Endoillumination growth amplifies tissue visualization
Endoillumination for vitreoretinal surgery continues to improve with the introduction of brighter, safer light sources with color filters that may allow opportunities for better tissue visualization.
Endoillumination for vitreoretinal surgery continues to improve with the introduction of brighter, safer light sources with color filters that may allow opportunities for better tissue visualization.
David R. Chow, MD, provided an overview of advances in endoillumination beginning with the introduction of xenon light sources in 2004 to the present day.
Dr. Chow explained that compared with existing halogen and metal halide light sources that were the industry gold standards, the xenon light sources, made available in 2004, delivered an exponential increase in brightness. They provided adequate illumination for performing 25-gauge vitrectomy and had sufficient power to provide adequate viewing for lighted instrumentation and chandelier systems.
Dr. Chow is assistant professor of ophthalmology and vision sciences, University of Toronto, Canada.
He noted that the chandelier systems introduced with the new xenon light sources represented a real clinical advancement, offering benefits that are two-fold. They maximized the working distance and the theoretic safety time for surgery. In addition, chandeliers allowed true bimanual surgery that affords surgeon independence and completion of complex maneuvers.
“I love not having to depend on anybody for assistance when trimming the vitreous base or performing complex diabetic dissections,” Dr. Chow said.
Filter evolution
Filter evolution
Introduction of filters has been another step in the endoillumination evolution and is an innovation that has brought benefits for improving tissue visualization and safety. Dr. Chow first investigated the effects of various filters on safety, brightness, and tissue visualization in a study he performed in 2005 on the Synergetics Xenon light source.
One key finding from that research was that a yellow filter improves safety, allowing brighter light to be used while maintaining a good viewing environment. Dr. Chow also found that use of a green filter enhanced visualization of the internal limiting membrane, although it did not increase safety. Use of a light filter above 475 nm will reduce the production of cytotoxic compounds from indocyanine green dye.
Findings from another study done with 25 surgeons who tested the various light filters that were added to the Stellaris PC (Bausch + Lomb) also highlighted the value of filters. In that study, there was a strong signal that the surgeons preferred the green tint for macular surgery except for those surgeons who use Brilliant Blue dye where the amber filter was preferred.
The Amber filter was the most polarizing filter with surgeons disliking the view it provided in most situations despite the exponential increase in safety. The exceptions were with the air-fluid exchange, where it was felt to reduce glare and when performing macular surgery with Brilliant Blue dye.
The next advances in endoillumination occurred in 2010 with the introduction of new light sources, including a mercury vapor light source that conferred a further increase in safety.
“When compared with some existing light sources, assuming the same gauge and working distance, the mercury vapor light was associated with a further increase in the theoretic retinal threshold time,” said Dr. Chow.
Worries about phototoxicity
However, the question arises as to whether there is a need to worry about phototoxicity from the light source used in vitreous surgery. The answer is yes.
“In 2004, most surgeons had never had a case of phototoxicity, but then the situation changed.” Dr. Chow explained. “Beginning in 2006, the FDA was receiving reports of phototoxicity with a xenon light source using a 420-nm filter, and results of surveys of graduating retina fellows also show these cases are still occurring.
“However, the percentage of retina fellows who report seeing at least one case of phototoxicity declined from about 33% in 2011 to just 16% in the most recent survey,” Dr. Chow added.
The most recent developments in endoillumination relate to the introduction of LED light sources. The EVA (DORC) features the first titratable color LED light source, which can be adjusted along a fixed pathway in 20 steps to a progressively yellow hue. There is no change in brightness across the gradations, but the safety time increases with each step from 8 minutes to a maximum that exceeds 2 hours.
A new optimized LED light source soon to be released for the EVA also was tested, which provided about a 30% increase in brightness across the product range. The increased brightness is important for 27-gauge vitrectomy, where the new enhanced LED light source for the EVA can provide adequate illumination levels.
Dr. Chow also discussed the new digitally assisted vitrectomy platform Ngeniuty (Alcon Laboratories). He pointed out that the new platform has opened a new world of visualization opportunities.
“The one comment you keep hearing from surgeons using this system is that they don’t need as much light as they did before because the HDR camera allows them to turn down the light levels,” Dr. Chow said. “Most surgeons report they can use about one-third of the light they normally would, and that results in a five-fold increase in safety time.”
With its digital enhancement capability and enhanced stereo, the system also provides opportunities for better tissue visualization. “These need to be evaluated to understand what can be done with the various settings to enhance visualization in different scenarios,” he added.
David R. Chow, MD
This article was adapted from a presentation that Dr. Chow delivered at the 2017 World Reina Congress. Dr. Chow is a consultant to and receives lecture fees from Alcon Laboratories. He also receives lecture fees from DORC and receives royalties from Synergetics for patents he holds.
