Retinal Vascular Diseases

Branch retinal artery occlusion (BRAO) most often occurs in older patients as an embolic complication of atherosclerosis. In younger patients, inflammatory

(infectious and autoimmune) diseases, thrombotic states, cardiac valvular disorders, vasospastic conditions, and exogenous embolic sources must be considered in the differential diagnosis. Branch retinal artery occlusions are usually unilateral and unifocal but may be bilateral or multifocal in unusual cases.

Symptoms

Branch retinal artery occlusion is characterized by sudden, painless loss of visual field or visual acuity. Occasionally, episodes of transient visual loss lasting minutes (amaurosis fugax) precede permanent retinal arteriolar occlusion.

Clinical Findings

Funduscopic examination reveals opacification of the inner retina (“ischemic retinal whitening”) in the distribution of the occluded branch retinal artery. In some patients, an embolus may be visible at an arterial bifurcation. The most common forms of emboli are fibrinplatelet, cholesterol, and calcific emboli. The ischemic retinal whitening usually clears within 3 weeks. Late funduscopic changes include segmental disc pallor and narrowing of the involved arteriole.

Multiple BRAOs may be observed in one or both eyes with or without associated systemic disease. Idiopathic recurrent BRAO is an unusual condition characterized by multiple BRAOs, hearing loss, and evidence of brain infarctions in otherwise healthy individuals. Multiple BRAOs may be seen in association with collagen vascular disorders (systemic lupus erythematosus), inflammatory conditions (toxoplasmosis, cat scratch neuroretinitis), and malignant hypertension. Branch retinal artery occlusions must be differentiated from cotton wool spots, Purtscher’s-like retinopathy, and myelinated nerve fibers.

Ancillary Testing

Fluorescein angiography may demonstrate delay or absence of filling in the affected retinal arteriole. However, particularly with fibrin-platelet or cholesterol emboli, retinal blood flow may be restored by the time the patient seeks attention.

Pathology/Pathogenesis

Ischemic retinal whitening occurs secondary to denaturation of intracellular proteins. Retinal arteriolar emboli originate from various sites including the carotid artery (platelet, cholesterol, or calcific emboli), cardiac valves (calcific, platelet, or septic emboli), and exogenous sources (such as talc or steroidal suspensions injected intravascularly). Purtscher’s-like retinopathy occurs in patients with long bone fractures, collagen vascular disease, acute pancreatitis, amniotic fluid embolism, incomplete central retinal artery occlusion, and other disorders. The multiple arteriolar occlusions in some patients with Purtscher’s-like retinopathy are thought to result from emboli composed of leukocyte aggregates occurring in response to systemic complement activation.

Treatment/Prognosis

Treatment of BRAO has two components: first, to minimize the effects of the retinal arteriolar occlusion, and second, to address the underlying systemic cause, if known. As with central retinal artery occlusion, the treating physician may attempt to move or dislodge the embolus by anterior chamber paracentesis, having the patient rebreathe into a paper bag, or having the patient inhale carbogen. However, treatment is not effective in most cases. If the occlusion is thought to be secondary to a systemic inflammatory disorder, treatment with systemic corticosteroids or immunosuppressive drugs, managed in cooperation with an internist, may be indicated.

The visual prognosis for BRAO is generally favorable, with most eyes retaining vision of 20/40 or better, provided the fovea is not involved. Visual field defects corresponding to the distribution of the BRAO are permanent.

Systemic Evaluation

Patients with atherosclerotic risk factors such as diabetes or hypertension require an embolic workup including carotid Doppler studies and echocardiography (transthoracic or transesophageal, depending on the recommendation of the cardiologist performing the study). Review of systems may direct further evaluation for coagulopathy, systemic or ocular inflammatory disorder, or embolic source.

A 64-year-old man with ischemic retinal whitening in the distribution of a small branch retinal arteriole. The ischemic retinal whitening results from infarction of the inner retinal layers.

A 36-year-old woman presented with a prominent superotemporal branch retinal artery occlusion. She had a history of migraines and was taking oral contraceptive medication. Her systemic evaluation was negative.

An intra-arterial embolus (Hollenhorst plaque) is observed at the first branching site of the superotemporal arteriole in the fellow eye of the same patient.

Fundus photograph 1 year after an inferotemporal branch retinal artery occlusion. Note the segmental disc pallor, nerve fiber layer dropout, and marked attenuation of the inferotemporal retinal arteriole.

