Branch Artery Occlusion
What Is Branch Artery Occlusion?
Understanding the anatomy behind BRAO helps explain why it affects a specific portion of your visual field rather than all of your sight at once.
The central retinal artery enters the eye through the optic nerve and divides into several smaller branch arteries. Each branch supplies blood and oxygen to a distinct area, or quadrant, of the retina. When one of these branches becomes blocked, only the retinal tissue downstream of that specific artery is affected, resulting in a wedge-shaped zone of ischemia.
In most cases, an embolus (a small fragment of cholesterol plaque, calcified material, or blood clot) travels from the carotid artery or heart and lodges in a branch retinal artery. The blockage interrupts blood flow, and the oxygen-starved retinal cells begin to swell and die. Primate studies suggest that irreversible damage can occur in as little as 90 minutes, though it may take up to four hours depending on the degree of occlusion.
A central retinal artery occlusion (CRAO) blocks the main artery before it branches, which affects the entire retina and typically causes much more severe vision loss. With BRAO, only a section of the visual field is involved, and central visual acuity is often preserved. Approximately 74 percent of patients with a permanent BRAO present with visual acuity of 20/40 or better, compared to only about 11 percent of CRAO patients.
Although vision loss from BRAO may be limited to one section of the visual field, the event signals significant cardiovascular risk. Studies have demonstrated a clear link between retinal artery occlusion and subsequent stroke or transient ischemic attack. Dr. Jerry Tsong and our retina specialists treat BRAO as both an eye condition and a warning sign that requires urgent systemic evaluation.
Causes and Risk Factors
The underlying causes of BRAO are closely related to conditions that affect blood vessels throughout the body.
The most common cause of BRAO is an embolus originating from atherosclerotic plaque in the carotid arteries or from the heart. Cholesterol-based emboli, known as Hollenhorst plaques, appear as bright, reflective fragments within the retinal arteries. Calcific emboli from damaged heart valves and platelet-fibrin emboli related to blood clotting abnormalities are less common but can also cause occlusion.
Several systemic health conditions significantly increase the likelihood of BRAO. These include:
- Hypertension (high blood pressure)
- Atherosclerosis and carotid artery disease
- Coronary artery disease
- Hypercholesterolemia (elevated cholesterol)
- Diabetes mellitus
- Atrial fibrillation and other heart rhythm abnormalities
Smoking is a well-established risk factor for BRAO, as it accelerates atherosclerosis and promotes plaque formation. BRAO occurs more frequently in patients over the age of 60 and is somewhat more common in men. Less common risk factors include sickle cell disease, hypercoagulable states, use of oral contraceptives, and intravenous drug use.
In older adults, giant cell arteritis (temporal arteritis) can cause inflammation of blood vessel walls and contribute to retinal artery occlusion. This inflammatory condition requires immediate treatment with corticosteroids to prevent further vascular damage, including potential involvement of the other eye.
Symptoms of Branch Artery Occlusion
BRAO typically presents with sudden visual changes in one eye, and recognizing the symptoms quickly is essential.
The hallmark symptom is the abrupt, painless loss of part of your visual field in one eye. Depending on which branch artery is blocked, you may notice a missing area of vision above, below, or to one side. Some patients describe it as a curtain or shadow covering a portion of their sight.
Unlike central retinal artery occlusion, BRAO usually spares the central part of your vision. More than half of patients experience relatively preserved visual acuity. However, if the blocked branch supplies the area near the macula, central vision can also be affected, leading to difficulty reading or recognizing faces.
In some cases, a BRAO is transient, meaning the embolus dislodges on its own and blood flow resumes. The visual field defect may last only seconds to minutes before resolving. Even when symptoms appear to resolve completely, a transient BRAO is still a significant vascular warning sign and warrants a full medical evaluation.
Diagnosis and Treatment
Diagnosing BRAO involves a thorough eye examination and imaging, followed by a systemic workup to identify the source of the embolus.
