Corneal Enantiomorphism in Normal and Keratoconic Eyes

PURPOSE: To evaluate the ability to discriminate between normal and keratoconic corneas by analyzing intereye corneal asymmetry parameters and defining a score of similarity that outlines the normal range of asymmetry between right and left eyes. METHODS: This prospective, non-randomized study included 102 normal corneas of 51 patients and 64 keratoconic corneas of 32 patients. Topographic and tomographic parameters of the right and left eyes were extracted from an elevation and Placido-based corneal topography. Asymmetry was determined by subtracting the right eye value from the left eye value for each variable and by considering the absolute value of the result. A discriminant function was constructed to separate the normal and keratoconic groups. RESULTS: The mean intereye asymmetry differences were statistically significant for all variables except the vertical and horizontal decentration of the thinnest point, the corneal thickness at 2.5, 3, 3.5, and 4 mm from the thinnest point, and the posterior keratometry at 4.5 mm from the thinnest point. The discriminant function was composed of three variables (the difference between flat and steep keratometry, the 3-mm irregularity, and the anterior elevation of the thinnest point) and reached an area under the receiver operator characteristic curve of 0.992, a sensitivity of 94%, and a specificity of 100%. CONCLUSIONS: A discriminant function constructed from the intereye difference of three corneal indices may be accurate and useful for the topography-based detection of advanced keratoconus. In the future, incorporating such data in automated artificial intelligence software may improve the detection ability of earlier forms of keratoconus.