Hi, I Was Diagnosed With GERD A Number Of Years

Hi, I was diagnosed with GERD a number of years ago. I still have break through symptoms even taking Dexilant in the morning and Ranitidine at night. I had an upper endoscopy in August 2011 that was negative for Barrett's esophagus and showed inflammation due to reflux disease. How often should I get the upper endoscopy done to check for Barrett's esophagus?