20Retinal vein occlusion

Retinal vein occlusion (RVO), one of the most frequently occurring retinal vascular disorders in elderly patients, develops predominantly in individuals over age 65 years.1–3 RVO generally is classified into central RVO (CRVO) and branch RVO (BRVO) according to the site of blockage in the retinal vein. CRVO is divided further into nonischemic and ischemic types according to the perfusion status based on fluorescein angiography. Ischemic CRVO is associated with greater than 10 disc areas in diameter of retinal capillary nonperfusion on fluorescein angiography.4 Ocular vascular leakage, retinal and iris neovascularization, and intractable elevation of the intraocular pressure may result from progression of ischemic CRVO. Large areas of retinal capillary nonperfusion in BRVO may develop neovascularization followed by vitreous hemorrhage. Macular edema is the major complication of significant visual loss in patients with CRVO and BRVO, and various treatments have been used to improve macular edema and cause regression of intraocular neovascularization. Recent pharmacologic agents primarily have targeted the improvement of macular edema secondary to CRVO and BRVO.5–15

The precise pathogenesis of CRVO remains uncertain. Three occlusive processes have been postulated as pathogenetic: (1) occlusion of the vein by external compression caused by sclerotic adjacent structures (the central retinal artery and fibrous tissue envelope); (2) occlusion by primary wall disease (degenerative or inflammatory in nature); and (3) hemodynamic disturbances resulting from various factors (subendothelial atheromatous lesions in the central retinal artery, arterial spasm, sudden reduction of blood pressure, blood dyscrasias, and further aggravation by arteriosclerosis or unfavorable anatomic relations). These produce stagnated flow in the central retinal vein and result in primary thrombus formation in susceptible eyes.20

BRVO always occurs at an arteriovenous crossing, where the retinal artery and vein share a common adventitial sheath. The rigidity of the arteriosclerotic artery caused by underlying arterial disease may compress the vein lumen at the crossing site, resulting in turbulent blood flow and vascular endothelium damage, followed by thrombosis and vein occlusion. Obstruction of the vein elevates venous pressure, which may overload the collateral drainage capacity and lead to macular edema and rupture of the vein wall with intraretinal hemorrhage.20

DISEASE PREVALENCE

Studies among older population-based samples reported that the prevalences of RVO range from 0.3% (CRVO 6 cases, BRVO 33 cases out of 15 466 persons) in the pooling of two large population-based cardiovascular studies in the Atherosclerosis Risk in Communities Study (12,642 persons aged 51–71 years) and Cardiovascular Health Study (2824 persons aged 73 years and older),16 0.7% (BRVO 31 cases, CRVO 7 cases out of 4822 persons aged 43–84 years) in the Beaver Dam Eye Study,17 to 1.6% (CRVO 18 cases, BRVO 41 cases out of 3654 persons aged 49 years and older) in the Blue Mountains Eye Study.2

RISK FACTORS

Systemic risk factors associated with CRVO include systemic vascular diseases (hypertension, diabetes mellitus, and cardiovascular diseases), blood dyscrasias (polycythemia vera, lymphoma, leukemia), para­ proteinemias and dysproteinemias (multiple myeloma and cyto­ globulinemia), vasculitis (syphilis and sarcoidosis), and autoimmune disease.18 Medications (oral contraceptives, diuretics, hepatitis B vaccine) also increase the risk of RVO.

Ocular risk factors associated with CRVO include open-angle glaucoma, ischemic optic neuropathy, pseudotumor cerebri, tilted optic nerve heads, and optic nerve head drusen.

The Eye Disease Case-Control Study of 270 patients with BRVO and 1142 controls reported that the systemic risk factors associated with BRVO were hypertension, a history of cardiovascular disease, an increased body mass index at 20 years of age, and higher serum levels of alpha 2-globulin. Ocular risk factors associated with BRVO include open-angle glaucoma and focal arteriolar narrowing and arteriovenous nicking.19

DIAGNOSIS AND ANCILLARY TESTING/ DIFFERENTIAL DIAGNOSIS

CENTRAL RETINAL VEIN OCCLUSION

CRVO is a venous retinal obstructive disease of the central retinal vein, resulting in elevated venous and capillary pressure with stagnated blood flow. The diagnosis is established based on characteristic fundus findings ofwidespreadextensivedot-blotandflame-shapedhemorrhage,engorge- ment and tortuosity of all branches of the central retinal vein, cottonwool patches, macular edema, and optic disc edema and hyperemia.

There are two types of CRVO: ischemic and nonischemic. Ischemic CRVO is severe, complete, or total vein obstruction. The fundus has extensive retinal hemorrhaging, venous dilatation and tortuosity, and scattered cotton-wool spots (Figure 20.1). Ischemic CRVO is rarely confused with other entities. Nonischemic CRVO is partial, incomplete, imminent, threatened, incipient, or impending vein obstruction. Nonischemic CRVO can be subtle, because the findings of venous engorgement and tortuosity are mild and cotton-wool patches and optic edema tend to be absent (Figure 20.2). Nonischemic or longstanding CRVO may be similar to the retinopathy of carotid occlusive disease. Although disc edema may be associated with CRVO, it is rare in carotid occlusive disease. Although the veins are engorged in both CRVO and carotid occlusive diseases, they are generally not tortuous in carotid occlusive diseases.

Fluorescein angiography is the most useful ancillary test for the evaluation of ocular neovascularization and macular edema. On fluorescein angiography, eyes with areas of nonperfusion of 10 disc areas or greater should be classified as ischemic (Figure 20.1B). Poor visual acuity (VA) and large areas of retinal capillary nonperfusion are significant factors associated with increased risk of the development of

Occlusion Vein• 20Retinalchapter