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Chapter 114 – Retinal Arterial Obstruction

Chapter 114 – Retinal Arterial Obstruction

 

JAY S. DUKER

 

 

 

 

Central Retinal Artery Obstruction

Branch Retinal Artery Obstruction

 

DEFINITION

• An abrupt diminution of blood flow through the central retinal artery severe enough to cause ischemia of the inner retina.

 

KEY FEATURES

• Abrupt, painless, severe loss of vision.

• Cherry-red spot.

• Box-carring of blood flow in the retinal vessels.

• Ischemic retinal whitening of the posterior pole.

 

ASSOCIATED FEATURES

• Amaurosis fugax.

• Visible embolus (25%).

• Carotid artery disease (33%).

• Giant cell arteritis (5%).

• Neovascularization of the iris (18%).

• Arterial collaterals on the optic disc.

 

DEFINITION

• An abrupt diminution of blood flow through a branch of the central retinal artery severe enough to cause ischemia of the inner retina in the territory of the affected vessel.

 

KEY FEATURES

• Retinal whitening in the territory of the obstructed vessel.

• Embolus (66%).

• Visual field defect that corresponds to the territory of the obstructed vessels.

 

ASSOCIATED FEATURES

• Carotid artery disease.

• Cardiac valvular disease.

• Cardiac myxoma, long-bone fracture, endocarditis, depot drug injection (rare).

• Systemic clotting disorder or vasculitis (rare).

 

 

 

CENTRAL RETINAL ARTERY OBSTRUCTION

INTRODUCTION

Retinal arterial obstructions are divided into the categories central and branch, depending on the precise site of obstruction. A central retinal artery obstruction occurs when the blockage is within the optic nerve substance itself and therefore the site of obstruction is generally not visible on ophthalmoscopy. A branch retinal artery obstruction occurs when the site of blockage is distal to the lamina cribrosa of the optic nerve.

Obstructions more proximal to the central retinal artery, in the ophthalmic artery, or even in the internal carotid artery may produce visual loss as well. Ophthalmic artery obstructions may be difficult to differentiate from central retinal artery obstruction. More proximal obstructions usually cause a more chronic form of visual problem—the ocular ischemic syndrome (see Chapter 118 ).

The majority of retinal arterial obstructions are either thrombotic or embolic in nature. The potential sources and various types of emboli generally do not differ between central retinal artery obstruction and branch retinal artery obstruction; however, a branch retinal artery obstruction is far more likely to be embolic than is a central retinal artery obstruction. It has been determined that over two thirds of branch retinal artery obstructions are caused by emboli, whereas probably less than one third of central retinal artery obstructions result from emboli.

The retina has a dual circulation with little to no anastomoses. The inner retina is supplied by the central retinal artery, which is an end artery. The outer retina receives its nourishment via diffusion from the choroidal circulation (see Chapter 101 ). Retinal artery obstructions selectively affect the inner retina only.

Because the accompanying visual loss tends to be severe and permanent, it is fortunate that retinal artery obstructions are rare occurrences. As there is a strong association with systemic disease, all patients who suffer retinal artery obstructions should undergo a systemic evaluation.

EPIDEMIOLOGY AND PATHOGENESIS

Central retinal artery obstruction is a rare event—it has been estimated to account for about 1 in 10,000 outpatient visits to the ophthalmologist. [1] Men are affected more commonly than women in the ratio 2:1. The mean age at onset is about 60 years, with a range of reported ages from the first to the ninth decade of life. Right eyes and left eyes appear affected with equal incidence. Bilateral involvement occurs in 1–2% of cases.

In central retinal artery obstruction, the site of obstruction is not usually visible on clinical examination and, in general, the central retinal artery is too small to image with most techniques; therefore, the precise cause is speculative. It is currently believed that the majority of central retinal artery obstructions are caused by thrombus formation at or just proximal to the lamina cribrosa. Atherosclerosis is implicated as the inciting event in most cases, although congenital anomalies of the central retinal artery, systemic coagulopathies, or low-flow states from more proximal arterial disease may also be present and render certain individuals more susceptible.

In only 20–25% of cases are emboli visible in the central retinal artery or one of its branches, suggesting that an embolic cause is not frequent. A more detailed discussion of embolus types is given later in the section on branch retinal artery obstruction.

