title: [Quantitative assessment of topographical parameters to differentiate keratoconus from pellucid marginal corneal degeneration and ].
abstract: BACKGROUND
  The purpose is to compare videokeratometric data (Fourier series harmonic analysis and wave-front analysis) in eyes with ectatic corneal disease (keratoconus; pellucid marginal corneal degeneration [PMCD]) and to determine parameters for early diagnosis and distinction of keratoconus and PMCD.
  
  
  METHODS
  13 eyes with PMCD, 32 eyes with keratoconus and 18 healthy eyes were included. Computerized videokeratographic methods were assessed, using Fourier series harmonic analysis, Zernike coefficients and eccentricity.
  
  
  RESULTS
  Irregular astigmatism (Fourier series harmonic analysis: decentration and/or irregularity) and the aberration coefficient were out of the normal range in all pathologic eyes. Both the nasal and the temporal eccentricities were greater than 0.63 in all PMCD patients, whereas either the superior or the inferior eccentricity was negative in all patients. In keraotoconic eyes, all quadrant eccentricities were positive and greater than 0.4.
  
  
  CONCLUSIONS
  Irregular astigmatism and the aberration coefficient are useful parameters in detecting ectatic corneal disease using a computerized videokeratoscope. The calculation of the spherical equivalent (Fourier series harmonic analysis: no decrease of spherical equivalent in PMCD subjects) and of quadrant eccentricities are useful tools in distinguishing PMCD and keratoconus.
authors.affiliation: Universitätsaugenklinik mit Poliklinik der Martin-Luther-Universität Halle-Wittenberg. claudia.gruenauer-kloevekorn@medizin.uni-halle.de
authors.forename: C
authors.initials: C
authors.lastname: Grünauer-Kloevekorn
authors.forename: U
authors.initials: U
authors.lastname: Kloevekorn-Fischer
authors.forename: K
authors.initials: K
authors.lastname: Kloevekorn-Norgall
authors.forename: G I
authors.initials: GI
authors.lastname: Duncker
mesh_terms: D002675:Child, Preschool; D003317:Corneal Dystrophies, Hereditary / Q000473:pathology*; D019781:Corneal Topography / Q000379:methods*; D003937:Diagnosis, Differential; D005260:Female; D006801:Humans; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D007640:Keratoconus / Q000473:pathology*; D008297:Male; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D012720:Severity of Illness Index