Retinal Vascular Occlusions
Ophthalmology · Retina · lean revision notes
Retinal Vascular Occlusions
Retinal vascular occlusions are a group of sight-threatening emergencies caused by interruption of arterial inflow or venous outflow of the retina. They are among the highest-yield retina topics for NEET PG because each entity has a near-pathognomonic fundus picture, a defined "investigation of choice", and a treatment paradigm built around anti-VEGF therapy and laser. The core skill tested is pattern recognition — matching a fundus description to the correct occlusion and its systemic association.
Classification
Occlusions are divided by the vessel involved (artery vs vein) and by extent (central vs branch). Arterial occlusions are ischaemic emergencies (minutes to save vision); venous occlusions cause haemorrhagic, oedematous retinopathy that evolves over weeks.
| Type | Full name | Vessel | Hallmark |
|---|---|---|---|
| CRAO | Central retinal artery occlusion | Central retinal artery (at lamina cribrosa) | Cherry-red spot, pale retina |
| BRAO | Branch retinal artery occlusion | A branch (usually superotemporal) | Sectoral retinal whitening |
| CRVO | Central retinal vein occlusion | Central retinal vein | Flame haemorrhages in all 4 quadrants, disc oedema |
| BRVO | Branch retinal vein occlusion | A branch at an A-V crossing | Sectoral haemorrhages, wedge points to crossing |
| Ophthalmic artery occlusion | OAO | Ophthalmic artery | No cherry-red spot (choroid also ischaemic), profound vision loss |
| Cilioretinal artery occlusion | — | Cilioretinal artery (from PCA) | Spares/affects only macula depending on context |
High-yield: A cherry-red spot occurs in CRAO because the thin fovea has no inner retinal layers — the intact choroidal (red) circulation shows through against the surrounding oedematous, opaque, ischaemic retina. The same cherry-red spot is seen in lysosomal storage diseases (Tay-Sachs, Niemann-Pick, Sandhoff) — but there the rest of the fundus is not pale.
Central Retinal Artery Occlusion (CRAO)
Etiology & pathophysiology
- The central retinal artery is an end artery (branch of ophthalmic artery → internal carotid). Occlusion produces inner retinal ischaemic infarction.
- Commonest cause: embolus — cholesterol (Hollenhorst plaque, from carotid), platelet-fibrin, or calcific (from cardiac valves).
- Other causes: thrombosis, giant cell (temporal) arteritis (must exclude in elderly), thrombophilia, vasospasm (migraine, cocaine), trauma.
- Irreversible retinal damage in experimental models begins by ~90–100 minutes; clinically a window of up to ~4–6 hours is quoted for intervention, though outcomes are usually poor.
Clinical features
- Sudden, painless, profound monocular vision loss (counting fingers or worse).
- Relative afferent pupillary defect (RAPD) — a key examination sign.
- Fundus: diffuse retinal whitening/oedema, cherry-red spot at fovea, boxcarring (segmentation of blood column) in arterioles, attenuated arteries.
High-yield: A cilioretinal artery (present in ~15–30%) is supplied by the posterior ciliary circulation, not the central retinal artery. In CRAO it stays perfused, so a small island of macula is spared → preserved central vision despite CRAO. Conversely, isolated cilioretinal artery occlusion causes a horizontal band of macular whitening.
Investigation
- Diagnosis is clinical (fundus).
- FFA (fundus fluorescein angiography): delayed arterial filling / prolonged arm-to-retina time.
- OCT (acute): inner retinal hyper-reflectivity and thickening; chronic → inner retinal thinning.
- Mandatory work-up: ESR, CRP, platelets (rule out GCA); carotid Doppler; ECG/echo (embolic source). In patients <50, thrombophilia screen.
High-yield: CRAO is a stroke equivalent / ocular TIA. Urgent referral for cerebrovascular work-up is the modern standard — treat like a posterior-circulation stroke, not merely an eye problem.
Management
Acute measures (low evidence, attempted within the window):
- Ocular massage (dislodge embolus, induce arteriolar dilatation) →
- Lower IOP — anterior chamber paracentesis, IV acetazolamide/mannitol, topical timolol →
- Rebreathing into a paper bag / carbogen (95% O₂ + 5% CO₂) to induce hypercapnic vasodilatation →
- Consider intra-arterial thrombolysis in selected hyperacute cases (specialist, controversial).
- If GCA suspected → immediate high-dose IV/oral steroids to protect the fellow eye (do not wait for biopsy).
High-yield: The single most important "do-not-miss" in an elderly CRAO/AION patient is giant cell arteritis — start systemic corticosteroids urgently to save the other eye.
Branch Retinal Artery Occlusion (BRAO)
- Usually embolic; emboli lodge at bifurcations, most often superotemporal branch.
- Sectoral retinal whitening corresponding to the occluded branch; altitudinal or sectoral field defect.
- Visual prognosis better than CRAO if macula spared.
- Same systemic work-up (carotid, cardiac, GCA). Susac syndrome (encephalopathy + BRAO + hearing loss) is a classic association in young women.
