Diabetic retinopathy progresses through several stages, with the most advanced stage possibly leading to blindness. Consultant diabetologist Sandro Vella tells Stephanie Fsadni about the causes and complications of this disease, and how regular screening is imperative to prevent the condition from worsening.

Diabetic retinopathy is the most common cause of visual impairment in type 1 diabetes worldwide, but it can affect patients with both type 1 and type 2 diabetes at different phases of the disease.

“Retinopathy rarely complicates type 1 diabetes within the first five years of diagnosis, but complicates in around 98 per cent of patients by the time 25 years have elapsed,” says consultant diabetologist Sandro Vella.

“Up to a third of newly diagnosed type 2 diabetes patients have evidence of diabetic retinopathy; approximately four per cent have sight-threatening advanced retinopathy.”

Diabetic retinopathy, which may affect one or both eyes, progresses through several stages. The earliest stages are completely asymptomatic (have no symptoms), as long as the disease is contained at that stage. The most serious stages are proliferative retinopathy and maculopathy (disease affecting the macula), which can lead to blindness.

“The former is characterised by new vessel formation as a result of a failure of the microcirculation of the retina. These vessels are particularly fragile and may rupture, resulting in haemorrhage,” explains Vella.

“Leakage from the capillaries in the macular region – which is the most sensitive and important part of the retina – results in oedema (swelling), impairing visual acuity.”

Vella says that it may be particularly difficult to realise one has retinopathy until a sight-threatening stage is reached as it is “largely a silent complication”, with no symptoms.

Then it emerges with “dramatic” results: “Diabetic maculopathy can present with reduced visual acuity. Retinal haemorrhage and detachment, which are complications of severe retinopathy, result in particularly acute, dramatic presentations, typically sudden loss of vision in the affected eye.”

All patients with type 2 diabetes need to commence screening as soon as the diagnosis is made

Retinal haemorrhage refers to bleeding into the retina, a thin layer at the back of the globe of the eye, containing the all important nerve cells responsible for vision. Retinal detachment sees new vessel formation within the retina which complicates advanced diabetic retinopathy. Bleeding from these vessels may eventually cause the retina to detach from the underlying cellular lining, causing serious damage.

Severe retinopathy may also be complicated by glaucoma, that is, an increase in the pressure within the globe of the eye.

It is thus imperative to prevent patients with early-stage retinopathy from developing advanced retinopathy.

“This is indeed the rationale behind annual screening of patients with type 1 and type 2 diabetes,” points out Vella.

“All patients with type 2 diabetes need to commence screening as soon as the diagnosis is made. Screening in type 1 diabetes can be deferred for five years as patients with the latter illness would be expected to be diagnosed soon after onset of the disease.”

Screening is typically carried out by the caring diabetologist or specialist in family medicine using a relatively simple instrument, an ophthalmoscope, after applying special eye drops to both eyes so as to dilate the pupils.

It is a painless procedure; patients are however advised to refrain from driving for a few hours after the procedure as application of eye drops renders the patient’s eyes transiently particularly sensitive the light. Visual acuity is assessed using a Snellen chart before eye drops are applied.

If one has early diabetic retinopathy, one may not need treatment right away but the eye doctor will closely monitor your eyes to determine if you need treatment.

There is no cure for advanced retinopathy and/or maculopathy but it can be treated with laser photocoagulation therapy.

“This essentially entails administration of focal laser burns to the retina in a bid to stabilise the disease and save vision. The process is carried out by an ophthalmologist, generally in an outpatient setting. It is a relatively simple and painless procedure, which entails aiming a beam of light though the pupil at a precise spot,” expounds Vella.

On the other hand, vitreous haemorrhage entails a major surgical procedure called a vitrectomy, wherein abnormal retinal fibrous tissue is cut and sucked out.

“While vision can be dramatically restored, prevention of advanced eye changes by screening and timely laser therapy is far preferable.”

Risk factors

Studies have identified several risk factors for diabetic retinopathy:

• Duration of diabetes: around 20 per cent of all patients with type 2 diabetes have proliferative (advanced, sight threatening) diabetic retinopathy after 25 years of the disease.

• Poor glycaemic control: patients whose sugar levels are consistently uncontrolled increase their risk of this complication.

• Poorly controlled hypertension: studies suggest that control of blood pressure have an even greater effect on the rate of progression of retinopathy than does tight control of blood glucose.

• High cholesterol and triglyceride levels.

• Coexistent kidney disease: often manifest by traces (or more) of protein in a urine specimen.

• Pregnancy: may accelerate progression of diabetic retinopathy.

• Possible association with smoking (particularly in type 1 diabetes).