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    Study identifies parameters that help diagnose ectatic disease

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

     

    Clinical implications

    Conscious interpretation of corneal shape analysis identifies early ectatic disease, which helps prevent iatrogenic progressive ectasia, Dr. Salomão said.1

    figure 2Corneal tomography allows the characterization of the front and back surfaces of the cornea, along with a pachymetric map. (Images courtesy of Marcella Q. Salomão, MD)There is an unquestionable need to improve the Ectasia Risk Score System, which was published in 2008 based on Placido disk-based topographic abnormalities, low residual stromal bed thickness, young age, and higher levels of correction. Although that was a landmark study, the researchers reported up to 8% of false negatives and 6% of false positives, Dr. Salomão said.2

    “Interpretation of corneal topography is a paramount factor, but we need to be objective, as we identified in the study from Ramos,” she said.3“In addition, abnormal corneal topography is reported as the most important preoperative risk factor. However, there are reports of post-LASIK ectasia in eyes with apparently normal topographies, which indicate we need to go beyond such classic and still important exam. As we read in the editorial from Randleman and Ambrósio, 4we are really seeking to identify very mild or susceptible cases, which may still have normal curvature.” she said.

    Ultimately, Dr. Salomão and fellow researchers believe there are two mechanisms responsible for ectasia ‒ preoperative abnormally weak innate biomechanical properties of the patient’s cornea and the amount of biomechanical weakening caused by the procedure.

    The challenge is to characterize each case in terms of the amount of biomechanical weakening they could withstand from the refractive procedure, Dr. Salomão said.1

    “Such integration has been developed using artificial intelligence by the BrAIN (Brazilian Study Group of Artificial Intelligence and Corneal Analysis), which aims to enhance safety for our patients,” she said.

    References

    1. Ambrosio R, Jr., Nogueira LP, Caldas DL, et al. Evaluation of corneal shape and biomechanics before LASIK. Int Ophthalmol Clin. 2011;51:11-38.
    2. Randleman JB, Trattler WB, Stulting RD. Validation of the Ectasia Risk Score System for preoperative laser in situ keratomileusis screening. Am J Ophthalmol. 2008;145:813-8.
    3. Ramos IC, Correa R, Guerra FP, et al. Variability of subjective classifications of corneal topography maps from LASIK candidates. J Refract Surg. 2013;29:770-5.
    4. Ambrosio R, Jr., Randleman JB. Screening for ectasia risk: what are we screening for and how should we screen for it? J Refract Surg. 2013;29:230-2.

     

    Marcella Q. Salomão, MD

    E: [email protected]

    This article was adapted from Dr. Salomão’s presentation at the American Society of Cataract and Refractive Surgery annual meeting in San Diego earlier this year. The presentation was entitled “Topometric and Tomographic Parameters for Diagnosis of Ectatic Disease.”

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