Diabetic retinopathy progresses in stages:

• Mild Nonproliferative Retinopathy:
  This earliest stage is marked by “dot” and “blot” hemorrhages and microaneurysms in the retina. It may occur without any changes in vision and often doesn't require treatment unless it progresses or is accompanied by diabetic macular edema (DME).
• Moderate Nonproliferative Retinopathy:
  In this stage, some retinal blood vessels become blocked, reducing the retina’s oxygen and nutrient supply.
• Severe Nonproliferative Retinopathy:
  A significant number of vessels are blocked, leading to retinal ischemia, or oxygen deprivation, which puts the retina at risk for further damage.
• Proliferative Retinopathy:
  This advanced stage involves the growth of abnormal, fragile blood vessels-a process called neovascularization-in response to ischemia. These vessels may bleed into the vitreous and can lead to vision-threatening complications, even if vision is still good. Prompt treatment is crucial to prevent permanent damage.