Diabetic retinopathy is a disorder of the retinal blood vessels defined as the presence of typical retinal microvascular signs in an individual with diabetes mellitus. It is one of the most common complications of diabetes mellitus, and is the leading cause of poor vision among working adults in developed countries. If left untreated, diabetic retinopathy can lead to blindness. Diabetics have a 25-fold increased risk of becoming blind compared to non-diabetic individuals because of diabetic retinopathy.
About 1 in 8 singaporeans suffers from diabetes mellitus and this number is expected to increase with time due to increasing affluence and changes in lifestyle. About 8.5% of the diabetics in Singapore suffer from diabetic retinopathy, with 13.3% of these having sight-threatening retinopathy.
Diabetic retinopathy occurs when blood vessels in the retina become damaged due to high blood sugar levels. These abnormal blood vessels stop nourishing the retina. The damaged blood vessels leak blood and fluid, resulting in bleeding and swelling of the retina as well as formation of lipid deposits called exudates. In more severe cases, diabetes leads to the formation of abnormal blood vessels that may rupture and bleed into the eye. Once diabetic retinopathy progresses to advanced stages, the treatment becomes more difficult and visual impairment can become irreversible.
- Poor control of diabetes
- Duration of diabetes
- High blood pressure
- Heart disease
- Renal involvement
At early stages, patients do not experience any symptom and the vision is not affected. Most diabetics become symptomatic in the later stage or when diabetic macula oedema is present.
Some common symptoms include:
- Blurring of vision
- Distorted vision
- Dark streaks or haze that blocks vision
Non-Proliferative Diabetic Retinopathy (NPDR)
NPDR is the earliest stage of diabetic retinopathy. It is characterised by microaneurysms, a balloon-like swelling of weak blood vessels in the retina. These incompetent blood vessels may leak small amounts of blood (known as haemorrhages) and fluid leading to swelling of the retina.
As the condition progresses, the blood vessels may become obstructed preventing supply of nutrients and oxygen to the affected area of the retina, leading to the appearance of white patches known as cotton wool spots on the retina. Vision is usually not affected at this stage.
Proliferative Diabetic Retinopathy (PDR)
PDR is the advanced stage of diabetic retinopathy and is characterised by new abnormal growth of blood vessels (called neovascularisation) on the retina. This occurs in response to the lack of oxygen due to the obstructed blood vessels. These abnormal new vessels are fragile and tend to rupture easily, causing bleeding into the clear vitreous gel that fills the space in front of the retina. Blood in the vitreous is known as vitreous haemorrhage. Vitreous haemorrhage prevents light from reaching the retina, causing floaters (dots or lines in your vision) that can obstruct vision.
The condition may progress into scar tissue formation. These scar tissues contract and pull on the retina, causing the retina to detach from its underlying layer (retinal detachment). In severe cases, neovascularisation of other structures in the eye such as the iris (rubeosis iridis) can lead to a type of glaucoma called neovascular glaucoma which is difficult to treat. If left untreated and allowed to progress, PDR will lead to permanent vision loss.
Diabetic Macular Oedema(DME)
DME can occur in either type of diabetic retinopathy. This is when blood vessels leak into the macula, the central portion of the retina that is responsible for sharp central vision, causing swelling of the macula region. It may occur concurrently with either NDPR or PDR. DME causes central vision to be blurred or distorted.
Visual Acuity Test, Dilated Retinal Examination, Serial Colour Retinal Photography, High-definition Optical Coherence Tomography (OCT) and Fundus Fluorescein Angiography can be performed to determine the presence of diabetic retinopathy and how it is affecting one’s vision.
Treatment depends largely on the extent and severity of the disease.
Laser Therapy (Panretinal Photocoagulation and/or Focal)
Patients with severe NPDR or PDR may be treated with panretinal photocoagulation (PRP) or “hot” laser. This involves directing an intense light beam (laser) on parts of the retina. The purpose of the laser is to destroy the ‘healthy’ retinal tissues so as to reduce the overall oxygen demand of the retina, hence reducing the ischemic drive preventing further progression of the disease.
Unfortunately the laser destroys ‘healthy’ retinal tissue. Therefore, patients who undergo the treatment may experience loss of certain parts of the peripheral visual field, decreased night vision and reduced colour vision. Recurrence of the abnormal vessels may develop after laser treatment and repeat treatment may be necessary.
In cases of DME, focal or grid laser is applied to the macula region to reduce the leakage and swelling. The Early Treatment Diabetic Retinopathy Study (ETDRS) showed that eyes with clinically significant macula oedema benefitted from focal laser, reducing the risk of visual loss and increasing the chances of visual improvement.
Its main objective is to prevent worsening of the condition which if left untreated might eventually lead to permanent and severe visual loss.
Anti-Vascular Endothelial Growth Factor Injections
Vascular endothelial growth factor (VEGF) is produced in response to a lack of oxygen, initiating the formation of new blood vessels to supply oxygen to the deprived retina. One anti-VEGF that has been approved by the FDA for use in treating DME is called ranibizumab (Lucentis). It decrease the leakage and swelling of the macula and at the same time decreases abnormal blood vessels formation. This in turn might stabilize, and in some cases, improve vision.
The procedure involves injection of the drugs directly into the eye as an intravitreal injection. Additional injections may be necessary and the eye will be monitored for response to the treatment and recurrence of the condition.
Vitrectomy surgery is performed to restore vision loss due to vitreous hemorrhage or tractional retinal detachment. The procedure involves surgical removal of blood or cloudy vitreous in the eye and where necessary, removal of tractional membranes over the retina through three small incisions on the white part (sclera) of your eye.
Early detection and treatment help to prevent significant vision loss from diabetic retinopathy. The earlier the detection of disease, the less invasive the treatment will need to be.
All diabetics should undergo diabetic eye screening regardless of whether they are on oral medication, insulin injections or dietary control. Adults with the more common type II diabetes should have an eye assessment immediately upon diagnosis of diabetes, and subsequently annually or according to the advice of the eye specialist. As the onset of type II diabetes is subtle, retinal changes may have already taken place by the time diabetes is first diagnosed.
Children who have diabetes and who requires insulin injections (called type I diabetes) should also be screened regularly beginning not later than 5 years after the initial diagnosis of diabetes, and subsequently annually or according to the advice of the eye specialist.