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Summary Table

Category	Details
Risk Factors	Age over 50, hypertension (most common), diabetes mellitus, hyperlipidemia, open-angle glaucoma, smoking, hyperviscosity syndromes (multiple myeloma, Waldenström), hypercoagulable states (in younger patients: factor V Leiden, antiphospholipid syndrome, OCP use)
Etiology	Thrombosis of the central retinal vein at the lamina cribrosa, typically caused by compression from an atherosclerotic central retinal artery sharing the same adventitial sheath
Patient Presentation	Sudden, painless, unilateral vision loss or blurring. Severity ranges from mild blur (non-ischemic) to severe loss with counting fingers vision (ischemic)
Classic Physical Exam	Reduced visual acuity, relative afferent pupillary defect (RAPD) in the ischemic subtype. Fundoscopy shows the "blood and thunder" picture: dilated, tortuous retinal veins, retinal hemorrhages in all four quadrants, cotton wool spots, optic disc edema, and macular edema
Key Diagnostic Results	Clinical diagnosis via dilated fundoscopy. Fluorescein angiography distinguishes ischemic from non-ischemic. Optical coherence tomography (OCT) quantifies macular edema. Systemic workup for blood pressure, glucose, lipids
Management	Treat underlying systemic disease, intravitreal anti-VEGF injections (ranibizumab, aflibercept, bevacizumab) for macular edema, intravitreal dexamethasone implant as alternative, panretinal photocoagulation if neovascularization develops
Keywords	"Blood and thunder fundus," sudden painless monocular vision loss, tortuous dilated veins, four-quadrant flame and dot-blot hemorrhages, elderly hypertensive patient, "ninety-day glaucoma"

1. Pathophysiology

The central retinal artery and central retinal vein travel together through the optic nerve, sharing a common adventitial sheath as they pass through the lamina cribrosa. This anatomical relationship is the foundation of the disease. When the artery becomes thickened from atherosclerosis (driven by chronic hypertension, diabetes, and hyperlipidemia), it compresses the adjacent vein. The resulting turbulent flow damages the venous endothelium and triggers thrombus formation within the vein lumen.

Once the vein is occluded, blood cannot drain from the retina. Hydrostatic pressure rises throughout the retinal venous and capillary system, forcing blood and plasma out of vessel walls. This produces the diffuse retinal hemorrhages in all four quadrants that define the classic appearance, along with macular edema (which is the principal cause of vision loss) and cotton wool spots from nerve fiber layer infarction.

CRVO exists on a spectrum with two clinically important subtypes. Non-ischemic CRVO (about 75 percent of cases) has preserved capillary perfusion, milder vision loss, no RAPD, and a favorable prognosis. Ischemic CRVO (about 25 percent) shows widespread capillary non-perfusion, severe vision loss, a positive RAPD, and a high risk of complications. The most feared complication is neovascular glaucoma, often called "ninety-day glaucoma" because it classically develops around 90 to 100 days after the occlusion. Retinal ischemia drives VEGF release, which stimulates abnormal new vessels to grow on the iris (rubeosis iridis) and in the anterior chamber angle, blocking aqueous outflow and causing a painful secondary angle-closure glaucoma.

2. Diagnostic Workup

Test	Role	Key Findings
Visual acuity and pupillary exam	Bedside triage	Reduced acuity, RAPD suggests ischemic subtype
Dilated fundoscopy	Best initial diagnostic test	"Blood and thunder" retina: four-quadrant hemorrhages, tortuous dilated veins, disc edema, cotton wool spots
Optical coherence tomography (OCT)	Quantifies macular edema	Increased central retinal thickness, intraretinal cystic spaces
Fluorescein angiography	Most accurate test for subtyping	Delayed venous filling. Ischemic CRVO: Greater than 10 disc areas of capillary non-perfusion
Intraocular pressure measurement	Baseline and follow-up	Monitors for neovascular glaucoma
Systemic workup	Identifies underlying cause	Blood pressure, fasting glucose, HbA1c, lipid panel, complete blood count
Hypercoagulability panel	Reserved for younger patients (under 50) or bilateral disease	Factor V Leiden, prothrombin gene mutation, antiphospholipid antibodies, homocysteine, protein C and S

The diagnosis of CRVO is clinical, made at the slit lamp with a dilated fundus exam. The best initial test is therefore dilated fundoscopy, which reveals the classic four-quadrant hemorrhagic picture. No imaging is required to make the diagnosis itself, but ancillary testing is essential for staging and management.

OCT is performed on every patient because it objectively measures macular edema, which guides whether to inject anti-VEGF therapy and tracks response over time. Fluorescein angiography is the most accurate test for distinguishing ischemic from non-ischemic CRVO, which carries major prognostic weight. Capillary non-perfusion exceeding 10 disc areas defines the ischemic subtype and identifies the patients at highest risk for neovascularization.

Because CRVO is fundamentally a marker of systemic vascular disease, every patient needs evaluation for hypertension, diabetes, and hyperlipidemia. In patients younger than 50 or those with bilateral or recurrent disease, a thrombophilia and vasculitis workup should be added.

