Ординатура / Офтальмология / Учебные материалы / Retinal Vascular Disease Joussen Springer

21.4.3.3.5 Retinal Arteriole Occlusion

Occlusion of the small retinal arterioles by microemboli can occur in a number of situations resulting in a characteristic clinical phenotype called Purtscher’s retinopathy. Please refer to Chapter 24.1 for full details on this entity. The obstructions result in large patches of retinal whitening and some hemorrhage, usually centered on the optic disk. The condition is invariably bilateral and results in marked visual impairment. Talc retinopathy may develop following the repeated intravenous injection of crushed tablets. Multiple intra-arteriole emboli may be seen at the macula resulting in ischemic retinal changes.

21.4.4 Differential Diagnosis

The differential diagnosis of a CRAO is listed in Box 7 and that for BRAO is listed in Box 8. In addition to CRAO, a cherry red spot of the macula has a number of causes (Box 9). These are mostly congenital metabolic disorders, affecting both eyes from a young age.

Box 7: The differential diagnosis of central retinal artery occlusion

Ophthalmic artery occlusion Multiple BRAO

Commotio retinae (Berlin’s edema) Macula hole

Acute retinal necrosis

Box 8: The differential diagnosis of branch retinal artery occlusion

CRAO

Cilioretinal artery occlusion Myelinated nerve fibers Acute retinal necrosis

Box 9: Causes of a cherry red spot at the macula

Central retinal artery occlusion Tay-Sachs disease

Sandhoff disease Niemann-Pick disease

Sialidosis Type 1 (Goldberg syndrome) Gangliosidosis GM1

Farber’s disease

21.4.5 Systemic Clinical Assessment

A systemic clinical assessment is necessary in cases of retinal arterial occlusion, as this may be the first presentation of a potentially serious medical condition [2, 58]. It is important to identify underlying medical conditions, which may be amenable to treatment to reduce the risk of further ocular or systemic morbidity. It is usually appropriate to refer patients with retinal arterial occlusion to a general physician for this medical assessment. A focused history should be taken to ascertain vascular risk factors such as those listed in Box 10. A general physical examination should be conducted for relevant clinical signs (Box 11).

Box 10: History relevant to retinal arterial occlusion

History of cerebrovascular disease History of ischemic heart disease Hypertension

Diabetes Smoking history

Hypercholesterolemia

Family history of vascular disease Symptoms of temporal arteritis Thrombophilia (personal or family history) Drug use (e.g., cocaine)

Trauma

Migraine

Box 11: Clinical examination of a patient with retinal arterial occlusion

Peripheral pulses – cardiac rhythm and presence of pulses Blood pressure

Auscultation of carotid arteries for bruits Cardiac auscultation for murmurs

Signs of temporal arteritis Signs of infective endocarditis

Neurological signs of cerebrovascular disease

21.4.6 Investigations

A wide range of different ancillary investigations have been used in the context of retinal arterial occlusions to both confirm the diagnosis and to identify any underlying cause. The choice of tests needs to be tailored to the individual patient, guided by the history and clinical examination [62].

21.4.6.1Investigations to Confirm the Diagnosis of Retinal Arterial Occlusion

21.4.6.1.1 Fluorescein Angiography

In cases of CRAO there is a marked delay in the transit time from the arm to the retina [25]. Often the

front edge of the fluorescein is seen slowly progressing along the branch arteries. The arteriovenous transit time is prolonged. The choroid fills normally. In BRAO there is no fluorescein beyond the point of occlusion while other unaffected branches fill normally. In some cases of BRAO retrograde filling of the occluded vessel can be seen from adjacent vessels

[59]. If there is occlusion of the ophthalmic artery in III 21 addition to poor perfusion of the retinal vessels there

is reduced choroidal perfusion.

21.4.6.1.2 Visual Fields

In BRAO there is usually an altitudinal visual field defect corresponding to the affected portion of the retina [68]. Visual field testing is rarely attempted in cases of CRAO, although some have reported preservation of temporal peripheral vision.

21.4.6.1.3 Doppler Ultrasound

Colour Doppler ultrasonography allows the determination of blood flow direction and velocity [74]. It has been used to measure the blood flow in the ophthalmic artery, central retinal artery and short posterior ciliary arteries. In cases of CRAO occlusion there is reduced flow in the CRA while that in the short posterior ciliary arteries is maintained [73].

