Accuracy and precision of the corneal analysis system and the topographic modeling system

Two computer-assisted topographic analysis systems were evaluated with calibrated spherical surfaces and normal human corneas. The Topographic Modeling System-1 (TMS-1) was found to be statistically more accurate in determining the power of calibrated spheres near the apex and at 1 mm from the apex than the Corneal Analysis System (CAS). The CAS, however, was statistically more accurate at 3 mm from the apex with each calibrated sphere. The small differences in accuracy between the two instruments, however, are unlikely to be of clinical significance. The topographic patterns on color-coded maps from 22 normal corneas of 11 subjects were similar with the two instruments. Simulated keratometry values with the CAS more accurately identified the keratometer-determined major cylinder axis compared with the TMS-1. Conversely, the TMS-1 was more accurate than the CAS at determining the level of corneal astigmatism.