April 26, 2003
ABC of diabetes : Clinical review (1)
BMJ 2003;326:924-926 ( 26 April )
Retinopathy
Blindness is one of the most feared complications of diabetes but also one of the most preventable. Diabetes is the commonest cause of blindness in people aged 30 to 69 years. Twenty years after the onset of diabetes, almost all patients with type 1 diabetes and over 60% of patients with type 2 diabetes will have some degree of retinopathy. Even at the time of diagnosis of type 2 diabetes, about a quarter of patients have established background retinopathy. Treatment can now prevent blindness in the majority of cases, so it is essential to identify patients with retinopathy before their vision is affected.
Classification of retinopathy
Diabetic retinopathy is due to microangiopathy affecting the retinal precapillary arterioles, capillaries, and venules. Damage is caused by both microvascular leakage from breakdown of the inner blood-retinal barrier and microvascular occlusion. These two pathological mechanisms can be distinguished from each other by fluorescein angiography.
Background retinopathy
Microaneurysms are small saccular pouches, possibly caused by local distension of capillary walls. They are often the first clinically detectable sign of retinopathy and appear as small red dots, commonly temporal to the macula.Haemorrhages may occur within the compact middle layers of the retina and appear as "dots" or "blots." Rarely, haemorrhages occur in the superficial nerve fibre layer, where they appear flame shaped; these are better recognised as related to severe hypertension. Hard exudates are yellow lipid deposits with relatively discrete margins. They commonly occur at the edges of microvascular leakage and may form a circinate pattern around a leaking microaneurysm. They may coalesce to form extensive sheets of exudate. Vision is affected when hard exudates encroach on the macula.Retinal oedema is due to microvascular leakage and indicates breakdown of the inner blood-retinal barrier. It appears as greyish areas of retinal thickening. The thickening may look like a petal shaped cyst on the macula, and this can cause severe visual deterioration.Clinically significant macular oedema requires treatment. It is defined as any one of the following:
Retinal oedema within 500 µm (one third of a disc diameter) of the fovea
Hard exudates within 500 µm of the fovea if associated with adjacent retinal thickening
Retinal oedema that is one disc diameter (1500 µm) or larger, any part of which is within one disc diameter of the fovea.
Twenty per cent of eyes with clinically significant macular oedema will have serious visual loss in two years without treatment compared with 8% of treated eyes.
Preproliferative retinopathy
Retinal ischaemia due to microvascular occlusion may lead to neovascular proliferation. Signs of ischaemia include cotton wool spots, large dark blot haemorrhages, venous beading and looping, and intraretinal microvascular abnormalities. Cotton wool spots appear as white patches with rather feathery margins and represent microinfarcts in the nerve fibre layer; they become clinically important when there are more than five.
Proliferative retinopathy
New vessel formation may occur at the optic disc (NVD) or elsewhere on the retina (NVE). New vessels on the disc are particularly threatening to vision, and if allowed to progress they often lead to vitreous haemorrhage. If untreated, 26% of eyes with "high risk" and neovascular proliferation on the disc will progress to severe visual loss within two years. With laser treatment, this figure is reduced to 11%.
Advanced eye disease
In advanced proliferative diabetic retinopathy, progressive fibrovascular proliferation leads to blindness due to vitreous haemorrhage and traction retinal detachment. Rubeosis iridis and neovascular glaucoma occur when new vessels form on the iris and in the anterior chamber drainage angle, leading to a painful blind eye that occasionally requires enucleation.
Posted by mehdi khanlari at April 26, 2003 12:44 PM