Illumination and Ergonomics are Paramount for Microscopes

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Article Date: 5/1/2005

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Illumination and Ergonomics are Paramount for Microscopes
Does the operating microscope you are evaluating offer something to streamline your procedures?
BY ROCHELLE NATALONI, CONTRIBUTING EDITOR

Optics and illumination in the form of cutting edge operating microscopes work hand in hand to optimize the retinal surgeon's view. While the primary purpose of an operating microscope is simple, thorough evaluation of today's complicated systems is anything but.

Acquisition of an operating microscope for a retinal practice represents a capital investment that must be evaluated on several levels. The first and most important question is, does the scope offer something that your current equipment lacks that will translate into improved clinical outcomes? The next crucial query should be, will the system provide relevant ergonomic benefits to all of the surgeons in the practice regardless of their surgical preferences? And finally, can the microscope be used for other surgical techniques in addition to the vitreoretinal surgeries for which it was primarily targeted?

A DISTINCT ADVANTAGE

A new operating microscope with a unique component designed specifically for retinal surgery reportedly offers several distinct advantages. Topcon's OMS-800 scope claims to facilitate easier, safer, and faster vitrectomies. The Optical Fiber Free Intravitreal Surgery System (OFFISS) component offers hands-free illumination. The light comes from within the microscope, which allows the surgeon to use two instruments simultaneously.

This system is potentially advantageous, says Stanley Chang, MD, the Edward S. Harkness professor of Ophthalmology and chairman of the Department of Ophthalmology at Columbia University in New York City, because surgeons can wield forceps to hold tissue and scissors to cut tissue while maintaining illumination from an external source.

Regardless of these capabilities, Dr. Chang says there are several questions that need to be addressed with respect to any system that provides this feature.

"Systems that allow us to see with a wider field of view often have different lenses, so you can get different fields of view. So another important question is can you change the lens?" says Dr. Chang.

He also stresses the importance of being aware of the presence of light reflexes because, "when you shine the light from outside the lens, light reflects off the surface of the lens and then goes into the eye," explains Dr. Chang. "Additional reflective surfaces may be troubling during air/fluid exchange [because they make it] difficult to see the tip of the flute needle."

Illumination capabilities are a paramount consideration when looking at operating microscopes, and other questions for surgeons to consider are: Is the illumination equivalent for peripheral and central work? Is there adequate illumination to visualize subtle macular detail? What is the phototoxicity risk profile? What percent of cases require supplemental use of endoillumination and can the illumination system be use for small gauge as well as standard gauge instruments?

"Is there adequate illumination for the monitor and for videotaping cases as well?" adds Paul Sternberg, MD, the George W. Hale professor and chair at the Vanderbilt Eye Institute at Vanderbilt University in Nashville, TN.

ERGONOMICS

Design with respect to ease of use and comfort level is another bit of crucial criteria by which to evaluate any capital equipment investment. A manufacturer may boast about the scope's ergonomically placed foot pedal, but if it's not easily adjustable to accommodate a variety of surgeons, the supposed perk can easily be an obstacle.

Topcon reports that its OMS-800 model has a multi-function footswitch which enables the surgeon to control all of the system's functions -- illumination intensity, zoom magnification, focus illumination, angle selection, and X-Y positioning -- without having to remove his or her hands from the operative field. Another feature of this system designed with comfort and ease of use is the "ergonomically designed optical head with built-in beam splitter that allows the surgeon to maintain a comfortable posture throughout the surgery." The comfort claim is based on variable angle binocular tubes that allow for the setting of a personal viewing angle from 45 degrees to 90 degrees.

The question of an operating microscope's applicability to surgeries other than those that it is specifically designed for is particularly germane in retinal surgery because of the increasing incidence of combined cataract and vitreoretinal surgery. In the case of the OMS-800, Topcon reports that this microscope provides an improved red-reflex and better shadow contrast even in situations with low luminance, resulting in particularly effective image quality during simultaneous cataract and vitreous surgery.

