MOHAMMAD GHOREISHI, MDISFAHAN UNIVERSITY OF MEDICAL SCIENCES

ISFAHAN, IRANNINFO@PERSIANEYECLINIC.COM

Pentacam Topography

Placido disc (reflection) based Elevation based

PAR Corneal Topography System (PAR CTS) Slit scanning (Orbscan) Scheimpflug imaging (Pentacam, Galilei ,..)

Topography systems

Problems with placido systems

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 distortedCurvature is reference basedElevations (shape) may not always be accurate

Elevation DataElevation represents true shape of the cornea It is independent of axis, orientation or

positioning.All subsequent maps (curvature …) can be

derived from accurate elevation dataThere 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 SystemsB & L OrbScan

Scanning Slit Accuracy? Relies on Placid augmentation

PAR CTS Rasterphotogrammetry Accurate but not commercially

available

Oculus Pentacam Rotating Scheimpflug images

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