Morphometric, Hemodynamic, and Biomechanical Factors Influencing Blood Flow and Oxygen Concentration in the Human Lamina Cribrosa

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 5000 finite-element eye models with detailed microcapillary networks of the LC and computed the oxygen concentration of the lamina retinal ganglion cell axons. For each model, we varied the intraocular pressure (IOP) from 10 mm Hg to 55 mm Hg in 5-mm Hg increments, the cerebrospinal fluid pressure (13 ± 2 mm Hg), cup depth (0.2 ± 0.1 mm), scleral stiffness (±20% of the mean values), LC stiffness (0.41 ± 0.2 MPa), LC radius (1.2 ± 0.12 mm), average LC pore size (5400 ± 2400 μm 2), the microcapillary arrangement (radial, isotropic, or circumferential), and perfusion pressure (50 ± 9 mm Hg). Blood flow was assumed to originate from the LC periphery and drain via the central retinal vein. Finally, we performed linear regressions to rank the influence of each factor on the LC tissue oxygen concentration. RESULTS. LC radius and perfusion pressure were the most important factors in influencing the oxygen concentration of the LC. IOP was another important parameter, and eyes with higher IOP had higher compressive strain and slightly lower oxygen concentration. In general, superior-inferior regions of the LC had significantly lower oxygen concentration than the nasal-temporal regions, resulting in an hourglass pattern of oxygen deficiency. CONCLUSIONS. To the best of our knowledge, this study is the first to implement a comprehensive hemodynamical model of the eye that accounts for the biomechanical forces and 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.

Differing Associations between Optic Nerve Head Strains and Visual Field Loss in Patients with Normal- and High-Tension Glaucoma

“…Interestingly, significant negative associations were found for any given tissue, whether neural or connective (Figure 3). According to the biomechanical theory of glaucoma, 21 IOP-induced strain could potentially: (1) directly induce mechanical damage to the RGCs, 22 (2) disrupt the microcapillary blood flow at the LC, choroid and the retina [23][24][25] and (3) disrupt the axoplasmic flow. 26 Therefore, it would be plausible that eyes with structurally weaker ONHs (and thus higher strains) would be more susceptible to visual field loss.…”

Lamina Cribrosa Morphology in Normal Tension Glaucoma According to the Location of Visual Field Defects

“…Lee et al 38 reported that the microvascular dropout in the parapapillary choroid has a strong relationship with initial PFS in POAG patients. Furthermore, Chuangsuwanich et al 39 investigated the link between the morphologic parameters and the hemodynamic changes of LC using finite-element analysis, and reported that the average oxygen concentration was lower in the central region than in the peripheral region of LC. In addition, when IOP was elevated, the oxygen concentration of LC declined and, notably, a greater cup depth and a weaker LC produced a lower oxygen concentration in LC.…”

Glaucoma and biomechanics

“…On the contrary, OCT, and its derivative elastography technique (optical coherence elastography [OCE]) [123,124], has superior spatial resolution, and in combination with biomechanical modeling, is a potent alternative for investigating ONH biomechanical properties in vivo [61 ▪▪ ,125 ▪ ,126]. Interestingly, OCT-driven morphologic reconstructions of the ONH can be used to generate patient-specific computer models to study ONH biomechanics [127] and hemodynamics [128], which may eventually be used as new tools for assessing progression of ONH pathological remodeling in glaucoma.…”