Quantifying retinal and choroidal contributions to macular oxygenation: a theoretical approach

Abstract

Purpose : The retinal and choroidal vasculature may play a role in the dry-to-wet conversion of age macular degeneration (AMD) through ischemia. Since the relationship between retinal or choroidal vasculature oxygen supplies and macular tissue oxygenation are not well understood, we developed a mathematical model to facilitate further study.

Methods : The macular region is modeled as a structure including 7 layers (Figure 1): nerve fiber layer, inner plexiform layer, inner nuclear layer, outer plexiform layer, outer nuclear layer, inner segment of photoreceptors layer, retinal pigmented epithelium. Each layer is characterized by specific levels of metabolic consumption. Oxygen supply is provided by the vitreous, the choroid, and by three retinal capillary plexi: superficial capillary plexus (SCP); intermediate capillary plexus (ICP); deep capillary plexus (DCP) (Figure 1). Oxygen profiles through the macular tissue are calculated by simulating the balance between O₂ supply, consumption and diffusion in: a) physiological baseline conditions; b) retinal blood flow reduced by 30% with respect to baseline (which diminishes O₂ supply); c) choroidal oxygen level diminished by 30% with respect to baseline.

Results : Model simulations predict that: 1) the oxygenation of the foveal avascular zone (FAZ) is not affected by reduction in retinal blood flow; 2) a reduction in choroidal oxygen supply is affecting mostly the outer layers, especially the photoreceptors and outer nuclear layers; 3) the impact of reduction in choroidal oxygen supply is greater more proximal to the macular center; vice versa, the impact of reduction in retinal blood flow is greater more proximal to the macular periphery (Figure 2).

Conclusions : Our mathematical model suggests that impairment in the choroidal and retinal O₂ supplies have varying impact on the oxygenation of the macular tissue, depending on the distance from the macula (center or periphery) and on the layers of the retina. Future studies will utilize the model to simulate pathological conditions, such as dry and wet AMD, in order to further the understanding of disease pathophysiology.

This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.

 

Schematic representation of the tissue layers within the macula

 

Relative difference in the partial pressure of oxygen between baseline conditions and: reduced choroidal oxygen supply (left); reduced retinal blood flow (right).