Diabetic retinopathy is damage to the retina (the light-sensitive inner lining of the back of the eye) associated with the systemic disease diabetes mellitus. Diabetic retinopathy is the leading cause of blindness among adults in Australia.
What causes diabetic retinopathy?
Diabetes mellitus (also simply called diabetes) is characterised by an altered metabolism of carbohydrates and lipids, resulting in a chronic elevation in blood sugar (hyperglycemia). Hyperglycemia can lead to long-term changes in the circulatory and nervous systems in the body. The hyperglycemia experienced by diabetics is related to an inability to produce sufficient insulin, a resistance to the effects of insulin, or both.
The diagnosis of diabetes is made based on a person's fasting plasma glucose (FPG) levels, (commonly referred to as the fasting blood sugar). An FPG level of 7.0mmol/l or higher indicates the presence of diabetes mellitus.
Diabetic retinopathy is a complication of diabetes in which the tiny blood vessels in the retina are damaged by the disease. Damage to the retinal blood vessels can cause a number of problems. In some cases, the damaged blood vessels leak fluid and lipids under the macula, the most sensitive part of the retina that allows us to see details. The fluid causes the macula to swell, blurring vision. In other cases, the retinal blood vessels can become blocked, causing portions of the retina to cease functioning because of lack of oxygen and nutrients.
In its advanced stage, diabetic retinopathy is characterised by the growth of fragile blood vessels along the retina and into the clear, gel-like vitreous that fills the inside of the eye. These tiny blood vessels can break open and bleed, causing vision to be obscured and permanent damage to the retina.
How common is diabetic retinopathy?
Approximately 1.5 million Australians have diabetes and 50% are unaware of their condition. All people with diabetes - those with Type 1 diabetes (previously called juvenile onset diabetes) and those with Type 2 diabetes (previously called adult onset diabetes) are at risk of developing diabetic retinopathy.
According to the National Eye Institute, nearly half of all people with diabetes will develop some degree of diabetic retinopathy in their lifetime. The longer a person has diabetes, the more likely they are to have diabetic retinopathy. After having diabetes for 15 years, about 80% of Type 1 diabetics will have some degree of retinopathy.
Risk factors for diabetes (and therefore diabetic retinopathy) include:
- Obesity (more than 20% heavier than your ideal body weight)
- A family history of diabetes
- Hypertension (blood pressure of 130/90 or higher)
- Having a high density lipoprotein (HDL or "good cholesterol") reading of 1.0 mmol/l or lower
- Elevated triglyceride levels (2.5 mmol/l or higher)
- Having been diagnosed with gestational diabetes during a pregnancy or having given birth to a baby weighing 9 pounds (4 kg) or more
- Being a member of a high risk ethnic group
What are the symptoms of diabetic retinopathy?
Diabetic retinopathy often has no early warning signs. There is no pain, and vision may remain unaffected until the disease becomes severe.
If leaking blood vessels cause swelling of the macula (called macular oedema) central vision will become blurred, making it hard to see clearly when driving or reading. Vision may get better or worse during the day, depending on the degree of oedema.
If leaking blood vessels cause bleeding in the eye, symptoms will vary based on how much blood is involved. With relatively limited bleeding, the visual disturbance may appear as spots floating in your visual field. These spots may go away after a few hours.
If bleeding is more severe, vision may suddenly become severely clouded. This can occur overnight during sleep. It may take months for the blood to clear from the eye, or it may not clear at all.
What is the treatment for diabetic retinopathy?
There are three treatments for diabetic retinopathy - laser surgery, vitrectomy and anti-VEGF injections. These surgical treatments are typically used only when diabetic retinopathy is in an advanced stage.
Laser surgery can be used to seal leaking blood vessels in the retina or to shrink fragile new blood vessels. Laser surgery is typically performed on an outpatient visit or in an ophthalmologist's office. You will be able to go home the same day.
Anti-VEGF injections such as Eyelea, Lucentis and Avastin are used primarily in cases of Diabetic Macular Oedema. DMO is where the macula area is affected by fluid from leaky blood vessels.
