Central Retinal Artery Occlusion

By Christiane Haddad, MD

          Central retinal artery occlusive disease (CRAO) is one of the most sudden and dramatic events seen in ophthalmology, though a less frequent chronic form also exists. It remains a disease of poor visual prognosis despite a multitude of studies and experimental trials.

CAUSES

            The most common association is atherosclerosis followed by arterial hypertension. Carotid artery disease occurs in 45%. The difference in etiology depends on age; if  presentation is at less than 30 years, it is more associated with migraine, trauma and coagulation disorders.

I. Embolization

A.     Emboli from the heart can be:

-         calcific, from aortic or mitral valve calcifications

-         vegetations, from bacterial endocarditis

-         thrombi, after myocardial infarction ‘mural thrombi’ and with mitral valve prolapse

-         myxomatous, from atrial myxomas mainly to the left eye

B.     Carotid artery disease: mainly due to atheromatous ulceration at the bifurcation of external and internal carotids. It is usually associated with chronic obstuction. Emboli can be:

-         cholesterol, yellow ‘Hollenhorst plaques’ at arteriolar bifurcations, usually asymptomatic

-         fibrinoplatelet, multiple dull gray emboli causing transient ischemic attacks (amaurosis fugax), with sudden loss of vision for 2 to 10 min. described as a curtain,or complete obstuction     

-         calcific, which are much more dangerous than the previous two because can cause permanent occlusion            

II. Vaso-obliteration

A.     Atherosclerosis, most common cause of CRAO

B.     Periarteritis, with systemic vasculitidies like systemic lupus and polyarteritis nodosa

C.     Hematologic disorders, like antiphospholipid syndrome and protein C and S deficiencies

D.     Retinal migraine, a rare cause, usually a diagnosis of exclusion

PRESENTATION

            Presentation is usually with a sudden painless loss of vision. The onset of obstruction is most often between midnight and 6 am and second most often from 6am to noon. Vision at presentation is usually counting fingers to light perception and often remains so regardless of treatmant. Studies have shown that about 35% get a VA of 20/200 or better and 20% have 20/40 or better. On average, the age range is between the 5^th and 6^th decades.

            The central retinal artery supplies the inner 2/3 rd of the retina, the outer 1/3 rd being supplied by the choroidal circulation. The most common site of obstruction is at the lamina cribrosa. Experiments have shown that the critical time after which irreversible damage occurs is about 90-100 min.

CLINICAL SIGNS

        -    Afferent pupillary defect (APD) or Marcus Gunn pupil

-         The retina appears white because of intracellular edema except at the fovea where it is thin and the choroid shows giving a ‘cherry red spot,’ but this is not a pathognomonic sign. In animal models, it was seen as early as 30 min after obstruction.

-         Narrowing and irregularities of the arterioles and venules

-         In 1/5^th of patients, a portion of the papillomacular bundle is supplied by a cilioretinal arteriole from the ciliary circulation. This may preserve central vision.

-         In few weeks, the white retina and cherry red spot disappear, optic atrophy occurs, foveal light reflect is absent, and arterial collaterals can develop.

-         Fluorescein angiography shows a marked delay in filling of the CRA and masfing of the choroidal hyperfluorescence. Venous filling is also slowed.

-         Visual field defects are usually profound, sometimes sparing a small portion of the temporal visual field.

BRANCH RETINAL ARTERY OCCLUSION

            It is caused mostly by emboli and gives altitudinal visual field defects. The retina appears white in the area of supply of the artery. Recanalization may leave only subtle changes on exam.

CILIORETINAL ARTERY OCCLUSION

            This artey is present in about 30% of people, arising from the posterior ciliary circulation. Obstuction causes retinal pallor in the posterior pole and maybe:

-         isolated, at young age associated  with systemic vasculitis and good prognosis

-         with CRVO, also at young age; prognosis is as with non-ischemic CRVO.

-         with anterior ischemic optic neuropathy, usually in the elderly with giant cell arteritis and poor prognosis

OPHTHALMIC ARTERY OCCLUSION

            It can be due to systemic cardiovascular diseases as CRAO or to local factors such as retrobulbar anesthesia or orbital disorders. Presentation is with a total APD, bare or no light perception, intense retinal whitening +/- cherry red spot and marked defects of retinal and choroidal perfusion on fluorescein angiography.

CHRONIC ARTERIAL OBSTRUCTION

            It is usually due to carotid artery disease, mainly atherosclerosis causing amaurosis fugax as described above and ocular ischemia syndromes ( unilateral retinopathy with cotton wool spots, dilatded artries and veins, sometimes dot and blot hemorrhages and microaneurysms). It can also be caused by emboli as mentioned above.

TREATMENT OF CRAO

            Results of treatment remain unsatisfactory. The goal is to restore blood flow as soon as possible in all cases seen within 48 hours. This includes the following:

-         supine position, helps maintain circulation

-         ocular massage, intermittently for at least 15 min, to increase blood flow, decrease intraocular pressure(IOP) and possibly dislodge emboli

-         decrease IOP, may perfuse the retina better and dislodge emboli. IV acetazolamide and topical beta blockers are used and sometimes anterior chamber paracentesis if needed.

-         ventilation with 100% oxygen was used before but not any more because of vasoconstriction. Combination of carbon dioxide and oxygen was also tried to supply enough oxygen to the choroidal circulation to reach the inner retina, but it was also found to be toxic to the retina.

-         vasodilators in the retrobulbar space can be given but not used to avoid hemorrhage

-         surgical cannulation of the supraorbital artery and perfusion with heparin, papaverine or streptokinase was used in trials

-         IV rt-PA was also used with variable results

-         Experimental studies: ice packs and IV dextromethorphan

The most serious complication of CRAO is neovascularization and the development of neovascular glaucoma which occurs in about 16% of patients and warrants treatment.

    Presence of cholesterol or fibrinoplatelet emboli points to atheromatous disease and the cardiovascular system should be evaluated. The two main lesions in the carotid arteries are atheromatous ulceration and stenosis. Investigation includes: palpation for a weak carotid pulse, auscultation for a carotid bruit, ophthalmodynamometry (by external pressure on the sclera and observation of the retinal artery pulsation), Duplex scanning, digital IV subtraction angiography, MRA, intra-arterial angiography (but high morbidity) and screening for risk factors (hypertension, diabetes, hypercholesterolemia, smoking and hypercoagulable states). Treatment of carotid disease includes: antiplatelet therapy (aspirin, aspirin+dipyridamole and clopidogrel), anticoagulation if necessary and carotid endarterectomy (mainly for symptomatic carotid artery stenosis >70% with other risk factors for stroke).