PMID: 7517283Mar 1, 1994Paper

Characterization of the inherent error in a spherically-biased corneal topography system in mapping a radially aspheric surface

Journal of Refractive and Corneal Surgery
C Roberts

Abstract

Accurate measurement of corneal topography is crucial for many clinical applications. Also, the human cornea is known to be an asphere. Therefore, the purpose of this study was to quantitatively evaluate the accuracy of the EyeSys Corneal Analysis System in measuring a radially aspheric test surface and characterize the error function. Curvature of a calibrated ellipsoid was determined using three techniques: 1) calculating theoretically, 2) modeling with a spherically-biased algorithm, and 3) measuring experimentally using the EyeSys system, both with the surface aligned and under conditions of misalignment. The inherent error steadily increased from center to periphery, with a maximum error greater than 3.00 diopters at a radius of 4 mm for an eccentricity of 0.5 and apical radius of curvature of 7.5 mm. The EyeSys Corneal Analysis System does not accurately measure the instantaneous radii of curvature of an ellipsoid. Misalignment error is small compared to the inherent error due to a spherically-biased reconstruction.

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