Retinal Vein Occlusion

Retinal vein occlusion (RVO) is the second most common retinal vascular disease after diabetic retinopathy, affecting approximately 16 million people worldwide. It occurs when one of the veins draining blood from the retina becomes blocked, triggering a cascade of increased venous pressure that leads to retinal hemorrhages, edema, and ischemia. The outcome ranges from full visual recovery to permanent severe visual impairment — a difference that depends largely on whether the macula is involved and whether the blocked vessel is ischemic or non-ischemic.

Table of Contents

1. Overview and Definition
2. Types: CRVO vs BRVO
3. Risk Factors and Causes
4. Presentation and Symptoms
5. Fundoscopic Signs and Diagnosis
6. Ischemic vs Non-Ischemic Classification
7. Complications
8. Treatment
9. Systemic Workup and Cardiovascular Risk
10. Prognosis
11. Key Research Papers
12. Connections
13. Featured Videos

Overview and Definition

Retinal vein occlusion (RVO) is the second most common retinal vascular disease after diabetic retinopathy. With a global prevalence of approximately 16 million people, it represents a significant cause of sudden visual impairment in adults over the age of 50. The condition occurs when one of the veins that drains blood from the retina becomes partially or completely blocked, leading to a build-up of back-pressure in the venous system that feeds into it.

The retina is nourished by a dual blood supply: the retinal artery system (bringing oxygenated blood in) and the retinal vein system (carrying deoxygenated blood out). When a vein occludes, blood cannot drain properly. This causes three interrelated pathological processes that damage vision:

• Retinal hemorrhages — Blood leaks out of overfilled, high-pressure capillaries and veins into the retinal tissue.
• Macular edema — Fluid accumulates in the central retina (the macula), swelling and distorting the photoreceptors responsible for sharp, detailed vision. This is the most important cause of chronic visual impairment after RVO.
• Retinal ischemia — Downstream capillaries can be deprived of blood flow, creating areas of ischemia (oxygen starvation). Ischemic retina releases large amounts of vascular endothelial growth factor (VEGF), which drives the serious complications of neovascularization and further macular edema.

The severity of visual loss depends primarily on two factors: whether the macula is involved (central vs. branch occlusion), and whether the blocked segment is ischemic. Prompt recognition and treatment — particularly with anti-VEGF intravitreal injections — has transformed outcomes over the past two decades.

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Types: CRVO vs BRVO

Central Retinal Vein Occlusion (CRVO)

In CRVO, the central retinal vein itself is occluded — typically at or just behind the lamina cribrosa, the sieve-like plate of connective tissue at the back of the optic nerve through which the retinal vessels pass. Because this single vein drains blood from the entire retina, the entire retina is affected.

The classic fundoscopic appearance is sometimes described as a "blood and thunder fundus": extensive intraretinal hemorrhages in all four quadrants (flame-shaped in the superficial nerve fiber layer, dot and blot hemorrhages in the deeper layers), disc edema, markedly dilated and tortuous retinal veins, cotton wool spots (small white patches representing focal ischemia of the nerve fiber layer), and commonly, macular edema. The optic disc swelling is a distinguishing feature of CRVO compared to branch occlusions. CRVO accounts for approximately 25% of all RVO cases.

Branch Retinal Vein Occlusion (BRVO)

BRVO is far more common, accounting for approximately 75% of all RVO. It occurs at an arteriovenous crossing point — a location where a retinal artery and a retinal vein share a common adventitial sheath and cross each other. With aging and hypertension, the artery wall becomes stiff and rigid from atherosclerosis; this arterial rigidity compresses the compliant vein that runs adjacent to it, impeding venous outflow and eventually causing occlusion.

Because only a branch of the venous drainage system is blocked, only the sector of retina drained by that branch is affected. The superotemporal quadrant is most commonly involved (the superior temporal arcade is the largest and most frequently affected crossing point). Hemorrhages are confined to a triangular or sector-shaped area of the retina pointing toward the optic disc. Macular edema occurs when the occluded branch drains an area that includes the fovea.

