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L. Schmetterer, E. Polska, G. Garhofer; Retinal Blood Flow in Patients With Diabetes During Euglycemic Euinsulinemic Clamps. Invest. Ophthalmol. Vis. Sci. 2008;49(13):4525.
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Retinal blood flow in diabetes has been measured in a variety of studies. The results of these studies are largely contradictory reporting increased, decreased or unaltered blood flow. A number of reasons may account for these discrepancies including methodological aspects, patient selection and glycemic control. The last point is critical, because both insulin and glucose have been shown to induce ocular vasodilatation. Accordingly, we studied retinal blood flow in diabetic patients during euglycemic euinsulinemic clamps.
In the present study 16 patients with insulin dependent diabetes, no or mild non-proliferative diabetic retinopathy, and serum cholesterol levels < 250 mg/dl were included. 16 healthy age- and sex-matched subjects served as controls. In diabetic patients retinal blood flow values were measured in the morning before the insulin morning dose and during euglycemic euinsulinemic clamps. During these clamps endogenous insulin production was inhibited with somatostatine. Retinal blood flow was measured by combining retinal venous diameters data obtained with the Retinal Vessel Analyzer and retinal blood velocity data obtained with bi-directional laser Doppler velocimetry. To gain information on total retinal blood flow all veins entering the optic nerve were measured and the data of the individual vessels were added.
Before morning insulin plasma glucose levels were 176 ± 21 mg/dl. This plasma glucose level was normalized during the euinsulinemic clamp to 102 ± 4 mg/dl. Retinal blood flow was 51.4 ± 5.5 µl/min before the clamp was started. During the euglycemic euinsulinemic clamps retinal blood flow was significantly reduced to 42.1 ± 5.2 µl/min (p < 0.01). As compared to retinal blood flow in the healthy control group (41.2 ± 4.1 µl/min) retinal blood flow in diabetic patients was increased before the euglycemic euinsulinemic clamps (p 0.6).
The present study indicates that retinal blood flow is increased in patients with diabetes at high plasma glucose levels, but not during euglycemic euinsulinemic clamps. These data indicate that in patients with plasma glucose retinal blood flow is fluctuating with fluctuating glucose plasma levels.
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