Ординатура / Офтальмология / Английские материалы / Clinical Ophthalmology A Systematic Approach 7th Edition_Kanski, Bowling_2011

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Fig. 13.38 (A) Inferior hemiretinal vein occlusion; (B) FA late phase shows extensive hypofluorescence due to capillary non-perfusion and mild perivascular hyperfluorescence

(Courtesy of C Barry)

Systemic treatment in retinal vein occlusion

1Control of systemic risk factors. This will also ameliorate adverse systemic vascular outcomes, because retinal vein occlusions are associated with cerebroand cardiovascular causes of death.

2Antiplatelet therapy with aspirin or an alternative agent should be considered according to systemic risk factors, and might reduce the risk of further venous occlusion.

3Hormone replacement therapy (HRT). The risk of HRT remains undefined. Most authorities would avoid commencing oestrogencontaining HRT following RVO in women not already taking this.

4Isovolaemic haemodilution. The results of trials are inconsistent, though benefit has been shown by some.

5Other. A range of treatment modalities (e.g. plasmapheresis) has been employed to try to improve visual outcomes in RVO, but as yet clear evidence for benefit is lacking.

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Retinal arterial occlusive disease

Aetiology

Atherosclerosis-related thrombosis

Atherosclerosis-related thrombosis at the level of the lamina cribrosa is by far the most common underlying cause of central retinal artery occlusion (CRAO), accounting for about 80% of cases. Atherosclerosis is characterized by focal intimal thickening comprising cells of smooth muscle origin, connective tissue and lipid-containing foam cells (Fig. 13.39). The incidence of atherosclerosis increases with age and is accelerated by hypertension, hyperlipidaemia, diabetes, oral contraceptives and hyperhomocysteinaemia. Other risk factors include obesity, tobacco smoking and a sedentary lifestyle.

Fig. 13.39 Atherosclerosis – the arterial lumen is narrowed by lipid-containing cells within the intima

(Courtesy of J Harry and G Misson, from Clinical Ophthalmic Pathology, Butterworth-Heinemann 2001)

Carotid embolism

Embolism is another key cause of retinal arterial compromise, including transient ischaemia. The origin of emboli is most commonly an atheromatous plaque at the carotid bifurcation, and less often the aortic arch and elsewhere. Since the ophthalmic artery is the first branch of the internal carotid artery, embolic material from the heart and carotid arteries has a fairly direct route to the eye. Carotid stenosis involves atheromatous narrowing, often associated with ulceration, at the bifurcation of the common carotid artery. The irregularity of the vessel wall may act as a source of cerebral and retinal emboli of the following types:

1Cholesterol emboli (Hollenhorst plaques) appear as intermittent showers of minute, bright, refractile, golden to yellow-orange crystals, often located at arteriolar bifurcations (Fig. 13.40A). They rarely cause significant obstruction to the retinal arterioles and are frequently asymptomatic.

2Calcific emboli may originate from atheromatous plaques in the ascending aorta or carotid arteries, as well as from calcified heart valves. They are usually single, white, non-scintillating and often on or close to the disc (Fig. 13.40B). When located on the disc itself, they may be easily overlooked as they tend to merge with the disc. They may cause permanent occlusion of the central retinal artery or one of its main branches.

3Fibrin-platelet emboli are dull grey, elongated particles which are usually multiple (Fig. 13.40C) and occasionally fill the entire lumen (Fig. 13.40D). They may cause a retinal transient ischaemic attack (TIA), with resultant amaurosis fugax, and occasionally complete obstruction.

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Fig. 13.40 Emboli arising fromthe carotid bifurcation. (A) Hollenhorst plaque; (B) calcific embolus at the disc; (C) fibrin-platelet emboli; (D) fibrin-platelet emboli extending fromthe disc to involve three branches

(Courtesy of L Merin – fig. A; C Barry – fig. B)

Uncommon causes

1Giant cell (temporal) arteritis (GCA) is a common cause of anterior ischaemic optic neuropathy but isolated CRAO is rare.

2Cardiac embolism from the heart and its valves may consist of calcific material, vegetations in bacterial endocarditis, thrombus from the left side of the heart and rarely myxomatous material from an atrial myxoma.

3Periarteritis associated with dermatomyositis, systemic lupus erythematosus, polyarteritis nodosa, Wegener granulomatosis and Behçet syndrome may occasionally be responsible for branch retinal artery occlusion (BRAO), which may be multiple and bilateral (Fig. 13.41A and B).

