Article

Ultra-High-Speed Vitrectomy Cutters: What’s the Limit?

The future of vitrectomy could be quick, safe, and office based.

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The first vitrectomy cutters, introduced in Japan and in the United States by Machemer in 1972 were large (17 gauge), reusable, multifunction instruments with cut rates of less than 300 cuts per minute (cpm).1 They were used primarily to cut the core vitreous, and membrane removal was either not performed or done with scissors. O’Malley then developed 20-gauge, 3-port vitrectomy, separating the vitrector from the infusion and illuminator. Nevertheless, these instruments were rudimentary, reusable, and had low cut rates. Complications associated with the low cut rates were common, including fluid instability causing traction on the retina from vitreous being inadequately cut by the vitrector, iatrogenic breaks from traction and from detached retina “jumping” toward the vitrectomy port, and dialyses. The maneuvers that could be performed with the vitrectomy cutter were rudimentary and limited mostly by the low cut rate and size of the probe, which was 19 gauge or 20 gauge for many decades.

Technological advances in the 1980s brought disposable probes with increasing cutting rates and linear proportional control of aspiration developed by Steve Charles, MD. This allowed for safer vitrectomies, because traction on the retina was reduced. Nonetheless, the cut rates at the time did not exceed 1,500 cpm in 20 gauge. In 1997, Alcon launched the Accurus, a fully integrated vitrectomy machine, and subsequently the dual-actuation springless Innovit cutter with cut rates of 2,500 cpm. The cut rates were limited particularly in pneumatic spring-return vitrectomy probes because the faster the cutting rate, the less time the probe’s aperture is open during a cutting cycle (duty cycle). Increases in cutting rates were accompanied by reductions in aspiration and flow rates, creating inefficient vitreous removal. This meant that although the vitrectomy probe could be brought closer to the vitreous base, retinal movement and traction were still common complications of vitrectomy, and most membrane peeling and removal was performed with ancillary instruments, namely scissors, bimanual techniques, tissue manipulators, and illuminated instruments. Vitreous base complications and tears were common, due to the excessive dragging and traction of vitreous.

MICROINCISIONAL VITRECTOMY

The most significant technologic advances for vitrectomy occurred after 2002 when microincisional vitrectomy (MIVS) and 25 gauge was introduced by Gene de Juan, MD.2 At its inception, MIVS was limited by the vitrectomy machine’s inability to provide efficient aspiration and cutting. The flow rate is reduced relative to the decreased inner lumen of the vitrectomy probe as per Poiseuille’s law:

(where FR is the flow rate, P is the pressure difference across the length of the probe needle, r is the inner radius of the vitrectomy probe, η is the viscosity, and L is the length of the probe needle).3 Dragging of vitreous was common, and thorough vitreous removal was difficult. Fortunately, manufacturers devised new vitrectomy machines with improved aspiration and flow rates, smaller gauge probes, and improved cutting speeds. This was achieved by extending the duty cycle, the time the probe is open during a given cutting cycle.

The first of these was Alcon’s Constellation, which appeared on the market in 2008 together with the Ultravit probe, which did not require spring mechanisms in the probe (Figure 1). It allowed for aspiration rates of up to 650 and cutting rates of 5,000 cpm. The probe design continued to improve to provide wider openings closer to the tips, as well as dual/pneumatic drive technology to keep the probe open for longer intervals between cuts (increased duty cycle) thus allowing for efficient flow and aspiration while minimizing traction on the retina from vitreous pull.4,5 In 2013, 27-gauge vitrectomy probes appeared and cutting speeds increased to 7,500 cpm.6 Probe improvements have continued as has MIVS technology. Now, 27-gauge vitrectors allow for aspiration rates of 650 and cutting rates of 10,000 cpm with beveled tips in the Alcon Constellation. The beveled tip technology allows for the probe to get closer to the retina and function as a pick, spatula, forceps, and scissors. It brings the opening of the vitrector 40% closer to the surface of the retina. Peak traction forces at 10,000 cpm are between 18% and 38% reduced at maximum aspiration, compared to the 7,500 cpm in the different gauges. The vitreous flow of the new 10,000 cpm beveled probes has also increased relative to the 7,500 cpm, ranging from 18% in 27 gauge to 42% in 23 gauge.7

Figure 1. Alcon Ultravit probe with dual-pneumatic drive technology.
IMAGE COURTESY ALCON.

