CFD analysis of cerebrospinal fluid dynamics in the optic nerve sheath: impact of distal drainage and permeability in glaucoma subtypes

The optic nerve subarachnoid space (ONSAS) serves as a crucial cerebrospinal fluid (CSF) conduit, implicated in the pathophysiology of disorders such as normal-tension glaucoma (NTG), idiopathic intracranial hypertension (IIH), and papilledema. However, its biomechanical role remains poorly understood due to challenges in imaging and invasive measurement limitations. In this study, we develop a computational fluid dynamics (CFD) framework leveraging anatomically accurate 3D reconstructions of ONSAS geometry derived from high-resolution T2-weighted MRI. Physiological intracranial pressure waveforms incorporating both cardiac and respiratory oscillations were applied to drive the flow, while a novel porous boundary condition was introduced at the distal ONSAS to model drainage into lymphatic pathways—supported by histological and tracer-based evidence [Killer et al., Brain 130, 514 (2007); Ma et al., Nature 565, 86 (2019)]. By varying Darcy permeability and outflow rates across various cases (healthy, NTG, and IIH), we quantified CSF velocities and pressure profiles with distinct flow patterns. Notably, NTG cases demonstrated increased proximal velocities linked to enhanced permeability or drainage, while IIH cases exhibited stagnation due to suppressed or obstructed outflow, consistent with clinical presentations. These trends were observed across anatomically defined bulbar and distal cross-sections, revealing condition-specific velocity signatures that cannot be captured by currently available method such as PC-MRI (phase-contrast MRI). The results offer a mechanistic explanation for optic nerve stress patterns seen in vivo and underscore the diagnostic potential of detailed CSF flow mapping in ophthalmic practice. [Berdahl et al., Ophthalmology 115, 763 (2008); Boye et al., Clin. Exp. Ophthalmol. 46, 511 (2018)]. The study underscores the limitations of PC-MRI in capturing local CSF dynamics and establishes CFD as a powerful alternative for high-fidelity modeling of CSF transport dynamics inside ONSAS. Furthermore, the current framework allows for future integration of fluid–structure interaction to assess optic nerve head deformation/displacement under varying intraocular and intracranial pressures.