Abstract
Purpose :
We developed a combined biomechanical and hemodynamic model of the human eye to estimate blood flow and oxygen concentration within the lamina cribrosa (LC), and rank the factors that influence LC oxygen concentration.
Methods :
We generated 4,000 finite element (FE) eye models with detailed LC microcapillary networks and computed the oxygen concentration within the axons at the level of the LC. We assumed that biomechanical loads (such as intraocular pressure [IOP] or cerebrospinal fluid pressure [CSFP]) could directly affect the 3D configurations and the lumen diameter of the LC microcapillary networks (Figure 1a-d), and thus influence hemodynamics and oxygen concentrations. For each model, we varied the IOP (38+-19 mmHg), the CSFP (19+-7 mmHg), cup-depth (0.2+-0.1 mm), scleral stiffness (+-20% of mean values), LC stiffness (0.41+-0.2 MPa), LC Radius (1.2+-0.1 mm), average LC pore size (5500+-2400 µm2) and the microcapillary arrangement (radial, isotropic or circumferential). Blood flow was assumed to originate from the LC periphery (arterial pressure: 50+-7 mmHg) and drainage occurred via the central retinal vein (venous pressure: 16+-5 mmHg). Finally, we performed linear regressions to rank the influence of each factor on the LC’s tissue oxygen concentration.
Results :
LC radius, arterial pressure and venous pressure were the most important factors influencing the oxygen concentration within the LC (Figure 1e). IOP was another important parameter and eyes with higher IOP had higher compressive strain and significantly lower oxygen concentration. On average, an increase in IOP of 40 mmHg resulted in a decrease in oxygen concentration of 2 mmHg. In general, supero-inferior regions of the LC had significantly lower oxygen concentration than naso-temporal regions, resulting in an hourglass pattern of oxygen distribution.
Conclusions :
This study presents a comprehensive hemodynamical model of the eye that accounts for the biomechanical forces and detailed morphological parameters of the LC. The results provide further insight into the possible relationship of biomechanical and vascular pathways leading to ischemia-induced optic neuropathy.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.