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    Study identifies parameters that help diagnose ectatic disease

    Topography, tomography are useful, but insufficient to detect milder forms

    Take-home message: Topometric and tomographic parameters helped researchers detect keratoconus in a study, but the integration of curvature and 3D analysis is needed to identify milder forms of ectatic corneal disease.

     

    Ectasia after LASIK is something that refractive surgeons naturally want to avoid. Identifying patients who have keratoconus preoperatively can help pinpoint who is at risk for postoperative ectasia.

    Two methods that could help surgeons going forward are topometric and tomographic parameters, said Marcella Q. Salomão, MD, Instituto de Olhos Renato Ambrósio, Rio de Janeiro, Brazil. Topometric parameters derive from the front surface curvature, and tomographic parameters derive from 3D elevation and thickness distribution.

    “Corneal tomography provides a three-dimensional reconstruction of the cornea, which allows the characterization of the front and back surfaces of the cornea along with a pachymetric map,” she said. “It allows a comprehensive evaluation of corneal geometry and architecture.”

    In a retrospective study led by Dr. Salomão from the Rio de Janeiro Corneal Tomography and Biomechanics Study Group, Pentacam HR (Oculus) indices were used from 282 patients with bilateral keratoconus (one eye was included in the study), 211 with forme fruste keratoconus (FFKC), and 266 normal patients. Forme fruste keratoconus was defined as the eye with a normal front curvature map from patients with keratoconus detected in the fellow eye and the “normal” eyes were the preoperative status of cases that had stable LASIK with more than two years of follow up.

    The use of topometric and tomographic indices successfully detected keratoconus in the study with a virtually perfect separation. However, while many parameters had statistically significant differences among normal and FFKC groups, further integration parameters from curvature and 3D analysis were necessary to enhance accuracy to identify more mild ectasia, Dr. Salomão reported.

    Parameters that most successfully identified keratoconus were the deviation (D) value on the Belin/Ambrósio Enhanced Ectasia Display, the Ambrósio Relational Thickness (ART) values, and the Index of Height Decentration (IHD).

    The integration of age, a surrogate of biomechanical properties of the cornea, along with other parameters, improved the ability to identify ectatic disease.

     

     

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