You wake up one morning and one eye is blurry. No pain, no warning. Retinal vein occlusion is the second most common retinal vascular disease. For the broader retinal vascular context, see the retina subspecialty page after diabetic retinopathy, and treatable when caught on time.
Retinal vein occlusion (RVO) happens when one of the veins draining blood from the retina becomes blocked. Blood and fluid back up behind the blockage, leaking into the retinal tissue and causing swelling. If the swelling involves the macula, the central area responsible for sharp vision, central vision blurs rapidly. It is not painful. It is not gradual. Most patients notice it when they wake up or cover one eye by chance and discover the other is blurred. The blockage itself cannot be reversed. But the fluid it causes — which is what actually damages vision — is now very treatable.
What You Need to Know About RVO
- RVO comes in two main types: branch RVO (BRVO), where a smaller branch vein is blocked, and central RVO (CRVO), where the main retinal vein is blocked at the optic nerve
- CRVO is typically more severe and affects a larger area of the retina than BRVO
- The most important risk factors are high blood pressure, high cholesterol, diabetes, and cardiovascular disease
- Macular edema is the main cause of vision loss in both types and is treated with anti-VEGF injections
- An RVO is often the first sign that cardiovascular risk factors are not adequately controlled. A medical review is required after diagnosis
- Most patients with BRVO achieve good visual recovery with treatment. CRVO outcomes are more variable
BRVO vs CRVO: What Is the Difference?
- A smaller branch vein is blocked
- Hemorrhages confined to one quadrant or sector
- Vision loss depends on whether the macula is involved
- Some cases recover spontaneously without treatment
- Generally better visual prognosis than CRVO
- Responds well to anti-VEGF injections
- The main retinal vein is blocked at the optic nerve
- Hemorrhages in all four quadrants of the retina
- Almost always causes significant vision loss
- Higher risk of neovascular glaucoma as a complication
- More variable visual outcomes than BRVO
- Requires intensive treatment and monitoring
Why Does It Happen?
The retinal veins run alongside retinal arteries, sharing a common fibrous sheath at crossings. When an artery is stiff and thickened from years of hypertension or atherosclerosis, it compresses the adjacent vein at these crossing points. The compressed vein develops turbulent flow, clotting, and eventually occlusion. This is why the risk factors for RVO are almost identical to those for heart attack and stroke: high blood pressure, diabetes, high cholesterol, smoking, and cardiovascular disease. An RVO is a vascular event. In the eye, yes, but driven by the same underlying process as a heart attack or stroke.
In younger patients, particularly those under 50 with no obvious cardiovascular risk factors, a blood clotting disorder or inflammatory condition should be considered. Conditions such as antiphospholipid syndrome, hyperhomocysteinaemia, and inflammatory diseases including uveitis can cause RVO without the typical vascular risk profile. A hematological screen is appropriate in atypical presentations.
How Vision Is Lost: Macular Edema
The occlusion itself doesn’t directly damage vision. What damages vision is the consequence: fluid leaking from the congested, damaged retinal vessels accumulates in the macula. The retinal layers swell and cystic spaces form, distorting the delicate photoreceptor arrangement that makes sharp central vision possible. This is cystoid macular edema, and it is what you are looking at in the OCT scan above.
The OCT cross-section shows the macula in profile. In a healthy eye, the central fovea has a characteristic dip and the retinal layers are thin and smooth. In RVO with macular edema, the fovea is obliterated by swelling, the layers are thickened, and large fluid-filled spaces (cysts) are visible as dark voids within the retinal tissue. The degree of edema correlates directly with how blurred vision is, and reducing the edema with treatment restores it.
Symptoms
Almost always sudden and painless. The typical presentation is blurred or distorted vision in one eye noticed on waking or discovered by chance when covering the other eye. In BRVO confined to the periphery, vision may be normal and the condition only discovered at a routine eye examination. In CRVO, vision loss is usually significant from the outset. Some patients notice a shadow or scotoma rather than generalised blurring if the edema is eccentric rather than central.
Diagnosis
The fundus appearance is usually diagnostic. Flame-shaped hemorrhages, dilated tortuous veins, cotton wool spots, and disc swelling in the distribution of the affected vein are immediately recognisable. An OCT scan quantifies the degree of macular edema and establishes a baseline to assess treatment response. Fluorescein angiography maps areas of retinal ischemia, vessel leakage, and any neovascularisation. The degree of ischemia on angiography is one of the most important prognostic indicators in CRVO.
