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J. Albon, S. Farrant, S. Akhtar, R. Young, M. Taylor, M.E. Boulton, J. Morgan; Morphology of the Tree Shrew Optic Nerve: A Model for Glaucoma? . Invest. Ophthalmol. Vis. Sci. 2005;46(13):3514.
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Purpose: To identify the structure and composition of the tree shrew optic nerve and compare it to that of the human optic nerve. Methods: Ten tree shrew optic nerves, aged between 4 weeks and 5 years, and human optic nerves, aged 18 to 86 years, were cryo–embedded for analysis of overall morphology and extracellular matrix immunolocalisation. Sections were probed with antibodies raised against collagen types I, III, IV, V, and VI, fibronectin, elastin and glial fibrillary acidic protein (GFAP). In addition, optic nerves were fixed in 2.5% glutaraldehyde and prepared for transmission and scanning electron microscopy for ultrastructural and structural analysis. Results: Collagen types I, III, IV, V, VI and elastin were present within the horizontal cribriform plates of the lamina cribrosa, the connective tissue septae, and the vessel walls of the central retinal artery and vein in both human and tree shrew optic nerves. GFAP–related immunofluorescence indicated a high concentration of astrocytic processes in the region of the lamina cribrosa, with a lower density in the pre– and postlaminar regions. Scanning electron microscopy confirmed that the lamina cribrosa in the tree shrew and human optic nerves was similar with respect to orientation of connective tissue. The tree shrew lamina cribrosa was approximately 512 µm in diameter and consisted of multi–layered connective tissue plates (6–8) stretching across the optic nerve at the level of the sclera. Ultrastructural studies further supported the horizontal and longitudinal orientation of collagen fibrils in the lamina cribrosa and postlaminar region respectively. Conclusions: In contrast to many rodent models for glaucoma, the morphology of the tree shrew optic nerve, including the lamina cribrosa, has many similarities to that in the human. The tree shrew therefore offers advantages to investigate the time–dependent pathological processes of glaucoma in a sub–primate model.
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