Branch Retinal Artery Occlusion

Embolic Causes (~90% of Cases)

Embolism is by far the most common mechanism of BRAO. Emboli preferentially lodge at arteriolar bifurcations — points of turbulent flow and reduced luminal diameter — and are classified by their composition and source:

• Cholesterol emboli (Hollenhorst plaques) — most common: Derived from atheromatous plaques in the ipsilateral carotid artery (particularly at the carotid bifurcation) or aortic arch; appear as glistening, refractile, orange-yellow crystals lodging at arteriolar bifurcations; may be asymptomatic (incidental finding) or cause acute ischaemia; their presence mandates urgent carotid Doppler and cardiovascular evaluation as they are a marker of significant systemic atherosclerosis and stroke risk
• Fibrin-platelet emboli — second most common: Arise from mural thrombi within the heart (atrial fibrillation, myocardial infarction, dilated cardiomyopathy), prosthetic cardiac valves, or carotid plaque surface thrombi; appear dull white, elongated, and may fragment and move during fundoscopic observation; associated with higher stroke risk than cholesterol emboli
• Calcific emboli: Originate from calcified cardiac valves (aortic stenosis, mitral annular calcification) or calcified aortic atherosclerotic plaques; appear solid white and opaque; typically larger than cholesterol emboli; often lodge at or near the optic disc; associated with more complete and permanent occlusion
• Fat emboli: Following long bone fractures, orthopaedic surgery, or liposuction; bilateral retinal involvement possible in systemic fat embolism syndrome; associated with Purtscher-like retinopathy
• Talc emboli: In intravenous drug users (e.g., crushed oral tablet injection); multiple small peripheral retinal emboli; may be bilateral; associated with Purtscher-like retinopathy and pulmonary talcosis
• Air emboli: Iatrogenic — following cardiac surgery, cardiopulmonary bypass, central venous catheter insertion, or carotid endarterectomy; often transient if small; important to identify post-operative context
• Tumour emboli: Rare; from cardiac myxoma, non-bacterial thrombotic endocarditis (marantic endocarditis in malignancy), or direct intravascular tumour extension; important consideration in young patients with malignancy

Non-Embolic Causes (~10% of Cases)

• In-situ thrombosis: Localised thrombus formation within the retinal arteriole at a site of endothelial damage or arteriosclerotic narrowing; associated with hypercoagulable states (thrombophilia, antiphospholipid syndrome); more common in younger patients without embolic risk factors
• Vasospasm: Transient arteriolar constriction precipitating acute ischaemia; associated with migraine with aura, Raynaud phenomenon, cocaine and other vasoconstrictive drug use, and certain medications (triptans, ergotamine); more likely to present as amaurosis fugax rather than permanent BRAO; visual recovery is possible if spasm resolves promptly
• Inflammatory vasculitis: Temporal arteritis (giant cell arteritis — GCA) is a critical cause to exclude, particularly in patients over 50; GCA can affect the posterior ciliary arteries and retinal arterioles; associated with jaw claudication, scalp tenderness, elevated ESR and CRP; requires urgent systemic steroid therapy to prevent bilateral involvement and permanent blindness
• Other vasculitic causes: Systemic lupus erythematosus, polyarteritis nodosa, Behçet disease, and sarcoidosis may cause retinal arteriolar occlusion through inflammatory vasculopathy
• Sickle cell disease: Sickling of erythrocytes within small retinal arterioles causes occlusion particularly at the retinal periphery; associated with HbSS and HbSC disease; produces peripheral arteriolar occlusion that may subsequently drive sea fan neovascularisation
• Increased intraocular pressure: Acute IOP elevation sufficient to exceed diastolic perfusion pressure (e.g., in acute angle closure crisis) can cause BRAO; acute angle closure may precipitate BRAO; also seen with retrobulbar haemorrhage or orbital compartment syndrome
• Coagulopathies: Antiphospholipid syndrome, protein C/S deficiency, Factor V Leiden; particularly relevant in young patients with BRAO and no conventional cardiovascular risk factors

Step 1 — Embolus Lodgement at Arteriolar Bifurcation

The central retinal artery divides sequentially into branch arterioles of progressively diminishing diameter as it traverses the retina. Emboli travelling through the retinal circulation are carried by blood flow until they reach a bifurcation whose lumen is too narrow to allow passage. At this point of lodgement, the embolus obstructs forward flow into the branch territory distal to the bifurcation. Turbulent flow at bifurcations accelerates lodgement. The most proximal (and therefore largest-calibre) bifurcations — typically near the disc — are the most commonly affected, explaining why the superotemporal artery, the first and largest branch of the superior temporal arcade, is the most frequently occluded vessel.

