Why Does the Visual Outcome in Nonischemic, Macula-Involving Branch Retinal Vein Occlusions Usually Vary with the Size of the Involved Retina?

In one study, vision-related quality of life as assessed by the Visual Function Questionnaire-25 was negatively impacted by BRVO even when the fellow eye was healthy.3 The severity of impact of unilateral BRVO was less than that of diabetic retinopathy, macular degeneration, and CRVO. Subscale responses were lower (that is, an impact on quality of life was evident) than those in healthy subjects.3

7.2 Central Retinal Vein Occlusion

7.2.1 Acute Phase

7.2.1.1 Symptoms

Patients with CRVO may be symptom-free, and the condition is discovered on a routine eye examination.48 When symptoms occur, the predominant one is painless blurring of vision, which may have sudden or gradual onset.47 It is rare to have a premonitory period of transient or purple blurring before the onset of constant blurring. If such a history is obtained, it may point to a nonischemic CRVO with associated cilioretinal artery insufÞciency.53,60 Patients frequently complain of worse vision in the morning improving over the course of the day, a phenomenon attributed to worse macular edema in the morning with lessening over the course of the day.57

The visual Þeld depends on the status of retinal capillary perfusion. In nonischemic CRVO, the visual Þeld frequently shows a central scotoma to small test objects but is normal to larger ones.47 Ischemic CRVO has more dramatic loss of visual Þeld, which can have irregular shapes.

The clinical picture of CRVO changes over time, so an awareness of duration of the condition is important in accurately interpreting the clinical picture.48,54

7.2.1.2 Clinical Signs

The clinical picture and deÞnition used in many clinical studies of CRVO is intraretinal hemorrhage and dilated, tortuous retinal veins in all four quadrants of the fundus (Fig. 7.12).10,28,112 Many other Þndings may be a part of the clinical picture, but these are the minimal requirements. Among the other Þndings commonly found are a relative afferent pupillary defect (RAPD), cotton wool spots, macular edema, disc edema (Fig. 7.12), perivenular retinal whitening (Fig. 7.13), cilioretinal arteriolar insufÞciency (CRAI) (Fig. 7.14), anterior segment neovascularization (ASNV), retinal neovascularization, and vitreous hemorrhage.

The severity of some of these signs roughly correlates with ischemia. Greater severity of a RAPD, intraretinal hemorrhages, and a greater number of cotton wool spots correspond to greater ischemia.47 Nonischemic CRVOs

Fig. 7.12 The natural history of ophthalmoscopic fundus signs of central retinal vein occlusion is variable and is time dependent. (a) Color fundus photograph of an acute nonischemic central retinal vein occlusion. Venous dilation is present in all four quadrants of the fundus, together with intraretinal hemorrhages. A peripapillary cotton wool spot is present superiorly (black arrow). The optic disc is edematous. An unrelated inferior peripapillary choroidal nevus is present and is partially obscured by intraretinal hemorrhage. (b) Color fundus photograph of the macula taken at the same time as (a). That the macula

is edematous can be inferred by the lack of darker macular color (the yellow oval). (c) One year later, most signs have spontaneously disappeared. Two small hemorrhages remain, one above and another below the disc (the black arrows). The optic disc edema has resolved, as has venous dilation. The resolution of these signs occurred in the absence of any treatment; optic disc collateral vessels did not develop. (d) Macular photograph taken at the same time as (c). The macular edema has spontaneously resolved with return of the normal darker macular color (the yellow oval)

comprise 50Ð81% and ischemic CRVOs 19Ð45% with the remainder as indeterminate (see Chap. 9).48,49,52,57,76,81,95,112 Subhyaloid macular bleeding is a variant of vitreous hemorrhage that has been reported in association with CRVO in young patients with attached posterior hyaloid (Fig. 7.12).75 Occasionally, break-

through bleeding into the vitreous cavity occurs during the acute phase of CRVO.26

There is a correlation of the degree of ischemia of a CRVO and the presence and magnitude of the relative afferent pupillary defect (RAPD) as determined by the use of neutraldensity Þlters or cross-polarized Þlters.

