The measurement of central corneal thickness (CCT) is important in ophthalmology. Most studies concerned the value at normal status, while rare ones focused on its dynamic changing. The commercial Corvis ST is the only commercial device currently available to visualize the two-dimensional image of dynamic corneal profiles during an air puff indentation. However, the directly observed CCT involves the Scheimpflug distortion, thus misleading the clinical diagnosis. This study aimed to correct the distortion for better measuring the dynamic CCTs. The optical path was first derived to consider the influence of factors on the use of Covis ST. A correction method was then proposed to estimate the CCT at any time during air puff indentation. Simulation results demonstrated the feasibility of the intuitive-feasible calibration for measuring the stationary CCT and indicated the necessity of correction when air puffed. Experiments on three contact lenses and four human corneas verified the prediction that the CCT would be underestimated when the improper calibration was conducted for air and overestimated when it was conducted on contact lenses made of polymethylmethacrylate. Using the proposed method, the CCT was finally observed to increase by 66±34 μm at highest concavity in 48 normal human corneas.
In this study, we developed a miniaturized optical coherence tomography (OCT) probe with a diameter of 4 mm. It was integrated with an air-jet indentation and air suction to induce deformation of tissue. The deforming process of tissue under suction or indentation was continuously monitored by OCT, and deformation of tissue was then derived from the transient OCT signals. Studies on phantoms with different stiffness were conducted. Results showed that the stiffness obtained by the OCT-based suction and indention well correlated with the stiffness detected using conventional mechanical testing. The probe was small enough for endoscopic use. In addition to the elasticity, the viscoelasticity of tissues can also be detected using creep indentation and suction test.