Pachymetry and posterior cornea asymmetry variables were key metrics differentiating clinically unaffected, highly asymmetric keratoconus from normal eyes when using a combined Scheimpflug/Placido device, a study published in the Journal of Cataract and Refractive Surgery found. 

The study looked at imaging from a combined Scheimpflug/Placido device in 26 clinically unaffected eyes of people with frank keratoconus in the fellow eye and 166 eyes from 166 patients with bilaterally normal corneal exams who had successful corneal refractive surgery and at least 1-year follow-up. They calculated the area under the curve, sensitivity, and specificity of 60 metrics using receiver operating characteristic curves.

They found that posterior wall inferior-superior (I-S) ratio, with receiver operating characteristics (ROC) of 0.862, was the most predictive individual metric that could differentiate between the case and control groups.


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“A combination model of 4 metrics (posterior wall I-S ratio in the central 3 mm, thinnest pachymetry coordinate on the x horizontal axis, posterior asymmetry and asphericity index, corneal volume) yielded an ROC of 0.936, with a sensitivity/specificity pair of 92.3%/87%,” according to investigators. “Variables related to elevation were not found significant.”

The study’s limitations include its small sample size studied in a single location (and so not representing a global consensus), no long-term follow-up, the fact that the “conjunction of notable point metric is only available in several devices from this manufacturer,” and that the metrics included depict corneal morphology and don’t analyze corneal biomechanics.

Reference

Golan O, Levinger S, Barequet IS, et al. Differentiating highly asymmetric keratoconus eyes using a combined Scheimpflug/Placido device. J Cataract Refract Surg. 2020; 46:1588–1595. doi: 10.1097/j.jcrs.0000000000000358