Intereye asymmetry in eyes with keratoconus and high ammetropia: Scheimpflug imaging analysis

Purpose: To evaluate intereye asymmetry using several parameters obtained from Scheimpflug imaging to discriminate between normal eyes, high-ammetropic eyes with very early keratoconus (VEKC), and keratoconus eyes in all stages. Methods: This prospective comparative study includes 685 patients (1370 eyes), of which 294 patients had bilateral keratoconus, 50 patients had high ammetropia, and 341 patients were normal. These patients were studied from July 2012 to July 2014. Thirty parameters, which were obtained from Scheimpflug imaging (Oculus GmBH) and derived from pachymetry, curvature, anterior and posterior elevation, asphericity, and others, were analyzed. Asymmetry was determined by subtracting the right eye value from the left eye value for each variable and by considering the absolute value of the result. Receiver operating characteristic curves and logistic regression analysis were used. Results: In the hyperopic astigmatism group, the mean intereye asymmetries in maximum keratometry, maximum posterior elevation, and maximum anterior elevation were 0.35 diopters (D), 4.67 μm, and 2.5 μm, respectively. In the myopic astigmatism group the asymmetries were 0.33 D, 5.38 μm, and 2.13 μm, respectively. In the astigmatism group the asymmetries were 0.18 D, 3.33 mm, and 1.66 mm, respectively. In the VEKC group the asymmetries were 0.96 D, 10.76 μm, and 4.95 μm, respectively. A mixed model that includes the asymmetry and the nonasymmetry values shows an AUROC value of 0.9957, discriminating between normal and VEKC eyes. Conclusions: Specific asymmetry values derived from the Scheimpflug analysis effectively discriminate between patients with VEKC and normal patients. Patients with VEKC showed higher asymmetry values than those presented in high-ammetropic groups.