During a dilated eye exam, our retina specialists can often identify the characteristic signs of BRAO, including a wedge-shaped area of retinal whitening (edema) corresponding to the blocked artery. An embolus may be visible within the vessel. The retinal whitening reflects the swollen, ischemic inner layers of the retina that have been deprived of blood flow.
Fluorescein angiography can reveal delayed filling in the affected artery, highlight the location of the embolus, and map the extent of retinal ischemia. Optical coherence tomography (OCT) is used to detect inner retinal thickening in the acute phase and inner retinal thinning as the condition progresses, providing a detailed cross-sectional view of the affected tissue.
Because BRAO is strongly associated with stroke risk, all patients should undergo evaluation by an internist or neurologist. This typically includes carotid artery ultrasound to check for atherosclerotic plaque, echocardiography to evaluate the heart valves, blood pressure and cholesterol testing, and screening for diabetes. Blood work to rule out inflammatory and hypercoagulable conditions may also be ordered. Referral to a stroke center is appropriate in many cases.
There is no universally proven acute treatment that consistently restores vision after BRAO. Some techniques that may be attempted in the early hours include ocular massage to try to dislodge the embolus and medications such as acetazolamide to lower intraocular pressure and improve retinal perfusion. However, because many BRAOs improve spontaneously and prolonged ischemia often produces irreversible damage, aggressive intervention is not always pursued.
The most critical aspect of managing BRAO is reducing the risk of future vascular events. Patients are typically started on antiplatelet therapy such as aspirin, along with statin medications to manage cholesterol. Blood pressure control and diabetes management are essential. In cases with significant carotid artery stenosis, surgical intervention such as carotid endarterectomy or stent placement may be recommended by the neurology or vascular surgery team.
Frequently Asked Questions
Yes, BRAO can cause a lasting visual field defect if the retinal tissue is deprived of blood flow long enough for irreversible damage to occur. However, the degree of vision loss is typically less severe than with a central retinal artery occlusion (CRAO). Many patients retain functional visual acuity of 20/40 or better, though a sector of the peripheral visual field may be permanently affected.
Patients over the age of 60 with cardiovascular risk factors are at the highest risk. A history of hypertension, high cholesterol, diabetes, carotid artery disease, smoking, or atrial fibrillation all increase the likelihood of developing a retinal artery occlusion. Men are affected slightly more often than women, though anyone with vascular risk factors should be aware of the possibility.
The prognosis for BRAO generally depends on the initial severity of vision loss. Among patients with permanent BRAO, about 89 percent maintain visual acuity of 20/40 or better at follow-up. For transient BRAO, essentially all patients retain good acuity. However, the affected section of the visual field may not fully recover, and ongoing monitoring with our retina specialists helps track any late complications such as retinal neovascularization.
BRAO involves a blockage of an artery carrying oxygen-rich blood to the retina, while a branch retinal vein occlusion (BRVO) involves a blockage in a vein carrying blood away from the retina. BRAO tends to cause more sudden and sharply defined visual field loss, whereas BRVO often causes swelling in the retina (macular edema) and retinal hemorrhages. Treatment approaches also differ: BRVO is frequently managed with anti-VEGF injections, while BRAO management focuses primarily on systemic vascular risk reduction.
Managing the underlying cardiovascular risk factors is the most effective way to reduce your risk. Keeping blood pressure and cholesterol within healthy ranges, maintaining good blood sugar control if you have diabetes, quitting smoking, and exercising regularly all help protect the blood vessels that supply the retina. Your primary care physician and our retina specialists can work together to create a prevention plan tailored to your needs.
Any sudden, painless loss of vision in one eye, whether partial or complete, warrants urgent evaluation. Even if the symptoms resolve on their own within minutes, this may indicate a transient occlusion that could be a precursor to a stroke. Contact our office or visit an emergency department right away so that a thorough evaluation, including a vascular assessment, can be performed as quickly as possible.
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