This one's a classic.  65 year old male with history of hypertension that has stopped his blood pressure medications recently in favor of diet and exercise.  He has not seen his primary care doctor for over a year. Sudden onset "spots in his right eye" was what led him to making the appointment. The above photograph reveals an obvious issue -- there's a lot of blood in the eye!

Central Retinal Vein Occlusions are often associated with underlying systemic medical conditions, chiefly hypertension and diabetes.  Any medical condition affecting blood flow can be a possible risk factor, from hypercoaguable blood disorders to hardened arteries from high cholesterol.  While it is possible to see vein occlusions in younger patients, over 90% of CRVOs occur in patients over age 55.

Retinal vein occlusions occur due to an obstruction in blood flow.  Somehow either due to a spike in blood pressure or hardening of a nearby artery wall, the flow of blood in the vein is blocked, causing a backflow of pressure and the vein to resultantly leak its contents into the nearby tissue.  In this case, the central retinal vein that delivers de-oxygenated blood out of the eye became obstructed, and blood then filled the entire retinal tissue as the vein leaked out.  You can see in this patient's photograph that the arteries are very thin; significantly narrowed compare to the veins.  This finding indicates chronic blood pressure issues (narrowed arterioles are a classic sign), but also this appearance is more exaggerated because the veins are dilated or larger than they would typically appear.  Due to the backflow of pressure following the occlusive event, the blood flow through the arteries and veins is very irregular and can lead to further ischemic (or oxygen loss) damage if the underlying systemic issues aren't improved.

Treatment for CRVO include controlling any underlying systemic conditions, and anti-VEGF injections to reduce swelling in the macula.  The CRUISE study solidified anti-VEGF treatment as a viable option for improving vision and also reducing macular edema on OCT imaging.  Vision may not return to normal despite best efforts, with worse presenting vision being associated with a worse prognosis for visual improvement.  Those eyes with more damage to the retinal tissue from oxygen loss (ischemic CRVOs) will have worse prognosis for visual outcome, and a greater risk for glaucoma and iris neovascularization after the event.  Even after resolution of CRVO, it is possible for hemorrhages to remain visible in the eye, and changes in blood vessel anatomy (collateral vessels) may occur as your eye tries to repair itself. At regular eye exams, your doctor will be looking for signs of ischemia or oxygen deprivation in the retina, as well as for any signs of increased eye pressure or possible glaucoma.