title: Effect of Photorefractive Keratectomy on Optic Nerve Head Topography and Retinal Nerve Fiber Layer Thickness Measured by Heidelberg Retina Tomograph 3.
abstract: OBJECTIVE
  To determine whether photorefractive keratectomy (PRK) has a significant effect on optic nerve head (ONH) parameters and peripapillary retinal nerve fiber layer (RNFL) thickness measured by the Heidelberg Retina Tomograph 3 (Heidelberg Engineering GmbH, Heidelberg, Germany) in eyes with low to moderate myopia.
  
  
  METHODS
  This prospective, interventional case series, includes 43 consecutive myopic eyes which were assessed on the day of PRK and 3 months postoperatively using the HRT3. Among the stereometric parameters, we compared disc area, linear cup disc ratio, cup shape measure, global rim area, global rim volume, RNFL height variation contour and mean RNFL thickness; out of the Glaucoma Probability Score (GPS) we assessed changes in global value, rim steepness temporal/superior, and temporal/inferior, as well as cup size and cup depth before and after PRK.
  
  
  RESULTS
  Mean refractive error before and after PRK were -3.24 ± 1.31 and -0.20 ± 0.42 diopters, respectively. No significant change occurred in disc area, linear cup disc ratio, cup shape measure, rim area and rim volume among the stereometric parameters; and in rim steepness temporal/superior and rim steepness temporal/inferior in the GPS before and after PRK using the default average keratometry. However, RNFL height variation contour, mean RNFL thickness, and cup size and depth were significantly altered after PRK (P < 0.05).
  
  
  CONCLUSIONS
  PRK can affect some HRT3 parameters. Although the most important stereometric parameters for differentiating normal, suspect or glaucomatous patients such as rim and cup measurements in stereometric parameters were not changed.
authors.affiliation: Department of Ophthalmology, Eye Research Center, Rassoul Akram Hospital, Iran University of Medical Sciences, Tehran, Iran.
authors.forename: Naveed
authors.initials: N
authors.lastname: Nilforushan
authors.affiliation: Eye Research Center, Farabi Eye Hospital, Tehran University of Medical Sciences, Tehran, Iran.
authors.forename: Pejvak
authors.initials: P
authors.lastname: Azadi
authors.affiliation: Department of Ophthalmology, Eye Research Center, Rassoul Akram Hospital, Iran University of Medical Sciences, Tehran, Iran.
authors.forename: Reza
authors.initials: R
authors.lastname: Soudi
authors.affiliation: Department of Ophthalmology, Eye Research Center, Rassoul Akram Hospital, Iran University of Medical Sciences, Tehran, Iran.
authors.forename: Yahya
authors.initials: Y
authors.lastname: Shaheen
authors.affiliation: Basir Eye Health Research Center, Basir Eye Clinic, Tehran, Iran.
authors.forename: Kourosh
authors.initials: K
authors.lastname: Sheibani
keywords: Glaucoma; Heidelberg Retina Tomograph; Myopia; Photorefractive Keratectomy