This is more common in hypertensive patients compared with normotensives. The most frequent occurrence is the central retinal vein occlusion (CRVO), although branch retinal vein occlusions can occur at arteriovenous crossings. The fundus appearance in CRVO is dramatic with numerous scattered haemorrhages and swelling of the optic disc, and the patient experiences sudden blurring of vision in one eye (Figure 21.12). This can be compared with occlusion of the central retinal artery, which is less common and in which the prognosis is uniformly worse. Here, the fundus appears pale and the arteries are narrowed. There is a cherry-red spot at the macula.
In older patients, the already narrowed vessels tend to show less dramatic changes. Hypertonicity of the vessel walls is not seen but arteriovenous nipping remains an important sign and haemorrhages might be present in more severe cases. The cotton-wool spots of hypertension reflect ischaemic damage to the nerve fibre layer caused by obstruction of the retinal precapillary arterioles. Exudates are caused by abnormal vascular permeability.
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