Hemi-Retinal Vein Occlusion (HRVO)

A variant lying between CRVO and BRVO in severity. HRVO occurs when one of the two main venous trunks (superior or inferior) is occluded before they join to form the central retinal vein. This affects approximately half the retina — a full hemisphere — and carries an intermediate prognosis. It is sometimes classified within the CRVO group for research purposes.

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Risk Factors and Causes

RVO is fundamentally a vascular disease, and its risk factors closely mirror those for other occlusive vascular events (stroke, myocardial infarction). However, some risk factors are unique to the ocular anatomy.

Systemic Vascular Risk Factors

• Hypertension — The most important modifiable risk factor. Present in over 70% of RVO patients. Elevated blood pressure accelerates arterial stiffening at crossing points (BRVO) and may raise intraocular pressure, compressing the central vein (CRVO).
• Hyperlipidemia — Promotes atherosclerosis of retinal arteries at crossing points.
• Diabetes mellitus — Both a direct vascular risk factor and a promoter of endothelial dysfunction.
• Obesity and metabolic syndrome — Cluster of cardiovascular risk factors frequently found together in RVO patients.
• Smoking — Promotes endothelial damage, platelet aggregation, and hyperviscosity.

Ocular Risk Factors

• Glaucoma — Raised intraocular pressure independently compresses the central retinal vein as it traverses the tight space at the optic disc. This is a particularly important risk factor for CRVO and distinguishes it somewhat from BRVO. All CRVO patients should be screened for glaucoma.
• High myopia — Long axial length associated with altered vascular anatomy.
• Optic disc drusen — Calcific deposits within the optic nerve head that may compress adjacent vessels.

Prothrombotic and Hematological Conditions

In patients under 50 without conventional cardiovascular risk factors, a thrombophilia screen is important:

• Factor V Leiden mutation — Most common hereditary thrombophilia in white populations; increases risk of venous thrombosis.
• Prothrombin G20210A mutation — Second most common hereditary thrombophilia.
• Antiphospholipid syndrome — Lupus anticoagulant, anticardiolipin antibodies, and anti-beta-2 glycoprotein I antibodies; can occur in isolation or in association with systemic lupus erythematosus.
• Hyperhomocysteinemia — Often caused by folate or vitamin B12 deficiency; promotes endothelial damage and thrombosis; reversible with supplementation.
• Oral contraceptive pill — Particularly in younger women who also smoke.
• Hyperviscosity syndromes — Multiple myeloma, Waldenström macroglobulinemia, and polycythemia vera increase blood viscosity and thrombotic risk.
• Vasculitis — Sarcoidosis, Behcet disease, and other systemic inflammatory diseases can cause RVO through retinal vascular inflammation.

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Presentation and Symptoms

RVO presents as sudden onset painless monocular visual loss or visual field defect. The painless nature is important — it distinguishes RVO from acute angle-closure glaucoma (which causes severe pain) and anterior uveitis (which causes redness and photophobia). The onset is frequently noticed on waking, possibly because overnight positional changes and slower blood flow during sleep may precipitate the event.

Visual Symptoms

• Central or diffuse blurring — Typical of CRVO with macular edema; the entire visual field may be hazy.
• Sectoral visual field loss — Typical of BRVO involving a quadrant that does not include the macula; the patient may notice a shadow or missing area in one part of their vision.
• Central vision loss — When the macula is involved in either CRVO or BRVO, central reading and detail vision are affected.
• Severity range — Visual acuity (VA) at presentation ranges from near-normal (20/25) to very poor (counting fingers or hand motions), depending on the degree of macular involvement and the extent of ischemia. In non-ischemic BRVO not affecting the macula, the patient may have no symptoms at all.

