Blood flow and glucose consumption in the optic nerve, retina and brain: effects of high intraocular pressure.

Glucose consumption and regional blood flow were determined using the [14C]-2-deoxyglucose (2-DG) method and microspheres in the optic nerve, the retina and different parts of the brain in monkeys. The relationship between the 2-DG accumulation and blood flow in the optic nerve head region was similar to that in grey matter of the brain under pentobarbital anaesthesia as well as under urethan anaesthesia. Pentobarbital anaesthesia resulted in lower values for blood flow and glucose metabolism in most regions. In the optic nerve the highest values were observed in the distal part; there was a fall in blood flow and metabolism along the nerve. There was a corresponding increase in myelin content. Artificial increments in intraocular pressure resulting in a perfusion pressure (mean arterial pressure minus intraocular pressure) of 40 cm H2O had no appreciable effect on the 2-DG accumulation. At a perfusion pressure of 20 cm H2O 2-DG accumulation in the retina and prelaminar part of the optic nerve was markedly increased indicating partial ischemia resulting in anaerobic glycolysis. At intraocular pressures higher than the systolic arterial blood pressure there was still some accumulation of 2-DG in the intraocular tissues, but no blood flow, which indicates that glucose could diffuse into the eye through the sclera. Behind the lamina cribrosa there was no indication of a reduction in blood flow or a metabolic disturbance. The results indicate that the blood flow and metabolism of the retina and prelaminar part of the optic nerve is disturbed only at very high intraocular pressures, and that even at extreme pressures there is no disturbance behind the lamina cribrosa in acute experiments. The 2-DG method will be useful in further studies on the nutritional status of the optic nerve head since it can detect abnormal glycolysis even in very discrete regions due to its high spatial resolution.