Which statement best differentiates proliferative from nonproliferative diabetic retinopathy?

• A. NPDR has neovascularization; PDR does not.
• B. Both have microaneurysms and hemorrhages.
• C. PDR has neovascularization and potential vitreous hemorrhage; NPDR does not.
• D. NPDR is defined by macular edema; PDR by cotton-wool spots.

Answer: (C)

Proliferative diabetic retinopathy is defined by the growth of new, abnormal blood vessels on the retina or optic disc. These neovascular vessels are fragile and can bleed into the vitreous, leading to vitreous hemorrhage and increasing the risk of tractional retinal detachment. In contrast, nonproliferative diabetic retinopathy shows vascular changes such as microaneurysms, hemorrhages, exudates, and cotton-wool spots, but there is no new vessel growth. Macular edema can occur in nonproliferative disease, but the presence of neovascularization distinguishes proliferative disease. So the best differentiator is that proliferative retinopathy has neovascularization (with potential vitreous hemorrhage), whereas nonproliferative retinopathy does not.