ОЦЕНКА ИЗМЕНЕНИЯ НАПРЯЖЕННО-ДЕФОРМИРОВАННОГО СОСТОЯНИЯ ГЛАЗА И ПОКАЗАТЕЛЕЙ ВНУТРИГЛАЗНОГО ДАВЛЕНИЯ ПОСЛЕ РЕФРАКЦИОННОЙ КОРРЕКЦИИ ГИПЕРМЕТРОПИИ

Abstract

The influence of the parameters of annular layer which is removed in surgical LASIK and IntraLASIK correction of hyperopia on the changes of the stress-strain state of the cornea is analized. The elastic system cornea-sclera is presented as two conjugate transversely isotropic spherical segments loaded by internal pressure. In order to estimate changes of the intraocular pressure measurements obtained by Goldmann (GAT) and Maklakov (MAT) applanation tonometers after hyperopia surgery, the problem of deformation of the cornea under the load with a flat base is considered. A comparison of the results of two different operations and a comparison of two methods of measuring intraocular pressure for each of these operations is carried out using in all cases the same true intraocular pressure. As a result of the finite element simulation, it was found that reduction in the cornea thickness as a result of annular layer removing during hyperopia surgical correction reduces the flexural rigidity of the cornea and, as a consequence, leads to decrease in the intraocular pressure readings obtained by GAT and MAT. According to calculations, the changes in the intraocular pressure readings depend on the inner and outer diameters of the annular layer, on the depth of the ablation zone, and on the thickness of corneal flap. Nevertheless it was obtained than changes in the intraocular pressure readings obtained by MAT are significantly less than changes obtained by GAT. Numerical calculations have shown the advantage of the IntraLASIK refractive correction of hyperopia compared to the LASIK correction. Because of the fact that during the LASIK surgery the annular layer with smaller inner and outer diameters is ablated and thicker corneal flap is cut, larger deformations and displacements in the thinning region of the cornea, as well as greater decrease of the flexural rigidity of the cornea, have been observed.