Nutwipa Teeyapant, MD¹, Pakornkit Phrueksaudomchai, MD²^,³

Background: Corneal biomechanics differ among different ethnicities. The cTBI is a parameter adjusted from the tomographic biomechanical index (TBI) for the Chinese population to maintain high sensitivity and increase specificity for detecting keratoconus.

Objective: To determine the sensitivity and specificity of cTBI compared with those of TBI in screening for keratoconus, and subclinical keratoconus patients and to determine the optimal cutoff values of TBI and cTBI in patients who came to the corneal refractive surgery clinic in Thailand.

Materials and Methods: Patients were included from a single center at Thammasat University Hospital. All patients who presented between January 2023 and April 2024 were evaluated and divided into three categories: keratoconus patients, subclinical keratoconus patients, and normal individuals. The optimal cutoff points for TBI and cTBI, which maximized both sensitivity and specificity, were found using the area under the receiver operating characteristic (AUROC) curves.

Results: Five patients were diagnosed with keratoconus. All patients had early keratoconus. Thirty-three patients were considered to have subclinical keratoconus, and 272 patients had normal profiles. AUROC curves revealed AUCs of 0.861 (95% CI 0.812 to 0.910) for cTBI, 0.842 (95% CI 0.793 to 0.892) for TBI, 0.809 (95% CI 0.742 to 0.875) for cCBI, and 0.808 (95% CI 0.732 to 0.884) for CBI. These results revealed that cTBI had the highest diagnostic performance among the other three Corvis parameters in differentiating between normal populations and subclinical keratoconus or keratoconus populations, although the difference was not statistically significant (p=0.451). The best threshold value from the study for cTBI was 0.17, with 89.5% sensitivity and 75.4% specificity. For the TBI, a cutoff value of 0.47 provided the optimum result, with 81.6% sensitivity and 78.3% specificity.

Conclusion: From this study, TBI is a reliable parameter for detecting early keratoconus and at-risk patients. The cTBI could help reduce the false positive rate of diagnosing patients with keratoconus or at-risk patients, albeit with decreased sensitivity. It is still necessary to combine several parameters to diagnose patients with keratoconus and guide further management.

Received 28 November 2025 | Revised 7 January 2026 | Accepted 20 January 2026

DOI: 10.35755/jmedassocthai.2026.5.03916