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Performance of new Corvis ST parameters in differentiating between healthy corneas and different stages of
B Omari1, C Khodriss1, C El Ouazzani1
1Ophthalmology Department, Mohammed VI University Hospital of Tangier, Faculty of Medicine and Pharmacy of Tangier, Abdelmalek Essaâdi University, Rabat avenue, Km 17 BP 398, Gzinaya, Tangier, Morocco.
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.
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