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M. J. Girard, A. Dahlmann, S. Vijay, P. T. Khaw, C. R. Ethier; Quantitative Mapping of Scleral Fiber Orientation in Normal Rat Eyes. Invest. Ophthalmol. Vis. Sci. 2010;51(13):2128.
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© ARVO (1962-2015); The Authors (2016-present)
Our recent work strongly suggests a major role for scleral biomechanics in the pathogenesis of glaucoma (ARVO 2009, 50:4889; 50:5217). Since fiber orientation is a key determinant of scleral biomechanics, we wish to determine its contribution to glaucomatous damage by combining its experimental characterization with computational modeling. In this study, we report experimental measurements of fiber orientation in whole normal scleras.
4 ostensibly normal brown rat eyes were fixed at 10 mm Hg. Scleras were cleaned of intra- and extra-orbital tissues and dissected into 5 patches, and each patch was glycerol-treated to maximize its transparency. Fiber orientation was measured using small angle light scattering. Briefly, each patch was laid flat between 2 glass slides, mounted in a custom holder, and scanned at predetermined locations (~1000 locations, 100 µm spacing) with a 5 mW red laser. The laser light was scattered by scleral fibers (mainly collagen), projected onto a diffuser screen and captured by a CCD camera. Scattering patterns were analyzed to extract 2 microstructural parameters at each scanned location: the preferred fiber orientation and the degree of alignment, yielding a fiber orientation map for each sclera.
Rat sclera is anisotropic (Figure) with several consistent features. At the limbus, fibers were highly aligned and organized into a distinct ring surrounding the cornea. In the equatorial region, fibers were primarily meridionally aligned. In the posterior and peripapillary region, scleral fibers were mostly circumferential but less aligned than those in the anterior and equatorial regions.
Circumferential scleral fibers may act as reinforcing rings to limit corneal and optic nerve head deformations, while equatorial meridional fibers may provide resistance against extra-ocular muscle forces.
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