Illustration of the treatment of diabetic macula oedema (DMO) with stem cell therapy (left) and a synthetic delivery system (blue) for the secretome (centre), the molecules secreted by a stem cell. In DMO the high blood sugar levels associated with diabetes lead to leaky blood vessels. This causes fluid to build in the macula at the centre of the retina, the light-sensitive layer at the back of the eye. It is the most common cause of sight loss in people with diabetes. Stem cell therapies are looking to target pericytes (pink), cells that wrap around capillaries and are critical for maintaining the selectively permeable space between the blood vessel and its surroundings.