Par corneal topography system (PAR CTS): The clinical application of close-range photogrammetry

Michael W. Belin, James L. Cambier, John R. Nabors, C. Derek Ratliff

Research output: Contribution to journalArticlepeer-review

31 Scopus citations


The PAR Corneal Topography System (CTS) is a computer-driven corneal imaging system which uses close-range photogrammetry (rasterphotogrammetry) to measure and produce a topographic map of the corneal surface. The PAR CTS makes direct point-by-point measurements of surface elevation using a stereo-triangulation technique. The CTS uses a grid pattern composed of horizontal and vertical lines spaced about 0.2 mm (200 ju.m) apart. Each grid intersection comprises a surface feature which can be located in multiple images and used to generate an (x, y, z) coordinate. Unlike placido disc-based videokeratoscopes, the PAR CTS requires neither a smooth reflective surface nor precise spatial alignment for accurate imaging. In addition to surface elevation, the PAR CTS computes axial and tangential curvatures and refractive power. Difference maps are available in all curvatures, refractive power, and in absolute elevation.

Original languageEnglish (US)
Pages (from-to)828-837
Number of pages10
JournalOptometry and Vision Science
Issue number11
StatePublished - Nov 1995


  • Elevation
  • Fluorescence
  • Keratoconus
  • Photogrammetry
  • Photorefractive
  • Placido
  • Rasterphotogrammetry
  • Stereogrammetry
  • Structured lighting
  • Tangential
  • Topography
  • Triangulation
  • Videokeratoscopes
  • “Forme fruste” keratoconus

ASJC Scopus subject areas

  • Ophthalmology
  • Optometry


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