Macular edema occurs when fluid and protein deposits collect in the eyeball on or under a part of the retina (the lining of the back of the eye) that is called the macula. This material causes the macula to thicken and swell, and it may distort a person's central vision.

The macula provides sharp, clear central vision that allows a person to see form, color, and detail that is directly in the line of sight.