Sleeping posture as a risk factor for retinal vein occlusion

Several studies have shown that increased intra-ocular pressure (IOP) is strongly associated with retinal vein occlusion (RVO) (Glacet-Bernard et al. 2010; Kim et al. 2013; Lee et al. 2013). Recently, it has been shown that in glaucoma patients, sleeping position affects the clinical outcome by increasing intra-ocular pressure (Kim et al. 2013). The effect of sleeping position on patients with RVO events is unknown (Kim et al. 2013; Lee et al. 2013). We conducted a study to evaluate the possible involvement of patients’ sleeping position in RVO events. Our hypothesis states that the patients’ preferred sleeping position (right lateral, left lateral, supine and alternating) is associated with the laterality of the RVO. Pantheon Eye Centre's electronic medical records were used. All the patients on the database (established 2007) with a diagnosis of RVO (CRVO or BRVO) were included in the study. Following ethical approval, the following information was obtained: Age, risk factors/associations with RVO: hypertension, high cholesterol, diabetes mellitus, glaucoma, smoking and provisional diagnosis of obstructive sleep apnoea; which eye was affected from RVO: right, left or both. Sleeping position: To specify the sleeping position, patients were specifically asked on which corner of the bed they usually find themselves when they awaken in the morning and which side do they normally turn to just before they fall asleep. If a patient specified turning to a specific side before falling asleep and finding themselves on the same side when waking up in the morning, this side was taken as their sleeping position. If a patient woke on a different side to the last sleeping position, then they were classed as having an alternate sleeping pattern. Eligible patients were excluded if: they declined participation, were unable to be located following three separate attempts to contact them or were unable to participate due to physical or mental impairments (e.g. aphasia following stroke). Results were tabulated, anonymized and analysed to determine their significance. The chi-square statistical test was used to determine the probability that the null hypothesis would be correct. Based on convention, a probability of less than 0.05 was used as the cut-off for rejecting the null hypothesis. In addition, to determine the degree of correlation between the sleeping position and the eye affected with RVO, correlation analysis was performed. A total of 207 patients were initially deemed as eligible for the study. Forty patients were excluded giving a total of 167 participants (see Table 1). Thirty-two per cent (32%, n = 67) of patients had an RVO on the same side as their preferred side of sleep and 17% (n = 36) of patients had an RVO on the opposite side to their preferred side of sleep. The chi-square test was as follows: χ2 (df = 2, N = 152) = 10.22 p = 0.006 (p < 5%) therefore rejecting the null hypothesis. The results indicate that the preferred sleeping position is related to the side where RVO occurs, with a correlation of 30.3%, when patients alternating from side-to-side were excluded from the calculation. A patient's preferred side of sleep is associated with an increased incidence of RVO on the same side. The role of increased IOP as a risk factor in the pathogenesis of RVO is well established. The hypothesis and hence the results of this study can be explained using this pathophysiology of RVO. We suggest that the sleeping position is a risk factor for RVO.