 

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Further indirect evidence against emboli as a frequent cause of central retinal artery obstruction is the 40% or less probability of finding a definitive embolic source on systemic evaluation and the small incidence (approximately 10%) of confirmed associated ipsilateral cerebral emboli in affected patients.[2]

Inflammation in the form of vasculitis (e.g., varicella infection), optic neuritis, or even orbital disease (e.g., mucormycosis) may cause central retinal artery obstruction.[3] [4] Local trauma that results in direct damage to the optic nerve or blood vessels may lead to central retinal artery obstruction.[5] Arterial spasm or dissection rarely produces retinal arterial obstruction. In addition, systemic coagulopathies may be associated with both central and branch retinal artery obstructions.[6]

Other rare causes include radiation retinopathy,[7] emboli associated with depot medication injection around the eye,[8] optic disc drusen, and prepapillary arterial loops. Medical examinations and manipulations (e.g., carotid angiography, angioplasty, chiropractic neck manipulation) rarely result in emboli to the central retinal artery.[9] [10] Although elevated intraocular pressure has been implicated as a cause of central retinal artery obstruction, unless the underlying perfusion of the eye is impaired markedly or prolonged external pressure is placed on the globe, it is unlikely that intraocular pressure can be raised high enough to block arterial inflow to the eye.

OCULAR MANIFESTATIONS

The hallmark symptom of acute central retinal artery obstruction is abrupt, painless loss of vision.[11] Pain is unusual and suggests associated ocular ischemic syndrome. Amaurosis fugax precedes visual loss in about 10% of patients. Rarely, in cases associated with arterial spasm, a relapsing and remitting course of visual loss precedes central retinal artery obstruction.[12]

Examination typically reveals a visual acuity of 20/800 (6/240) or worse.[13] Hand motion or light perception vision can occur, but no light perception vision is uncommon except in the setting of an ophthalmic artery obstruction or temporal arteritis. If a patent cilioretinal artery is present and perfuses the fovea, normal central acuity may occur. An afferent pupillary defect on the affected side is the rule.

Anterior segment examination is normal except in the setting of concurrent ocular ischemic syndrome with neovascularization of the iris.

Within the first few minutes to hours after the obstruction, the fundus may appear relatively normal ( Fig. 114-1 , A and B). [1] Eventually, the decreased blood flow results in ischemic whitening of the retina in the territory of the obstructed artery, which is most pronounced in the posterior pole (where the nerve fiber

 

 

 

 

 

 

Figure 114-1 The left eye of a healthy 37-year-old man. The patient had a 3-hour history of visual loss and a visual acuity of 20/60 (6/18). A, Retinal whitening is very subtle and the retinal vessels appear normal. B, Fluorescein angiography reveals abnormal arterial filling with a leading edge of dye that confirms central retinal artery obstruction. C, The same eye 24 hours later. Despite intravenous urokinase, visual acuity dropped to hand movements, and intense retinal whitening with a cherry-red spot is present. Note the interruption in the blood column of the retinal arteries.

layer of the retina is thickest). Acutely, the arteries appear thin and attenuated. In severe blockages, both veins and arteries may manifest “box-carring” or segmentation of the blood flow ( Fig. 114-2 ).

A cherry-red spot of the macula is typical and arises in this area because the nerve fiber layer is thin. Transmission of the normal choroidal appearance, therefore, is not diminished, which contrasts distinctly with the surrounding area of intense retinal whitening that blocks transmission of the normal choroidal coloration. Although other conditions may be associated with a macular cherry-red spot ( Box 114-1 ), these are usually differentiated easily from central retinal artery obstruction. Splinter retinal hemorrhages on the disc are common, but more extensive retinal hemorrhaging suggests an alternative diagnosis. If pallid swelling is present, temporal arteritis must be suspected. A patent cilioretinal artery results in a small area of retina that appears normal ( Fig. 114-3 ).

By 4–6 weeks after obstruction, the retinal whitening is usually resolved, the optic disc develops pallor, and arterial collaterals may form on the optic disc. No foveolar light reflex is apparent, and fine changes in the retinal pigment epithelium may be visible.

