Evaluation of Intereye Corneal Asymmetry in Patients with Keratoconus. A Scheimpflug Imaging Study

Abstract

PurposeTo assess the correlation between keratoconus severity and intereye asymmetry of pachymetric data and posterior elevation values and to evaluate their combined accuracy in discriminating normal corneas from those with keratoconus.MethodsThis study included 97 patients: 65 subjects with bilateral normal corneas (NC) and 32 with keratoconus (KC). Central corneal thickness (CCT), thinnest corneal thickness (ThCT) and posterior elevation (PE) at the thinnest point of the cornea were measured in both eyes using Scheimpflug imaging. Intereye asymmetry and its correlation with keratoconus severity were calculated for each variable. The area under the receiver operating characteristic curve (AUROC) was used to compare predictive accuracy of different variables for keratoconus.ResultsIn normal eyes, intereye differences were significantly lower compared with the keratoconus eyes (p<0.001, for CCT, ThCT and PE). There was a significant exponential correlation between disease severity and intereye asymmetry of steep keratometry (r2 = 0.55, p<0.001), CCT (r2 = 0.39, p<0.001), ThCT (r2 = 0.48, p<0.001) and PE (r2 = 0.64, p<0.001). After adjustment for keratoconus severity, asymmetry in thinnest pachymetry proved to be the best parameter to characterize intereye corneal asymmetry in keratoconus. This variable had high accuracy and significantly better discriminating ability (AUROC: 0.99) for KC than posterior elevation (AUROC: 0.96), ThCT (AUROC: 0.94) or CCT (AUROC: 0.92) alone.ConclusionsThere is an increased intereye asymmetry in keratometry, pachymetry and posterior corneal elevation values in keratoconic patients compared to subjects with normal corneas. Keratoconus patients with more severe disease are also more asymmetric in their disease status which should be taken into account during clinical care.

Intereye asymmetry in bilateral keratoconus, keratoconus suspect and normal eyes and its relationship with disease severity

“…In contrast with our findings, Dienes et al 14 reported strong intraclass correlations in CCT, TCT and PE in patients with KC, which were much higher than our study. Similarly, in most of the literature, the intraclass correlations were reported to be significantly higher in normal eyes 9 13 14 21.…”

“…In our study, the asymmetry in the severe stage of KC was significantly greater than in mild and moderate stages in most of the parameters. Similar to our findings, Nichols et al 10 and Dienes et al 14 reported that the intereye asymmetry of K values, CCT, TCT and PE correlated significantly with KC severity. These findings may conclude that KC is an asymmetrical disease; the asymmetry appears at the start and early stages of the disease and by the progression of the disease through severe stages, the asymmetry increases more.…”

“…However, the mean intereye asymmetry of flat and steep K, CCT, TCT and PE in our patients with KC was higher than Henriquez et al ’s13 study and the values of CCT, TCT and PE were lower than Dienes et al ’s14 study. Most of the intereye asymmetry values in our normal participants were lower than previous reports.…”

“…Most of the intereye asymmetry values in our normal participants were lower than previous reports. The mean intereye asymmetry in flat and steep K, CCT, TCT and PE in our normal participants was lower than the Falavarjani et al ,21 Henriquez et al 13 and Dienes et al ’s14 studies.…”

“…Dienes et al 14 reported that TCT and PE, measured by Scheimpflug imaging topography, had excellent ability in discriminating KC from normal eyes (AUROC=0.99 and 0.96, respectively). Moreover, they reported that intereye asymmetry of TCT and PE had higher accuracy, sensitivity and specificity in discriminating KC from normal eyes than TCT or PE measurements alone 14.…”