Accuracy of the Corvis Biomechanical Index in Keratoconus Screening
Purpose: To evaluate the accuracy of the Corvis Biomechanical Index (CBI) in screening of patients with Keratoconus.
Study Design: Cross sectional study.
Place and Duration of Study: Amanat Eye Hospital Peshawar from July 2018 to June 2019.
Material and Methods: One thousand eyes were included in this study. Patients who came for keratorefractive laser procedure or collagen cross linkage were included in the study by convenient sampling technique. Six hundred and eleven patients had early Keratoconus and 389 were normal controls. Control group included those individuals who had visual acuity of 6/6 with no clinical feature of Keratoconus and normal TBI. All individuals included in the study underwent a thorough ocular examination, CBI and TBI tests. SPSS version 23 was used for statistical analysis of collected data.
Results: The mean CBI value was 0.3186 ± 0.407 standard deviation (SD), the standard error (SE) of the mean was 0.0129 with a 95% confidence interval (CI) of 0.293 to 0.343. The minimum CBI value was 0.00 and the maximum value was 1.00. The mean Tomographic Biomechanical Index (TBI) value was 0.465 ± 0.392 SD, SE was 0.124 with a 95% CI of 0.222 to 0.708. The range of TBI values was 0.00 to 1.00. For CBI, sensitivity was 58.2%, specificity was 100%, positive predictive value was 100%, and negative predictive value was 61.2%.
Conclusion: Although CBI is accurate in terms of specificity and sensitivity, the result should be interpreted in combination with clinical data and other topographic and tomographic parameters.