Secondary ocular neovascularization is not uncommon after central retinal artery obstruction. Iris neovascularization occurs in about 18% of patients,[14] [15] with many of these eyes going on to neovascular glaucoma. Panretinal photocoagulation appears to reduce the risk of neovascular glaucoma moderately.[16] Neovascularization of the optic disc occurs after about 2% of

 

 

Figure 114-2 Central retinal artery obstruction. The right eye of a 68-year-old woman. Note box-carring of the blood column in the superotemporal arteries and superior veins. Cilioretinal artery sparing is apparent just temporal to the optic disc.

 

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Figure 114-3 A central retinal artery obstruction. A prominent cherry-red spot with cilioretinal artery sparing in the papillomacular bundle.

 

 

 

Other Causes of a Cherry-Red Spot

Tay–Sachs disease

 

Farber’s disease

 

Sandhoff’s disease

 

Niemann–Pick disease

 

Goldberg’s syndrome

 

Gaucher’s disease

 

Gangliosidase GM1, type 2

 

Hurler’s syndrome (mucopolysaccharidosis I H)

 

ß-Galactosidase deficiency (mucopolysaccharidosis VII)

 

Hallevorden-Spatz disease

 

Batten–Mayou–Vogt–Spielmeyer disease

 

 

 

 

central retinal artery obstruction ( Fig. 114-4 ).[17] Vitreous hemorrhage may ensue.

DIAGNOSIS AND ANCILLARY TESTING

Diagnosis of central retinal artery obstruction is straightforward when diffuse ischemic retinal whitening is present in the setting of abrupt, painless visual loss. Fluorescein angiography may help if the diagnosis is in doubt. A delayed arm-to-retina time with a leading edge of dye visible in the retinal arteries is typical (see Fig. 114-1 , B). In some cases, it may be minutes before the retinal arterial tree fills with fluorescein. Arteriovenous transit is delayed as well, and late staining of the disc is common.

Electroretinography characteristically reveals a decreased to absent b-wave with intact a-wave. Visual fields show a remaining temporal island of peripheral vision. If a patent cilioretinal artery is present, a small intact central island is found as well.

Color Doppler imaging is a form of ultrasonography that can help to determine the blood flow characteristics of the retrobulbar circulation. Color Doppler studies of acute central retinal artery obstruction show diminished to absent blood flow velocity in the central retinal artery, generally with intact flow in the ophthalmic and choroidal branches. Color Doppler imaging can be used to detect calcific emboli at the lamina cribrosa and also may be used to monitor blood flow changes induced by therapy. In addition, carotid artery studies may be carried out concurrently with ocular blood flow determinations to evaluate the possible causes of the central retinal artery obstruction.

DIFFERENTIAL DIAGNOSIS

The differential diagnosis of central retinal artery obstruction is given in Box 114-2 .

 

 

 

 

Figure 114-4 A 26-year-old diabetic man. A, Central retinal artery obstruction caused by a platelet-fibrin embolus. B, After 3 months, extensive neovascularization of the disc is present. (Courtesy of Larry Magargal, MD.)

 

 

 

Differential Diagnosis of Central Retinal Artery Obstruction

Single or multiple branch retinal artery obstruction

 

Cilioretinal artery obstruction

 

Severe commotio retinae

 

Necrotizing herpetic retinitis

 

 

 

 

SYSTEMIC ASSOCIATIONS

Although systemic diseases are found commonly in patients who suffer from retinal artery obstruction, the true cause and effect may not be clear. About 60% of patients have concurrent systemic arterial hypertension, and diabetes is present in 25%. Systemic evaluation reveals no definite cause for the obstruction in over 50% of affected patients. Potential embolic sources are found in less than 40% of cases.[1] [14] [18]

The most common pathogenetic association uncovered is hemodynamically significant ipsilateral carotid artery disease, which is present in about one third of affected patients.[1] [14] Carotid noninvasive testing should be considered for all patients who have central retinal artery obstruction, although disease in those younger than 50 years of age is quite rare ( Fig. 114-5 ). An embolic source from the heart is present in less than 10% of patients with central retinal artery obstruction; however, echocardiography and Holter monitoring should be performed, especially in younger patients. In some cases, transesophageal echocardiography is necessary to reveal embolic sources.[19]

Even though it is present in less than 5% of cases, it is of paramount importance that temporal arteritis be ruled out in all patients older than 50 years who have a central retinal artery obstruction.

