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Abstract

An improved photokeratoscopic method and apparatus for measuring corneal curvature and topography. The principal of parallax is used by generating a reference light point outside of the relevant plane of a ring generator, such that the relative apparent position of the reference light point with respect to the projected light rings provides a calibration reference that varies with distance of a cornea from the photokeratoscope. More particularly, the invention determines the coordinates in space and the tangent angle of the reflection point on the corneal surface of the image of the reference light point. This information defines the actual corneal topography at the reflection point, without making assumptions. These coordinates and tangent angle can be used to determine the actual distance d from the photokeratoscope lens to the apex of the cornea. An exact value of d permits better accuracy in calculating the central corneal radius of curvature and corneal topography. The present invention can be used with any known photokeratoscope geometry, including planar, spherical, or conical ring generators. The algorithm for computing d, and for calculating the central corneal radius of curvature and corneal topography, is shown in pseudocode, and may easily be implemented as a computer program.

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First Claim