Branch Retinal Artery Occlusion (BRAO)

01Pathophysiology

The central retinal artery, a terminal branch of the ophthalmic artery (itself arising from the internal carotid artery), enters the globe through the optic nerve head and divides into superior and inferior arcades, which further branch into temporal and nasal arterioles. Each branch supplies a defined sector of the inner retina. In BRAO, one of these branches becomes occluded, most often by an embolus originating from the ipsilateral carotid artery or the heart.

The inner retina (ganglion cell layer, inner plexiform layer, inner nuclear layer) depends entirely on the retinal arterial circulation. The outer retina, including the photoreceptors, is supplied by the underlying choroidal circulation and is therefore spared. When a branch becomes occluded, the inner retinal cells in that territory undergo acute ischemic injury and cytotoxic edema. The intracellular swelling renders the normally transparent retina opaque, producing the characteristic segmental retinal whitening visible on fundoscopy.

Unlike central retinal artery occlusion (CRAO), the classic cherry-red spot is typically absent in BRAO because the fovea is usually not within the ischemic territory. However, if the branch supplying the papillomacular bundle (the temporal arteriole feeding the macula) is occluded, central visual acuity drops significantly and a localized cherry-red appearance may emerge in that quadrant.

The reason a BRAO is painless is that the retina has no pain fibers. The visual field defect corresponds directly to the vascular territory supplied by the occluded branch. A superior temporal branch occlusion, for example, produces an inferior nasal field defect, because retinal image projection is inverted relative to the visual field.

From the exam-writer's perspective, BRAO is conceptualized as a "retinal TIA/stroke equivalent." It signals active embolic disease and carries a significantly elevated short-term risk of cerebral infarction, which is why the workup parallels that of an acute ischemic stroke.

02Classification and Clinical Manifestation

By Embolus Type

By Clinical Course

By Anatomic Location

03Diagnostic Workup

Dilated fundoscopy is the best initial test and is often diagnostic on its own. The examiner will describe segmental retinal pallor or whitening confined to a single arteriolar territory, often with a visible embolus (Hollenhorst plaque) sitting at a vessel bifurcation. This finding alone is sufficient to make the clinical diagnosis.

Fluorescein angiography is the most accurate retinal vascular study. It demonstrates delayed or absent filling of the occluded branch during the arterial phase, with normal filling of adjacent, unaffected branches. It also reveals late-phase vessel wall staining and helps distinguish BRAO from other causes of focal retinal edema. FA is not always required for diagnosis but is valuable when the clinical picture is ambiguous or when assessing for residual perfusion.

OCT is increasingly used and shows increased inner retinal thickness acutely (due to cytotoxic edema), which transitions to inner retinal thinning over subsequent weeks as atrophy sets in. This finding is highly characteristic and supports the diagnosis.

After confirming the retinal diagnosis, the workup shifts to identifying the embolic source. Carotid duplex ultrasonography of the ipsilateral internal carotid artery is essential because carotid atherosclerosis is the leading source of retinal emboli. If significant stenosis (>= 70%) is found, the patient may be a candidate for carotid endarterectomy.

Echocardiography and ECG/Holter monitoring evaluate for cardiac embolic sources, including valvular vegetations, mural thrombus, atrial fibrillation, and patent foramen ovale. A transthoracic echocardiogram (TTE) is performed first; if it is non-diagnostic and cardiac embolism remains suspected, transesophageal echocardiography (TEE) follows.

In any patient over 50, ESR and CRP must be checked to rule out giant cell arteritis. If these inflammatory markers are elevated and there are accompanying symptoms (headache, jaw claudication, scalp tenderness, polymyalgia), treatment with high-dose corticosteroids must begin immediately, without waiting for biopsy confirmation. Temporal artery biopsy is the gold standard for confirmation but should never delay treatment.

