In the BDES, diabetes mellitus was a risk factor for prevalence of BRVO with an OR of 2.43 (95% CI 1.04, 5.70), but not for 5- or 15-year incidence of BRVO.95,96

6.2.2.3 Central Retinal Vein Occlusion

Among patients with CRVO and no diagnosis of diabetes, 23% have been reported to have an abnormal glucose tolerance test.71 In many case series of patients with CRVO, the prevalence of diabetes in patients with CRVO has ranged from

6% to 75%.6,17,39,58-60,69,74,89,90,117,118,207 In a case

series that compared prevalences of systemic associations to a gender-, race-, and age-matched national cohort, diabetes was more prevalent in ischemic CRVO than in the comparison group.75 This was not true for nonischemic CRVO.75

Individual case-control series are inconsistent; some Þnding and others not Þnding an association between diabetes and CRVO.39,99,147,181 In a meta-analysis of ten case-control studies, the pooled OR for diabetes as a risk factor for CRVO was 2.0 (95% CI 1.2Ð3.4).142

The BDES studied risk factors for 15-year incidence of CRVO and in a multivariate analysis found diabetes to be an independent risk factor with OR 6.35 (95% CI 1.90Ð21.27, P = 0.003).96

6.2.3 Hyperlipidemia

Certain forms of hyperlipidemia are associated with atherosclerosis and arterial disease, so the inconsistently observed association with RVO is plausible.190 Distinctions must be made between classes of lipids, because some appear to be protective (e.g., high-density lipoprotein (HDL) cholesterol), whereas others appear to be risk factors (e.g., low-density lipoprotein (LDL) cholesterol).174,206 When associations have been detected, they have generally been weaker than the association with hypertension.

6.2.3.1 Pooled Retinal Vein Occlusions

In a retrospective study using a national insurance database, the prevalence of hyperlipidemia among patients with RVO was 53.1% compared

to 1.3% among ageand gender-matched controls.86 In various case-control studies, some have reported an increased prevalence of hyperlipidemia among patients with pooled RVO and others not.39,142,147 In a meta-analysis of 21 pooled studies, the overall OR for hyperlipidemia as a risk factor for RVO was 2.5 (95% CI 1.7Ð3.7).142 The PAR% for hyperlipidemia as a factor contributing to RVO was 20.1% (95% CI 5.9Ð43.8%).142

In a population-based study from Japan, there was no association of total cholesterol, triglycerides, or HDL cholesterol and prevalence of pooled RVO.206 In the BMES, there was no association between 10-year incidence of pooled RVO and any of the following lipid measurements Ð total cholesterol, HDL cholesterol, or serum triglycerides.32

6.2.3.2 Branch Retinal Vein Occlusion

The reported prevalence of hypercholesterolemia in BRVO has ranged from 10% to 79% across sampled populations.39,58,87,147,195 In the EDCCS, presence of hyperlipidemia was a risk factor for BRVO.180 An increasing HDL cholesterol was a protective factor against BRVO.180 Total cholesterol was not a risk or protective factor for BRVO.180 In a meta-analysis of 11 pooled casecontrol studies, the pooled OR for hyperlipidemia as a risk factor for BRVO was 2.3 (95% CI 1.5Ð3.5) and other case-control studies since that meta-analysis have been in agreement.142,147

In the BDES, none of the following were associated with prevalence or 5-year incidence of BRVO: serum total cholesterol, serum HDL cholesterol, or total cholesterol to HDL cholesterol ratio.95 In the BDES after adjusting for age, HDL cholesterol was not associated with 15-year incidence of BRVO.96

6.2.3.3 Central Retinal Vein Occlusion

Elevated serum cholesterol has been reported in 8Ð72% of patients with CRVO.6,39,87,118,147 Elevated serum total lipoprotein and triglycerides have been reported in 9Ð33% of patients with CRVO.6,39,68,87,123 In one case series of 612 patients, the proportions of patients with CRVO with