Diabetic Retinopathy — Symptoms, Causes & Treatment | MyMedicPlus

Diabetic retinopathy is a progressive microvascular complication of diabetes mellitus that damages the blood vessels of the retina — the light-sensitive layer at the back of the eye responsible for processing visual information. It is the leading cause of new blindness in working-age adults (20-64 years) globally. Approximately 1 in 3 people with diabetes have some degree of retinopathy; among those who have had diabetes for 20 or more years, 60-80% develop the condition. The disease progresses through two main stages: non-proliferative diabetic retinopathy (NPDR — characterised by microaneurysms, haemorrhages, and venous changes) and proliferative diabetic retinopathy (PDR — neovascularisation of the retina and optic disc, carrying risk of vitreous haemorrhage and traction retinal detachment). Diabetic macular oedema (DMO) can occur at any NPDR or PDR stage and is the most common cause of visual loss in diabetic patients. Optimal blood glucose and blood pressure control dramatically reduce the risk of developing and progressing retinopathy, making this a largely preventable cause of vision loss.

Chronic hyperglycaemia damages retinal capillaries through several pathological mechanisms: activation of protein kinase C (PKC) and the polyol pathway, oxidative stress, formation of advanced glycation end-products (AGEs), and upregulation of vascular endothelial growth factor (VEGF) — the primary driver of pathological neovascularisation. Endothelial cell death and pericyte loss increase vascular permeability (causing retinal oedema and hard exudate deposition) and ultimately capillary occlusion (causing ischaemia and new vessel formation). Key risk factors for developing and worsening retinopathy: duration of diabetes (the single most important factor — retinopathy is rare in the first 5 years but present in 80% after 20 years); poor HbA1c control; hypertension (requires co-management); dyslipidaemia (high LDL and triglycerides worsen macular oedema); pregnancy (accelerates progression — monitoring every trimester is essential); smoking; diabetic nephropathy (kidney disease and retinopathy track closely together — microalbuminuria indicates systemic microvascular damage); and anaemia (worsens retinal ischaemia). Both Type 1 and Type 2 diabetes carry significant risk.

Early and moderate non-proliferative diabetic retinopathy is typically completely asymptomatic — which is precisely why annual structured screening is mandatory for all diabetic patients. Visual symptoms emerge at two critical stages: first, diabetic macular oedema (DMO) — fluid accumulation in the macula causes blurred or distorted central vision (metamorphopsia), difficulty reading and recognising faces, reduced colour contrast, and fluctuating vision correlating with blood glucose swings; second, proliferative retinopathy complications — fragile new blood vessels rupture causing vitreous haemorrhage (sudden onset of floaters, dark spots, cobwebs, or curtain of vision loss), while fibrovascular membrane traction causes retinal detachment presenting as a curtain or shadow across vision, accompanied by flashing lights (photopsia). Additional features include difficulty adapting to low light and washed-out colour perception from macular involvement. Crucially, diabetic retinopathy rarely causes eye pain — even when vision loss is severe. This makes regular screening the only reliable way to detect the condition before irreversible vision loss occurs.

Structured annual digital retinal photography (two-field fundus photography — macula-centred and disc-centred fields) is the standard screening method for diabetic retinopathy in most national programmes. Disease severity is graded using the International Clinical DR Disease Severity Scale: mild NPDR (microaneurysms only); moderate NPDR (haemorrhages, hard exudates, cotton wool spots); severe NPDR (4-2-1 rule: haemorrhages in all 4 quadrants, venous beading in 2 quadrants, intraretinal microvascular abnormalities in 1 quadrant — 50% progress to PDR within 1 year); proliferative DR (PDR — neovascularisation of disc or retina). Optical coherence tomography (OCT) is the gold standard for detecting diabetic macular oedema — provides cross-sectional retinal imaging and quantifies central retinal thickness; essential for monitoring treatment response. OCT angiography (OCTA) maps the foveal avascular zone without fluorescein injection. Fluorescein angiography (FA) confirms neovascularisation, identifies ischaemia, and guides laser planning. HbA1c, blood pressure, eGFR, and lipid profile must be reviewed at every ophthalmology visit — retinal findings reflect systemic diabetic control.

