Diabetic Retinopathy
Ophthalmology · Retina · lean revision notes
Diabetic Retinopathy
Diabetic retinopathy (DR) is a chronic, progressive microvascular complication of diabetes mellitus and the leading cause of preventable blindness in the working-age population (20–65 years) worldwide. It is a near-certain favourite in NEET PG ophthalmology because of its crisp staging, trial-derived numbers (DCCT, ETDRS, DRS), and well-defined laser/anti-VEGF indications.
Definition & burden
DR is damage to the retinal microvasculature caused by chronic hyperglycaemia, producing capillary non-perfusion, increased vascular permeability, and (in advanced disease) neovascularisation. Prevalence rises with duration of diabetes (the single most important risk factor) and degree of glycaemic control. Nearly all type 1 diabetics and >60% of type 2 diabetics have some DR after 20 years.
High-yield: Duration of diabetes is the strongest risk factor for development of DR; glycaemic control (HbA1c) is the strongest modifiable factor for progression.
Other risk factors: hypertension, dyslipidaemia, nephropathy/proteinuria, pregnancy (can cause rapid progression), anaemia, and puberty.
Pathophysiology
Chronic hyperglycaemia drives several biochemical pathways that converge on pericyte loss and endothelial damage:
- Polyol pathway → aldose reductase converts glucose to sorbitol → osmotic damage, pericyte death.
- Advanced glycation end-products (AGEs) → basement membrane thickening.
- Protein kinase C (PKC) activation → altered permeability and blood flow.
- Oxidative stress & VEGF upregulation → the final common pathway for permeability and neovascularisation.
Sequence of events: Pericyte loss → microaneurysm formation → capillary basement membrane thickening → increased permeability (oedema, exudates) → capillary closure/non-perfusion (ischaemia) → VEGF release → neovascularisation → fibrovascular proliferation → tractional complications.
High-yield: The earliest histological change is selective loss of pericytes (intramural pericytes). The earliest clinically/ophthalmoscopically visible lesion is the microaneurysm.
Classification
DR is broadly divided into non-proliferative (NPDR) and proliferative (PDR), with diabetic macular oedema (DMO/DME) as a separate, parallel threat that can occur at any stage and is the commonest cause of visual loss in type 2 diabetes.
Lesions and their basis
| Lesion | Mechanism | Significance |
|---|---|---|
| Microaneurysm | Focal capillary wall outpouching (pericyte loss) | Earliest visible sign |
| Dot & blot haemorrhages | Bleeds in inner nuclear/outer plexiform layers | Deep, rounded |
| Flame-shaped haemorrhage | Bleeds in nerve fibre layer | Superficial (more typical of HTN) |
| Hard exudates | Lipid/lipoprotein leakage | Marker of chronic oedema; macular threat |
| Cotton-wool spots (CWS) | Nerve fibre layer microinfarcts | Marker of ischaemia |
| IRMA | Intraretinal microvascular abnormalities (shunts) | Sign of severe ischaemia, pre-proliferative |
| Venous beading/loops | Dilated irregular veins | Strong predictor of progression to PDR |
| Neovascularisation (NVD/NVE) | VEGF-driven new vessels | Defines PDR |
High-yield: Cotton-wool spots = nerve fibre layer microinfarcts (NOT exudates). Hard exudates are lipid deposits. Don't confuse them.
NPDR severity (modified Airlie House / ETDRS)
| Grade | Findings |
|---|---|
| Mild NPDR | At least one microaneurysm; lesions less than moderate |
| Moderate NPDR | More than just microaneurysms but less than severe |
| Severe NPDR | 4-2-1 rule (any one): haemorrhages/microaneurysms in 4 quadrants; venous beading in 2 quadrants; IRMA in 1 quadrant |
| Very severe NPDR | Any two of the 4-2-1 criteria |
High-yield mnemonic — "4-2-1" for severe NPDR: 4 quadrants of haemorrhages, 2 quadrants of venous beading, 1 quadrant of IRMA. Any one criterion = severe NPDR.
Severe NPDR carries roughly a 15% risk and very severe NPDR about a 45–50% risk of progressing to PDR within one year — hence close follow-up or early intervention.
Proliferative DR (PDR)
Defined by neovascularisation in response to widespread retinal ischaemia:
- NVD — new vessels on or within one disc diameter of the disc.
- NVE — new vessels elsewhere.
- NVI / NVA — neovascularisation of iris (rubeosis iridis) / angle → neovascular glaucoma.
New vessels are fragile and grow on the posterior hyaloid → vitreous haemorrhage and tractional retinal detachment.
