9.3 Central Retinal Vein Occlusion |
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In the Face of Evidence that Fluorescein Angiography Is Poorly Predictive of Ischemia in Acute Central Retinal Vein Occlusion, Why Is It Widely Used?
The evidence is strong that in acute CRVO the FA is poorly predictive of ischemic status because capillary nonperfusion cannot be assessed in 38–60% of cases, capillary closure may not occur immediately after CRVO, and reproducibility of interpretation of FAs for extent of capillary nonperfusion is poor across clinicians even when the study is technically excellent.22,53,54 Nevertheless, FA is used in the majority of published studies and in clinical practice to define an eye as ischemic or nonischemic. The eyes with indeterminate status are simply treated as though they are ischemic because 88% have been found to eventually fall into that group on follow-up.49 FA is an ancillary test that is reimbursed by health care payers in the United States. There may be an economic incentive to use this test. No such economic incentive is provided for the more reliable quantitative measurement of RAPD, which is not confounded by presence of intraretinal hemorrhage. In fact, there may be an economic disincentive to use the RAPD, as it would require the ophthalmologist to examine the patient in the undilated state first (to assess the pupils) and then again after dilation (to examine the fundus). Most retina specialists delegate pupil testing to less trained technicians, only examining the patient personally after dilation. It may not be surprising, therefore, that the quantitative measurement of RAPD in CRVO is little used in practice. Also, although FA is poorly predictive over a population of patients with CRVO, in particular cases with clear media and lacking obscuring intraretinal hemorrhage, it can be definitive in addressing the issue of ischemia (Fig. 9.5).
Fig. 9.5 A 74-year-old female with diabetes, hypertension, hypercholesterolemia, and a previous history of two strokes presented with loss of vision in her left eye. Examination revealed a double HCRVO with an ischemic superior HCRVO and a nonischemic inferior HCRVO. The visual acuity in the left eye was light perception. (a) Monochromatic fundus photograph of the left eye shows two hemicentral retinal veins. The superior HCRV is more distended (the green arrow) than the inferior HCRV (the red arrow). (b) Monochromatic fundus photograph centered on the macula of the left eye. Superiorly, there is an area with a paucity of intraretinal hemorrhages (the yellow oval) with a featureless appearance compared to a symmetrical area inferior to the horizontal raphe (the turquoise oval). This can be a sign of ischemia. (c) Frame from the mid-phase fluorescein
angiogram shows absence of capillary perfusion superiorly (the yellow oval) but good capillary detail inferiorly (the turquoise oval). (d) Frame from the late-phase fluorescein angiogram showing intense hyperfluorescence in the superior hemiretina (the yellow oval) compared to the inferior hemiretina (the turquoise oval). (e) The OCT false-color map shows that retinal thickening correlates with the degree of hyperfluorescence. Retinal thickness is over twice as great above the horizontal raphe as below as shown from the ETDRS subsector mean values. Although there is not a great deal of hemorrhage, the inner segment/outer segment junction is discontinuous (the yellow arrow) presumably because the extensive swelling has led to photoreceptor swelling and misalignment. In the fovea, where swelling is greatest, the inner segment/outer segment junction is not seen
230 |
9 Ischemia and Retinal Vein Occlusions |
IR 30° ART [HS] |
800 |
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Average Thickness [ m] |
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Vol [mm3] |
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700 |
7.60 |
1056 |
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e |
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1.45 |
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1135 |
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600 |
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0.88 |
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Average |
808 |
932 |
500 |
[Thickness |
1.11 |
0.72 |
300 |
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400 |
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Center: |
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m] |
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200 |
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926 848 750
0.730.65 1.03
629
0.48
405
0.55
907 m
763 m
1182 m
Circle diameters: 1,2.22, 3.45 m
100
0
OCT 30° (8.7 mm) ART (4) Q: 17 [HS]
Fig. 9.5 (continued)
9.3 Central Retinal Vein Occlusion |
231 |
hypertension, and atherosclerotic cardiovascular disease; and presence of preexisting glaucoma. Not all of these tests or pieces of information are typically obtained in every patient, and no universally accepted formula exists to reach the diagnosis of ischemic versus nonischemic CRVO (see Chap. 4).
