Minimally Invasive Vitrectomy Surgery Using Small-gauge Instrumentation

ALAN J. FRANKLIN, MD, PhD • GUARAV SHAH, MD • HARPREET WALIA, MD

The introduction of microincision sutureless vitrectomy systems and associated small-gauge instrumentation has revolutionized retinal surgery and led to better practice results across a range of vitreoretinal and macular disorders.

Advanced vitreoretinal instrumentation allows for the effective treatment of a variety of vitreous and retinal pathologies, with high-speed vitrectomy probes, forceps, scissors, endolaser probes, and new light sources facilitating safer surgeries. The higher cut rates that are now achievable also help to minimize vitreous turbulence and to reduce traction on the retinal surface.

Microincision technology and small-gauge transconjunctival vitreous surgery provide greater patient convenience and the prospect of faster recovery and visual rehabilitation.

Moreover, a full complement of vitreoretinal surgical instrumentation is available for the small-gauge platforms that have expanded the surgical indications of minimally invasive vitreoretinal surgery to more complicated vitreoretinal pathologies.

SHIFT IN SURGEON PRACTICE

Retina specialists have progressively shifted away from 20-gauge vitrectomy¹ toward the use of either 23- or 25-gauge vitrectomy in the majority of total vitrectomy surgeries.

Both the 23- and 25-gauge systems offer the advantages of excellent visual outcomes without compromising any of the intraoperative approaches required for various vitreoretinal pathologies during surgery.

Using these smaller-incision transconjunctival approaches, the average duration of surgery is shorter and less traumatic than 20-gauge surgery, leading to statistically significantly better and faster postoperative recovery, as well as increased patient comfort and satisfaction.

The results from the 2013 Preferences and Trends survey of the American Society of Retina Specialists showed that, in the United States and internationally, more than 90% of retina specialists most often utilize 23- or 25-gauge systems for vitrectomy surgery.

Approximately 40% of retina specialists in the United States most often use 25-gauge vitrectomy as their preferred gauge approach, while more than 10% of international specialists and 5% of US retina specialists said that they have tried 27-gauge vitrectomy (Figure 1, page 46).

Figure 1. Evaluation of global trends in usage of small-gauge vitrectomy surgery.

Furthermore, illumination systems allow for the use of a chandelier bimanual technique with fibers as narrow as 27-gauge, facilitating minimally invasive sutureless vitrectomy in a variety of different cases.

Compared with 25-gauge surgery, 23-gauge instruments are stiffer and larger, making surgical handling easier in more advanced cases. Suture closure is required in 1% to 20% of 25-gauge cases and 21% to 50% of 23-gauge cases, according to a large study of both US and international respondents.

Smaller and more precise wound construction promotes self-sealing and helps to prevent hypotony. Therefore, eyes may be less prone to vitreous prolapse and ensuing endophthalmitis, supporting current interest in 27-gauge pars plana vitrectomy for appropriately selected indications.

LANDMARK LAUNCH

Instrumentation companies continue to refine and improve the available microincision instrument range to further enhance ophthalmic surgery.

In 2010, Oshima et al demonstrated excellent surgical results in an experimental, interventional case series study evaluating the efficiency, safety, and feasibility of a 27-gauge instrument system for microincision vitrectomy in a number of vitreoretinal diseases.²

These cases included epiretinal membrane, idiopathic macular holes, diabetic vitreous hemorrhage, vitreous opacity with suspicion of intraocular lymphoma, focal diabetic traction retinal detachment, macular traction syndrome, and macular edema secondary to central retinal vein occlusion.

The instrument system included an infusion line, a high-speed vitreous cutter, an illumination system and a variety of vitreoretinal instruments, including membrane forceps and sharp-tipped endophotocoagulation probes.

The duty cycle of the 27-gauge cutter was found to be equal to or better than that of the 25-gauge cutter, while assessment of the fluid dynamics showed that vented gas-forced infusion could be set to range from 20 to 30 mm Hg to control intraocular pressure during 27-gauge vitrectomy.

In terms of surgical results, anatomic success was achieved in all 31 study eyes, and 20 eyes (65%) experienced visual improvement of 3 lines or more. All sclerotomies self-sealed without hypotony from day 1 postoperatively.

