 The disease Ocular Ischemic Syndrome OIS is not a well described entity. It occurs after a long-standing period of extremely low blood supply to the retina caused by atherosclerosis of the carotid arteries. In this study we will analyze why OIS is developed in some patients and not developed in others. The patients with OIS will be thorough examined and will be compared with 1 a control group of healthy people and 2 with control group of patients with diabetic retinopathy. Furthermore the impact of vascular surgery on OIS will be analyzed. 