Of all CRVOs, the nonischemic type make up 50 to 81% and the ischemic type 19–45%, with the remainder indeterminate.18-21,25,27,28,32,35,40,44 As a simple rule, approximately 25% of CRVOs are ischemic and 75% nonischemic at baseline. If one factors in the 34% of initially nonischemic CRVOs that eventually become ischemic over 3 years of follow-up, approximately 50% of eyes with CRVO eventually end up in the ischemic category.31
Many eyes with CRVO have so much intraretinal hemorrhage that the capillary detail of the FA is obscured making a determination of perfusion status impossible (Fig. 8.3).18,49,53 Such eyes generally behave as though they are ischemic and should be managed as such with the more intensive follow-up schedule (monthly for at least 6 months) reserved for ischemic CRVOs.49 Eighty-three percent of indeterminate CRVOs either eventually manifest ischemic status on FA or else develop ASNV before retinal perfusion status can be determined.49
The proportions of ischemic and nonischemic HCRVOs parallel those for CRVO. In a consecutive series of 41 HCRVOs from a single clinic, 66% were nonischemic and 34% were ischemic.20 A later report from the same clinic in a larger number of patients revised these estimates to 78% nonischemic and 22% ischemic.18
Patients with nonischemic CRVO are, on average, younger and less likely to have diabetes mellitus compared to patients with ischemic CRVO.26 There are no differences in prevalence of many factors between ischemic and nonischemic CRVOs, including gender, hypertension, ischemic heart disease, smoking, and cerebrovascular disease.26 Differences among studies in the systemic associations that they report can arise from the different ways the studies define ischemic and nonischemic CRVO.25 Thus, for example, the Eye Disease Case-Control Study differed in its
definitions of ischemic and nonischemic CRVO from Hayreh, making it invalid to compare results across these two studies.26,51
The baseline VA in eyes with nonischemic CRVO is better than in ischemic CRVO. In a series of 29 nonischemic CRVOs, 90% had a baseline visual acuity of 20/40 or better.16 In general terms, presence of a greater number of intraretinal hemorrhages and more cotton wool spots correlates with increasing ischemia, but there are many exceptions (Fig. 9.1).7,48 Many nonischemic CRVOs have some cotton wool spots, and some very ischemic CRVOs show few hemorrhages. Thus, the fundus picture has poor specificity for predicting if the CRVO is ischemic in type or not.22 Two fundus signs are associated with nonischemic status of a CRVO – presence of optic disc collateral vessels and presence of macular lipid.7 Presence of more severe macular thickening on stereoscopic grading of macular fundus photographs is associated with ischemic status of a CRVO (more ME suggests worse ischemia).7 Many of these clinical variables capture similar prognostic information regarding eventual development of ASNV. Therefore, in multivariate models attempting to predict eventual ASNV, a few variables capture almost all of the predictive power. The presence of an RAPD is the most important sign of those variables regularly assessed.7
Visual acuity is a good predictor of fluorescein angiographically defined ischemia in recently diagnosed CRVO. It is not so good for CRVOs of longer duration. During the acute phase of CRVO, if the VA is better than 6/120, the probability is 88% that the CRVO is nonischemic. VA of less than 20/200 in an acute CRVO reliably predicts the CRVO to be ischemic.50 In a large single institution case series with a strict definition of ischemia, all eyes with an ischemic CRVO had initial visual acuity of 20/70 or less.26 In eyes for which the diagnosis of CRVO is made within 1 month of symptoms, if the initial VA is less than 20/200, there is a 54% chance of developing ASNV, usually within the first 8 months.49 Careful follow-up is mandatory with gonioscopy of the undilated eye as NVA precedes NVI in 12% of cases.7