Joan Rivers Doctor Mugs for Camera In Celine Dion Movie

9/17/2014 4:45 PM PDT

Joan Rivers' Doctor Mugs for Camera in Celine Dion Movie (VIDEO)


The doctor who was performing a procedure on Joan Rivers when she stopped breathing allowed cameras into her office for a Celine Dion documentary ... performing a vocal cord procedure and joking around with the famous singer.

Dr. Gwen Korovin checked out Celine's strained vocal cords for the singer's 2010 documentary, "Through the Eyes of the World."  

The procedure is called a laryngoscopy ... in which the mouth/oral cavity is numbed so the patient can respond to the doctor's commands.

Check out the photos of her famous patients lining the walls ... patients that include Lady Gaga, Hugh Jackman, John Mayer and Brooke Shields.  

Korovin was not certified to perform medical services on Joan during her endoscopy. She was reportedly performing a biopsy when Joan stopped breathing and CNN is reported the doctor took a selfie while Joan was under.