According to the ETDRS classification, which of the following features MOST reliably predicts progression to high-risk proliferative diabetic retinopathy and mandates prompt pan-retinal photocoagulation?
- A Clinically significant macular oedema with hard exudates within 500 μm of the fovea
- B Severe non-proliferative diabetic retinopathy (4-2-1 rule) ✓
- C Vitreous haemorrhage obscuring disc assessment
- D New vessels elsewhere (NVE) involving less than half the disc area
Correct answer: B. Severe non-proliferative diabetic retinopathy (4-2-1 rule)
Explanation
The 4-2-1 rule defines severe NPDR: haemorrhages/microaneurysms in all 4 quadrants, or venous beading in 2 or more quadrants, or IRMA in 1 or more quadrant. The ETDRS showed that 50% of eyes with severe NPDR progress to high-risk PDR within one year. CSME mandates focal/grid laser for macular oedema. Vitreous haemorrhage suggests established PDR. NVE less than half the disc area alone is moderate-risk PDR, not high-risk.
Reference: Khurana Comprehensive Ophthalmology, 7th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.