title: Is the image "right" for everyone? Introduction to the parallax effect in laparoscopic surgery.
abstract: OBJECTIVE
  During minimally invasive abdominal surgery, a laparoscope is used to film the procedure, which is transmitted to a flat screen monitor. The horizontality of the image depends on the orientation in space and the visual comfort of the surgeon. Observing the screen via a lateral angle of incidence frequently results in the camera assistant making errors in determining the horizontality of the image. Thus, what is "right" for the camera assistant is not necessarily 'right' for the surgeon. We aimed to explain the impact of these errors in laparoscope manipulation, by the description of the parallax effect.
  
  
  METHODS
  To describe this phenomenon of perceptions changing depending on the angle of view, from the basis of the parallax effect, we observed the change of position and for two observers, (the surgeon and the camera assistant) seated at two different locations, using an experimental set up (i.e., photography equipment, a screen and a pelvitrainer).
  
  
  RESULTS
  The position of the camera assistant positioned at an angle of incidence of 45° from the surgeon, the observation of the screen with a lateral incidence changes the perception of the image viewed on the screen. For correcting the conflict between the subjective visual perception of the camera assistant and the actual image horizon, the camera assistant instinctively rotates the image, which can lead to an "incorrect" image, deleterious for the surgeon.
  
  
  CONCLUSIONS
  This article introduces a previously unexplained concept in medical literature, called the parallax effect. The parallax effect results in the camera assistant making systematic errors in determining image horizontality on the screen.
authors.affiliation: Department of Digestive Surgery, Rouen University Hospital, 1, rue Germont, 76031 Rouen cedex, France.
authors.forename: J
authors.initials: J
authors.lastname: Cahais
authors.affiliation: Department of Digestive Surgery, Rouen University Hospital, 1, rue Germont, 76031 Rouen cedex, France.
authors.forename: L
authors.initials: L
authors.lastname: Schwarz
authors.affiliation: Department of Digestive Surgery, Rouen University Hospital, 1, rue Germont, 76031 Rouen cedex, France.
authors.forename: V
authors.initials: V
authors.lastname: Bridoux
authors.affiliation: Department of Digestive Surgery, Rouen University Hospital, 1, rue Germont, 76031 Rouen cedex, France.
authors.forename: E
authors.initials: E
authors.lastname: Huet
authors.affiliation: Department of Digestive Surgery, Rouen University Hospital, 1, rue Germont, 76031 Rouen cedex, France. Electronic address: jean-jacques.tuech@chu-rouen.fr.
authors.forename: J-J
authors.initials: JJ
authors.lastname: Tuech
mesh_terms: D006801:Humans; D020706:Laparoscopes; D010535:Laparoscopy / Q000295:instrumentation* / Q000379:methods; D009039:Motion Perception; D015588:Observer Variation; D065287:Robotic Surgical Procedures / Q000295:instrumentation* / Q000379:methods; D013523:Surgical Equipment; D014796:Visual Perception
keywords: Laparoscopy; Navigation in minimally invasive surgery; Parallax effect; Surgical training