Note that rhesus monkey age is considered to be approximately one third of human age. Eight rhesus monkeys were included in the study, without any apparent ocular abnormality, classified into two age groups: four were younger than 2.1 years (1.5 В± 0.7 years) and four were older than 18 years (22.9 В± 5.3 years). 13, 46вЂ“ 50 Finally, we derived eye-specific sets of scleral biomechanical properties based on the experimental observations using an inverse FE method, 45 then tested the hypothesis that these parameters vary significantly with age.ДЄll experiments adhered to the ARVO Statement for the Use of Animals in Ophthalmic and Vision Research. 45 We then modeled the monkey's posterior sclera as a nonlinear, anisotropic, inhomogeneous soft-tissue using a fiber-reinforced constitutive theory that includes stretch-induced stiffening and multidirectionality of the collagen fiber. In the present one, we used our latest ex vivo method to experimentally measure the 3-D deformation pattern and thickness of posterior sclera from both eyes of four young and four old monkeys exposed to an experimental IOP elevation from 5 to 45 mm Hg. In recent studies, we reported the 1-D, 41вЂ“ 43 2-D, 44 and 3-D 45 deformation patterns of posterior and peripapillary sclera using ex vivo experimental protocols. In this study, we investigated the effects of aging on the biomechanical behavior of posterior sclera obtained from monkey eyes. Age-related stiffening of the sclera may significantly influence ONH biomechanics and potentially contribute to age-related susceptibility to glaucomatous vision loss. Posterior sclera of old monkeys is significantly stiffer than that of young monkeys and is therefore subject to higher stresses but lower strains at all levels of IOP. No difference was found in the preferred collagen fiber orientation and fiber concentration factor between age groups. On average, scleral collagen fibers were circumferentially oriented around the optic nerve head (ONH). The sclera was significantly thinner ( P = 0.038) and tangent modulus and structural stiffness were significantly higher in old monkeys ( P < 0.0001). The posterior sclera exhibited inhomogeneous, anisotropic, nonlinear mechanical behavior. The model yielded 3-D deformations of posterior sclera that matched well with those observed experimentally.

Displacements, thickness, stress, strain, tangent modulus, structural stiffness, and preferred collagen fiber orientation were mapped for each posterior sclera.

An inverse finite element (FE) method incorporating a fiber-reinforced constitutive model was used to extract a unique set of biomechanical properties for each eye. Each scleral shell's geometry was digitally reconstructed from data generated by a 3-D digitizer (topography) and 20-MHz ultrasound (thickness). The posterior scleral shell of each eye was mounted on a custom-built pressurization apparatus, then intraocular pressure (IOP) was elevated from 5 to 45 mm Hg while the 3D displacements of the scleral surface were measured with speckle interferometry. To investigate the age-related differences in the inhomogeneous, anisotropic, nonlinear biomechanical properties of posterior sclera from old (22.9 В± 5.3 years) and young (1.5 В± 0.7 years) rhesus monkeys.

Sims 4 eye wrinkles