Branch retinal artery occlusion (BRAO) is defined as occlusion of a branch of the central retinal artery causing ischemia in that region of the retina. BRAO represents 38% of all retinal artery obstructions. There are two subtypes of BRAO: permanent and transient. Studies of central retinal artery occlusion (CRAO) showed that ischemic retinal damage occurs after 97 minutes, causing long-term decreased visual acuity (VA) and visual field defects.

BRAO is characterized by acute, painless vision loss, amaurosis fugax, and a visual field defect (central or sectoral). The patient may in fact be asymptomatic. A BRAO can result from an embolus, as seen in 62% of cases, or from nonembolic conditions. Embolic sources include calcified cardiac valves, fat emboli from long bone fractures, air emboli from trauma or surgery, talc emboli from IV drug use, and synthetic emboli from interventional procedures.

Nonembolic causes of BRAO include vasospasm secondary to migraines, cocaine, and sildenafil; vasculitic disorders such as Behçet disease and giant cell arteritis; coagulopathies; and infectious conditions such as toxoplasmosis, herpes zoster, and Lyme disease. Susac syndrome is a rare disease with clinical features including encephalopathy, sensorineural hearing loss, and BRAO. This particular cause of BRAO possesses an autoimmune etiology, with anti-endothelial cell antibodies playing an important role.

Risk factors for BRAO include hypertension, carotid stenosis, coronary artery disease, hyperlipidemia, diabetes mellitus, and smoking. BRAO predominantly occurs in the elderly population and is extremely rare in the pediatric population.

Visual prognosis after BRAO seems to be correlated to presenting VA, with patients with an initial VA of 20/40 or better usually remaining at 20/40 or better. Visual prognosis is good with 60%-89% of patients ending up with VA of 20/40 or better, and only 3% of patients ending up with VA of worse than 20/200. Transient BRAOs tend to have a much better visual prognosis than permanent BRAOs.

There are no definitive therapies for BRAO, but an urgent evaluation is necessary to find the cause and risk factors of the BRAO.