High-risk PDR (DRS criteria) — indication for urgent panretinal photocoagulation:
- NVD ≥ ⅓–¼ disc area, or
- Any NVD with vitreous/preretinal haemorrhage, or
- NVE ≥ ½ disc area with vitreous/preretinal haemorrhage.
High-yield: Advanced diabetic eye disease = vitreous haemorrhage + tractional retinal detachment + neovascular glaucoma — the end-stage triad.
Diabetic macular oedema (DMO) & CSME
DMO is retinal thickening from breakdown of the inner blood–retinal barrier. The classic ETDRS definition of Clinically Significant Macular Oedema (CSME) — a must-know — requires any one:
- Retinal thickening within 500 µm of the centre of the fovea.
- Hard exudates within 500 µm of the fovea with adjacent retinal thickening.
- A zone of retinal thickening ≥1 disc area (DA), any part of which is within 1 DA of the foveal centre.
High-yield: Memorise the CSME numbers — 500 µm, 500 µm + exudates, 1 DA within 1 DA. This is one of the most repeated ophthalmology MCQs.
Modern OCT-based classification (centre-involving vs non-centre-involving DMO) now guides anti-VEGF therapy, but the ETDRS CSME definition remains the exam answer for "criteria."
Clinical features
- Often asymptomatic until macula or vitreous involved — hence screening is essential.
- Gradual blurring/decreased visual acuity (macular oedema).
- Sudden floaters / sudden painless visual loss → vitreous haemorrhage.
- Distortion (metamorphopsia) with macular oedema.
- Advanced: severe loss with TRD; painful red eye with neovascular glaucoma.
Investigations / Investigation of choice
| Investigation | Role |
|---|---|
| Dilated fundus examination (slit-lamp + 90D / indirect ophthalmoscopy) | Screening and staging — first-line |
| OCT (Optical Coherence Tomography) | Investigation of choice for macular oedema; quantifies thickness, monitors therapy |
| Fundus Fluorescein Angiography (FFA) | Maps capillary non-perfusion, microaneurysms, neovascular leakage; identifies ischaemic zones |
| OCT-Angiography | Non-invasive, dye-free mapping of capillary dropout / FAZ enlargement |
| B-scan ultrasonography | When media opaque (dense vitreous haemorrhage/cataract) to exclude RD |
High-yield: OCT is the investigation of choice to detect and monitor macular oedema; FFA is the gold standard to demonstrate capillary non-perfusion and neovascular leakage. On FFA, microaneurysms show as hyperfluorescent dots; areas of non-perfusion are dark (hypofluorescent).
Screening guidelines
- Type 1 DM: first screen 5 years after diagnosis (rare before puberty), then annually.
- Type 2 DM: screen at the time of diagnosis (often long-standing undiagnosed disease), then annually.
- Pregnancy with pre-existing DM: screen in the first trimester, then every trimester and post-partum (gestational diabetes does NOT require routine screening).
High-yield: Type 1 → screen at 5 years; Type 2 → screen at diagnosis. Pregnancy accelerates DR.
Management
Stepwise approach
Control systemic factors → stage the retinopathy → treat the macula (DMO) → ablate ischaemia (PRP for PDR/severe NPDR) → surgery for advanced complications.
1. Systemic / risk-factor control (foundation for all stages)
- Tight glycaemic control (HbA1c target individualised, generally <7%).
- Blood pressure and lipid control (fenofibrate shown to slow progression in FIELD/ACCORD-Eye).
- Manage nephropathy, anaemia.
High-yield: DCCT (type 1) and UKPDS (type 2) proved that intensive glycaemic control reduces incidence and progression of DR. Beware "early worsening" of DR on rapid tightening of control.
2. Diabetic macular oedema (CSME / centre-involving DMO)
- Intravitreal anti-VEGF (ranibizumab, aflibercept, bevacizumab) = first-line / drug of choice for centre-involving DMO with vision loss.
- Intravitreal steroids (dexamethasone implant, triamcinolone) — second-line, especially in pseudophakic or anti-VEGF non-responders.
- Focal/grid laser photocoagulation — for non-centre-involving CSME or as adjunct (historic ETDRS standard; reduces moderate visual loss by ~50%).
3. Severe NPDR / PDR
- Pan-Retinal Photocoagulation (PRP) — the definitive treatment to ablate ischaemic retina, reduce VEGF drive, and cause regression of neovascularisation. ~1200–2000 burns over several sittings, sparing the macula.
- Indication: high-risk PDR (DRS criteria), and considered for severe/very severe NPDR (especially type 2, poor compliance, before cataract surgery, or one-eyed patients).
- Anti-VEGF can be an adjunct/alternative (DRCR Protocol S showed anti-VEGF non-inferior to PRP for PDR).
