Abstract
Purpose :
During macular edema fluid accumulation typically occurs in the fovea, although this is an avascular region. We propose an explanation of this finding, based on the use of a mathematical model of fluid and solute transport in the retina.
Methods :
Müller cell (MC) density varies along the retina, being very low in the fovea and much larger in the parafovea. Moreover, MCs are orthogonal to the retinal surface at their extremities and inclined in the middle layer. We hypothesize that this reduces tissue permeability there, and we justify this assumption by a calculation based on homogenization theory. We then study motion in the retina in the presence of leakage from damaged vasculature, modeling the tissue as a non-homogeneous, anisotropic, poro-elastic medium. We assume that the undeformed retinal thickness is constant and consider an axial symmetric solution, with the center of the fovea being the origin of the radial coordinate. We assume that fluid and proteins exude from capillaries at a given distance from the axis of symmetry, owing to impairment of the blood retinal barrier.
Results :
The overall hydraulic conductivity of the retinal tissue predicted by our model is 1.2 x 10-11 m2/s/Pa, in good agreement with the value measured by Fatt et al. (1971) of 9.4 x 10-12 m2/s/Pa. The fluid circulation model predicts that fluid accumulates in the fovea (Fig.1), where the pressure is largest and the tissue is more deformable, because of the low density of MCs. Fluid moves a long distance from the exudation region along the retina because tissue permeability is low the middle layer (see streamlines in Fig.1).
Conclusions :
Our model suggests that the density and conformation of MCs have a significant impact on fluid motion in the retina during macular edema. Fluid accumulates in the foveal region since this region is more compliant than the rest of the retina and the pressure there is higher.
This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.