 

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Figure 114-5 Acute central retinal artery obstruction. Secondary to an embolus at the lamina cribrosa. Note two other emboli in the superior retinal vessels. Ipsilateral carotid artery disease was present.

 

 

 

Systemic Conditions Associated with Retinal Artery Obstructions

 

ATHEROSCLEROTIC CARDIOVASCULAR DISEASE

Ophthalmic artery plaques, stenosis,

 

or dissection

 

Carotid artery plaques, stenosis,

 

or dissection

 

Aortic plaques, stenosis, or dissection

 

 

CARDIAC

Valvular disease (including

 

rheumatic fever)

 

Ventriculoseptal defects

 

Papillary fibroelastoma

 

Cardiac myxoma

 

Mural thrombus

 

Arrhythmias

 

Subacute bacterial endocarditis

 

 

COAGULOPATHIES

Antiphospholipid antibodies

 

Protein C deficiency

 

Protein S deficiency

 

Antithrombin III deficiency

 

Elevation of platelet factor 4

 

 

ONCOLOGIC

Metastatic tumors

 

Leukemia

 

Lymphoma

 

 

RADIOLOGIC AND MEDICAL PROCEDURES

Angiography

 

Angioplasty

 

Chiropractic neck manipulation

 

Depot corticosteroid injection

 

 

SYSTEMIC VASCULITIS

Susac’s disease

 

Systemic lupus erythematosus

 

Polyarteritis nodosa

 

Temporal arteritis

 

Sneddon–Wilkinson disease

 

Wegener’s granulomatosis

 

Inflammatory bowel disease

 

Kawasaki’s syndrome

 

 

SYSTEMIC INFECTIONS

Syphilis

 

Mediterranean spotted fever

 

Loiasis

 

 

LOCAL TRAUMA

Direct ocular compression

 

Penetrating injury

 

Retrobulbar injection

 

Orbital trauma

 

Retrobulbar hemorrhage

 

Purtscher’s disease

 

 

LOCAL OCULAR

Prepapillary arterial loops

 

Optic nerve drusen

 

Necrotizing herpetic retinitis

 

Orbital mucormycosis

 

Toxoplasmosis

 

 

MISCELLANEOUS

Amniotic fluid embolism

 

Pancreatitis

 

Migraine

 

Pregnancy

 

Oral contraceptives

 

Cocaine abuse

 

Intravenous drug use

 

 

 

 

An immediate erythrocyte sedimentation rate must be obtained, and if it is elevated or if clinical suspicion exists, corticosteroid therapy and a temporal artery biopsy should be considered.

Other rare associated systemic diseases include blood-clotting abnormalities such as antiphospholipid antibodies, protein S deficiency, protein C deficiency, and antithrombin III deficiency.[20] [21] A list of systemic associations for retinal artery obstructions is given in Box 114-3 .

 

 

 

 

Figure 114-6 Central retinal artery occlusion. A, A trichrome-stained section shows an organized thrombus (T) that occludes the central retinal artery within the optic nerve (V, vein). B, A histological section at the early stage shows edema of the inner neural retinal layers and ganglion cell nuclei pyknosis. Patient had a cherry-red spot in fovea at time of enucleation. IM, Internal limiting membrane; IN, inner nuclear layer; NG, swollen nerve fiber and ganglion layers; ON, outer nuclear layer; OP, outer plexiform layer; PR, photoreceptors. (From Yanoff M, Fine BS. Ocular pathology, ed 5. St. Louis: Mosby, 2002.)

PATHOLOGY

Histopathological examination shows coagulative necrosis of the inner retina. Acute, early, intracellular edema is followed by complete loss of the inner retinal tissue. Chronically, a diffuse acellular zone replaces the nerve fiber layer, ganglion cell layer, and inner plexiform layer. The outer retinal cells remain relatively intact. Sections of the obstructed central retinal artery may reveal a thrombus or embolus that is often recanalized ( Fig. 114-6 ).

