Comparison of corneal biomechanical properties in healthy thin corneas with matched keratoconus eyes

Abstract

Purpose: 

To compare corneal biomechanical parameters of normal thin corneas with matched keratoconus eyes.

Setting: 

Eye Research Center, Mashhad University of Medical Sciences, Mashhad, Iran.

Design: 

Cross-sectional comparative study.

Methods: 

Dynamic corneal response parameters of Corvis ST were compared in 61 eyes with keratoconus with 61 matched healthy thin corneas (corneal thinnest point <500 μm), while corneal thickness, biomechanically corrected intraocular pressure, and age were considered covariates. The receiving operator sensitivity curve analysis was used to determine the cutoff point with the highest sensitivity and specificity, and the area under the curve (AUC) for each parameter.

Results: 

All biomechanical parameters were statistically significant between the 2 groups except for the first (P = .947) and second (P = .582) applanation length, first (P = .783) and second (P = .301) applanation velocity, and deformation amplitude in the highest concavity phase (P = .106). The highest mean difference between groups (12.89 ± 2.03 mm Hg/mm) was related to the stiffness parameter at the first applanation (SPA1). Although the Corvis biomechanical index and tomographic biomechanical index had the highest detection ability based on their AUC (0.912 and 0.959, respectively), among the standard and combined biomechanical parameters except for keratoconus screening parameters, the highest discriminative ability was related to SPA1 with AUC, sensitivity, and specificity of 0.793, 60.66%, and 90.16%, respectively.

Conclusions: 

Keratoconus corneas were significantly softer compared with healthy thin corneas of matched thickness. Optimal cutoff points close to the maximum value defined for screening parameters limit their clinical use for differentiation purposes in these particular types of cases.

In Brief

Keratoconus corneas were biomechanically weaker than healthy thin corneas of matched thickness. Similarity of the cutoff points of CBI and TBI with the maximum value defined limits to their clinical application.