6.2 Systemic Associations

Table 6.1 Abbreviations used in association studies of retinal vein occlusion

cally adjust for the increased chance of Þnding an association based on the number of hypothesis tests performed.75

Some studies pool all RVOs, and others split them into two categories. In studies that split, BRVO and CRVO are always separated, but HCRVO is sometimes included with BRVO and other times with CRVO.75 The issue is controversial. In a large consecutive case series, there was no difference in prevalence of any systemic disease between CRVO and HCRVO tending to support the practice of lumping these two together.75 Some authors have found no difference in associated risk factors between BRVO and CRVO, perhaps because the sample sizes were too small to enable small distinctions to be made.151 Others insist that the proÞle of associations differs.75 For example, the association of glaucoma and CRVO is stronger than the association of glaucoma and

BRVO, and average IOP tends to be lower in BRVO than CRVO.52,84 Ideally, studies should not pool all types of RVO as there is evidence that there are important differences in pathophysiology and risk factors.6 Nevertheless, the literature on pooled RVOs is large, and it is not ignored here.

The methods used in determining systemic and ocular associations with RVO are the same as those used in epidemiologic studies of demographic variables. The deÞnition of important terms and concepts in these types of studies are deÞned in Chap. 5 and are not repeated here. Table 6.1 lists the terms abbreviated in this chapter.

6.2 Systemic Associations

In some studies, a veritable Þshing expedition for associations with RVO was launched. If there is no plausible reason to suspect that a systemic condition is related to the pathophysiology of RVO and no association has been found, such negative data is ignored here. As an example, there is no reason to suspect that cataract is related to the pathogenesis of RVO, so data on such associations is omitted from this chapter.95

The list of suggested systemic associations with RVOs of all types is extensive. Across studies, the associations observed have been inconsistent. Generally, systemic hypertension is the strongest systemic association with all forms of RVO. However, even for hypertension, the literature includes counterexamples challenging its signiÞcance.98 After hypertension, less strongly associated systemic risk factors include diabetes, hyperlipidemia, cardiovascular disease, and stroke. Their relative importance varies with the type of RVO under consideration.32,81,132,151 Many other systemic diseases and laboratory studies are inconsistently associated with RVO.132

Patients with RVOs often have multiple systemic risk factors for their condition, some of which are genetic and some which are acquired.108 The focus of Chap. 3 was on the genetic risk factors. This chapter focuses on factors that are not clearly genetic, although they, too, may have a genetic component. In the interaction of genetic and acquired risk factors for retinal vein