[The effect of intraocular pressure on refractive power of the cornea and the human eye, based on the Liou-Brennan model eye]. / A szemnyomás változásának hatása a szaruhártya és a szem töroerejére a Liou­Brennan-modellszem alapján.

INTRODUCTION: It is a clinical experience that with significantly higher intraocular pressure, glass ordering may be inaccurate, therefore, it should be performed after adjustment of intraocular pressure. OBJECTIVE: To analyze the effect of intraocular pressure on the refractive power of the cornea and of the eye, using geometrical properties of the Liou-Brennan model eye and finite element modeling. METHODS: Using corneal parameters of the Liou-Brennan model eye, a parametric geometrical model and with these data finite element modelling, using the Ansys (Ansys, Canonsburg, PA, USA) program, has been performed. Corneal tissue properties have been defined based on trilinear material model of Wollensak and boundary conditions based on Pandolfi. The effect of changes in intraocular pressure on geometrical corneal properties with optical impact (corneal curvature at the anterior and posterior corneal surface at the optical center and axial displacement of the anterior and posterior corneal surface points at the optical center) have been analyzed. Based on the geometric characteristics obtained, using the paraxial ray tracing method, changes in the optical properties of the cornea and the eye have been calculated. RESULTS: With increasing intraocular pressure load, anterior and posterior central corneal radius of curvature decreased and corneal surface points at the optical center at the anterior and posterior surface moved forwards, the cornea thinned. Axial displacement of corneal volume points was maximal for all pressure load values at the optical center of the posterior corneal surface. The refractive power of the cornea decreased as eye pressure increased, while the refractive power of the entire eye increased. CONCLUSION: We verified using the Liou-Brennan model eye and finite element modelling that a change of the intraocular pressure load between 10 and 30 mmHg may result in 0.31-0.86 mm decrease of the corneal radius of curvature, in 1.5-4.8 D increase in the keratometric values and in about 1.2-3.9 D increase in the total optical power of the eye. A decrease of 0.14 D to 0.69 D has been measured in the corneal optical power in the examined eye pressure range. Orv Hetil. 2022; 163(47): 1872-1879.

Laboratory tests for strength paramaters of brain aneurysms.

The presentation is focused on the analysis of biophysical properties of cerebral aneurysms, diagnosed and delineated in living human individuals. An aneurysm is a bulging out of a part of the wall of a blood vessel. The aim of our research was to delineate flow patterns inside the aneurysm and its parent artery, to estimate stresses at critical points of the aneurysm wall, to model the haemodynamic effect of different surgical and endovascular tools in order to define the optimal one in a particular case, and to estimate the likelihood of a later aneurysm rupture. For this reason we carried out a lot of different laboratory tests to analyse the mechanical parameters of the aneurysm wall. We made a comparative study of some material models reported in the literature to describe the mechanical response of arteries. These are models for incompressible materials. For this reason we perform uniaxial and biaxial measurements to have appropriate parameters for the models of underlying material.