Abstract
BACKGROUND: Longstanding diabetes mellitus results in a disturbed
microcirculation. A new imaging oximeter was used to investigate the effect of
this disturbance on retinal vessel oxygen saturation. METHODS: The haemoglobin
oxygen saturation was measured in the retinal arterioles and venules of 41
diabetic patients (65 +/- 12.3 years) with mild non-proliferative through
proliferative diabetic retinopathy (DR). Twelve individuals (61.3 +/- 6.2 years,
mean +/- standard deviation) without systemic or ocular disease were investigated
as controls. Measurements were taken by an imaging oximeter (oxygen module by
Imedos GmbH, Jena). This technique is based on the proportionality of the oxygen
saturation and ratio of the optical density of the vessel at two wavelengths (548
nm and 610 nm). RESULTS: Whereas there were no significant differences in the
arterial oxygen saturation between controls and diabetic retinopathy at any
stage, the venous oxygen saturation increased in diabetic patients with the
severity of the retinopathy: controls 63 +/- 5\%, mild non-proliferative DR 69 +/-
7\%, moderate non-proliferative DR 70 +/- 5\%, severe non-proliferative DR, 75 +/-
5\%, and proliferative DR 75 +/- 8\%. CONCLUSIONS: The increase of retinal vessel
oxygen saturation in diabetic retinopathy points to a diabetic microvascular
alteration. This may be due to occlusions and obliterations in the capillary bead
and the formation of arterio-venous shunt vessels. On the other hand,
hyperglycaemia-induced endothelial dysfunction, with subsequent suppression of
the endothelial NO-synthase and disturbance of the vascular auto-regulation, may
contribute to retinal tissue hypoxia.
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