Hydraulic network model of fluid mechanics in the optic nerve head: insights into the development of optic disc edema

Long-duration space travel is accompanied with numerous physiological challenges, among which vision-related complications are of particular concern. Spaceflight-associated neuro-ocular syndrome leads to neuro-ophthalmic issues, including swelling of the optic disc or optic disc edema (ODE), choroidal folds, cotton-wool spots, and more. Recent research suggests a predominant role of cerebrospinal fluid flow in the optic nerve head and optic nerve sheath in the development of ODE. We are developing a hydraulic network model that solves the fluid mechanics of water-like fluid, that includes cerebrospinal fluid, interstitial fluid, and axonal fluid, in the optic nerve head. To this end, we implement a steady, zero-dimensional form of the Navier-Stokes equation, allowing the quantification of pressure and volumetric flow rate in different compartments of the optic nerve-head such as the extracellular spaces, axons, perivascular spaces, and the subarachnoid space. We probe key factors leading to ODE, which includes increased intracranial pressure, perivenous congestion, and alterations of the glymphatic system in microgravity. We also perform a parametric study to find the key parameters that contribute to ODE. Overall, the study advances our understanding of the mechanisms behind the ODE pathology in terrestrial and microgravity conditions.