Central Retinal Vein Occlusion (CRVO)
Etiology & pathophysiology
- Thrombosis of the central retinal vein, typically at/behind the lamina cribrosa, where artery and vein share a common adventitial sheath.
- Risk factors: hypertension (commonest systemic association), diabetes, glaucoma/raised IOP, age, hyperviscosity (polycythaemia, myeloma, Waldenström), thrombophilia, OCPs.
- Raised venous pressure → stasis → endothelial damage → thrombosis → transudation and haemorrhage; ischaemia drives VEGF release → macular oedema and neovascularisation.
Clinical features
- Variable painless vision loss (mild blur to severe).
- Fundus: flame-shaped and dot-blot haemorrhages in all four quadrants ("blood and thunder" / "splashed tomato" fundus), dilated tortuous veins, disc oedema, cotton-wool spots, macular oedema.
Ischaemic vs non-ischaemic CRVO — the favourite MCQ
| Feature | Non-ischaemic (perfused) | Ischaemic (non-perfused) |
|---|---|---|
| Frequency | ~75% | ~25% |
| Visual acuity | Usually > 6/60 | Usually < 6/60 |
| RAPD | Absent / mild | Marked RAPD |
| Haemorrhages | Mild–moderate | Extensive, dense |
| Cotton-wool spots | Few | Many |
| Capillary non-perfusion on FFA | < 10 disc areas | ≥ 10 disc areas |
| ERG b-wave | Normal/near-normal | Reduced b:a ratio |
| Risk of neovascular glaucoma | Low | High (90-day glaucoma) |
High-yield: Ischaemic CRVO → "90-day glaucoma" / 100-day glaucoma — neovascularisation of the iris (rubeosis) and angle leading to neovascular glaucoma, classically ~3 months after onset. A marked RAPD + extensive haemorrhages predicts conversion. Examine the iris and angle (gonioscopy) at every follow-up.
Investigation
- FFA = investigation of choice to grade ischaemia (extent of capillary non-perfusion) and detect neovascularisation.
- OCT quantifies and monitors macular oedema (the main treatable cause of vision loss).
- Systemic: BP, fasting glucose/HbA1c, lipids, IOP; in young patients add thrombophilia/hyperviscosity screen.
Management
- Macular oedema → intravitreal anti-VEGF (ranibizumab, aflibercept, bevacizumab) — first-line. Intravitreal steroid (dexamethasone implant — Ozurdex; triamcinolone) is an alternative.
- Neovascularisation / ischaemic CRVO → pan-retinal photocoagulation (PRP); anti-VEGF can supplement.
- Treat systemic risk factors (BP, diabetes, IOP).
- Landmark trials: CRUISE (ranibizumab), COPERNICUS/GALILEO (aflibercept), SCORE (steroids), and the older CVOS (defined ischaemic thresholds and the role of PRP for anterior segment neovascularisation).
High-yield: For CRVO/BRVO macular oedema, anti-VEGF is the drug of choice. PRP is reserved for neovascular disease (iris/angle/retinal NV), not for macular oedema per se.
Branch Retinal Vein Occlusion (BRVO)
- The commonest retinal vascular occlusion overall (more common than CRVO).
- Occurs at an arteriovenous (A-V) crossing where the artery and vein share a sheath; the thickened arteriole compresses the vein. Almost always the artery lies anterior to the vein at the crossing.
- Superotemporal quadrant most commonly affected → field defect points to the crossing apex.
- Strongly linked to systemic hypertension.
- Sectoral flame haemorrhages and dilated tortuous veins in the drainage territory; a wedge of haemorrhage with apex at the A-V crossing.
- Complications: macular oedema (commonest cause of vision drop), retinal neovascularisation → vitreous haemorrhage.
Management
- Macular oedema → intravitreal anti-VEGF (first-line) or dexamethasone implant. Historic Grid laser (from the BVOS trial) for persistent macular oedema is now second-line.
- Sectoral / scatter laser PRP to the involved quadrant for neovascularisation.
- Trials: BRAVO (ranibizumab), VIBRANT (aflibercept), BVOS (grid/scatter laser).
High-yield: BVOS established that grid laser improves macular-oedema vision and scatter (sectoral) laser is used once neovascularisation appears in BRVO. Anti-VEGF has since become first-line for the oedema.
Stepwise approach to a "sudden painless loss of vision" stem
Painless loss + RAPD + cherry-red spot + pale retina → CRAO → check GCA (ESR/CRP), carotid, cardiac.
Painless variable loss + haemorrhages in ALL quadrants + tortuous veins + disc oedema → CRVO → FFA to grade ischaemia → anti-VEGF for oedema / PRP for NV.
Sectoral haemorrhages, wedge at A-V crossing → BRVO → anti-VEGF for macular oedema.
Sectoral retinal whitening, altitudinal field defect → BRAO → embolic work-up.
So the reasoning chain is: Symptom onset → pupil (RAPD) → fundus pattern (white vs haemorrhagic) → distribution (central vs sectoral) → systemic association → investigation → treatment.
