The Role of Retinal Venous Congestion in Diabetic Retinopathy

Diabetic retinopathy (DR) is among the leading global causes of blindness and a major cause of vision loss in the working population of developed countries. The lack of understanding of the pathophysiology of DR hinders the development of efficient disease prevention and treatment. In DR, breakdown of the blood-retinal barrier occurs that causes leakage of blood and blood constituents into the retinal tissue. Several factors have been suggested as causes for the blood-retinal barrier breakdown, including metabolic, inflammatory, and hydrostatic. The purpose of this manuscript is to analyze available scientific reports concerning involvement of increased retinal venous hydrostatic pressure in DR. Data are presented from studies that investigated ocular blood flow and ocular morphology that suggest involvement of retinal vein congestion in the pathogenesis of DR. The results from fundus photography indicated that retinal venous dilation is associated with incidence and progression of DR. Fluorescein angiography studies found increased arterio-venous passage time and increased retinal venous filling time in patients with DR than in control subjects. Increased resistivity index was detected using Color Doppler imaging of the retrobulbar central retinal vein in patients with progression of DR that also suggests increased resistance to venous outflow. Retinal venous pressure measured by ophthalmodynamometry was higher in patients with DR, than in control subjects and in diabetic patients without DR. This evidence suggests an involvement of retinal venous congestion in DR. Future studies should focus on the effect of increased hydrostatic pressure in the retinal veins in the pathogenesis of DR.