Diabetes & Diabetic retinopathy

Diabetic retinopathy

In the UK there are approximately 1 million diabetics, of whom 20 per cent are insulin dependent and 80 per cent non-insulin dependent. Blindness amongst diabetics is 10 times the rate amongst the general public, and diabetic retinopathy is the most common reason for blindness in the working age group.

Diabetes causes damage through its effects on both large vessels
(myocardial infarction and stroke) and small vessels (retinopathy, nephropathy, neuropathy,).

In the eye, initial damage is to the small vessel wall and results in microaneurysms with subsequent leakage of blood & plasma

This is known as background diabetic retinopathy. Typical findings include haemorrhages, hard exudates and retinal oedema.

If this affects the macular area, associated swelling in the retina reduces vision ('maculopathy').

Background diabetic retinopathy is commonly present at diagnosis of maturity-onset diabetes, but in juvenile-onset diabetes only 50 per cent of patients will have retinopathy after 10 years, while 90 per cent will be affected after 20 years.

As blood vessel damage progresses capillary closure occurs, inducing ischaemia by preventing the supply of oxygen to that area of retina. This can cause further changes including:-Cotton wool spots (microinfarcts), blot haemorrhages, abnormalities in the retinal veins (Venous beading and venous loops) and Intraretinal micro-vascular abnormalities (IRMA).

This appearance is referred to as 'preproliferative retinopathy'.

Once approximately one-quarter of the retina is ischaemic, further changes can occur:- New vessels grow at the optic nerve head and elsewhere in the retina, which can be associated with fibrotic membrane formation, and the retinal oxygen starvation can cause new vessels to grow on the iris.This is known as 'proliferative retinopathy'.

Complications: There are several reasons why vision can be lost in diabetic eye disease:
Severe macular oedema from long-standing maculopathy
Ischaemic retina at the macula
Vitreous haemorrhage from ruptured new vessels
Fibrotic membranes associated with new vessel formation causing tractional retinal detachment

Malignant glaucoma associated with new vessel growth on the iris (Rubeosis or Rubeotic Glaucoma)

CARE OF THE DIABETIC PATIENT
Strict control of both average blood glucose levels and the daily swing in values is the best way of reducing the risk of diabetic complications/disease progression.

The control of any hypertension or raised blood pressure, raised cholesterol levels, anaemia or poor renal function should be more rigerous in a diabetic poatient than the non-diabetic if complications are to be minimised.

All patients should be refrain from smoking.

Dilated (mydriatic) examinations of the retina should occur every 12 months unless there are significant retinal complications. This is usually done by the patients optometrist and can include retinal photography and Slit Lamp Microscope examination using indirect ophthalmoscopy techniques. This is the method in place in the PortsmouthArea, where the Queen Alexandra Hospital Optometry based Diabetic Screening Scheme has been in place for 8-9 years.

In some areas there is a community mobile photography scheme in place, eg Southampton.

In advanced retinopathy follow up appointments are hospital based under the care of a consultant ophthalmologist

RETINOPATHY TREATMENT
The mainstay of treatment is argon laser photocoagulation (Pan-retinal photocoagulation). This is delivered via a slit lamp as an out patient.

This procedure is sometimes painful and patients can have diffuculty in holding their eyelids open during treatment. In such cases, a local anaesthetic injection can be given beforethe treatment begins.

This procedure destroys some of the visual field, and patients should be warned that treatment might result in failure to maintain the standard demanded to hold a driving licence

Maculopathy
Maculopathy is treated with light argon laser treatment. The laser beam can either be aimed at a leaking point in the retina, or for more generalized oedema a scattered grid pattern across the macula is employed. The former is usually very successful, while the latter is gnerally less so.

Ischaemia
The characteristic fundal changes can be quantified by fluorescein angiography The argon laser is again the mainstay of treatment, but it is used in a destructive capacity. The burns are meant to kill the underlying retina and therefore reduce the ischaemic load. Treatment involves scattering 1000-4000 laser burns around the peripheral retina ('pan-retinal photocoagulation') while sparing the macular area In most cases, new vessel growth can be reversed with involution of the vessels. See photo above.

Vitreous haemorrhage
Persistent haemorrhage that does not clear can be removed by vitrectomy. An endolaser can be used during the operation to apply further pan-retinal photocoagulation.

Traction retinal detachment and fibrous membranes
The fibrotic membranes can be segmented and traction relieved using special scissors after vitrectomy has been carried out