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Proceedings Paper

Corneal topometry by fringe projection: limits and possibilities
Author(s): Robert Windecker; Hans J. Tiziani; H. Thiel; Benedikt J. Jean M.D.
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Paper Abstract

A fast and accurate measurement of corneal topography is an important task especially since laser induced corneal reshaping has been used for the correction of ametropia. The classical measuring system uses Placido rings for the measurement and calculation of the topography or local curvatures. Another approach is the projection of a known fringe map to be imaged onto the surface under a certain angle of incidence. We present a set-up using telecentric illumination and detection units. With a special grating we get a synthetic wavelength with a nearly sinusoidal profile. In combination with a very fast data acquisition the topography can be evaluated using as special selfnormalizing phase evaluation algorithm. It calculates local Fourier coefficients and corrects errors caused by imperfect illumination or inhomogeneous scattering by fringe normalization. The topography can be determined over 700 by 256 pixel. The set-up is suitable to measure optically rough silicon replica of the human cornea as well as the cornea in vivo over a field of 8 mm and more. The resolution is mainly limited by noise and is better than two micrometers. We discuss the principle benefits and the drawbacks compared with standard Placido technique.

Paper Details

Date Published: 15 January 1996
PDF: 13 pages
Proc. SPIE 2628, Optical and Imaging Techniques for Biomonitoring, (15 January 1996); doi: 10.1117/12.229991
Show Author Affiliations
Robert Windecker, Univ. Stuttgart (Germany)
Hans J. Tiziani, Univ. Stuttgart (Germany)
H. Thiel, Univ. Tuebingen (Germany)
Benedikt J. Jean M.D., Univ. Tuebingen (Germany)

Published in SPIE Proceedings Vol. 2628:
Optical and Imaging Techniques for Biomonitoring
Hans-Jochen Foth; Renato Marchesini; Halina Podbielska M.D.; Michel Robert-Nicoud; Herbert Schneckenburger, Editor(s)

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