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A method for estimating the mechanical state of the individual human eye on the basis of standard static measurement proceduresтезисы доклада
- Авторы: Stein A.A., Moiseeva I.N., Lyubimov G.A.
- Сборник: 7th World Congress of Biomechanics, July 6-11, 2014, Boston, Massachusets
- Тезисы
- Год издания: 2014
- Место издания: Organ Biomechanics Boston, Massachusets
- Первая страница: 474
- Аннотация: Our investigation is aimed at obtaining reliable estimates for the elastic characteristics and intraocular pressure of the individual human eye on the basis of noninvasive static measurements. Such measurements (tonometry and similar procedures) are used in clinics for diagnostics and their data are commonly processed within elementary models which often yield unreliable mechanical results. On the other hand, detailed mechanical models of the eye contain a lot of parameters (elastic constants, etc.) which cannot be determined for the living eye investigated. However, as experiments demonstrate, the elastic characteristics of the eye are strongly individual and using average characteristics can essentially distort the results. 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 dependence of the intraocular volume on the intraocular pressure and the force applied (volume function) is calculated for various tonometer shapes and elastic moduli present in the model. Using this function, it is possible to determine changes in the intraocular volume in response to the introduction of known fluid volumes, including under a mechanical load, and changes in pressure at a constant volume (tonometry, differential tonometry). 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.
- Добавил в систему: Моисеева Ирина Никитична