Diabetes mellitus is a disorder of sugar and fat metabolism which results in damage to the small blood vessels in various organs, this includes the retina - the part of the eye that processes light into a nerve impulse. This leads to damage and blindness via various different mechanisms that are not fully understood. In this study the objective is to recruit people with diabetes and various stages of diabetic eye disease and measure a large number of different chemicals within the blood that might be associated with damage and dysfunction within the retina. Additionally, it will examine the different bacteria within the gut that might affect disease in the eye via chemicals circulating in the blood. This will require participants to have blood samples taken and to provide urine samples. The blood will be analysed with specialised instruments to identify specific molecules circulating within the blood. Participants will also need to allow researchers to look at their medical records, previous photographs and specialist scans of the back of the eye to grade their diabetic retinopathy. This will allow us to identify potential ways in which these could be targeted for future benefit for people with diabetes to hopefully prevent deterioration of their vision.