A computational framework to investigate retinal haemodynamics and tissue stress

The process of vision begins in the retina, yet the role of biomechanical forces in the retina is relatively unknown and only recently being explored. This contribution describes a computational framework involving 3D fluid-structure interaction simulations derived from fundus images that work towards creating unique data on retinal biomechanics. We developed methods to convert 2D fundus photographs into 3D geometries that follow the curvature of the retina. Retina arterioles are embedded into a six-layer representation of the retinal tissue with varying material properties throughout the retinal tissue. Using three different human retinas (healthy, glaucoma, diabetic retinopathy) and by varying our simulation approaches, we report the effects of transient versus steady flow, viscosity assumptions (Newtonian, non-Newtonian and Fåhræus-Lindqvist effect) and rigid versus compliant retinal tissue, on resulting wall shear stress (WSS) and von Mises stress. In the retinal arterioles, the choice of viscosity model is important and WSS obtained from models with the Fåhræus-Lindqvist effect is markedly different from Newtonian and non-Newtonian models. We found little difference in WSS between steady-state and pulsatile simulations (< 5%) and show that WSS varies by about 7% between rigid and deformable models. Comparing the three geometries, we found notably different WSS in the healthy (3.3 ± 1.3 Pa), glaucoma (5.7 ± 1.6 Pa) and diabetic retinopathy cases (4.3 ± 1.1 Pa). Conversely, von Mises stress was similar in each case. We have reported a novel biomechanical framework to explore the stresses in the retina. Despite current limitations and lack of complete subject-specific physiological inputs, we believe our framework is the first of its kind and with further improvements could be useful to better understand the biomechanics of the retina.