Neovascularization from scleral wound as cause of vitreous rebleeding after vitrectomy for proliferative diabetic retinopathy

PURPOSE: To determine the site of rebleeding into the vitreous after vitrectomy in patients with diabetic retinopathy. METHODS: We studied in detail 4 eyes of 4 patients in whom rebleeding into the vitreous followed successful vitrectomy for proliferative diabetic retinopathy. In addition, the fibrous membrane removed at surgery was studied by light and electron microscopy. RESULTS: In these 4 eyes, the second operation revealed that the source of the vitreous rebleeding was from a fibrovascular proliferation around the scleral wounds of the initial surgery, and no other neovascularization and/or reproliferation were observed in the whole retina. Rebleeding in these 4 eyes developed at an average of 9 weeks after initial surgery. The proliferative membrane was oval in shape and expanded from the residual vitreous that had been incarcerated in the scleral wound. The proliferative membrane removed during vitrectomy was poor in cellular components and contained extracellular matrix. Blood vessels of various sizes were also present. Electron microscopy showed the membrane was rich in extracellular components and contained high and low electron density cells. These cells often had microvilli and seemed to be of epithelial origin. CONCLUSIONS: These findings show that vitreous rebleeding may develop from fibrovascular proliferation from the scleral wound created during initial surgery. The proliferated membrane showed histological similarities with the fibrovascular proliferation usually seen in the diabetic retina and may represent a type of anterior proliferation secondary to retinal ischemia.