Effects of the scleral collagen structure on the biomechanical response of the optic nerve head

The sclera is a fiber-reinforced material composed of dense superimposed lamellae of type I collagen fibrils embedded in a matrix of elastin and proteoglycan. Recent Wide-Angle X-ray Scattering (WAXS) experiments (Meek, 2009) showed that the collagen lamellae are strongly aligned circumferentially in the region closest to the optic nerve head (ONH). The collagen structure was more disperse and heterogeneous away from the peripapillary region. The collagen structure of the sclera directly influences its material stiffness properties and therefore the level of strain transmitted to the tissues of the ONH, which is the primary site of damage in glaucoma. The effects of the fiber structure on the ONH biomechanics have been studied on the monkey eye (Girard, 2009), but not on the human eye. Recent work evaluating the influence of the human sclera on ONH biomechanics approximated the scleral behavior as linear elastic (Sigal, 2009) or hyperelastic orthotropic (Eilaghi, 2009)