3. Management and Treatment

Treatment	Indication	Notes
Intravitreal anti-VEGF (ranibizumab, aflibercept, bevacizumab)	First-line for macular edema	Monthly injections initially, then individualized
Intravitreal dexamethasone implant	Alternative or adjunct for macular edema	Useful in pseudophakic patients or when anti-VEGF fails. Avoid in glaucoma
Panretinal photocoagulation (PRP)	Neovascularization of iris, angle, disc, or retina	Treats ischemic complications, prevents neovascular glaucoma
Systemic risk factor control	All patients	Manage hypertension, diabetes, hyperlipidemia, stop smoking
Anticoagulation	Not routine	Only if a separate systemic indication exists

Acute management centers on addressing macular edema, which is the dominant cause of vision loss in non-ischemic disease. Intravitreal anti-VEGF injection is the first-line therapy. Standard regimens use ranibizumab 0.5 mg, aflibercept 2 mg, or off-label bevacizumab 1.25 mg, given monthly for the first 6 months and then transitioned to a treat-and-extend or pro re nata schedule based on OCT findings. Intravitreal dexamethasone implant (Ozurdex 0.7 mg) lasting roughly 3 to 6 months is an alternative, especially valuable in patients who cannot return for frequent injections, but it raises intraocular pressure and accelerates cataract formation, so it is avoided in patients with glaucoma or phakic eyes when possible.

The next best step in any patient who develops new vessels on the iris, angle, optic disc, or elsewhere on the retina is panretinal photocoagulation. PRP destroys ischemic peripheral retina, lowers VEGF drive, and is the definitive treatment to prevent and manage neovascular glaucoma. In ischemic CRVO, monthly follow-up for the first 6 months is standard to catch neovascularization early.

Long-term management is aggressive control of systemic vascular risk: blood pressure target around 130/80 mmHg, HbA1c individualized but typically under 7 percent, statin therapy for elevated LDL, and smoking cessation. Routine systemic anticoagulation is not indicated for CRVO itself; it does not improve visual outcomes and exposes the patient to bleeding risk including vitreous hemorrhage. Anticoagulation is given only if the patient has a separate indication such as atrial fibrillation or a confirmed thrombophilia with prior thromboembolism.

Contraindications and cautions: anti-VEGF agents are pregnancy category C and are generally avoided in pregnancy and breastfeeding. Intravitreal steroids are avoided in active glaucoma, ocular infection, or ocular hypertension.

4. Differential Diagnosis and Distractors

Differential Diagnosis	Why it is similar	Key Discriminator
Central retinal artery occlusion (CRAO)	Sudden painless monocular vision loss in an elderly vasculopath	Pale retina with a cherry-red spot at the macula, "boxcar" segmentation of arterioles, no hemorrhages. CRVO has hemorrhages everywhere
Branch retinal vein occlusion (BRVO)	Same hemorrhagic pathology, similar risk factors	Hemorrhages confined to one quadrant (typically superotemporal), often respecting the horizontal raphe. CRVO involves all four quadrants
Hypertensive retinopathy	Hemorrhages, cotton wool spots, vascular changes	Bilateral and chronic, with AV nicking and copper or silver wiring. CRVO is unilateral and acute
Diabetic retinopathy	Hemorrhages, microaneurysms, neovascularization	Bilateral, with microaneurysms and dot-blot hemorrhages predominantly in the posterior pole. CRVO is unilateral with diffuse flame hemorrhages
Ocular ischemic syndrome	Mid-peripheral hemorrhages, neovascularization in an elderly patient	Caused by severe ipsilateral carotid artery stenosis. Hemorrhages are in the mid-periphery rather than diffuse, and patients often describe pain or amaurosis fugax
Vitreous hemorrhage	Sudden painless vision loss	View of the retina is obscured by blood in the vitreous cavity, no fundus detail visible. Often caused by proliferative diabetic retinopathy or retinal tear
Papilledema	Optic disc swelling	Bilateral, associated with headache and raised intracranial pressure. CRVO has unilateral disc edema with hemorrhages throughout the retina

5. Traps and High-Yield Pearls

The most common way students miss CRVO questions is confusing it with central retinal artery occlusion. Both present with sudden painless monocular vision loss in an elderly vasculopath, so the answer lives entirely in the fundus description. If the vignette says cherry-red spot and pale retina, the answer is CRAO. If it says dilated tortuous veins with hemorrhages in all four quadrants, the answer is CRVO. The mnemonic that helps: arteries carry blood in, so when an artery occludes, the retina goes pale and starves; veins carry blood out, so when a vein occludes, blood backs up and the retina hemorrhages everywhere.

A second common trap is reflexively reaching for anticoagulation. CRVO is a thrombotic event, so students assume heparin or warfarin is the answer. It is not. Anti-VEGF injection is the cornerstone of therapy, and systemic anticoagulation has no role unless there is a separate indication. A third trap is forgetting to look forward in time. The question may not stop at diagnosis; it may ask what complication develops 3 months later. The answer is neovascular glaucoma from rubeosis iridis, and the next best step is panretinal photocoagulation, not more anti-VEGF alone.

A fourth trap is the younger patient. If the vignette describes a woman in her thirties on oral contraceptives, or a young man with recurrent miscarriages or prior DVT, the test wants you to order a thrombophilia and antiphospholipid antibody workup, not just check her blood pressure.

The core competency being tested is twofold: pattern recognition of the "blood and thunder" fundus to anchor the diagnosis, and understanding the natural history well enough to anticipate ischemic complications and know when to escalate from anti-VEGF injections to panretinal photocoagulation.

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