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EFFECT OF NONLINEARITY OF THE ELASTIC PROPERTIES OF THE CORNEA ON THE RESULTS OF SCHIØTZ TONOMETRY: ESTIMATION BASED ON A TWO-COMPONENTстатья
- Авторы: Moiseeva I.N., Stein A.A.
- Журнал: Biophysics
- Том: 67
- Номер: 6
- Год издания: 2022
- Издательство: Maik Nauka/Interperiodica Publishing
- Местоположение издательства: Russian Federation
- Первая страница: 983
- Последняя страница: 991
- Аннотация: During Schiøtz tonometry the cornea of the eye, previously loaded with a concave heavy stamp (footplate), is additionally loaded with a rod (plunger), by the depth of immersion of which into the cornea the intraocular pressure is estimated. Mathematical modeling of this process is performed on the basis of an effective model of the eyeball, previously developed and tested by the authors. In contrast to the basic (physically linear) version of this model, the elastic properties of the system are characterized here not by two, but by three essential parameters, one of which is responsible for the nonlinearity of the elastic behavior of the cornea. The influence of such a nonlinearity on the tonometric difference, i.e., the excess of the tonometric pressure (in the eye loaded with a tonometer) over the true one (before loading), is analyzed numerically. The possibility of a nonmonotonic dependence of the tonometric difference on the true pressures when the latter are small, which is absent in the linear model, is found. The correction introduced by the nonlinearity into the calculation of the true pressure from the tonometric one is estimated. This correction has a different sign depending on the true pressure and turns out to be significant for sufficiently high values of this quantity: in this case, taking into account the nonlinearity reduces the tonometric difference. However, the dependence on both stiffnesses present in the model (corneal and scleral) is in most cases more significant than the effect of nonlinearity. The use of the average values of these stiffnesses instead of individual ones when calculating the true pressure can lead to fatal errors for the eyes, the stiffness of which strongly deviates from the average, which, in particular, occurs in glaucoma. The dependences used in the clinic during the standard processing of Schiøtz tonometry data can give correct results with practical accuracy for some values of elastic parameters, but deviate significantly from the calculated ones even at average values of these constants, and the more noticeably the greater the weight of the plunger. A completely correct approach to estimating the mechanical state and mechanical characteristics of the eye should include several measurements with at least two different tonometers, followed by numerical processing of the results.
- Добавил в систему: Моисеева Ирина Никитична