A: The retina’s blood vessels are small, matching the delicate nature of the tissue, making these vessels particularly susceptible to damage from high blood sugar levels. The condition progresses through four stages as the retina faces increasing damage:

  1. Mild nonproliferative retinopathy. The retina’s blood vessels swell, which may cause fluid leakage in the retina.
  2. Moderate nonproliferative retinopathy. Blood vessels swell and distort, causing them to become incapable of transporting blood.
  3. Severe nonproliferative retinopathy. Many blood vessels are blocked, depriving blood supply to areas of the retina. In response, these areas secrete growth factors, signalling to the retina to grow new blood vessels.
  4. Proliferative diabetic retinopathy (PDR). In this stage, new blood vessels are created but they are fragile, leading to increased leakage and bleeding. This continued damage creates scar tissues, which contracts causing retinal detachment, meaning the retina pulls away from the underlying tissue. As the retina sends visual images to the brain via the optic nerve, this detachment can cause permanent vision loss.