Table 7.1 Abbreviations used in natural history of retinal vein occlusions

7.1Branch Retinal Vein Occlusion

7.1.1 Acute Phase

7.1.1.1 Symptoms

Symptomatic BRVO causes blurred vision, metamorphopsia, and a painless scotoma that may have a sudden or gradual onset.74 Visual acuity is compromised most commonly by macular edema.71 The perceived scotoma is relative rather than absolute if enough perfusion exists to sustain the involved inner retina.25,94 Aside from macular edema, visual acuity is also compromised by macular capillary nonperfusion or foveal hemorrhage.25 Peripheral BRVOs are underdiagnosed because they are asymptomatic (Fig. 7.1).25

Fig. 7.1 Example of an asymptomatic, peripheral branch retinal vein occlusion (BRVO). A 65-year-old woman with hypercholesterolemia was found to have a sector of intraretinal hemorrhage in the superotemporal periphery of the right eye on a routine eye examination. The black arrow indicates the arteriovenous crossing at which a BRVO has occurred. The blue arrows denote the borders of the involved retinal sector with intraretinal hemorrhages. It would be unusual for a small peripheral BRVO such as this to be associated with later retinal neovascularization

7.1.2 Clinical Signs

In a population-based study, BRVO occurred at an arteriovenous crossing in 85% of cases (see Chap. 1).79 In a meta-analysis of 12 case series of BRVOs totaling 495 patients, the percentages of superotemporal and inferotemporal BRVOs were 62% and 33%, respectively, with the remaining 5% in the nasal quadrants.107 Other series support these observations.7,71,96,148 BRVO in the nasal quadrants is usually asymptomatic unless subsequent neovascularization with vitreous hemorrhage develops.7 Fifty-two percent of BRVOs are at second-order arteriovenous crossings and 40% at third-order crossings.148 Occasionally, BRVO occurs at a site other than an arteriovenous crossing. In most of these cases, the etiology of the thrombus has been attributed to inßammation, for example, from toxoplasmosis chorioretinitis or a sarcoid granuloma adjacent to a vein.30,84

Clinically, acute BRVO manifests as a sector of intraretinal hemorrhage associated with venous dilation. The vein is dilated distal to the arteriovenous crossing at which the obstruction occurs.

The proximal vein is often narrowed because of decreased blood ßow proximal to the occlusion (Fig. 7.2).145 The closer to the disc the occlusion occurs, the greater the retinal area involved by the distribution of hemorrhages. The artery may be narrowed in the involved sector of the retina.103 Common associations include capillary microaneurysms (30Ð90-m diameter, nearly universal) (Fig. 7.3), capillary nonperfusion detectable by

ßuorescein angiography (Fig. 7.4), cotton wool spots (33%) (Fig. 7.2), macular edema (18Ð28%) (Fig. 7.3), and subretinal ßuid detectable by OCT

(29Ð71%) (Fig. 7.5).25,67,72,74,78,100,101,103,121,130,133,138,144

Microaneurysms and macroaneurysms result from increased intraluminal pressure acting on a weakened, ischemic vessel wall. Cotton wool spots represent focal areas of decreased axoplasmic transport caused by focal ischemia and

Fig. 7.2 Fundus images of a patient with an inferotemporal branch retinal vein occlusion. (A) Monochromatic fundus photograph of the right eye. The occlusion occurred at the crossing of a retinal vein over a retinal artery, a rare occurrence. Usually, the artery crosses over the vein. Hemorrhages and cotton wool spots are present. (B) MagniÞed view of the vein crossing over the artery (the green arrow). The segment of the occluded vein between the occlusion and the downstream vein has no ßow and is narrowed (the purple arrow). (C) Frame from

a the laminar venous phase of the ßuorescein angiogram showing no ßow in the occluded vein (the yellow arrow) but normal laminar venous ßow in the adjacent branch retinal vein (the orange arrow). (D) Frame from the late phase of the ßuorescein angiogram showing speckled hyperßuorescence (the turquoise arrow) in the upstream section of the occluded vein, a sign of stagnant blood ßow. Normal blood ßow in the adjacent vein is signaled by the homogenous hyperßuorescence (the tan arrow)

