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J. T. Siegwart, Jr., T. T. Norton, C. E. Strang, Y. Long, Q. C. Ngumah, K. T. Keyser, C. A. Girkin; Intracameral Injection of Latex Microspheres Elevates IOP and Produces Optic Nerve Damage in Tree Shrews. Invest. Ophthalmol. Vis. Sci. 2008;49(13):3681.
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The lamina cribrosa of the tree shrew (Tupaia glis belangeri) has a load-bearing beam structure similar to primates that may make it a useful animal model for glaucoma research. To determine if the tree shrew is a suitable pressure model we tested whether intracameral injections of latex microspheres would elevate intraocular pressure (IOP) and produce optic nerve damage.
Latex microspheres (10 and 15 µm mix) were injected into the right eye anterior chamber of six tree shrews (3 months to 5 yrs old). Injections were given 1 to 5 times during an 8 to 19 week treatment period. IOP was measured at approximately 1 week intervals with a Tonopen (n=3, anesthetized) or a TonoLab rebound tonometer (n=3, awake). At the end of the treatment period, the animals were euthanized and perfused with 4% paraformaldehyde. The optic nerves were post fixed in glutaraldehyde, osmicated, dehydrated and embedded in Spurr. Optic nerve damage was assessed at the light microscopic level in p-phenylenediamine-stained sections and at the EM level.
Microsphere administration produced elevation of IOP in the treated eye relative to the fellow uninjected control eye that was variable in onset latency, amount of elevation, and duration. The average IOP during treatment was significantly higher in the treated eye in all six animals (40%, 54%, 28%, 38%, 41%, 52%, all p < 0.05). In 4 of the 6 animals, there was evidence of degenerating axons characteristic of optic nerve damage. Fig. 1 shows p-phenylenediamine-stained sections from comparable locations in a 5 year old animal that received 4 injections and had elevated pressure for 11 weeks. The control eye (left) shows normal myelinated axons while the treated eye (right) shows clear evidence of degenerating axons.
Intracameral injection of latex microspheres raises IOP and produces optic nerve damage in tree shrews. The tree shrew shows promise as an animal model for investigating IOP-induced changes in the lamina cribrosa at a lower cost than current primate models.
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