series of 26 patients with pooled RVO and 23 patients with pooled retinal artery occlusions, carotid stenosis greater than 50% was more common in the patients with pooled retinal artery occlusions.135 Based on the available evidence, presence of RVO is not in itself an indication to pursue a carotid disease workup.

As with carotid artery disease, investigations regarding associations of peripheral vascular disease and RVOs are few and not deÞnitive. In a large case series, patients with BRVO had a signiÞcantly higher prevalence of peripheral vascular and venous disease than did patients with CRVO.75 In a case-control study, deep venous thrombosis was more prevalent in 294 patients with BRVO than in controls (4.8% vs. 0.7%, P < 0.01).195 In a large case series, patients with ischemic CRVO and nonischemic CRVO had similar proportions of peripheral vascular disease (4.1% and 4.9%, respectively).75

6.2.5Rheologic and Hematologic Abnormalities

Although many early studies suggested that rheologic and hematologic abnormalities might be associated with RVO, the possible effects of confounding became clearer later, and more recent studies suggest that rheologic and hematologic associations are weaker than earlier supposed.198 There are many technical and interpretational difÞculties with these types of studies. Controls must be appropriately chosen, as gender affects hematocrit (males have higher values).198 Age, gender, and smoking can affect erythrocyte aggregation. Therefore, laboratory comparisons of erythrocyte aggregation need to be adjusted for these potential confounding variables.26,61 Moreover, patients with CRVO and BRVO should not be pooled when investigating associations involving whole-blood viscosity, because ESR is elevated in CRVO, but not in BRVO, and because an elevated ESR can inßuence wholeblood viscosity.200 In tests of platelet aggregation, it is important to adjust for levels of serum lipids which can affect this variable.41 With the

exception of those clinicians who use isovolumic hemodilution, it is unusual for a hematologic or rheologic abnormality to drive a therapeutic response in the management of RVO.

There are so many possible laboratory associations with RVO that how these Þndings might inßuence patient management is problematic. For example, in an uncontrolled case series of 535 consecutive patients with CRVO, HCRVO, and BRVO, Hayreh and colleagues have reported on the prevalence of abnormalities of many hematologic and assorted other laboratory tests including hematocrit, hemoglobin, white blood cell count, platelet count, erythrocyte sedimentation rate, blood urea nitrogen, creatinine, glucose, cholesterol, triglycerides, total protein, albumin, uric acid, calcium, phosphorus, ßuorescence treponemal antibody, Venereal Disease Research Laboratory antigen, and antinuclear antibody.79 CRVO and HCRVO were classiÞed as ischemic and nonischemic. BRVO was classiÞed as major and macular. The highest prevalences of abnormalities were blood urea nitrogen found in 46.6% of patients with ischemic CRVO and HCRVO pooled into a single group, and antinuclear antibodies, found in 45.7% of patients with nonischemic HCRVO.79 Many tests had prevalences of abnormalities greater than 10%, and no recommendations were offered for how the results of such testing might be useful in the care of patients with RVO. Without correction for multiple statistical hypothesis testing, there were a few tests that had statistically signiÞcant differences across different types of RVO, but none of the differences persist if correction is applied for the many tests applied in the paper.79 The ability to interpret this wealth of data is hampered by the lack of a control group in the study to allow for comparison of the reported prevalences of abnormal laboratory values.79

The associations of rheologic and hematologic variables with pooled RVO that have been reported in the literature are inconsistent as portrayed in Table 6.2. None of these laboratory studies is routinely obtained in the clinical care of patients with RVO.

In the BMES in which 10-year incidence of pooled RVO was the outcome variable, there was no association with hemoglobin, hematocrit, white

*Not adjusted for ESR, absence of gender distribution

*Disproportionate percentage of men in the ischemic group,# absence of gender information