ИСТИНА

In order to solve the inverse problem of finding the mechanical characteristics of the individual eye efficiently, we developed a rough model of the eyeball loaded by an external device (tonometer). Basing on data that the cornea weakly resists to bending, we represent the cornea by an isotropic, linearly elastic homogenous two-dimensional membrane shell and the sclera, with tissues surrounding it, by an elastic element characterized by a single elastic constant (“scleral stiffness”) [1]. The model contains three elastic constants but our test calculations showed that for clinical estimations two constants are only important. Our asymptotic analysis showed that the approximation proposed is correct for tonometry by the stamp with a sufficiently broad contact area or the plunger of sufficiently small diameter, thus being, for example, applicable to the Maklakoff and Schiøtz, not to Goldmann, tonometers. The data obtained by the latter can only be processed correctly within a more detailed model The relative simplicity of the model makes it possible to practically solve the inverse problem and determine the individual elastic constants of the eye and the true intraocular pressure by performing differential tonometry using impression and applanation tonometers in combination, which is possible in clinical examination. However, further simplification is possible since it turned out that the results of differential impression tonometry (by two weights) are weakly dependent on the cornea stiffness and thus practically sufficient for estimating the scleral stiffness and the intraocular pressure. The additional applanation tonometry by two different weights (elastotonometry) makes it possible to estimate additionally the cornea stiffness and the integral volume extension modulus. Separately from the individual elastic properties of the eye (at least scleral stiffness) the true intraocular pressure cannot be estimated even approximately. Moreover, two elastic parameters are additional characteristics of the eye that may be used in diagnostics. The results are compared with experimental data. The method proposed is being tested in clinics.