Background: Most studies have assessed the accuracy of videokeratographic systems using spheres, ellipsoids, or toric surfaces. Most human corneas are asymmetric to some degree and many pathological corneas are markedly asymmetric. To date, little work has been done to ascertain the accuracy of videokeratographic systems for measuring the shape of asymmetric objects.
Purpose: The purpose of this study is to determine the accuracy with which the Tomey Topographic Modeling System can evaluate the topography of asymmetric surfaces.
Methods: Calibrated ellipsoidal test objects were tilted with respect to the videokeratometric axis to create asymmetric test surfaces with known characteristics.
Results: Root mean squared error of all the measured surface elevations varied from 0.7 microm to 11.3 microm. Although there was a trend for greater error with the more asymmetric surfaces, the trend was not statistically significant. Accuracy was not dependent on apical radius. Measurement error increased toward the periphery.
Conclusions: For the Tomey Topographic Modeling System, the accuracy in measurement of smooth, asymmetric surfaces is comparable the accuracy in measurement of symmetric surfaces.