Sequelae of intravitreal phagocytic activity in response to microparticles

Cynomolgus monkeys were injected intravitreally with a colloidal suspension of carbon microparticles (size 20-70 nm) under aseptic surgical conditions. An intravitreal cellular proliferation occurred, inducing retinal detachment and neovascularization that started from the optic nerve head, ciliary body and ora serrata. Transmission electron microscopy revealed the features of the intravitreal cellular response to be inflammatory cells, mononuclear phagocytes (the predominant cell type), and fibroblasts. Newly-formed collagen fibrils (banding 70 nm) were found in the vitreous. The newly-formed vasculature generally showed continuous endothelial lining, but some intravitreal cellular proliferation is primarily a macrophagic response. We suggest that mononuclear phagocytes play a major role by triggering the collagen formation and neovascularization in the vitreous.