Preventing vision loss from Diabetic Eye Disease

Regular examinations of the back of the eye (fundoscopy) are proven to reduce the risk of vision loss. Vision threatening diabetic eye disease may not give out any warning signs to the patient until the vision drops. Regular screening can save vision by the early recognition and treatment of such cases. Screening visits may vary from 3 months to 2 years depending on the severity of diabetic eye disease. Although we now have a number of treatment modalities to control diabetic eye disease, it is very important for the patient to fully engage in their diabetes management and really try to obtain the best possible blood glucose control and blood pressure control. Cholesterol is also important. Patients should also seriously consider stopping smoking. The aim of screening diabetic eye disease is to reduce the risk of severe vision loss by early treatment of sight threatening disease and the reduction of the number of cases with advanced diabetic eye disease that require vitrectomy surgery.

Diabetic Retinopathy

The main eye problem of Diabetes is its effect on the Retina, the light sensing part at the back of the eye. The retina is made up from highly specialised nerve cells, similar to those seen in the Brain. Unlike many other cell types in our body , these retina nerve cells do not regenerate. Diabetes damages the tiny blood vessels called capillaries, which supply oxygen to these nerve cells, causing them to leak fluid and/or block up. If fluid leakage (aka macular oedema) affects the central part of the retina responsible for our central and sharp vision, the vision is reduced. Blockage of blood vessels starves these nerve cells and causes them to malfunction and then die. This is another cause of vision loss, if this affects the central part of the retina. If the blood vessel blockage is extensive, large areas of the retina become starved of oxygen and this causes the release of a special hormone by tissues in the eye called VEGF, which causes new blood vessels to grow inside the eye. One would have thought that this would be a good thing but unlike blood vessels that form when we are embryos in the womb, these new blood vessels can not deliver more oxygen to the retina. Instead they form scarring membranes that contract, bleed and pull the retina off the back of the eye (retinal detachment).

Treatments for Diabetic Macular Oedema

For patients with fluid threatening but not actually affecting their vision, treatment with laser is usually given. Newer laser modalities include the use of micro-pulsed laser (laser beam chopped into tiny pulses) do not leave scars on the retina like traditional laser treatment. 

If there is significant vision loss from fluid leakage in the macula, a series of injections, just like in Wet AMD, may be required. Please see the section on Wet AMD for more details on the individual drugs. Although Diabetic Maculopathy and Wet AMD are fundamentally different, they both result in fluid leakage that damages the macula and both conditions can be managed by injections with drugs that neuralise VEGF in the eye.

The degree of any visual improvement depends on the amount of pre-existing damage to the tiny capillary blood vessels delivering oxygen to the central macula. Sometimes, diabetes can cause the loss of these blood vessels. The benefit of any treatment on drying the macula from fluid would be limited effect on, depending on the degree of capillary blood vessel loss. 

Treatment of Proliferative Diabetic Retinopathy and Advanced Diabetic Eye Disease

When new blood vessels develop on the surface of the retina, this is in response to an imbalance between the high requirements of the retina for oxygen and the reduction of blood circulating in the retina due to closure of the tiny capillary vessels. This is called proliferative diabetic retinopathy. Retinal cells secrete VEGF, a hormone secreted when oxygen supply to the tissues is compromised. VEGF causes the growth of new blood vessels. The treatment for new blood vessels is by applying continuous wave laser in a scatter fashion throughout the retina but avoiding the macula (Pan Retinal Photocoagulation - PRP Laser). This reduces the oxygen demand by the retina and as a result VEGF production stops. If the new blood vessels are caught at an early stage, they shrink and disappear. If the new blood vessels are established, scar membranes also form alongside these new vessels and even with treatment, the scar membranes may persist. Sometimes these membranes contract and lift off the retina causing a tractional retinal detachment (different to the usual type of retinal detachment).  If the detachment affects the macula, the vision drops and often can not be recovered to its pre-existing state. If membranes threaten vision, surgery may be indicated to cut off these membranes in an attempt to preserve as much vision as possible. We use Avastin or Lucentis in advanced diabetic eye disease when preparing the eye for surgery by injecting it 3 days before the operation, in order to reduce bleeding during surgery and improve visualisation during surgery. Surgery for advanced diabetic eye disease is one of the most risky types of retinal surgery and the success of any screening programme for diabetic retinopathy is to prevent as many cases of advanced diabetic eye disease by detecting new blood vessels early and applying PRP laser.

The importance of controlling Diabetes
The most important treatment of diabetic eye disease is actually controlling blood sugar, blood pressure, cholesterol, body weight and taking up exercise. These measures are  proven to  reduce the risk of severe vision loss in the long term and every diabetic, especially those with established eye disease, should strive to achieve them with the help of their physicians.