Biomechanical Analysis of Subclinical Keratoconus With Normal Topographic, Topometric, and Tomographic Findings

PURPOSE: To investigate the corneal biomechanical responses of subclinical keratoconus with normal topographic, topometric, and tomographic findings. METHODS: In this prospective observational study, the study group was selected from patients with clinically evident keratoconus in one eye and subclinical keratoconus with normal topographic, topometric, and tomographic findings in the fellow eye. The control group was selected from candidates for contact lens use. The biomechanical analyses were performed using the Corvis ST (Oculus Optikgeräte, Wetzlar, Germany). The following parameters were analyzed: A1 velocity, A2 velocity, A1 length, A2 length, deformation amplitude ratio, stiffness parameter at the first applanation, Corvis Biomechanical Index, and Tomographic and Biomechanical Index (TBI). RESULTS: The study group consisted of 21 patients (10 men and 11 women; mean age: 27.7 ± 6.9 years), and the control group consisted of 35 patients (17 men and 18 women; mean age: 26.1 ± 5.8 years). No significant differences were found between the eyes with subclinical keratoconus and normal eyes in corrected distance visual acuity and the topographic, topometric, and tomographic parameters ( P > .05). Significant differences were found in the values of A2 length, A1 velocity, A2 velocity, and TBI between the subclinical keratoconus group and the control group ( P < .05). In distinguishing eyes with subclinical keratoconus from normal eyes, the TBI showed the highest area under the curve (0.790; cut-off: 0.29; sensitivity: 67%; specificity: 86%) in the receiver operating characteristic analysis. CONCLUSIONS: Biomechanical analysis with the Corvis ST may be used as a complementary diagnostic method in detecting subclinical keratoconus. [ J Refract Surg . 2019;35(4):247–252.]