The investigators found that, while fluid dynamics and cutting efficiency are lower compared with 25-gauge surgery, the 27-gauge system is feasible and may reduce wound sealing-complications in selected cases.

Evolution of the System

According to Poiseuille’s law, flow rate is related to the radius to the fourth power; therefore, a significant reduction in the flow rate was anticipated with the reduction lumen diameter for 27-gauge instrumentation.

The initial infusion rate, measured in balanced salt solution, of 27-gauge instruments was 61% of the 25-gauge of the Alcon system (Fort Worth, TX) at the time, while the aspiration of 27-gauge was 81%, compared to 25-gauge instrumentation.

To address the observed reduction in aspiration and flow rates, several initial adjustments were made that included increased port size area, increased vitreous cutting rate (in cuts per minute), and higher duty cycle and aspiration to achieve improved fluidics that were more comparable to 25-gauge surgical parameters at that time.

Dutch Ophthalmic Research Center (DORC; Exeter, NH) was the first ophthalmic instrumentation company to introduce the Oshima/Tano one-step 27-gauge transconjunctival system in 2010. For sutureless minimally invasive vitreoretinal surgery, DORC designed a comprehensive range of 27-gauge instruments with rigid shafts that provide surgeons with added performance and functionality.

RANGE OF NEW INSTRUMENTATION EXPANDS

DORC offers a one-step MVR cannula system in 23-, 25-, and 27-gauge for lowered traumatic impact, incorporating a new MVR blade that requires more than 50% less insertion pressure than previous models and better wound architecture (Figure 2). The new removable closure valve provides enhanced visualization when inserting instruments.

Figure 2. Mean piercing forces (initial entry) of DORC’s new MVR one-step cannula compared with previous and competing models.

The DORC product range includes a 23-, 25- and 27-gauge twin duty cycle (TDC) cutter, representing a new generation of vitrectomy cutters for efficient and safe removal of vitreous, and it also provides constant aspiration flow independent from cutting speed at a duty cycle of 92%.

This modified cutter design incorporates a larger rectangular aperture in the inner tube of the cutter and a blade with two sharp cutting edges, increasing the amount of vitreous that is cut in a single motion.

Double cutting speed reduces traction on surrounding tissue and offers increased aspiration flow up to three times more than the normal rate. Reduced “surge” turbulence at the aspiration port results from constant opening of the aspiration port (Figure 3).

Figure 3. Key features of the DORC twin duty cycle 27-gauge vitrector.

A 27-gauge TDC cutter, part of the DORC portfolio, is available in two different speed formats, one with a maximum of 6,000 cpm and another with a maximum of 8,000 cpm, the TDC cutter design delivering effective cut rates of up to 12,000 cpm and 16,000 cpm, respectively. A double-action cutting speed reduces traction on surrounding tissue and provides a higher flow rate at faster cut rates than larger-gauge cutters.

The Alcon Constellation system has also refined many of these modifications to develop a 27-gauge surgical platform that can address a wide variety of surgical pathologies with characteristics that are favorable, compared to many of the earlier 25-gauge surgical technologies (Figure 4, page 48).

Figure 4. Comparison of vitrectomy handpiece size and design. The 27-gauge vitrectomy handpiece size is less than 50% of the 20-gauge handpiece. Port diameter of the 27-gauge is 60% of the 20-gauge probe to enhance fluidics of the smaller probe when combined with improved duty cycle and flow rates. The distance from the port to tip of the vitrectomy handpiece is smaller with 25- and 27-gauge instruments to permit more precise removal of preretinal tissue.

The highest initial 27-gauge cutting rate was 2,500 cpm. Currently, the 27+ Constellation vitrectomy probe operates at 7,500 cpm, to produce a duty cycle of 50%, which approximates that of current 25-gauge surgical technology.

In addition, the ability to increase the aspiration to 650 mm Hg does increase flow rate in balance saline solution, similar to what was initially reported for 25-gauge surgical systems.

IOP and Flow Rates

Intraocular pressure and aspiration flow rates are important considerations in vitreoretinal surgery, and intraoperative hypotony is associated with choroidal detachment and suprachoroidal hemorrhage.

