Which ocular ischemic syndromes cause sudden visual loss?

Updated: Dec 11, 2019
  • Author: Jean Deschênes, MD, FRCSC; Chief Editor: Edsel Ing, MD, MPH, FRCSC  more...
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Answer

Persistent eye ischemia can be classified into central retinal artery occlusion (CRAO), branch retinal artery occlusion (BRAO), or ischemia of the optic nerve, which is caused by involvement of the posterior choroidal blood supply of the nerve (anterior ischemic optic neuropathy [AION]).

Origin of central retinal artery (CRA) from the ophthalmic artery is variable. The vessel has several segments on its way to the retina. To reach the fundus, the CRA penetrates the lamina cribrosa. At this point, it narrows; the tissue around the vessel acts as a mechanical barrier to dilatation. This area is not visible on ophthalmoscopy and is most often the site of embolic or inflammatory diseases (eg, GCA). The narrowest area of the CRA is where the artery enters through the dural sheath of the optic nerve, [8] also making this region susceptible to emboli.

The major symptom of CRAO is sudden, painless blindness with permanent visual loss. Perception of hand movement or light can be preserved in parts of the visual field. Diagnosis is confirmed by ophthalmoscopy, which reveals partial or complete arrest of retinal circulation. Cardinal signs include attenuated retinal arteries and veins (very early only), and a cloudy whitening of the retina (ie, edema) with the consequent cherry-red spot in the macula in the affected eye, as well as slow segmental blood flow in arterioles (ie, "box-carring"). [4] If the occlusion lasts more than 1 hour, the retina becomes irreversibly infarcted.

In BRAO, visual defects and retinal ischemia are more focal and have an altitudinal, lateral, or scotomatous quality. The incidence of carotid artery and valvular disease is not very different than in CRAO, but temporal arteritis is less commonly the cause.

In AION, the patient usually develops painless visual loss in the eye, which is noted on awakening in the morning without worsening thereafter. The degree of loss is variable but most often incomplete. Ophthalmoscopy shows edema of the optic disc and splinter hemorrhages at the disc margins. When the ischemia is posterior to the disc, the disc may look normal, but this is uncommon and may point toward arteritis as the cause. Subsequent involvement of the other eye is common.

Other ocular ischemic syndromes involve the retinal vein. Retinal vein occlusions are retinal vascular disorders that are classified clinically as branch retinal vein occlusion (BRVO), hemiretinal vein occlusion, and central retinal vein occlusion (CRVO). See the image below.

Central retinal vein occlusion - Diffuse retinal h Central retinal vein occlusion - Diffuse retinal hemorrhages extending to periphery of fundus, "blood and thunder" appearance.

BRVO involves one of the branch retinal veins. Most involve the superior or inferior temporal arcades and occur at an arteriovenous crossing where the vein is compressed by a sclerotic artery. The superior or inferior temporal arcades cause macular vein occlusion with profound visual deficit. Hemispheric vein occlusion involves the venous drainage of either the superior or inferior retina.

BRVO affects males and females equally, occurring most frequently in adults aged 60-70 years. Regardless of the primary pathogenic processes, it is clear that disease of the arterial wall and the presence of common adventitia between the artery and the vein at arteriovenous crossings play a role in the pathogenesis. The common symptoms of BRVO are blurring and distortion of vision. During the acute stage, multiple superficial and deep retinal hemorrhages are seen in a pie configuration in the distribution of the affected vein. The veins in the occluded segment usually are dilated and tortuous.

Fluorescein angiography is helpful to delineate the hemodynamic changes that occur in the retinal vasculature. Angiography usually shows slow venous return without complete occlusion of the vein. Approximately 50% of patients recover good visual acuity, although 2 complications may lead to reduced visual acuity—macular edema, which develops in more than 50% of patients, and retinal neovascularization. Management can involve photocoagulation to ablate the ischemic peripheral retina, administration of intravitreal antivascular endothelial growth factor (VEGF) injections, or corticosteroid therapy. [9]

CRVO involves occlusion of the main central vein, which usually occurs at the level of the lamina cribrosa. Consequent macular edema may develop, with reduction in visual acuity. [10] The mechanism is unknown, but the most important local factor is chronic open-angle glaucoma, which is present in over 20% of patients. CRVO primarily affects adults aged 45 years and older, [11] but well-documented cases in younger persons have been reported. Risk factors for CRVO include hypertension, open angle glaucoma, dyslipidemia, peripheral arterial disease, and diabetes mellitus. [12, 13]

CRVO has 2 types: ischemic and nonischemic. These types are characterized by the severity of the retinal vein ischemia, although both have very similar ophthalmological findings. [14] Nonischemic is the more common form and occurs when blood flow and oxygen delivery are restored following vein blockage. [10] Visual complaints vary from mild to moderate blurring of vision, which may be transient. Visual fields are usually normal except for occasional central scotomas.

Ophthalmoscopic features of nonischemic CRVO include moderate dilatation and tortuosity of all retinal veins with multiple punctate hemorrhages in the peripheral retina and few scattered retinal hemorrhages in the posterior pole. Most hemorrhagic activity resolves over several months. Some patients may be left with some permanent visual loss due to nonresolving cystoid macular edema, macular cystic degeneration, macular retinal pigment epithelial changes, and preretinal fibrosis.

Ischemic CRVO presents as sudden, painless vision loss. Vision is usually markedly decreased, but most patients will be able to count fingers or see hand movement. Peripheral visual fields are almost always normal with a dense central or centrocecal scotoma. One definition includes the presence of an afferent pupillary defect in the affected eye, which has been found to be both sensitive and specific. [10]

The ophthalmoscopic features of ischemic CRVO include marked tortuosity and dilatation of all the retinal branch veins, diffuse retinal hemorrhages extending from the optic disc to the periphery of the fundus, and multiple cotton-wool spots. The prognosis is poor; central vision seldom recovers, owing to ischemic maculopathy or cystic macular degeneration, macular holes and cysts, macular epithelial fibrosis, macular edema, anterior segment and retinal neovascularization, [9] or secondary glaucoma. [10]

Patients with nonarteritic ischemic optic neuropathy (NAION) usually have painless vision loss and decreased central visual acuity, peripheral visual field loss, or both. The etiology of NAION is unknown, but a small cup disc and "ischemic spiral" is often associated with mild pallid swelling of the optic disc, often sectoral. Individuals with NAION are at risk during the subsequent 5 years of developing involvement of the other eye; risks for fellow eye involvement include poor baseline acuity and diabetes mellitus, but interestingly not age, sex, smoking, or aspirin use. Spontaneous improvement of vision may occur. [15]


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