Step 2 — Acute Inner Retinal Ischaemia

Within seconds to minutes of arteriolar occlusion, the inner retinal layers in the affected territory — supplied exclusively by the retinal circulation — become ischaemic. The outer retinal layers (photoreceptors, RPE) are maintained by the choroidal circulation via diffusion and are not directly affected by arterial occlusion. The ganglion cell layer and inner plexiform layer are most metabolically vulnerable and suffer first. The clinical consequence is disruption of axoplasmic transport in the nerve fibre layer, producing cytotoxic oedema that renders the inner retina opaque and white — the acute retinal whitening that is the clinical hallmark of BRAO.

Step 3 — The Ischaemic Time Window

Retinal neurons are highly sensitive to ischaemia. Experimental data suggest that irreversible inner retinal damage begins within 90–100 minutes of complete arterial occlusion. Beyond approximately 4 hours, neuronal loss is severe and largely irreparable regardless of reperfusion. This time-sensitive pathophysiology underpins the rationale for emergency treatment attempts (ocular massage, IOP reduction) in the acute setting — though clinical evidence of efficacy for BRAO specifically remains limited.

Step 4 — Spontaneous Embolus Movement and Reperfusion

A proportion of emboli — particularly fibrin-platelet emboli — may spontaneously fragment, move distally to a smaller arteriole, or lyse within hours to days. This explains why some patients with BRAO experience partial or complete visual recovery. Clinicians may observe emboli moving position between examinations or note spontaneous reperfusion of the previously occluded territory on fluorescein angiography — an important prognostic observation, as eyes with early reperfusion have substantially better visual outcomes. Cholesterol emboli rarely move spontaneously as they are firm crystalline deposits.

Step 5 — Chronic Inner Retinal Atrophy

Over weeks to months, the acute retinal whitening (oedema) resolves as fluid is reabsorbed. What remains is permanent inner retinal atrophy — a thinning of the ganglion cell layer, inner plexiform layer, and nerve fibre layer in the affected territory, detectable on OCT as focal inner retinal thinning. The retinal nerve fibre layer develops a corresponding sector defect, visible as a wedge-shaped RNFL defect on OCT. The arteriole in the occluded territory may become sheathed or remain attenuated. The visual field defect corresponding to this zone of atrophy persists permanently.

By Embolic Composition

By Anatomical Location

• Major BRAO (superotemporal, inferotemporal, superonasal, inferonasal): Occlusion of one of the four main branch arterioles draining a full retinal quadrant; superotemporal is most common (~60%); produces the most visually significant sectoral field defect; if the papillomacular bundle is involved, central VA may be reduced
• Macular BRAO: Occlusion of a small arteriole supplying the macular capillary bed; presents with paracentral or central scotoma; may markedly reduce VA even though the central fovea is often perfused by a cilioretinal artery; OCT shows inner nuclear layer and ganglion cell layer loss at the macula
• Peripheral BRAO: Occlusion of a small peripheral arteriole beyond the arcades; often asymptomatic or noticed only as a peripheral field defect during perimetry; may be discovered as an incidental finding on fundus examination years after the event; retinal whitening has typically resolved, leaving inner retinal thinning on OCT
• Cilioretinal artery occlusion: The cilioretinal artery (present in ~20–35% of eyes) arises from the posterior ciliary circulation rather than the central retinal artery; its occlusion spares the territory supplied by the central retinal artery but causes a specific visual field defect corresponding to the cilioretinal territory; usually temporal to the disc; an important subtype that may accompany CRVO

By Temporal Stage

• Hyperacute (<1 hour): Retinal whitening developing; embolus often visible; cattle-trucking or box-carring of blood column in the occluded arteriole may be seen; window of maximum opportunity for perfusion-restoring interventions
• Acute (1–72 hours): Well-established chalky white retinal oedema in the affected sector; arteriole attenuated or thread-like; embolus may be visible; no significant haemorrhage (distinguishing from BRVO)
• Subacute (days to weeks): Retinal whitening begins to fade as oedema reabsorbs; arteriole remains attenuated or sheathed; inner retinal thinning begins to develop on OCT
• Chronic (>4–6 weeks): Retinal whitening fully resolved; sector of inner retinal atrophy on OCT; RNFL wedge defect on OCT; arteriole may be sheathed or ghost-like; visual field defect persists

