From ages 20 to 74 years, diabetes is the leading cause of blindness and macular edema is one of the two primary disorders that can cause this vision loss. The macula is the area around the center of the retina that is responsible for sharp, detailed vision. In diabetic patients, elevated blood pressure and blockages in retinal blood vessels can cause leakage of fluid into the macula that leads to the macular swelling known as macular edema. Accumulation of fluid in the macula causes blurring of vision that can progress to permanent loss of vision through a process that is poorly understood. Macular edema can also occur in patients who do not have diabetes as a result of eye diseases that cause inflammation, blockage of a retinal vein, or inflammation after surgery. The latter phenomenon is referred to as Irvine-Gass syndrome.