Performance of new Corvis ST parameters in differentiating between healthy corneas and different stages of keratoconus in a North African population.

PURPOSE: To determine the accuracy of various biomechanical parameters, including the updated version of the stress-strain index (SSIv2), the Corvis Biomechanical Factor (CBiF), and the Chinese Corvis Biomechanical Index (cCBI), in differentiating between normal corneas and keratoconus at different stages in a North African population.

METHODS

This prospective observational case-control study included three groups: the normal group (100 eyes), moderate keratoconus group (KC grade 1: 56 eyes), and severe keratoconus group (KC Grade 2: 51 eyes). Each eye underwent Corvis ST examination to determine the stiffness parameter at first applanation (SP-A1), Ambrósio relational thickness (ARTh), integrated inverse radius (IIR), velocity at first applanation (velocity A1), biomechanical-corrected IOP (bIOP), tomographic and biomechanical index (TBI), CBI, and the new parameters SSIv2, CBiF, and cCBI. Comparison of biomechanical parameters between groups was performed using ANOVA or Kruskal-Wallis tests (with P<0.05). The performance of these parameters was evaluated using ROC (Receiver Operating Characteristic) curves by determining AUCs (Area Under the Curve), which were compared using DeLong's test.

RESULTS

Before and after correction for age, central corneal thickness, and bIOP, most biomechanical parameters were significantly different among the three groups (P<0.05). The TBI had the highest diagnostic accuracy (AUC=0.997) in detecting keratoconus, followed by the CBI (0.975), ARTh (0.948), and IIR (0.939). The CBI and ARTh presented the highest efficacy in differentiating between keratoconus severities (AUC=0.861 and 0.850, respectively). CBiF and cCBI showed excellent ability to diagnose keratoconus (AUC=0.937 and 0.933, respectively). SSIv2 demonstrated good potential (AUC=0.796) for detecting keratoconus.

CONCLUSION

In a North African population, the TBI best distinguished keratoconus eyes from normal eyes, followed by the CBI and ARTh. CBiF, cCBI, and SSIv2 demonstrated excellent performance, albeit less so.