Idiopathic recurrent multifocal branch retinal artery occlusions in a 59-year-old man. There were unusual fibrin-platelet aggregates within multiple branch retinal arterioles. The periphery had a featureless, ischemic appearance.

Fluorescein angiography of the same patient demonstrates multifocal branch retinal artery occlusions and midperipheral retinal ischemia.

BRANCH RETINAL VEIN OCCLUSION

Branch retinal vein occlusion (BRVO) is a common retinal vascular disease. Branch retinal vein occlusion appears most frequently between the sixth and eighth decades and affects men and women equally. Branch retinal vein occlusion is unilateral, with a 5% to 10% risk to the fellow eye. Risk factors for BRVO include hypertension, cardiovascular disease, increasing age, elevated body mass, glaucoma, and possibly diabetes mellitus.

Symptoms

Symptoms of BRVO include blurred vision, metamorphopsia, visual field loss, and floaters. Individuals may be asymptomatic, depending on the location

of the BRVO.

Clinical Features

Occlusion of a retinal vein occurs almost invariably at an arteriovenous crossing site where the artery lies anterior to the vein. Acute retinal findings include venous dilation and tortuosity, superficial and deep retinal hemorrhages, cotton wool spots, and retinal edema. Chronic retinal findings are variable. The retinal hemorrhages may resolve in weeks to months. Dilated capillaries and microaneurysms may be seen in the territory of the vein occlusion. Macular edema may be associated with lipid exudation and blood-filled cysts. Small, tortuous venous collateral vessels may cross the horizontal raphe or “bridge” the site of venous occlusion. There may be sheathing of retinal arteries and veins in the region of the BRVO. The major complications of BRVO are macular edema and retinal neovascularization with vitreous hemorrhage.

Ancillary Testing

Fluorescein angiography reveals delayed venous filling and prolonged venous circulation time of the involved vein. The retinal vascular bed may show microvascular abnormalities such as microaneurysms, telangiectasis, and macroaneurysm formation. Leakage of fluorescein from microvascular abnormalities is common. Capillary nonperfusion and disruption of the foveal capillary ring may be seen in cases of macular ischemia. Areas of neovascularization are characterized by intense hyperfluorescence and are usually located at the junction of perfused and nonperfused retina.

Pathology/Pathogenesis

At an arteriovenous crossing site, the vein and artery share a common advential sheath. Atherosclerosis and hypertension may result in increased rigidity of the artery wall and contraction of the common advential sheath. This, in turn, results in compression of the venous lumen and predisposes the venule to thrombosis and venous occlusion.

Treatment/Prognosis

In general, BRVOs are followed up for 3 to 4 months for spontaneous improvement prior to consideration of laser surgery. The Branch Retinal Vein Occlusion Study provides clear guidelines for the treatment of BRVO. Macular grid photocoagulation to areas of macular edema increases the likelihood of visual recovery and reduces the risk of visual loss. If retinal neovascularization develops, scatter photocoagulation to the ischemic retina reduces the risk of vitreous hemorrhage and further visual loss. Long-term visual loss is usually related to chronic macular edema and macular ischemia.

Systemic Evaluation

It is important for individuals to have a systemic evaluation to identify potentially treatable risk factors for BRVO including hypertension. In atypical cases, investigation for coagulopathy or inflammatory disease is also considered.

Acute branch retinal vein occlusion produces intraretinal hemorrhages in the distribution of the occluded branch retinal vein. Flame-shaped hemorrhages are in the nerve fiber layer, whereas dot/blot hemorrhages are in the deeper retinal layers. The white lesions are cotton wool spots.

Macular edema is the most common complication following a branch retinal vein occlusion (BRVO). This BRVO is characterized by marked macular edema and lipid exudation.

An arteriovenous crossing site, where the artery lies anterior to the vein, is where branch vein occlusions occur. Note the prominent venous narrowing at the proximal crossing site along the superotemporal arcade.

Preretinal/vitreous hemorrhage and neovascularization may occur in branch retinal vein occlusions associated with retinal ischemia.

Fluorescein angiography in branch retinal vein occlusion (BRVO) shows a delay in the venous circulation time as well as capillary nonperfusion in the distribution of the BRVO. The capillaries are dilated and tortuous and leak throughout the study.

This chronic branch retinal vein occlusion reveals sheathing of the involved vein. There are retinal pigment epithelial alterations in the fovea as a result of chronic macular edema. The capillaries in the involved area are dilated and tortuous.