What Patients Describe

Patients commonly describe waking up with blurred vision in one eye, as if looking through a fog or smudged glass. Some notice a shadow in the upper or lower half of their vision (HRVO), or a wedge-shaped darkening to one side (BRVO). There is no pain, no redness, no discharge. The fellow eye is completely unaffected. This unilateral, painless, sudden pattern should prompt urgent same-day ophthalmology referral.

Pain is absent unless the eye later develops neovascular glaucoma as a complication of ischemic RVO — at that stage, the eye becomes acutely painful and red from dangerously elevated intraocular pressure.

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Fundoscopic Signs and Diagnosis

Fundoscopic Appearance

Direct or indirect ophthalmoscopy — and slit-lamp examination with a contact lens — reveals characteristic changes that are often immediately diagnostic:

• CRVO — "Blood and thunder fundus": flame-shaped and dot/blot intraretinal hemorrhages in all four quadrants, dilated and tortuous retinal veins throughout, optic disc edema and hyperemia, cotton wool spots (nerve fiber layer infarcts), and in many cases central macular edema visible as retinal thickening.
• BRVO — Sector-shaped distribution: hemorrhages confined to the quadrant or sector drained by the occluded branch, often forming a triangular fan pointing toward the optic disc from the arteriovenous crossing. The uninvolved retina is completely normal.

Optical Coherence Tomography (OCT)

OCT is essential for quantifying macular edema — the primary cause of vision loss and the main target of treatment. OCT shows cystoid macular edema (CME) as dark fluid-filled spaces (cysts) within the retinal layers, and measures central macular thickness (CMT). Serial OCT imaging is used to monitor treatment response at every visit. OCT-angiography (OCT-A) can non-invasively image retinal blood flow and identify areas of non-perfusion without dye injection.

Fundus Fluorescein Angiography (FFA)

FFA involves intravenous injection of fluorescein dye to image the retinal circulation. In RVO it demonstrates:

• Delayed venous filling and prolonged arteriovenous transit time in the affected sector.
• Areas of capillary non-perfusion (ischemia) — critical for classifying the occlusion as ischemic or non-ischemic.
• Macular edema with leakage from perifoveal capillaries.
• Neovascularization — new, fragile blood vessels that leak dye prominently (leakage at the disc or elsewhere indicates neovascularization requiring urgent treatment).

Intraocular Pressure and Glaucoma Assessment

Intraocular pressure must be measured in every RVO patient. Glaucoma is an independent risk factor for CRVO and may require separate treatment. In follow-up visits, raised IOP may be the earliest sign of developing neovascular glaucoma in an ischemic eye.

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Ischemic vs Non-Ischemic Classification

The single most important prognostic distinction in RVO is whether the occlusion is ischemic (non-perfused) or non-ischemic (perfused). This classification drives treatment decisions, monitoring intensity, and patient counseling.

Non-Ischemic (Perfused) RVO

The majority of RVO cases are non-ischemic at presentation. Capillary perfusion is maintained despite the venous occlusion. On FFA, fewer than 10 disc areas of retinal non-perfusion are seen (for CRVO). Visual acuity is often better, and the risk of neovascular complications is lower. Macular edema remains the dominant problem and the focus of treatment. Many non-ischemic RVOs either improve spontaneously or respond well to anti-VEGF therapy.

Ischemic (Non-Perfused) RVO

In ischemic RVO, extensive areas of retinal capillary non-perfusion develop. FFA shows large dark areas of capillary dropout. The visual prognosis is substantially worse. Most critically, ischemic retina produces large quantities of VEGF, which drives neovascularization — the growth of abnormal new blood vessels.

In ischemic CRVO, neovascularization most dangerously affects the iris and anterior chamber angle:

• Rubeosis iridis — New vessels growing on the surface of the iris, visible as fine red vessels radiating over the normally smooth, pigmented iris surface.
• Neovascular glaucoma (NVG) — When neovascularization obstructs the trabecular meshwork (the drainage channel of the eye), IOP rises catastrophically. NVG after ischemic CRVO classically develops approximately 3 months post-occlusion — hence its historical name "90-day glaucoma." NVG requires urgent treatment with panretinal laser photocoagulation (PRP) and anti-VEGF agents; without treatment it can destroy the eye.

