title: Comparison of Placido-based, rasterstereography, and slit-scan corneal topography systems.
abstract: OBJECTIVE
  Elevation-based topography systems have received growing recognition. We compared a Placido-based (EyeSys), a rasterstereography (PAR), and a slit-scan system (Orbscan) for human subjects.
  
  
  METHODS
  Measurements were obtained from 221 eyes of 119 human subjects. We made statistical comparisons central curvature, keratometric curvatures, and meridians between the three systems. We also compared the optical pachymetry of the slit-scan system with an ultrasonic device. We analyzed cases of subclinical keratoconus, central island, photorefractive keratectomy for myopia, and hyperopia correction with arcuate keratotomy.
  
  
  RESULTS
  The statistical comparison showed better correlation between the Placido-based and the rasterstereography systems in measurement of central curvature (R=0.95). The slit-scan system showed better correlation with the Placido system in the preoperative and postoperative radial keratotomy group (R=0.73) than in the group that included postoperative PRK eyes (R=0.69). Similar results were obtained for keratometric curvatures and meridians. The Orbscan pachymetry correlation with ultrasonic was R=0.69 and increased when the postoperative PRK eyes were excluded (R=0.95).
  
  
  CONCLUSIONS
  Slit-projection topography and pachymetry seemed to be affected by hydration in the postoperative PRK group. The pachymetric map was useful in predicting the final outcome of refractive surgery and in the diagnosis of keratoconus.
authors.affiliation: Stanford University, Division of Mechanics and Computation, CA 94305, USA. Fabio@e-cornea.com
authors.forename: Fabio A
authors.initials: FA
authors.lastname: Guarnieri
authors.forename: José C
authors.initials: JC
authors.lastname: Guarnieri
mesh_terms: D003315:Cornea / Q000473:pathology*; D019781:Corneal Topography / Q000379:methods*; D006801:Humans; D006956:Hyperopia / Q000473:pathology / Q000601:surgery; D007640:Keratoconus / Q000175:diagnosis*; D054018:Lasers, Excimer; D009216:Myopia / Q000473:pathology / Q000601:surgery; D018903:Photorefractive Keratectomy; D016896:Treatment Outcome