5.4.2.3 CRVO

In many case-control studies, clinical trials, and case series, males make up a disproportionate percentage of cases of CRVO. In six studies comprising 2,094 cases of CRVO, males made up 55.1% of cases.11,20,35,38,50,52 However, in popula- tion-based studies, gender has not been a risk factor for CRVO.29

5.4.2.4Hemicentral Retinal Vein Occlusions

A case series and a case-control study suggest that males are disproportionately represented among HCRVO cases. In two studies comprising 107 cases of HCRVO, males made up 53.3% of cases.2,47 The absence of population-based data, however, makes this suggestion suspect, together with the consensus that the pathogeneses of HCRVO and CRVO are the same.

5.4.3 Race

In a meta-analysis of 15 population-based studies, the prevalences of pooled RVO and BRVO were found to vary by race (Table 5.3).44 Hispanics had the highest prevalence and whites the lowest among the four groups analyzed. Because most of the 15 studies were of subjects from a single race, the observed differences could be due to differences in study methodologies rather than true racial differences.51 The prevalence of CRVO prevalence did not vary by race.44

Results from case series and case-control studies have differed from the results of population-

based studies. In a case-control study of pooled RVO, race was not associated with RVO.43 In the EDCCS, race was not associated with increased or decreased risk for BRVO.51 In a case-control study of 265 BRVOs, no significant difference was seen in racial proportions between the group with BRVOs compared to the control group.25 Greater weight should be given to the results derived from population-based studies.

5.4.4 Laterality

There is inconsistency in the literature on the significance of laterality. One case series reported that CRVO was more common in right than left eyes.19 In earlier case series of CRVOs from the same author, however, a preponderance of left eyes was reported.16,17 Major BRVO was reported to be more common in right eyes.17 There were no statistically significant differences in proportions for HCRVOs and macular BRVOs.17 In a population-based study, however, laterality was not associated with BRVO or CRVO.29 No biologically plausible reason for a disproportionate involvement of one side or another has been advanced for RVO.

5.4.5 Body Mass Index

Body mass index (BMI) is calculated as the weight in kilograms divided by the squared height (in meters).13 In the EDCCS, BMI was not associated with RVO.52 In the BDES, among a

population of age 43–86, the mean BMI of patients with pooled RVO was 29.2 (95% CI 27.9–30.5) compared to 28.8 (95% CI 28.6–28.9) for subjects without RVO.8 In the BMES, among a population greater than or equal to 49, the mean BMI was 25.5 (95% CI 24.3–26.6) compared to 26.2 (95% CI 26.0–26.3) for subjects without RVO.8 When analyzed by dividing BMI into three groups, the distributions of subjects were not statistically different between those with and without pooled RVO in both the BDES and the BMES.8,39 In a population-based study from Japan, BMI was not associated with prevalence of BMI.59

In the BMES, BMI was not a risk factor for prevalence or 10-year incidence of pooled RVO.9,39 In the BDES, BMI was not associated with prevalence or 5-year incidence of BRVO.29 On the other hand, obesity, defined as a BMI greater than or equal to 30, was a significant risk factor for pooled RVO with an age-adjusted OR of 2.16 (95% CI 1.02–4.56).9

5.4.6 Education

A case-control study found that a person who completed at least 12 grades of education had 60% of the risk of developing CRVO compared to a person who had completed fewer than 12 grades of education.52 Similarly, increased education was associated with protection from HCRVO.47

case-control study found that subjects with the highest level of physical activity had half the risk of developing CRVO compared to those with the lowest level of physical activity.52 Higher levels of physical activity were more protective for CRVO than HCRVO. In the latter, no protective effect was found, but the number of cases of HCRVO studied was only a third of the number of patients with CRVO studied.47

5.4.8Miscellaneous Factors Explored and Not Found Important

In a prospective clinical series of 557 patients with CRVO, 129 patients with HCRVO, and 345 patients with BRVO, no seasonal variation was observed in the time of onset of any type of RVO.18

In a retrospective study using a national insurance database from Taiwan, the prevalence of residence from any of four regions of the country did not differ among patients with pooled RVO.21 In the EDCCS, iris color, marital status, and parity were examined and not found to be associ-

ated with pooled RVO.52

5.5Bilaterality of Retinal Vein Occlusion, Different Types of Retinal Vein Occlusion

in the Same Eye, and Sequential Retinal Vein Occlusion

in Same and Fellow Eye

Evidence of the relationship of exercise to RVO is inconsistent. A population-based study from Japan found no association of regular exercise and pooled RVO.59 In the EDCCS, increased physical activity was a protective factor against BRVO.51 In the BDES, after adjusting for age, physical activity was not associated with 15-year incidence of BRVO.33 As for CRVO, one

Multiple cases have been reported of the same or different types of RVO in one eye (Fig. 5.6).17,49 Twenty-one instances were documented among 1,229 eyes with RVO in one report.19 In the BMES, 59 subjects had RVO of any type at baseline of whom three (5.1%) had bilateral RVO.39 Over a 5-year period of follow-up, three (6.4%) developed a second RVO.9 In a case series of

1,229 pooled RVOs, the risk for a fellow eye involvement was 8% and 12% at 2 and 4 years, respectively.19 The risk of developing a second episode of the same or different types of RVO in the same eye was 1% within 2 years and 2.5% within 4 years.19

a

c

5.5.2 Branch Retinal Vein Occlusion

Among patients with BRVO in one eye, 3–11% have been reported to have simultaneous evidence of BRVO present in the fellow eye, and up

b

d

Fig. 5.6 Fundus images of a 66-year-old, hypertensive man with a history of coronary artery disease who was seen in 2008 with a history of 1 month of blurred vision of the right eye. At presentation, he had three independent BRVOs in two eyes, and under observation, he developed a fourth BRVO. (a) Monochromatic fundus photograph of the right eye shows a fresh superotemporal branch retinal vein occlusion (the turquoise arrow) and an unsuspected, old inferotemporal BRVO (the yellow arrow). (b) Monochromatic fundus photograph of the left eye shows an unsuspected, old superonasal macular BRVO (the yellow oval). (c) Frame from the late-phase fluorescein angiogram of the right eye shows no hyperpermeability of the retinal venules and capillaries associated with the right eye inferotemporal BRVO (the yellow oval) but prominent hyperpermeability of the capillaries associated with the superotemporal BRVO (the turquoise oval). (d) Frame from the late-phase fluorescein angiogram of the left eye

showing a focus of hyperpermeable capillaries associated with the superonasal macular branch retinal vein occlusion (tan arrow). The green arrow indicates the site of a second BRVO that developed in this eye in 2011, 3 years after the date of this photograph. The vein distal to this point may be slightly distended compared to the venous segment proximal to this arteriovenous crossing. (e) Frame from the late-phase fluorescein angiogram of the right eye taken 3 years later. Both BRVOs in the right eye now show resolved microvascular hyperpermeability (the yellow and turquoise ovals). The tan arrow indicates the arteriovenous crossing associated with the inferotemporal occlusion. (f) A fresh superotemporal BRVO has developed in the left eye at the arteriovenous crossing indicated by the turquoise arrow. This BRVO is ischemic with venous wall staining and more than five disk areas of capillary nonperfusion. The original macular BRVO is indicated by the yellow oval