Diabetic microvascular disease - Complications of diabetes

Diabetic retinopathy

Definition

Diabetes can affect almost all the structures of the eye but the retina and the lens are most commonly affected.

Incidence

Leading cause of blindness under the age of 65 in the developed world. After 20 years of diabetes almost all patients have some retinopathy. Around 40% of type 1 and 20% of type 2 diabetics have proliferative retinopathy.

Aetiology

Control of blood sugars and concomitant hypertension has been shown to reduce risk of retinopathy and other microvascular complications.

Pathophysiology

There is a thickening of the capillary basement membrane and hyaline arteriosclerosis. Microaneurysms (dot haemorrhages) occur in some vessels while others become occluded. The weakening of the vessel walls leads to blot haemorrhages, and transudates of fluid and lipid (hard exudates). The obliteration of capillaries causes retinal ischaemia (cotton wool spots) which in turn stimulates the formation of new vessels at the surface of the retina and iris.

Clinical features

All patients with diabetes should be screened regularly for diabetic retinopathy.

Background diabetic retinopathy is the earliest sign of diabetic retinopathy. Initially there are microaneurysms later accompanied by blot haemorrhages and scattered hard exudates. Vision is generally unaffected.

Diabetic maculopathy causes gradual loss of vision due to:

·        Capillary leakage causing macular oedema

·        Lipid deposition

·        Extensive obliteration of macular capillaries

Preproliferative retinopathy is seen most commonly in young patients on insulin for about 10 years. Retinal ischaemia is seen as ‘soft exudates’ or cotton wool spots. Fifty per cent of patients with pre-proliferative changes develop proliferative retinopathy within a year.

Proliferative retinopathy: New vessels develop most commonly at the optic disc on the venous side adjacent to the temporal vessels. They grow into the vitreous and round to the front of the eye when they are visible on the iris. These vessels may bleed either as vitreous (blue-grey opacity) or preretinal haemorrhages (usually flat upper surface), which may cause obscuring of vision for months or years. Scar formation leads to a traction retinal detachment. New vessels forming at the iris are accompanied by obstruction at the drainage angle causing a neovascular or thrombotic glaucoma (a type of secondary closed angle glaucoma).

Complications

Proliferative retinopathy may cause sudden loss of vision from extensive haemorrhage or retinal detachment. Thrombotic glaucoma may also occur.

Investigations

Screening is by fundoscopic or retinal camera examination. Patients require dilation of the pupils. Fluorescein angiography can be used to show very early disease. Acuity testing should be performed to detect early macular disease.

Management

No specific treatment is required for background retinopathy except to maximise diabetic control and manage any coexisting hypertension.

Maculopathy is treated by laser to the centre of a hard exudate.

Proliferative retinopathy is treated by panretinal photocoagulation (PRP), widespread pinpoint laser treatment to the periphery of the retina, destroying the is-chaemic retina. There is then reduction in the growth factors which promote neovascularisation and hence regression of new vessels. Laser treatment also helps prevent neovascular glaucoma.

Surgery may be required to remove vitreous haemorrhage and fibrous tissue or to repair a detached or torn retina.

Prognosis

Prevention is the best management, by regular screening and good control of blood sugar.