Article

Is Smaller Than 27 Gauge Possible?

Exploring possible added benefit to ultramicroincisional surgery.

Vitreoretinal surgeons continually strive to integrate technological advancements into their practice. The introduction and improvements in microincisional small-gauge instrumentation have revolutionized vitreoretinal surgery. Since its introduction, retinal surgeons have progressively shifted toward microincisional, transconjunctival small-gauge technology.1,2 Small-gauge surgery allows effective treatment for a variety of vitreal, retinal, and macular pathologies while lending itself to improved patient comfort and faster symptomatic and visual rehabilitation.

Dutch Ophthalmic and Alcon provide commercially available full complements of small-gauge instrumentation, including high-speed vitrectomy probes, forceps, scissors, endolaser probes, and new light sources, whose usage has expanded to include complicated vitreoretinal pathology (Figure 1). Bausch + Lomb and Synergetics have 27-gauge instrumentation pending. As such, a looming question on the horizon is whether smaller than 27 gauge is possible. In this article, we explore this issue and provide our conjectures to this theoretical question.

Figure 1. Alcon’s 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, soft-tip aspiration probe, light source, backflush brush, forceps, scissors, laser, and diathermy.

THE ROAD TO SMALL-GAUGE SURGERY

In 2002, 25-gauge vitrectomy was introduced by Fujii et al.3 The transition from 20 gauge to 25 gauge represented a substantial savings of time by almost eliminating the need to construct incisional wounds and by greatly reducing the need to suture them. 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 while maintaining successful outcomes.3,4

Excessive flexibility and the flow limitations of early iterations of 25-gauge instruments were problematic. Eckhart et al developed a 23-gauge platform that permitted greater instrument stability and more expedient core vitreous removal.5 The introduction of 25+-gauge instrumentation further improved rigidity.

Drs. Stallman, Chin Yee, and Walia are from Georgia Retina, PC, in Atlanta, Georgia. The authors report no disclosures related to this article. Dr. Walia can be reached at paul.s.walia@gmail.com.

In 2010, Oshima et al introduced 27-gauge vitrectomy with an incision size of 0.40 mm to facilitate improved wound construction and self-sealing and prevent leaking and potential hypotony, vitreous prolapse, and endophthalmitis.6 This system also enabled one-step trocar insertion that provided additional benefit for cases with thin scleras, specifically young and myopic patients.

The 25+ gauge and 27-gauge instruments have improved stiffness and provide improved access to small spaces to facilitate dissection and allow work close to the retinal surface (Figures 2 and 3). These factors highlight the notion that smaller is better and lead one to wonder not only whether it is possible but whether there is added benefit to ultramicroincisional surgery.

Figure 2. Comparison of vitrectomy probe stiffness for the 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.

Figure 3. Comparison of vitrectomy handpiece size and design. The 27-gauge vitrectomy handpiece is less than 50% the size of the 20-gauge handpiece. Port diameter of the 27-gauge is 60% that of the 20-gauge probe to enhance fluidics of the smaller probe when combined with improved duty cycle and flow rates. The distance from port to tip of the vitrectomy handpiece is smaller with 25- and 27-gauge instruments to permit more precise removal of preretinal tissue.10

IS SMALLER THAN 27 GAUGE POSSIBLE?

The question posed is essentially whether further size reductions would be advantageous. While 23-, 25+-, and 27-gauge instruments are here to stay, the need for further miniaturization of sub-27 gauge is debatable. Size matters, but have we reached a point of diminishing returns? The engineering feasibility to create even smaller instrumentation certainly may be possible; however, the clinical outcomes and applicability may not necessarily warrant it.

One significant advantage to small-gauge instruments is that the distance from the port to the tip of the vitrectomy handpiece is less. This permits more usage as a dissection instrument and more precise removal of preretinal tissue and membranes. Numerous techniques have been reported with use of the 27-gauge cutter to grasp and peel the internal limiting membrane. Theoretically, sub-27-gauge cutters may obviate the usage of picks, scissors, and even forceps.

However, numerous obstacles seem apparent. An obvious initial obstacle is that of flow rate through sub-27-gauge instruments. In vitreoretinal surgery, Poiseuille’s law always prevails (Figure 4). This delineates that the flow rate is related to the radius to the fourth power of the lumen radius. A substantial reduction in the flow rate through sub-27-gauge instruments would undoubtedly be a hindrance. However, innovation in vitrectomy cutters and infusion compensation technology with new-generation vitrectomy machines may potentially mitigate this pitfall, as has been shown in the past with the transition to 27-gauge surgery.

Figure 4. Poiseuille’s law.

Regarding cutters, a twin-duty cycle (TDC) cutter, available in the DORC product line in 23, 25, and 27 gauge, represents a new generation of vitrectomy cutters for efficient and safe removal of vitreous and also provides constant 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, with faster cut rates than larger-gauge cutters. Reduced “surge” turbulence at the aspiration port results from constant opening of the aspiration port (Figure 5). In 27 gauge, two TDC speed options are available, one with a maximum of 6,000 cuts per minute (CPM) and another with a maximum 8,000 CPM. This TDC cutter design delivers an effective cut rate of up to 12,000 CPM or 16,000 CPM, respectively.

