PurposeScleral stiffening has been proposed as a treatment for glaucoma to protect the lamina cribrosa (LC) from excessive intraocular pressure–induced deformation. Here we experimentally evaluated the effects of moderate stiffening of the peripapillary sclera on the deformation of the LC.MethodsAn annular sponge, saturated with 1.25% glutaraldehyde, was applied to the external surface of the peripapillary sclera for 5 minutes to stiffen the sclera. Tissue deformation was quantified in two groups of porcine eyes, using digital image correlation (DIC) or computed tomography imaging and digital volume correlation (DVC). In group A (n = 14), eyes were subjected to inflation testing before and after scleral stiffening. Digital image correlation was used to measure scleral deformation and quantify the magnitude of scleral stiffening. In group B (n = 5), the optic nerve head region was imaged using synchrotron radiation phase-contrast microcomputed tomography (PC μCT) at an isotropic spatial resolution of 3.2 μm. Digital volume correlation was used to compute the full-field three-dimensional deformation within the LC and evaluate the effects of peripapillary scleral cross-linking on LC biomechanics.ResultsOn average, scleral treatment with glutaraldehyde caused a 34 ± 14% stiffening of the peripapillary sclera measured at 17 mm Hg and a 47 ± 12% decrease in the maximum tensile strain in the LC measured at 15 mm Hg. The reduction in LC strains was not due to cross-linking of the LC.ConclusionsPeripapillary scleral stiffening is effective at reducing the magnitude of biomechanical strains within the LC. Its potential and future utilization in glaucoma axonal neuroprotection requires further investigation.

The lamina cribrosa (LC) is a complex mesh-like tissue in the posterior eye. Its biomechanical environment is thought to play a major role in glaucoma, the second most common cause of blindness. Due to its small size and relative inaccessibility, high-resolution measurements of LC deformation, important in characterizing LC biomechanics, are challenging. Here we present a novel noninvasive imaging method, which enables measurement of the three-dimensional deformation of the LC caused by acute elevation of intraocular pressure (IOP). Posterior segments of porcine eyes were imaged using synchrotron radiation phase contrast micro-computed tomography (PC μCT) at IOPs between 6 and 37 mmHg. The complex trabecular architecture of the LC was reconstructed with an isotropic spatial resolution of 3.2 μm. Scans acquired at different IOPs were analyzed with digital volume correlation (DVC) to compute full-field deformation within the LC. IOP elevation caused substantial tensile, shearing and compressive devformation within the LC, with maximum tensile strains at 30 mmHg averaging 5.5%, and compressive strains reaching 20%. We conclude that PC μCT provides a novel high-resolution method for imaging the LC, and when combined with DVC, allows for full-field 3D measurement of ex vivo LC biomechanics at high spatial resolution.

Citation: Feola AJ, Coudrillier B, Mulvihill J, et al. Deformation of the lamina cribrosa and optic nerve due to changes in cerebrospinal fluid pressure. Invest Ophthalmol. Vis Sci. 2017;58:207058: -207858: . DOI:10.1167 PURPOSE. Cerebrospinal fluid pressure (CSFp) changes are involved or implicated in various ocular conditions including glaucoma, idiopathic intracranial hypertension, and visual impairment and intracranial pressure syndrome. However, little is known about the effects of CSFp on lamina cribrosa and retrolaminar neural tissue (RLNT) biomechanics, potentially important in these conditions. Our goal was to use an experimental approach to visualize and quantify the deformation of these tissues as CSFp increased.METHODS. The posterior eye and RLNT of porcine eyes (n ¼ 3) were imaged using synchrotron radiation phase-contrast micro-computed tomography (PC lCT) at an intraocular pressure of 15 mm Hg and CSFps of 4, 10, 20, and 30 mm Hg. Scans of each tissue region were acquired at each CSFp step and analyzed using digital volume correlation to determine 3-dimensional tissue deformations. RESULTS.Elevating CSFp increased the strain in the lamina cribrosa and RLNT of all three specimens, with the largest strains occurring in the RLNT. Relative to the baseline CSFp of 4 mm Hg, at 30 mm Hg, the lamina cribrosa experienced a mean first and third principal strain of 4.4% and À3.5%, respectively. The corresponding values for the RLNT were 9.5% and À9.1%. CONCLUSIONS.CSFp has a significant impact on the strain distributions within the lamina cribrosa and, more prominently, within the RLNT. Elevations in CSFp were positively correlated with increasing deformations in each region and may play a role in ocular pathologies linked to changes in CSFp.

Functional adaptation of the femur has been studied extensively by embedding remodelling algorithms in finite element models, with bone commonly assumed to have isotropic material properties for computational efficiency. However, isotropy is insufficient in predicting the directionality of bone's observed microstructure. A novel iterative orthotropic 3D adaptation algorithm is proposed and applied to a finite element model of the whole femur. Bone was modelled as an optimised strain-driven adaptive continuum with local orthotropic symmetry. Each element's material orientations were aligned with the local principal stress directions and their corresponding directional Young's moduli updated proportionally to the associated strain stimuli. The converged predicted density distributions for a coronal section of the whole femur were qualitatively and quantitatively compared with the results obtained by the commonly used isotropic approach to bone adaptation and with ex vivo imaging data. The orthotropic assumption was shown to improve the prediction of bone density distribution when compared with the more commonly used isotropic approach, whilst producing lower comparative mass, structurally optimised models. It was also shown that the orthotropic approach can provide additional directional information on the material properties distributions for the whole femur, an advantage over isotropic bone adaptation. Orthotropic bone models can help in improving research areas in biomechanics where local structure and mechanical properties are of key importance, such as fracture prediction and implant assessment. © 2014 The Authors. International Journal for Numerical Methods in Biomedical Engineering published by John Wiley & Sons, Ltd.

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