Objective and subjective diagnostic parameters in the fellow eye of unilateral keratoconus

Abstract

Background: Keratoconus (KC) is usually a bilateral corneal ectatic disease. For significant asymmetric presentation (so called unilateral KC), the fellow eye has the mildest and earliest form of the disease, which is typically called forme fruste keratoconus. The aim of this study was to evaluate the sensitivity and specificity of parameters derived from a Scheimpflug imaging system (Pentacam) as well as the changes in the quality of mesopic vision in the apparently normal fellow eye (forme fruste) to detect the earliest and most sensitive parameters.

Methods: Patients with clinical keratoconus in one eye and forme fruste keratoconus in the fellow eye were compared to subjects with normal eyes. The patients were examined using a rotating Scheimpflug imaging system (Pentacam).The following parameters were evaluated: keratometry, minimum corneal thickness, pachymetry progression index (PPI), Ambrósio relational thickness (ART), posterior elevation, back difference elevation (BDE) and multimetric D index(D index). Receiver operating characteristic (ROC) curves were analyzed by evaluating the area under the curve (AUC) to detect the sensitivity and specificity of each parameter. Mesopic vision evaluations were performed by contrast sensitivity and glare tests for each group.

Results: A total of 48 patients with clinical keratoconus in one eye and forme fruste keratoconus in the fellow eye and 72normal subjects were evaluated. In the clinical keratoconus eyes, the mean K, back difference elevation (BDE), pachymetric progression index maximum(PPI max), and multimetric D were significantly higher compared to the normal subjects, whereas the corneal pachymetry and Ambrósio relational thickness maximum (ART max) were significantly lower. In the forme fruste eyes, the ROC analysis showed that the AUC values of the mean K, thinnest pachymetry, ARTmax, BDE, D index, and PPI max were 0.82, 0.61, 0.88, 0. 67, and 0.64, respectively. The contrast sensitivity and glare tests were significantly affected in the forme fruste cases.

Conclusion: In forme fruste keratoconus eyes, the ART max is considered a highly sensitive objective parameter. Contrast sensitivity and glare is an important subjective test, which is affected in forme fruste patients.

Keywords: Ambrósio relational thickness; Contrast sensitivity and glare; Forme fruste; Pentacam.

Conflict of interest statement

Ethics approval and consent to participate

This study was approved by the institutional research board of the Mansoura faculty of medicine(IRB) (R/17.05.25) and was performed in accordance with the ethical standards of the Declaration of Helsinki. All patients included in the study provided informed consent.

Consent for publication

Not applicable for this study.

Competing interests

The authors declare that they have no competing interest.

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Figures

Fig. 1

a ROC curve for Ambrósio relational thickness (ART max) and thinnest pachymetry. b combined ROC curves of multimetric D index(D), back difference elevation (BDE), Posterior elevation(PE) and pachymetric progression index maximum (PPI max) between the forme fruste and control cases

Fig. 2

a ROC curve for Ambrósio relational thickness (ART max) and thinnest pachymetry. b combined ROC curves of multi metric D index(D), back difference elevation (BDE), Posterior elevation (PE) and steepest Keratometry (Ks) between the clinical keratoconus and control cases