Retinal Photograph of a patient with Diabetic Macular Edema. The yellow circle shows swelling in the center of the retina (the macula). The white arrow points to one of several spots of blood in the retina.

Fluorescein Angiogram: The yellow arrow points to one of many oval, and circular whitish areas. These are areas of swelling within the retina.

Please see How the Eye Works for an introduction. Within the retina is a system of blood vessels – arteries, veins, and capillaries. This system of blood vessels nourishes the retina with oxygen. One large artery, the central retinal artery, carries blood to the retina. As the artery enters the eye, many branches spread out throughout the retina. The blood then goes through a fine network of very small vessels called capillaries. After the blood moves through this network of capillaries, it enters branches of veins, called, branch retinal veins. These then join together to form the large vein called the central retinal vein that drains the blood from the eye. Diabetes causes damage to retinal vessels. This is called diabetic retinopathy. Diabetic macular edema occurs when the small capillaries in the retina have become leaky due to diabetic retinopathy. As serum (the clear sticky party of blood) leaks from these damaged capillaries, it collects in the retina and causes swelling. This blurs and distorts vision.

Optical Coherence Tomography Study: The yellow arrows point to two of several dark oval shaped areas. These are cysts within the retina due to fluid selling the retina