21.4.6.1.4 Electroretinography

Electroretinograms (ERG) from eyes with CRAO usually have an intact a-wave (derived from the photoreceptors) and a reduction or loss of the b-wave (from Müller and bipolar cells) [78]. In cases of BRAO multifocal ERG find similar abnormalities in the area of retina affected. In ophthalmic artery occlusion there is absence of both a- and b-waves [14].

21.4.6.2Investigations of the Cause of Retinal Arterial Occlusion

21.4.6.2.1 Hematological Investigations

As many systemic conditions have been associated with retinal arterial occlusion numerous different blood tests could be requested (Box 12). However, a focused, stepwise approach is recommended. All patients should be tested for hyperglycemia and hyperlipidemia. In patients older than 50 years the ESR and CRP are measured as part of the evaluation for temporal arteritis. In younger patients and in older patients for whom no underlying cause for retinal arterial occlusion is initially found, various additional tests should be considered (Box 12).

Box 12: Hematological investigation of retinal arterial occlusion

All patients:

Glucose Lipid profile

Older patients:

Erythrocyte sedimentation rate (ESR)

III C-reactive protein (CRP)

21

Additional tests (young or second line):

Full blood count Clotting screen

Thrombophilia screen (see Box 4) Homocysteine

Plasma electrophoresis Hemoglobin electrophoresis Auto-antibody screen

Anti-phospholipid antibodies Anti-nuclear antibodies (ANA)

Anti-neutrophil cytoplasmic antibodies (ANCA) Infection screen

Toxoplasma gondii serology

Bartonella henselae serology (Cat-scratch disease) Borrelia burgdorferi serology (Lyme disease)

21.4.6.2.2 Carotid Artery Assessment

The carotid arteries can be assessed in a number of ways: Doppler ultrasonography, magnetic resonance angiography and selective contrast angiography. Carotid ultrasonography is usually the first line investigation. It is non-invasive and provides information about the extracranial portion of the carotid artery. Among individuals with symptomatic retinal arterial occlusion, 19 % had a significant carotid artery occlusion [64]. However, the presence of a visible embolus on retinal examination is a poor predictor of significant carotid stenosis [64]. Therefore, all adults with retinal arterial occlusion should have an ultrasound scan of the carotid arteries regardless of whether there is a visible embolus.

21.4.6.2.3 Cardiac Assessment

Patients are often referred to a physician for a cardiac assessment, which may involve various investigations. An electrocardiogram (ECG) is performed to screen for ischemic heart disease. A 24-h ambulatory ECG recording is made if arrhythmias are suspected. Transthoracic echocardiography is advised for all young patients and any with “high-risk” features [62, 66]. “High-risk” features include a history of myocardial infarction, rheumatic fever, valve disease, bacterial endocarditis or a cardiac murmur on auscultation. Transesophageal echocardiography may sometimes identify cardiac embolic sources not seen by transthoracic echocardiography [42].

21.4.7 Pathology

Animal models of central retinal artery occlusion have shown that irreversible damage of the retina develops after 100 min [34]. There is initially intracellular edema in the inner retina. Subsequently, necrosis of the inner retina develops with loss of the normal cellular architecture. Photoreceptors survive as they continue to receive nourishment from the choroidal circulation.

21.4.8 Management

The management of acute retinal arterial occlusion is difficult and the outcomes are often disappointing. There are no proven treatments. This is because retinal arterial occlusions are relatively rare events, so studies have been either retrospective or small case series without a randomly allocated control group.

Several different therapeutic maneuvers are advocated [47]. The aim of the treatment is to restore the retinal blood supply as soon as possible, increase oxygen delivery to the retina or limit the damage from hypoxia. Some of the interventions are simple and non-invasive while others are invasive, complex and have potentially serious side effects. For treatment to have any prospect of success it must be started immediately as irreversible visual loss develops after 100 min. If a patient with a CRAO presents within 24 h, most clinicians would attempt several of the non-invasive treatments described below. In some ophthalmic centers if a CRAO is diagnosed within a few hours of onset more invasive treatments may be performed. As the visual outcome for BRAO is relatively good invasive treatment is not indicated, although some clinicians would attempt to dislodge an embolus by ocular massage or a paracentesis.

21.4.8.1 Lie Patient Flat

Lie the patient flat to try to increase retinal perfusion pressure.