Next-generation vitrectomy machines utilize built-in infusion compensation technology to counteract the higher infusion and aspiration pressures that are typically necessary using 23-, 25-, or 27-gauge probes to remove vitreous.

Aspiration flow rates with both the DORC 25-gauge and 27-gauge TDC cutter are maintained at constant rates without a decrease as probe cut rates are increased, measured in balanced salt solution at a vacuum level of 550 mm Hg (Figure 5).

Figure 5. Aspiration flow evaluations of the DORC twin duty cycle (TDC) 27-gauge vitrectome.

Clinically, the vitrectomy instrument is marginally slower for core vitreous removal, but it can facilely release adherent vitreomacular adhesions. Similar to the DORC platform, the faster cutting rate of the Alcon Constellation permits diminished vitreous traction, and there is an association of a reduced rate of peripheral retinal breaks with smaller sclerotomy size.

A broad selection of 27-gauge instruments is available from DORC, including reusable diathermy, long and short light pipes, scissors, reusable and disposable microforceps, backflush instruments, stepped laser probes with adaptors, two disposable high-flow, high-speed vitrectomy probes, and two disposable ultrahigh-speed TDC cutters. A 27-gauge viscous fluid injection cannula allows for efficient silicone oil injection through the 27-gauge cannula system.

Backflush instruments include a backflush instrument with a 27-gauge blunt needle and active aspiration, as well as a 27-gauge brush backflush needle designed with a silicone brush tip, with active aspiration for atraumatic “brushing” of the retinal surface and aspiration. There is also a selection of disposable and reusable 27-gauge microforceps.

Illumination

Available 27-gauge light fibers consist of a 27-gauge chandelier fiber with a guidance needle or to be inserted into additional 27-gauge cannulas and endoilluminators in the wide view (Totalview from DORC), standard focal view and shielded view styles. All incorporate a longer shaft and stable neck for added control and stability.

Modifications to the System

Another historic pitfall of small-incision surgery is instrument shaft flexibility that limits access to the anterior retina. The Constellation system has addressed this issue by both increasing the stiffness throughout the shaft and with a proximal sleeve that stabilizes the instrument at the trocar interface.

These modifications increase instrument stiffness to a range roughly between what was initially developed for 25-gauge Alcon surgical platform and the current Constellation 25+ technology (Figure 6).

Figure 6. Comparison of vitrectomy probe stiffness for Constellation platform. Alcon has used materials engineering to enhance vitrectomy probe staff stiffness and in addition to adding a 1 mm proximal stiffening sleeve achieves instrument stability closer to the current 25+ gauge technology than the initial Alcon 25-gauge technology. Similar shaft stabilities are observed with instrumentation of the postequatorial retina.

One potential advantage of 27-gauge technology is the improved precision of the smaller instruments. The instruments indeed allow for precise delamination of taut ERMs and internal limiting membrane.

Moreover, the smaller diameter allows for access of the vitrectomy cutter to tenacious preretinal fibrosis, associated with proliferative diabetic and vitreoretinopathy. In practice, this can simplify the approach to complex preretinal membrane removal and increased surgical efficiency.

The Constellation 27+ now also has a full complement of 27-gauge instruments that include forceps, laser, scissors, diathermy, and heavy liquid capabilities to allow a comprehensive and effective surgical platform to address a variety of surgical pathologies (Figure 7).

Figure 7. The Alcon 27-gauge Constellation surgical platform. Alcon has also achieved a robust 27-gauge surgical platform with a variety of vitrectomy instruments. These instruments include: a vitrectomy handpiece, valved trocars, a soft-tip aspiration probe, a light source, a backflush brush, forceps, scissors, laser, and diathermy.

ADDRESSING LIMITATIONS

In theory, smaller-gauge surgical instrumentation and high cutting rates should be safer because the combination increases fluidic stability and potentially minimizes vitreous turbulence by allowing only small pieces of vitreous to enter the port. Reduced traction should lower the chance of iatrogenic damage to the retinal surface and intraoperative retinal tears.

As incision size decreases, the issues of greater instrument flexion and diminished endoillumination arise. Although many of these issues have now been addressed, both the 25- and 27-gauge systems would still nonetheless benefit from stiffer instruments, better fluidics, and further enhanced illumination to broaden their potential applications.

