Several retinovascular diseases have been shown to be VEGF dependent including retinal vein occlusion, wet age-related macular degeneration, and diabetic retinopathy. The role of the vitreous or composition of the vitreous cavity has been examined in diabetic retinopathy on many occasions in the past and clinically it has been felt that a posterior vitreous separation leads a quieting and involution of diabetic retinopathy, both proliferative as well as pre-proliferative retinopathy. This clinical observation has never had any basic science data to support it. However, it has recently been shown that in cat eyes with posterior vitreous separation the vitreous cavity has a much lower VEGF concentration than in cat eyes with an attached posterior vitreous. This may be due to the fact that flow of oxygen from the retinal vasculature is increased by PVD. Vitreous oxygen levels are inversely associated with vitreous VEGF levels. As oxygen tension increases, VEGF levels will decline. This suggests if higher amounts of VEGF are present in the eye without PVD perhaps a powerful anti-VEGF drug, such as ranibizumab, may be of greater benefit to treat VEGF dependent retinovascular disease. To try and answer this question clinically, we have suggested that an analysis of the vitreous status in treatment naive eyes with retinal vein occlusion beginning ranibizumab therapy be undertaken to see if eyes without a posterior vitreous separation would achieve greater improvement in vision and a return to more normal retinal physiology compared to eyes with a posterior vitreous separation. No study has assessed PVDs in RVO patients receiving potential treatment.