Cardiovascular and Embolic Risk Factors (Major)

• Carotid artery atherosclerosis: The most important source of cholesterol emboli; significant ipsilateral carotid stenosis (>50%) is present in a substantial proportion of BRAO patients; carotid endarterectomy or stenting may be indicated; risk of stroke from ipsilateral carotid disease is high and time-critical
• Atrial fibrillation (AF): Promotes cardiac mural thrombus formation in the left atrial appendage; fibrin-platelet emboli to the retinal circulation; AF may be paroxysmal and not detected on a single ECG — continuous ECG monitoring (Holter) may be required; anticoagulation is the primary treatment
• Valvular heart disease: Aortic stenosis with calcified valves, mitral valve prolapse (particularly myxomatous valves), infective endocarditis (Roth spots), non-bacterial thrombotic endocarditis (marantic endocarditis in malignancy)
• Myocardial infarction: Mural thrombus at the site of left ventricular wall akinesia is a potent embolic source; BRAO occurring in the context of recent MI requires urgent cardiology assessment
• Systemic hypertension: Accelerates carotid and aortic atherosclerosis; present in 60–70% of BRAO patients; elevated BP at presentation should prompt immediate measurement and management
• Hyperlipidaemia: Drives atheromatous plaque formation in the carotid and aortic vessels; dyslipidaemia is a modifiable risk factor; statin therapy reduces the risk of recurrent embolic events
• Diabetes mellitus: Promotes endothelial dysfunction, accelerates atherosclerosis, and increases blood viscosity; also associated with in-situ arteriolar thrombosis
• Smoking: Major independent risk factor for atherosclerosis and platelet aggregation; strongly associated with carotid artery disease and BRAO
• Patent foramen ovale (PFO): Allows paradoxical embolism from the venous to arterial system; particularly important in young patients with BRAO and no conventional embolic source; indicated by Valsalva manoeuvre-triggered episodes

Haematological and Thrombophilic Risk Factors

• Hypercoagulable states: Antiphospholipid syndrome, Factor V Leiden, prothrombin mutation, protein C/S deficiency — particularly relevant in patients under 50 with BRAO and no embolic source; thrombophilia screen is warranted in this group
• Sickle cell disease/trait: Sickling within small arterioles; important in patients of African, Mediterranean, and South Asian descent; peripheral BRAO is more common in sickle cell disease
• Polycythaemia vera: Elevated haematocrit increases blood viscosity and promotes in-situ thrombosis
• Oral contraceptive pill and hormone therapy: Oestrogen-mediated hypercoagulability; important in younger women with BRAO without other identified cause

Other Risk Factors

• Prior amaurosis fugax: Transient monocular visual loss lasting seconds to minutes — a retinal TIA that often precedes a permanent arterial occlusion; approximately 25% of patients with untreated amaurosis fugax develop a permanent BRAO or stroke; should be treated as an emergency equivalent to TIA
• Giant cell arteritis (GCA): In patients over 50 with systemic symptoms (headache, jaw claudication, scalp tenderness, polymyalgia rheumatica); urgent ESR, CRP, and temporal artery biopsy; high-dose steroids must be started immediately if GCA is suspected without waiting for biopsy confirmation
• Migraine with aura: Vasospasm-mediated transient arteriolar occlusion; more common in younger women; typically resolves spontaneously; recurrent events may require prophylactic migraine therapy and avoidance of vasoconstrictors
• Increased IOP / acute angle closure: Acute IOP rise sufficient to reduce ocular perfusion pressure can precipitate arterial occlusion; always measure IOP in BRAO patients

