Comparison of Corneal Tomography and a New Combined Tomographic Biomechanical Index in Subclinical Keratoconus

PURPOSE: To investigate and compare the diagnostic ability of corneal tomography and biomechanical and combined parameters for detection of corneal ectasia. METHODS: Consecutive patients with subclinical keratoconus (SCKC) and age-matched controls were included. Only one eye from each patient was selected for analysis. The final D value from the Belin/Ambrosio Enhanced Ectasia Display (BAD) was obtained from the Pentacam (Oculus Optikgerate, Wetzlar, Germany). The tomographic biomechanical index (TBI) was derived from the Pentacam and Corvis ST (Oculus Optikgerate). Classification analysis between normal and subclinical keratoconus (SCKC) was evaluated using receiver operating characteristic (ROC) curves. The area under the ROC curve (AUC) and partial AUC (pAUC) with specificity of 80% or greater were compared. RESULTS: Twenty-three eyes with SCKC and 37 normal eyes were included. All Pentacam-derived parameters (P < .001) and all but two Corvis ST-derived parameters (P < .020) were significantly different between normal and SCKC eyes. A significant difference was found in the final D value (P = .020) and TBI (P = .040) between normal and SCKC eyes. For differentiating normal and SCKC eyes, TBI and BAD final D value demonstrated the highest AUC (0.925 and 0.786, respectively) and pAUC (0.150 and 0.088, respectively). TBI demonstrated 84.4% sensitivity and 82.4% specificity using a cut-off of 0.16. Comparative analysis between these parameters showed that AUC and pAUC of TBI were significantly higher than all parameters from Pentacam (P = .032). CONCLUSIONS: In the current study, combined use of tomographic and biomechanical parameters demonstrated a higher capability in differentiating normal and SCKC eyes when compared to tomographic analysis alone.