Venous loops and reduplications in diabetic retinopathy Prevalence, distribution, and pattern of development

Purpose Venous loops and reduplications are rare manifestations of diabetic retinopathy, and knowledge of their natural history is therefore limited to descriptions from a few casuistic reports. The purpose of the present study was to describe the prevalence and clinical characteristics of venous loops and reduplications based on a large data material from the screening clinic for diabetic retinopathy at the Department of Ophthalmology, Arhus University Hospital. Methods Fundus photographs of 4418 patients were reassessed for the presence of venous loops or reduplications. Results Venous loops or reduplications occurred in 29 (0.66%) of the examined patients, and in 26 of 338 patients with proliferative diabetic retinopathy (7.7%). The abnormalities were most frequent on the larger retinal veins, and in advanced retinopathy, but were unlinked to the development of the proliferative retinopathy. The development of the venous abnormalities was seen to be preceded by a gradual occlusion of a larger vein with the formation of multiple smaller collateral vessels, one or some of which to become the venous loop or reduplication. The epidemiology, localization, and pattern of development of the occlusion preceding the formation of loops or reduplications was different from that of retinal vein thrombosis. Conclusion The findings suggest that retinal venous loops and reduplications secondary to diabetic retinopathy are shunt vessels developed to bypass a nonthrombotic occlusion of a larger retinal vein.