History
Patients with branch retinal artery occlusion (BRAO) typically present with acute, unilateral, painless, partial visual loss. Visual field defects may be central or sectoral. Patients also may be asymptomatic.
Risk factors include smoking, hypertension, hypercholesterolemia, diabetes, coronary artery disease, or history of stroke or transient ischemic attack (TIA). Seventy-five percent of patients have hypertension or carotid occlusive disease.
Patients may give a history of temporary episodes of visual loss (amaurosis fugax) or neurologic loss (TIA). A study showed a prevalence of amaurosis fugax of 14.2% in BRAO. [21]
The physician should ask about any medical problems related to increased risk for embolus formation (eg, heart valve disorders, history of endocarditis, carotid stenosis, coagulopathies, atrial fibrillation), as well as family history of blood clots or clotting disorders. These patients have a significantly higher risk for stroke or cardiovascular events compared with the general population, so appropriate evaluation and referral are necessary. [22]
Physical
Partial visual field deficit may respect the horizontal midline but never the vertical midline.
Funduscopic examination shows retinal whitening along the distribution of the affected artery. The site of obstruction most often is at the bifurcation of the arteries where emboli are most likely to become lodged. Affected retina may be edematous.
Narrowed branch retinal artery, boxcarring, segmentation of the blood columns, cotton-wool spots, and emboli are other possible findings. Emboli are visible in 62% of eyes with a BRAO.
Some of the more common emboli include the following:
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Cholesterol emboli (also known as Hollenhorst plaques) appear as iridescent, reflective, thin yellow plates. These yellow plates are white rhomboid crystals measuring 10-250 µm in length and less than 3 µm in thickness. They appear yellow on funduscopic examination because of blood showing through their translucent thinness. Digital pressure on the eye can make them turn within the vessel causing them to become more or less visible to the examiner. They usually do not cause occlusion of the artery by themselves because blood can flow around them. However, if they occur in conjunction with platelet-fibrin or if they are large, then they can obstruct arterial blood flow. Because their sources most likely are atheromatous plaques in the aorto-carotid system, even asymptomatic patients need a medical workup.
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Platelet-fibrin emboli appear as whitish-gray, nonreflective plugs that are mobile. They may appear in "showers" and may pass through without causing an occlusion. They usually are associated with mural thrombus in the carotid artery or cardiac valvular structures.
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Calcific emboli appear as large, yellowish-white, nonreflective plaques. They more likely are found in the larger arterioles near the optic disc. They are associated with calcified cardiac valves and atheromatous plaques of the carotid artery.
One study demonstrated that attempts to categorize emboli into cholesterol, calcific, or other by funduscopic examination had large intraobserver and interobserver variability. [23] The authors recommended that systemic evaluation not be based on qualitative assessment of the type of emboli.
Auscultation of the heart and carotid arteries and comparison of ophthalmodynamometry may help identify the source of emboli.
Causes
In elderly patients, embolic disease is the most common etiology of a BRAO. In a study of 70 patients with retinal emboli, 40 were found to have cholesterol emboli, 8 platelet-fibrin emboli, 6 calcific emboli, and 1 possible myxomatous embolus. [24] These types of emboli can be iatrogenically displaced during cardiac angiography, catheterization procedures, or any interventional embolization of any branch of the carotid artery.
Types of emboli (endogenous and exogenous) include the following:
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Cholesterol – Atheromatous plaques from the aorto-carotid system
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Platelet-fibrin – Carotid or cardiac thrombosis
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Calcific - Calcified cardiac valves and atheromatous plaques of the carotid artery
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Leukoemboli -Vasculitis, Purtscher retinopathy, septic endocarditis
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Fat emboli - Following long bone fractures
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Amniotic fluid emboli - Complication of pregnancy
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Tumors - Atrial myxoma, mitral valve papillary fibroelastoma
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Talc emboli - Long-term intravenous drug abusers
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Corticosteroid emboli - Complication of intralesional or retrobulbar steroid injection
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Air emboli – Following trauma or surgery
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Synthetic particles – From synthetic materials used in artificial cardiac valves and other vascular procedures; facial dermal filler (Restylane)
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Interventional embolization material (Onyx) (this has been observed at the current authors’ institution)
Color fundus photo of left eye with branch retinal artery occlusion caused by embolization of ethylene vinyl alcohol copolymer (Onyx), a liquid embolic agent used in the treatment of saccular aneurysms, into the retinal circulation. Courtesy of Vanderbilt Eye Institute.
