- Victor Chong, head of department
- 1Oxford Eye Hospital, Oxford University Hospitals, Oxford OX3 9DU, UK
Retinal vein occlusion is one of the most common causes of sudden painless unilateral loss of vision. It is the second most common retinal vascular disease after diabetic retinopathy.1 Occlusion may occur in the central retinal vein or branch retinal vein.
Although specific ocular risk factors for central retinal vein occlusion include increased intraocular pressure and anatomical variation of the optic disc, systemic risk factors occur in patients with both types of occlusion.2 3 In a linked case-control study based on data from Danish national registries (doi:10.1136/bmj.e7885), Bertelsen and colleagues investigated comorbidity in patients with branch retinal vein occlusion.4 They were wise to study only patients with branch retinal vein occlusion because patients with central retinal vein occlusion may have ocular risk factors, so combining patients with both types of occlusion in one study of systemic risk factors could bias the findings.
Patients with retinal vein occlusion usually present with sudden loss of vision in …