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7 The Clinical Picture and Natural History of Retinal Vein Occlusions |
Retinal Whitening Does Not Equal Infarction
The literature on cilioretinal arteriolar circulatory changes in CRVO implies that when whitening occurs in the distribution of the cilioretinal artery, infarction has occurred.91,124 In some cases it has, and in these cases a scotoma is permanent.115 In most cases, however, the fundus signs resolve, as do the scotomata, implying that no infarction has occurred. The opaciÞcation of the retina is not equivalent to infarction but may just be a sign of temporary insufÞcient perfusion and tissue hypoxia, which has been termed cilioretinal arteriolar insufÞciency.16
For example, in their article on cilioretinal artery ÒocclusionÓ in CRVO, Schatz and colleagues write, ÒAlthough evidence of retinal infarction is present because of the presence of white (pale) retina in the area of the cilioretinal artery, it appears that the visual function can improve.124Ó What this statement means is that ischemic retinal whitening is not equivalent to infarction. There are levels of whitening that imply dysfunction, but in which cellular death has not occurred. There is no scotoma on visual Þeld testing, nor is there atrophy of the nerve Þber layer after the whitening has resolved.51,143
A Clinical Picture Predicted by a Hypothesis
The explanation for cilioretinal arteriolar insufÞciency in CRVO predicts an interesting clinical picture yet to be documented. If one were to have a patient with a HCRVO and a cilioretinal artery partially feeding the zone of retina drained by the blocked HCRV and partially feeding the zone supplied by the unobstructed HCRV, then one would expect to see ischemic retinal whitening only in the part of the zone fed by the cilioretinal artery that is in the distribution of the obstructed HCRV.89 Cases of HCRVO with a cilioretinal artery have been reported, but this phenomenon has not yet been observed.51
Although the clinical picture of acute CRVO is fairly speciÞc, the retinopathy of carotid occlusive disease, sometimes called the ischemic ocular syndrome, has been confused with CRVO by clinicians. The features that distinguish this condition are the low central retinal artery perfusion pressure, best assessed by lightly pressing on the eye during ophthalmoscopy, and the uniform absence of optic disc edema.68
7.2.1.3 Visual Acuity
The visual acuity at the time of diagnosis of CRVO can vary from 20/20 to hand motions depending on the degree of ischemia.56,86,140 Twenty-nine percent of eyes with CRVO have baseline visual acuity of greater than or equal to
20/40, 43% of eyes have visual acuity 20/50Ð 20/200, and 28% of eyes have baseline visual acuity less than 20/200.140 In a population-based study, the visual acuity of 60% of patients with CRVO was less than 20/200.96 The median baseline visual acuity in eyes with CRVO in a large randomized clinical trial was 20/80.140 In the pop- ulation-based BDES, the average decrease in visual acuity of patients with incident CRVO was 22 ETDRS letters.72
Baseline visual acuity in CRVO depends on the perfusion status of the retina. Using the Hayreh deÞnition for classifying eyes with CRVO as nonischemic or ischemic, the median baseline visual acuity for nonischemic CRVO in one study was 20/40Ð20/60.56 The median visual acuity for ischemic CRVO was counting Þngers.56