Systemic risk factor control remains the most important intervention at all disease stages: intensive glycaemic control (each 1% reduction in HbA1c reduces microvascular complication risk by 37% — UKPDS trial); tight blood pressure control (target below 130/80 mmHg — ACE inhibitors such as ramipril and ARBs such as losartan provide additional renoprotective benefit); and statin therapy for dyslipidaemia (fenofibrate reduces need for laser treatment by 30% — FIELD trial). Anti-VEGF intravitreal injections are first-line for centre-involving diabetic macular oedema: ranibizumab (Lucentis 0.5 mg), bevacizumab (Avastin 1.25 mg — off-label), and aflibercept (Eylea 2 mg) given monthly for 5-6 injections then PRN; aflibercept is preferred for initial vision below 6/12. Intravitreal corticosteroid implants (dexamethasone 700 mcg / Ozurdex; fluocinolone acetonide / Iluvien 190 mcg) are used for pseudophakic patients with refractory or chronic DMO. Pan-retinal photocoagulation (PRP) laser: applies 1,200-1,600 burns to peripheral ischaemic retina, reducing VEGF production and regression of neovascularisation — first-line for high-risk PDR; may reduce peripheral vision and night vision. Vitreoretinal surgery (vitrectomy): indicated for dense non-clearing vitreous haemorrhage (after 1-3 months), traction retinal detachment involving or threatening the macula, and refractory proliferative disease.

Untreated or inadequately managed diabetic retinopathy leads to progressive and potentially irreversible visual impairment. Diabetic macular oedema (DMO) is the most common cause of moderate visual loss — impaired central vision affects reading, driving, and recognising faces, significantly impacting employment and independence. Vitreous haemorrhage: neovascular vessels rupture into the vitreous cavity causing sudden floaters then dense visual loss; while haemorrhage may absorb over weeks to months, non-clearing haemorrhage requires vitrectomy. Traction retinal detachment: fibrovascular membrane contraction pulls the retina from the retinal pigment epithelium — macular involvement causes permanent central vision loss without urgent surgery; outcomes are worse than rhegmatogenous detachment. Neovascular glaucoma: VEGF-driven iris neovascularisation (rubeosis iridis) obstructs trabecular outflow, causing intractable raised intraocular pressure, severe pain, and rapid vision loss — one of the most difficult conditions to manage in ophthalmology. Bilateral severe visual loss causes significant disability, loss of employment, depression, and social isolation, and critically impairs the patient's ability to self-manage diabetes — monitoring blood glucose, administering insulin, and identifying hypoglycaemia all become more difficult when vision is severely impaired.

Maintaining HbA1c below 7% (53 mmol/mol) is the single most important preventive measure — the UKPDS study demonstrated that each 1% reduction in HbA1c reduces microvascular complication risk by 37%. Achieve blood pressure below 130/80 mmHg using ACE inhibitors or ARBs, which also provide renoprotection in diabetic patients. Control LDL cholesterol with high-intensity statin therapy; fenofibrate as add-on reduces retinopathy progression and the need for laser treatment. All diabetic patients should attend annual structured retinal screening from the time of diagnosis for Type 2 diabetes, or within 1 year of diagnosis for Type 1 diabetes. Quit smoking — smoking accelerates microvascular disease and doubles the risk of diabetic complications. Maintain a healthy weight and exercise regularly (150 minutes per week of moderate-intensity activity). Control co-existing risk factors: treat dyslipidaemia, manage renal disease, and ensure tight control during pregnancy (three-monthly retinal monitoring during all diabetic pregnancies). Promptly report any new visual symptoms — floaters, blurred vision, flashing lights, or any visual change — to your ophthalmologist; do not wait for the next scheduled screening appointment.

Seek emergency eye care immediately for: sudden loss of vision in one or both eyes, sudden onset of floaters or flashing lights (new symptoms — possible vitreous haemorrhage or retinal detachment), a shadow, curtain, or dark area in the visual field (possible traction retinal detachment — requires same-day ophthalmology review). Diabetic retinopathy rarely causes pain, so vision changes are the key warning sign. Attend annual diabetic eye screening appointments — these exist specifically to detect pre-symptomatic retinopathy before vision is threatened. All people with diabetes (Type 1 and Type 2) should be enrolled in a structured retinal screening programme from: diagnosis for Type 2 diabetes; within 1 year of diagnosis for Type 1 diabetes. If screening is not available or was missed, request a dilated fundal examination from your GP or diabetes team. Report any visual changes to your GP or ophthalmologist promptly — do not wait for your next annual screening appointment.