This is a blockage of the main vein that drains blood out of the eye. Without this drainage, blood can’t get out of the eye and it backs up into the retina. The retina can become swollen with blood, causing serious problems. Depending upon the severity of the swelling, vision can be severely affected, though it sometimes improves with time (though rarely as good as new). Treatment may involve a fluorescein angiogram to evaluate the extent of damage and sometimes laser therapy or anti-VEGF injections if there is residual retinal swelling. One potential problem after a CRVO is neovascularization … this is the formation of abnormal blood vessels inside the eye that can cause future retinal damage and, if the new vessels block the angle, a severe angle closure glaucoma as well.