In addition, the posterior sclera, peripapillary sclera, annular ring, pia mater, and dura mater were modeled bu using an anisotropic hyperelastic constitutive model,
35 which treated the tissue as a Mooney-Rivlin solid with embedded collagen fibers. The fiber orientations for each tissue were assumed to follow a von Mises distribution,
36,39 specified by parameters representing the local preferred fiber direction, θ
P, and collagen fiber concentration factor,
kf. The orientation of collagen fibers in the posterior sclera, peripapillary sclera, and annular ring were taken from recently published reports using human specimens.
38,39 In the peripapillary sclera, the annular ring, and the posterior sclera, fibers were assumed to lie in the local tangent plane to the sclera. In the peripapillary sclera and the annular ring, fibers were preferentially aligned circumferentially about the scleral canal, with values of
kf = 0.85 and 1.85, respectively, adapted from previous measurements on human scleral tissues.
37–39 In the posterior sclera, the fiber distribution was assumed to be planar isotropic, obtained by setting
kf = 0.
38,39,47 There are differing reports on collagen fiber orientation in the pia mater and dura mater, with one report stating fibers are primarily oriented parallel to the optic nerve with some circumferential wrapping, and another reporting a planar isotropic orientation.
48,49 For simplicity, we treated the fiber distributions in the pia mater and dura mater as planar isotropic (
kf = 0).
48,49