21.4.8.2 Ocular Massage

Ocular massage has been reported to occasionally help to dislodge an embolus [56]. Pressure is applied to the globe (through the eyelid or via a three-mirror contact lens) for 10 s and then suddenly released. This cycle is repeated for up to 15 min.

21.4.8.3 Anterior Chamber Paracentesis

Anterior chamber paracentesis is performed to rapidly reduce the intraocular pressure. The procedure is outlined in Box 13. Anecdotally this has been

reported to help dislodge emboli. However, a retrospective review of paracentesis combined with carbogen treatment did not demonstrate any benefit [5]. Postparacentesis endophthalmitis has been reported.

Box 13: How to perform an anterior chamber paracentesis

Anesthetize the ocular surface with topical anesthetic Instil a drop of povidone iodine 5 % into the conjunctiva to

reduce bacterial contamination

Support the eyelids with an eyelid speculum

Perform the paracentesis at the slit lamp or under an operating microscope

Use a tuberculin syringe with a 30-gauge needle to perform the paracentesis. Remove the plunger

The needle should enter the eye through the temporal limbus, ensuring that the tip remains over the iris at all times

Allow 0.2 ml of aqueous fluid to drain and then withdraw the needle

Instil a drop of antibiotic after the procedure

21.4.8.4Pharmacological Reduction of Intraocular Pressure

Drugs to lower the intraocular pressure are given to try to augment the effect of massage or anterior chamber paracentesis in the hope of dislodging an embolus and improving the retinal perfusion (Box 14). Care should be taken to ascertain that the patient does not have a contraindication to any drug used.

Box 14: Drugs used to lower intraocular pressure in CRAO

Acetazolamide 500 mg i.v. or orally Topical -blocker (e.g., timolol) Topical apraclonidine

Mannitol i.v.

21.4.8.5 Pharmacological Vasodilatation

Improved retinal blood flow may be achieved by vasodilatation of the vessels [47]. A number of drugs have been tried: pentoxifylline, glyceryl trinitrate and -blockers. In one small study pentoxifylline was found to improve blood flow but not visual outcome [36].

21.4.8.6 Carbogen

Carbogen is a combination of carbon dioxide (5 %) and oxygen (95 %). It is used in some ophthalmic centers because it is thought that the carbon dioxide promotes dilation of the arterioles and the high concentration of inspired oxygen improves the oxygenation of ischemic retina. However, this effect is questionable, as vasodilatation was not found in healthy volunteers [26]. A retrospective study of carbogen

and paracentesis did not find an improved outcome

[5].It is used for 10 min every 2 h for the first 2 days.

21.4.8.7Hyperbaric Oxygen

Hyperbaric oxygen therapy produces a marked increase in the arterial oxygen tension. This results

in an increase in the diffusion distance of oxygen III 21 from the choroid into the retina. This may be enough

to sustain the retina until there is a spontaneous recanalization of the retinal artery. The patient is placed in 100 % oxygen at 2.8 atmospheres absolute (ATA) for 90 min twice a day for 3 days and then once daily thereafter [8]. The treatment needs to be commenced within 8 h of the onset of the CRAO to be effective. In the largest retrospective study 83 % of patients treated in hyperbaric oxygen had an improvement of three or more lines of Snellen acuity compared to 30 % in those not treated with hyperbaric oxygen [8].

21.4.8.8 Steroids for Temporal Arteritis

If temporal arteritis is thought to be the cause of the retinal arterial occlusion, high-dose systemic corticosteroid treatment is indicated. Treatment schedules vary and need to be adjusted to the patient. An initial adult dose of 60 – 80 mg of oral prednisolone is usually used for several days. The dose is gradually reduced in line with improvement in symptoms and inflammatory markers (ESR and CRP). Intravenous methylprednisolone is sometimes used for the initial treatment followed by oral prednisolone. Patients need to be counselled about potential side effects and monitored for these during the course of the treatment. The patient is usually referred to a physician for the management of steroid treatment.

21.4.8.9 Thrombolysis

Thrombolysis has been used to treat both CRAO and BRAO. It has been delivered either directly into the ophthalmic artery via selective catheterization from the femoral artery [3, 60] or peripherally through an intravenous cannula [69]. Currently, the only data available are retrospective case series, some of which have found better outcomes among patients treated with thrombolysis [3, 60]. However, a metaanalysis of published studies found the effect to be only marginal [7]. These procedures can be complicated by stokes or hemorrhages. There are also major challenges in delivering the treatment within a time-frame for it to be effective. There is a need for a prospective randomized controlled trial to evaluate the role of thrombolysis in retinal arterial occlusion.

