Laboratory Studies
Laboratory tests to consider in patients with suspected branch retinal artery occlusion (BRAO) include the following:
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In patients older than 50 years, consider ordering an immediate erythrocyte sedimentation rate (ESR) to help rule out giant cell arteritis.
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In patients younger than 50 years or in patients with the appropriate risk factors, consider the following tests to evaluate for coagulopathies: antitreponemal antibody, antiphospholipid antibody, antinuclear antibody, rheumatoid factor, serum protein electrophoresis, hemoglobin electrophoresis, prothrombin time/activated partial thromboplastin time (PT/aPTT), fibrinogen, protein C and S, antithrombin III, and factor V Leiden.
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A CBC count is obtained to evaluate for anemia, polycythemia, and platelet disorders.
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Fasting blood sugar, glycosylated hemoglobin, cholesterol, triglycerides, and lipid panel are obtained to evaluate for atherosclerotic disease.
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Blood cultures are obtained to evaluate for bacterial endocarditis and septic emboli.
Imaging Studies
Acute BRAO or central retinal artery occlusion should be treated as ocular and systemic emergencies, as they can be harbingers for subsequent stroke. Thus, guidelines necessitate urgent imaging and clinical evaluation. [22] Imaging studies are imperative to determine the etiology of the embolus for the purpose of treatment and subsequent prevention of further artery occlusions or stroke.
Two-dimensional or transesophageal echocardiography
Elderly patients and patients with high-risk characteristics for cardioembolic disease warrant medical workup involving either 2-dimensional or transesophageal echocardiography. High-risk characteristics include a history of rheumatic heart disease, mitral valve prolapse, prosthetic valve placement, history of subacute bacterial endocarditis, recent heart attack, intravenous (IV) drug abuse, any type of valvular heart disease (congenital or acquired), detectable heart murmurs, and ECG changes (eg, atrial fibrillation, changes indicating myocardial damage).
Carotid ultrasonography studies and magnetic resonance angiography
Considering the higher incidence of fatal stroke in the elderly population, atherosclerotic disease should be evaluated if no other etiology is obvious.
ECG/Holter monitor
ECG/Holter monitor is used to evaluate for atrial fibrillation.
MRI
MRI can be used to evaluate for additional, possibly occult, vessel occlusions in the brain. In cases of suspected Susac syndrome, MRI may be helpful to look for classic findings in the corpus callosum. Any concern for concurrent stroke symptoms would warrant the appropriate brain imaging and workup, usually guided by neurologic consultation.
Fluorescein angiography
Delayed filling of the affected artery and hypofluorescence in the surrounding retina will be visible immediately after onset of the occlusion. Vessels distal to the site of obstruction may show retrograde filling from surrounding perfused capillaries. Late staining of the vessel walls may be seen.
After resolution of the obstruction, reperfusion can occur, and flow may return to normal. However, narrowing or sclerosis of the affected artery can occur. Artery-to-artery collaterals may form in the retina and are highly suggestive of an old BRAO.
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.
Fluorescein angiogram of right eye with inferior branch retinal artery occlusion. Delayed filling of the artery (arrow heads) by the fluorescein is noted.
Optical coherence tomography
Optical coherence tomography (OCT) has been used to demonstrate structural damage of the retinal layers after retinal artery occlusion. [26]
Increased thickening and hyperreflectivity of the inner retinal layers with decreased reflectivity of the photoreceptors and retinal pigment epithelium is often present, which supports the pathophysiology of increasing intracellular fluid within the inner retinal layer. The inner retina, rather than the outer retina, is preferentially affected, because the inner retinal layers receive blood flow from the central retinal artery and its branches, whereas the outer retinal layers are fed by the choroidal vasculature.
One study used OCT to demonstrate the long-term structural results after arterial occlusion. One year after diagnosis of BRAO, the authors found segmental inner retinal layer and peripapillary retinal nerve fiber layer thickness to be reduced. They correlated visual field deficits with OCT thickness and found that a worse functional outcome was associated with a more extensive thinning of the macula and retinal nerve fiber layer.
Another study suggested that spectral domain OCT may be a useful adjunct in the acute phase in characterizing retinal artery emboli, including perfusion characteristics (eg, extent of luminal occlusion) and emboli characteristics and embolus structure (eg, more crystalline in appearance or softer and more conforming to the shape of the vessel lumen). [27]
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.
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.
Optical coherence tomography angiography
Optical coherence tomography angiography (OCTA) is a newer imaging technique that can noninvasively segment and visualize retinal and choroidal microvasculature. In cases of retinal artery occlusions, OCTA can be used to evaluate the superficial and deep capillary plexuses in the inner retina, which conventional fluorescein angiography is unable to do. While limited, studies of OCTA in retinal artery occlusions have shown perfusion abnormalities in both the superficial and deep plexuses, with the degree of nonperfusion changing as the arterial occlusion process evolves. [28]
OCTA does have limitations, with studies showing that slow-flowing capillaries may not be visible on the angiograms. Thus, nonperfusion on OCTA should be interpreted with caution. [29] While further studies of OCTA are warranted, it may allow for assessment of the extent of macular ischemia and monitoring of vascular flow changes over the course of retinal vascular diseases.
Other Tests
Serial Humphrey visual field testing reveals any field deficits and can be used to monitor the stability or improvement of these deficits.
An electroretinogram (ERG) is of limited usefulness. Findings may be normal. In the case of a large BRAO, it may show loss of oscillatory potential and transient depression of the B wave.
Procedures
Because the prognosis for branch retinal artery occlusion (BRAO) is very good, no interventions usually are taken. In the event of involvement of the perifoveolar capillaries, treatment as for central retinal artery occlusion (CRAO) may be attempted (see Central Retinal Artery Occlusion).
Intra-arterial thrombolysis with recombinant tissue-type plasminogen activator (rt-PA) via a guiding catheter inserted into the femoral artery, placed into the internal carotid artery, and advanced into the ophthalmic artery has been used for CRAO with varying success. This also has been applied to some patients with BRAO with limited benefit compared with conventional forms of therapy or observation. Given the high rate of adverse events (37.1% in the EAGLE study), intra-arterial thrombolysis is not recommended in the management of arterial occlusions. [30]
Another procedure that has been attempted for both BRAO and CRAO is transluminal Nd:YAG laser embolysis or TYE. This method relies on the Nd:YAG laser to shatter the embolus, clear the arteriole lumen, and improve perfusion without harming the vessel wall. Potential risks include retina tears, vitreous and retinal hemorrhages, choroidal neovascularization, and epiretinal membrane formation. One study found visual improvement to occur immediately after the embolysis. A meta-analysis suggests possible visual benefit of TYE, especially in patients with poor visual acuity; however, further research is warranted. [31]
Histologic Findings
BRAO causes ischemia to the inner layers of the retina, which causes inner and intracellular edema and a coagulative necrosis.
Eventually, loss of the inner retinal layers occurs, including the nerve fiber layer to the inner nuclear layer.
Because the glial cells also have been destroyed, usually no gliosis is noted.
Histologic evidence of emboli or other etiology may be present.
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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.
