Point

Are Sutures Necessary in

MIVS is Safe!

PRAVIN U. DUGEL, MD

Rarely does advancement in medicine come as a "eureka" moment. Usually, a new strategic approach is first evaluated on its potential rather than its initial outcomes. If the potential of a new approach is worthwhile, then the next step is to ask whether shortcomings can be rectified. Then, typically there is a phase of intense research to fine-tune the problematic steps of the procedure. This phase typically requires not only a significant amount of time, but a significant amount of faith. This is the most vulnerable stage in any medical technology development, as it is a time for rampant criticism. Those pioneers who continue to proceed despite these obstacles do so with the conviction that this new procedure will eventually benefit their patients.

In my career, the most relevant example of this type of progress is phacoemulsification surgery. Although in its infancy phacoemulsification was thought of as barbaric, some pioneers saw the potential of this procedure and directed their energy to solving some of the shortcomings. Soon thereafter, phacoemulsification was adopted as the standard of care over extracapsular cataract surgery. However, if the outcomes of phacoemulsification in its first year or so were judged against the outcomes of extracapsular cataract surgery, the former would likely be inferior to the latter. If that was the end of the story, no progress would have occurred. Similarly, when we judge the attributes of microincisional vitrectomy surgery, we must judge it in this same context. In its early years, many aspects of this new technology could be appropriately criticized: poor wound construction, lack of available instrumentation, flexibility of instrumentation, inferior fluidics, etc. However, the potential of providing care in a more comfortable manner, with better fluidics and faster recovery, encouraged clinicians and scientists to pursue this new surgical strategy.

Let us address the main concerns regarding microincisional vitrectomy surgery: endophthalmitis, instrument flexibility, and decreased flow. The most serious concern, of course, is endophthalmitis. The initial exuberance for microincisional vitrectomy surgery was tempered by a paper by Dr. Kunimoto and Dr. Kaiser¹ from the Wills Eye Institute that showed a 12-fold increase of endophthalmitis in patients underlying 25-gauge vitrectomy in contrast to patients undergoing the traditional 20-gauge vitrectomy. Although the alarmingly high rate of endophthalmitis has been often quoted, it has never been duplicated. This study does have several irregularities and shortcomings: the use of unbeveled incisions, the use of Kenalog injections, the routine use of gentamicin in the infusion fluid, the lowest rate of endophthalmitis ever reported in the 20-gauge vitrectomy group, etc. However, this was not the only study reporting a higher rate of endophthalmitis with microincisional vitrectomy surgery. A multicenter retrospective review by Ingrid Scott, MD, and associates also showed a higher rate of endophthalmitis.² These 2 reports appropriately caused significant concern.

Figure 1. (A-D) Insertion of 23-gauge trocars and microcannulas. The microcannulas are inserted through the conjunctiva into the eye by means of a trocar. Insertion is accomplished by first displacing the conjunctiva laterally by approximately 2 mm. An initial oblique, then a perpendicular tunnel is made parallel to the limbus through the conjunctiva and sclera, thus, creating a self-sealing wound.

The source of the increased endophthalmitis risk was quickly identified to be faulty wound construction. It was obvious that in the rapid adoption of microincisional vitrectomy surgery, the attention paid to proper wound construction was simply insufficient. As with most other scientific investigations, the problem was addressed and studied in the laboratory. Excellent wound-construction studies were conducted in the laboratories of Peter Kaiser, MD,³ Jay Stewart, MD,⁴ and Barry Kupperman, MD.⁵ All these studies were consistent in their findings. The key to preventing the influx of external bacteria is a beveled incision. Elegant India ink studies⁴ showed that bacteria can migrate into incisions that are not properly beveled. However, proper beveling of these incisions effectively prevents bacterial migration, as simulated by India ink. Additionally, conjunctival displacement and flattening of the sclera have also been shown to be important in proper wound construction.

