Comparison of Topographic Technologies in Anterior Surface Mapping of Keratoconus using Two Display Algorithms and Six Corneal Topography Devices

Purpose: To evaluate anterior surface topographic technologies and display algorithms in mapping keratoconus. Materials and methods: A total of 27 eyes of 17 subjects clinically diagnosed with keratoconus were imaged on six topographers: EyeSys, Alcon EyeMap, Keratron, TMS-1, Orbscan and PAR corneal topography system. Axial distance (AD) and instantaneous radius of curvature (IROC) algorithms were generated, and the cone apex was determined manually using a cursor. Intermachine comparisons for cone magnitude (steepest curvature), as well as cone location in radius and meridian were performed for each display algorithm using both AD and IROC. Significance (p < 0.05) was determined using repeated measures analysis of variance (ANOVA) on successive mean values. Maps were also evaluated for processability, defined by the ability to reconstruct a reasonable map for each subject, not map quality. Results: There were no significant differences between successive means for cone location in either radial or meridional directions. For AD, Orbscan was greater than both small mire Placido devices (Keratron and TMS-1), which were not different from each other. The small mire devices had significantly greater curvature magnitude than the large mire placido devices (EyeSys, Alcon EyeMap) which were not different from each other. Finally, PAR was significantly lower than the large mire Placido devices. For IROC, the pattern was the same with the exception that the Orbscan was not different than the small mire Placido devices in curvature magnitude. For processing success, the PAR had 100% processability, and all other devices were between 73 and 77%. Conclusion: In monitoring keratoconus, evaluation of change over time is fundamental to treatment decisions, making understanding of topographic technology differences in mapping keratoconic corneas extremely important.