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    Corneal tomography: Beyond but not in lieu of topography


    “In the quest for enhanced ectasia diagnosis, we have to go beyond topography, which only provides 2-dimensional information about the front surface of the cornea. Corneal topography does augment sensitivity to detect keratoconus in many cases with normal biomicroscopy and normal corrected visual acuity and is also efficient for identifying clinical keratoconus. But the occurrence of cases of post-LASIK ectasia in eyes without identifiable risk factors shows the need to better identify subclinical disease and characterize inherent ectasia susceptibility,” said Dr. Ambrósio, professor of ophthalmology, Federal University of the State of Rio de Janeiro (UniRIO), Brazil.

    While objective indices for the categorization of tomographic data have been developed, recognizing that ectasia risk is influenced by the biomechanical status of the cornea supports the use of biomechanical characterization. The integrated Scheimpflug-based corneal tomography and biomechanical analysis provided with the Pentacam and Corvis systems (both Oculus) generates the Tomographic and Biomechanical Index (TBI), which was developed to enhance diagnostic sensitivity, Dr. Ambrósio said. 

    The TBI was developed by Dr. Ambrósio and colleagues in a multicenter study including one randomly selected eye from subgroups of patients with normal (n=480) or keratoconic corneas (n = 204) and using the random forest method with leave-one out cross-validation, an efficient artificial intelligence technique for classification.1 The study also included 94 eyes with normal topography from patients with VAE. The latter eyes were considered to have normal topography if they presented with KISA <60, IS-value <1.45, central K <47, and no positive finding on the topometric classification.

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