Fluid accumulation in the outer layer of the macula lutea that results from intraocular or systemic insults. It may develop in a diffuse pattern where the macula appears thickened or it may acquire the characteristic petaloid appearance referred to as cystoid macular edema. Although macular edema may be associated with various underlying conditions, it is most commonly seen following intraocular surgery, venous occlusive disease, diabetic retinopathy, and posterior segment inflammatory disease. (From Survey of ophthalmology 2004; 49(5) 470-90)