Methods and devices for performing surgery in a patient are provided. A cannula provides a working channel for access to a location in the patient. A clamp assembly is removably engaged to the cannula. The clamp assembly allows use of an endoscopic viewing system or can be removed to allow use of a microscopic viewing system in order to view the surgical site in the patient through the working channel. The clamp assembly includes a viewing element mounting portion having a length along which an endoscopic viewing element can be selectively positioned.