Biomechanical changes in the sclera of monkey eyes exposed to chronic IOP elevations.

Academic Article

Abstract

  • PURPOSE: To characterize scleral biomechanics in both eyes of eight monkeys in which chronic intraocular pressure (IOP) elevation was induced in one eye. METHODS: Each posterior sclera was mounted on a pressurization apparatus, IOP was elevated from 5 to 45 mm Hg while the 3D displacements of the scleral surface were measured by speckle interferometry. Finite element (FE) models of each scleral shell were constructed that incorporated stretch-induced stiffening and multidirectionality of the collagen fibers. FE model predictions were then iteratively matched to experimental displacements to extract unique sets of scleral biomechanical properties. RESULTS: For all eyes, the posterior sclera exhibited inhomogeneous, anisotropic, nonlinear biomechanical behavior. Biomechanical changes caused by chronic IOP elevation were complex and specific to each subject. Specifically: (1) Glaucomatous eyes in which the contralateral normal eyes displayed large modulus or thickness were less prone to biomechanical changes; (2) glaucomatous scleral modulus associated with an IOP of 10 mm Hg decreased (when compared with that of the contralateral normal) after minimal chronic IOP elevation; (3) glaucomatous scleral modulus associated with IOPs of 30 and 45 mm Hg increased (when compared with that of the contralateral normal) after moderate IOP elevation; and (4) FE-based estimates of collagen fiber orientation demonstrated no change in the glaucomatous eyes. CONCLUSIONS: Significant stiffening of the sclera follows exposure to moderate IOP elevations in most eyes. Scleral hypercompliance may precede stiffening or be a unique response to minimal chronic IOP elevation in some eyes. These biomechanical changes are likely to be the result of scleral extracellular matrix remodeling.
  • Keywords

  • Age Factors, Animals, Anisotropy, Biomechanical Phenomena, Chronic Disease, Compliance, Disease Models, Animal, Elasticity, Extracellular Matrix, Glaucoma, Intraocular Pressure, Macaca mulatta, Models, Biological, Nonlinear Dynamics, Sclera, Tonometry, Ocular
  • Digital Object Identifier (doi)

    Author List

  • Girard MJA; Suh J-KF; Bottlang M; Burgoyne CF; Downs JC
  • Start Page

  • 5656
  • End Page

  • 5669
  • Volume

  • 52
  • Issue

  • 8