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Ayesha Baig, Alan Le, Andrew Shin, Vadims Poukens, Nathan Long, Joseph L Demer; Age-Related, Bilaminar Hypertrophy and Elastosis of the Human Optic Nerve Sheath (ONS).. Invest. Ophthalmol. Vis. Sci. 2017;58(8):1738.
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© ARVO (1962-2015); The Authors (2016-present)
It has been suggested that tension exerted by the ONS on peripapillary sclera in adduction may be an intraocular pressure-independent cause of optic neuropathy in glaucoma. We show at this meeting that the inner & outer ONS layers exhibit differing viscoelastic properties (Shin et al, ARVO’17). We here aimed to evaluate possible anatomical correlates of differing laminar biomechanics of the human ONS.
Eight orbits ages 1.4, 4, 44, 57, 59, 64, 65, and 93 yrs were paraffin embedded, serially sectioned at 10 mm thickness, and stained with Masson trichrome and van Giesson elastin stains. Light microscopy was used to distinguish the 2 ONS layers based on collagen fiber density and weave. Digital colorimetry was used to quantify elastin fiber density on a per pixel basis as a percentage of total pixels in the inner and outer layers. ONS thickness was measured in 10 sites at each of the superior, inferior, medial, and lateral quadrants.
Distinct inner and outer layers were present in the ONS of adults but not children. Elastin fibers stained dark black with van Giesson stain and had 3 different orientations within each layer: circumferential, longitudinal, & crisscross diagonal weave. In the 6 orbits demonstrating dual layers, mean inner layer elastin density was 6.1±0.6% (SEM), significantly greater than the corresponding density of the outer layer at 3.0±0.4% (P<10-5). Elastin density increased significantly with age by 0.05±0.01% per year (linear regression, R2=0.7, P=0.01), while ONS thickness increased by 4.9±0.9 mm/yr (R2=0.8, P<10-5). The ON sheath at the inferior and lateral quadrants tended to be thicker than in superior and nasal quadrants.
The human ONS becomes bilaminar after childhood. While substantially higher elastin density of the inner than outer layer suggests that the inner is stiffer, both elastin density & ONS thickness increase progressively with age. These findings correlate with biomechanical observations of greater ONS stiffness in the inner layer that inserts on the scleral canal, as well as increasing ONS stiffness with age that would tend to transfer strain from the ONS to the peripapillary sclera when the ONS is under tensile loading in adduction.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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