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Pentacam Topography. Mohammad Ghoreishi , MD Isfahan University of Medical sciences Isfahan, Irann info@persianeyeclinic.com. Topography systems. Placido disc (reflection) based Elevation based PAR Corneal Topography System (PAR CTS) Slit scanning (Orbscan)

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slide1

Pentacam Topography

Mohammad Ghoreishi, MD

Isfahan University of Medical sciences

Isfahan, Irann

info@persianeyeclinic.com

slide2

Topography systems

  • Placido disc (reflection) based
  • Elevation based
    • PAR Corneal Topography System (PAR CTS)
    • Slit scanning

(Orbscan)

    • Scheimpflug imaging

(Pentacam, Galilei ,..)

problems with placido systems
Problems with placidosystems
  • Assuming sphero-cylindrical optics on a smoothly reflective convex surface that falls within certain pre-determined parameters
  • Can not read if the cornea is badly distorted
  • Curvature is reference based
  • Elevations (shape) may not

always be accurate

elevation data
Elevation Data
  • Elevation represents true shape of the cornea
  • It is independent of axis, orientation or positioning.
  • All subsequent maps (curvature …) can be derived from accurate elevation data
  • There is no reason for an elevation based topography system to incorporate Placido derived data unless their elevation data is unreliable

Michael W. Belin, M.D., AAO Annual Meeting 2003, Anaheim, CA

elevation based systems
Elevation Based Systems
  • B & L OrbScan
    • Scanning Slit
    • Accuracy?
    • Relies on Placid augmentation
  • PAR CTS
    • Rasterphotogrammetry
    • Accurate but not commercially available
  • Oculus Pentacam
    • Rotating Scheimpflug images
slide6

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