Controversies In Care

Microincisional Vitrectomy Surgery: Gauging the Best Approach

Edited By Michael Colucciello, MD

Robert Machemer, MD, revolutionized ophthalmic surgery and blazed a trail for the field of retinal surgical specialization in ophthalmology with the introduction of pars plana vitrectomy surgery in 1968. At that time, vitrectomy surgery was performed with one-port intravitreal access: a 3.5-mm pars plana incision (7-gauge!) port was made in the superotemporal quadrant to allow for intravitreal placement of the Vitrectomy Infusion Suction and Cutting (VISC) instrument, with a tip diameter of 2.5 mm. Machemer introduced a divided system, with a three-port intravitreal approach, in 1972. Eventually, a three-port 20-gauge (0.8 mm diameter) system was favored. A conjunctival peritomy was used for scleral access, and the ports were sutured closed at the conclusion of the procedure.

In the mid-2000s, transconjunctival microincisional vitrectomy began to be favored. In contrast to the 20-g ports, the smaller-gauge ports (23-g = 0.6 mm; 25-g = 0.5 mm; 27-g = 0.4 mm) do not require sutures when beveled incisions are used.

The advantages of sutureless, trans-conjunctival, microincisional surgery over what had been the standard for decades, 20-g surgery, include decreased operative times, less postoperative discomfort, quicker recovery, less astigmatism and improved fluid dynamics, especially with the introduction of the new valved trocars.

A feature of the smaller-gauge surgery vitrectomy instrument that adds considerably to the advantage over the 20-g surgery vitrector is the shorter distance from the port to the tip of the probe. This change enhances precision and makes the usage of microscissors less necessary.

Currently, the majority of retina surgeons use microincisional, trans-conjunctival surgery (23-, 25- and 27-g) for pars plana vitrectomy. Controversy now exists regarding the “best” gauge: Are the reduced flow rates in the smallest gauges a detriment? (Poiseuille's law states that the flow in a cylindrical pipe is proportional to the fourth power of the pipe's radius.) Is the increased flexibility of the 25- and 27-g instruments, compared to the 23-g instruments, a problem? Is the potential for reduced illumination in the smallest-gauge endoilluminators an issue? Do the smaller gauges have distinct advantages regarding the prevention of hypotony and endophthalmitis? How about other complications, such as retinal tears and detachment?

Dr. Andrew Moshfeghi (medical director of the Bascom Palmer Eye and assistant professor of ophthalmology at University of Miami Miller School of Medicine) and Dr. John Pollack (of Illinois Retina Associates in Chicago and assistant professor of ophthalmology at Rush University Medical Center) will discuss various aspects of microincisional vitrectomy in this month's Controversies in Care.

Small-gauge Vitrectomy Has Come a Long Way

Andrew A. Moshfeghi, MD

Since the introduction of transconjunctival sutureless vitrectomy, there has been an evolution of the available instrumentation, surgical platforms and cutting technology. These innovations and expanded choices have lowered the barriers to entry for use of transconjunctival, sutureless vitrectomy systems for most vitreoretinal surgeons. Initially, these systems were marketed as a way to perform vitrectomies more quickly, to avoid the placement of conjunctival and scleral sutures, and to speed the patient's surgical recovery.

Soon after their introduction, vitreoretinal surgeons gained steady experience with these platforms. While they did appreciate the quick recovery times patients experienced following transconjunctival, sutureless vitrectomy, they also lamented some of the shortcomings of the earliest versions of these systems. First and foremost was the fact that transconjunctival, sutureless vitrectomy often turned out to be just plain old sutured vitrectomy when incompetent scleral wounds frequently necessitated the placement of a transconjunctival or transscleral suture closure. When this level of vigilance with wound closure was not exercised, unanticipated cases of postoperative hypotony, choroidal effusions and/or endophthalmitis were observed. Unfortunately, poor scleral wound competence was encountered even when the surgeon utilized the recommended beveled-incisional approach with good conjunctival placement and/or massaging of the wound at the conclusion of the case.

In addition to hypotony by palpation, the presence of a conjunctival filtering bleb (aqueous or air) typically indicated to the surgeon at the end of the case that wound integrity was not optimal. Sometimes the poor wound integrity was observed at the conclusion of the case and then handled with appropriate suture closure; however, in other instances, the shortcomings were not observed until later the next day or in the first postoperative week.

