that compared prevalences of systemic associations to a gender-, race-, and age-matched national cohort, hypertension was more prevalent in pooled CRVO and HCRVO than in the comparison group.75 In that study, the proportion of patients with hypertension was consistently higher in patients with ischemic CRVO than in patients with nonischemic CRVO across the three age groups examined.75 Not all studies are in agreement.39

In a meta-analysis of ten pooled, mostly casecontrol studies, the overall OR for systemic hypertension as a risk factor for CRVO was 3.8 (95% CI 1.9Ð7.4).142 Other case-control studies not in the meta-analysis are in agreement and further demonstrate a gradient of increasing risk as either DBP or SBP increases.142 The risk gradient is steeper for SBP than for DBP.99,181

Hayreh has made a point of differentiating hypertension at home from that present in the doctorÕs ofÞce. He emphasizes that the dangers of treating hypertension present only at the doctorÕs ofÞce may outweigh the beneÞts of treating hypertension at home.72

Several studies have found no differences in the systemic associations of CRVO and HCRVO, leading them to pool the two groups.6,75 The association of hypertension with HCRVO is widely considered to be the same as with CRVO.

6.2.2 Diabetes Mellitus

Diabetes mellitus is a risk factor for all forms of RVO for biologically plausible reasons. It leads to changes in endothelium and the clotting and Þbrinolytic system that can be summarized as a hypercoagulable state.24 For all forms of RVO, the importance of diabetes as a risk factor is secondary to that of hypertension and hyperlipidemia.36,142

6.2.2.1 Pooled Retinal Vein Occlusion

In a retrospective study using a national insurance database, the prevalence of diabetes among patients with RVO was 43.4% compared to 3.1% among ageand gender-matched controls (P < 0.001).81 Case-control studies vary in whether they show an association between pooled RVO

and diabetes with some showing an association and others not.147,151In a meta-analysis of 21 pooled studies, the pooled OR for diabetes as a risk factor for pooled RVO was 1.5 (95% CI 1.1Ð2.0) and other studies since not included in that metaanalysis are consistent.36,142,147 The PAR% for diabetes as a factor contributing to RVO was 4.9% (95% CI 0.8Ð11.5%).142

In the BDES, diabetes was more prevalent among subjects with RVO than subjects without pooled RVO (18.4% vs. 8.9%, respectively, P = 0.04). On the other hand, in the BMES, no difference was found in the prevalence of diabetes among subjects with pooled RVO compared to subjects without RVO (8.6% vs. 7.7%, respectively; P = 0.79).31 In accord with this result, fasting blood glucose was not a risk factor for prevalence of pooled RVO in the BMES.132 In a population-based study from Japan, there was no association of diabetes and pooled RVO.206

Fasting serum glucose was not a risk factor for incidence of pooled RVO in the BMES.32

6.2.2.2 Branch Retinal Vein Occlusion

Patients with BRVO have a higher area of immunoreactive insulin in plasma during oral glucose tolerance testing than normal control patients, indicating insulin resistance.143 In multiple case series, the prevalence of diabetes mellitus in patients with BRVO has been reported to range

from 3% to 33%.6,17,39,58,69,84,148,163,173,193,195,207 In a

case series that compared prevalences of systemic associations to a gender-, race-, and age-matched national cohort, diabetes was more prevalent in BRVO patients less than 45 years old than in an historical comparison group.75 This association did not hold for patients 45 years or older.75

In three case-control studies, prevalence of diabetes did not differ between patients with BRVO and the control groups.39,84,147 In the EDCCS, presence of diabetes was a risk factor for BRVO in univariate analysis, but not in multivariate analysis.180 However, the small sample sizes of most case-control studies limits the statistical power to detect a difference. In a metaanalysis of 11 pooled case-control studies, the pooled OR for diabetes as a risk factor for BRVO was 1.1 (95% CI 0.8Ð1.5).142