There are many causes of macular edema. It is frequently associated with diabetes, where damaged blood vessels in the retina begin to leak fluids, including small amounts of blood, into the retina. Sometimes deposits of fats may leak inside the retina. This leakage causes the macula to swell. Eye surgery, including cataract surgery, can increase your risk of developing macular edema due to blood vessels becoming irritated and leaking fluids. Macular edema that develops after cataract surgery is called cystoid macular edema (CME).