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Retinal Arteriolar Diameter, Blood Velocity, and Blood Flow Response to an Isocapnic Hyperoxic Provocation in Early Sight-Threatening Diabetic Retinopathy

¹From the Multi-Disciplinary Laboratory for the Research of Sight-Threatening Diabetic Retinopathy, Department of Ophthalmology and Vision Science, University of Toronto, Ontario, Canada; and the ²School of Optometry, University of Waterloo, Waterloo, Ontario, Canada.

PURPOSE. To quantify the magnitude of retinal arteriolar vascular reactivity in diabetic patients stratified by severity of retinopathy and in age-matched control subjects. The sample comprised 21 nondiabetic control subjects (group 1), 19 patients with no clinically visible DR (group 2), 19 patients with mild-to-moderate nonproliferative DR and without clinically evident diabetic macular edema (DME) (group 3), and 17 patients with DME (group 4).

METHODS Subjects initially breathed air, followed by oxygen, while isocapnia was maintained. Retinal arteriolar diameter and blood velocity measurements were acquired simultaneously.

RESULTS. Changes in blood velocity and wall shear rate (WSR) were significantly less in groups 3 and 4 (P < 0.0001 and P = 0.0002, respectively) than in groups 1 and 2. Change in blood flow was significantly less in group 4 (P < 0.004) than in groups 1 and 2. The change in maximum-to-minimum (max:min) ratio was significantly less in groups 2 and 4 than in group 1 (P = 0.001). There was a significant relationship between baseline objective edema indices and vascular reactivity. The magnitude of vascular reactivity in response to isocapnic hyperoxia was reduced in those individuals with clinically evident DR relative to subjects without diabetes.

CONCLUSIONS. The differences in vascular reactivity occurred in the absence of any difference in baseline hemodynamic values. Vascular reactivity is impaired in early sight-threatening DR, and this impairment is related to the objectively defined magnitude of retinal edema.

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