Illustration of treatments for neuron (nerve cell, three across lower centre) damage caused by diabetic retinopathy. The retina is the light-sensitive layer at the back of the eye. Diabetic retinopathy is damage to the blood vessels (one across lower centre, red) of the retina caused by the high blood sugar levels associated with diabetes. The damage to the blood vessels leads to a lack of blood flow to the neurons and, along with direct neuronal damage, causes neurodegeneration that can lead to blindness. Drugs, stem cells and gene therapy are all being investigated as treatments for neuron damage in diabetic retinopathy.