MICROSCOPE FACILITATES BIMANUAL VITRECTOMIES.
Light source allows two-handed instrument manipulation.

A deft hand and a bright light are two of the key components of vitreoretinal surgery. The development of an instrument that maximizes both makes bimanual vitreous surgery possible. Topcon's OMS-800 operating microscope Optical Fiber Free Intravitreal Surgery System (OFFISS) component eliminates the need for hand-held fiber-optic illumination, which means the surgeon can use both hands for manipulating surgical instruments during vitrectomies. According to Ricardo Amiron, product manager, Topcon, this is a first in intravitreal surgery. "The surgeon is free to simultaneously use two instruments such as scissors and forceps, intraocular probes and forceps or two forceps," he said.

OFFISS affords illumination over the entire operative field, including the peripheral area. According to internationally-based retinal surgeons who have incorporated this equipment into their practices, this feature results in more efficient and safer procedures. Even in patients with small pupils, surgeons have a clear stereoscopic view because of a built-in stereo variator.

Three types of illuminations are available with the OMS-800: retro illumination, three-angle illumination (combining retro and inclined illumination), and yellow filter to protect the retina against phototoxicity. With the yellow filter, a surgeon can operate for 111 minutes without inducing phototoxicity. This claim is based on the difference between the amount of radiation produced by the OMS-800 with OFFISS and the threshold for retinal damage due to phototoxicity. The retinal irradiation with OFFISS is 30mW per square centimeter. The threshold for retinal damage is 200 Joules per square cm.

According to Amiron, built-in slit illumination facilitates fundus observation with high contrast and less flare than conventional operating microscopes. "What's more," says Amiron, "OFFISS provides exceptional working distance between the 40D non-contact lens and the patient's eye."

Clinical Studies

The concept of bimanual surgery is not foreign in ophthalmic surgery, but it is relatively new to the retinal field. A Japanese study of the bimanual vitreal surgery technique using the OMS-800 with OFFISS resulted in confirmation of the system's efficacy. Masyayuki Horiguchi, MD, Yoshihisa Kojima, MD, and Yoshiaki Shimada, MD, of the department of Ophthalmology at Fujita Health University School of Medicine in Toyoake, Japan, performed bimanual vitrectomy in 37 eyes with preretinal membranes due to diabetic retinopathy or
proliferative vitreoretinopathy.¹ The surgeons reported that the membrane dissection and hemostasis were performed without incident, and an improvement in visual acuity of two or more lines was achieved in 30 of the 37 eyes. Five eyes resulted in no changes in two or more lines and two eyes had a decrease in visual acuity of more than two lines. There was no evidence of phototoxicity in any of the cases.

A recent development in the system's evolution is the addition of a multicoated contact lens. The new lens is made of quartz, and its multicoated surface has properties that decrease light reflection and increase light absorption, according to Amiron.

This reusable lens is placed on the cornea, and the coaxial light from the operating microscope alone enables surgeons to obtain a clear image of the retinal surface. This new vitrectomy contact lens is particularly useful in the bimanual surgical treatment of eyes with proliferative membranes according to its creators, Kazuaki Kadonosono, MD, Kazuro Yabuki, MD, Tadayuki Nishide, MD, Eiichi Nomura, MD, Eiichi Uchio, MD, and Tadashi Yamakawa, MD²

Drs. Kadonosono, Yabuki, Nishide, Nomura, and Uchio are from Yokohama City University Medical Center's department of ophthalmology, and Dr. Yamakawa is from that facility's department of endocrinology and diabetes. The contact lens is not yet available in the United States. They have no financial interest in the contact lens.

Footnotes

1. Horiguchi, M et al. New System for fiberoptic-free bimanual vitreous surgery. Arch Ophthalmol. 2002; 120:491-494.

2. Kadonosono K, et al. Multicoated contact lens for bimanual vitreous surgery without endoillumination. Arch Ophthalmol. 2004;122:367-368.

Retinal Physician, Issue: May 2005

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