In addition to questionable wound integrity, surgeons were also faced with issues with reduced flow rates due to lower internal vitrectomy probe diameters. The reduced flow rates compared with 20-g vitrectomy platforms were most noticeable with the 25-g systems, but they were noticeably reduced with 23-g systems as well. So while surgeons may have been saving time by not having to place sutures, they noticed that a core vitrectomy took longer on average with the microincisional systems than it had taken them with the 20-g platform.

Of course, this slower vitreous-removal problem became even more aggravating if the surgeon had to end up throwing a stitch or two through chemotic conjunctiva at the conclusion of the case. To add insult to injury in these worst-case scenarios, not only did the case take longer and not only did the surgeon have to use unanticipated sutures to close the wounds, but it was also more expensive to do this because of the premium placed on the transconjunctival, sutureless vitrectomy packs, as compared to the standard surgical packs. Along the same lines, induction of a posterior hyaloidal separation was more of a challenge with early 25-g, and less so with 23-g, platforms.

Another drawback of the early transconjunctival, sutureless vitrectomy systems was the fact that these more slender instruments were much more flexible and prone to bending or breaking compared with the conventional instrumentation. This was most noticeable with cases requiring anterior manipulation (eg, proliferative vitreo-retinopathy cases or cases involving lenticular manipulation).

Surgeon's view of typical vitrectomy incision sites, right eye (arrows).

With these shortcomings and my early experience in mind, I initially reserved transconjunctival sutureless vitrectomy instrumentation only for routine macular cases, such as epiretinal membrane and repair of macular hole. Personally, I found the early 25-g systems to be useful in providing reliable wound closure in an air- or gas-filled eye with quick patient recovery. Although I became accustomed to the control provided by trocar-cannula based vitrectomy systems, I did not find their use to be uniformly applicable in all cases due to the above shortcomings. I especially found myself needing to close 23-g wounds most of the time in most cases with the earliest versions of this technology.

Because I liked the control afforded by trocar/cannula-based vitrectomy so much, when doing 23-g cases I would purposefully open the conjunctiva at the outset of the case to make the planned wound closure easier at the conclusion of the case. Because I knew I would be closing the sclerotomies at the end of the case, I did not feel a need to bevel these incisions.

THINGS HAVE CHANGED

Fortunately, most of the problems described above have been solved by the newest generation of microincisional 25-g and 23-g vitrectomy systems. I have not had any experience with the DORC 27-g system to provide insight on it. At present, I utilize the Alcon Constellation Vision System, with a mixture of 25+ and 23-g instrumentation. I still use 25+ for macular cases and cases that do not require extensive anterior manipulation.

Although the stiffness of the instruments is significantly improved over that of the previous generation, excessive torque on the instrumentation can still result in noticeable bending of the instruments. Rarely do I find the need to close the conjunctiva with sutures with the 25+ platform, utilizing a beveled-incisional approach, displacement of the conjunctiva, and cotton swab tamponade of the sclerotomy sites at the conclusion of the case. One exception to the avoidance of suture closure might be an eye with immobile conjunctiva due to conjunctival scarring from multiple previous surgeries or other etiologies.

For cases requiring anterior manipulation, I implement 23-g vitrectomy instrumentation. I generally do not have issues with instrument bending, and I still have excellent cannula-based control. I may have to remove one of the cannulas to carry out lensectomy with the fragmatome handpiece or to introduce larger-bore instrumentation (ie, a lens hook).

Although 20/23-g vitrectomy is still necessary for these few instances, fortunately, novel viscous fluid injection/removal cannulas have been introduced that obviate the need for removal of the cannula when using silicone oil.

Other helpful microincisional vitrectomy instrument innovations include the introduction of valved cannulas that prevent aqueous reflux through an empty cannula. One has to be aware when using valved cannulas, however, to be careful when using instruments such as the soft-tipped extrusion cannula or the Tano diamond dusted membrane scraper from catching on the edges of the valves. In some instances, it can be difficult even to get these instruments into the eye as a result of the valves. That said, the valved cannulas are great in a vitrectomized eye to prevent copious saline reflux through the cannulas.

There are no cases for which I still use conventional 20-g vitrectomy instrumentation. The control afforded by the trocar/cannula systems with 23-gauge and 25-gauge vitrectomy instrumentation. Optimizing fluidics and improving instrument stiffness will be even more important as this trend continues.

Which Vitrectomy System is “Best”? 23-g, 25-g or 27-g?

