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Multi-Field Coupled Simulation of Aqueous Humor in Rabbit Eye

Understanding the variation of the pressure difference between Anterior Chamber (AC) and Posterior Chamber (PC), as well as the state of aqueous flow, is the focus problem to know more about the progression and blinding mechanism of glaucoma. Aqueous humor is developed in the PC at the ciliary body, then flows into the AC through the pupil, and is finally absorbed through trabecular meshwork at the angle of AC. This flow process plays an important role in intraocular pressure (IOP) and the increased IOP is one of the major risk factors for the primary angle closure glaucoma. Although there are so many studies about aqueous humor flow, most of them are greatly simplified without considering the physiological variation of the Pressure Difference between PC and AC (PDPA), and the coupling effects of fluid-solid-heat are rarely implemented. The aim of the present study is to investigate the aqueous humor flow based on the coupling effects of fluid-solid-heat and considering multiple influence factors by means of numerical simulation method. Based on 24h continuous in vivo test of PDPA for both normal and high IOP rabbit eyes, 3D rabbit eye models were reconstructed based on eye rabbit tissue sections, and finite element models for multi-field coupling analyses were established so as to mimic and analyze the variation rules of aqueous humor flow. Iris, cornea and lens are all of linear elastic property. The aqueous humor is incompressable laminar viscous Newtonian fluid. The upper and lower surfaces of iris and the inner suface of conea are contated with aqueous humor, and they are the interface of fluid-solid interaction where the no-slip condition is satisfied. The temperature at the inner surface of conea is 33 o C, and elsewhere 37 o C. According to different boundary conditions, two models were constructed for simulation. Model A is for multi-field coupling and Model B is for fluid-solid interaction under condition of normal IOP. ADINA (ADINA Inc.，USA) software was applied to mimic the aqueous humor flow and analyze the distribution of temperature, velocity, pressure and stress. The variation of node velocities in Model B is of little difference with Model A. With the action of PDPA, the iris bulges forward and results in the decrease of chamber angle. Meanwhile, deformation and stress develop in the cornea and iris during the aqueous humor flow process, with the maximum stress locating at the center for the cornea and at the root for the iris. The temperature difference in the AC induced buoyancy force drives the aqueous humor to flow through the iris and the cornea, then two symmetric vertices develop in the AC. The contour of temperature demonstrates multiple peaks with larger value near the pupil. There is a temperature difference in the anterior segments, which plays an important role in the aqueous humor flow and affects the flow pattern and distribution. Considering the low temperature of 33 o C on the surface of cornea is of significance to exhibit the temperature distribution and flow pattern of the aqueous humor flow. It is necessary to perform multi-field coupling simulation based on realistic PDPA measurement when studying the aqueous humor flow in eyes.