Analysis of Corneal Biomechanical Parameters for Differentiation of Keratoconus and Healthy Thin Corneas

Aim: To evaluate and compare corneal hysteresis (CH) and corneal resistance factor (CRF) in healthy eyes with a central corneal thickness (CCT) ≤500µm with CH and CRF in gender-, age-, and CCT-matched keratoconus cases, and to estimate the sensitivity and specificity of these parameters for discriminating between the two groups. Study Design and Method: Prospective comparative case control study, in total 40 healthy eyes with CCT ≤500µm, and 40 eyes from CCT-, gender- and age-matched keratoconus cases were enrolled. Patients underwent a complete clinical eye examination, corneal tomography (Allegro Oculyzer, WaveLight AG, Erlangen, Germany). Biomechanical metrics (CH and CRF) were measured using the Ocular Response Analyzer (ORA Reichert Ophthalmic Instruments, New York, USA) and then compared. A receiver operating characteristic (ROC) curve was used to identify cut-off points to maximize the sensitivity and specificity for discriminating between the groups. Results: CCT was 491.35±8.4µm (range 471-500) in healthy thin corneas and 490.92±17.96µm (range 459-527) in keratoconus; (p=0.863). CH was 8.58±1.7mm Hg (range: 5.3-12.3mm Hg) in group KC and 9.41±1.51mm Hg (range: 5.8-12.8) in group N (p=0.027). The mean CRF was 8.02± 2.16mm Hg (range: 4.3-13.4) in group KC and 9.26±2.04mm Hg (range: 5.9-13.6) in group N (p=0.010). ROC curve analysis showed a poor overall predictive accuracy of CH (cut-off, 8.90mmHg; sensitivity, 62.5%; specificity, 62.5%; test accuracy, 63%) and CRF (cut-off, 6.7mmHg; sensitivity, 35%; specificity, 92.5%; test accuracy, 66.8%) for detecting keratoconus in the eyes studied. Conclusion: CH and CRF were statistically lower in keratoconus than in healthy thin corneas. However they have a poor overall predictive accuracy with AUROC (area under ROC curve) 0.7.