title: Clinical validation of point-source corneal topography in keratoplasty.
abstract: OBJECTIVE
  To validate the clinical performance of point-source corneal topography (PCT) in postpenetrating keratoplasty (PKP) eyes and to compare it with conventional Placido-based topography.
  
  
  METHODS
  Corneal elevation maps of the anterior corneal surface were obtained from 20 post-PKP corneas using PCT (VU topographer, prototype; VU University Medical Center, Amsterdam, The Netherlands) and Placido-based topography (Keratron, Optikon 2000, Rome, Italy). Corneal surface parameters are calculated in terms of radius and asphericity. Corneal aberrations were characterized using standard Zernike convention. An artificial surface with quadrafoil feature (SUMIPRO, Almelo, The Netherlands) was measured and used as a reference to assess instrument performance compared with the gold standard.
  
  
  RESULTS
  The differences (mean ± std of PCT - Placido) found between the two types of topographers in measurements of post-PKP eyes are 0.02 ± 0.21 mm (p=0.64) for radius of curvature, 0.14 ± 0.49 (p=0.23) for asphericity, -0.19 ± 1.67 μm (p=0.61) for corneal astigmatism, -0.25 ± 1.34 μm (p=0.41) for corneal coma, 0.23 ± 0.82 μm (p=0.23) for corneal trefoil, and 0.15 ± 0.28 μm (p=0.02) for corneal quadrafoil. The PCT measured the artificial surface more accurate (rms error 0.16 μm; 0.12 eq. Dpt.) than the Placido-based topographer (rms error 1.50 μm; 1.15 eq. Dpt.).
  
  
  CONCLUSIONS
  PCT is more accurate than Placido-based topography in measuring quadrafoil aberration.
authors.affiliation: Centre of Expertise for Blind and Partially Sighted People, Huizen, The Netherlands. annevrijling@visio.org
authors.forename: Anne C L
authors.initials: AC
authors.lastname: Vrijling
authors.forename: Boy
authors.initials: B
authors.lastname: Braaf
authors.forename: Joris J
authors.initials: JJ
authors.lastname: Snellenburg
authors.forename: Fleur
authors.initials: F
authors.lastname: de Lange
authors.forename: Michel J W
authors.initials: MJ
authors.lastname: Zaal
authors.forename: Rob G L
authors.initials: RG
authors.lastname: van der Heijde
authors.forename: Victor A D P
authors.initials: VA
authors.lastname: Sicam
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D019781:Corneal Topography / Q000379:methods* / Q000592:standards*; D016039:Corneal Transplantation; D057108:Corneal Wavefront Aberration / Q000175:diagnosis*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011182:Postoperative Care