John S. Pollack, MD

I believe that the ideal sutureless vitrectomy system is one that provides us with all the instrument stiffness we need to achieve our surgical goals safely and efficiently through reliably leak-free, pressure-resistant wounds. Based on my experience thus far, 23-g vitrectomy systems deliver the optimal combination of these features.

With the majority of vitrectomy systems in use today supporting a wide range of cut rates and variable duty cycles, excellent, finely tunable flow characteristics are readily available for both 23- and 25-g cutters. Consequently, I don't believe that flow and tissue control are major distinguishing features between these two gauges. On the other hand, flow limitations will be far more noticeable with 27-g vitrectomy due to the 20% reduction of the internal diameter.

When it comes to illumination, we now have the capacity to drive so much light through small fibers that both 23- and 25-g light pipes and chandeliers can deliver adequate illumination for all surgeries. Results are as yet inconclusive with 27-g illumination. It also appears that the risks of endophthalmitis and hypotony-related complications are equally low with both 23- and 25-g systems when angled-trocar insertion techniques are employed,^1-3 and although we have no large studies looking at endophthalmitis risk after 27-g surgery, I suspect this will be acceptably low as well.

Retinal detachment risk has also been found to be similarly low in 25-, 23- and 20-g surgery.⁴ So is there any clinically significant difference between our small-gauge options? My answer would be an emphatic yes. The big distinguishing feature is superior 23-g instrument stiffness, which I believe translates to superior control, efficiency and safety, at least in my hands.

23-G DELIVERS GREATER CONTROL AND EFFICIENCY

Just as “beauty” is in the eye of the beholder, I believe that the “best-gauge vitrectomy system” is in the eye (or hands) of the surgeon. In my hands, the greater control afforded by the stiffer 23-g instruments translates into safer and more efficient vitrectomy surgery, making it preferable to 25-g vitrectomy. The significantly greater flexibility and fragility of 27-g vitrectomy instruments makes them even less appealing for me than 25-g.

I find that stiffer 23-g instruments provide firm and reliable control of the eye and, more importantly, excellent control of the instrument tips themselves. These features represent a marked benefit over 25-g instruments, even those employing stiffeners around the base of instrument shafts in an attempt to mitigate their greater flexibility.

Importantly, 23-g instruments greatly facilitate my ability to rotate the eye far enough so that I can easily inspect and treat the retinal periphery out to the ora serrata. This becomes particularly valuable when performing 360° anterior panretinal photocoagulation and dissecting anterior proliferative membranes.

A typical case in which I find the added stiffness of 23-g instruments particularly important is during vitrectomy repair of a retinal detachment. For these cases, I use a 25-g chandelier light source and sclerally depress with one hand while shaving back the vitreous base and lasering the anterior periphery with the other. In these cases I am particularly grateful for the superior stiffness and control provided by 23-g instruments, as well as their ability to counteract readily the various vector forces resulting from scleral depression.

Conversely, these maneuvers can be quite challenging with 25-g instruments. Although pivoting 25-g instruments around the cannulas can help reduce instrument flexion, I do not find this technique useful when working anteriorly with scleral depression, particularly in patients with a moderately large nose or with relatively deep orbits.

In summary, my ideal sutureless vitrectomy system is one that provides me with all the instrument functionality I need to achieve my surgical goals safely and efficiently. In my experience, 23-g vitrectomy systems allow me to do that best. RP

REFERENCES

1. Wu L, Berrocal MH, Arévalo JF, et al. Endophthalmitis after pars plana vitrectomy: Results of the Pan American Collaborative Retina Study Group. Retina. 2011 Mar 9. [e-pub ahead of print]
2. Oshima Y, Kadonosono K, Yamaji H, et al.; Japan Microincision Vitrectomy Surgery Study Group. Multicenter survey with a systematic overview of acute-onset endophthalmitis after transconjunctival microincision vitrectomy surgery. Am J Ophthalmol. 2010;150:716-725.
3. Pollack JS. Standardized cannula insertion and removal technique minimizes sclerotomy leaks and postoperative hypotony after 23G vitrectomy. Paper presented at: Annual Meeting of the American Society of Retina Specialists; Vancouver, BC; August 30, 2010.
4. Rizzo S, Belting C, Genovesi-Ebert F, di Bartolo E. Incidence of retinal detachment after small-incision, sutureless pars plana vitrectomy compared with conventional 20-gauge vitrectomy in macular hole and epiretinal membrane surgery. Retina. 2010;30:1065-1071.