The head-mounted microscope

Authors

  • Ting Chen MD,

    1. Department of Otolaryngology–Head and Neck Surgery, Fujian Provincial College of Fujian Medical University, Fuzhou, China
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  • Seth H. Dailey MD,

    Corresponding author
    1. Division of Otolaryngology–Head and Neck Surgery, Department of Surgery, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin, U.S.A
    • K4/760 Clinical Science Center, 600 Highland Avenue, Madison, WI 53792-7395
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  • Sawyer A. Naze,

    1. Division of Otolaryngology–Head and Neck Surgery, Department of Surgery, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin, U.S.A
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  • Jack J. Jiang MD, PhD

    1. Division of Otolaryngology–Head and Neck Surgery, Department of Surgery, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin, U.S.A
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  • The authors have no funding, financial relationships, or conflicts of interest to disclose.

Abstract

Microsurgical equipment has greatly advanced since the inception of the microscope into the operating room. These advancements have allowed for superior surgical precision and better post-operative results. This study focuses on the use of the Leica HM500 head-mounted microscope for the operating phonosurgeon. The head-mounted microscope has an optical zoom from 2× to 9× and provides a working distance from 300mm to 700mm. The headpiece, with its articulated eyepieces, adjusts easily to head shape and circumference, and offers a focus function, which is either automatic or manually controlled. We performed five microlaryngoscopic operations utilizing the head-mounted microscope with successful results. By creating a more ergonomically favorable operating posture, a surgeon may be able to obtain greater precision and success in phonomicrosurgery. Phonomicrosurgery requires the precise manipulation of long-handled cantilevered instruments through the narrow bore of a laryngoscope. The head-mounted microscope shortens the working distance compared with a stand microscope, thereby increasing arm stability, which may improve surgical precision. Also, the head-mounted design permits flexibility in head position, enabling operator comfort, and delaying musculoskeletal fatigue. A head-mounted microscope decreases the working distance and provides better ergonomics in laryngoscopic microsurgery. These advances provide the potential to promote precision in phonomicrosurgery. Laryngoscope, 2012

INTRODUCTION

Laryngeal microsurgery techniques and instrumentation have advanced since the 1960s, when the use of a surgical microscope for endoscopic laryngeal surgery was first documented. 1 Advancements like adjustable focal length microscopes, smaller tipped instruments, subepithelial infusion techniques and suspension devices have helped improve surgical precision and provide patients with improved postoperative vocal function. 1, 2 Precision is especially crucial in executing effective endolaryngeal surgery, as there is a small margin for success. 1 Stabilization of the arms has been shown to improve accuracy in fine manipulations and reduce natural tremor in microsurgical procedures, which play a critical role in surgical precision and affect the overall success of microsurgery. 3

Traditional microscopes used in laryngeal microsurgery are mounted on a stand and have a fixed working distance, often 400 mm. This creates a position in which the surgeon is required to have an upright posture with his/her shoulders as stationary as possible and forearms extended nearly parallel to the operating surface to perform the procedure (Fig. 1). 4 This position may promote the early onset of fatigue during procedures, and may also decrease the ability of the surgeon to sustain steady control of the surgical instruments.

Figure 1.

Comparative ergonomic positions in phonomicrosurgery with different microscopes. (1) Illustrates the surgeon's ergonomic position with the stand microscope. A is the length of the eyepiece, B is the length of the objective lens mount, and C is the focal distance. The sum of A, B, and C is the working distance, which is approximately 74.5 cm. The angle between upper arm and forearm (α) is approximately 123°. Note the considerable extension at the elbow. (2) Illustrates the surgeon's ergonomic position with the head-mounted microscope. The working distance (a) is approximately 63.5 cm. The distance from the surgeon's eye to the target is shortened by elimination of the optical piece mount. The angle between upper arm and forearm (β) is approximately 88°. Note the surgeon's reduced extension at the elbow. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]

Figure 2.

Microlaryngoscopic screen shots. (1) Illustrates a glottis with bilateral vocal fold scar that underwent bilateral vocal fold subepithelial scar lysis under maximum magnification with the stand microscope. (2) The same glottis under 9× magnification with the head-mounted microscope. Although the stand microscope has more powerful magnification, the lighting and color resolution are favorable in each case. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]

Here we present a preliminary report on the application of the Leica HM500 head-mounted microscope (Leica Microsystems Inc., Bannockburn, IL) in combination with the arm support in laryngeal microsurgery. This application might create a more ergonomically favorable operating posture, allowing the surgeon to obtain greater stability in manipulation, leading to increased precision and better phonomicrosurgical results.

TECHNIQUE

Equipment

The Leica HM500 has a weight of 297 g and measures 73 × 120 × 63 mm (length × width × height). The ergonomic headset with infinitely variable height adjustment and adjustment of main movement axes distributes the weight evenly on the head. Its optical zoom allows magnification from 2× to 9× and offers a focus function (automatic or manually through the use of a foot pedal) with a working distance of 300 mm to 700 mm (from eyepiece lens to object). The field of view varies between 30 to 224 mm, depending on the selected enlargement factor and the working distance. The eyepieces are articulated, and the thickness of the optical piece is 100 mm.

Laryngoscope Microsurgery With the Head-Mounted Microscope and Armrests

We performed five phonomicrosurgical procedures using the head-mounted microscope. There were no equipment failures or unfavorable intraoperative events that were attributed to the optical system. The light source provided by the microscope was strong enough to illuminate the glottis. A comfortable angle for the surgeon to monitor the operative field through the laryngoscope was easy to obtain, due to the adjustability of the eyepiece positioning and the freedom of the surgeon's head position. The autofocus function's 1-second delay caused initial difficulties for the surgeon during head movements, but the surgeon adjusted to it quickly. The clearest focus was obtained through manual adjustment using the foot pedal. Figures 2 and 3 display screen shots of bilateral vocal fold polyps and a bilateral vocal fold subepithelial scar lysis procedure under the head-mounted microscope.

