Abstract
Purpose :
The choriocapillaris fulfills many functions essential to retinal homeostasis. It supports the delivery of metabolism substrates to the photoreceptors, clears metabolic waste products from the subretinal space and may passively regulate the temperature of the back of the eye. Previous experimental and theoretical work have shown that the choriocapillaris comprises diffusion-limited regions, where the passive transport of material is dominantly diffusive. We sought to characterize the salient features of mass transport within these regions and to identify the structural and functional parameters determining their physical characteristics.
Methods :
This analysis relied on three-dimensional mathematical models of the choriocapillaris informed by the angioarchitecture of the human choroid as observed through whole mounts stained with Ulex Europaeus Agglutinin I. Blood was modelled as a Newtonian fluid, and analytical and numerical solutions for the blood flow were obtained by solving the Navier-Stokes equation. Mass was modeled as a passive scalar, and its concentration field was determined by solving the advection-diffusion equation. Transfers to the retina were simulated by imposing a Dirichlet boundary condition on the upper surface of the choriocapillaris and studying spatial variations of the Nusselt number.
Results :
Diffusion-limited regions represent areas of reduced exchange with the outer retina. Their number is equal to the number of arteries and vein connected to the choriocapillaris, which makes them ubiquitous. The width of these regions is solute-specific and increases with molecular diffusivity. It is mainly determined by the relative arrangement of arteriolar and venular insertions into the choriocapillaris, arterial flow rate and the vascular volume fraction of this capillary bed.
Conclusions :
Exchange between the choriocapillaris and outer retina is markedly reduced over diffusion-limited regions. The location and surface area of these regions is determined by both structural and functional parameters, some of them quantifiable using imaging techniques. Their existence and characteristics may partly explain the spatial selectivity of several pathologies associated with degenerative diseases of the retina.
This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.