title: Comparison of Scheimpflug imaging analysis of pellucid marginal corneal degeneration and keratoconus.
abstract: OBJECTIVE
  To determine and compare various quantitative parameters of pellucid marginal degeneration (PMD) and keratoconus with against-the-rule astigmatism (KC-ARA) obtained by elevation-based Scheimpflug imaging and to identify characteristics that can be used to discriminate PMD from KC-ARA.
  
  
  METHODS
  Ophthalmology Clinic, Ministry of Health Ankara Training and Research Hospital, Ankara, Turkey.
  
  
  METHODS
  Retrospective case-control study.
  
  
  METHODS
  Patients with ARA, a butterfly or crab claw pattern in the curvature maps, a kissing bird pattern in the elevation maps and the bell sign in the pachymetric maps were identified, and 60 eyes of 40 patients were chosen for the evaluation. The patients were divided into two groups: the PMD group (29 eyes of 18 patients) and the KC-ARA group (31 eyes of 22 patients). By moving the cursor manually, the pachymetric maps and Scheimpflug images were searched for a thinner location than the automatically identified thinnest location. The coordinates and thickness of this manually identified location were evaluated.
  
  
  RESULTS
  In the PMD group, 7 (24.1%) eyes did not have any thinner location than the automatically identified thinnest location on the pachymetric maps and the Scheimpflug images, and in 22 (75.8%) eyes, a thinner location, which was located more peripherally, was found by manual evaluation of the pachymetric maps or Scheimpflug images. In 9 (31.0%) eyes of these 22, the manually identified thinnest locations were visible on pachymetric maps, and in 13 (44.8%) eyes the more peripheral thinnest locations were not visible on pachymetric maps but on Scheimpflug images. In the KC group, no patients had thinner locations than the automatically identified thinnest points on the pachymetric maps and the Scheimpflug images.
  
  
  CONCLUSIONS
  A more peripheral thinner location than the automatically identified thinnest location exists in most of the eyes with PMD. In KC-ARA eyes, a thinner location than the automatically found thinnest point does not exist. Accordingly, a more peripheral thinner point than the identified thinnest point is a very strong indication for PMD.
authors.affiliation: Ophthalmology Clinic, Ministry of Health Ankara Training and Research Hospital, Ankara, Turkey.
authors.forename: Yusuf
authors.initials: Y
authors.lastname: Koçluk
authors.forename: Zuleyha
authors.initials: Z
authors.lastname: Yalniz-Akkaya
authors.forename: Ayse
authors.initials: A
authors.lastname: Burcu
authors.forename: Firdevs
authors.initials: F
authors.lastname: Örnek
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D001251:Astigmatism / Q000175:diagnosis; D016022:Case-Control Studies; D003315:Cornea / Q000473:pathology; D003317:Corneal Dystrophies, Hereditary / Q000175:diagnosis*; D003952:Diagnostic Imaging / Q000379:methods*; D003941:Diagnostic Techniques, Ophthalmological / Q000295:instrumentation*; D005260:Female; D006801:Humans; D007640:Keratoconus / Q000175:diagnosis*; D008297:Male; D008875:Middle Aged; D012189:Retrospective Studies; D055815:Young Adult