21.4.8.10 Secondary Prevention

The clinical assessment and investigations described above may identify underlying medical problems that require ongoing treatment by a physician. Effective treatment of these may reduce the risk of repeat vascular occlusion in the same or in the fellow eye, as

21 III well as preventing other co-morbidity such as a stroke. This will involve the control of hypertension, diabetes and hypercholesterolemia if present. The use of aspirin or warfarin may be indicated. Some patients with carotid artery disease may meet the criteria for consideration for carotid endarterectomy surgery.

21.4.9 Outcome and Follow-up

The prognosis for vision following a retinal arterial occlusion depends on the location and duration of the occlusion. Ophthalmic artery obstruction usually results in no perception of light [14]. In cases of CRAO about 10 % of cases may show some improvement in vision; however, the vast majority will have a final visual acuity of counting fingers or worse [5, 13]. The prognosis for BRAO is much better with 80 % having a final visual acuity of 6/12 or better [79].

Follow-up of patients with retinal vascular occlusion is important. Iris neovascularization (NVI) is common (18 %) in CRAO but rare in BRAO. The onset of neovascularization has been documented to occur between 12 days and 15 weeks after the CRAO [30]. Panretinal photocoagulation is reported to be effective promoting regression of the NVI and preventing neovascular glaucoma [29].

References

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Core Messages

Secondary to severe carotid artery disease, described as “venous stasis retinopathy,” now mostly named as “ocular ischemic syndrome“ Symptoms: abrupt or gradual loss of vision, dull aching pain, amaurosis fugax (15 %)

Kearns and Hollenhorst [23] described the ocular symptoms and signs occurring secondary to severe carotid artery obstructive disease in 1963 [23]. They named the entity “venous stasis retinopathy” and noted it was present in approximately 5 % of patients with marked carotid artery insufficiency. Confusion has arisen using this term since it has also been used to refer to mild central retinal vein obstruction [17]. Other alternative names have been proposed, including ischemic ocular inflammation [24], ischemic coagulopathy [41], and the ocular ischemic syndrome [6, 7]. Histopathology of eyes with the disease generally does not reveal inflammation [20, 30], and thus the descriptive term we prefer is ocular ischemic syndrome.

The pathophysiologic, demographic, and clinical features of the ocular ischemic syndrome will be addressed. Ancillary diagnostic studies will be discussed, as will systemic abnormalities associated with the ocular ischemic syndrome, therapeutic modalities and the differential diagnosis.

21.5.1 Pathophysiology

Signs: iris neovascularization, narrowed arteries, dilated veins, microaneurysms, neovascularization of the retina

Therapy: panretinal photocoagulation (iris neovascularization), endarterectomy, aspirin (if carotid stenosis is < 70 %)

Typically, a 90 % or greater stenosis of the ipsilateral carotid arterial system is present in eyes with the ocular ischemic syndrome [6]. Flow abnormalities within the vessel are seen when the stenosis reaches 70 %, and it has been demonstrated that a 90 % carotid stenosis reduces the ipsilateral central retinal artery perfusion pressure by about 50 % [22, 25]. The obstruction can be present within the common carotid or internal carotid artery (Figs. 21.5.1, 21.5.2). In approximately 50 % of cases the affected vessel is 100 % obstructed and in 10 % of cases there is bilateral 100 % carotid artery obstruction [6].

In select cases, obstruction of the ipsilateral ophthalmic artery can also be responsible for the ocular ischemic syndrome [6, 8, 26]. Rarely, a chronic central retinal artery obstruction alone can cause the dilated retinal veins and retinal hemorrhages seen in eyes with the ocular ischemic syndrome [27].

