Change of Retinal Arteriolar Diameter, Blood Velocity and Flow during an Isocapnic Hyperoxic Provocation in Early Diabetic Retinopathy

Abstract

Abstract: : Purpose: To define the magnitude of change of retinal arteriolar diameter, blood velocity and flow in response to an isocapnic hyperoxic provocation in patients with diabetes stratified by grade of retinopathy (DR) and in non–diabetic controls. Methods:The sample comprised 7 non–diabetic controls (Group 1; mean age 50 yrs, SD 7 yrs), 4 patients with no DR (Group 2; mean age 60 yrs, SD 8 yrs), 6 patients with mild–to–moderate non–proliferative DR (Group 3; mean age 49 yrs, SD 14 yrs). Subjects underwent a baseline assessment, including logMAR visual acuity, lens opacity grading and a comprehensive retinal examination. Retinal arteriolar diameter, blood velocity and flow measurements were acquired using the Canon Laser Blood Flowmeter model 100 (CLBF). Measurements were acquired from either a supero–, or infero–, temporal arteriole of one eye of each subject. Subjects breathed via a sequential rebreathing circuit (Hi–Ox SR, Viasys). CLBF measurements were acquired during each stimulus condition (air or oxygen). Isocapnia was maintained throughout. Systemic respiratory parameters were continually monitored, while blood glucose and blood pressure were assessed prior to and after provocation. Results: The group mean reduction in retinal arteriolar diameter was 11%, 3% and 4% in Groups 1, 2 and 3, respectively. The group mean reduction in blood velocity was 42%, 44% and 27% in Groups 1, 2 and 3, respectively, while blood flow reduced by 47%, 47% and 30%. There was a statistically significant reduction in retinal blood velocity (one–tailed, paired t–test, p=0.002 Group 1, p=0.01 Groups 2 & 3) and flow for all 3 Groups (p=0.001 Group 1, p=0.04 Group 2, p=0.05 Group 3). The change in blood velocity (one–tailed, unpaired t–test, p=0.02) and flow (p=0.03) was significantly less in Group 3 than that of Group 1. Conclusions: Isocapnic hyperoxia resulted in a statistically significant reduction of retinal arteriolar blood velocity and flow for the diabetic and non–diabetic groups. The magnitude of change in blood velocity and flow was reduced in those individuals with mild–to–moderate non–proliferative diabetic retinopathy relative to non–diabetic controls.

Keywords: diabetic retinopathy • blood supply • retina