Laser surgery usually cannot restore vision that has already been lost. Therefore, early detection of diabetic retinopathy is the best way to prevent serious vision loss from the disease.
If a significant amount of blood has leaked into the vitreous, a vitrectomy may be required to restore vision. In this procedure, the surgeon makes a tiny incision in the sclera and gently suctions out the bloody vitreous, replacing it with a sterile clear fluid. After the surgery, you may be able to go home the same day or you may be asked to stay in the hospital overnight.
Can retinopathy be unequal in each eye?
Asymmetric diabetic retinopathy must be differentiated from Ocular Ischaemic Syndrome (OIS) and venous stasis retinopathy. OIS can present with ocular pain and sudden or gradual visual loss with common findings including advanced cataract, uveitis, iris neovascularisation and amaurosis fugax. Venous stasis retinopathy or non-ischaemic central retinal venous occlusion is characterised by midperipheral microaneurysms, small dot-and-blot intraretinal hemorrhages, or nerve fibre layer splinter haemorrhages. Disease processes associated with retinal thinning or atrophy can have a protective effect and retard the development of diabetic retinopathy. These conditions include posterior vitreous detachment, uniocular glaucoma, optic atrophy, chorioretinal scarring, trauma, unilateral recurrent panuveitis and Fuchs' heterochromic iridocyclitis, myopia greater than 5 dioptres, retinal pigment epithelial atrophy, anisometropia, tumour, vitreous loss and radiation. It is important to exclude carotid artery disease in the presence of asymmetric diabetic retinopathy. It has been reported that in the absence of other risk factors, 20% of cases of asymmetric diabetic retinopathy presented with haemodynamically significant carotid artery disease. Ipsilateral carotid disease has been reported to be associated with both a worsening and protection of the eye from retinopathy. If carotid stenosis was present prior to the development of retinopathy this can act as a protective factor. Alternatively if carotid stenosis develops subsequent to the onset of diabetic retinopathy, then the increased ischaemic insult can increase the progression of retinopathy.
Can diabetic retinopathy be prevented?
It's estimated that 50% of people with Type 2 diabetes are unaware of their condition. In some cases, detection of their diabetes takes place during a routine eye exam.
During a routine eye exam, your optometrist will examine your retina and look for early signs of diabetes. These signs include:
- Small haemorrhages from leaking blood vessels
- Macular oedema
- Areas of pale retina (called cotton wool spots) where blood supply has been obstructed
- Yellowish, waxy-appearing deposits in the retina caused by lipid deposits
If your optometrist detects signs of diabetic retinopathy that require treatment, or diabetic macular oedema then you will be referred to an ophthalmologist for additional testing and therapy.
Most cases of Type 2 diabetes can be managed through proper diet and exercise. Daily exercise and a high fibre diet with restricted amounts of carbohydrates, cholesterol, and saturated fat can improve overall health and help lower blood glucose levels. In cases where diet and exercise cannot sufficiently reduce blood glucose levels, oral medicines or injections of insulin may be added to the treatment plan.
It is also worth noting that according to the ACCORD Study that very tight blood sugar control decreased the progression of diabetic retinopathy by about one-third, from 10.4 percent to 7.3 percent, over four years.
In addition, compared with simvastatin treatment alone, combination lipid therapy with fenofibrate (Lipidil) plus simvastatin (Zocor) also reduced diabetic disease progression by about one-third, from 10.2 percent to 6.5 percent, over four years. So if you have diabetic retinopathy it would be worthwhile discussing with your practitioner whether you are a candidate to be prescribed Lipidil to reduce progression of your retinopathy.
Another recent study has determined that omega-fatty acids obtained from oily fish twice weekly was associated with a reduced risk of sight-threatening diabetic retinopathy in middle-aged and older patients with type 2 diabetes.
If you have been diagnosed with diabetes, you should have an annual dilated eye exam to monitor the health of your retina. (Depending on your individual needs, your optometrist may recommend more frequent exams.) Annual eye exams are also recommended if you are not a diabetic but have one or more of the risk factors for diabetes listed above.
Author: Stuart Macfarlane