Effects of Peripapillary Scleral Stiffening on the Deformation of the Lamina Cribrosa (original) (raw)
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… ophthalmology & visual …, 2009
PURPOSE. To evaluate the biomechanical effect of intraocular pressure (IOP) elevation on the optic nerve/lamina cribrosa complex (ON/LC) and peripapillary sclera (PS) of porcine eyes before and after localized collagen cross-linking. METHODS. Eighteen porcine globes were divided evenly into three groups. The optic nerves were transected to expose the ON/LC, and each globe was infused through an in-line pressure transducer for direct IOP control. Surface wave velocity, a nondestructive measure of tissue stiffness, was measured across the ON/LC and PS before and after collagen crosslinking at IOPs of 10 and 30 mm Hg (groups 1 and 2) and at each globe's preinflation IOP and 80 mm Hg (group 3). In group 3, papillary strain was measured by analyzing the displacement of fiducial marks immediately adjacent to the ON/LC by using digital photography. Cross-linking in group 1 was achieved with riboflavin-ultraviolet A (UVA) delivery to the entire ON/LC and PS and, in groups 2 and 3, with an annular sponge soaked in glutaraldehyde (GTA) and applied only to the PS. RESULTS. Native PS was significantly stiffer than the ON/LC across all experiments. Before cross-linking, IOP elevation caused significant stiffening of both the ON/LC and PS. After cross-linking with either technique, IOP elevation stiffened the PS but not the ON/LC region. In group 3, papillary strain during IOP elevation was significantly reduced after PS cross-linking. CONCLUSIONS. Stiffening of the peripapillary scleral ring reduces the biomechanical sensitivity of the ON/LC complex to IOP elevation and may represent a novel mechanism for neuroprotection in glaucoma.
Investigative Ophthalmology & Visual Science, 2005
To test the hypothesis that changes in the viscoelastic material properties of peripapillary sclera are present within monkey eyes at the onset of early experimental glaucoma detected by confocal scanning laser tomography (CSLT). METHODS. Short-term (3-9 weeks), moderate (Յ44 mm Hg) intraocular pressure (IOP) elevation was induced in one eye of each of eight male monkeys by lasering the trabecular meshwork. This procedure generated early experimental glaucoma, defined as the onset of CSLT-detected optic nerve head (ONH) surface change, in the treated eye. Scleral tensile specimens from the superior and inferior quadrants of the eight earlyglaucoma eyes were subjected to uniaxial stress relaxation and tensile tests to failure and the results compared with similar data obtained in a previous study of 12 normal (nonglaucomatous) eyes. Linear viscoelastic theory was used to characterize viscoelastic material property parameters for each specimen. Differences in each parameter due to quadrant and treatment were assessed by analysis of variance (ANOVA). RESULTS. Peripapillary sclera from the early-glaucoma eyes exhibited an equilibrium modulus (7.46 Ϯ 1.58 MPa) that was significantly greater than that measured in normal eyes (4.94 Ϯ 1.22 MPa; mean Ϯ 95% confidence interval, P Ͻ 0.01, ANOVA). Quadrant differences were not significant for the viscoelastic parameters within each treatment group. CONCLUSIONS. The long-term viscoelastic material properties of monkey peripapillary sclera are altered by exposure to moderate, short-term, chronic IOP elevations and these alterations are present at the onset of CSLT-detected glaucomatous damage to the ONH. Damage to and/or remodeling of the extracellular matrix of these tissues may underlie these changes in scleral material properties. (Invest Ophthalmol Vis Sci. 2005;46: 540 -546)
Perilimbal sclera mechanical properties: Impact on intraocular pressure in porcine eyes
PloS one, 2018
There is extensive knowledge on the relationship of posterior scleral biomechanics and intraocular pressure (IOP) load on glaucomatous optic neuropathy; however, the role for biomechanical influence of the perilimbal scleral tissue on the aqueous humor drainage pathway, including the distal venous outflow system, and IOP regulation is not fully understood. The purpose of this work is to study the outflow characteristics of perfused porcine eyes relative to the biomechanical properties of the perilimbal sclera, the posterior sclera and the cornea. Enucleated porcine eyes from eleven different animals were perfused with surrogate aqueous at two fixed flow rates while monitoring their IOP. After perfusion, mechanical stress-strain and relaxation tests were conducted on specimens of perilimbal sclera, posterior sclera, and cornea from the same perfused eyes. Statistical analysis of the data demonstrated a strong correlation between increased tangent modulus of the perilimbal sclera tiss...
PloS one, 2015
The biomechanical behavior of the sclera determines the level of mechanical insult from intraocular pressure to the axons and tissues of the optic nerve head, as is of interest in glaucoma. In this study, we measure the collagen fiber structure and the strain response, and estimate the material properties of glaucomatous and normal human donor scleras. Twenty-two posterior scleras from normal and diagnosed glaucoma donors were obtained from an eyebank. Optic nerve cross-sections were graded to determine the presence of axon loss. The specimens were subjected to pressure-controlled inflation testing. Full-field displacement maps were measured by digital image correlation (DIC) and spatially differentiated to compute surface strains. Maps of the collagen fiber structure across the posterior sclera of each inflated specimen were obtained using synchrotron wide-angle X-ray scattering (WAXS). Finite element (FE) models of the posterior scleras, incorporating a specimen-specific represent...
Regional changes in the elastic properties of myopic Guinea pig sclera
Experimental Eye Research, 2019
Biomechanical changes in the sclera likely underlie the excessive eye elongation of axial myopia. We studied the biomechanical characteristics of myopic sclera at the microscopic level using scanning acoustic microscopy (SAM) with 7-μm in-plane resolution. Guinea pigs underwent formdeprivation (FD) in one eye from 4-12 days of age to induce myopia, and 12-μm-thick scleral cryosections were scanned using a custom-made SAM. Two-dimensional maps of the bulk modulus (K) and mass density (ρ) were derived from the SAM data using a frequency-domain approach. We assessed the effect on K and ρ exerted by: 1) level of induced myopia, 2) region (superior, inferior, nasal or temporal) and 3) eccentricity from the nerve using univariate and multivariate regression analyses. Induced myopia ranged between −3D and −9.3D (Mean intraocular difference of −6.2 +/− 1.7D, N = 11). K decreased by 0.036 GPa for every 1.0 D increase in induced myopia across vertical sections (p < 0.001). Among induced myopia right eyes, K values in the inherently more myopic superior region were 0.088 GPa less than the inferior region (p = 0.002) and K in the proximal nasal region containing the central axis were 0.10 GPa less than temporal K (p = 0.036). K also increased 0.12 GPa for every 1 mm increase in superior vertical distance (p < 0.001), an effect that was blunted after 1 week of FD. Overall, trends for ρ were less apparent than for K. ρ values increased by 20.7 mg/cm 3 for every 1.00 D increase in induced myopia across horizontal sections (p < 0.001), and were greatest in the region containing the central posterior pole. ρ values in the inherently more myopic superior region were 13.1 mg/cm 3 greater than that found in inferior regions among control eyes (p = 0.002), and increased by 11.2 mg/cm 3 for every 1 mm increase in vertical distance (p = 0.001). This peripheral increase in ρ was blunted after 1 week of FD. Scleral material properties vary depending on the location in e