Lamina Cribrosa Pore Shape and Size as Predictors of Neural Tissue Mechanical Insult

Abstract

PurposeThe purpose of this study was to determine how the architecture of the lamina cribrosa (LC) microstructure, including the shape and size of the lamina pores, influences the IOP-induced deformation of the neural tissues within the LC pores using computational modeling.MethodsWe built seven specimen-specific finite element models of LC microstructure with distinct nonlinear anisotropic properties for LC beams and neural tissues based on histological sections from three sheep eyes. Changes in shape (aspect ratio and convexity) and size (area and perimeter length) due to IOP-induced hoop stress were calculated for 128 LC pores. Multivariate linear regression was used to determine if pore shape and size were correlated with the strain in the pores. We also compared the microstructure models to a homogenized model built following previous approaches.ResultsThe LC microstructure resulted in focal tensile, compressive, and shear strains in the neural tissues of the LC that were not predicted by homogenized models. IOP-induced hoop stress caused pores to become larger and more convex; however, pore aspect ratio did not change consistently. Peak tensile strains within the pores were well predicted by a linear regression model considering the initial convexity (negative correlation, P < 0.001), aspect ratio (positive correlation, P < 0.01), and area (negative correlation, P < 0.01). Significant correlations were also found when considering the deformed shape and size of the LC pores.ConclusionsThe deformation of the LC neural tissues was largely dependent on the collagenous LC beams. Simple measures of LC pore shape and area provided good estimates of neural tissue biomechanical insult.

Cerebrospinal Fluid Pressure: Revisiting Factors Influencing Optic Nerve Head Biomechanics

“… 56 , 66 – 69 Elsewhere we studied the relationship between model detail and predicted LC strain by developing models with a detailed microarchitecture of the beams and pores of the LC. 70 , 71 We found that models with detailed LCs predicted higher strains, particularly in the pores adjacent to the sclera. However, when observed at a larger, mesoscale resolution, the models predicted LC strains between 2% and 4%, similar to the levels we reported here.…”

“…We also aim to inspire others to do more comprehensive analysis of the powerful models they develop. Work is ongoing within our lab 70 , 71 and others 72 – 74 to create improved computational models that capture the anisotropy, 75 – 80 nonlinearity, 75 , 76 , 79 , 81 , 82 and inhomogeneity 79 , 80 , 83 – 85 of the ONH. Another limitation of this work is that the pressure variations were all within the normal range.…”

Peripapillary sclera architecture revisited: A tangential fiber model and its biomechanical implications

“…Following the approaches used elsewhere to study the mechanical effects of PPS collagen fiber architecture [23, 29, 30], we modeled the ONH as a disk (Fig. 2).…”

“…This pressure was calculated based on the law of Laplace for a thin walled-sphere, with a hoop stress multiplier (one half the ratio of the sphere radius to the wall thickness) equal to 10 as in our previous studies. [29, 30] This loading created a state of in-plane biaxial tensile stress in the ONH. Readers interested in more details on the usage, assumptions, and limitations of the law of Laplace are directed to our previous work.…”

Anatomy of the Human Optic Nerve: Structure and Function

“…The relationship between pore shape and neural tissue insult was observed for undeformed configurations. When deformed by intraocular pressure (IOP)-induced hoop stress, the pores became larger and more convex possibly reducing the risk for further insult [80].…”