Abstract
Corneal biomechanical parameters were compared in 100 keratoconus eyes with abnormal elevation on the back corneal surface only (group 1), versus both the back and front surfaces (group 2). Scheimpflug tomography with Pentacam HR, corneal biomechanical assessments using Corvis ST and Ocular Response Analyzer (ORA) and corneal epithelium thickness maps using anterior segment optical coherence tomography were assessed. There were no significant differences in the IOP measured using Corvis ST and ORA, age or sex between the two groups. Statistically significant differences were found in all corneal shape parameters and all new parameters of Corvis ST: corneal stiffness parameter at first applanation (SP-A1), integrated inverse radius (IR) and deformation amplitude ratio (DAR)) between groups (p < 0.001). The classic parameters of ORA including corneal hysteresis (CH) and corneal resistance factor (CRF) were about 1.00 mmHg higher in group 1 (p < 0.001). In conclusion, keratoconus eyes with abnormal elevation limited to the back corneal surface have lower grade, stiffer corneal biomechanical parameters and less asymmetric shape. This is consistent with progressive biomechanical weakening from the first detectable back surface elevation to manifestation on the front surface as the severity overwhelms the ability of the epithelium to compensate.
Highlights
Corneal biomechanical parameters were compared in 100 keratoconus eyes with abnormal elevation on the back corneal surface only, versus both the back and front surfaces
The best fit sphere (BFS) radius was significantly steeper in the group with abnormal elevations at both corneal surfaces than in the group with abnormal elevations limited to the posterior corneal surface (p < 0.05)
By examining the elevation data relative to the BFS, it is evident that there is significant difference in the maximum elevation values in the front (p < 0.001) and back (p = 0.001) corneal surfaces with greater elevation in relation to the BFS was observed in the group with abnormal elevations at both corneal surfaces
Summary
Corneal biomechanical parameters were compared in 100 keratoconus eyes with abnormal elevation on the back corneal surface only (group 1), versus both the back and front surfaces (group 2). Keratoconus eyes with abnormal elevation limited to the back corneal surface have lower grade, stiffer corneal biomechanical parameters and less asymmetric shape. This is consistent with progressive biomechanical weakening from the first detectable back surface elevation to manifestation on the front surface as the severity overwhelms the ability of the epithelium to compensate. Presence of abnormal elevation on the back corneal surface was reported as a primary sign of early ectatic change in keratoconus and may be used in the differential diagnosis of keratoconic corneas from normal corneas; its effectiveness in detecting subclinical forms of keratoconus has not been confirmed[4]. Recent evidence has shown the complementary role of corneal biomechanical features in discriminating keratoconic corneas from the normal o nes[5,6,7], and its role in detecting keratoconus in the initial stages prior to the topographical manifestations of k eratoconus[8]
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