Figure 1.

Classification of DR by severity and the major clinicopathological features associated with different stages. In no retinopathy, the retina shows no microvascular abnormalities. Hyperglycemia damages the normal retina, resulting in mild NPDR, characterized by microaneurysms. In moderate NPDR, microaneurysms and other microvascular abnormalities are observed. Severe NPDR is basically characterized by one or a combination of the following: (1) more than 20 retinal hemorrhages; (2) venous beading; (3) retinal microvascular abnormalities but not meeting the criteria for PDR. The progression to the PDR stage is marked by the appearance of NVD or NVE, along with preretinal or vitreous hemorrhage. Microvasculopathy is the main characteristic of the NPDR stage, while neovascularization is the main characteristic of the PDR stage. As the condition worsens, patients experience visual loss. Abbreviations: neovascularization of optic disc, NVD; neovascularization of elsewhere, NVE; non-proliferative diabetic retinopathy, NPDR; proliferative diabetic retinopathy, PDR.