Scleral Biomechanics in the Glaucomatous Monkey Eye
- Scleral Biomechanics in the Glaucomatous Monkey Eye
- Michael J.A. Girard; 서준교; Michael Bottlang; Claude F. Burgoyne; J. 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 . 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 .
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 .
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