retinal vessels after BRVO lack tight junctions.109 The clinical correlate of this is leakiness to ßuorescein during ßuorescein angiography, a discriminating point from collateral vessels within the retina (Figs. 7.7 and 7.11). Proliferation of new vessels with accompanying Þbrous tissue can lead to traction, vitreous hemorrhage (Fig. 7.11), traction retinal detachment, retinal breaks, and rhegmatogenous retinal detachment.6,24,33,103,119,137

Iris neovascularization is not common after BRVO but can occur, especially if the area of capillary nonperfusion is large.57,119 Extrafoveal vitreous traction detected by OCT has been reported in 24% of cases with BRVO.102 Vitreous

attachment to the retina in BRVOs with extensive capillary nonperfusion is a risk factor for development of retinal neovascularization.65 Ischemic BRVO evolves with thinning of the ganglion cell and nerve Þber layer and sectoral optic disc atrophy.44

7.1.3.2 Visual Acuity

Older retrospective series with imperfect comparability provide a rough idea of the natural history of BRVO visual acuity outcomes.74,94 Based on a combined sample of 135 eyes followed for at least 1 year, the weighted averages for visual

Fig. 7.8 A 51-year-old woman developed a superotemporal branch retinal vein occlusion in the left eye with macular edema. Visual acuity was 20/50. (A) Monochromatic fundus photograph shows optic disc collateral vessels (yellow arrow). (B) A frame from the latephase ßuorescein angiogram shows that the disc collaterals do not leak ßuorescein dye (the yellow arrow). Macular edema is present. (C) A false-color map from time domain

optical coherence tomography (OCT) shows macular edema. (D) A line scan from time domain OCT shows macular thickening with cysts. (E) Follow-up color fundus photograph shows a macular hole (the green arrow) with a cuff of subretinal ßuid (the black arrow). (F) Spectral domain OCT shows a macular hole with cysts of edema in the border tissue. (G) False-color map from spectral domain OCT shows persistent macular edema superiorly

Fig. 7.8 (continued)

Fig. 7.9 Fundus image of a chronic branch retinal vein occlusion involving the right eye. The visual acuity is 20/32. Lipid exudates are present at the border of edematous and normal retina and tend to be heavier closer to the horizontal raphe and the macula (the black arrow) and lighter peripherally (the green arrow). A cluster of leaking microaneurysms is present within the oval area deÞned by the interrupted lipid ring

outcomes suggest that 42% of eyes end with visual acuity better than or equal to 20/40, 27% with visual acuity in the 20/50Ð20/100 range, and 31% with visual acuity of 20/200 or worse (Table 7.2).74,94 One older meta-analysis of natural history studies of BRVO found that 53% of patients with BRVO end with a Þnal visual acuity of 20/40 or better.103 A meta-analysis of more recent studies reported that the mean change in visual acuity during follow-up ranged from 1 Early Treatment Diabetic Retinopathy Study (ETDRS) letter at 6 weeks to 28 ETDRS letters at 12Ð24 months.117

The most reliable data on the natural history of visual acuity data in BRVO comes from popu- lation-based studies of incident cases. In the Beaver Dam Eye Study (BDES), 61 eyes suffered incident BRVO during 15 years of follow-up. For these, the average drop in visual acuity caused by the BRVO was 12 ETDRS letters.72 The BDES

Fig. 7.10 A 77-year-old man with hypertension had a history of bilateral branch retinal vein occlusions (BRVO). The left BRVO occurred in 1997 and was associated with macular edema treated by grid laser, but the eye never regained better than 20/200 visual acuity. In 2007, examination showed a macular epiretinal membrane and chronic cystoid macular edema. (a) Frame from the middle-phase ßuorescein angiogram shows the irregular telangiectasia superotemporal to the fovea. (b) Frame from the late-phase of the ßuorescein angiogram shows petalloid hyperßuorescence surrounding a

hypoßuorescent area (yellow oval) that was a large cyst (see (c)). (c) A linear SD-OCT scan shows the large central cyst (the green arrow) and a macular epiretinal membrane (the yellow arrow). (d) Four linear SD-OCT scans that straddle the central scan of C from the Þve-raster display show different cuts through the large macular cyst and the overlying epiretinal membrane (the yellow arrow). Surgery was not offered to the patient in view of the 10-year history of the problem and poor vision and the low probability of improving visual function even with technically successful surgery