Figure 3.

Microlaryngoscopic screen shots. (1) Illustrates a glottis with bilateral polyps under maximum magnification with the stand microscope. (2) The same glottis under 9× magnification with the head-mounted microscope. Although the stand microscope has more powerful magnification, the lighting and color resolution of the head-mounted microscope are favorable in each case. Head-mounted microscopic image resolution is artificially degraded in these images because of the size of the computer file that is able to be captured with the image capture equipment of the head-mounted microscope. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]

DISCUSSION

In laryngeal microsurgery, there is an inherently small margin for success. 5 Yet, the surgeon is required to precisely manipulate long-handled cantilevered instruments through the narrow-bore of a laryngoscope using a microscope. Tremor is amplified due to the length of the long-handled surgical instruments (nearly 30 cm), and an upright posture with stationary shoulders and forearms extended nearly parallel to the operating surface.

Bones serve as levers and muscular force adheres to mathematical principles. The levers of the musculoskeletal system magnify motion rather than force. Muscles producing motion with larger levers require more force. The shorter the arm lever, the more stable motion is, and the less force muscles are required to exert, thereby delaying musculoskeletal fatigue. 6

This principle for modeling human motion is relevant to phonomicrosurgery. By creating a more ergonomically favorable operating posture, a surgeon may be able to obtain greater precision and success in phonomicrosurgery. This principle is especially pertinent in surgeons with shorter upper extremities because their lever arm is lengthened. However, decreasing the arm lever is currently limited because it is impossible to insert instruments into a laryngoscope when the stand microscope is too close. 7

Traditional stand-mounted microscopes are fitted with an objective lens with a nearly 400-mm focal distance. The focal distance of a microscope is calculated from the objective lens to its clearest focusing point. The working distance is the distance between the front lens of a microscope and the object when the instrument is correctly focused. For a stand microscope, it is the length of eyepieces (A) plus the length of the optical piece (B) (typically 350–450 mm) and the clearest focusing distance (C) (around 400 mm) (Fig. 2-1) . With a head-mounted microscope, the working distance is calculated from the lenses of the eyepieces to the clearest focusing point (120 mm plus the clearest focusing distance), which is 300 to 700 mm. Within this range the microscope can focus automatically (Fig. 2-2). The working distance achievable with a head-mounted microscope is therefore substantially reduced when compared to a stand microscope, even considering the angulation during operation.

Burns et al. noted that the stand-mounted microscope is not well suited for use in procedures, like microstereo-laryngoscopic lipoinjections, which require the use of large instrumentation, as the fixed working distance has “substantial technical restrictions in performing the procedure.” Intraoperatively, a 400-mm lens on a stand-mounted microscope provides a “distance of approximately 20 cm between the microscope and the proximal lumen of the laryngoscope.” 7 With the shorter optical piece on the head-mounted microscope, the distance between the objective lens and the entrance of the laryngoscope is larger than that found with the stand-mounted microscope. This provides more space for the adequate manipulation of long and bulky instrumentation. Another restriction of the stand-mounted microscope is that it is coaxial in view with the laryngoscope. This requires constant adjustment and positioning of the microscope and patient during the surgery for the surgeon to gain a sufficient view of the operative site. However, with the articulated eyepieces and variable focus on the head-mounted microscope, the surgeon is able to obtain an adequate view of the glottis with simple small adjustments in the head position and without a fixed focal length.

Research supports that the ideal ergonomic posture during microlaryngoscopy places the surgeon with the arms and feet supported, shoulders in a nonraised, neutral anatomic position, upper arms neutrally positioned 20° to 45° from the torso, lower arms neutrally positioned 60° to 100° from the torso, and wrists extended or flexed <15°. 8 This posture contributes most to the comfort of the surgeon and will help postpone the onset of musculoskeletal fatigue. The articulated eyepieces of the head-mounted microscope allow a surgeon to freely modify his/her body posture to a comfortable position without limitation by the location of eyepieces. Its design also enables the user to view objects to the side and below and above the lens. Through the use of the head-mounted microscope, in combination with a surgical chair with armrests, the best ergonomic posture is easy to acquire. 3 These refinements in equipment and positioning may aid not only in increased precision in manipulation, but also can decrease musculoskeletal occupational damage.

In one neurosurgery study using the head-mounted microscope, the autofocus was found to be ineffective when operating in deep structures during “keyhole” approaches. 9 As laryngoscopic microsurgery is more superficial in the changes of operation field depth compared with neurological microsurgery, we found that the head-mounted microscope provided adequate depth perception and focus during these cases. As the weight of the headset (297 g) is distributed evenly on head and neck, combined with adjustable eyepieces, neck fatigue was not encountered. The current zoom range is from 2× to 9×, although larger magnifications may be achieved with customized eyepieces.

Although the surgeon did not note considerable variation in image quality because the brain is able to integrate changing visual images induced by physical tremor into a stable subjective image, one notable limitation of the head-mounted microscope is reduction of the image quality projected on screen to a video monitor when compared to a stand microscope. 10

CONCLUSION

A head-mounted microscope decreases the lever-arm distance and provides better ergonomics in laryngoscopic microsurgery. Head-mounted microscopes, in assistance with surgical armrests, provide potential to promote precision in laryngoscope microsurgery. Based on our successful surgical results using the Leica HM500, we can recommend its application in phonomicrosurgical procedures.

Ancillary