Moire-based corneal topographer suitable for discrete Fourier analysis

Franciscus H. M. Jongsma; Fons C. Laan; Bertho A. Th. Stultiens

doi:10.1117/12.178554

23 June 1994 Moire-based corneal topographer suitable for discrete Fourier analysis

Franciscus H. M. Jongsma; Fons C. Laan; Bertho A. Th. Stultiens

Author Affiliations +

Proceedings Volume 2126, Ophthalmic Technologies IV; (1994) https://doi.org/10.1117/12.178554
Event: OE/LASE '94, 1994, Los Angeles, CA, United States

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.

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Franciscus H. M. Jongsma, Franciscus H. M. Jongsma, Fons C. Laan, Fons C. Laan, Bertho A. Th. Stultiens, Bertho A. Th. Stultiens, } "Moire-based corneal topographer suitable for discrete Fourier analysis", Proc. SPIE 2126, Ophthalmic Technologies IV, (23 June 1994); doi: 10.1117/12.178554; https://doi.org/10.1117/12.178554

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