TREATMENT

No proved treatment exists for central retinal artery obstruction, but treatment strategies center around the following goals:

• Increase retinal oxygenation

• Increase retinal arterial blood flow

• Reverse arterial obstruction,

• Prevent hypoxic retinal damage

Theoretically, retinal oxygenation can be increased by breathing carbogen (95% oxygen, 5% carbon dioxide). Investigationally, the high concentration of oxygen has been shown to elevate oxygen tension at the inner retina via diffusion through the intact choroidal circulation. The carbon dioxide prevents the normal retinal autoregulatory mechanisms from inducing constriction of the retinal arteries. No clinical study indicates efficacy for carbogen therapy, and one retrospective study suggests that it has no beneficial effect.[22] In most centers, it is no longer used.

 

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An increase in retinal arterial blood flow is attempted by lowering intraocular pressure. This is accomplished by ocular massage, paracentesis, and the administration of ocular antihypertensive medications. Medical attempts to dilate retinal arteries or block vascular spasm have been tried as well. Sublingual nitroglycerin, pentoxifylline (oxpentifylline), calcium channel blockers, and ß-blockers have all been used with no proof of efficacy.[11] [23]

Reversal of arterial obstruction through the use of anticoagulation and fibrinolytic mediations has been reported. To date, the utility of these mediations has not been proved by controlled clinical trials; however, anecdotal reports of success with intravenous heparin, tissue plasminogen activator, streptokinase, and urokinase exist. In addition, an intra-arterial injection of tissue plasminogen activator, streptokinase, or urokinase during selective catheterization of the ophthalmic artery has been attempted, with reported success in some selected cases.[24] [25]

At present, prevention of hypoxic damage to the retina is only theoretically possible.[26] Antioxidant medications (e.g., superoxide dismutase) and N-methyl-D-aspartate (NDMA) inhibitors are two classes of compounds that may accomplish retinal rescue pharmacologically and are under study.

Cases of central retinal artery obstruction associated with temporal arteritis are treated emergently with high-dose corticosteroids. Without therapy, the risk to the second eye is great. Although the first-affected eye rarely recovers, instances exist in which high-dose intravenous methylprednisolone induced visual recovery from central retinal artery obstruction associated with temporal arteritis. [27]

COURSE AND OUTCOME

Most central retinal artery obstructions result in severe, permanent loss of vision. About one third of patients experience some improvement in final vision in terms of presentation acuity, either with or without conventional treatment. Three or more Snellen lines of improved visual acuity occur in only about 10% of patients, whether treated by current methods or untreated. On occasion, some patients experience significant restoration of normal vision.

Experimentally, if an obstruction exists in the primate retina for more than 100 minutes, complete irreversible death of the inner retina occurs. [28] In practice, a rare patient has experienced total spontaneous recovery even after several days of documented visual loss.[29] Spontaneous recovery may be more common in young children.[6] [8]

BRANCH RETINAL ARTERY OBSTRUCTION

INTRODUCTION

Branch retinal artery obstruction represents a rarely encountered retinal vascular disorder. Although current treatments are not effective, in the majority of cases the source of the obstruction can be determined. As associated systemic implications occur, diagnosis and systemic evaluation of these patients are critical.

EPIDEMIOLOGY AND PATHOGENESIS

Branch retinal artery obstruction is a rare event, even less common than central retinal artery obstruction overall. The exception to this comparative incidence is with young patients, in whom branch retinal artery obstruction is the more common type of retinal artery obstruction.[30] Overall, men are more affected than women by a 2:1 ratio, which reflects the higher incidence of vasculopathic disease in men. In the subset of young patients (less than 50 years of age), women and men are affected equally. The mean age of affected patients is 60 years, with a range from the second decade of life to the tenth. The great majority of patients are in the sixth or seventh decade of life. The right eye (60%) is affected more commonly than the left (40%), which probably reflects the greater possibility of cardiac or aortic emboli traveling to the right carotid artery.[11] Branch retinal artery obstruction strikes the temporal retinal circulation far more frequently than the nasal, consistent with the greater blood flow to the macular retina.

