What is diabetic retinopathy?

Diabetic retinopathy (DR) is a complication of diabetes mellitus and is one of the main causes of blindness in working-age adults around the world. It occurs when diabetes damages the tiny blood vessels inside the retina, which is the light-sensitive tissue at the back of the eye. A healthy retina is essential for good vision.

Diabetic retinopathy often has no early warning signs. But over time, it can get worse and in the moderate to late stages, it can cause vision loss. Diabetic retinopathy usually affects both eyes, though one eye may be more severely affected.

What are the types of diabetic retinopathy?

There are 2 main types of diabetic retinopathy: 

• Non-proliferative diabetic retinopathy, also known as background diabetic retinopathy is the early stage of diabetic retinopathy and occurs when the small retina blood vessels become affected and begin to leak and bleed. At this stage, vision is usually not affected.
  
  
• Proliferative diabetic retinopathy (PDR) is associated with a high risk of permanent loss of vision. There is growth of abnormal new blood vessels in the retina. These abnormal new vessels can rupture, causing significant bleeding that will lead to loss of vision. The abnormal blood vessels can also cause scar formation and retinal detachment. In some cases, abnormal blood vessels can block fluid outflow from the eye and cause a severe type of glaucoma called neovascular glaucoma, which carries a high risk of optic nerve damage and blindness.
  
  

Besides bleeding and retinal detachment, another way that DR can affect vision is by causing leakage from blood vessels and swelling of the retina, called diabetic macular edema (DME).  This tends to occur in the central part of the retina called the macula, which is important for sharp central vision. Swelling of the macula causes degeneration of the retinal cells over time, and affects central vision. DME is now the most common cause of vision loss from DR.

Proliferative diabetic retinopathy with abnormal new blood vessels, bleeding and leakage in the retina 

Proliferative diabetic retinopathy causing retinal detachment 

What are the symptoms of diabetic retinopathy?

Diabetic retinopathy has no warning signs in the early stages; sight may not be affected until the condition is severe or in the moderate to late stages.

As the condition progresses, symptoms may include:

• Blurred vision
• Floaters or dark spots in your vision
• Difficulty seeing at night
• Sudden vision loss
• Colors appearing faded or washed out
  
  

If DME develops, symptoms may include blurring of central vision when reading or driving, loss of the ability to see colour, and or distortion of images (straight lines appearing as abnormally curved or "wavy").

Small spots or floaters may be a symptom of bleeding in the eye from abnormal new vessels. In the most severe form, with PDR, there may be sudden severe vision loss from bleeding or retinal detachment.

Because the disease initially shows no symptoms, and can be treated in the earlier stages, it is important for all patients with diabetes to have an eye examination at least once a year, and to seek medical attention immediately if you experience any of these visual symptoms. Late diagnosis and treatment can result in irreversible vision loss.

How is diabetic retinopathy prevented?

There is no way to completely prevent diabetic retinopathy. However, vision loss in the large majority of cases can be prevented with early detection and treatment. You can help protect your sight by having your eyes checked at least once a year by an ophthalmologist, or with specialised diabetic retinal photography.

You can also help slow down the development of diabetic retinopathy by keeping your blood glucose levels in check. The HbA1c is a measure of blood sugar level over a three-month period and in most patients, it should ideally be less than 7%. Control of high blood pressure is also key in preventing the development and progression of diabetic retinopathy.

Other medical conditions such as high cholesterol, kidney disease and heart disease should be treated and kept under control. In certain cases, medications for high cholesterol such as fenofibrate can help to reduce the risk of diabetic retinopathy worsening. Stop smoking and exercise regularly to reduce your risk of developing diabetic retinopathy.

What causes diabetic retinopathy?

Diabetes can lead to various eye conditions, one of which is diabetic retinopathy, where the small blood vessels in the etina become damaged. These damaged vessels can lead to poor blood flow (ischemia), inflammation and ultimately blindness if not treated.

What are the risk factors for diabetic retinopathy?

All diabetics are at risk of developing diabetic retinopathy. Overall, about 30-40% of diabetics will develop DR, and about 5-10% will have more severe, vision-threatening disease. The risk of DR increases if diabetes is long-standing. After 20 years, most diabetics will develop this complication to some degree. Those who have poorly controlled diabetes are at higher risk of developing diabetic retinopathy earlier, and at more severe stages.

People with diabetes should get an eye examination or screening at least once a year. If you have diabetic retinopathy, your ophthalmologist can recommend treatment to help prevent its progression.