Fig. 7.11 Fundus images of a 47-year-old man with unsuspected hypertension and a right inferotemporal branch retinal vein occlusion with retinal neovascularization and a subhyaloid hemorrhage. (a) Monochromatic fundus photo-

graph showing the subhyaloid hemorrhage (the turquoise arrows) and neovascularization (the yellow arrow). (b) Frame from the middle-phase ßuorescein angiogram showing the leaky neovascularization (the yellow arrow)

identiÞed 31 persons with BRVO at baseline. Twenty-three were alive and examined 5 years later. In these subjects, best corrected visual acuity did not change.71

The untreated arm of the Branch Vein Occlusion Study (BVOS) provided natural history data on 35 eyes with BRVO of duration 3Ð18 months excluding cases with macular ischemia and foveal hemorrhage. For such eyes, over 3 years, the average change in visual acuity was 0.23 Snellen lines of improvement.138 Thirtyseven percent of eyes gained two lines of visual acuity, and 34% had vision better than or equal to 20/40 at 3 years of follow-up.138 The sham arm of the Ranibizumab for the Treatment of Macular Edema Following Branch Retinal Vein Occlusion (BRAVO) study provided natural history information on visual acuity for an initial 3 months in mostly BRVOs (13% were HCRVOs) with durations of 0Ð16 months.18 In the Þrst 3 months after diagnosis, 17% of 132 eyes in the sham group gained greater than or equal to three lines of visual acuity.18

The prognosis for visual outcome depends on the extent and severity of the initial obstruction, the extent of involvement of the FAZ border, the initial visual acuity, the extent and timing of collateral vessel formation, the age of the patient, and comorbidities of the involved retina.94,115 Of eyes with initial visual acuity greater than or equal to 20/50 and followed without treatment, 90% end with visual acuity greater than or equal to 20/50. Of eyes with initial visual acuity less than or equal to 20/200, 14Ð33% end with visual acuity greater than or equal to 20/50.43,115 Of eyes with initial visual acuity greater than or equal to 20/50, 0Ð5% end with visual acuity less than or

equal to 20/200. Of eyes with initial visual acuity less than or equal to 20/200, 50Ð83% end with visual acuity less than or equal to 20/200.43,115

Extent of capillary nonperfusion may inßuence the natural history of visual outcome. The smaller the sector of the foveal avascular zone border involved, the better the visual prognosis.25,94 Presence of subretinal blood is a negative prognostic sign as it leads to RPE metaplasia. Causes for poor Þnal vision in BRVO are foveal lipid deposition, submacular scarring, severe cystoid macular edema, and a combination of superior and inferior BRVO.74,94

A case series of 45 BRVOs found that eyes that developed collaterals had statistically signiÞcantly better visual outcomes than eyes that did not.63 Because eyes with BRVOs usually develop venous collaterals Ð and reproducibility of grading collaterals has not been demonstrated Ð this conclusion is an interesting hypothesis in need of further testing, but not a consensus.

For macular BRVO, three studies provide information on the course of visual acuity in untreated cases.5,64,106 In a series of 35 patients followed without treatment for 24 months, the average baseline visual acuity was logMAR 0.42 ± SD 0.13 (Snellen equivalent 20/50) and improved without treatment by an average of 10 ETDRS letters at 3 months and 14 ETDRS letters by 12 months.106 No further visual acuity improvement was noted between 12 and 24 months.106 In a second study of 64 patients, 20% of eyes experienced an improvement of greater than or equal to two lines.64 In a third series of 35 patients, the mean visual acuity over 2 years improved from 20/50 to 20/30.4