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Proceedings Paper

Moire-based corneal topographer suitable for discrete Fourier analysis
Author(s): Franciscus H. M. Jongsma; Fons C. Laan; Bertho A. Th. Stultiens
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Paper Abstract

Because of the inherent limitation of techniques using the cornea as a mirror, we developed a corneal topographer based on diffusely emitted images obtained from two orthoscopically projected grids on the cornea. The additive moire pattern on the cornea was the starting point of the accurate reconstruction of the corneal topography including limbal and apical zone. In general, moire contouring instruments have inherent limitations on their accuracy because of limitations on maximum line frequencies versus depth of field. We eliminated this problem by using discrete Fourier analysis directly on the separately measured grids. For the reconstruction of the corneal height image, we removed all disturbance with a combination of fluorescence-, polarizing- and redundancy-techniques. With these improvements in hardware and extra digital filter techniques in software, we reconstructed the corneal height image with an axial resolution of 3 micrometers and a lateral resolution of approximately 40 X 30 micrometers in a 21.5 X 14.5 X 4 mm3 measuring area. Starting from this 3D topographic cast, other corneal parameters like optical axis, radius of curvature and corneal astigmatism could be calculated.

Paper Details

Date Published: 23 June 1994
PDF: 8 pages
Proc. SPIE 2126, Ophthalmic Technologies IV, (23 June 1994); doi: 10.1117/12.178554
Show Author Affiliations
Franciscus H. M. Jongsma, State Univ. Limburg (Netherlands)
Fons C. Laan, State Univ. Utrecht (Netherlands)
Bertho A. Th. Stultiens, TLA Engineering (Netherlands)


Published in SPIE Proceedings Vol. 2126:
Ophthalmic Technologies IV
Jean-Marie A. Parel; Qiushi Ren, Editor(s)

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