The Perspective Effect of Wide-Angle Lenses in Laparoscopes

Abstract

INTRODUCTION IN MINIMALLY INVASIVE SURGERY (MIS), the use of small incisions to provide access and the use of an endoscope for visualization result in some limitations for the surgeon. 1,2 For example, instrument motion is mirrored because the incision acts as a pivoting point. Furthermore, in comparison with natural vision, endoscopic vision is monocular and usually presents the operating area from an unnatural viewpoint. In the literature, these effects are known to disturb the surgeon's spatial perception 1,3 and hand-eye coordination. [4][5][6] This study reports an additional effect that disturbs the visual information from the operating area: the perspective effect, which results from the use of wide-angle lenses in laparoscopes. Its possible consequences on hand-eye coordination during endoscopic manipulation are evaluated. Perspective effect definedTo provide a large field-of-view inside the abdomen, laparoscopes are equipped with a wide-angle lens. Typically, the angle of view (a in Fig. 1) is about 70 degrees. An inherent characteristic of wide-angle lenses is that they show extreme perspective; in comparison with objects farther away, objects close to the lens appear much larger than would be expected from the difference in distance. As a result, movements of an instrument in a plane not parallel to the endoscope lens (b , 90 degrees in Fig. 1) appear distorted on the monitor. Rotations of the instrument around the incision can appear as translations perpendicular to the shaft on the monitor. This effect is visualized in Figures 1 and 2 and is what we define as the perspective effect. The effect increases when the angle b decreases and when the distance between the lens Methods:Sixteen subjects repeatedly performed a standardized positioning task in a pelvi-trainer under two conditions. The subjects had no prior experience with endoscopic manipulation. In one condition, a wide-angle lens with considerable perspective distortion was used; in the other, a telephoto lens without perspective distortion was used. Task time and number of errors were measured.Results: Task time and the number of errors did not significantly increase in the condition with a wide-angle lens.Conclusions: The perspective effect did not influence task performance in endoscopic manipulation in this experiment. Subjects indicated that they even preferred the wide-angle lens because its extreme perspective improved their perception of depth.

Defining optical distortion in rigid endoscopes

“…Perspective distortion occurs whenever the angle between the distal face of the endoscope and the plane of the object being viewed is not zero, and it is greater as RA is increased. There have been concerns that the use of angled endoscopes can be less safe and can lead to disorientation; and it has been observed that surgical performance is reduced for just a small contribution from perspective distortion . Perspective distortion is often not fully appreciated, particularly the fact that it can occur as much in the standard 0° endoscope, which is favored in many branches of endoscopic surgery because it is considered to exhibit less field distortion, as it can in any angled endoscope.…”

“…b), which occurs when the optical axis of the endoscope lens is not perpendicular to the surface of the object. Accurate localization, distance perception, and image feature registration are dependent on the endoscopist compensating for these artifacts, either consciously or subconsciously …”