Corneal asymmetry analysis by pentacam scheimpflug tomography for keratoconus diagnosis

To evaluate intereye corneal asymmetry in Pentacam (Oculus Optikgeräte GmbH, Wetzlar, Germany) indices as a diagnostic method between normal patients and patients with keratoconus.

A retrospective, observational case series of 177 healthy, 44 indeterminate, and 121 patients with keratoconus classified by Pentacam ectasia detection indices, randomized to analysis and validation datasets. Intereye asymmetry in 20 Scheimpflug tomography corneal descriptors was calculated and compared to develop diagnostic models.

Intereye asymmetry was not correlated with anisometropia in healthy controls but was correlated with the ectasia grade of the worse eye in patients with keratoconus. Patients with keratoconus had significantly greater intereye asymmetry in all descriptors except for relational thickness indices. Intereye asymmetry in front elevation at the thinnest corneal location afforded the single highest diagnostic performance (71% sensitivity and 85% specificity), whereas the best multivariate model combining intereye asymmetry in anterior and posterior keratometry, corneal thickness, and front and back elevation at the thinnest point provided 65% sensitivity and 97% specificity. Multivariate models upheld their performance in the validation dataset. Most (more than 90%) indeterminate patients, according to conventional Pentacam analysis, showed within-normal-range corneal asymmetry.

Healthy corneas are markedly symmetric irrespective of anisometropia, but corneal asymmetry analysis does not provide sufficient sensitivity to be used alone for detecting keratoconus. However, its remarkable specificity suggests that it could be used combined with conventional single cornea Pentacam analysis to reduce the false-positive rate or in dubious cases.