04Management and Treatment

Acute stabilization in BRAO is less aggressive than in CRAO because the visual prognosis is generally better and the ischemic territory is smaller. Nonetheless, if a patient presents within a few hours of onset, intermittent digital ocular massage (pressing on the globe through closed lids for 5 to 15 seconds, then releasing) may dislodge the embolus distally. Anterior chamber paracentesis, which lowers intraocular pressure to improve arterial perfusion pressure, can be attempted but has limited supporting evidence for BRAO.

The "next best step" after the acute window is to initiate antiplatelet therapy and begin a full embolic source evaluation. Aspirin 81 to 325 mg daily is the standard antiplatelet agent. If the workup reveals atrial fibrillation or another cardioembolic source, the patient should be transitioned to anticoagulation with a direct oral anticoagulant (e.g., apixaban 5 mg twice daily or rivarelbaan 20 mg daily) or warfarin (target INR 2 to 3).

If carotid duplex demonstrates ipsilateral internal carotid stenosis of 70% or greater, the patient should be referred for carotid endarterectomy, ideally within 2 weeks of the event, because the stroke risk is highest in this early period.

If giant cell arteritis is suspected (patient older than 50, elevated ESR often exceeding 50 mm/hr, temporal headache, jaw claudication), do not wait for biopsy results. Begin IV methylprednisolone 1 g daily for 3 days, followed by oral prednisone 1 mg/kg/day with a slow taper guided by symptom resolution and inflammatory marker normalization. Temporal artery biopsy should be performed within 1 to 2 weeks of starting steroids, as histologic findings remain diagnostic for up to 2 weeks after treatment initiation.

Long-term management focuses on aggressive cardiovascular risk reduction: high-intensity statin therapy, blood pressure optimization, glycemic control, and smoking cessation. These patients carry a stroke risk comparable to that of TIA patients and should be managed with the same urgency.

Contraindications and cautions: Aspirin is contraindicated in patients with active gastrointestinal bleeding or true aspirin allergy; clopidogrel 75 mg daily is the alternative. In patients with giant cell arteritis and diabetes, corticosteroid-induced hyperglycemia requires close monitoring and insulin adjustment. Carotid endarterectomy is generally avoided if ipsilateral stenosis is less than 50%, as the procedural risk outweighs the benefit.

05Differential Diagnosis and Distractors

06Traps and High-Yield Pearls

The single most common trap with BRAO is mistaking it for a benign, isolated eye problem and failing to pursue a systemic embolic workup. Exam questions on this topic are rarely testing your ability to diagnose the retinal finding itself; instead, they are testing whether you understand that BRAO is a stroke equivalent demanding the same urgency as a TIA. The "next best step" after identifying a branch retinal artery occlusion on fundoscopy is almost always to order carotid duplex ultrasonography and cardiac evaluation, not simply to refer to ophthalmology and move on.

A second common error is confusing BRAO with branch retinal vein occlusion. Both produce sudden, painless, monocular visual changes in a sectoral distribution. The discriminator is the fundoscopic picture: BRAO produces a pale, edematous retina (ischemia), while BRVO produces hemorrhages and venous dilation (congestion). If the vignette describes hemorrhage, it is venous. If it describes pallor, it is arterial.

Third, students frequently forget to check ESR and CRP in patients over 50. Giant cell arteritis can present with retinal artery occlusion (central or branch), and missing this diagnosis is catastrophic because the fellow eye can be lost within days without corticosteroid treatment. Any elderly patient with a retinal artery occlusion and even a single symptom suggestive of GCA (headache, jaw claudication, scalp tenderness, polymyalgia) requires immediate high-dose corticosteroids before biopsy confirmation.

Finally, watch for the Hollenhorst plaque trap. Exam writers sometimes describe an incidental Hollenhorst plaque found on routine fundoscopy in an asymptomatic patient. Even without symptoms, this finding demands a carotid and cardiac evaluation because it indicates active atheroembolism and elevated stroke risk.

The core competency being tested is the ability to recognize BRAO as a systemic vascular emergency, to sequence the workup correctly (retinal exam first, then embolic source evaluation), and to initiate secondary stroke prevention without delay.