Enhancing early detection of keratoconus suspects using interocular corneal tomography asymmetry.

Purpose: To evaluate corneal tomography asymmetry of both eyes in keratoconus (KC), keratoconus suspects (KCS), and normal (NL) eyes, and to introduce an interocular asymmetry index (IAI) for early diagnosis of keratoconus.

Methods: This prospective case-control study included 210 NL eyes, 140 eyes with KCS, and 40 eyes with KC. New Scheimpflug imaging scans were performed to obtain corneal tomographic parameters. Based on the high and low values of tomographic parameters, each eye was categorized as "worse" or "better." Intragroup correlation coefficients (ICC) were used to compare interocular asymmetry. Logistic regression indices were constructed using interocular differences. Receiver operating characteristic (ROC) curves were used to analyze the sensitivity, specificity, and cutoff values of the IAI.

Results: In the KC group, 86.7% of the parameters significantly differed between the worse and better eyes. In the KCS group, 66.7% of the parameters showed significant differences between the worse and better eyes, with high consistency between the central and thinnest corneal thickness groups (ICC > 0.6). Strong intragroup correlations were observed in the NL group (ICC > 0.6). IAI effectively distinguished the NL from the KCS group (area under the ROC [AUROC] = 0.891), reaching 67.1% sensitivity and 97.1% specificity at a cutoff value of 0.494. At a cutoff value of 0.778, the IAI reached 95.0% sensitivity and 96.2% specificity in distinguishing NL from KC (AUROC = 0.954).

Conclusion: Interocular asymmetry in keratoconus suspects can be detected in the early stages, with increased asymmetry compared to NL eyes observed as keratoconus progresses. Interocular asymmetry can complement monocular diagnostic parameters.