The longer a person has diabetes, the higher their chances of developing diabetic retinopathy. Prolonged periods of high blood sugar levels cause damage to the small blood vessels in the retina at the back of the eye. These blood vessels initially become leaky, and then may become blocked off. This causes haemorrhages (spots of blood) and exudates (proteins) from the blood vessels on to the retina. It may also cause swelling, known as oedema of the retina. The blocked vessels can starve the retina of oxygen, leading to the growth of new abnormal vessels from the retina. Good control of diabetes by controlling the blood sugar level helps to reduce the chances of developing retinopathy. | 
