Exoscopic technology

1.1

Introduction

Microsurgical procedures have been developed during the last decades in several specialties. The operating microscope was indeed extensively used to perform fine and delicate surgeries in many fields. In particular, ENT surgeons usually perform ear, microlaryngeal, and skull base surgery with the operating microscope in daily surgical activity. Moreover, head and neck free flap reconstruction is now widespread in many ENT centers. The technological growth of the last decades have developed several instruments allowing for more precise surgery. In this context, exoscopic technology was introduced in the last decade as a new surgical visualization and magnification tool. The term “Exoscope” is derived from the Greek words “exō” (out of) + skopeîn (to look). In fact, the exoscope serves for observing and illuminating the surgical field from a position set apart from the patient's body. The surgeon could perform the microsurgical procedure by watching images on a screen thanks to advanced digital technology. Moreover, the novel three-dimensional exoscopes improved the hand and eye coordination allowing for the finest surgical maneuvers.

Several exoscopic devices have been developed during the last decade such as the VITOM (Karl Storz), Orbeye (Olympus), and Modus V (Synaptive Medical). Karl Storz's video telescope operating monitor (VITOM) was released in 2011, determining a change in direction for surgeries that used the traditional operating microscope. Several technical characteristics differentiate these devices such as illumination, magnification power, and the diameter of the field of view. Moreover, some important differences should be highlighted according to their portability other than from an economic perspective.

This chapter aims to provide a comprehensive analysis of technical characteristics of the exoscopic system to better understand its applicability in the various otolaryngology microsurgical procedures deeply explained in the following chapters.

1.2

VITOM 2D

Around 2008, a new visualization system has been introduced in surgery in alternative to the operative microscope. The high definition exoscope (HDXO-SCOPE) allowed to see the operating field from outside the body, in opposition to the endoscope in which the device is introduced into the body cavities. The telescope consisted in an autoclavable rigid lens ( Fig. 1.1 ), which could be connected with a fiber optic light source (Xenon Nova 300; Karl Storz).

The telescope was characterized by a 10-mm outer diameter and a shaft length of 14 cm, allowing for a mean focal distance of 200 mm with a depth of field of 12 mm. It provided a high-resolution image with minimal spherical aberrations or chromatic distortions and a wide viewing angle comparable to the operating microscope. The telescope was connected to a three-chip sterilizable high-definition (HD) digitized camera with optical zoom and focus features. A medical-grade 23-in. HD (2 million pixels) video monitor (NDS Surgical Imaging, San Jose, California) was used for video display and documentation. The telescope was held in position by a pneumatic endoscope holder (Point Setter; Mitaka Kohki Co, Tokyo, Japan) with a wide range of motion. The device allows for push-button rapid repositioning with minimal drift, similarly to the hydraulic counterbalance system of the operating microscope. Since the first exoscope system was developed in a two-dimensional view, the major limit was the relative lack of stereopsis compared to the operating microscope, resulting in a lack of image depth on the screen. This had an important impact on the overall surgical outcomes. It rendered difficult an accurate manipulation of microsurgical instruments and the hand-eye coordination was reduced when operating using a two-dimensional image. Depth perception can be obtained even in a monocular view thanks to interposition, motion, familiar size, and proximity-luminance covariance of the surgical field, allowing the surgeon to orient himself during surgery. However, this may not be enough under high magnification, especially in microsurgery, which requires even a higher precision.

1.3

Three-dimensional exoscopes introduction

The introduction of three-dimensional systems, which imply wearing dedicated glasses during surgery, mainly aimed to remedy the depth perception issue that characterized the 2D systems. The main advantage of three-dimensional exoscope systems is in fact the perception of objects' volume and the depth of structures for planning, targeting, and controlling fine movements, which was more difficult with two-dimensional visualization.

This innovative and different approach to microsurgery encountered some resistance at first, as the adverse effects on the main operator were considerable in terms of visual strain, potential headache, and facial discomfort. Moreover, despite the higher image definition and the increased stereopsis, coordinating hand movements while looking at the screen was considered uncomfortable, especially compared to the operating microscope.