Cellular proliferation in the vitreous: the use of vitreous explants as a model system

An in vitro model of cellular proliferation in the vitreous has been developed using explants of bovine vitreous gel. Various cell types, including chick embryo pigmented retinal epithelium, choroidal fibroblasts, retinal glial cells, bovine retinal capillary endothelial cells, and peritoneal mouse macrophages, were cultured at 37 degrees C on vitreous gels for periods up to 8 days and compared for their effects on the structure of the gel. Choroidal fibroblasts caused a very marked reduction in the size of the gel and produced the strongest traction on the gel fibril structure; in contrast, peritoneal macrophages caused virtually no reduction in vitreous volume and little or no visible traction on the gel as detected by phase-contrast microscopy. The remaining cell types usually formed sheets on the surface of the gel; this was associated with an initial reduction in vitreous volume of approximately 50%, but little change thereafter. The cell mediated traction events on the structure of the vitreous gel were followed by time lapse video microscopy and by electron microscopy at various times after seeding of cells on the gels. The appearances corresponded closely with reported clinico-pathological studies of cellular proliferation in the vitreous. We believe that this in vitro model has several advantages over in vivo models of cellular proliferation in the vitreous, in that it permits analysis of individual cell behaviour and it is eminently suitable for pharmacologic manipulation.