Relationship of corneal biomechanical profile to structural charecteristics in normal, forme fruste keratoconic, keratoconic and crosslinked eyes

Purpose: To evaluate the correlation of corneal biomechanical parameters to structural characteristics in normal, forme fruste keratoconic, keratoconic and collagen crosslinked eyes. The study was based at Macquarie University eye clinic, Sydney and Sydney Cornea Clinic, Sydney Methods: This was a prospective observational study of 50 normal, 10 forme fruste keratoconic, 100 keratoconic and 25 crosslinked eyes. All eyes were imaged using the Scheimpflug camera Pentacam and the Ocular response analyser. The main outcome measures were central corneal thickness (CCT), corneal volume (CV), maximal keratometry (Kmax), corneal hysteresis (CH) and corneal resistance factor (CRF). Results: Significant differences were noted between all four groups of eyes for CCT, CV, Kmax, CH and CRF values (p < 0.05 by ANOVA). CH and CRF correlated negatively (CH: r = −0.40, CRF: r = −0.44, both p < 0.0001) with the Pentacam topographic keratoconus classification. Both CH and CRF correlated positively with CCT and CV for normal, keratoconic and crosslinked eyes. In contrast, significant negative correlations were observed between CH, CRF and Kmax in keratoconic eyes (CH: r = −0.43, CRF: r = −0.53; both p < 0.0001) whereas no association was noted for normal and crosslinked eyes. Conclusions: Corneal biomechanical parameters progressively decrease as severity of keratoconus increases. CH and CRF are influenced by corneal structure, with higher values noted in corneas with greater thickness and volume and flatter curvature. Collagen cross linking appears to normalise the relationship of corneal curvature to biomechanical profile in keratoconic eyes.