Other risk factors of diabetic retinopathy include:

• Poor Blood Sugar Control: Constantly elevated blood sugar levels raise the risk.
• High Blood Pressure and Cholesterol: These conditions can exacerbate damage to the blood vessels in the retina.
• Pregnancy: Pregnant women with diabetes could be at higher risk for developing retinopathy.
  
  

How is screening done for diabetic retinopathy?

Screening for diabetic retinopathy can be done either by eye examination by an ophthalmologist or eye-care provider, or by specialised retinal photography. In Singapore, retinal photography is a service provided at polyclinics and at some primary care facilities.

The Singapore Integrated Diabetic Retinopathy Programme (SiDRP) uses telemedicine to enable fundus retinal photographs taken at the polyclinic or other primary care facilities to be transmitted electronically to specialist eye care centres for reading and diagnosis. This provides a safe, reliable and quality-assured DR screening programme for Singapore.

If there are any abnormalities in the photograph, or if the quality is insufficient for adequate assessment, you will be referred to an ophthalmologist for further assessment and management.

How is diabetic retinopathy diagnosed?

When you see an ophthalmologist for DR assessment and diagnosis, you will have eye drops administered to enlarge (dilate) the pupils temporarily so that they can examine the retina and macula.

Sometimes, in addition to clinical examination, your ophthalmologist may order additional tests and evaluations, such as:

• Fundus Fluorescein Angiogram (FFA)
  In this test, a fluorescent dye is injected into a vein in your arm. Over the next few minutes, photographs are taken of the blood vessels in your eye as the dye passes through. This helps to highlight abnormal or "leaky" blood vessels, or areas of the retina where blood flow is insufficient. Uncommonly, complications due to the injection can arise, such as nausea, or in very rare cases, severe allergic reactions or heart problems.
  
  
• Optical Coherence Tomography (OCT)
  OCT is similar to an ultrasound scan, except that the latter uses sound waves to capture images. OCT uses light waves instead, and can capture very detailed, cross-sectional images of the retina and macula. OCT is a good method for the assessment of DME. OCT imaging is very fast and convenient. You will be asked to place your head on a chin rest and hold still for several seconds while the images are obtained. The light beam used is painless, and unlike X-rays, does not involve any radiation.
   
  
• Optical Coherence Tomography Angiography (OCT-A)
  In some cases, the blood vessels in the retina can be examined with OCT-A. Based on the same technology as OCT, OCT-A uses light waves to capture very detailed images of blood vessels in the eye.  OCT-A does not require any fluorescent dye injection, and also does not involve any radiation.
  
  

 OCT scan showing diabetic macular edema

How is diabetic retinopathy treated?

In the early stages of DR, treatment within the eye is not required, and cases can be observed safely with close monitoring, and control of the blood glucose level to prevent DR from worsening.

In more severe cases where PDR has developed, or if there is a high risk of PDR, your ophthalmologist may recommend a laser treatment to reduce the risk of complications and vision loss.  This laser treatment, called panretinal photocoagulation (PRP) is used to treat the peripheral retina, so as to prevent or stop the growth of the abnormal new blood vessels, and reduce the risk of severe vision loss.

In general, each eye may require two to three sessions for PRP to be completed. You will be expected to go for regular treatments over a period of six to twelve months before diabetic retinopathy is controlled adequately. In some patients with PDR, an alternative treatment may be with regular injections of medications into the eye, called intravitreal injections with anti-VEGF (anti-vascular endothelial growth factor) medications. If this is an option, your ophthalmologist will discuss the pros and cons of the different treatment options with you.

In patients with loss of central vision due to DME, the treatment options also include laser treatment, or intravitreal injections of anti-VEGF medication. Bevacizumab (Avastin), ranibizumab (Lucentis) and aflibercept (Eylea) are some medications that are frequently used to treat DME and DR. Other new medications are also in development, and may be available soon. These treatments can reduce the macular swelling and improve vision.

Often, multiple injections at intervals of one month or longer are required to resolve the swelling. Repeated injections at longer intervals may also be required to maintain the visual improvement.

In cases of severe PDR causing massive bleeding in the eye, or retinal detachment, then surgery may be required. Surgery for PDR involves a vitrectomy, a form of "keyhole" surgery that uses small instruments to enter the eye to remove the vitreous gel and blood within the eye. If necessary, scar tissue causing retinal detachment can also be peeled off and removed during surgery. A gas bubble or silicone oil may be injected into the eye at the end of surgery, to maximise the chances of success. In severe cases of PDR, recovery of vision may be limited, even with successful surgery.