The Influence of Racioethnicity and Glaucoma on Mechanical Properties of Posterior Ocular Tissues

Glaucoma refers to a group of neuronal degenerative diseases that damage the optic nerve in the eye. The known risk factors include racioethnicity, age, family history, elevated intraocular pressure and the optic nerve head (ONH) biomechanics. In the US, the disease is more prevalent in people of African descent and Hispanic ethnicity groups. This dissertation explores computational approaches to investigate the biomechanics of the ONH, specifically the lamina cribrosa (LC) and posterior sclera. Two photon images of human LC samples were collected during pressure inflation experiments. A subdomain-based inverse finite element (iFE) framework was developed using the two photon image volumes to create finite element geometries, impose displacement boundary conditions and quantify anisotropic material properties of the LC. This framework is applied to investigate differences in material stiffness across three racioethnic groups and normal & glaucomatous human samples. Moreover, bright field axon images are utilized to study the correlation between the LC biomechanics and axon counts. In the last aim, a similar subdomain inverse approach is applied to sequential digital image correlation images of the posterior sclera to determine anisotropic material properties. Our results indicate that those of African descent-AD background have significantly larger shear modulus in the inferior-peripheral region than those of European descent-ED and Hispanic ethnicity-HE (p-value = 0.0001) where the median AD shear modulus = 899.35 [IQR: 227.97 - 1194.54] kPa, ED = 23.90 [IQR: 9.17 - 52.19] kPa, HE = 23.47 [IQR: 13.18 - 46.39] kPa. In addition, the ED group has smaller shear modulus in the superior-inferior region compared to AD and HE (p-value = 0.04) where AD = 68.01 [IQR: 12.63 - 1104.10] kPa, ED = 7.84 [IQR: 4.11 - 34.90] kPa, HE =197.05 [IQR: 34.37 - 792.52] kPa. In addition, the shear modulus results from the ED glaucomatous group were significantly larger (p=0.014). Our findings strongly suggest that the differences in the biomechanical response across groups may be attributed to the mechanical properties instead of the LC geometry or morphometry. This work advances our understanding of the ONH biomechanics. The results are insightful as we study the progression and development of glaucoma