title: Changes in posterior corneal elevations after combined transepithelial photorefractive keratectomy and accelerated corneal collagen cross-linking: retrospective, comparative observational case series.
abstract: BACKGROUND
  To compare the changes in anterior and posterior corneal elevations after combined transepithelial photorefractive keratectomy (PRK) and accelerated corneal collagen cross-linking (CXL) and after PRK.
  
  
  METHODS
  Medical records of 82 eyes of 44 patients undergoing either combined transepithelial PRK and CXL (PRK-CXL group) or transepithelial PRK (PRK group) were examined retrospectively. Changes in anterior and posterior corneal elevations were calculated by fitting an 8.0-mm diameter best-fit sphere and best-fit toric ellipsoid (BFTE) to the corneal shape with a fixed eccentricity of 0.4 using Scheimpflug tomography (Pentacam HR; Oculus Optikgeräte GmbH, Wetzlar, Germany) preoperatively and 6 months postoperatively.
  
  
  RESULTS
  In anterior corneal elevation, both groups demonstrated a similar trend of a forward displacement of peripheral anterior corneal surface and a backward displacement of central anterior corneal surface. In posterior corneal elevation, a forward displacement of peripheral posterior corneal surface was induced in both groups, along with a backward displacement of central posterior corneal surface, regardless of the calculation method. The magnitudes of displacement of peripheral and central posterior corneal surfaces were significantly smaller in the PRK-CXL group than in the PRK group. Moreover, the PRK-CXL group showed a backward displacement of posterior corneal surface at maximum corneal elevations when the BFTE was used as the reference surface.
  
  
  CONCLUSIONS
  Transepithelial PRK combined with prophylactic CXL significantly reduced the magnitudes of displacement of peripheral and central posterior corneal surfaces, with the radius of the BFTE was set to 8.0-mm on the Scheimpflug tomography system.
authors: Department of Ophthalmology, International St. Mary's Hospital, Catholic Kwandong University College of Medicine, Incheon, South Korea.|The Institute of Vision Research, Department of Ophthalmology, Yonsei University College of Medicine, Seoul, South Korea.
authors: Hun
authors: H
authors: Lee
authors: Eyereum Eye Clinic, Seoul, South Korea.
authors: David Sung Yong
authors: DS
authors: Kang
authors: Eyereum Eye Clinic, Seoul, South Korea.
authors: Byoung Jin
authors: BJ
authors: Ha
authors: Eyereum Eye Clinic, Seoul, South Korea.
authors: Jin Young
authors: JY
authors: Choi
authors: The Institute of Vision Research, Department of Ophthalmology, Yonsei University College of Medicine, Seoul, South Korea.|Corneal Dystrophy Research Institute, Department of Ophthalmology, Yonsei University College of Medicine, Seoul, South Korea.
authors: Eung Kweon
authors: EK
authors: Kim
authors: The Institute of Vision Research, Department of Ophthalmology, Yonsei University College of Medicine, Seoul, South Korea.
authors: Kyoung Yul
authors: KY
authors: Seo
authors: The Institute of Vision Research, Department of Ophthalmology, Yonsei University College of Medicine, Seoul, South Korea. tikim@yuhs.ac.
authors: Tae-Im
authors: TI
authors: Kim
mesh_terms: D000328:Adult; D003094:Collagen / Q000378:metabolism; D003131:Combined Modality Therapy; D003315:Cornea / Q000473:pathology*; D003319:Corneal Stroma / Q000378:metabolism; D019781:Corneal Topography; D003432:Cross-Linking Reagents / Q000627:therapeutic use*; D019573:Epithelium, Corneal / Q000601:surgery; D005260:Female; D006801:Humans; D008297:Male; D009216:Myopia / Q000601:surgery*; D010778:Photochemotherapy; D018903:Photorefractive Keratectomy / Q000009:adverse effects / Q000379:methods; D017319:Photosensitizing Agents / Q000627:therapeutic use; D011183:Postoperative Complications; D012189:Retrospective Studies; D014057:Tomography, X-Ray Computed; D055815:Young Adult
chemical_list: D003432:Cross-Linking Reagents; D017319:Photosensitizing Agents; D003094:Collagen
keywords: Accelerated corneal collagen cross-linking; Best-fit toric ellipsoid; Posterior corneal elevations; Scheimpflug tomography; Transepithelial photorefractive keratectomy