G. Hilmantel et al., Accuracy of the Tomey Topographic Modeling System in measuring surface elevations of asymmetric objects, OPT VIS SCI, 76(2), 1999, pp. 108-114
Background Most studies have assessed the accuracy of videokeratographic sy
stems using spheres, ellipsoids, or toric surfaces. Most human corneas are
asymmetric to some degree and many pathological corneas are markedly asymme
tric. To date, little work has been done to ascertain the accuracy of video
keratographic systems for measuring the shape of asymmetric objects. Purpos
e. The purpose of this study is to determine the accuracy with which the To
mey Topographic Modeling System can evaluate the topography of asymmetric s
urfaces. Methods. Calibrated ellipsoidal test objects were tilted with resp
ect to the videokeratometric axis to create asymmetric test surfaces with k
nown characteristics. Results. Root mean squared error of all the measured
surface elevations varied from 0.7 mu m to 11.3 mu m. Although there was a
trend for greater error with the more asymmetric surfaces, the trend was no
t statistically significant. Accuracy was not dependent on apical radius. M
easurement error increased toward the periphery. Conclusions. For the Tomey
Topographic Modeling System, the accuracy in measurement of smooth, asymme
tric surfaces is comparable the accuracy in measurement of symmetric surfac
es.