Angustia (1987)

John, a loutish optometrist orderly, louses up on the job and is dismissed. His odd, little mother, using a form of hypnosis, sends him out on a killing spree, starting with Caroline, the woman who caused his dismissal. But this is all just a movie titled "The Mommy" being shown to a small matinee crowd at a seedy movie theater in Los Angeles. As it happens, two teenage girls in the audience, the strong-willed Linda and the squeamish Patty, discover that one of the patrons sitting near them is a real maniac. In the old movie, when the scalpel-wielding John enters a movie theater and beings killing the patrons and theater employees one by one, and removing their eyeballs for his mother's collection, the killer in the audience, armed with a silenced .38 pistol, begins killing the patrons and employees of the theater in a manner which parallels the action on the movie screen.