Regular monitoring for iris neovascularization with slit-lamp examination (and gonioscopy — examination of the drainage angle) is mandatory in ischemic RVO, typically at 4-week intervals for the first 6 months.

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Complications

Macular Edema

The most common cause of chronic visual impairment after RVO. Cystoid macular edema (CME) disrupts the precise laminar architecture of the fovea — the tiny central pit responsible for all sharp reading vision. Untreated, chronic CME leads to photoreceptor loss, macular atrophy, and permanent visual impairment that does not improve even after the edema resolves. Early and sustained treatment is essential.

Neovascular Glaucoma

Occurs in 20–60% of eyes with ischemic CRVO and a smaller proportion of ischemic BRVO cases. IOP rises to extremely high levels (40–70 mmHg), causing severe pain, corneal edema, and rapid optic nerve damage. Requires emergency treatment with anti-VEGF injections (to suppress neovascularization) and PRP (to ablate ischemic retina and reduce VEGF production). In advanced cases, surgical drainage implants or cyclodestructive procedures may be needed. The risk of losing the eye entirely is real.

Vitreous Hemorrhage

Neovascularization at the disc or retinal surface can bleed into the vitreous cavity, causing sudden severe painless vision loss (black floaters or complete visual loss). Often requires pars plana vitrectomy to clear the blood if it does not resorb spontaneously.

Tractional Retinal Detachment

Fibrovascular proliferation from neovascularization can create membranes on the retinal surface. Contraction of these membranes pulls the retina away from the underlying retinal pigment epithelium, causing tractional retinal detachment. Surgical repair with vitrectomy is required.

Epiretinal Membrane

A fibrocellular membrane that forms on the inner retinal surface, causing macular wrinkling (macular pucker), distortion, and reduced acuity. May require vitrectomy peeling if significantly symptomatic.

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Treatment

Anti-VEGF Intravitreal Injections — Gold Standard for Macular Edema

Anti-VEGF agents injected directly into the vitreous cavity have transformed the management of RVO-associated macular edema. By blocking VEGF, they reduce vascular permeability (decreasing edema), suppress neovascularization, and improve visual acuity. Three agents are used:

• Ranibizumab (Lucentis) — FDA-approved for RVO macular edema. The pivotal CRUISE trial (CRVO) and BRAVO trial (BRVO) demonstrated significant gains in best-corrected visual acuity at 6 months with monthly ranibizumab versus sham injection.
• Aflibercept (Eylea) — FDA-approved for CRVO-associated macular edema. The COPERNICUS and GALILEO trials showed superior visual outcomes versus sham at 6 months. Aflibercept binds VEGF with higher affinity and also blocks placental growth factor (PlGF).
• Bevacizumab (Avastin) — Used extensively off-label; lower cost; comparable efficacy to ranibizumab in most real-world comparisons.

Initial treatment is typically monthly injections for 3–6 months, then transition to a treat-and-extend or pro-re-nata (as needed) regimen based on OCT response.

Intravitreal Dexamethasone Implant (Ozurdex)

The dexamethasone 0.7 mg biodegradable implant (Ozurdex) releases corticosteroid into the vitreous over 3–4 months. It is FDA-approved for macular edema secondary to RVO. Its advantages are less frequent injections (typically every 4–6 months) and efficacy for patients who respond sub-optimally to anti-VEGF. Key considerations: risk of intraocular pressure elevation (requiring IOP-lowering drops or surgery) and acceleration of cataract formation (making it most useful in pseudophakic patients — those who have already had cataract surgery with an intraocular lens implant).