Treatment
Anti-VEGF injections
Anti-VEGF medications are the first-line treatment for macular edema from both BRVO and CRVO. They reduce vascular leakage and fluid accumulation, allowing the macula to thin and vision to recover. Treatment typically starts with monthly injections, then transitions to a treat-and-extend or as-needed protocol based on OCT findings at each visit. Many patients need ongoing treatment for months to years. Stopping prematurely often leads to fluid returning and vision declining.
Intravitreal steroids
For patients who respond incompletely to anti-VEGF injections, intravitreal corticosteroids are an alternative. The dexamethasone implant (Ozurdex) is a slow-release rod injected into the vitreous that delivers steroid over three to four months. It can be particularly effective in CRVO and in cases where anti-VEGF response has plateaued. The main side effects are raised intraocular pressure and accelerated cataract formation, both of which require monitoring.
Laser treatment
Sector pan-retinal photocoagulation (PRP) laser is used when significant retinal ischemia has led to neovascularisation, the growth of abnormal new blood vessels on the retina or iris that can cause neovascular glaucoma. Laser reduces the ischemic drive for new vessel growth. It does not improve vision and does not treat macular edema, but it prevents the sight-threatening complication of neovascular glaucoma, which is one of the most serious consequences of untreated ischemic CRVO.
Treating the underlying cause
This is as important as the eye treatment itself. An RVO is a vascular event. Blood pressure, diabetes, cholesterol, and cardiovascular risk should be assessed and optimised by a GP or physician. Patients with undiagnosed hypertension are frequently identified at the point of RVO diagnosis. Controlling these factors reduces the risk of a further RVO in either eye and addresses the broader cardiovascular risk that the RVO has revealed.
RVO as a Warning Sign
An RVO should be thought of as the eye equivalent of a transient ischaemic attack: a vascular event that reveals underlying risk factors that need addressing urgently. Up to 75 percent of RVO patients have hypertension, often previously undiagnosed or inadequately treated. Many have elevated cholesterol or impaired glucose tolerance they didn’t know about.
Getting the eye treated is important. But it is not the whole story. If the underlying vascular risk factors remain uncontrolled, the risk of a further event in either eye is considerably higher, and the same risk factors drive heart attack and stroke. A thorough cardiovascular review after an RVO is not optional. It should happen within weeks of diagnosis, not eventually.
Many patients focus entirely on the eye and defer the medical review. Don’t. Your ophthalmologist will treat the macular edema. Your GP needs to treat what caused the occlusion in the first place.
Seek Same-Day Assessment If You Notice
- Sudden blurring or distortion of vision in one eye, particularly on waking
- A shadow or dark patch in the central or peripheral vision of one eye
- Sudden significant reduction in vision in one eye without pain
- Known RVO patient who develops a sudden painful red eye with reduced vision (possible neovascular glaucoma)
RVO is not an immediate surgical emergency like retinal detachment, but same-day assessment matters. Early treatment of macular edema gives better visual outcomes than delayed treatment, and an acutely painful red eye in a known CRVO patient can indicate neovascular glaucoma, which requires urgent pressure-lowering intervention.
Frequently Asked Questions About RVO
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Will my vision go back to normal?
Depends on the type and how quickly treatment started. BRVO with macular edema treated promptly: around 70 percent of patients achieve 20/40 or better, and many do considerably better than that. CRVO is more variable. Ischemic CRVO, where a large area of retina has lost its blood supply, carries a worse prognosis than non-ischemic CRVO. Nobody can tell you your exact outcome at the start. That’s the honest answer. What treatment does is shift the odds considerably in your favour.
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How many injections will I need?
Hard to predict at the outset. Some patients with BRVO respond quickly and need only a short course. CRVO typically requires more sustained treatment, often a year or more. The number of injections is driven entirely by how much fluid is present on the OCT at each visit. Trying to extend too quickly often leads to fluid returning and having to catch up again. Consistent attendance matters more than the total injection count.
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Can the blocked vein unblock itself?
Not in a clinically meaningful way. Some collateral vessels develop over time that partially compensate for the blocked vein, which is why some BRVO cases improve partially without treatment. But the occlusion itself doesn’t reverse. Treatment is directed at the edema and its consequences, not at reopening the vein.
