Diabetes-related eye complications are common. If left untreated, they lead to the deterioration of vision and, ultimately, blindness. There are two eye diseases that result from diabetic microvascular complications: diabetic retinopathy and macular oedema.
Diabetic retinopathy is caused by damage to the small blood vessels of the retina in the back of the eye. The small vessels can be damaged by high blood glucose and high blood pressure.
The main stages of diabetic retinopathy are:
- non-proliferative – background diabetic retinopathy, characterized by the development of occasional small blisters (microaneurysms) caused by enlarged capillaries and small haemorrhages on the surface of the retina. Moderately severe to very severe non-proliferative diabetic retinopathy is also known as pre-proliferative diabetic retinopathy.
- proliferative – symptoms of which include: blurred or double vision; reduced vision; and dark or floating spots.
In the non-proliferative stages, abnormal blood vessel permeability results in the leaking of water, blood cells, proteins and fats into the surrounding retinal tissue. At this stage, diabetic retinopathy is usually without symptoms unless accompanied by diabetic macular oedema.
People progress from pre-proliferative to proliferative diabetic retinopathy when new blood vessels grow from, and across, the retina in response to lack of oxygen delivered by the original vessels. This is called neovascularisation. However, these new vessels are very weak and are even more likely to break and bleed into the clear gel (the vitreous) that fills the back cavity of the eye, blocking vision. Scar tissue may also form near the retina, detaching it from the back of the eye and resulting in blindness.
Diabetic macular oedema
This is a common complication associated with diabetic retinopathy. It corresponds to a swelling in the macula, one of the areas of the retina. When some of the small blood vessels in the retina become blocked, the surrounding ones dilate to compensate for this. The dilated vessels are generally leaky and fluid builds up in the macula, which in turn causes the macula to swell and cease to function. It is the most common cause of visual impairment in patients with non-proliferative retinopathy. Loss of vision can occur suddenly and treatment is not as successful.
There is no pharmaceutical therapy available at present that stops the progression of diabetic retinopathy by treating the underlying process of microvascular damage.
Current treatment options (generally reserved for late stage pre-proliferative and proliferative diabetic retinopathy and sight-threatening diabetic macular oedema) include two different forms of laser surgery:
- pan-retinal photocoagulation for diabetic retinopathy.
- focal photocoagulation for diabetic macular oedema.
Laser therapy seals the leaking blood vessels in the macula, slowing the swelling that causes impaired vision.This procedure does not improve blurred vision but it can prevent it from worsening. While laser surgery can usually prevent vision from deteriorating, in most cases it cannot restore vision that has already been lost.
- Diabetic retinopathy is the leading cause of vision loss in adults of working age (20 to 65 years) in industrialised countries. It is estimated that more than 2.5 million people worldwide are affected by it.
- 74 percent of people who have diabetes for 10 years or more will develop some form of diabetic retinopathy.
- Approximately 14 per cent of people with diabetes have diabetic macular oedema and prevalence increases to 29 per cent for people with diabetes who use insulin for more than 20 years.
- Left untreated, 25 per cent of people with diabetic macular oedema will develop moderate vision loss within three years.
- Estimates of the rate of annual eye exams vary greatly by country and study, but the rate of screening is generally fairly low (from 40 to 65 percent).
Worldwide guidelines recommend annual screenings ideally with a dilated eye exam from an optometrist for people with diabetes.