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C.L. Miller, C.B. Y. Kim, T.M. Nork; Regional Variation in Hypoxic Responses to Acutely Elevated Intraocular Pressure in the Rabbit Retina . Invest. Ophthalmol. Vis. Sci. 2006;47(13):491.
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Choroidal blood flow is known to decrease in response to rising intraocular pressure (IOP). Retinal ischemia may play a role in various human ocular diseases, including chronic glaucoma. This study assessed the regional variation in hypoxic effects of acutely elevated IOP–induced choroidal ischemia.
A Lewicky self retainer connected to a balanced salt solution reservoir via IV tubing was inserted into the anterior chamber of one eye in each of three male New Zealand Black rabbits. Intraocular pressure (IOP) was elevated to between 40 and 50 mmHg. Multifocal electroretinograms (mfERGs) were recorded in the cannulated eye using a 103 hexagonal array both after cannulation (baseline) and again after IOP elevation. At 0.5 – 1 hour post–IOP elevation, 280 mg/m2 IV pimonidazole hydrochloride (Hypoxyprobe–1, Chemicon International) was injected into the marginal ear vein. 1–2 hours following pimonidazole administration rabbits were euthanized and both eyes were enucleated. Tissue was analyzed by immunohistochemical staining using the Hypoxyprobe–1Mab1 antibody.
Robust baseline mfERG responses were abolished following IOP elevation. In all three animals the cannulated eye showed markedly greater staining with Hypoxyprobe–1Mab1 when compared to the contralateral control eye. Labeling was much greater in the region of the visual streak when compared to the superior or inferior peripheries. This labeling occurred most intensely in the ganglion cell layer, with more moderate activity in the inner nuclear layer and photoreceptors.
Relatively greater ischemic effects in the visual streak indicate that this neuron–dense region is more sensitive to oxygen deprivation than the more sparsely populated periphery. Whether this effect is owing to regional variation in blood flow or oxygen demand (or both) remains to be determined.
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