Complications
| Occlusion | Key complications |
|---|---|
| CRAO | Permanent vision loss, optic atrophy, rarely rubeosis; fellow-eye loss if GCA missed |
| CRVO (ischaemic) | Neovascular glaucoma (90-day), vitreous haemorrhage, persistent macular oedema, optic atrophy |
| BRVO | Macular oedema (commonest visual loss), retinal NV, vitreous haemorrhage, tractional retinal detachment |
| BRAO | Permanent sectoral field defect |
High-yield: Neovascular glaucoma is the dreaded end-stage of ischaemic CRVO (and proliferative diabetic retinopathy and OIS). Management = PRP + anti-VEGF + IOP control; once the angle is closed by synechiae, prognosis is poor.
Key differentials
- Ocular ischaemic syndrome (OIS): severe carotid stenosis; dull ocular ache, mid-peripheral dot-blot haemorrhages, narrowed arteries with dilated (not tortuous) veins, and retinal artery pressure low (spontaneous arterial pulsation on gentle pressure). Differs from CRVO by less tortuosity and presence of pain.
- Diabetic retinopathy: bilateral, microaneurysms, hard exudates, dot-blot haemorrhages distributed around posterior pole — not confined to one venous territory.
- Hypertensive retinopathy / papilloedema: bilateral, A-V nicking, no single-territory haemorrhage.
- Anterior ischaemic optic neuropathy (AION): sudden painless loss + pale, swollen disc + altitudinal field defect; arteritic AION (GCA) is the overlap to remember.
- Cherry-red spot mimics: Tay-Sachs, Niemann-Pick, Sandhoff, GM1 gangliosidosis, commotio retinae (Berlin oedema), quinine toxicity — but surrounding retina differs.
Mnemonics & eponyms
- "Blood and thunder" fundus = CRVO.
- Hollenhorst plaque = bright refractile cholesterol embolus at an arteriolar bifurcation (carotid source).
- Boxcarring = segmented blood column in CRAO arterioles.
- Susac syndrome triad — remember "BEE": Branch retinal artery occlusion, Encephalopathy, Ear (sensorineural hearing loss).
- Cherry-red spot storage diseases — "TNS": Tay-Sachs, Niemann-Pick, Sandhoff.
- CRVO risk factors — "HALT": Hypertension, Age/atherosclerosis, Lipids, Tension (raised IOP/glaucoma).
Recently asked / exam angle
- Cherry-red spot — most common single-line MCQ; differentiate CRAO (pale retina around it) from storage diseases (normal retina around it).
- Ischaemic vs non-ischaemic CRVO — distinguishing features, RAPD, ≥10 disc areas non-perfusion on FFA, and the 90-day neovascular glaucoma link.
- Investigation of choice = FFA for grading CRVO ischaemia; OCT for monitoring macular oedema.
- Drug of choice for macular oedema = intravitreal anti-VEGF; PRP only for neovascularisation.
- BRVO occurs at A-V crossing, artery anterior to vein, superotemporal commonest; commonest retinal vascular occlusion.
- CRAO = ocular stroke / GCA must be excluded in elderly — start steroids urgently for suspected arteritic cause.
- Cilioretinal artery sparing of central vision in CRAO.
- OIS vs CRVO — pain, arterial narrowing, low retinal arterial pressure distinguish OIS.
- Trials: CRUISE/COPERNICUS/GALILEO (CRVO), BRAVO/VIBRANT (BRVO), CVOS/BVOS (laser thresholds).
Rapid revision
- CRAO = sudden painless loss + RAPD + cherry-red spot + pale oedematous retina + boxcarring; an end-artery infarct and ocular stroke.
- In elderly CRAO/AION always exclude giant cell arteritis (ESR, CRP) and start steroids urgently to protect the fellow eye.
- Cilioretinal artery (from posterior ciliary circulation) can spare central vision in CRAO.
- Cherry-red spot without surrounding pallor → suspect a storage disease (Tay-Sachs, Niemann-Pick, Sandhoff).
- CRVO = haemorrhages in all four quadrants, dilated tortuous veins, disc oedema = "blood and thunder" fundus; commonest systemic link is hypertension.
- Ischaemic CRVO → marked RAPD, VA < 6/60, ≥10 disc areas non-perfusion on FFA → risk of neovascular (90-day) glaucoma.
- FFA grades CRVO ischaemia; OCT monitors macular oedema.
- Anti-VEGF (ranibizumab/aflibercept/bevacizumab) is first-line for macular oedema in CRVO and BRVO; steroid implant is an alternative.
- PRP / scatter laser is for neovascularisation, not for macular oedema; NVG is treated with PRP + anti-VEGF + IOP control.
- BRVO is the commonest retinal vascular occlusion, occurs at an A-V crossing (artery anterior to vein), most often superotemporal.
- BVOS trial: grid laser for macular oedema, scatter laser for NV in BRVO.
- Ocular ischaemic syndrome (carotid stenosis): ocular ache, narrowed arteries, dilated non-tortuous veins, low retinal arterial pressure — distinguishes it from CRVO.