CHARACTERIZATION OF THE INHERENT ERROR IN A SPHERICALLY-BIASED CORNEAL TOPOGRAPHY SYSTEM IN MAPPING A RADIALLY ASPHERIC SURFACE

BACKGROUND: Accurate measurement of corneal topography is crucial for many clinical applications. Also, the human cornea is known to be an a sphere. Therefore, the purpose of this study was to quantitatively eva luate the accuracy of the EyeSys Corneal Analysis System in measuring a radially aspheric test surface and characterize the error function. METHODS: Curvature of a calibrated ellipsoid was determined using thre e techniques: 1) calculating theoretically, 2) modeling with a spheric ally-biased algorithm, and 3) measuring experimentally using the EyeSy s system, both with the surface aligned and under conditions of misali gnment. RESULTS: 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. CONCLUSIONS: The EyeSys Corneal Analysis System does not accur ately measure the instantaneous radii of curvature of an ellipsoid. Mi salignment error is small compared to the inherent error due to a sphe rically-biased reconstruction.