Diabetic retinopathy screening

What it is

Diabetic Retinopathy (DR) is the most common cause of blindness in people with diabetes. It comes in two forms. Non-proliferative disease is increased vascular permeability and retinal ischemia. Proliferative disease is the growth of abnormal blood vessels.

It is also set out in grades. Grade 1, the non proliferative grade, is microaneurysms and exudates; grade 2 is venous hemorrhage and cotton wool spots; grade 3 is neovascularization. Put the other way, the background type is flame hemorrhages, microaneurysms and hard or soft exudates, the cotton-wool spots, on the retina, while the proliferative type is more advanced disease with neovascularization easily visible around the fundus, that is hyperemia, and hard exudates. It occurs after approximately 10 yrs of diabetes, and there is a direct correlation with the levels of HgA1c: the higher the levels, the higher the incidence.

How it presents

On the retina, non-proliferative disease shows microaneurysms, dot and blot hemorrhages, hard exudates, which are lipid deposits and are non-specific for DR, and macular edema. Advanced non-proliferative disease, or pre-proliferative, is those findings plus venous beading in 2 or more of the 4 retinal quadrants and intraretinal microvascular anomalies (IRMA) in 1 of the 4 quadrants. IRMA are dilated, leaky vessels within the retina, and they give cotton wool spots, which are nerve fiber layer infarcts. On funduscopy the diabetic retina reads differently from the hypertensive one. In diabetic retinopathy the retina is wet, with multiple hemorrhages, extensive edema and multiple exudates, few cotton wool spots, rare flame shaped hemorrhages, and the visually abnormal blood vessels are the veins. In hypertensive retinopathy the retina is dry, hemorrhages are few, edema and exudates are rare, cotton wool spots are multiple, flame shaped hemorrhages are common, and the abnormal vessels are the arteries. The three terms come down to this: dots and blots are microaneurysm and retinal hemorrhage, cotton wool is retinal infarcts, and exudates are the deposition of lipids leaked from vessels. On fundoscopy the diabetic retinopathy signs are dot and blot haemorrhages, cotton wool spots, neovascularisation and retinal fibrosis, seen by following the blood vessels out from the optic disc into each of the 4 quadrants. Cotton wool spots are not the diabetes alone: their causes are HIV infection per se, anaemias, infective endocarditis, leukaemias and diabetic retinopathy.