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M. M. Chen, J. W. Kiel; Effects of Graded Hypoxia on Aqueous Production. Invest. Ophthalmol. Vis. Sci. 2008;49(13):3707.
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To assess the effects of reducing oxygen delivery to the ciliary body at two different levels.
This study used pentobarbital anesthetized rabbits (n=10, 2.37 ± 0.06 kg) in which the following variables were measured: mean arterial pressure (MAP), intraocular pressure (IOP), hemoglobin percent saturation (HbO2%, pulse oximeter), arterial partial pressure of oxygen (PaO2, intra-arterial fiber optic probe), ciliary blood flow (BFcil, laser Doppler flowmetry), carotid blood flow (BFcar, ultrasound flowmeter) and aqueous flow (Flow, fluorophotometry). Baseline measurements were made for 60 min followed by 75 minutes of measurements during the first systemic hypoxic event followed by 75 minutes of the second systemic hypoxic event. Hypoxia was induced by respiring the animals with a mixture of nitrogen and room air. Responses were evaluated by repeated measures ANOVA.
Data are presented as mean ± SE.* p-value < 0.05 for Hypoxia 1 vs control+ p-value < 0.05 for Hypoxia 2 vs Hypoxia 1
When arterial oxygen content is reduced moderately (15-20% reduction), aqueous production does not significantly decrease. However, with a more substantial decrease (30-40% reduction) in arterial oxygen content, aqueous production decreases significantly. Although previous studies have shown a similar relationship between ciliary blood flow and aqueous production, the data in our study supports the theory that below a threshold level of ciliary blood flow, decreased aqueous production is due to insufficient oxygen delivery rather than inadequate delivery of metabolic fuel or removal of metabolic waste. The results of the study indicate that the aqueous production decreases when oxygen delivery is reduced below a threshold level, independent of ciliary blood flow.
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