 4.5-mm EKR and simulated keratometry may be used as an alternative to clinical history method to predict corneal power when pre-keratorefractive surgery data are unavailable; however, wide LoA should be considered in the calculations.
authors.affiliation: Eye Research Center, Iran University of Medical Sciences, Rassoul Akram Hospital, Sattarkhan-Niayesh Street, Tehran, Iran. drghasemi@yahoo.com
authors.forename: Khalil Ghasemi
authors.initials: KG
authors.lastname: Falavarjani
authors.forename: Masih
authors.initials: M
authors.lastname: Hashemi
authors.forename: Mahmoud
authors.initials: M
authors.lastname: Joshaghani
authors.forename: Pejvak
authors.initials: P
authors.lastname: Azadi
authors.forename: Mohammad J
authors.initials: MJ
authors.lastname: Ghaempanah
authors.forename: Gholam H
authors.initials: GH
authors.lastname: Aghai
mesh_terms: D003198:Computer Simulation; D003315:Cornea / Q000473:pathology / Q000503:physiopathology*; D019781:Corneal Topography; D003941:Diagnostic Techniques, Ophthalmological; D006801:Humans; D009216:Myopia / Q000503:physiopathology* / Q000601:surgery*; D010781:Photography / Q000295:instrumentation*; D018903:Photorefractive Keratectomy; D011184:Postoperative Period; D012029:Refraction, Ocular