4Thrombophilic disorders that may be associated with retinal artery occlusion, especially in younger individuals, include hyperhomocysteinaemia, antiphospholipid antibody syndrome and inherited defects of natural anticoagulants.

5Sickling haemoglobinopathies.

6Retinal migraine may very rarely be responsible for retinal artery occlusion in young individuals. However, the diagnosis should be made only after other more common causes have been excluded.

7Susac syndrome (retinocochleocerebral vasculopathy) is a microangiopathy characterized by the triad of retinal artery occlusion, sensorineural deafness and encephalopathy.

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Fig. 13.41 (A) and (B) Multiple bilateral branch retinal artery occlusions in polyarteritis nodosa

Systemic assessment

All patients

Many patients will have a history of vascular disease; enquiry should be made about smoking.

1Symptoms of GCA such as headache, jaw claudication, scalp tenderness, limb girdle pain, weight loss and existing polymyalgia rheumatica (see Ch. 19).

2 Pulse, particularly to detect atrial fibrillation.

3Blood pressure.

4 Cardiac auscultation.

5Carotid examination.

aPalpation of severe or complete stenosis is associated with a diminished or absent carotid pulse.

bAuscultation over a partial stenosis gives rise to a bruit, best detected with the bell of the stethoscope. It is important to perform auscultation along the entire length of the artery and to ask the patient to hold his breath. The most ominous bruit is one that is high-pitched and soft because it indicates tight stenosis. When the lumen is narrowed by 90% or more, the bruit disappears.

6ECG to detect arrhythmia and other cardiac disease.

7 Erythrocyte sedimentation rate and C-reactive protein to detect the remote possibility of GCA.

8Other blood tests include FBC, random glucose, lipids, urea and electrolytes.

9Carotid duplex scanning is a non-invasive screening test involving a combination of high-resolution real-time ultrasonography with Doppler flow analysis. If significant stenosis is present, surgical management may be considered.

Selected patients

The following additional tests can be considered on a targeted basis in some patients, particularly if younger and with no known cardiovascular risk factors.

1Further carotid imaging (see Ch. 19)

2Cranial MRI or CT may be indicated to rule out intracranial or orbital pathology; may be required prior to fibrinolysis.

3Echocardiography. Usually performed if there is a specific indication such as a history of rheumatoid fever, known cardiac valvular disease, or intravenous drug use.

4 Chest X-ray. Sarcoidosis, tuberculosis, left ventricular hypertrophy in hypertension. 5 24-hour ECG (Holter monitor) to exclude intermittent arrhythmia.

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6Additional blood tests

aFasting plasma homocysteine level to exclude hyperhomocysteinaemia.

b'Thrombophilia screen’. By convention refers to heritable thrombophilias, which have predominantly been implicated in venous rather than arterial thromboses.

cPlasma protein electrophoresis to detect dysproteinaemias such as multiple myeloma.

d Thyroid function tests, especially if atrial fibrillation is present; may be associated with dyslipidaemia. e Autoantibodies. Rheumatoid factor, anti-nuclear antibody, anti-DNA antibody.

fBlood cultures.

Amaurosis fugax

Amaurosis fugax is characterized by painless transient monocular loss of vision, often described as a curtain coming down over the eye, usually from top to bottom, but occasionally vice versa; it is common for patients to be unaware of whether transient unilateral visual loss affects one eye or the ipsilateral hemifield (cerebral ischaemia) of both. Visual loss, which may be complete, usually lasts a few minutes.

Recovery is in the same pattern as the initial loss, although usually more gradual. Frequency of attacks may vary from several times a day to once every few months. The attacks may sometimes be accompanied by ipsilateral cerebral TIA, with contralateral neurological features. Investigation and systemic management is carried out as for persistent arterial occlusion.

Branch retinal artery occlusion

Diagnosis

1Presentation is with sudden and profound painless altitudinal or sectoral visual field loss. It can sometimes go unnoticed, particularly if central vision is spared.

2VA is variable.

3RAPD is often present.

4Fundus (Fig. 13.42 and 13.43).

•Narrowing (attenuation) of arteries and veins with sludging and segmentation of the blood column (‘cattle trucking’/’boxcarring’).

•Cloudy white oedematous (‘ground glass’) retina corresponding to the area of ischaemia.

•One or more emboli may be seen, especially at bifurcation points including the point of occlusion.

•Signs may sometimes be subtle.

5FA shows delay in arterial filling and hypofluorescence of the involved segment due to blockage of background fluorescence by retinal swelling (Fig. 13.43B).

