Abstract
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.
Highlights
Identification and exclusion of Forme Fruste Keratoconus prior to any photorefractive procedure is Received: May 28, 2020 Accepted: June 25, 2020Revised: June 22, 2020 important because it can develop into established Keratoconus after surgery resulting in deterioration of vision.[1]
The current study showed acceptable accuracy of Corvis Biomechanical Index (CBI) in terms of specificity and sensitivity
The result should be interpreted in combination with clinical data and other topographic and tomographic parameters
Summary
Identification and exclusion of Forme Fruste Keratoconus prior to any photorefractive procedure is Received: May 28, 2020 Accepted: June 25, 2020Revised: June 22, 2020 important because it can develop into established Keratoconus after surgery resulting in deterioration of vision.[1]. If early Keratoconus is diagnosed, collagen cross linking can arrest the progression of Keratoconus.[2,3,4] Keratoconus is a bilateral disease in which there is thinning and steepening of the central and paracentral cornea, appearing around puberty. Different devices are used nowadays for Keratoconus screening, incorporating corneal tomography or pachymetry and topography These include; Orbscan II6 (Bausch & Lomb, New York, US), Pentacam[7] (Oculus Optikgeräte GmbH, Wetzlar Germany), Galilei G48 (Ziemer, Port, Switzerland), and SIRIUS9 (CSO, Firenze, Italy). These devices measure corneal curvature, corneal thickness, and elevation of the anterior and posterior corneal surface. It has been found that changes in biomechanical stability of the cornea precedes topographic and tomographic changes in Keratoconus.[10,11] To study the biomechanical behavior of cornea, currently used devices are Ocular Response Analyzer R (ORA; Reichert, New York, US) and the Corneal Visualization Scheimpflug Technology Corvis ST; (Oculus Optikgerate GmbH, Wetzlar, Germany)
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