We used two computerized corneal topography instruments (EyeSys Laboratories' Corneal Analysis System and the Topographic Modeling System (TMS-1) from Computed Anatomy, Inc.] to evaluate 18 eyes (ten patients) with abnormal corneas. The diagnoses included keratoconus, corneal scars, and residual postoperative astigmatism following refractive surgery. The patients were randomly selected from a busy corneal practice to include those with significant corneal refractive error whose management, it was believed, would benefit from corneal topography imaging. Images were taken with both systems, and comparisons were made of the ease of operation, the accuracy of corneal readings, and the usefulness of generated data. Three millimeter zone (Corneal Analysis System) and Simulated Keratometry (TMS-1) values were also compared to each other and to standard keratometric readings. We found the two systems to be very similar in their application and results, although certain differences were apparent in terms of operation, patient acceptance, and the ability to obtain useful data from the more distorted corneas. Neither system worked ideally for severely irregular surfaces.