Fig. 13.42 Embolic inferotemporal branch retinal artery occlusion

(Courtesy of P Gili)

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Fig. 13.43 (A) Superior branch retinal artery occlusion due an embolus at the disc; (B) FA shows lack of arterial filling of the involved artery and hypofluorescence of the involved segment due to blockage of background fluorescence by retinal swelling

(Courtesy of C Barry)

Follow-up

A single follow-up assessment in 3 months may be warranted to review the appearance of the fundus and provide advice on prognosis. This also provides an opportunity for a systemic management review, to ensure care by an appropriate specialist team was implemented.

Prognosis

In patients where central vision is severely compromised, the prognosis is commonly poor unless the obstruction is relieved within a few hours (see below). The visual field defect is likely to be permanent and the affected artery remains attenuated. Occasionally, recanalization of the obstructed artery may leave subtle or absent ophthalmoscopic signs.

Central retinal artery occlusion

Diagnosis

1Presentation is with sudden and profound loss of vision, painless except in GCA.

2VA is severely reduced except when a portion of the papillomacular bundle is supplied by a cilioretinal artery, when central vision may be preserved. No perception of light usually indicates either GCA, or ophthalmic artery occlusion affecting both the retinal and choroidal circulation.

3 RAPD is profound, sometimes total (amaurotic pupil).

4Fundus shows similar changes to BRAO but more extensive (Fig. 13.44).

•The orange reflex from the intact choroid stands out at the thin foveola, in contrast to the surrounding pale retina, giving rise to the ‘cherry-red spot’ appearance.

•The peripapillary retina may appear especially swollen and opaque

•An occasional small haemorrhage is not unusual.

•Emboli are visible in 20%, when Nd:YAG embolysis may be considered.

•In eyes with a cilioretinal artery part of the macula will remain of normal colour (Fig. 13.45A).

•Retinal signs can sometimes be subtle; note that retinal oedema may take several hours to develop.

5FA shows delay in arterial filling and masking of background choroidal fluorescence by retinal swelling. However, a patent cilioretinal artery will fill during the early phase (Fig. 13.45B).

6Electroretinography may be helpful to establish the diagnosis if in doubt, particularly to distinguish from optic nerve disease, typically when signs are subtle; a diminished b-wave is present.

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Fig. 13.44 Recent central retinal artery occlusion with a ‘cherry-red’ spot at the macula

(Courtesy of L Merin)

Fig. 13.45 (A) Central retinal artery occlusion with a patent cilioretinal artery; (B) FA shows blockage of background fluorescence by retinal swelling but normal perfusion at the posterior pole

(Courtesy of L Merin)

Follow-up

The patient should be seen by an ophthalmologist in 3–4 weeks and again a month later in order to detect incipient neovascularization, particularly of the anterior segment. In the minority of cases where referral to a specialist vascular team is not indicated, it should be ensured that the results of systemic investigations have been reviewed and necessary systemic treatment initiated.

Prognosis

The prognosis is poor due to retinal infarction. Over a few days to weeks the retinal cloudiness and ‘cherry-red spot’ gradually disappear although the arteries remain attenuated. Later signs include optic atrophy (Fig. 13.46A), vessel sheathing, and patchy inner retinal atrophy and RPE changes. Histology shows atrophy of the inner retina and ganglion cells (Fig. 13.46B). Rubeosis iridis may occur in up to about 1 in 5, typically earlier than in CRVO (4–5 weeks compared with 3 months), and along with very poor vision may indicate ophthalmic artery

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occlusion. About 2% of eyes with CRAO develop retinal or disc neovascularization. PRP should be performed as for ischaemic CRVO, and intravitreal injection of vascular endothelial growth factor (VEGF) inhibitor might be considered.

Fig. 13.46 Old central retinal artery occlusion. (A) Vascular attenuation and optic atrophy; (B) histology shows atrophy of the inner retina and ganglion cells with preservation of a few bipolar cells

(Courtesy of J Harry – fig. B)

Cilioretinal artery occlusion

A cilioretinal artery, present in 20% of the population, arises from the posterior ciliary circulation but supplies the retina, commonly in the area of the macula and papillomacular bundle.

1 Isolated (Fig. 13.47A) typically affects young patients with an associated systemic vasculitis.

2Combined with CRVO (Fig. 13.47B) has a similar prognosis to non-ischaemic CRVO.

3Combined with anterior ischaemic optic neuropathy (Fig. 13.47C) typically affects patients with giant cell arteritis and carries a very poor prognosis.

