Diabetic Retinopathy Part 2

This article is best viewed in a PDF Format.

View PDF 

View PDF 

View PDF 

Cotton-wool spots

Cotton-wool spots are due to a fracture of nerve fibres in the nerve fibre layer, resulting from small areas of vascular occlusion. The nerve fibres break and axonal fluid leaks into the retina. They are sometimes called ‘soft exudates’ because of their hazy borders, but this is a somewhat archaic term and potentially leads to confusion with exudates in general, so is not encouraged. The pallor is probably due to an increase in retinal thickness and increases in extracellular fluid volume. This fluid pushes on adjacent vessels which may deviate around cotton-wool spots, giving a characteristic feature. The presence of many such lesions is clearly a sign of significant ischaemia, as is visualised most dramatically on a fluorescein angiogram, where the lesions appear black due to the absence of perfusion. As they are characteristic of ischaemia, cotton-wool spots are found in many conditions where there is limitation of perfusion, for example, inflammatory conditions such as Behçet’s and systemic lupus erythematosus, blood and circulatory diseases such as sickle cell anaemia, ischaemic central retinal vein occlusion, and malignant hypertension, and congenital conditions such as Coats’ disease. It is also known that HIV infection causes a specific retinopathy where there are several cotton-wool spots present in the absence of significant vascular changes and this occurs prior to the impact of any opportunistic secondary infection related to AIDS.