A Comparison of Super Wide Field Microscopy Systems in Mohs Surgery

December 2014 | Volume 13 | Issue 12 | Original Article | 1463 | Copyright © 2014

Anne Goldsberry MD MBA, C. William Hanke MD MPH, and Nicholas B. Countryman MD MBA

The Laser and Skin Surgery Center of Indiana, Carmel, IN

Abstract

Microscopic frozen section interpretation is one of the cornerstones of Mohs surgery. The recent development of super wide field (SWF) microscopy can improve accuracy and efficiency while reading microscope sections, and also decrease the physician’s musculoskeletal and ocular strain.1,2 Super wide field microscopy systems increase viewable field area (VA) by combining low magnification objectives, eg, 1x or 2x (Figure 1), with eyepieces that have a higher field number.2,3 This article reviews 3 SWF microscopy systems: Leica DM2000 (Leica Microsystems, Wetzlar, Germany), Nikon Eclipse Ni (Nikon Instruments Inc., Melville, NY), and Olympus BX43 (Olympus, Center Valley, PA). The Leica DM2000’s 1.25x objective results in a VA of 314.16 mm2. The Nikon Eclipse Ni’s 1x objective results in a VA of 490.87 mm2. The Olympus BX43’s 1.25x objective results in a VA of 352.99 mm2. The maximum VA at the lowest objective for Nikon is nearly 40% greater than for the Olympus and over 50% greater than for the Leica. The Nikon Eclipse Ni has a significantly higher maximum VA than the other 2 systems.

J Drugs Dermatol. 2014;13(12):1463-1465.

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INTRODUCTION

The ability to visualize what is invisible to the naked eye is critical in medicine. Robert Hooke invented the first simple microscope in the 1660s and used it to visualize cells. Many advances in design have occurred since then.

In 1938, Frederick Mohs developed a surgical technique that combined tumor excision with histological analysis of frozen sections. He named the method “micrographically controlled tumor excision.” It was later renamed Mohs micrographic surgery (MMS).4 Mohs micrographic surgery improved the accuracy and precision of tumor removal, while sparing normal tissue. However, the high cure rate associated with MMS is dependent on slide quality and interpretation.5-7

Improvements in magnification, lens objectives, and viewable field area (VA) have helped with visualization of frozen sections. In addition, new techniques for tissue embedding and cutting microscope sections have allowed histology technicians and surgeons to incorporate larger tissue specimens onto single slides.8 (Figure 1). The recent development of super wide field (SWF) microscopy increased the VA of the microscope. Super wide field microscopy has the potential to improve physician accuracy and efficiency when reading slides.2 Despite the availability of SWF systems, many Mohs surgeons are unaware of the new technological advances. We have evaluated 3 SWF microscopy systems: Leica DM2000 (Leica Microsystems, Wetzlar, Germany), Nikon Eclipse Ni (Nikon Instruments Inc., Melville, NY), and Olympus BX43 (Olympus, Center Valley, PA).

DISCUSSION

In order to fully understand the impact of the SWF microscopy parameters, it is important to understand a few basic equations that define the principles of microscopy. Viewable field area is calculated using 2 equations:

table 1

Most microscope systems have tube lens magnification factors equal to 1, which will be assumed in all of the calculations. The field number (FN) refers to the diaphragm diameter of an eyepiece. Following the equations, a 25% increase in the FN would result in a 156% increase in the VA, assuming all other variables were held constant. Consequently, increasing the VA from 20 mm to 25 mm results in a 156% increase in the viewable area.

Super wide field microscopy systems combine lower magnification objectives (1x or 2x) with eyepieces that have a higher FN in order to increase VA.2 Traditional wide field eyepieces have a FN of 18 mm to 22 mm. The newer SWF eyepieces have a FN of 25 mm to 26.5 mm.2 Comparison of the 3 systems highlights the benefits of SWF microscopy (Figure 2).

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