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Numerical and Experimental Study of the Spatial Stress Distribution on the Cornea Surface During a Non-Contact Tonometry Examination
The determination of biomechanical properties of the cornea by a non-contact tonometry (NCT) examination requires a precise knowledge of the air puff generated in the device, which is applied to the cornea surface. In this study, a method is proposed to identify the resulting stress profile on the surface, which may be used to numerically solve an inverse problem to obtain the material properties. This method is based on an experimental characterization of the air puff created by the Corvis ST in combination with computational fluid dynamic (CFD) simulations, which are adjusted to the experimental data. The identified nozzle inlet pressure of approximately 25 kPa (188.5mmHg) is then used for a numerical influence study of the interaction between the air puff and the cornea deformation. Therefore, eleven cornea deformation states based on measurements are implemented in the CFD model. A more realistic model is also analyzed by the geometrical reproduction of the human face, which is used for a further influence study. The outcomes showed a dependence between the cornea deformation and the pressure as well as the shear stress distribution. However, quantitatively, the shear stress component can be considered of minor importance being approximately one hundred times smaller than the pressure. The examination with consideration of the human face demonstrates that the pressure and shear stress distributions are not rotationally symmetric in measurements on real humans, which indicates the requirement to include more complex stress distributions on the eye. We present the detailed stress distribution on the cornea during a non-contact tonometry examination, which is made accessible for further investigations in the future by analytical nonlinear functions. © 2018, Society for Experimental Mechanics.