Factors Influencing the Diagnosis of Keratoconus by Corneal Topography

Abstract

Abstract: : Purpose: To study factors influencing the diagnosis of keratoconus based on corneal topography. Methods: Elevation corneal topography (Orbscan II) was performed in 12 patients (24 eyes), independent anterior (ABFS), posterior best fit sphere elevation (PBFS), axial power keratometry (APK) and, pachymetry maps (PM) were evaluated by 10 masked observers and, classified as normal, suspect or keratoconus. Images with an interobserver agreement of 60% or higher were selected to build 3 theoretical maps (normal, suspect and, keratoconus). Each map included 4 individual selected images (ABFS, PBFS, APK and, PM). Eighty one theoretical corneal topography maps were generated using facet theory (Borg, I. 1995). Twenty observers independently examined 81 maps and sorted them in two steps. In the first sort the expert used 3 categories and 5 in the second sort. A distance matrix was generated through a Q sort data collection technique (Groves & Wilson 1992). Factors involved in the diagnostic decision of keratoconus were identified using the psychometric procedure of multidimensional scaling. Results: The data was displayed in one, two and, three dimensions using the ordinal level of measurement. The goodness of fit of the model had a Kruskal’s stress index below 0.15. Axial power keratometry map had the highest impact in the diagnosis followed by the posterior best fit sphere elevation map. The pachymetry map appeared as a weak factor in the diagnosis. Conclusions: The appearance of the APK map substantially positively relates to the diagnosis of keratoconus.

Keywords: keratoconus • imaging methods (CT, FA, ICG, MRI, OCT, RTA, S • clinical (human) or epidemiologic studies: bio