High-yield: PRP (laser photocoagulation) is the treatment of choice for proliferative diabetic retinopathy. Argon green / 532 nm laser is classically used. PRP reduces severe visual loss by >50% (DRS).
4. Advanced disease — Pars plana vitrectomy (PPV) Indications:
- Non-clearing vitreous haemorrhage (>1–3 months, or earlier in type 1).
- Tractional retinal detachment involving or threatening the macula.
- Combined tractional-rhegmatogenous RD.
- Dense premacular subhyaloid haemorrhage.
5. Neovascular glaucoma
- Urgent PRP/anti-VEGF to regress rubeosis + IOP-lowering medication; cyclodestruction or drainage device for refractory cases.
Laser specifics (exam pointers)
- Focal/grid laser for macular oedema — targets leaking microaneurysms / diffuse thickening.
- PRP for ischaemia/PDR — peripheral retina, spares posterior pole (one disc diameter temporal to fovea and the vascular arcades preserved).
- Side effects of PRP: reduced peripheral and night vision, transient worsening of macular oedema, mild reduction in colour vision.
Complications
- Diabetic macular oedema (commonest cause of visual loss, esp. type 2).
- Vitreous haemorrhage.
- Tractional retinal detachment.
- Neovascular glaucoma (rubeosis iridis).
- Macular ischaemia (irreversible central vision loss).
- Accelerated cataract; recurrent vitreous haemorrhage post-vitrectomy.
Key differentials
| Condition | Distinguishing features |
|---|---|
| Hypertensive retinopathy | Flame haemorrhages, AV nipping, copper/silver wiring, macular star; symmetrical, no microaneurysm-rich picture |
| Central retinal vein occlusion (CRVO) | "Blood-and-thunder" fundus, usually unilateral, sudden, sectoral if BRVO |
| Ocular ischaemic syndrome | Mid-peripheral dot haemorrhages, carotid disease, dilated non-tortuous veins |
| Radiation retinopathy | History of radiotherapy; CWS, microaneurysms resembling DR |
| Retinal vasculitis / Eales disease | Younger patients, peripheral neovascularisation, recurrent vitreous haemorrhage |
High-yield: Diabetic retinopathy is bilateral and roughly symmetrical; marked asymmetry should prompt a search for carotid stenosis on the less-affected side (ocular ischaemic syndrome / reduced perfusion is protective on that side).
Recently asked / exam angle
- CSME criteria (500 µm rule) — repeatedly tested as a single-best-answer; know the exact 500 µm and 1 DA numbers.
- 4-2-1 rule for severe NPDR — direct factual recall.
- Earliest sign: microaneurysm (clinical) vs pericyte loss (histological) — both appear as MCQ distractors; read the stem carefully.
- Cotton-wool spots = nerve fibre layer infarcts, not exudates.
- Treatment of choice for PDR = PRP; treatment of choice for centre-involving DMO = intravitreal anti-VEGF.
- Investigation of choice for macular oedema = OCT; FFA for non-perfusion/neovascular leakage.
- Trial data: DCCT, UKPDS (glycaemic control); DRS (PRP, high-risk PDR); ETDRS (focal laser, CSME definition, defer PRP in NPDR); DRCR Protocol S/T (anti-VEGF). Trial-to-conclusion matching is a popular format.
- Screening intervals by diabetes type and in pregnancy.
- Drug of choice and indications for vitrectomy.
Rapid revision
- Duration of diabetes = strongest risk factor; glycaemic control = strongest modifiable factor.
- Earliest histological change = pericyte loss; earliest visible lesion = microaneurysm.
- Cotton-wool spots = NFL microinfarcts; hard exudates = lipid; both differ in pathology.
- Severe NPDR = 4-2-1 rule (4 quadrants haemorrhage, 2 venous beading, 1 IRMA).
- PDR is defined by neovascularisation; high-risk PDR by DRS criteria → urgent PRP.
- CSME: thickening within 500 µm, exudate+thickening within 500 µm, or ≥1 DA thickening within 1 DA of fovea.
- OCT = investigation of choice for macular oedema; FFA = gold standard for capillary non-perfusion.
- PRP (laser) = treatment of choice for PDR; anti-VEGF = first-line for centre-involving DMO.
- Vitrectomy for non-clearing vitreous haemorrhage and tractional RD threatening the macula.
- Screen type 1 at 5 years, type 2 at diagnosis, pregnancy in first trimester.
- DCCT/UKPDS = glycaemic control prevents DR; ETDRS/DRS = laser; DRCR = anti-VEGF.
- Advanced diabetic eye disease = vitreous haemorrhage + tractional RD + neovascular glaucoma; DR is bilateral and symmetrical.