Fig. 7.3 Fundus images of an old macular branch retinal vein occlusion in a 56-year-old male with best corrected visual acuity of 20/25 in the right eye. (A) Red-free fundus photograph of the right eye. Few stigmata are present to suggest the old event. A dot hemorrhage is present along the superotemporal arcade (the yellow arrow), and some telangiectatic small venules are present along the superotemporal border of the foveal avascular zone (the orange arrow). (B) Frame from the early phase of the ßuorescein angiogram showing dilated capillaries superotemporal to the foveal avascular zone (turquoise arrow), the hypoßuorescent dot hemorrhage seen in panel a (the yel-

low arrow), and other microaneurysms (the tan arrows) not suspected on the red-free photograph. The more widespread distribution of abnormalities than suspected on the red-free fundus photograph points to the site of the occlusion as having been at the arteriovenous crossing indicated by the purple arrow. (C) Late frame of the ßuorescein angiogram shows petalloid hyperßuorescence temporal and superior to the fovea. (D) The false-color map obtained from OCT scans shows macular thickening (the red area) congruent with the area of ßuorescein leakage. (E) The OCT line scan shows cystoid changes in the inner and outer nuclear layers

Fig. 7.4 Clinical images from the case of an asymptomatic 68-year-old female glaucoma suspect with treated hypertension and hypercholesterolemia. Her visual acuity was correctable to 20/20 bilaterally. She was found on a routine examination to have microvascular abnormalities in the left superotemporal macula. (A) Monochromatic fundus photograph of the left eye shows the occluded branch vein with a smaller diameter proximal segment (the red arrow) and a distended distal segment (the green arrow). Tortuous collateral venules (the yellow arrows) drain the venous return around the blocked site to adjacent venous beds. A region of relatively featureless retina is typical of an ischemic zone (the blue oval, compare to (B)). (B) A frame from the middle phase of the ßuorescein

angiogram shows a large microaneurysm (the turquoise arrow) and the nonperfused region (the blue oval, compare to (A)). (C) Frame from the late phase of the ßuorescein angiogram shows late ßuorescein leakage in the distribution of the occluded vein. The fovea is uninvolved. (D) Optical coherence tomography images of the left macula. The false-color map shows retinal thickening superiorly (the black arrow), and the line scan shows cystic change in the outer nuclear layer of the perifovea (the white arrow) with preservation of the foveal depression. (E) The 24Ð2 Humphrey visual Þeld of the left eye has a region of increased threshold (the gray oval) inferonasally that corresponds to the superotemporal area of macular edema

Fig. 7.5 Subretinal ßuid in branch retinal vein occlusion. Fundus images from an 86-year-old woman who suddenly developed central blurring of the right eye. Best corrected visual acuity was 20/63 on the right. (A) Monochromatic fundus photograph shows an inferotemporal macular branch retinal vein occlusion with a denser area of intraretinal hemorrhage surrounded by a sparser area. (B) Frame from the mid-phase ßuorescein angiogram showing dilated, telangiectatic capillaries inferior to the fovea.

The intraretinal hemorrhage is so dense that capillary perfusion is impossible to assess. (C) Frame from the latephase ßuorescein angiogram showing late intraretinal hyperßuorescence. (D) False-color map OCT display showing that the area of the retinal thickening colocalizes with the area of the intraretinal hemorrhage. (E) OCT line scan showing marked thickening of the outer nuclear layer, moderate thickening of the inner nuclear layer, and subretinal ßuid under the fovea (the yellow arrow)

sometimes infarction (see Chap. 2).88 Retinal hemorrhages in BRVO are typically in the nerve Þber layer accounting for their ßame shape and orientation along the familiar lines of the ganglion cell axons as they travel to the optic nerve.25 More peripherally, round hemorrhages are found.94 Hemorrhage may accumulate in parafoveal cysts which can show bloodÐserous ßuid levels. A rare presentation is a dense retinal hemorrhage at an arteriovenous crossing which may be erroneously interpreted as a ruptured arteriolar macroaneurysm (Bonnet sign). Over time, such cases evolve into a more typical picture of acute BRVO with a sector of hemorrhages.70

A BRVO can be nonischemic or ischemic, terms which have varying deÞnitions that engender controversy (see Chaps. 4 and 9). Hayreh reported that most major BRVOs were ischemic.48,57 However, other studies report that nonischemic BRVOs are more common.79 A BRVO that is initially nonischemic can become ischemic. The frequency with which this occurs depends on the deÞnitions used. In one study, the conversion rate was 29% over the course of 1 year of follow-up.2 There is a rough correlation between the degree of ischemia and the extent and density of intraretinal hemorrhages, although there are cases in which a nonischemic BRVO has severe intraretinal hemorrhage.44