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Cortical activity following restoration of elevated intraocular pressures to normal pre-laser pressures in a primate model of glaucoma Jim, Janey

Abstract

Glaucoma is a group of diseases that affects the optic nerve, causing debilitating visual deficits with no known cures. The primate model of glaucoma was developed to enable investigators to study this disease. Research in glaucoma has examined the disease at the level of the eye and optic nerve head. Recent evidence has also emerged extending glaucomatous injury to the central nervous system. While changes in metabolic activity in response to elevated intraocular pressure (IOP) have been reliably demonstrated, few studies exist that examine metabolic activity following the lowering of elevated levels of IOP to normal values. This study looks at the effects of lowering IOP, following elevated IOP levels of 2 and 4 weeks, by comparing the metabolic activity levels between ocular dominance bands in the primary visual cortex. Elevated IOP (> 30 mmHg) was induced by unilateral lasering of the trabecular " meshwork of primates. The animals' IOP was periodically monitored over a period of 2, 4, 8, and 16 weeks. The first set of animals was sacrificed following the designated period of elevated IOP. A second set of animals had their IOP returned to normal prelaser values (< 20 mmHg) by trabeculectomy following deprivation. They were allowed to survive for several months with normal pre-laser IOP values before being sacrificed. All animals' cortices were histochemically processed for cytochrome oxidase (CO). OD ratios comparing the CO density values of ocular dominance bands were obtained. CO density was found to be lower in deprived eye columns than in non-deprived eye columns as early as 2 weeks post elevated IOP, suggesting that a decrease in metabolic activity in the eye subjected to elevated IOP occurs. Further, OD ratios comparing the metabolic activity between deprived and non-deprived eye bands are affected by the duration of deprivation. Animals subject to longer periods of elevated IOP had ratios further away from values of normal animals. Moreover, animals without pressure lowering therapy had lower OD ratios compared to animals with trabeculectomy performed. Our results suggest that lowering elevated IOP to normal levels has an effect on metabolic activity within the primary visual cortex.

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