Composite fundus photographs of the right eye of a patient with central retinal vein occlusion (CRVO). CRVO is a blockage of the main vein that drains the retina, the light-sensitive layer at the back of the eye. The blockage causes blood and fluid to leak into the retina and the lack of oxygen can lead to damage or death of nerve cells. It causes blurred, or loss of, vision in the affected eye. Injections of drugs into the eye can stop the leakage from the vein. However, any underlying cause, such as high blood pressure or diabetes, needs to be treated to prevent a reoccurrence of the occlusion.