Acute Funduscopic Signs

• Sectoral retinal whitening (opacification): The cardinal sign of BRAO; a chalky white or grey-white area of inner retinal oedema strictly confined to the drainage territory of the occluded arteriole; the whitening is caused by cytotoxic oedema and disrupted axoplasmic transport in ischaemic nerve fibres; it is sharply demarcated at the sector boundary, with the adjacent non-occluded retina appearing normal; the spatial distribution exactly mirrors the vascular territory of the blocked vessel
• Visible embolus: Present in approximately 60–70% of acute BRAO; appears at the point of occlusion, typically at an arteriolar bifurcation; embolus type can be identified on biomicroscopy — Hollenhorst plaques (glistening refractile yellow-orange), calcific emboli (solid white opaque), fibrin-platelet emboli (dull white elongated); may be discovered incidentally without associated retinal whitening if emboli have moved or the territory is peripheral
• Attenuated arteriole: The affected arteriole distal to the occlusion site appears pale, thin, and thread-like due to reduced blood flow; in complete occlusion, the vessel may be almost invisible; careful comparison with the unaffected companion vein or the opposite arteriole highlights the degree of attenuation
• Cattle-trucking / box-carring: Segmentation of the blood or plasma column within the occluded arteriole; blood columns alternate with gaps of plasma or stasis — creating an appearance resembling cattle trucks or boxes; a sign of very acute, complete arterial occlusion; resolves as flow is re-established or stasis progresses
• No cherry red spot: Unlike central retinal artery occlusion (CRAO), BRAO does not produce a cherry red spot because the fovea retains its normal choroidal perfusion and only one sector of the perifoveal area is affected; the foveal reflex remains intact unless the affected territory includes the fovea (macular BRAO)
• Absence of haemorrhage: A critical distinguishing feature from venous occlusion; BRAO does not produce intraretinal haemorrhages — any haemorrhage visible in the affected territory should prompt consideration of combined arterial and venous occlusion or an alternative diagnosis

Chronic / Resolved Phase Signs

• Inner retinal thinning on OCT: The most sensitive chronic finding; selective thinning of the ganglion cell layer (GCL), inner plexiform layer (IPL), and nerve fibre layer in the previously ischaemic sector; OCT provides spatial mapping of the area of permanent inner retinal loss
• RNFL wedge defect: Sectoral thinning of the retinal nerve fibre layer around the optic disc corresponding to the affected arteriolar territory; detectable on OCT RNFL analysis as a focal RNFL defect; important for documenting permanent retinal damage
• Arteriolar sheathing: Periarteriolar white sheathing in the previously occluded segment; represents organised fibrous tissue around the vessel wall; a marker of previous occlusion
• Persistent visible embolus: Hollenhorst plaques frequently persist indefinitely as they do not lyse; may be visible on fundus examination years after the original event; an important clue to previous BRAO or carotid disease in a patient presenting for a routine eye examination
• Neovascularisation (NVE): Occurs in approximately 3–10% of ischaemic BRAO eyes; most common at the boundary between ischaemic and perfused retina, typically 3–6 months after the occlusion; visible as elevated frond-like red vessels; requires scatter laser photocoagulation
• Optic disc sectoral pallor: Corresponding to the affected arteriolar territory; develops over weeks to months as ganglion cell axons degenerate within the optic nerve

Anterior Segment and Systemic Signs

• Relative afferent pupillary defect (RAPD): A subtle RAPD may be detectable in BRAO if the affected sector includes a significant proportion of the macular nerve fibre bundle (the papillomacular bundle); typically mild unless a major quadrant is completely infarcted
• Carotid bruit: Auscultation of the ipsilateral neck may reveal a carotid bruit suggesting significant carotid stenosis; however, absence of bruit does not exclude significant stenosis; carotid Doppler is always required
• Cardiac murmur: Aortic stenosis or mitral valve disease may manifest as a cardiac murmur; detectable on bedside auscultation; echocardiography required to characterise embolic source
• Irregular pulse: Atrial fibrillation may be detected on pulse palpation; ECG and/or Holter monitoring required for definitive assessment

