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    Drugs & Diseases > Ophthalmology

    Central Retinal Artery Occlusion (CRAO)

    Updated: Jun 11, 2019
    • Author: Robert H Graham, MD; Chief Editor: Andrew G Lee, MD  more...
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    Overview

    Background

    Central retinal artery occlusion (CRAO) was first described by Van Graefe in 1859 as an embolic event to the central retinal artery in a patient with endocarditis. In 1868, Mauthner suggested that “spasmodic contractions” could lead to retinal artery occlusion. CRAO has various causes, but patients typically present with sudden, severe, and painless loss of vision.

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    Pathophysiology

    Visual loss due to CRAO occurs once the inner two-thirds of the retina has lost its blood supply. The ophthalmic artery is the first branch of the internal carotid artery and enters the orbit underneath the optic nerve through the optic canal. The central retinal artery, the first intraorbital branch of the ophthalmic artery, enters the optic nerve 8-15 mm behind the globe to supply the retina. The short posterior ciliary arteries branch distally from the ophthalmic artery and supply the choroid. Cilioretinal arteries, an anatomic variant present in 15%-30% of the population, branch from the short posterior ciliary artery. These arteries supply the macula in addition to the choroidal circulation. In CRAO in these patients, the central visual acuity may be preserved (>20/50), since the cilioretinal artery often supplies the papillomacular bundle and is a direct extension of the posterior ciliary artery. [1, 2, 3] In 10% of eyes, the cilioretinal artery supplies some or all of the foveola. Nevertheless, even with cilioretinal artery-sparing CRAO, peripheral vision remains poor. [2, 4]

    Acute obstruction of the central retinal artery results in inner layer edema and death of the ganglion cell nuclei. The retina loses its transparency and becomes yellow-white in appearance owing to ischemic necrosis. The opacity is most dense in the posterior pole as a result of the increased thickness of the nerve fiber layer and ganglion cells in the macula. Furthermore, the foveola assumes a cherry-red spot because of a combination of 2 factors: (1) The foveolar retina remains transparent because it is nourished by the choriocapillaris and (2) the intact retinal pigment epithelium and choroid underlying the fovea are outlined by the opaque surrounding retina. The late stage of CRAO shows a homogenous scar replacing the inner layer of the retina. After a few weeks, the opacification resolves, and the retina remains thin and atrophic; although there may be arteriolar narrowing and optic atrophy, the retina may otherwise appear deceptively normal. [5]

    Opacification of the retina in CRAO takes as little as 15 minutes to several hours before becoming evident and resolves in 4-6 weeks. The resulting pathology reflects a catastrophic insult to the inner retinal layers with attenuated retinal arterioles and optic nerve pallor. Pigmentary changes are typically absent since the retinal pigment epithelium remains unaffected; however, vesicular, pearly, and sometimes pigmented patches may appear in the retina, demonstrating remnants of hemorrhages and areas of severe degeneration. [5] A “boxcarring” appearance of the impaired blood column can be seen in both arteries and veins. This finding was previously seen by Wolf and Davies by experimentally occluding both ophthalmic arteries and veins with a clamp. [5] Hayreh et al have shown that irreversible cell injury occurs after 90-100 minutes of total CRAO in a healthy and young primate model [6] Additional studies on the hypertensive, elderly, or middle-aged atherosclerotic rhesus monkey showed the morphologic optic nerve damage starts after 105 minutes and is total after 240 minutes of occlusion. [7]

    However, a 2018 meta-analysis by Tobalem et al suggests that retinal ischemia probably occurs within 12-15 minutes and that earlier experimental evidence suggesting a window of 90-120 minutes could be flawed and not applicable to the general population, since most of the experiments supporting this theory were performed in animals in a controlled environment of hypothermia and under barbiturate anesthesia, which have additional neuroprotective effects. This could explain why most rescue efforts in acute CRAO do not provide significant benefit. [8]

    After some months, the optic disc becomes atrophic and pale. [5] Controversy exists regarding the optimal window of treatment in humans, but the conservative approach involves treatment up to 24 hours.

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    Epidemiology

    Frequency

    United States

    CRAO is found in 1 per 10,000 outpatient visits. Of these patients, only 1%-2% present with bilateral involvement. The incidence of CRAO is slightly less than 2 per 100,000 among whites in the United States [9] and usually affects adult patients with cardiovascular risk factors [10] such as hypertension, hyperlipidemia, and diabetes.

    Mortality/Morbidity

    Patients with visualized retinal artery emboli, regardless of the presence of obstruction, have a 56% mortality rate over 9 years, compared to 27% in an age-matched population without retinal artery emboli. Life expectancy among patients with CRAO is 5.5 years, compared to 15.4 years in an age-matched population without CRAO.

    Sex

    CRAO is slightly more common in men than in women.

    Age

    The mean age of CRAO presentation is in the early seventh decade of life, although a few cases have been reported in patients younger than 30 years. The likely etiology of occlusion changes depending on the age at presentation.

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    Prognosis

    Most patients with CRAO continue to experience severe vision loss, in the counting fingers to hand motion range. [11]

    As many as 10% of patients retain central vision because of the presence of a cilioretinal artery. In this case, visual acuity improves to 20/50 or better in 80% of cases over a 2-week period.

    The presence of a retinal embolus is associated with a 56% mortality rate over 9 years compared to 27% in patients without arterial emboli.

    The life expectancy of patients with CRAO is 5.5 years compared to 15.4 years for an age-matched population without CRAO.

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    Patient Education

    Patients with CRAO must understand that the prognosis for visual recovery is poor and that the visual changes usually result from a systemic process that needs treatment. The most important education is to control the cardiovascular risk factors that may lead to other complications such as cerebrovascular accident, among others. 

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