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Repeatability of corneal topography measurement in keratoconus with the TMS-1
Timothy T McMahon1, Robert J Anderson, Cynthia Roberts
1Department of Ophthalmology & Visual Sciences, University of Illinois College of Medicine at Chicago, Chicago, Illinois (TTM), the Division of Epidemiology & Biostatistics, School of Public Health, University of Illinois at Chicago, Chicago, Illinois (RJA), the Department of Ophthalmology, The Ohio State University, Columbus, Ohio (CR, AMM), the Department of Ophthalmology, University Hospitals of Cleveland, Case Western Reserve University, Cleveland, Ohio (LBSF), the Ohio State University, College of Optometry, Columbus, Ohio (TWR), the School of Optometry, University of California, Berkeley, California (NEF), and the College of Optometry, University of Missouri-St. Louis, St. Louis. Missouri (LJD).
Purpose:
The purpose of this study was to report the test-retest variability of simulated indices derived from the TMS-1 topography instrument (Tomey Technology, Waltham, MA) in keratoconus subjects enrolled in the Collaborative Longitudinal Evaluation of Keratoconus (CLEK) Study.
Methods:
Four images were taken at an initial visit and at a repeat visit several weeks later. From these images, 17 indices were simulated from published formulas. Mixed-model analysis was used on test-retest data from the TMS-1 videokeratography instrument during the baseline year. This analysis yields estimates of within- and between-visit variability.
Results:
Repeatability analysis revealed that within-visit standard errors were 1.0 to 5.9 times greater in keratoconus eyes than in normal controls when two images were analyzed from each visit. These values changed only slightly when more images were used. The ratio of between-visit standard errors of the indices were nearly equally greater than normal controls for (0.9-4.6 and 0.9-4.3) two images per eye and all images per eye, respectively.
Conclusions:
These results suggest that the repeatability of simulated indices derived from TMS-1 topography in keratoconus subjects is poorer than in normal controls.