4Presentation is with acute severe loss of central vision.

5 Signs. Cloudiness localized to that part of the retina normally perfused by the vessel. 6 FA shows a corresponding filling defect (Fig. 13.47D).

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Fig. 13.47 Cilioretinal artery occlusion. (A) Isolated; (B) combined with central retinal vein occlusion; (C) combined with anterior ischaemic optic neuropathy; (D) FA shows hypofluorescence at the macula due to lack of filling and masking by retinal swelling

(Courtesy of S Milewski – fig. D)

Treatment of acute retinal artery occlusion

Retinal artery occlusion is an emergency because it causes irreversible visual loss unless the retinal circulation is re-established prior to the development of retinal infarction. It appears that the prognosis for occlusions caused by calcific emboli is worse than those resulting from either cholesterol or platelet emboli. Theoretically, timely dislodgement of thrombus or emboli may ameliorate subsequent visual loss. The following treatments may be tried in patients with occlusions of less than 24–48 hours duration at presentation, though evidence of benefit is limited. The number of measures tried and the intensity of treatment should be tailored to the individual (more aggressive if lower duration of occlusion, good general health, monocularity; more aggressive systemic treatment may be avoided in the frail elderly); options, including the lack of evidence for clear benefit and the risks, should be discussed before use.

1Adoption of a supine posture might improve ocular perfusion.

2Ocular massage using a three-mirror contact lens (allows direct artery visualization) for approximately 10 seconds, aiming to achieve central retinal artery pulsation or cessation of flow (for BRAO), followed by 5 seconds of release. The aim is to mechanically collapse the arterial lumen and cause prompt changes in arterial flow. Self-massage through closed eyelids can be continued by the patient.

3Anterior chamber paracentesis should be carried out in most cases. Instil povidone-iodine 5% and topical antibiotic prior to the procedure and a short course of antibiotic afterwards.

4Topical apraclonidine 1%, timolol 0.5%and intravenous acetazolamide 500 mg to achieve a more sustained lowering of intraocular pressure.

5Sublingual isosorbide dinitrate to induce vasodilation.

6‘Rebreathing’ into a paper bag in order to elevate blood carbon dioxide and respiratory acidosis has been advocated, as this may promote vasodilation.

7Breathing a high oxygen (95%) and carbon dioxide (5%) mixture, ‘carbogen’, has been advocated for a possible dual effect of retarding ischaemia and vasodilation.

8Hyperosmotic agents. Mannitol or glycerol have been used for their possibly more rapid IOP-lowering effect as well as increased intravascular volume.

9Transluminal Nd:YAG laser embolysis has been advocated for BRAO or CRAO in which an occluding embolus is visible; shots of 0.5–1.0 mJ or higher are applied directly to the embolus using a fundus contact lens. Embolectomy has been said to occur if the embolus is ejected into the vitreous via a hole in the arteriole. The main complication is vitreous haemorrhage.

10Thrombolysis. Extrapolating from successful treatment of stroke and myocardial infarction, various strategies have been used to deliver thrombolytic agents to the ophthalmic artery, including local arterial (internal carotid and ophthalmic) and intravenous infusion. Many studies suggest that this may improve the visual outcomes in CRAO, with a low risk of serious complications. However, no benefit over conservative treatment has been conclusively demonstrated, though there is evidence that improvement is more likely if commenced within the first 6 hours of presentation.

Systemic prophylaxis following retinal arterial occlusion

The risk of stroke is relatively high in the first few days following retinal artery occlusion or amaurosis fugax, and ‘fast-track’ referral to a specialist stroke clinic is advisable.

1General risk factors as discussed above should be addressed and smoking should be discontinued. Urgent referral to an appropriate physician is mandatory for significant cardiac arrhythmia.

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2Antiplatelet therapy is commenced provided there are no contraindications; an immediate loading dose of 600 mg may be given; alternative/additional agents include dipyridamole and clopidogrel. If fibrinolysis (see above) is being considered, this should be discussed with a physician prior to starting antiplatelet treatment.

3 Oral anticoagulation (e.g. warfarin) may be prescribed for some patients, particularly those with atrial fibrillation.

4Carotid endarterectomy may be indicated in patients with symptomatic stenosis greater than 70%.

Asymptomatic retinal embolus

It is not uncommon to identify a retinal embolus on routine examination of an asymptomatic older patient. This indicates a substantially increased risk of stroke and ischaemic heart disease, and management should consist of evaluation and treatment of risk factors discussed above. A higher threshold for carotid surgery is appropriate.

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