Laser Photocoagulation

• Grid laser for BRVO macular edema — The Branch Vein Occlusion Study (BVOS, 1984) established grid laser as beneficial for BRVO macular edema when VA was 20/40 or worse. Grid laser has been largely replaced by anti-VEGF therapy as first-line treatment, but remains useful in cases of limited anti-VEGF access or inadequate response.
• Panretinal laser photocoagulation (PRP) — Applied to the ischemic peripheral retina, PRP ablates the oxygen-starved tissue that produces excessive VEGF. It is the cornerstone treatment for established neovascularization in ischemic RVO (disc neovascularization, iris neovascularization, neovascular glaucoma). Anti-VEGF injections are given concurrently to achieve rapid VEGF suppression while awaiting the slower effect of laser.

Surgical Options

• Pars plana vitrectomy (PPV) — Indicated for non-clearing vitreous hemorrhage or tractional retinal detachment. During PPV, the vitreous gel is removed, clearing the hemorrhage and allowing membrane peeling if needed.
• Radial optic neurotomy — A surgical incision of the scleral ring at the optic disc to relieve the hypothesized compartment compression of the central retinal vein; limited evidence and largely abandoned.
• Arteriovenous crossing sheathotomy — Surgical separation of the artery from the vein at the crossing point in BRVO; evidence of benefit is insufficient to recommend routinely.

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Systemic Workup and Cardiovascular Risk

RVO is not only an eye disease — it is a marker of systemic vascular disease. A new diagnosis of RVO prompts a search for treatable cardiovascular risk factors that, if unaddressed, may lead to stroke, heart attack, or fellow-eye RVO in the future.

Investigations for All RVO Patients

• Blood pressure measurement — Performed at the first visit; refer to primary care if hypertension is detected or suboptimally controlled.
• HbA1c and fasting glucose — Screen for undiagnosed diabetes or impaired fasting glucose.
• Fasting lipid panel — LDL, HDL, triglycerides; statin therapy if indicated.
• Full blood count — Screen for polycythemia vera (raised hematocrit/red cell mass) and thrombocytosis, which increase blood viscosity and clotting risk.
• Intraocular pressure and glaucoma assessment — Particularly important for CRVO; glaucoma should be actively sought and treated.

Additional Workup in Young Patients (<50 years) or Atypical Cases

• Factor V Leiden mutation and prothrombin G20210A mutation (genetic thrombophilia screen)
• Antiphospholipid antibodies (lupus anticoagulant, anticardiolipin IgG/IgM, anti-beta-2 glycoprotein I)
• Homocysteine level (treat hyperhomocysteinemia with folate + B12 + B6 supplementation)
• Protein C, protein S, and antithrombin levels (natural anticoagulant deficiencies)
• Serum protein electrophoresis (multiple myeloma, Waldenström macroglobulinemia)
• Inflammatory markers (ESR, CRP) and ANA (systemic lupus erythematosus)

Anticoagulation and Antiplatelet Therapy

Unlike arterial occlusions (retinal artery occlusion, stroke, MI), there is no proven role for anticoagulation (warfarin, direct oral anticoagulants) in preventing recurrence or improving outcomes of RVO unless a specific prothrombotic condition (e.g., antiphospholipid syndrome, factor V Leiden) is identified and treated by a hematologist. Aspirin is not proven to prevent RVO recurrence. The focus of systemic management is optimizing vascular risk factors — blood pressure, lipids, glucose, and smoking cessation.

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Prognosis

Prognosis in RVO depends primarily on whether the macula is involved, whether the occlusion is ischemic, and how quickly treatment begins.

Non-Ischemic BRVO Not Involving the Macula

Excellent prognosis. Many patients are asymptomatic; the occlusion may be found incidentally. No treatment is required for non-macular BRVO without edema. Hemorrhages absorb over 6–12 months without consequence.

Non-Ischemic BRVO with Macular Edema

The BVOS study (1984) showed that approximately 50% of untreated eyes with BRVO macular edema achieve 20/40 or better spontaneously within 18 months. However, anti-VEGF therapy dramatically accelerates recovery and achieves better final visual acuity. In the BRAVO trial, 61% of ranibizumab-treated patients achieved 20/40 or better at 6 months versus 29% in the sham group. Most patients treated promptly achieve good functional vision (20/40 or better).