Atherosclerosis within the carotid artery is the cause of the majority of the ocular ischemic syndrome cases [6]. Dissecting aneurysm of the carotid artery has also been reported [13], as has giant cell arteritis [16]. In theory, entities such as Beh¸cet’s disease [11], fibromuscular dysplasia [14, 28], trauma [34], and inflammatory diseases that cause carotid artery ob-

21 III struction could also produce the ocular ischemic syndrome.

21.5.2 Demography

The demographic features associated with the ocular ischemic syndrome are listed below:

Gender – male : female ratio is 2 : 1 [6]

Age range – 50’s to the 80’s [6]

Mean age – 65 years [6]

Bilaterality – 20 % [6]

Incidence – 7.5 cases/year/million population [38]

No ethnic predilection

21.5.3 Clinical Features

The clinical features and their associated frequencies of occurrence are shown below. In instances in which the incidence is uncertain, none is given.

Fluorescein angiography can demonstrate iris neovascularization (Fig. 21.5.5)

Flare – 50 %+ (most cases with iris neovascularization) Cells – 18 %, no greater than 2+ on a 0 – 4+ classification [35]

Posterior segment (Figs. 21.5.7 – 21.5.18) [6]

Narrowed retinal arteries – 90 % (Figs. 21.5.7, 21.5.9) Dilated (not tortuous) retinal veins – 90 % (Figs. 21.5.7,

21.5.9)

Retinal hemorrhages – 80 % (Fig. 21.5.8) Microaneurysms – 80 % (Fig. 21.5.12) Neovascularization of the optic disk – 35 % (Fig. 21.5.13)

Macular edema [5] – 14 % – often with less thickening clinically than evident with fluorescein angiography due to diminished retinal arterial perfusion pressure

(Fig. 21.5.17)

Cherry red spot – 12 % – usually develops when neovascular glaucoma causes the intraocular pressure to exceed that in the central retinal artery

Neovascularization of the retina – 8 % (Fig. 21.5.14) Cotton-wool spots – 6 %

Vitreous hemorrhage – 4 %

Spontaneous retinal arterial pulsations – 4 % Retinal emboli (cholesterol) – 2 %

Anterior ischemic optic neuropathy [4] – 2 % Acquired retinal arteriovenous communications [2]

A. Symptoms

Abrupt loss of vision – 12 % [6]

Often associated with a cherry red spot and iris neovascularization as the intraocular pressure exceeds that within the central retinal artery

Gradual visual loss over days to weeks – 80 % [6]

Ocular or periorbital pain – 40 % [6]

Dull aching pain

Referred to as “ocular angina“

Etiology: ischemia to the globe, increased intraocular pressure and/or ischemia to the ipsilateral meninges

Prolonged visual recovery after exposure to bright light [12, 40]

Amaurosis fugax – 15 % [31]

B. Signs [6]

Vision

Initial vision 20/20 – 20/50: 43 %; 20/800 or worse: 37 % One year 20/20 – 20/50: 24 %: 20/800 or worse: 58 %

Head

Collateral vessels from the external to internal carotid arterial system (Fig. 21.5.3)

Anterior chamber

Iris neovascularization – 67 %

Only half of such eyes develop increased intraocular pressure; poor ciliary body perfusion diminishes aqueous production in the others (Figs. 21.5.4 – 21.5.6)

Fig. 21.5.3. Prominent collateral vessel from the external carotid system on the right side in a patient with a left 100 % common carotid artery obstruction

Fig. 21.5.4. Neovascularization on the brown iris of a patient with the ocular ischemic syndrome

Fig. 21.5.5. Fluorescein angiogram at 86 s after injection discloses hyperfluorescence from iris neovascularization occurring secondary to the ocular ischemic syndrome

Fig. 21.5.6. Gonioscopic view of iris neovascularization (arrow) closing off the anterior chamber angle in an eye with ocular ischemia

III 21

a

b

Fig. 21.5.8. a Mid-peripheral dot and blot retinal hemorrhages in the eye of a patient with the ocular ischemic syndrome (courtesy of Neal Atebara, MD). b. Histopathology of a retinal hemorrhage in an eye with the ocular ischemic syndrome. Blood is present throughout the entire thickness of the retina. (Courtesy of W. Richard Green, MD). H&E, ×40

Fig. 21.5.7. Ocular ischemic syndrome in an eye with a 100 % ipsilateral carotid artery obstruction demonstrates dilated, beaded (but not tortuous) retinal veins, while the retinal arteries are narrowed

Fig. 21.5.9. Ocular ischemic syndrome fundus in a 65-year-old man with a 100 % left internal carotid obstruction. The retinal arteries are very narrowed and the veins dilated. The myelinated nerve fibers at the inferior border of the optic disk are unrelated to the ocular ischemia