Abnormal retinal autoregulation is detected by provoked stimulation with flicker light in well-controlled patients with type 1 diabetes without retinopathy.

AIMS: Investigation of retinal vasodilation under flickering light is considered a dynamic analysis in contrast to the static analysis of retinal vessel equivalents (mean retinal vessel diameter). We investigated whether dynamic analysis apart from the static one in type 1 diabetic patients without diabetic retinopathy with well-controlled diabetes could lead to additional information regarding retinal autoregulation. METHODS: 18 normotensive type 1 diabetic patients without retinopathy and 19 healthy subjects were included. Diameter of retinal vessels was measured with Dynamic Vessel Analyzer. Changes in vasodilation are expressed as percent change over baseline values. RESULTS: HbA(1c) was 7.5+/-1.0% in diabetic patients. In arteries, the response to flicker was diminished in diabetic patients compared to healthy volunteers (p<0.023). In patients flicker stimulation increased arterial diameter by +2.7% in contrast to +4.4% in controls. Venous vessel diameter increased by +3.1% in diabetic individuals and by +5.3% in the control group (p<0.002). There were no differences in static analysis between both groups. CONCLUSIONS: Diabetic patients without retinopathy with relatively good glycemic control show reduced retinal vasodilation after flicker indicating dysfunction in retinal autoregulation. The use of provocation test in conjunction with static analysis could lead to additional information regarding abnormal retinal autoregulation.

Diabetic patients with retinopathy show increased retinal venous oxygen saturation.

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.

Influence of flickering light on the retinal vessels in diabetic patients.

OBJECTIVE: Stimulation of the retina with flickering light increases retinal vessel diameters in humans. Nitric oxide is a mediator of the retinal vasodilation to flicker. The reduction of vasodilation is considered an endothelial dysfunction. We investigated the response of retinal vessels to flickering light in diabetic patients in different stages of diabetic retinopathy. RESEARCH DESIGN AND METHODS: We studied 53 healthy volunteers, 68 type 1 diabetic patients, and 172 type 2 diabetic patients. The diameter of retinal vessels was measured continuously online with the Dynamic Vessel Analyzer (DVA). Diabetic retinopathy was classified using Early Treatment Diabetic Retinopathy Study criteria. Changes in vasodilation are expressed as percent change over baseline values. RESULTS: After adjustments for age, sex, and antihypertensive treatment, the response of retinal arterioles to diffuse luminance flicker was significantly diminished in patients with type 1 diabetes compared with healthy volunteers. The vasodilation of retinal arterioles and venules decreased continuously with increasing stages of diabetic retinopathy. The retinal arterial diameter change was 3.6 +/- 2.1% in the control group, 2.6 +/- 2.5% in the no diabetic retinopathy group, 2.0 +/- 2.7% in the mild nonproliferative diabetic retinopathy (NPDR) group, 1.6 +/- 2.2% in the moderate NPDR group, 1.8 +/- 1.9% in severe NPDR group, and 0.8 +/- 1.6% in proliferative diabetic retinopathy group. CONCLUSIONS: Flicker responses of retinal vessels are abnormally reduced in diabetic patients. This decreased response deteriorated with increasing stages of retinopathy. The response was already reduced before clinical appearance of retinopathy. The noninvasive testing of retinal autoregulation with DVA might prove to be of value in early detection of diabetic vessel pathological changes.