The Relationship of Macular Microcirculation to Visual Acuity in Diabetic Patients

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Abstract
Objective: To assess the perifoveal microcirculation in diabetic maculopathy without clinically significant macular edema and its relationship to visual acuity. Design: Prospective analysis. Setting: A teaching hospital. Patients: Fifteen patients with impaired visual acuity of 20/50 or worse, a diabetic control population with unaffected visual acuity (matched age, gender, retinopathy stage), and 52 healthy controls were enrolled. Interventions: Study consisted of video-fluorescein angiography with image analyses and hemoglobin A1c measurements. Main Outcome Measures: Macular capillary blood velocity, capillary density (perifoveal intercapillary area), and foveal avascular zone. Results: The capillary blood velocity was significantly reduced in both diabetic groups (P<.001) when compared with healthy controls, but did not differ significantly among the two diabetic groups. The perifoveal intercapillary area and foveal avascular zone were significantly enlarged in both diabetic groups compared with healthy controls (P<.001). The foveal avascular zone (P<.01) and perifoveal intercapillary area (P=.01) were further enlarged in the diabetics with reduced visual acuity. The visual acuity correlated significantly with foveal avascular zone (R2=.51) and perifoveal intercapillary area (R2=.24), indicating an association between enlargement and declined visual acuity. Conclusions: Capillary blood velocity remained unchanged regardless of presence of visual impairment, whereas foveal avascular zone and perifoveal intercapillary area indicated ischemia. This may help in defining a critical hypoxic threshold for visual loss and identifying the presence of an ischemic diabetic maculopathy.