Chandelier illumination assists in both improving illumination and permitting manipulation to the anterior retina by scleral indentation by either the surgeon or assistant.

Slightly more than half of retina specialists in the United States said in response to the ASRS 2013 Practices and Trends survey that they do not use a chandelier in vitrectomy cases, while 44% use a chandelier in 1% to 25% of vitrectomy cases.

The majority of 27-gauge vitrectomy cases are performed without the use of a chandelier, although some surgeons opt to use chandelier augmentation for enhanced visualization in certain situations.

A Learning Curve

Smaller instruments require surgical training due to reduced flow rate and aspiration rate, more flexibility, and less endoillumination. There is a learning curve involved for all surgeons when first using 27-gauge vitrectomy instrumentation; however, surgeons who already are comfortable with 25-gauge procedures generally have an easier transition.

In our surgical practices, we use 27-gauge instrumentation in approximately 10% to 15% of cases, and we believe that this usage will increase as the instrumentation range expands. The case mixes in particular centers determine the uptake and use of 27-gauge surgery. Depending on the surgical case population, some retinal centers use 27-gauge instrumentation in up to 50% of referred vitreoretinal cases.

Reduced flow and aspiration rates, in addition to the increased instrument flexibility and illumination challenges observed in 25-gauge and, to a greater extent, in 27-gauge procedures require surgical training to successfully convert to the smaller gauge platforms.

For retinal fellows in training, the focus should be on learning to remove vitreous tissue, which requires more time using narrower-gauge instruments. Our recommendations are to encourage fellows to first learn to use 27-gauge forceps in a 23-gauge surgical setting initially and to transition to 25-gauge surgery prior to moving directly to 27-gauge.

OUTCOMES DRIVING CHANGES

Surgeon interest in minimally invasive vitreoretinal surgery and newer small-gauge techniques is driven by the advantages of smaller self-sealing incisions and better wound construction, as well as faster recovery, to provide similar or better patient outcomes to those observed using larger gauge approaches.

Results from a small prospective, consecutive case series evaluating outcomes using 27-gauge instrumentation for primary PPV and using the Bright Star Xenon Illumination System (DORC) to treat rhegmatogenous retinal detachments showed that all of the retinas were attached, and all of the patients experienced improvement in VA.³

A retrospective study comparing clinical outcomes and complication rates between 27-gauge transconjunctival nonvitrectomizing vitreous surgery and 25-gauge transconjunctival sutureless vitrectomy surgery for idiopathic ERM removal found that 27-gauge nonvitrectomizing vitreous surgery was equally effective to vitrectomy in the treatment of ERM, with less progression of cataract.⁴

Our outcomes, both anatomical and functional, using 27-gauge pars plana vitrectomy instrumentation, have been excellent, but we have been careful in our initial case selection. We now have employed 27-gauge surgery to repair ERM, macular hole, some cases of vitreomacular traction, and PDR, with or without scleral buckle and heavy liquids. Even during the first few days following 27-gauge vitrectomy for macular pucker, patients have zero to minimal perception that they had undergone a procedure

LOOKING FORWARD

After careful case selection and navigating the learning curve of 27-gauge surgery, the benefits include enhanced wound sealing, cutting efficiency, reduced surgical trauma, and faster postoperative recovery, to achieve an overall improvement in surgical efficacy and efficiency even in challenging vitreoretinal disorders.

In addition, narrower-gauge instrumentation with higher achievable flow rates offers better options to surgeons looking for optimal fluidic stability during surgery. Many cases in tertiary retinal practices still require the instrumentation and benefits of the 23-gauge platform.

There is a role for all gauges, and all gauge options should be made available to patients. Some indications and pathologies are more applicable to 27-gauge surgery. However, we expect that 27-gauge surgery will, over time, provide similar performance features to 25-gauge instrumentation, with further innovations and advances in material design, handling properties, and lighting likely leading to increased migration toward and better outcomes with smaller-gauge vitrectomy.

While minimally invasive 27-gauge vitreoretinal surgery is here to stay, it’s not the size alone that matters, it’s the clinical outcomes achieved. RP

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