In Vivo Measurements of Prelamina and Lamina Cribrosa Biomechanical Properties in Humans

Abstract

To develop and use a custom virtual fields method (VFM) to assess the biomechanical properties of human prelamina and lamina cribrosa (LC) in vivo. METHODS. Clinical data of 20 healthy, 20 ocular hypertensive (OHT), 20 primary openangle glaucoma, and 16 primary angle-closure glaucoma eyes were analyzed. For each eye, the intraocular pressure (IOP) and optical coherence tomography (OCT) images of the optic nerve head (ONH) were acquired at the normal state and after acute IOP elevation. The IOP-induced deformation of the ONH was obtained from the OCT volumes using a three-dimensional tracking algorithm and fed into the VFM to extract the biomechanical properties of the prelamina and the LC in vivo. Statistical measurements and P values from the Mann-Whitney-Wilcoxon tests were reported. RESULTS. The average shear moduli of the prelamina and the LC were 64.2 ± 36.1 kPa and 73.1 ± 46.9 kPa, respectively. The shear moduli of the prelamina of healthy subjects were significantly lower than those of the OHT subjects. Comparisons between healthy and glaucoma subjects could not be made robustly due to a small sample size. CONCLUSIONS. We have developed a methodology to assess the biomechanical properties of human ONH tissues in vivo and provide preliminary comparisons in healthy and OHT subjects. Our proposed methodology may be of interest for glaucoma management.

General finite-element framework of the Virtual Fields Method in Nonlinear Elasticity

“…The VFM was previously applied to identify multiaxial hyperelastic properties of murine dissecting aneurysm samples [29, 30, 25] or hyperelastic properties in human ocular tissues [23]. This permitted significant progress especially in the characterization of heterogeneous material properties of lesions exhibiting complex morphologies, with different regions characterized by localized changes in tissue composition, microstructure, and properties.…”

“…For many years, full-field data were mostly available in two-dimensional bodies (membranes, shells) on which displacement fields could be measured using the DIC technique [22, 27, 31]. However, bulk measurements of displacements fields using digital volume correlation and imaging techniques such as Optical Coherence Tomography or Magnetic Resonance Imaging are becoming commonplace in soft tissues [23, 24, 25, 32, 33, 34, 35], offering more and more applications for the VFM in the biomedical field.…”

“…In the more and more common situations when full-field measurements are available [20, 21, 22, 7, 23, 24, 25], an alternative to FEMU is possible: the Virtual Fields Method (VFM), which has been shown to be more direct and robust with respect to unknown boundary conditions in these situations [26].…”

“…the expression of virtual fields used in most of previous studies [27, 30, 31] was well adapted to the 2D geometries such as membranes or shells but there is a range of samples or materials in which boundary conditions or geometries or both cannot be straightforwardly designed or chosen to be 2D. With the acquisition of fully volumetric deformation fields which is expanding for soft tissues [23, 24, 25, 32, 33, 34, 35], there is a need for a method that can provide virtual fields for any 3D geometry and virtual field.…”

General Finite-Element Framework of the Virtual Fields Method in Nonlinear Elasticity

“…In the more and more common situations when full-field measurements are available [7,[20][21][22][23][24][25], an alternative to FEMU is possible: the Virtual Fields Method (VFM), which has been shown to be more direct and robust with respect to unknown boundary conditions in these situations [26].…”