Visual Symptoms

• Sudden onset sectoral visual field loss: The most common presenting symptom; onset is abrupt — patients typically describe a sudden appearance of a dark, grey, or blank area in a portion of the visual field, often noticed on waking or during a specific activity; the field defect corresponds precisely to the drainage territory of the occluded arteriole; an altitudinal or quadrantic defect is most typical of BRAO affecting a major branch
• Preserved central visual acuity: Because the superotemporal artery (the most commonly occluded) does not supply the fovea directly in most patients, central vision is typically preserved; patients may report "my reading is fine but part of my side vision has gone"; this can paradoxically delay presentation as patients do not perceive their vision as severely impaired
• Paracentral scotoma: If the affected territory abuts the fovea, patients notice a dark patch just off centre, interfering with reading or face recognition; detected on Amsler grid testing; may be the first symptom noticed
• Reduced visual acuity: Occurs when the occluded territory includes the papillomacular bundle, a cilioretinal artery supplying the fovea is occluded (cilioretinal BRAO), or when a macular BRAO involves the foveal region directly; may range from mild blur to counting fingers depending on foveal involvement
• Colour vision disturbance: Mild dyschromatopsia may be present if the papillomacular bundle is involved; acquired red-green deficiency is the most common pattern; Ishihara plates or D-15 testing may reveal the deficit
• Asymptomatic (incidental finding): Peripheral BRAO affecting small arterioles away from the macula may produce no symptoms and is discovered only on routine fundus camera examination or when fundus photography is performed for another indication; the chronic phase presents as inner retinal thinning on OCT and a visible arteriolar sheathing or persistent embolus

Preceding Symptoms (Amaurosis Fugax)

A significant proportion of patients with BRAO report a preceding episode of amaurosis fugax — transient monocular visual loss lasting seconds to minutes, typically described as a "curtain" or "shade" descending over part or all of the visual field that spontaneously resolves. Amaurosis fugax represents a transient retinal TIA and is an important warning sign that a permanent arterial occlusion may follow. Any patient presenting with amaurosis fugax should be managed as an emergency TIA equivalent even if vision has fully recovered.

Visual Complications

• Permanent sectoral visual field defect: The most common complication; corresponds to the area of permanent inner retinal atrophy; complete visual field recovery is unusual after BRAO unless reperfusion occurs within the first 90–100 minutes; most patients retain good central acuity but have a permanent sector defect on perimetry
• Reduced central visual acuity: Occurs when the papillomacular bundle or foveal area is involved; may be mild (6/12) to severe (counting fingers) depending on the extent of macular ischaemia; permanent reduction in VA is the primary determinant of functional disability
• Visual field impairment affecting fitness to drive: BRAO may create a visual field defect that fails binocular visual field standards for driving; formal visual field assessment by Humphrey perimetry is required for driving fitness evaluation; patients must be advised not to drive until formally assessed

Ocular Complications

• Retinal neovascularisation (NVE): Occurs in approximately 3–10% of ischaemic BRAO cases; appears at the boundary of the ischaemic and perfused retina as elevated red frond-like new vessels; most common 3–6 months post-occlusion; requires fluorescein angiography for diagnosis and sector laser photocoagulation for treatment
• Vitreous haemorrhage: Rupture of NVE fronds into the vitreous; presents with sudden floaters or visual loss superimposed on the pre-existing field defect; if dense and non-clearing, vitrectomy may be required
• Epiretinal membrane: Uncommon sequela; fibrocellular proliferation on the inner retinal surface in the previously ischaemic zone; may cause metamorphopsia; typically mild in BRAO compared to venous occlusions
• Recurrent BRAO in the same eye: Indicates ongoing embolic source; recurrence mandates urgent reassessment of the embolic source and adequacy of antiplatelet or anticoagulant therapy

Systemic Complications — The Primary Concern

Carotid Artery Disease

• Ipsilateral carotid stenosis: The most common and actionable systemic finding; significant ipsilateral internal carotid artery stenosis (>50–70%) is found in a substantial proportion of BRAO patients presenting with cholesterol emboli; carotid endarterectomy for symptomatic carotid stenosis >70% reduces 5-year stroke risk by approximately 50% (NASCET trial)
• Aortic arch atherosclerosis: An important source of cholesterol and fibrin emboli; complex aortic plaques (>4 mm) detected on transoesophageal echocardiography are a significant embolic risk; managed with antiplatelet therapy and statin

Cardiac Sources of Embolism

• Atrial fibrillation: Cardioembolic source with highest stroke risk if left untreated; anticoagulation (DOAC or warfarin) substantially reduces embolisation risk; paroxysmal AF may require prolonged ECG monitoring (implantable loop recorder) to detect
• Valvular heart disease: Calcified aortic valve, mitral valve prolapse with regurgitation, infective endocarditis (Osler nodes, Roth spots, Janeway lesions), and prosthetic valve thrombosis are all potential embolic sources
• Left ventricular thrombus / cardiomyopathy: Mural thrombus after myocardial infarction; dilated cardiomyopathy with poor ejection fraction; detected on transthoracic or transoesophageal echocardiography; anticoagulation is indicated
• Patent foramen ovale (PFO): Paradoxical embolism through a PFO; important in cryptogenic BRAO in patients under 60; detected on contrast echocardiography (bubble study); PFO closure may be considered in selected younger patients

