Diabetic retinopathy is a complication of diabetes that damages the retina — the light-sensitive layer of nerve tissue at the back of the eye responsible for sending visual images to the brain. It is caused by persistently elevated blood glucose damaging the small blood vessels that supply the retina, and it remains one of the leading causes of preventable blindness among working-age adults in Singapore and worldwide.
Diabetic retinopathy can develop in anyone with Type 1 or Type 2 diabetes, and the risk rises the longer diabetes has been present and the less well blood glucose has been controlled. Its most serious feature is that it is frequently silent in its early, most treatable stages — significant retinal damage can occur well before a person notices any change in vision. This is why regular eye screening is recommended for every person with diabetes, regardless of whether they have any visual symptoms at all.
How Diabetic Retinopathy Affects the Eye
The retina requires a constant, well-regulated blood supply to function. Persistently high blood glucose damages the walls of the small blood vessels (capillaries) that feed the retina, setting off a progressive chain of changes:
- Capillary damage and leakage: Weakened vessel walls develop tiny bulges (microaneurysms) and begin to leak blood and fluid into the retina, the earliest visible sign of diabetic retinopathy.
- Capillary blockage (ischaemia): As more vessels become damaged and blocked, areas of the retina are starved of oxygen and nutrients.
- Neovascularisation: In response to this oxygen starvation, the retina releases a signalling protein called vascular endothelial growth factor (VEGF), which triggers the growth of new, abnormal blood vessels. These new vessels are fragile, poorly structured, and prone to bleeding, they mark the transition to the more advanced, sight-threatening stage of the disease.
- Fluid accumulation in the macula: Leaking vessels can also cause fluid to build up in the macula, the small central area of the retina responsible for sharp, detailed vision, a complication called diabetic macular edema (DME).
Stages of Diabetic Retinopathy
Diabetic retinopathy is classified by severity, which guides how frequently a person needs to be screened and when treatment becomes necessary.
- Mild Non-Proliferative Diabetic Retinopathy (NDPR): The earliest stage, marked by microaneurysms — small areas of balloon-like swelling in the retina's blood vessels. Usually causes no visual symptoms. Annual screening is generally recommended at this stage.
- Moderate NDPR: Blood vessels that nourish the retina become increasingly blocked, and additional signs such as haemorrhages and hard exudates appear. Considered “referable” for specialist eye assessment, with more frequent monitoring.
- Severe NDPR: A significant number of blood vessels are blocked, depriving multiple areas of the retina of blood supply. This signals to the retina to grow new blood vessels, marking a high risk of progression to proliferative disease within about a year. Requires prompt specialist referral.
- Proliferative NDPR: The advanced stage, in which abnormal new blood vessels grow on the surface of the retina or into the vitreous (the gel-like substance filling the eye). These fragile vessels are prone to bleeding and can lead to scar tissue formation, vitreous haemorrhage, or retinal detachment. Requires urgent treatment to prevent severe vision loss.
- Diabetic Macular Edema: Fluid accumulation in the macula, which can occur at any stage of diabetic retinopathy, including mild disease. DME is the most common cause of vision loss in people with diabetic retinopathy, because it directly affects the area of the retina responsible for central, detailed vision.
Symptoms of Diabetic Retinopathy
Diabetic retinopathy typically causes no symptoms in its early stages. Your vision often remains completely normal even as changes are occurring in the retina. This is the primary challenge of the disease as by the time symptoms appear, the condition has often already progressed significantly.
- Blurred or fluctuating vision, which may vary with blood glucose levels
- Difficulty seeing well at night or in low light
- Dark spots, “floaters,” or cobweb-like shapes drifting across the field of vision
- Impaired or washed-out colour vision
- A dark or empty area appearing in the centre of vision, suggestive of macular involvement
- Sudden, significant vision loss, a possible sign of vitreous haemorrhage or retinal detachment, requiring urgent same-day assessment
Risk Factors for Diabetic Retinopathy
Everyone with diabetes carries some risk of developing diabetic retinopathy, but certain factors substantially increase that risk:
- Duration of diabetes: This is the single strongest risk factor; risk rises the longer a person has had diabetes, regardless of type
- Poor blood glucose control: Persistently elevated HbA1c significantly accelerates retinal damage
- High blood pressure (hypertension): Compounds the damage to already-weakened retinal blood vessels
- High cholesterol: Associated with increased retinal exudates and a higher risk of vision-threatening disease
- Pregnancy: Diabetic retinopathy can progress rapidly during pregnancy in women with pre-existing diabetes, warranting closer monitoring
- Tobacco use: Worsens blood vessel damage throughout the body, including in the retina
- Kidney disease: Diabetic nephropathy and retinopathy often progress together, as both reflect the cumulative effect of small blood vessel damage
Complications of Diabetic Retinopathy
Left untreated, diabetic retinopathy can lead to several serious, sight-threatening complications:
- Vitreous haemorrhage: Fragile new blood vessels bleed into the vitreous, causing floaters or a sudden loss of vision depending on the extent of bleeding
- Retinal detachment: Abnormal blood vessels can stimulate scar tissue that pulls the retina away from the back of the eye, a sight-threatening emergency
- Neovascular glaucoma: Abnormal blood vessels growing in the front part of the eye can block normal fluid drainage, raising eye pressure and damaging the optic nerve
- Diabetic macular edema: The most common cause of vision impairment in diabetic retinopathy, arising from fluid accumulation in the central retina
- Irreversible vision loss or blindness: The cumulative endpoint of poorly controlled or untreated disease, which is why early detection and treatment are so important
How Diabetic Retinopathy is Diagnosed
Diabetic retinopathy is diagnosed and staged through a comprehensive eye examination, since the retinal changes that define each stage can only be seen by directly examining the back of the eye.
- Dilated Eye Examination: Eye drops are used to widen the pupil, allowing an ophthalmologist to examine the retina directly using special lenses to look for microaneurysms, haemorrhages, exudates, and abnormal new blood vessels.
- Visual Acuity Test: A standard eye chart test to measure how well each eye is currently seeing, providing a baseline to track against over time.
- Optical Coherence Tomography (OCT): A non-invasive imaging scan that produces detailed cross-sectional images of the retina, allowing precise detection and measurement of fluid accumulation in diabetic macular oedema.
- Fluorescein Angiography: A dye is injected into a vein in the arm and photographs are taken as it circulates through the retinal blood vessels, highlighting areas of leakage, blockage, or abnormal new vessel growth in more detail than a standard examination.
- Retinal Photography Screening: Digital photographs of the retina, often used for structured population screening programmes. In Singapore, people with diabetes are typically recommended annual retinal screening if no or only mild disease is found, with more frequent specialist review recommended once moderate or worse disease is detected.
Reducing Your Risk: Prevention and Early Detection
- Attend recommended eye screening even if your vision feels completely normal. The earliest, most treatable stages of diabetic retinopathy are typically symptom-free
- Keep blood glucose within your target range, as reflected by regular HbA1c monitoring
- Manage blood pressure and cholesterol alongside blood glucose, since both independently affect retinal blood vessel health
- Avoid smoking, which accelerates blood vessel damage throughout the body
- Attend more frequent eye reviews if you are pregnant with pre-existing diabetes, or if you have any degree of retinopathy already identified
- Seek same-day assessment for any sudden change in vision, new floaters, or a dark area in your field of vision. Do not wait for your next scheduled screening
