Cystoid macular edema is a well recognized complication associated with RP. It is thought to occur in about fifty percent of RP cases at some stage in the disease. Cystoid macular edema causes a build up of fluid in the macula. The macula is the central portion of the retina responsible for perceiving fine visual detail. Some, but not all, patients who develop cystoid macular edema will experience a reduction of their central vision.