Central Retinal Vein Occlusion (CRVO) occurs when the central retinal vein becomes blocked. When the central retinal vein is blocked, blood circulation is reduced. This can cause macular edema, or an excessive accumulation of fluid in the retinal tissue, which can cause blurry or distorted vision. Additionally, CRVO can be classified as ischemic (very poor blood flow to the eye) or non-ischemic (favorable blood flow to the eye). Ischemic CRVO has a poorer visual prognosis due to the lack of blood flow to the eye.