nonproliferative diabetic retinopathy

NPDR results from chronic hyperglycemia-induced damage to retinal capillaries via mechanisms including pericyte loss, basement membrane thickening, and increased vascular permeability (via polyol pathway, AGE formation, and protein kinase C activation). This leads to microaneurysms (earliest sign, seen as small red dots on fundoscopy), dot-and-blot hemorrhages (deeper retinal hemorrhages), flame hemorrhages (superficial nerve fiber layer), hard exudates (lipid deposits from leaky vessels), cotton-wool spots (nerve fiber layer infarcts due to microvascular occlusion), and venous beading/looping (sign of more severe ischemia).

NPDR is classified into mild, moderate, and severe based on extent of hemorrhages, microaneurysms, venous beading, and intraretinal microvascular abnormalities (IRMA) using the '4-2-1 rule' for severe NPDR. Unlike proliferative diabetic retinopathy (PDR), NPDR lacks neovascularization because it precedes the significant hypoxia-driven VEGF upregulation that drives new vessel growth.

Clinically, NPDR may be asymptomatic or cause blurred vision, especially if macular edema develops (diabetic macular edema, DME)—the most common cause of vision loss in diabetics with NPDR. Diagnosis is via dilated fundoscopic exam, fundus photography, and optical coherence tomography (OCT) to assess for macular edema. Fluorescein angiography can reveal capillary nonperfusion and leakage.

Management includes optimizing glycemic control (reduces progression, per DCCT and UKPDS trials), blood pressure and lipid control, and regular ophthalmologic monitoring. Anti-VEGF injections (e.g., ranibizumab) or laser photocoagulation may be used if DME develops. Progression to PDR requires more aggressive treatment with panretinal photocoagulation or anti-VEGF therapy. NPDR is a major cause of vision loss in diabetic patients and a key board topic linking systemic disease to microvascular complications.