Cerebrovascular Disease

• Concurrent ischaemic stroke: In some BRAO patients, particularly those with cardiac or large-vessel embolic sources, concurrent or near-concurrent ischaemic stroke may occur; MRI brain (DWI sequences) should be performed urgently to exclude acute stroke in all BRAO patients presenting to emergency services
• Silent cerebral infarcts: Subclinical white matter lesions or lacunar infarcts visible on MRI are more common in patients with retinal artery occlusion than in age-matched controls, reflecting shared small vessel disease burden

Giant Cell Arteritis (GCA)

• An important and treatable cause of BRAO in patients over 50; GCA-related occlusion carries risk of rapid bilateral visual loss if untreated; systemic symptoms (headache, jaw claudication, scalp tenderness, proximal muscle ache, weight loss, fever) are key diagnostic clues
• ESR (>50 mm/h) and CRP (>2.45 mg/dL) are typically markedly elevated; temporal artery biopsy provides definitive diagnosis but must not delay treatment
• High-dose IV methylprednisolone (500 mg–1 g/day for 3 days) followed by oral prednisolone (1 mg/kg/day) must be started immediately if GCA is clinically suspected — treatment before biopsy is appropriate and safe

Clinical Diagnosis

BRAO is a clinical diagnosis based on the characteristic combination of acute sectoral retinal whitening confined to the territory of one arteriole, with or without a visible embolus, in the context of sudden painless visual field loss. No additional imaging is required for the diagnosis, but multimodal imaging is essential for confirming ischaemia, planning treatment, and monitoring for neovascularisation.

• Best-corrected visual acuity (BCVA): Documents the baseline VA; typically well-preserved in major BRAO if the fovea is spared; significantly reduced in macular or cilioretinal BRAO
• Colour vision testing: Acquired dyschromatopsia may be subtle; Ishihara plates as a screening tool; formal colour vision testing (Farnsworth D-15) if papillomacular bundle involvement is suspected
• Pupil examination — RAPD: A subtle RAPD may be present in large territory BRAO; important to document; compare with fellow eye baseline
• Intraocular pressure: Must be measured at presentation; both elevated IOP (as a contributing cause) and low IOP (possible in the context of retrobulbar disease or orbital compartment syndrome) are relevant
• Colour fundus photography: Documents the sectoral retinal whitening, visible embolus position, arteriolar attenuation, and ischaemic zone for comparison with future visits; essential for medicolegal and monitoring purposes
• Visual field testing: Confrontation visual fields as a bedside test; formal Humphrey automated perimetry (24-2 or 30-2) documents the scotoma extent and depth; important for driving fitness assessment

Optical Coherence Tomography (OCT)

• Acute phase: Inner retinal hyperreflectivity and thickening in the affected sector — the OCT correlate of the clinically visible retinal whitening; involves the ganglion cell layer (GCL), inner plexiform layer (IPL), and nerve fibre layer (NFL); the outer retina (ONL, IS/OS, RPE) remains normal, distinguishing BRAO from conditions affecting the outer retina
• Chronic phase: Selective inner retinal thinning — focal thinning of the GCL and IPL in the ischaemic sector; the outer retina is preserved, creating a characteristic "inner retinal infarction" pattern on OCT cross-section; the extent of GCL thinning correlates with the permanent visual field deficit
• RNFL analysis: Sectoral RNFL thinning on circumpapillary OCT corresponding to the affected arteriolar territory; useful for documenting permanent optic nerve fibre loss
• Macular OCT: Ganglion cell analysis (GCA) map shows focal GCL-IPL thinning in the ischaemic zone; provides a spatial map of neuronal loss at the macula that correlates with the visual field defect

Fluorescein Angiography (FA)

• Delayed or absent arterial filling: FA shows delayed filling of the occluded arteriole in the affected sector; in complete occlusion, the arteriole may not fill during the entire arterial phase; the perfusion defect directly delineates the ischaemic territory
• Prolonged arteriovenous transit time: Delayed venous filling from the affected sector due to reduced arterial inflow
• Capillary non-perfusion: The capillary bed within the ischaemic sector shows absence of normal fluorescence — "dark" zones on FA; extent of non-perfusion predicts neovascularisation risk
• Embolus: May appear as a filling defect at the point of occlusion; cholesterol emboli may autofluoresce slightly and obstruct dye transit
• Reperfusion: FA performed days after the acute event may show partial or complete reperfusion of the occluded arteriole — an important prognostic marker; if the arteriole refills, better visual recovery is expected
• NVE leakage: Late hyperfluorescence from neovascularisation at the ischaemic border; guides timing and extent of sector laser photocoagulation

