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Tomographic corneal analysis may yield markers for later development of kerectasia, keratoconus
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BOSTON — Measurement of the corneal plane using tomographic analysis may yield early warning signs of keratoconus, according to a speaker here.
In a study of 226 normal eyes from 113 patients and 88 eyes diagnosed with keratoconus based on clinical exam of 44 patients, a formula that considers the cornea's thinnest point and relative pachymetric increase (RPI) was more efficient in differentiating keratoconic corneas than thinnest value alone, Renato Ambrosio, MD, PhD, said at the World Cornea Congress preceding the American Society of Cataract and Refractive Surgery meeting.
The RPI is calculated from pachymetric measurements of the cornea using the Pentacam (Oculus). "At each point, a progression value is calculated referencing to the mean curve. These ratios are averaged to get a single value for each meridian," Dr. Ambrosio said.
When the value of the thinnest point on Pentacam analysis is divided by the average of the RPI in each meridian, it yields a single value that Dr. Ambrosio has named Ambrosio's relation thinnest average (ART-Avg). When the thinnest point is divided by maximal RPI value, it results in the ART-Max.
In addition to potentially being an early marker of ectatic changes on the corneal plane, the tomographic analysis pattern may also be relevant for identifying patients with seemingly normal corneas but weak and currently undetectable biomechanical properties that lead to late ectatic changes after refractive surgery.
Dr. Ambrosio is planning a retrospective review of LASIK patients with preoperative Pentacam readings who later developed keratoconus to see if early warning signs can be detected.
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