Dependence of cornea deformation on system parameters under high-rate non-stationary loading

Mathematical modeling of the deformation of the eyeball under non-stationary action of external pressure applied in a limited area of the cornea is performed in a wide range of parameters characterizing the system. The pressure first increases and then decreases in such a way that the pressure–time curve turns out to be symmetrical. The characteristic time of the entire process is of the order of several tens of milliseconds. Such a dependence corresponds to the effect on the eye, which is realized in the Eye Response Analyzer (ORA). The authors' previously developed approach is used, based on the representation of the cornea as a soft two-dimensional surface and of the scleral region as a zero-dimensional element. The deformation of the cornea is described by linear viscoelastic relations of the Voigt type, and the scleral ele-ment is considered linearly elastic. Twice (under loading and unloading) the central region of the cornea takes a shape close to flat. The dependence of the values, which characterize the location of flattening moments on the pressure–time curve, on the true intraocular pressure, mechanical properties of eye tissues, and maximum loading pressure is investigated. It is shown that the average flattening pressure (half the sum of the flattening pressures during loading and unloading) can be used to estimate the true intraocular pressure, but taking into account individual mechanical (elastic and viscoelastic) properties of eye tissues can introduce certain corrections. The value of corneal hysteresis (the difference in flattening pressures) significantly depends on the true intraocular pressure and, in general, cannot be considered as a characteristic directly reflecting the degree of viscoelasticity of the cornea. A technique for effectively estimating the parameter characterizing its viscoelasticity, based on experimentally determined data, is proposed.