Corneal topography system including single-direction shearing of

Details Corneal topography system including single-direction shearing of Corneal topography system including single-direction shearing of

1992-11-05

1994-04-26

Arnold, Bruce Y.

Optics: eye examining, vision testing and correcting

Eye examining or testing instrument

Objective type

351221, 351246, 356345, 356353, A61B 310, A61B 300, G01B 902

Patent

active

053070976

ABSTRACT:
A system for producing a three-dimensional image of a surface, such as a surface of a cornea, includes a laser beam that passes through a beamsplitter and an objective lens to produce a spherical wavefront that impinges on the cornea and is reflected by the cornea as a return beam back through the objective lens. The return beam is reflected by the beamsplitter through an imaging lens that focuses the return beam onto an imaging screen, through a dual phase plate, and onto a photosensitive array. The dual phase plate includes two sets of spaced periodic refractive features spaced along orthogonal directions. The phase plate is modulated by incrementing it at a 45 degree angle relative to the first and second directions, thereby simultaneously producing phase shear along the two orthogonal directions. The resulting intensities at each pixel of a CCD camera are digitized and used to compute an optical phase difference (OPD) map consisting of the relative deviation of the cornea surface from the impinging spherical wavefront at each pixel. The OPD map then is summed with a "spherical map" of the impinging spherical wavefront, which has height coordinates measured relative to a limbus plane under the cornea, to obtain a complete three-dimensional image of the cornea. Various d-spacings of the dual phase plate patterns, in conjunction with corresponding capture intervals or shifts produced by the incrementing, allow scaling of the sensitivity of the system to allow "close up" viewing of the cornea.

REFERENCES:
patent: 3829219 (1974-08-01), Wyant
patent: 3936160 (1976-02-01), Von Bieren
patent: 4863260 (1989-09-01), Gersten et al.
patent: 5062702 (1991-11-01), Bille
Rimmer, et al. "Evaluation of Large Aberrations Using a Lateral-Shear Interferometer Having Variable Shear" Applied Optics, vol. 14, No. 1, Jan. 1975.

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