TWO-DIMENSIONAL CUTTERS

In 2015, DORC launched its 2-dimensional cutter engineered by Mineki Hayafuji for the port to remain constantly open during the cutting cycles. In any given cycle, cutting occurs twice by a pneumatically driven dual blade guillotine. This double cutting per cycle results in cutting rates of 16,000 cpm with no closed interval, thus a 92% duty cycle open-port design with almost constant, uninterrupted flow.8 This technology allows for no change in aspiration flow irrespective of the cpm. The aspiration is the same at 2,000 cpm as at 16,000 cpm. This is accomplished by the design of a large rectangular aperture in the cutter and a blade with 2 sharp cutting edges, by which vitreous is constantly being aspirated. The blade cuts in both a forward and backward motion (Figure 2). This allows for efficient vitreous removal even with very small gauges. The dual-blade design has been incorporated into other commercially available surgical systems, including TDC probes by DORC Dutch Ophthalmic, OS4-continuos flow vitrectomy, Oertli Instruments, and the Greuder machines. Alcon will be releasing a new probe in 25 gauge and 27 gauge with the dual-blade technology coupled with the springless Ultravit probe that will allow 20,000 cpm and a duty cycle of more than 90%. This should make the speed of vitreous removal with 27 gauge comparable to the 25 gauge vitrectors now on the market.

Figure 2. DORC two-dimensional cutter. Two cutting areas result in a continuous open aspiration port, with constant aspiration independent of flow.
IMAGE COURTESY DORC.

ULTRASONIC VITRECTOMY

Ultrasound vitrectomy was introduced in 1975 but it did not become popular at that time.9 Ultrasound or hypersonic vitrectomy is dependent of ultrasonic power for vitreous flow but is not affected by gauge. Bausch + Lomb recently developed the Vitesse hypersonic vitrectomy system for its Stellaris Elite vitrectomy machine. It utilizes ultrasound power of 28.7 KHz and a stroke length of 0 µm to 60 µm for liquefaction of vitreous. It has a single 23 gauge, 33 mm stainless steel needle with a 255 µm opening port that is open 100% of the time and oscillates and liquefies tissue in a localized zone at the edge of the port with user-controlled amplitude (Figure 3). The port has a single lumen that removes the liquefied vitreous through a larger inner lumen. This mechanism results in reduced resistance from a larger inner radius, and no decline in flow rate with increased ultrasonic power.10 A study by Stanga et al showed noninferiority relative to guillotine cutters and a direct correlation of flow with increased aspiration levels and ultrasound power.11 Also available are single blade cutters with speeds of 7,500 cpm as well as dual-blade cutters in 25 gauge and 27 gauge with effective cut rates of 15,000 cpm.

Figure 3. Vitesse hypersonic vitrectomy.
IMAGE COURTESY BAUSCH + LOMB.

The optimized technology in the vitreous cutters, in particular the reduced traction seen with 10,000 cpm to 16,000 cpm has revolutionized the way pars plana vitrectomy is performed. Maneuvers that were unthinkable in the past are now possible. These include shaving the vitreous and membranes from the surface of the retina, including detached retina, accessing tight tissue planes with the vitrectomy probe, peeling and cutting membranes, performing retinectomies, and peeling epiretinal membranes and the internal limiting membrane with the vitrectomy probe. The probe advancements have allowed for most vitrectomy cases to be performed solely with the vitrectomy probe without the need of ancillary instrumentation.12 The advantages of this are immense, not only are surgeries faster and more streamlined but complications are reduced, in particular iatrogenic breaks from vitreous base traction and multiple instrument exchanges.

WHAT’S THE LIMIT?

Augmenting the cutting rate may likely reach some plateau unless technology improves to optimize flow (because of Poiseuille’s law).13 Many possibilities exist: larger inner lumens from different metal alloys, different vitrectomy cutter designs, and better fluidics in new machines. The global vitreoretinal technology market is more than $2 billion, and constant, fast-paced innovation has been the norm since the introduction of MIVS, so we can expect many positive surprises.

When 25 gauge vitrectomy was introduced, there was great skepticism as to its benefit and longevity. The concept seemed ideal but the technology of both the first vitrectors and vitrectomy machines were suboptimal for the smaller gauges. Amid debate in a roundtable discussion at the REACT meeting in Costa Rica in 2004, the late Prof. Yasuo Tano stated that MIVS was the future, and that ideas come first and then technology improves to catch up. As he predicted, industry rose to the occasion and developed vitrectomy machines with increased duty cycles, higher speed cutting, and improved flow rates. Aspiration became available, as did vitrectomy probes with larger apertures, increased inner lumens, and superb performance even in 27 gauge. Technology will continue to improve and 27 gauge will possibly become the standard in the near future. As for the more distant future, many questions remain. Will higher cut rates be beneficial or will the benefits plateau? Will ultrasonic technologies prove to be advantageous and safe? Will it be possible to remove vitreous in a more expedient manner with minimal invasion through even smaller gauges than 27 gauge? All of these are unknowns, but we can envision an ideal future in which one can remove the vitreous in a quick, safe, maybe office-based setting and thus prevent the complications of many pathologies before they can begin to affect vision. RP

REFERENCES

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