Scleral Biomechanics in the Glaucomatous Monkey Eye

Scleral Biomechanics in the Glaucomatous Monkey Eye
Michael J.A. Girard서준교Michael BottlangClaude F. BurgoyneJ. Crawford Downs
Glaucoma; Scleral Biomechanics; Intra Ocular Pressure
Issue Date
ASME 2009 Summer Bioengineering Conference
The sclera is the outer shell and principal load-bearing tissue of the eye, and consists primarily of avascular lamellae of collagen fibers. Ninety percent of the collagen fibers in the sclera are Type I, which provide the eye with necessary mechanical strength to withstand intraocular pressure (IOP). A small hole pierces the posterior sclera, known as the scleral canal, through which the retinal ganglion cell axons turn and pass out of the eye on their path to the brain. The scleral canal is spanned by a fenestrated connective tissue called the lamina cribrosa that provides structural and nutritional support to the axons as they leave the eye. This region, including the peripapillary sclera (the sclera closest to the canal), the lamina cribrosa, and the contained retinal ganglion cell axons, is collectively known as the optic nerve head or ONH. Glaucoma is the second leading cause of blindness worldwide and manifests as damage to the neural and connective tissues of the ONH at normal and elevated levels of IOP. We have previously shown that the biomechanical properties of the peripapillary sclera are altered in early experimental glaucoma using uniaxial testing and linear viscoelastic theory [1]. From this study, we described an increase in the equilibrium modulus of the peripapillary sclera from glaucomatous monkey eyes but no changes in the time-dependent viscoelastic parameters between contralateral normal and glaucomatous monkey eyes. These results, as well as those from several computational studies, suggest that the sclera plays an important role in the development and progression of glaucoma, which is also supported by other investigators [2]. In this study, we model the posterior sclera as a nonlinear, anisotropic, inhomogeneous soft tissue using a fiber-reinforced constitutive theory that includes stretch-induced stiffening and multidirectional collagen fiber distributions [3].
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