A clinicopathological study of venous loops and reduplications in diabetic retinopathy.

Purpose: To study possible causes of the gradual venous occlusion that precedes the formation of venous loops and reduplications in diabetic retinopathy using histopathological techniques.
Methods: Casts of the retinal vascular system from six eyes of five diabetic patients were used to identify venous loops and reduplications. Subsequently the lesions were studied by immunohistochemistry using antibodies against cellular and non-cellular components previously shown to be disturbed in the diabetic retina.
Results: In all eyes the venous abnormalities identified on the casts were accompanied by abnormal wall partitions dividing the venous lumen. These partitions consisted of a double layer of flat cells displaying immunoreactivity to von Willebrand factor and actin (endothelial cells), but not to glial fibrillary acid protein or S-100 protein (glial cells), CD3, CD20, CD68, or neutrophil elastase (leucocytes). Neutrophile granulocytes adhering to the walls of larger retinal venules were unrelated to the venous partition and to capillary occlusion in the adjacent retinal areas.
Conclusions: Venous loops and reduplications are associated with partitions of the larger retinal venules consisting of a double layer of endothelial cells anchored to a thin basement membrane. An elucidation of the factors distinguishing this endothelial cell proliferation from preretinal new vessel formation may be important for understanding the pathophysiology of proliferative diabetic retinopathy.