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    Why single-instrument screening for keratoconus remains a dream


    “The results of our study specifically argue against the opinions presented in the Global Consensus paper, as the metrics they identified as being required were in fact not found in the majority of our patient population,” Dr. Randleman said.

    The problem is that each instrument currently on the market evaluates different metrics. Ophthalmologists might prefer one instrument or another, or use multiple instruments to assess questionable eyes, but the decision to perform refractive surgery remains a highly subjective process.

    “Most eyes are appropriate for LASIK, but you frequently want more information on up to 10 % of eyes you see on initial screening,” Dr. Randleman said. “At this point, subjective analysis remains absolutely critical for good results. That is why it is imperative the surgeons continue learning what is normal and what is suspicious, and keep up to date with the current literature. And for now, you have to rely on different metrics from multiple instruments.”           

    The Pentacam HR has been considered by some to be the most useful instrument to diagnose early keratoconus using Scheimpflug imaging, Dr. Randleman said, but there has been little evidence to support that assumption.

    He presented the results of a study comparing 25 clinically normal eyes of patients with definitive keratoconus in the contralateral eye with 50 eyes from 50 patients that had normal evaluations by multiple imaging devices with uneventful LASIK and at least one year of follow-up.

    The study evaluated anterior curvature, thickness, topometric maps, Zernike maps, and the enhanced ectasia map. The goal was to evaluate objective metrics derived from Pentacam Scheimpflug imaging and determine their relative value in distinguishing between normal control eyes and the less affected eye of patients with high asymmetric keratoconus.

    No metrics achieved excellent or good scores. Three metrics were scored fair in distinguishing suspect eyes from normal eyes, ISV keratoconic index from the topometric map, and the D score and ARTmax from the enhanced ectasia map. None of the three metrics were particularly useful individually or in combination, Dr. Randleman said. ISV identified 20 % of suspect eyes, D score 12 % and ARTmax 24 %, but the three metrics all identified different eyes.

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