Advances in cutter technology

jose 13 September, 2018 1459 No Comments

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Since the 1970s, new approaches to vitreous removal have been focused on increasing cut speed, maximizing cutting port surface, and enlarging the diameter of the probe’s inner lumen. However, the cost will be a consideration in new technology development.

The following characteristics have been essential targets in the development and improvement of new cutter devices:

Cutter size

One of the major advances in retinal surgery is the reduced size of cutters. The transition from conventional 20-gauge to the micro-incision vitrectomy system (MIVS) using 25- or23-gauge vitrectomy due to smaller size appears to provide better patient comfort , less conjunctival scarring, less postoperative inflammation, reduced operating times and earlier visual recovery. More recently, 27-gauge instruments have shown encouraging results.1The thinner instrument can be safely introduced into smaller spaces between membranes and retina, serving as a multifunctional device and facilitating tissue dissection.1Furthermore, vitrectomy instruments with smaller gauge are better suited to the narrower spaces of pediatric eyes.2

On the other hand, aspiration rate produced by smaller-gauge vitreous cutters is proportionally decreased due to a reduced port size and smaller diameter and needs higher infusion and aspiration pressures to remove vitreous. Although increasing the port diameter of a vitreous cutter would increase the flow, the system reduces its effectiveness as the port becomes larger.3

Although it is feasible to create even smaller instrumentation, the clinical outcomes and applicability may not necessarily warrant it. Rigidity and limited illumination are among the major limitations of sub-27-gauge instruments.4Despite the advantages, these small-gauge instruments may also have some disadvantages, such as the increased flexibility, fragility, small vitrector port size, and an initial learning curve in wound construction.5

Cutter speed

The underlying premise for the ultra-high-speed cutters is that increasing the cut rate reduces the size of the vitreous pieces; and despite the dramatically reduced diameter of the vitreous cutters, the resulting less viscous gel is more easily aspirated and removed.6 Faster cutting speeds are generally associated with increased vitreous removal and, therefore, surgery efficiency and shorter procedure time.1

Efforts also have been made to improve the duty cycle (DC) –the percentage of time the cutter port is open relative to the complete cutting cycle –7of vitreous cutters, particularly at higher cut rates. The smaller vitreous pieces obtained with higher cut rates are more easily aspirated through the probe; hence, the relationship between cut rate, duty cycle, and flow rate becomes more dynamic.8

Duty cycle is highly variable from one vitreous cutter to another, but there is an inverse correlation between cut rate and duty cycle in that the higher the cut rate the lower is the duty cycle.9

At high-speed velocity, most conventional cutters decrease their DC, or percent of port open time, throughout the cut cycle; and consequently, there is an expected decrease in the water and vitreous flow rates and a corresponding increase in the surgical time required. Most vitrectomy machines allow controlling the aspiration and cut rates, but not the DC.6

Vitrectomy system with dual pneumatic cutters makes DC control available, allowing three duty-cycle options: the cutter can be biased-open for maximum efficiency during core vitrectomy, neutral (50 percent open/50 percent closed) or biased-closed for maximum safety when working close to the retina.10 This technology is included in the portable Synergetics Versavit vitrectomy system (Bausch and Lomb) that provides a linear high-tech control of cut rate to a maximun of 6,000 cuts per minute (cpm), and with an excellent design to remove the vitreous and membranes near the surface of the retina, in both simple and complex cases.11The cut rate is adjustable in 500 cpm increments from 2,500–6,000 cpm. Below 2,500 cpm, adjustments to maximum cut rates can be made in increments of 200–600 cpm.10With the introduction of this new variable, different DC settings may be used, affecting the surgical technique and the flow behavior during surgery.6,8

While the flow rates of current-generation cutters decrease with increasing speeds, the new-generation cutters maintain their high flow rates as the speed increases. With the new cutters during core vitrectomy, the surgeon will now have the ability to run at higher cut rates, taking smaller ‘bites’ out of the vitreous while maintaining high flow rate.7

A substantial increase in cutting speeds has been observed since current vitreous cutters are capable of delivering cut rates of up to 16000cuts per minute(cpm), depending on the vitrectomy platform.1

Faster cut rates appear to apply less mechanical stress on the vitreous base, thus reducing the risk of iatrogenic tears.12This feature is particularly beneficial during delicate procedures, such as traction retinal attachment in an eye with diabetic retinopathy, increasing vitreous removal and surgery efficiency, while reducing procedure time. Laboratory studies have demonstrated that use of higher cutting speed results in less vitreous turbulence.12

Port geometry and blade design

The blade design and port geometry of the vitreous cutter may have an enormous influence on vitrectomy surgery.1