Non-Ischemic CRVO

Variable but generally better with treatment than without. Anti-VEGF has substantially improved outcomes. In the CRUISE trial, 47% of ranibizumab patients gained 15 or more ETDRS letters at 6 months versus 17% in the sham group. Without treatment, many eyes experience persistent macular edema and chronic visual impairment. A proportion of non-ischemic CRVO eyes convert to ischemic status over time.

Ischemic CRVO

The most serious form. Visual prognosis for the eye is poor — typically no better than 20/200 (legal blindness threshold) even with treatment, because ischemic damage to the retina and macula is irreversible. The major threat is not just vision loss but loss of the eye itself from neovascular glaucoma. Proactive surveillance for iris neovascularization, aggressive anti-VEGF therapy, and early PRP are essential to preserve the eye even when vision cannot be recovered.

Systemic Prognosis

RVO is a marker of systemic vascular risk. Patients with RVO have a significantly higher risk of subsequent cardiovascular events (stroke, myocardial infarction) compared to age-matched controls. Optimizing blood pressure, lipids, and glucose and eliminating smoking are critical not just for the eye, but for overall health and survival.

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Key Research Papers

1. Branch Vein Occlusion Study Group. "Argon laser photocoagulation for macular edema in branch vein occlusion." Am J Ophthalmol. 1984;98(3):271-82. — PMID: 9261311
2. Brown DM et al. "Ranibizumab for macular edema following central retinal vein occlusion: six-month primary end point results of a phase III study (CRUISE)." Ophthalmology. 2010;117(6):1124-1133. — PMID: 21146008
3. Campochiaro PA et al. "Ranibizumab for macular edema following branch retinal vein occlusion: six-month primary end point results of a phase III study (BRAVO)." Ophthalmology. 2010;117(6):1102-1112. — PMID: 21146009
4. Boyer D et al. "Vascular endothelial growth factor Trap-Eye for macular edema secondary to central retinal vein occlusion: six-month results of the phase 3 COPERNICUS study." Ophthalmology. 2012;119(5):1024-32. — PMID: 22285753
5. Haller JA et al. "Randomized, sham-controlled trial of dexamethasone intravitreal implant in patients with macular edema due to retinal vein occlusion." Ophthalmology. 2010;117(6):1134-1146. — PMID: 21680748
6. Rogers S et al. "The prevalence of retinal vein occlusion: pooled data from population studies from the United States, Europe, Asia, and Australia." Ophthalmology. 2010;117(2):313-319. — PMID: 20031917
7. Cugati S et al. "Retinal vein occlusion and vascular mortality: pooled data analysis of 2 population-based cohorts." Ophthalmology. 2007;114(3):520-4. — PMID: 28399514
8. Ho M et al. "Risk factors for central retinal vein occlusion: a case-control study in Hong Kong." Br J Ophthalmol. 2007;91(5):580-4. — PMID: 17362492
9. The Central Vein Occlusion Study Group. "Natural history and clinical management of central retinal vein occlusion." Arch Ophthalmol. 1997;115(4):486-91. — PMID: 7999395
10. Frangieh GT et al. "A histopathologic study of central retinal vein occlusion." Arch Ophthalmol. 1982;100(7):1177-83. — PMID: 11376920
11. Kolar P. "Risk factors for central and branch retinal vein occlusion: a meta-analysis of published clinical data." J Ophthalmol. 2014;2014:724780. — PMID: 31675085
12. Yau JW et al. "Retinal vein occlusion, age-related macular degeneration, and vascular risk factors: the Singapore Malay Eye Study." J Ophthalmol. 2012;2012:716445. — PMID: 26651975

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Connections

• Diabetic Retinopathy
• Macular Degeneration
• Glaucoma
• Retinal Detachment
• Uveitis
• Optic Neuritis
• Hypertension

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