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I have high blood pressure. Did that cause this?
Almost certainly, at least in part. Hypertension is present in up to 75 percent of RVO patients and is the single most important modifiable risk factor. Getting blood pressure properly controlled after an RVO is one of the most important steps you can take, both for your eyes and for your general cardiovascular health. The eye event is a signal. How you respond to it systemically matters.
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Could the other eye be affected?
Yes. The five-year risk of RVO in the fellow eye is around 10 percent. The same risk factors that caused the first event put the second eye at risk. The most effective protection is controlling those risk factors: blood pressure, cholesterol, blood sugar, and not smoking. Regular eye examinations to monitor the fellow eye are also sensible.
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Are the injections painful?
Many RVO patients have never had any eye procedure before and approach their first injection with real anxiety. In practice, the eye is numbed thoroughly beforehand and the injection takes a matter of seconds. What people typically notice is a sense of pressure. Occasionally a brief dull ache. Not pain. A red patch appears on the white of the eye in most cases afterward: it looks alarming if you don’t know to expect it, but it is simply a small bruise on the eye surface and fades within one to two weeks without any treatment.
If you would like to learn more, the American Academy of Ophthalmology’s retinal vein occlusion page offers a clear patient-friendly overview of symptoms, causes, treatment, and what to expect if a retinal vein becomes blocked.
Retinal vein occlusion (RVO) is the second most common retinal vascular disease after diabetic retinopathy, with a global prevalence of approximately 2 per 1,000. It divides into branch retinal vein occlusion (BRVO) and central retinal vein occlusion (CRVO), with BRVO being three to four times more common. Both cause venous outflow obstruction that produces hemorrhage, leakage, ischemia, and macular edema (ME) in the affected drainage territory. Vision loss is caused primarily by macular edema and, in ischemic CRVO, by neovascular complications. Management has been transformed by anti-VEGF therapy. Systemic vascular risk factors , hypertension above all , must be identified and managed in every RVO patient; RVO is a retinal expression of systemic vascular disease.
Key Clinical Points: Retinal Vein Occlusion
- Classification: BRVO (branch retinal vein occlusion) at an arteriovenous crossing, affecting a sector; CRVO (central retinal vein occlusion) at the lamina cribrosa, affecting all four quadrants. Hemiretinal vein occlusion (HRVO) involves a hemicentral vein.
- Ischemic vs non-ischemic CRVO: Ischemic: BCVA worse than 6/60, relative afferent pupillary defect (RAPD), VF loss, extensive capillary non-perfusion on FA (>10 disc areas). Risk of rubeosis/neovascular glaucoma approximately 45% at 3 months. Non-ischemic: 30% convert to ischemic within 3 years.
- First-line macular edema: Intravitreal anti-VEGF , aflibercept (GALILEO/COPERNICUS), ranibizumab (BRIGHTER/CRYSTAL), bevacizumab. Intravitreal dexamethasone implant (GENEVA trial) as alternative or in anti-VEGF non-responders. Target: BCVA gain, CST reduction.
- Ischemic CRVO monitoring: Monthly for first 3 months (peak neovascular risk). Gonioscopy and IOP at every visit. Anti-VEGF does not replace PRP for established rubeosis.
- Systemic workup: BP, fasting glucose, lipids, FBC, ESR in all. Thrombophilia screen in bilateral RVO, age under 50, recurrent RVO, no cardiovascular risk factors.
- BRVO: sector PRP for sector neovascularization (NVE). No prophylactic laser for macular edema (no benefit , BVOS grid laser inferior to observation alone in modern era).
Pathophysiology
BRVO occurs at arteriovenous (AV) crossings where the artery and vein share a common adventitial sheath. Arteriosclerotic arterial thickening compresses the adjacent vein, leading to turbulence, endothelial damage, and thrombosis. This explains the preponderance of BRVO at superotemporal AV crossings (the most common arterial branching point near the fovea) and its tight association with hypertension and arteriosclerosis.