Over two thirds of branch retinal artery obstructions are secondary to emboli to the retinal circulation.[1] [11] [31] In most cases, the emboli are clearly visible in the arterial tree. Emboli to the retinal circulation may originate at any point in the proximal circulation from the heart to the ophthalmic artery. Risk factors reflect the vasculopathic mechanisms that produce disease within the cardiovascular system. These include predisposing family history, hypertension, elevated lipid levels, cigarette smoking, and diabetes mellitus.

Three main types of retinal emboli have been identified:

• Cholesterol (Hollenhorst plaque)

• Platelet-fibrin

• Calcific.

Cholesterol emboli typically emanate from atheromatous plaques of the ipsilateral carotid artery system, although the aorta or heart valves may also be a source. They are yellow-orange in color, refractile, and globular or rectangular in shape. They may be small and do not always result in blockage of blood flow. Platelet-fibrin emboli are long, smooth, white-colored, intra-arterial plugs that may be mobile or break up over time. Usually, they are associated with carotid or cardiac thromboses. Calcific emboli are solid, white, nonrefractile plugs associated with calcification of heart valves or the aorta.

Less commonly seen embolic types include tumor cells from atrial myxoma[32] or a systemic metastasis, septic emboli associated with septicemia or endocarditis, fat emboli associated with large bone fractures, emboli dislodged during angioplasty or angiography, and depot drug preparations from intra-arterial injections around the eye or face.

Rarely, local ocular conditions produce branch retinal artery obstruction. These include inflammatory diseases, such as toxoplasmosis or acute retinal necrosis, or structural problems, such as optic disc drusen or prepapillary arterial loops.[1] [11]

Systemic hematological or clotting problems may induce isolated branch retinal artery obstruction or even multiple recurrent branch retinal artery obstruction.[33] [34] Systemic vasculitides, such as polyarteritis nodosa or local vasculitis associated with varicella infection, may be associated with branch retinal artery obstruction. Oral contraceptive use and cigarette smoking have been implicated as possible risk factors, especially in young, otherwise healthy women.[18] [30]

OCULAR MANIFESTATIONS

Abrupt, painless loss of vision in the visual field corresponding to the territory of the obstructed artery is the typical history of presentation. Unlike the situation in retinal venous obstruction, patients can typically define the time and extent of visual loss precisely. Amaurosis fugax occurs in about one fourth of patients prior to frank obstruction, especially in the setting of carotid disease. Rarely, patients develop bilateral simultaneous branch retinal artery obstruction, which can mimic homonymous field defects.

Acutely, examination reveals intact central acuity in about 50% of patients. A relative afferent pupillary defect is common, the presence of which is determined by the extent of retinal involvement.

Retinal whitening that corresponds to the areas of ischemia is the most notable finding. The whitening stops at adjacent retinal veins, as these vessels mark the extent of the territory of the retinal arteries ( Fig. 114-7 ). Retinal emboli are seen in over two thirds of branch retinal artery obstructions. Flame hemorrhages at the margins of the retinal ischemia are not uncommon, and

 

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Figure 114-7 Superior hemispheric branch retinal artery obstruction. The site of obstruction is probably within the optic nerve substance itself. Note that the dual trunk of the central retinal artery obstruction has separated proximal to the lamina. Only the superior trunk was affected.

 

 

 

Differential Diagnosis of Branch Retinal Artery Obstruction

Cotton-wool spot(s)

 

Central retinal artery obstruction

 

Cilioretinal artery obstruction

 

Retinal astrocytoma

 

Inflammatory or infectious retinitis

 

 

 

 

local areas of more intense inner retinal whitening that resemble scattered cotton-wool spots can develop.

A syndrome of multiple, recurrent, bilateral branch retinal artery obstruction in young, otherwise healthy patients has been reported. A few of the patients also manifest vestibuloauditory symptoms.[35] Although the underlying pathology in this subset of patients is probably heterogeneous, some probably have Susac’s syndrome, a rare disorder that manifests as a microangiopathy of the central nervous system. Others probably have various types of systemic clotting abnormalities.[36]

In the chronic phase, when the retinal whitening has diminished, a loss of the nerve fiber layer in the affected area may be apparent. In most instances, the affected retina appears normal. At the site of obstruction, localized sheathing of the arteriole is common. Arteriolar collaterals on the optic disc or at the site of obstruction may develop.

