Depth estimation is one of the most fundamental challenges for performing minimally invasive surgical (MIS) procedures. The requirement of accurate 3D instrument navigation using limited visual depth cues makes such tasks even more difficult. With the constant expectation of improving safety for MIS, there is a growing requirement for overcoming such constraints during MIS. We present in this paper a method of improving the surgeon's perception of depth by introducing an "invisible shadow" in the operative field cast by an endoscopic instrument. Although, the shadow is invisible to human perception, it can be digitally detected, enhanced and re-displayed. Initial results from our study suggest that this method improves depth perception especially when the endoscopic instrument is in close proximity to the surface. Experiment results have shown that the method could potentially be used as an instrument navigation aid allowing accurate maneuvering of the instruments whilst minimizing tissue trauma.