Central Retinal Vein Occlusion (CRVO)

01Pathophysiology

The central retinal artery and central retinal vein share a common adventitial sheath as they pass through the lamina cribrosa of the optic nerve. This anatomical relationship is the foundation of the disease. In patients with longstanding hypertension or atherosclerosis, the central retinal artery becomes rigid and sclerotic. Because both vessels are bound together in a tight fibrous channel, the hardened artery compresses the adjacent vein against the lamina cribrosa, leading to turbulent flow, endothelial damage, and eventual thrombus formation within the vein.Once the central retinal vein is occluded, venous outflow from the entire retina is obstructed. This causes a rapid rise in intraluminal venous pressure, which transmits back to the retinal capillary bed. The elevated capillary pressure overwhelms the vessel walls, leading to widespread rupture and the characteristic diffuse, four-quadrant retinal hemorrhages seen on fundoscopy. Simultaneously, increased hydrostatic pressure forces plasma out of the capillaries into the retinal interstitium, producing macular edema, which is the primary cause of vision loss.

In more severe cases, the degree of venous stasis is so profound that retinal capillary perfusion drops critically. This results in retinal ischemia, which triggers the upregulation of vascular endothelial growth factor (VEGF). VEGF drives the formation of abnormal new blood vessels (neovascularization) on the iris (rubeosis iridis), the optic disc, and the retina. These fragile new vessels are prone to bleeding and can obstruct the trabecular meshwork, leading to neovascular glaucoma, the most feared complication of ischemic CRVO. This is why the ischemic subtype is sometimes called the "100-day glaucoma" since neovascular complications typically emerge around 3 months after the initial event.

02Classification and Clinical Manifestation

CRVO is classified into two subtypes based on the degree of retinal capillary perfusion, which determines prognosis and complication risk.

The clinical distinction between these two subtypes is arguably the most tested concept about CRVO. The presence of a relative afferent pupillary defect (RAPD) in the affected eye is a bedside clue that strongly suggests the ischemic variant, reflecting extensive retinal ganglion cell dysfunction. Non-ischemic CRVO may convert to the ischemic form over the following months, which is why close follow-up with serial fundoscopic examination is necessary.

03Diagnostic Workup

Dilated fundoscopy is the best initial step. The classic "blood and thunder" or "stormy sunset" appearance with hemorrhages spanning all four retinal quadrants is essentially diagnostic. This distinguishes CRVO from a branch retinal vein occlusion (BRVO), where hemorrhages are confined to a single quadrant or sector corresponding to the affected branch.

Fluorescein angiography is the gold standard for classifying the occlusion as ischemic or non-ischemic, a distinction that directly drives management. In the ischemic subtype, FA reveals large areas of capillary dropout (non-perfusion exceeding 10 disc areas). In non-ischemic CRVO, capillary perfusion is largely maintained, and the dominant finding is delayed venous filling with dye leakage.

OCT is used alongside FA to evaluate and follow macular edema, which is the principal cause of decreased visual acuity. It provides objective, quantifiable measurements of retinal thickness and guides the need for anti-VEGF therapy.

A targeted systemic workup should be performed in all patients. Hypertension and diabetes are the most common associated conditions. In patients younger than 50 or those without traditional vascular risk factors, a comprehensive hypercoagulability workup is warranted to rule out prothrombotic states.

04Management and Treatment

Anti-VEGF therapy has become the cornerstone of treatment for CRVO-associated macular edema, supported by landmark trials (CRUISE, COPERNICUS, GALILEO). These agents inhibit VEGF, reducing vascular permeability and macular edema. Treatment is initiated with monthly injections, and the interval is extended once the macula shows a stable response on OCT (treat-and-extend protocol).

Intravitreal dexamethasone implants are a reasonable alternative, particularly in pseudophakic eyes (where cataract formation is not a concern) or in patients who do not respond adequately to anti-VEGF. The key trade-off is the risk of steroid-induced intraocular pressure elevation, which requires monitoring.

Panretinal photocoagulation (PRP) is not applied prophylactically. It is reserved for eyes that develop confirmed neovascularization. PRP works by ablating ischemic peripheral retina, thereby reducing the overall VEGF load. It does not improve visual acuity and is used solely to prevent complications such as vitreous hemorrhage and neovascular glaucoma.

For neovascular glaucoma, management is urgent and multimodal. An intravitreal anti-VEGF injection is given first to rapidly regress the new vessels on the iris and angle. PRP is then applied for sustained VEGF reduction. Intraocular pressure is managed with topical agents (timolol, brimonidine) or surgical intervention (tube shunt) if medical therapy fails.

Systemic anticoagulation or antiplatelet therapy has not been shown to improve outcomes in CRVO and is not routinely recommended unless a confirmed systemic prothrombotic condition is identified.

05Differential Diagnosis and Distractors

06Traps and High-Yield Pearls

The most common trap in CRVO questions is confusing it with CRAO. Both present as sudden, painless, unilateral vision loss, but the fundoscopic findings are opposite. CRVO produces a hemorrhagic, "stormy" fundus with engorged veins, while CRAO produces a pale, ischemic fundus with a cherry-red spot and threadlike arterioles. If the vignette describes "diffuse retinal hemorrhages in all four quadrants," the answer is CRVO. If it describes "pallor with a cherry-red macula," the answer is CRAO.

A second common pitfall is failing to differentiate CRVO from BRVO. The key is distribution: four-quadrant hemorrhages point to central vein occlusion, while hemorrhages limited to one sector indicate a branch occlusion.

The third trap involves management logic. Students often select "laser photocoagulation" as the first-line treatment for macular edema. This is incorrect. PRP is reserved only for neovascularization, not for macular edema. The correct first-line treatment for macular edema in CRVO is intravitreal anti-VEGF injection. A vignette describing decreased visual acuity with macular thickening on OCT is asking for anti-VEGF, not laser.

Finally, remember the concept of "100-day glaucoma." If a question describes a patient who had a painless vision loss event 2 to 3 months ago and now presents with eye pain, a red eye, and elevated intraocular pressure, this is neovascular glaucoma complicating ischemic CRVO. The presence of an RAPD at initial presentation is the strongest clinical predictor that the patient has the ischemic subtype and is at high risk for this devastating complication.