Figure 5. Key features of the DORC twin-duty cycle 27-gauge vitrector.

Intraocular pressure and aspiration flow rates are important considerations in vitreoretinal surgery, as intraoperative hypotony can result in undesired choroidal detachment and disastrous suprachoroidal hemorrhage. Newer-generation vitrectomy machines utilize built-in infusion compensation technology to allow a temporary increase in infusion to prevent hypotony, while at the same time avoiding the need for continuously elevated IOP. This counteracts higher infusion and aspiration pressures that are typically necessary using larger-gauge cutters to remove vitreous. Aspiration flow rates with both the DORC 25-gauge and 27-gauge TDC cutters are maintained constant without a decrease as probe cut rates are increased, measured in balanced salt solution (BSS) at a vacuum level of 550 mmHg (Figure 5).

Other limitations to sub-27-gauge instruments would be rigidity and limitation in illumination. Historically, the smaller-gauge instruments have increased shaft flexibility that limits access to the anterior retina. Noncontact wide-angle viewing systems have far less reliance on maintaining an axial position throughout surgery, and access to the anterior and peripheral retina is facilitated by rotating the eye using pressure on the instrument shafts.

The Alcon Constellation system has improved this by increasing the stiffness throughout the shaft and using a proximal sleeve that stabilizes the instrument at the trocar interface (Figure 2). Shortening of shaft lengths has also been implemented to increase rigidity, but places limitations in range and reach to the posterior pole, limiting their use for cases requiring limited vitreous dissection. In regard to illumination concerns, the advent of high-intensity LED illumination, as provided with the DORC EVA system, compensates for reduced transmission through smaller probes and is safe without ultraviolet and infrared toxicity, which may enable enough illumination in a sub-27-gauge system. Additional illumination can also be compensated for by implementing chandelier illumination, which can potentially overcome limited light transmission through a sub-27-gauge setting.

OTHER CONSIDERATIONS

Another overall challenge is the economics of implementing another surgical platform. Most retina surgeons currently already use a small-gauge platform. Surgeons in an ambulatory surgery center would be faced with the financial burden of incorporating this new technology. In the setting of a surgery center, the economics favors reusable instruments. Sub-27-gauge instruments would be exquisitely delicate and, even with the most conscientious staff and autoclaving process, very susceptible to breakage. Thus, the complement of instruments would almost certainly be disposables. The fixed and variable costs associated with incorporating sub-27 technology would unquestionably pose a financial burden. In the current practice environment, surgeons are becoming progressively less able to invest in newer technology that does not carry a distinct, proven benefit.

INTEGRATED USE

If sub-27-gauge instrumentation is on the horizon, will it need complementary pieces to be successfully incorporated into clinical use? In addition to simply size, will smaller instruments be able to incorporate newer technologies? Several other technological advancements in vitrectomy instruments have been reported, and the possibility of incorporating these in a sub-27 gauge could be promising.

Bausch + Lomb is awaiting the release of the new “hydrotome,” an instrument that utilizes hypersonic liquefaction in lieu of the conventional guillotine cutter through a single needle on a continuously open port. The needle is mounted on a piezoelectric transducer element that vibrates harmonically to create a cut rate of approximately 1.7 million cuts per minute.7

The University of Leuven in Belgium recently announced a robotic system to utilize an ultrathin 30 µ custom microneedle to cannulate retinal veins.8 Precision-geared, antitremor robotic-assisted surgery may also couple with sub-27-gauge instrumentation. Incorporating such technology may be difficult, as seen with the difficulty of transitioning fragmatome technology from 20 gauge to smaller gauges, but it could be an avenue to further any sub-27-gauge instruments.

Additionally, other vitreoretinal surgery explorations may be furthered by incorporating sub-27-gauge instrumentation. For instance, suprachoroidal surgery and suprachoridal drug delivery may be enhanced with the use of sub-27-gauge probes. There may be a trend in the future toward office-based vitrectomy and compact systems geared toward portability that may facilitate sub-27-gauge instrumentation. Several prototypes are in design and usage, including the SurgiCube system, which enable office-based sterile work environments.9 In an office-based setting, sub-27-gauge instrumentations may assist with any transition to office-based vitrectomy for minimally complex pathologies.

CONCLUSION

Vitrectomy surgery has benefitted from numerous improvements since its introduction. Size matters, and small-gauge surgery has been one of the most revolutionary advancements our field has undergone. After an initial learning curve, surgeons have become comfortable employing 25- and 27-gauge instrumentation for routine use.

Is it possible to go smaller, or have we hit a wall of diminishing returns? Our practice routinely uses 25-gauge instrumentation in our ambulatory surgery center. We feel that with TDC cutter technology, 25-gauge instrumentation provides exceptional surgical efficiency and superior outcomes by balancing flow, rigidity, and incision size. We are presently reluctant to conclude that sub-27 gauge will provide additional benefit, and it may not represent a continued advancement in vitreoretinal surgery. RP

REFERENCES

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  2. American Society of Retina Specialists Preference and Trends (PAT) Survey 2013. Available at: http://www.asrs.org/asrs-community/pat-survey .
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