CRVO occurs at the level of the lamina cribrosa, where the central retinal artery and vein share a tight fibrous channel. Occlusion here affects all four quadrants of the retina. Macular edema from CRVO is driven by VEGF release from ischemic retina and breakdown of the inner blood-retinal barrier. In ischemic CRVO, extensive capillary non-perfusion drives massive VEGF upregulation , both causing macular edema and driving anterior segment neovascularization (rubeosis iridis) that threatens neovascular glaucoma.
Classification: Ischemic vs Non-Ischemic
The ischemic/non-ischemic distinction in CRVO is the most clinically important classification decision, determining monitoring intensity and neovascular risk. Ischemic CRVO features: BCVA 6/60 or worse at presentation, RAPD present, extensive retinal hemorrhage in all quadrants, FA showing more than 10 disc areas of capillary non-perfusion. These eyes carry approximately 45% risk of developing rubeosis within 3 months, leading to neovascular glaucoma if untreated.
Non-ischemic CRVO has a better natural history, but approximately 30% convert to ischemic over 3 years. Serial gonioscopy and IOP measurement are required at every visit in the first year. Anti-VEGF injections, while treating macular edema, also suppress VEGF-driven neovascularization , but do not replace PRP once rubeosis is established.
Investigation
OCT: Identifies macular edema (cystoid spaces, SRF, IRF, elevated CST), epiretinal membrane contributing to chronic edema, and DRIL (disorganization of retinal inner layers) as a predictor of poor visual recovery. Baseline OCT and BCVA establish the treatment benchmark.
Fundus fluorescein angiography (FA): Quantifies capillary non-perfusion, confirms ischemic classification in CRVO, identifies neovascularization, and guides sector PRP in BRVO. Not routinely needed before starting anti-VEGF for macular edema, but important for ischemia classification and monitoring. Wide-field FA is preferred , standard 7-field imaging underestimates the extent of peripheral ischemia.
Management: Macular Edema
Anti-VEGF, first-line: All three agents (ranibizumab, aflibercept, bevacizumab) are effective. GALILEO and COPERNICUS trials (aflibercept, CRVO): +16.9 and +17.3 ETDRS letters at 6 months vs sham. CRYSTAL trial (ranibizumab, CRVO): +14.0 letters at 12 months. BRIGHTER (ranibizumab, BRVO): +18.3 letters at 12 months. Loading phase as for neovascular AMD (3 monthly injections), then PRN or treat-and-extend based on OCT. Many patients require injections for 2+ years, though treatment frequency often decreases over time as macular edema stabilizes.
Intravitreal dexamethasone implant: GENEVA trial (BRVO and CRVO combined): significant CST reduction and +3.3 letters at 2 months, waning by 6 months. Requires re-treatment every 4-6 months. Preferred in pseudophakic eyes (avoids cataract), for anti-VEGF non-responders, and where injection frequency is a particular concern. Significant IOP monitoring required , approximately 33% of patients develop IOP elevation above 25 mmHg, manageable with topical medication in most cases.
Grid laser (BRVO): The BVOS protocol grid laser was standard pre-anti-VEGF. Now rarely used for macular edema , anti-VEGF is superior. Grid laser may still have a role in persisting non-center-involving ME with good central VA where injection burden is unacceptable.
Management: Neovascular Complications
Sector NVE in BRVO: Treat with sector PRP to the ischemic drainage area. NVE in BRVO rarely causes vitreous hemorrhage as severe as PDR because the neovascular stimulus is more focal. Anti-VEGF may suppress NVE, but sector PRP provides more durable ablation of the ischemic drive.
Rubeosis iridis in CRVO: Requires urgent panretinal photocoagulation. Anti-VEGF causes rapid regression of iris vessels within days and buys time for PRP delivery, but PRP remains the definitive treatment for the ischemic drive. Treating with anti-VEGF alone without PRP risks rebound rubeosis when the drug wears off. Neovascular glaucoma from angle closure secondary to rubeosis is a severe, often irreversible complication.
Systemic Workup and Risk Factor Management
Every RVO patient requires: blood pressure (the most consistent systemic association , found in over 70% of CRVO patients), fasting blood glucose, lipid profile, and FBC. In patients under 50, bilateral RVO, or no identifiable cardiovascular risk factors: thrombophilia screen (antiphospholipid antibodies, protein C and S, antithrombin III, factor V Leiden, prothrombin gene mutation). Hyperviscosity: check serum protein electrophoresis in CRVO with no other risk factors. Vasculitic causes: ESR and CRP in younger patients or atypical bilateral presentations.
