Improvement of Depth Perception and Eye-Hand Coordination 
                in Laparoscopic Surgery

		      Paul Breedveld

	       Delft University of Technology, 
	  Fac. of Design, Engineering & Production, 
     Dept. of Mechanical Engineering & Marine Technology,
            Man-Machine Systems & Control Group, 

        Mekelweg 2, 2628 CD, Delft, the Netherlands 
            E-mail: P.Breedveld@wbmt.tudelft.nl

Introduction

Laparoscopic surgery is a minimally invasive surgical technique which
is performed by using an endoscopic camera and long and slender
instruments that are inserted through small incisions in the abdominal
wall. The surgeon performs the operation indirectly by spatially
manipulating the instruments and by observing the camera pictures on a
monitor. Advantages of laparoscopic surgery are that it reduces the
damage of the body and in principle also the risk of infection and the
recovery time. Disadvantages are that the indirect way of observing
and manipulating complicates the surgeon's depth perception and
disorders the surgeon's eye-hand coordination.

Depth perception

A human can use a number of depth information sources to determine
spatial distances and movements from the image seen by the eyes. One
of the most important sources is movement parallax, which concerns
shifts in the retinal image when the observer moves the head. Since
conventional endoscopes are controlled by a camera assistant, however,
the surgeon is not able to use movement parallax as a depth
information source. Motion parallax is present to some extent when the
assistant moves the endoscope, but the amount of information is
limited since the endoscope movements are limited. The abdominal
incision point acts like a spherical joint that limits the degrees of
freedom of the endoscope from six to four. This makes it impossible to
observe the anatomic structure from aside while keeping the viewpoint
in focus.

Eye-hand coordination

Eye-hand coordination problems arise from discrepancies between
expected and observed instrument movements on the monitor. The
endoscope is inserted into the abdominal wall at a location and at an
angle where it does not hamper the surgeon and the operation team in
their activities. As a result, the camera's line-of-sight is usually
different from the surgeon's natural line-of-sight when looking
directly into the abdomen. Consequently, the instrument tips on the
monitor move in a different direction than expected. The surgeon has
to compensate this misorientation by rotating the hand movements
mentally. This is very confusing.

Flexible 90 o endoscope

The presence of misorientations and the absence of movement parallax
make it very difficult for a resident surgeon to get used to the
operation technique. As a result, a long and intensive training period
is required. The presentation describes a concept of a new endoscope
positioning system that eliminates misorientations by using a 90o
endoscope with a flexible tip. The tip can always be rotated such that
its line-of-sight corresponds with the surgeon's natural line-of-sight
when looking directly into the abdomen. It can also be used to observe
the anatomic structure from aside while keeping the viewpoint in
focus. Movement parallax can be realised by means of a motorised
endoscope positioner that is controlled by the surgeon's head
movements.