 Within the retina there are small blood vessels which supply it with nutrition. Sometimes in eye disease such as diabetes these blood vessels can grow abnormal new branches stimulated by growth factors such as VEGF which leave the retina and grow into the vitreous space. Because these new vessels are very fragile they have a tendency to get damaged and bleed. When they bleed into the vitreous space it creates a large collection of blood haemorrhage which prevents the focused light from the lens reaching the retina. This dramatically reduces the vision in this eye for the patient and prevents healthcare practitioners from examining the eye and giving further treatment for the cause of the bleed. This often means an eye operation is required to clear the blood from the vitreous space, to allow the patient to see and to allow further treatment to prevent worsening of the eye disease. 