DIAGNOSIS AND ANCILLARY TESTING

Ancillary testing is not usually necessary to make the diagnosis. Fluorescein angiography reveals an abrupt diminution in dye at the site of the obstruction and distally. Filling in the adjacent retinal veins is slow to absent, and late staining or even leakage from the embolus site may occur.

Visual field testing can confirm the extent of visual loss and may pick up contralateral field loss from previous emboli or other associated conditions.

DIFFERENTIAL DIAGNOSIS

The differential diagnosis of branch retinal artery obstruction is given in Box 114-4 .

SYSTEMIC ASSOCIATIONS

Systemic evaluation of patients who have branch retinal artery obstruction discloses evidence of an embolic source from the carotid arteries or the heart in many cases. Other rare systemic conditions associated with branch retinal artery obstruction include

 

 

Figure 114-8 Cytoid body formation in neural retinal nerve fiber layer. Histological counterpart of the clinical cotton-wool spot. (From Yanoff M, Fine BS. Ocular pathology, ed 5. St. Louis: Mosby, 2002.)

amniotic fluid embolism, pancreatitis, sickle cell disease, homocystinuria, and Kawasaki disease. Young patients, especially those who have multiple or recurrent branch retinal artery obstruction, should be evaluated for systemic clotting abnormalities such as protein S deficiency, protein C deficiency, antithrombin III deficiency, platelet abnormalities (“sticky platelet syndrome”), and antiphospholipid antibodies.

Branch retinal artery obstruction associated with temporal arteritis is exceedingly uncommon.[37] It is not usually necessary to obtain an erythrocyte sedimentation rate unless other evidence of temporal arteritis exists. Box 114-3 lists the systemic conditions most commonly associated with retinal artery obstructions.

PATHOLOGY

Early, coagulative necrosis of the inner layers of the neural retina, which are supplied by the retinal arterioles, is manifest by edema of the neuronal cells during the first few hours after arterial occlusion and becomes maximal within 24 hours. The intracellular swelling accounts for the gray, retinal opacity seen clinically. If the area of coagulative necrosis is small and localized, it appears as a cotton-wool spot, the clinical manifestation of a microinfarct of the nerve fiber layer of the neural retina. The cytoid body observed microscopically ( Fig. 114-8 ) is a swollen, interrupted axon in the neural retinal nerve fiber layer. Histologically, the swollen end bulb superficially resembles a cell, hence the term cytoid body. A collection of many cytoid bodies, along with localized edema, marks the area of the microinfarct. A cotton-wool spot represents a localized accumulation of axoplasmic debris in the neural retinal nerve fiber layer and results from interruption of the orthograde or retrograde organelle transport in ganglion cell axons, that is, obstruction of axoplasmic flow.

The outer half of the neural retina is well preserved. The inner half of the neural retina, however, becomes “homogenized” into a diffuse, relatively acellular zone, which generally contains thick-walled retinal blood vessels. Because the glial cells die along with the other neural retinal elements, gliosis does not occur.

TREATMENT

No proved treatment exists for branch retinal artery obstruction. Because the visual prognosis is much better for branch retinal artery obstruction than for central retinal artery obstruction, invasive therapeutic maneuvers of dubious utility are not typically performed. On occasion, ocular massage or paracentesis is successful in dislodging an embolus. Laser photocoagulation has been employed to “melt” an embolus, without improvement in the vision.[38]

One report suggests that hyperbaric oxygen therapy may improve the visual loss associated with multiple branch retinal artery obstruction in Susac’s syndrome.[39]

 

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In the rare patient who has branch retinal artery obstruction accompanied by a systemic clotting disorder, systemic anticoagulation may prevent further events.

COURSE AND OUTCOME

Most patients remain with a fixed visual field defect but intact central acuity. About 80% of eyes recover to 20/40 (6/12) or better central acuity. Retinal neovascularization has been reported but is distinctly uncommon. Iris neovascularization does not occur.[11]

OPHTHALMIC ARTERY OBSTRUCTION

Acute simultaneous obstruction of both the retinal and choroidal circulations is referred to as an ophthalmic artery obstruction. In some cases a single site of blockage in the ophthalmic artery is present, and in others simultaneous interruption of the retinal and posterior choroidal circulations with multiple blockage sites is found.