OCT Angiography (OCTA)

• Non-invasive delineation of capillary flow voids in the superficial and deep capillary plexuses within the ischaemic sector; provides excellent spatial resolution of the perfusion defect without dye injection
• Useful for monitoring reperfusion over time and for quantifying the extent of macular ischaemia
• Does not show active leakage — FA is still required to assess NVE activity and confirm neovascularisation
• Particularly useful in patients with contraindications to fluorescein (allergy, renal failure)

Acute Ocular Interventions (Within Hours of Onset)

No ocular intervention has been proven in a randomised controlled trial to improve visual outcomes in BRAO. The following measures are widely attempted in the acute setting within the first few hours (ideally within 90 minutes) based on physiological rationale, but clinical evidence of efficacy is limited. Systemic vascular management is significantly more evidence-based than ocular treatment.

• Digital ocular massage: Application of intermittent pressure to the globe through closed eyelids (5 seconds on, 5 seconds off for 10–15 minutes) may dislodge a lodged embolus distally into a smaller arteriole, restoring some perfusion; the rationale is haemodynamic — cyclic IOP rises and falls create pulsatile pressure waves to disturb the embolus; most effective if performed within 90 minutes; harmless if performed promptly; not effective beyond 4–6 hours
• IOP lowering: Reducing IOP increases the arteriovenous perfusion pressure gradient across the occluded vessel, potentially facilitating embolus movement or restoring partial flow; options include: topical timolol 0.5% drops; oral acetazolamide 500 mg (if no contraindications); anterior chamber paracentesis (AC tap) — withdrawing 0.1–0.2 mL of aqueous reduces IOP acutely to near-zero, maximising perfusion pressure; paracentesis is performed by ophthalmologists in a slit-lamp setting and has the highest evidence base among ocular interventions (case series)
• Carbogen inhalation (95% O₂ + 5% CO₂): The CO₂ component induces retinal arteriolar vasodilation while oxygen increases retinal tissue oxygenation; experimental; limited availability; variable evidence; not widely adopted as standard practice
• Hyperbaric oxygen: Increases dissolved oxygen delivery to ischaemic retinal tissue; case reports suggest benefit if initiated within hours; requires specialist hyperbaric facility; not routinely available
• Pentoxifylline / haemodilution: Theoretical benefit through reducing blood viscosity; no RCT evidence in BRAO; not standard of care

Systemic Vascular Management (Most Critical)

• Antiplatelet therapy: Aspirin 300 mg loading dose then 75–100 mg daily is recommended for all patients with BRAO of embolic/atherosclerotic origin, following the TIA management pathway; clopidogrel is an alternative or addition (dual antiplatelet therapy may be used in high-risk cases for 21 days per TIA guidelines); reduces the risk of recurrent arterial thromboembolic events
• Anticoagulation: Indicated if atrial fibrillation, intracardiac thrombus, prosthetic heart valve, or confirmed antiphospholipid syndrome is identified; direct oral anticoagulants (DOACs) — apixaban, rivaroxaban, dabigatran — are preferred over warfarin in non-valvular AF per current guidelines; started after neuroimaging to exclude haemorrhagic stroke
• Carotid endarterectomy (CEA) or carotid artery stenting (CAS): For symptomatic ipsilateral carotid stenosis >70% (NASCET criteria), CEA reduces 5-year stroke risk from ~26% to ~9% (NASCET trial); CEA is ideally performed within 2 weeks of the embolic event when benefit is greatest; CAS is an alternative for patients who are high surgical risk
• Blood pressure management: Target BP <130/80 mmHg; acute hypertension at presentation should be carefully managed — rapid BP lowering in the immediate post-ischaemic period may reduce perfusion to borderline ischaemic territories; longer-term BP control with antihypertensives is essential for secondary prevention
• Statin therapy: High-intensity statin (atorvastatin 80 mg or rosuvastatin 40 mg) is indicated for all BRAO patients with atherosclerotic embolic source (cholesterol embolus, carotid or aortic atherosclerosis); target LDL <1.8 mmol/L for secondary prevention of cardiovascular events; provides plaque stabilisation beyond lipid-lowering effects
• Glycaemic control: HbA1c target <53 mmol/mol (7.0%) in diabetes; optimisation of glycaemic control reduces endothelial dysfunction and thrombotic risk
• Giant cell arteritis treatment: If GCA is suspected (patient >50 with systemic symptoms), high-dose IV methylprednisolone 500 mg–1 g daily for 3 days then oral prednisolone 1 mg/kg/day must be initiated immediately without waiting for biopsy results; bilateral visual loss may occur within hours if GCA is untreated; adjuvant tocilizumab (IL-6 inhibitor) is now licensed for GCA and reduces relapse rate and cumulative steroid dose
• Smoking cessation: Reduces ongoing risk of carotid atherosclerosis progression and further embolic events; refer for smoking cessation support
• PFO closure: Considered in selected patients under 60 with cryptogenic BRAO and confirmed PFO; evidence from CLOSE and REDUCE trials in cryptogenic stroke suggests benefit in younger patients

