Key Facts

Diabetic retinopathy is largely preventable with good glycaemic and BP control. The UK screening programme has significantly reduced blindness. Anti-VEGF therapy has revolutionised treatment of DMO.

Epidemiology

Affects ~40% of T1DM and ~30% of T2DM. Nearly all T1DM patients have some retinopathy after 20 years. Sight-threatening retinopathy (PDR or DMO) in ~10% of diabetic patients.

Aetiology

Duration of diabetes and glycaemic control are the strongest risk factors. Other: hypertension, dyslipidaemia, smoking, pregnancy, renal disease (proteinuria), anaemia.

Pathophysiology

Chronic hyperglycaemia → pericyte loss (earliest change), capillary basement membrane thickening, endothelial damage → microaneurysm formation, capillary occlusion → retinal ischaemia → VEGF upregulation → neovascularisation (new fragile vessels) → vitreous haemorrhage, tractional retinal detachment. Macular oedema: breakdown of blood-retinal barrier → leakage of fluid/lipid into macula → central visual loss.

Non-Proliferative DR (NPDR)

• Background: microaneurysms (earliest), dot/blot haemorrhages, hard exudates (lipid deposits)
• Pre-proliferative: cotton wool spots (nerve fibre layer infarcts), venous beading/loops, IRMA (intraretinal microvascular abnormalities), extensive haemorrhages
• Often asymptomatic

Proliferative DR (PDR)

• Neovascularisation: disc (NVD) or elsewhere (NVE)
• Vitreous haemorrhage: sudden painless visual loss (floaters → dense loss)
• Tractional retinal detachment: progressive visual loss
• Rubeosis iridis: new vessels on iris → neovascular glaucoma

Diabetic Macular Oedema (DMO)

• Central visual loss, distortion (metamorphopsia)
• Can occur at any NPDR or PDR stage
• Commonest cause of visual impairment in diabetic patients

Red Flags

• Sudden visual loss → vitreous haemorrhage or retinal detachment → urgent ophthalmology
• New floaters/flashes → possible PDR complication
• Gradual central vision loss → DMO

Screening

• Annual digital retinal photography: NHS Diabetic Eye Screening Programme
• Two 45° retinal images per eye (macula-centred and disc-centred)
• Classification: R0 (no retinopathy), R1 (background), R2 (pre-proliferative), R3 (proliferative); M0 (no maculopathy), M1 (maculopathy)

Specialist Assessment

• Slit-lamp biomicroscopy: detailed retinal examination
• OCT (optical coherence tomography): quantifies macular oedema thickness; essential for DMO management
• Fluorescein angiography (FFA): identifies ischaemia, neovascularisation, leakage; guides laser treatment
• Ultra-widefield imaging: peripheral retinal assessment

Prevention (Most Important)

• Glycaemic control: HbA1c target ≤48 mmol/mol (DCCT: 76% reduction in retinopathy risk)
• BP control: <130/80 mmHg (UKPDS: 34% risk reduction)
• Lipid management: statins; fenofibrate has specific retinal benefit (FIELD, ACCORD-Eye trials)

NPDR

• Background (R1): annual screening; optimise glycaemic/BP control
• Pre-proliferative (R2): refer to ophthalmology; more frequent monitoring (3-6 monthly)

PDR (R3)

• Panretinal photocoagulation (PRP): laser burns to peripheral retina; reduces VEGF production; reduces severe visual loss by ~50% (DRS/ETDRS trials)
• Intravitreal anti-VEGF: ranibizumab, aflibercept — increasingly used as alternative to PRP for PDR (CLARITY trial)

DMO

• Intravitreal anti-VEGF injections: ranibizumab 0.5mg (NICE TA274), aflibercept 2mg (NICE TA346) — first-line for centre-involving DMO; monthly loading then PRN
• Intravitreal steroid implant: dexamethasone implant (Ozurdex — NICE TA349) or fluocinolone acetonide (Iluvien — NICE TA301) — if anti-VEGF insufficient, pseudophakic, or poor anti-VEGF response
• Macular laser: focal laser for non-centre-involving DMO

Surgical

• Vitrectomy: non-clearing vitreous haemorrhage (>1 month), tractional retinal detachment, combined tractional-rhegmatogenous detachment

Referral Criteria

• R2 (pre-proliferative): routine ophthalmology referral
• R3 (proliferative): urgent ophthalmology referral (within 2 weeks)
• DMO: ophthalmology referral
• Sudden visual loss: emergency ophthalmology (same-day)

With screening and modern treatment (anti-VEGF, laser), rates of severe visual loss have decreased significantly. DCCT: intensive glycaemic control reduces retinopathy risk by 76% in T1DM. Untreated PDR: ~50% develop severe visual loss within 2 years. With PRP: risk reduced by >50%. DMO treated with anti-VEGF: ~30-40% gain ≥3 lines of visual acuity.

DR Classification (UK National Screening Programme)

Key Retinopathy Trials