Fig. 7.13 Fundus image of an eye with a nonischemic central retinal vein occlusion (CRVO) and perivenular ischemic retinal whitening (the yellow arrows). This is a clinical sign of CRVO most often found in younger patients with low blood pressure. It resolves without sequelae after a few days as retinal venous blood ßow increases, presumably through the action of optic disc collaterals

Nonischemic CRVO is associated with a RAPD less than 0.3 log units in amplitude. An RAPD greater than or equal to 0.9 log units implies that a CRVO is ischemic. Ischemic CRVO is not

associated with an RAPD less than 0.6 log units, and in 91% of cases are associated with an RAPD greater than or equal to 1.2 log units.128 The test is less useful in patients with poorly reactive pupils, but in such cases, the quantitative brightness comparison test can provide similar clinical information.15

Cotton wool spots are white areas of axoplasmic ßow stasis in areas of ischemia (see Chaps. 1 and 2). In CRVO, they form a ring around the optic disc in the area roughly served by the radial peripapillary capillaries (Fig. 2.24) Their mean distance from the optic disc is 2.02 ± SD0.88 disc diameters.83 A white zone of axoplasmic ßow stasis within an area of retinal opaciÞcation from cilioretinal arteriolar insufÞciency is sometimes confused with cotton wool spots.51

The intraocular pressure of an eye with CRVO is frequently lower than normal in the Þrst month after the occlusion.51,55,59 The mechanism is unknown.51 Occasionally, patients with acute RVO present with simultaneous angle closure glaucoma due in some cases to a suprachoroidal

effusion.40,92,93,132

Serous retinal detachment (SRD) was known to occur in CRVO in the era before optical coherence tomography (OCT), but the modalities of clinical examination with contact lens, noncontact lens, and ßuorescein angiography underestimated its frequency.123,134 With OCT, 82% of cases of acute CRVO have been found to have serous retinal

detachment along with cystoid macular edema.104 It has been speculated that presence of SRD may be an indicator of ischemia or retinal traction by epiretinal membranes.33,123 Part of the reason for the modest correlation of OCT-measured macular thickness and best corrected visual acuity in CRVO may be the presence of subretinal ßuid.

Fig. 7.14 Images from a 56-year-old female with a nonischemic central retinal vein occlusion of the left eye with associated cilioretinal artery insufÞciency. The visual acuity was 20/20 in the left eye, and her complaint was of an inferior paracentral scotoma on the left. (A) Color fundus photograph of the left eye shows dilated retinal veins in all four quadrants with scant intraretinal hemorrhages in all quadrants and mild nasal rim optic disc edema. The perimacular retina supplied by a superotemporal cilioretinal artery is relatively opaciÞed, reßecting decreased blood ßow and hypoxia (the black oval circles the opaciÞed area). The distribution of hemorrhages is no different in the area of cilioretinal arteriolar insufÞciency than in the retina supplied by the central retinal artery, a clinical observation that falsiÞed an older hypothesis that central retinal artery obstruction was necessary to produce the pattern of hemorrhages seen in human CRVO.87 (B) Frame

from the early venous phase of the ßuorescein angiogram of the left eye. The purple arrow denotes the cilioretinal artery. The blue arrow denotes a branch retinal artery that supplies an adjacent area of the retina. Note that the origins of the branch retinal artery and the cilioretinal arteries are distinct. The yellow arrow denotes a second-order cilioretinal arteriole that supplies the hypoxic, opaciÞed retina. There is no infarction. The perfusion of capillaries is sustained. The hypoxia is functional, relating to an imbalance between the available blood ßow and the high oxygen demands of the perimacular inner retina. (C) MagniÞed view of the disc and superior macula. The cilioretinal artery is indicated by the black arrow. (D) MagniÞed view of the disc and superior macula from the early venous phase ßuorescein angiogram. The red arrow denotes the distinct origin of the cilioretinal artery compared to the adjacent branch retinal artery

Perivenular ischemic retinal whitening (PIRW) is characterized by a small zone of retinal whitening immediately adjacent to venules within the affected region, presumably because the blood in this zone is more deoxygenated than in zones adjacent to arterioles (Fig. 7.13).14 PIRW occurs in the perimacular region, but not the peripheral retina. Capillary perfusion as assessed by ßuorescein angiography is maintained in PIRW. Therefore,

PIRW represents a functional insufÞciency in which the oxygen delivery is subnormal and induces loss of retinal transparency. However, the tissue is perfused and is capable of return of function and transparency if the hemodynamic circumstances improve, which frequently occurs in a few days. In some cases, the ischemic whitening is not so localized to the perivenular retina but is clearly not conÞned to the distribution of an artery as in a