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David Huang1,2, Maolong Tang2,1
1Cole Eye Institute, Cleveland Clinic Foundation, Cleveland, OH
2Department of Biomedical Engineering, Ohio State University, Columbus, OH
Background: Keratoconus is a frequent contraindication for corneal refractive surgery. Corneal topography is routinely performed to rule out keratoconus and forme fruste keratoconus before surgery. Diagnosis of keratoconus on the widely used axial map is complicated because cone appearance is heavily influence by location and coexisting astigmatism. The purpose of this study is to develop a new type of corneal topographic map that improves cone detection.
Methods: We map the convexity of the cornea by applying the Laplacian operator on corneal height. The convexity map is computed for simulated normal, astigmatic, and variants of keratoconic topographies. Diagnostic screening using convexity map and indices are tested in 12 keratoconus eyes and 12 normal eyes. The axial power-based Rabinowitz indices are used for comparison.
Results: The convexity map shows the same cone appearance regardless of location on the cornea or coexisting astigmatism. Both convexity indices and the combined Rabinowitz index (KISA) have 100% sensitivity and specificity.
Conclusion: Convexity indices perform as well as Rabinowitz indices in this small sample. Keratoconus pattern is simple and easy to recognize on convexity maps. The theoretical advantages of convexity mapping in keratoconus screening need to be explored in larger trials.
Supported by Whitaker Foundation grant RG 99-0302.
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