Blood and nutrient circulation to and from the surface of the retina is mostly done through one vein and one artery. If these passages or any of the smaller branches connected to them are blocked, blood flow to the retina can become seriously disrupted. Blockage of one of these passages is known as occlusion, and can result in sudden vision loss. Although there is no cure for retinal vein occlusions, there are treatment options to improve the vision and minimize risk of recurrence.