Ophthalmic artery obstructions can be differentiated clinically from central retinal artery obstruction by the following features[40] :

• Severe visual loss—bare or no light perception;

• Intense ischemic retinal whitening that extends beyond the macular area;

• Little to no cherry-red spot;

• Marked choroidal perfusion defects on fluorescein angiography;

• Nonrecordable electroretinogram; and

• Late retinal pigment epithelium alterations.

Cases of ophthalmic artery obstruction usually have associated local orbital or systemic diseases, which include orbital mucormycosis, orbital trauma, retrobulbar anesthesia, depot corticosteroid injection, atrial myxoma, or carotid artery disease. Temporal arteritis usually does not produce ophthalmic artery obstruction in the absence of ipsilateral ischemic optic neuropathy.

As with central retinal artery obstruction, no proved therapy exists and significant visual recovery usually does not occur. In the absence of local causes, systemic evaluation must include testing for temporal arteritis, carotid artery disease, and cardiac disease.

CILIORETINAL ARTERY OBSTRUCTION

A cilioretinal artery exists in about 30% of individuals. It is a vessel that perfuses the retina and is derived directly from the posterior ciliary circulation rather than from the central retinal artery. For this reason, it may remain patent in the setting of a central retinal artery obstruction. Such vessels are usually observed to emanate from the temporal disc margin. They may be multiple and can also perfuse the nasal retina. On fluorescein angiography, they fill 1–3 seconds prior to the retinal circulation. Cilioretinal artery obstruction exists in three clinical variations:

• Isolated

• Cilioretinal artery obstruction combined with central retinal vein obstruction

• Cilioretinal artery obstruction combined with ischemic optic neuropathy

Isolated cilioretinal artery obstructions usually occur in young patients in the setting of collagen vascular disorders. They carry a good visual prognosis, with 90% of eyes left with 20/40 (6/12) or better vision.[41]

Cilioretinal artery obstruction combined with central retinal vein obstruction is not an uncommon variant in young patients ( Fig. 114-9 ). It generally behaves as a nonischemic central retinal vein obstruction with a good central visual prognosis. The scotoma from the artery obstruction is usually permanent. Although the mechanism of this association is unclear, it is hypothesized that some eyes harbor a primary optic disc vasculitis (papillophlebitis) that affects both the arterial and venous circulation.[42] It is more common in men than in women and patients

 

 

Figure 114-9 Cilioretinal artery obstruction. In conjunction with mild nonischemic central retinal vein obstruction. Note the retinal whitening just inferior to the fovea in the distribution of the cilioretinal artery.

 

 

Figure 114-10 Combined central retinal artery obstruction and central retinal vein obstruction. Visual acuity in this 21-year-old woman who had lupus was light perception, and neovascularization of the iris ensued.

are generally healthy; however, this entity has been seen in conjunction with inflammatory bowel disease and leukemia.

In contrast to the first two groups discussed before, cilioretinal artery obstruction with ischemic optic neuropathy carries a grim visual prognosis and a strong association with temporal arteritis.

COMBINED ARTERY AND VEIN OBSTRUCTIONS

Central retinal artery obstruction combined with simultaneous central retinal vein obstruction rarely occurs. Such patients present with acute, severe loss of vision, usually to bare or no light perception. Examination shows a cherry-red spot combined with features of a central retinal vein obstruction, which include dilated, tortuous veins that have retinal hemorrhages in all four quadrants ( Fig. 114-10 ).[43] Associated systemic or local disease is the rule—collagen vascular disorders, leukemia, orbital trauma, retrobulbar injections, and mucormycosis have been implicated. The visual prognosis is generally poor and the risk of neovascularization of the iris is about 75%. Exceptionally, a patient may manifest spontaneous improvement. [44]

Branch retinal artery obstruction combined with simultaneous central retinal vein obstruction has also been reported.[45] This rare entity behaves as a central retinal vein obstruction. Neovascularization of the iris is possible, but systemic associations other than hypertension and diabetes have not been confirmed.

 

 

REFERENCES

 

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