Estimating the elastic properties of the eye from differential tonometry by the Schiøtz tonometer: Analysis of the measurement procedure on the basis of a two-component mathematical model

Resumo

The procedure of differential tonometry by the Schiøtz tonometer is modeled using a two-component model of the eyeball in which the cornea is represented by a momentless deformable and linearly elastic surface and the sclera region by an elastic element that responds to changes in intraocular pressure via changes in volume. Numerical calculations showed that the dependence of intraocular pressure on the weight of a cornea- deforming rod (a plunger) is almost linear. This makes it possible to take the slope of its plot (pressure difference coefficient) as a characteristic of the eye. The coefficient is studied as a function of the elastic characteristics of the eye and the pressure in the unloaded eye. An analysis based on the dimensional theory and confirmed by calculations made it possible to conclude that in the first approximation the pressure-difference coefficient depends on the elastic constants through their ratios to the intraocular pressure. A comparison was made with the standard method of processing the data of differential tonometry.