In younger patients, other more obscure and diverse etiologies are more likely. In patients younger than 30 years with retinal arterial obstruction (RAO), associations have been noted with migraines, coagulation abnormalities, trauma, increased intraocular pressure, optic nerve drusen, oral contraceptives, and other entities, which merit a more comprehensive review. Atheromatous disease is a rare cause of RAO in this age group, and routine carotid angiography for embolic cause is not recommended. Visual prognosis is similar to older patients.
Nonembolic causes of BRAO include the following:
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Thrombosis - Atherosclerosis, chemotherapeutic agents, bone marrow transplants
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Inflammatory conditions - Syphilis, toxoplasma, retinochoroiditis, Behçet disease, Lyme disease, pseudotumor cerebri, Bartonella infection, HIV infection, posterior scleritis, varicella-zoster infection, multifocal retinitis with optic nerve edema, West Nile virus infection, giant cell arteritis
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Vasospasm - Migraines, cocaine abuse, sildenafil citrate use
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Coagulopathies - Sickle cell disease, Hodgkin disease, pregnancy, anemia, platelet and clotting factor abnormalities, protein C, protein S, antithrombin III, factor V Leiden deficiencies, oral contraceptives, homocystinuria, antiphospholipid syndrome, chelation therapy
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Autothrombosis - From a ruptured arteriolar macroaneurysm
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Compression - Preretinal arterial loops, vitrectomy surgery, trauma
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Idiopathic - Syndrome involving recurrent episodes of multiple BRAOs in otherwise healthy individuals, association with Susac syndrome (microangiopathy of brain, retina, and cochlea) in some patients
Complications
Stroke is a devastating complication of emboli in the arterial circulation. [25] Few studies report the prospective association between retinal emboli and risk for stroke and stroke mortality. One study reported a 10-fold increase in the annual rate of stroke in patients with retinal emboli compared with controls after a follow-up period of 3.4 years. Another study found a 3-fold higher risk of 8-year mortality from stroke in patients with documented retinal emboli at baseline compared with patients without emboli. A case series reported that 15% of patients with retinal emboli died within 1 year, and a mortality rate of 54% was shown within 7 years.
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Fluorescein angiogram of right eye with inferior branch retinal artery occlusion. Delayed filling of the artery (arrow heads) by the fluorescein is noted.
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Red-free photograph (before injection of fluorescein) of right eye with inferior branch retinal artery occlusion. The red-free photograph greatly accentuates the retinal whitening surrounding the occluded artery.
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Color fundus photo of right eye with inferior branch retinal artery occlusion from a platelet-fibrin embolus. Retinal whitening surrounding the occluded artery is noted.
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Optical coherence tomography (OCT) of right eye with inferior branch retinal artery occlusion. Cross-section goes through inferior retina to superior retina, capturing the abnormally thickened retina associated with intracellular edema.
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Optical coherence tomography (OCT) over time of a branch retinal artery occlusion. Taken 24 hours after symptom onset, A shows an unaffected portion of the macula, while B shows swelling of the inner retina in the area affected by the branch retinal artery occlusion (BRAO). Two weeks later, this swelling/increased thickness is beginning to resolve (C). Two months later, the inner retina has thinned notably, and the inner plexiform layer, inner nuclear layer, and outer plexiform layer are difficult to distinguish from one another. Courtesy of British Journal of Ophthalmology.
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Color fundus photo of left eye with branch retinal artery occlusion caused by embolization of ethylene vinyl alcohol copolymer (Onyx), a liquid embolic agent used in the treatment of saccular aneurysms, into the retinal circulation. Courtesy of Vanderbilt Eye Institute.
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Color fundus photo of right eye with inferior branch retinal artery occlusion. Courtesy of Vanderbilt Eye Institute.
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Color fundus photo of right eye with superior branch retinal artery occlusion. Courtesy of Vanderbilt Eye Institute.