The standard guillotine-shaped vitrectomy blade has been used for many years. However, its movement to cut the vitreous, with complete port closure, may result in flow instability, fluid acceleration, and retinal traction. New blades have been designed in order to increase the cut rate and overall surgery efficiency while maintaining a safe environment.1 The MID Labs Bi-Blade™ Vitrectomy Cutter has an additional cutting edge which allows cutting twice in a single motion (8000 cpm x 2) with no additional impact on retinal traction; and a continuously open port that enables high aspiration efficiency independent of the cut rate. This consistent aspiration flow rate and enhanced intraoperative fluidics stability, allow the surgeon to perform procedures using smaller gauge instruments while maintains the same flow rates that are seen with conventional cutters. These features lead to enhanced performance, improved surgical control, and an increased surgical efficiency.13

New technology

An alternative vitreous removal tool could be VitesseTM handpiece®, the first and only hypersonic device for vitreous removal, available exclusively with the new Stellaris Elite vision system.14 This device uses a novel, single-needle design and a continuously open-port system. A study carried out to compare this new technology developed by B&L to currently available pneumatic guillotine vitrectors (GVs) systems concluded that this might be a promising new alternative to the currently available guillotine-based technologies.15

The technological advances in surgical devices have allowed not only increased surgical efficiency but also broaden the repertoire of indications. Remarkable advances in this field through the last decade (and more particularly in the last few years) include the changes in the vitrectomy cutters, their fluidics interaction, the wide-angle viewing systems, and the evolution of endoillumination.Smaller cutter size and higher cut rates increase efficacy and safety of vitrectomy.

References:

  1. de Oliveira, P. R. C., Berger, A. R. & Chow, D. R. Vitreoretinal instruments: vitrectomy cutters, endoillumination and wide-angle viewing systems. Int. J. Retin. Vitr. 2, 28 (2016).
  2. Mohamed, S., Claes, C. & Tsang, C. W. Review of Small Gauge Vitrectomy: Progress and Innovations. J. Ophthalmol. 2017, 6285869 (2017).
  3. Pavlidis, M. Two-Dimensional Cutting (TDC) Vitrectome: In vitro flow assessment and prospective clinical study evaluating core vitrectomy efficiency versus standard vitrectome. J. Ophthalmol. 2016, (2016).
  4. By JAY B. STALLMAN, MD, FACS • DAVID S. CHIN YEE, MD • HARPREET S. WALIA, M. Is Smaller Than 27 Gauge Possible? Retinal Physician Available at: https://www.retinalphysician.com/issues/2017/may-2017/is-smaller-than-27-gauge-possible. (Accessed: 27th February 2018)
  5. Callou, T. P. et al. Advances in femtosecond laser technology and its applications. Clin. Ophthalmol. 20, 697–703 (1999).
  6. Diniz, B. et al. Analysis of a 23-gauge ultra high-speed cutter with duty cycle control. Retina 33, 933–8 (2013).
  7. Fang, S. Y., DeBoer, C. M. T. & Humayun, M. S. Performance analysis of new-generation vitreous cutters. Graefe’s Arch. Clin. Exp. Ophthalmol. 246, 61–67 (2008).
  8. Abulon, D. J. K. Vitreous flow rates through dual pneumatic cutters: Effects of duty cycle and cut rate. Clin. Ophthalmol. 9, 253–261 (2015).
  9. Hubschman, J. P. et al. Effect of cutting phases on flow rate in 20-, 23-, and 25-gauge vitreous cutters. Retina 29, 1289–1293 (2009).
  10. Gaurav K. Shah, MD, and V. Y. H. Vitrectomy Platforms Go To The Next Level – Retina-Specialist.com. Retina Specialist (2016). Available at: http://www.retina-specialist.com/article/noninfectious-uveitis-enriching-our-toolbox-1. (Accessed: 6th March 2018)
  11. Borne, M. J. & Kunimoto, D. Y. VersaVit 2.0 Vitrectomy System The first and only simplified, small-form vitrectomy system that provides creative solutions.
  12. STANISLAO RIZZO, MD, and TOMASO CAPOROSSI, M. High-Speed Vitrectomy in Practice. Retin. Surg. Glob. Perspect. (2014).
  13. News Release 1 — MID Labs – Vitreoretinal Ophthalmic Medical Devices. Available at: https://www.midlabs.com/news-release-1/. (Accessed: 10th April 2018)
  14. Vitesse handpiece. LONG TERM VISION | FOR YOUR PATIENTS | FOR YOUR PRACTICE 2017 Quarter 2 a (2017).
  15. Stanga, P. E., Pastor-Idoate, S., Zambrano, I., Carlin, P. & McLeod, D. Performance analysis of a new hypersonic vitrector system. PLoS One 12, e0178462 (2017).

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