Management of Retinal Neovascularisation

• Sectoral laser photocoagulation: Applied to the ischaemic retinal sector when NVE is detected on FA; ablates the ischaemic retina to reduce the VEGF drive to neovascularisation; well-established treatment from the Branch Vein Occlusion Study (extended to arterial occlusion by analogy with BRVO); performed by ophthalmologists using slit-lamp laser delivery
• Intravitreal anti-VEGF: May be used adjunctively to rapidly suppress neovascularisation pending laser treatment; or as primary therapy in cases where laser is technically difficult; no specific RCT evidence for BRAO-related NVE but extrapolated from BRVO data
• Vitrectomy: For vitreous haemorrhage secondary to NVE rupture if dense and non-clearing after 1–3 months; intraoperative endolaser applied to the ischaemic sector

Monitoring Schedule

Visual Prognosis

• Central visual acuity is typically well preserved: Because the fovea is most commonly spared in major BRAO, most patients retain VA of 6/12 or better; population-based and clinic-based series report that approximately 80% of BRAO eyes maintain VA ≥6/12 at final follow-up
• Visual field defect is usually permanent: The sectoral visual field defect corresponding to the infarcted retinal territory rarely recovers completely; partial recovery may occur if partial reperfusion takes place within the first hours; patients typically adapt functionally over time but the scotoma persists on formal perimetry
• Factors associated with better visual outcome: Peripheral BRAO not involving the papillomacular bundle; early spontaneous embolus movement (observed during fundoscopy); reperfusion on FA within hours to days; fibrin-platelet embolus (more likely to lyse than cholesterol); acute presentation within the ischaemic window
• Factors associated with worse visual outcome: Involvement of the papillomacular bundle (producing central or paracentral scotoma); cilioretinal artery occlusion with foveal involvement; macular BRAO; calcific embolus (unlikely to move); complete arteriolar occlusion with extensive ischaemia; late presentation (>6 hours from onset)
• Spontaneous recovery: Partial or complete visual field recovery may occur in approximately 20–30% of cases, typically within the first 1–3 months; recovery beyond 3 months is uncommon; patients should be counselled that recovery, when it occurs, is usually maximal within the first 3 months

Systemic Prognosis — The Primary Determinant of Overall Outcome

• Stroke risk: The most important prognostic consideration; 2-year risk of ischaemic stroke is approximately 5–12%; risk is highest in the first 90 days (comparable to hemispheric TIA); aggressive antiplatelet, antihypertensive, and statin therapy substantially reduces this risk
• Myocardial infarction: 5-year risk of MI is approximately 2–4 times that of age-matched controls; shared atherosclerotic risk burden underlies both events; cardiology review and optimisation of cardiovascular risk factors are life-saving interventions
• Recurrent ocular events: Fellow eye BRAO or BRAO in the same eye may occur, particularly if the embolic source is not identified and treated; risk of CRAO (central retinal artery occlusion) in the affected or fellow eye is also elevated in patients with significant carotid or cardiac disease
• Long-term vascular mortality: Population studies show elevated all-cause cardiovascular mortality in patients with retinal artery occlusion compared to age-matched controls; BRAO is a marker of advanced systemic vascular disease that requires lifelong cardiovascular risk management