Retinal Venous Thrombosis
Branch vein occlusion is about three times more common than central vein occlusion. The patients are typically aged 50 years or more. The predisposing factors include diabetes, hypertension, and arteriosclerosis Patients present with painless unilateral visual impairment over a period of hours, often during the night (noticed first in the morning).In a complete occlusion ophthalmoscopy shows an oedematous retina and optic disc, widespread dot and blot haemorrhages in the retina congested and tortuous veins and retinal microinfarcts ("cotton wool spots") In partial occlusion the findings are less severe and in branch vein occlusion the changes are only in the affected quarter of the fundus, most commonly in the upper temporal quadrant and often with oedema and haemorrhages also in the macula.
Up to one third of central vein and almost all branches vein occlusions are of ischaemic type (capillary closure). These may lead to angiogenesis in the retina, iris and the anterior chamber angle. New vessels cause vitreous haemorrhages and neovascular secondary glaucoma refractory to treatment that may develop in 3 months. Prompt laser treatment of the retina (panretinal photocoagulation) stops the angiogenesis, as shown in randomized controlled studies.
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