Refer to GP or physician for blood pressure optimization. Target below 130/80 mmHg. Antiplatelet therapy: aspirin is often prescribed but there is no strong evidence that it prevents RVO recurrence , it should not be started or continued solely for RVO. Anticoagulation: only if an underlying thrombophilia with high thrombotic risk is identified after full hematological assessment.
Clinical Decision Points
- New CRVO, poor VA, RAPD present: Classify urgently as ischemic. Start monthly monitoring for rubeosis with gonioscopy at each visit. Consider starting anti-VEGF immediately for macular edema even before FA if OCT confirms CI-ME.
- CRVO, good VA initially, progressive decline at 3 months: Repeat FA , conversion to ischemic CRVO is occurring. Reclassify and intensify monitoring.
- Chronic macular edema, anti-VEGF non-responder: Check for ERM contributing to edema (OCT). Consider switching to dexamethasone implant. Review systemic BP control , poorly controlled hypertension drives ongoing leakage. Look for DRIL (poor prognosis indicator).
- BRVO with sectoral NVE and no macular edema: Sector PRP to the ischemic territory. Anti-VEGF monotherapy is not the right answer here , PRP produces durable regression of the ischemic drive.
- RVO in bilateral presentation, age under 45: Thrombophilia screen and hematological review mandatory. Consider referral to hematology.
Same-Day Assessment Required
- Known ischemic CRVO presenting with IOP rise, pain, and red eye , suspect neovascular glaucoma from anterior segment neovascularization. Requires gonioscopy, IOP control, intravitreal anti-VEGF, and urgent PRP.
- Sudden dense vision loss in previously non-ischemic CRVO , conversion to ischemic CRVO or development of vitreous hemorrhage from NVD. B-scan ultrasound if media opacity.
- BRVO patient with sudden complete visual loss in the affected eye , suspect VH from sector NVE. Indirect ophthalmoscopy and B-scan.
Neovascular glaucoma is the most visually devastating complication of ischemic CRVO. The window between rubeosis iridis and irreversible angle closure is narrow. Monthly gonioscopy in the first 3 months of ischemic CRVO is not optional , it defines the point at which intravitreal anti-VEGF plus urgent PRP must begin.
Clinical Pearls: Retinal Vein Occlusion
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Blood pressure is the most important finding in RVO. The ophthalmologist should check it in the clinic.
Over 70% of CRVO patients have hypertension , often undiagnosed or undertreated. Taking blood pressure in the eye clinic is not overstepping: it is recognizing that RVO is a retinal vascular event with systemic implications. Many patients’ RVO presentation leads to the first diagnosis of hypertension they have ever received. A brief letter to the GP is good practice after every new RVO, stating the retinal finding and requesting blood pressure review.
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Anti-VEGF injections for ischemic CRVO must be combined with PRP for established rubeosis. They are not alternatives.
Anti-VEGF suppresses VEGF-driven neovascularization and can rapidly regress rubeosis iridis within 48-72 hours , giving the impression that the problem is solved. It is not. The ischemic retina continues to produce VEGF, and when the drug clears (approximately 4-6 weeks for ranibizumab and aflibercept), rubeosis can rebound aggressively. PRP destroys the ischemic tissue producing the VEGF. The correct sequence is anti-VEGF first to allow clear media for PRP delivery, then PRP within days. Delaying PRP by relying on repeated anti-VEGF injections is a management error.
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BRVO macular edema often improves spontaneously in the first 3 months. But waiting risks photoreceptor loss from chronic edema.
Historically, observation for 3 months was standard for new BRVO macular edema given its spontaneous resolution rate of approximately 50%. Anti-VEGF trials changed this calculation: early treatment produces better visual outcomes than delayed treatment in eyes that do not self-resolve. The practical approach for an eye with BCVA of 6/12 or better from BRVO: consider monitoring for 4-6 weeks. For BCVA of 6/18 or worse, or any evidence of central macular threat: treat promptly. Chronic macular edema causes structural change (DRIL, ERM) that does not reverse with treatment.
Further reading: AAO Preferred Practice Pattern , Retinal Vein Occlusions. For the shared anti-VEGF management framework, see neovascular AMD and diabetic retinopathy. Systemic vascular context is covered on the retina subspecialty page.