A speculum is an instrument designed to allow a doctor to view the inside of a passage or cavity of the body. Rectal speculums are used in the conduction of an anoscopy, a preliminary examination before a proctoscopy or sigmoidoscopy. The rectal speculum dilates the anus and allows the physician to see the anal canal more clearly, in order to establish whether there is anything that will block the route of the proctoscope or sigmoidoscope.