Diabetic Retinopathy: Classification and Management for Residents

Last updated: October 2026

Diabetic retinopathy is the condition you will grade, treat and counsel for more than almost any other. This page gives you the classification, the exact definitions examiners expect, and a modern treatment framework based on the landmark trials.

Screening: when to start

• Type 1 diabetes: first examination about 5 years after diagnosis, then at least yearly.
• Type 2 diabetes: at diagnosis, because retinopathy may already be present, then at least yearly.
• Pregnancy: examine before conception or early in pregnancy, and follow more closely; retinopathy can progress quickly.
• Shorten the interval as retinopathy becomes more severe.

International (ICDR) classification

The 4-2-1 rule for severe NPDR

• 4 quadrants with severe intraretinal haemorrhages (20 or more in each quadrant), or
• 2 quadrants with definite venous beading, or
• 1 quadrant with prominent intraretinal microvascular abnormalities (IRMA)

Two or more of these features makes it "very severe" NPDR. These eyes carry a high risk of progressing to PDR within a year, so follow them closely.

High-risk PDR (Diabetic Retinopathy Study)

• NVD of at least about one-quarter to one-third of a disc area, or
• Any NVD with vitreous or preretinal haemorrhage, or
• NVE of at least half a disc area with vitreous or preretinal haemorrhage

Eyes with high-risk characteristics need prompt treatment. See landmark trials for DRS and ETDRS.

Diabetic macular oedema

• Modern practice: classify DME on OCT as centre-involving or non-centre-involving. This decides treatment.
• Classic ETDRS definition of CSME (still asked in exams), any one of:
  • Retinal thickening within 500 µm of the centre of the macula
  • Hard exudates within 500 µm of the centre with adjacent retinal thickening
  • A zone of thickening one disc area or larger, any part of which is within one disc diameter of the centre
• On OCT, look for intraretinal cysts, subretinal fluid, hyperreflective foci and DRIL. See OCT reading tips.

Treatment framework

Systemic control: the ophthalmologist's job too

• Tight control of blood sugar, blood pressure and lipids slows retinopathy. Tell the patient's physician what you have found.
• Fenofibrate has been shown to slow retinopathy progression in type 2 diabetes in large trials. Discuss it with the physician.
• Watch for early worsening: rapid improvement in HbA1c, pregnancy, and cataract surgery can all temporarily worsen retinopathy or DME. Examine before and soon after.
• Check kidney function in patients with severe retinopathy; retinopathy and nephropathy often travel together.

Viva pearls

• The earliest clinical sign of DR is a microaneurysm; the earliest pathological changes are pericyte loss and basement membrane thickening.
• IRMA are shunt vessels within the retina; NVE grow on the retinal surface and leak on angiography.
• Cotton-wool spots are infarcts of the nerve fibre layer, not exudates.
• Rubeosis needs urgent treatment (PRP plus anti-VEGF) before the angle closes.