Some studies have reported a strong seasonal pattern to central retinal vein occlusion (CRVO) occurrence with a peak in January, but other studies have failed to replicate this finding. The authors sought to determine data for Stockholm’s seasonal variation in CRVOs and retrospectively reviewed the charts of all patients presenting to the main Stockholm eye hospital – St Eriks – between 2008 and 2013. There were 854 such cases in the study period with an incidence of 2/10,000 in the over 40, and 7/10,000 in the over 85 year group. Attendance records showed a peak in the late winter / early spring period which was significantly higher than the late summer / early autumn (p<0.0002). Could it be that Swedes are too busy sailing in the archipelago to bother about sight loss in the summer? Or do the cold winters freeze their eyes? The authors suggest a number of possible explanations to account for this finding. Cold temperatures have been shown to be able to result in increased blood viscosity and clotting factors, and blood pressure too has been reported to increase during the winter months. However, the most compelling reason given is that Vitamin D levels slowly run out during the winter months and the timing of the lowest level of Vitamin D coincides with the highest rate of CRVO. Could this just be a coincidence? Though causality cannot be proven, a recent meta-analysis has shown that low Vitamin D levels are associated with high blood pressure and endothelial dysfunction including changes to clotting factors. The authors cite a study in which patients at increased risk of CRVO (type II diabetics) were given Vitamin D supplements and this improved their blood pressure and endothelial cell responsiveness to changes in flow. At the moment this all remains speculative, but fascinating.

Seasonality and incidence of central retinal vein occlusion in Sweden: a 6-year study.
Epstein D, Kvanta A, Lindqvist PG.
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Jonathan CP Roos

Harvard, Cambridge & Moorfields-trained Consultant Oculoplastic Surgeon and academic based in London at Publishes in the world’s leading medical journals and lectures internationally on aesthetics, eyelid diseases and thyroid eyes.

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