Branch Retinal Artery Occlusion (BRAO) is a serious eye condition involving a sudden blockage of blood flow to a part of the retina. This ischemic event deprives the affected retinal tissue of oxygen and nutrients, causing rapid visual impairment. Because the mechanism involves a blood vessel blockage, BRAO is often colloquially termed an “eye stroke.” This article clarifies the nature of BRAO, its relationship to a traditional cerebral stroke, and the urgent medical response required.
Defining Branch Retinal Artery Occlusion
Branch Retinal Artery Occlusion occurs when a smaller artery branching off the central retinal artery becomes blocked. The central retinal artery is the main vessel supplying the inner layers of the retina with blood. When a branch is obstructed, the specific segment of the retina supplied by that vessel suffers from ischemia.
The retina is neural tissue highly sensitive to oxygen deprivation, meaning the loss of blood supply causes rapid and permanent damage. BRAO is typically caused by a small clot or plaque fragment, known as an embolus, that travels through the bloodstream and lodges in the narrower retinal artery. This event presents as a sudden, painless loss of vision affecting a specific section of the visual field in one eye.
Distinguishing BRAO from a Cerebral Stroke
Branch Retinal Artery Occlusion is medically classified as a retinal vascular occlusion, an acute ischemic event localized to the eye. Although colloquially termed an “eye stroke,” BRAO is distinct from a cerebral stroke, which involves a blockage or rupture of a blood vessel in the brain. Both conditions share the underlying mechanism of vascular blockage (ischemia) and require immediate medical attention.
The key difference lies in the anatomical location and resulting symptoms. A cerebral stroke affects the brain, leading to neurological deficits like weakness, difficulty speaking, or cognitive impairment. In contrast, BRAO is confined to the eye, causing only visual deficits, such as a blind spot or shadow in the field of vision. The American Heart Association recognizes retinal artery occlusions as an ocular presentation of acute ischemic stroke, underscoring the shared pathophysiology and the need for a stroke workup.
The highest risk for a cerebral stroke occurs immediately following a retinal artery occlusion, linking the two events. Studies show that a significant percentage of patients who experience BRAO also have evidence of a recent, often asymptomatic, acute ischemic lesion in the brain. Therefore, while BRAO is not a stroke of the brain, it is a powerful indicator of a systemic vascular problem that can lead to one.
Systemic Conditions That Cause BRAO
BRAO is rarely an isolated problem; it is a strong warning sign of serious underlying cardiovascular and cerebrovascular disease. The embolus causing the blockage almost always originates from a distant source in the body. The most frequent source is atherosclerotic plaque buildup in the carotid arteries, the major blood vessels in the neck that supply blood to the brain and eyes.
These plaques can shed small fragments of cholesterol, known as Hollenhorst plaques, which travel up the internal carotid artery and lodge in a retinal artery branch. Another common source is the heart, where cardiac emboli can form due to conditions like atrial fibrillation or valvular heart disease. In these cases, the embolus is often a small clot or calcified material.
Risk factors for BRAO are identical to those for stroke and heart attack, highlighting the systemic nature of the disease. These include hypertension, elevated cholesterol levels, diabetes mellitus, and cigarette smoking. Because an etiology can be identified in up to 90% of patients, a BRAO diagnosis mandates a full systemic medical investigation. Finding and treating the source of the embolus is the primary way to prevent a future cerebral stroke.
Urgent Diagnosis and Treatment
Branch Retinal Artery Occlusion is an ocular emergency, and seeking immediate care is paramount to preserve vision. Irreversible damage to the inner retina can begin in as little as 90 minutes after the blood supply is completely blocked. Patients should be immediately evaluated in an emergency setting, preferably one with stroke center capabilities.
Initial diagnosis is made through a comprehensive eye examination, including a fundus examination to look directly at the retina. During this exam, the affected retinal area often appears pale or whitened due to swelling and lack of blood flow. Sometimes the embolus itself can be seen lodged at a vessel bifurcation. Fluorescein angiography, an imaging test using a fluorescent dye, may be performed to visualize the extent of the blockage.
Immediate acute treatments are sometimes attempted to dislodge the embolus and restore blood flow, though their effectiveness is uncertain. Interventions may include ocular massage to transiently lower intraocular pressure, or breathing a mixture of carbon dioxide and oxygen to dilate the retinal vessels. The most important step following the acute event is mandatory systemic testing. This testing involves a carotid ultrasound, an electrocardiogram (EKG), and blood tests to identify the underlying cause of the occlusion and initiate preventative therapy.