In DME, excess fluid from blood vessels in the retina leaks into the macula, causing swelling. Because the macula is responsible for sharp central vision, the swelling causes blurred or distorted of central vision, loss of contrast sensitivity, and can include changes in color perception. A patient with macular edema may or may not also have ischemia, an abnormal reduction in blood flow to the retina due to blockage of the retinal blood vessels. In macular ischemia, inadequate blood supply to the central retina results in a loss of retinal cell function and irreversible central vision loss. DME is most often treated with a focal laser application or an injection of an anti-vascular endothelial growth factor (anti-VEGF) drug into the eye to stop leaky vessels.