In order to make the wound construction triad of conjunctival displacement, scleral flattening, and wound beveling automatic, various types of insertion plates have been designed. Subsequently, a large, single-center, retrospective study;⁶ and a multicenter prospective study⁷ have not shown an increased risk of endophthalmitis with microincisional vitrectomy surgery. It is important to state that studies concerning endophthalmitis are notoriously difficult to conduct. To compare a difference between 2 patient populations in an incident that occurs very rarely requires a large patient study. Unless and until such a study is done, it is admittedly not possible to make any definitive statements regarding risk of endophthalmitis. It is my impression that the risk of endophthalmitis was unacceptably high early in the introduction of microincisional vitrectomy surgery. However, due to significant advances made in the understanding of wound construction and subsequent awareness amongst surgeons, I believe that the risk of endophthalmitis in microincisional vitrectomy surgery, done properly, is acceptably low and likely no higher than with traditional 20-gauge vitrectomy surgery.

Why did surgeons continue to press on with refining microincisional vitrectomy surgery despite the probable increased risk of endophthalmitis early in its introduction? The answer is simple: Most surgeons felt that microincisional vitrectomy surgery had the potential to be better for their patients. Studies from the United States,⁸ Europe,⁹ Asia,¹⁰ and South America¹¹ confirm the advantages of microincisional vitrectomy surgery. The advantages include patient comfort, visual and functional recovery, and surgical efficiency. A prospective multicenter study⁷ showed that visual recovery occurred within 1 week with 23-gauge vitrectomy surgery. Other studies showed that patient comfort and satisfaction were significantly improved.

New vitrectomy systems have addressed the problems of flexibility and fluidics of small-gauge surgery. Newer instrument designs are 25% stiffer. Moreover, the port has been placed closer to the tip of the probe, allowing for the vitrectomy probe to be used safely for delicate work, close to the retinal surface. The vitrectomy probe, with port optimization, is now a multifunctional tool allowing for membrane dissection that would have previously often required scissors. The inner lumen area of the probe, particularly the 25-gauge probe, has also been increased, providing increased fluid flow.

Fluid flow was another concern with microincisional vitrectomy surgery. Steve Charles, MD, has advanced the concept of "port-based flow-limiting" vitrectomy. He suggests that flow limited by high cutting rate may be beneficial and indeed desirable in certain cases. For instance, removing vitreous from a detached retina would be dangerous in a high-flow situation. However, a fast cutting rate with port-based flow limiting would allow fluidics stability and minimal vitreous traction. Therefore, he has advocated the concept that increased flow is not necessarily desirable. In fact, decreased flow in certain situations may be the safest option. In this vein, I have suggested the term "effective-flow vitrectomy": the least amount of flow required to get the job done. I believe that effective-flow vitrectomy is the safest possible vitrectomy.

There are additional features in new vitrectomy systems that will enhance the benefits of microincisional vitrectomy: duty cycle control, aspiration flow limiting, and intraocular pressure control. Duty cycle is a new control parameter that will either increase or decrease flow without changing cut rate or vacuum. Duty cycle is defined as the percentage of time that the port remains open in a given cut cycle. New vitrectomy systems will function at a cut rate of 5000 cuts a minute or higher. Duty cycle control will allow the surgeon to operate at the highest possible cut rate while varying the flow rate. Aspiration flow limit is another mechanism to maintain fluidic stability when the viscosity of the dissected tissue changes. It is an advanced version of maintaining fluidic stability during what anterior segment surgeons term "occlusion break." The flow through the vitrectomy system is constant as long as the viscosity of the concerned fluid or tissue is constant. However, inside the eye, the viscosity may change between vitreous, saline, lens material, and fibrous tissue. If retained lens material, for instance, occludes the port, then the flow is zero. However, as soon as the lens material deforms and is aspirated into the port, a sudden surge of flow occurs. Aspiration flow control will stabilize the flow during this surge by varying the vacuum level to maintain constant flow rates. Another new factor in obtaining fluidic stability is intraocular pressure control. Thus far, intraocular pressure is controlled by the infusion pressure set at the console. During no-flow conditions, the intraocular pressure will equal the set infusion pressure. However, as soon as flow occurs, there is a pressure drop across the infusion cannula as determined by the hydraulic resistance of the cannula.

Intraocular pressure control is a method of maintaining the IOP during flow conditions by automatically increasing the infusion pressure to compensate for the pressure drop across the infusion cannula. Advanced vitrectomy systems measure the pressure drop across the infusion cannula during a calibration routine during system prime. A noninvasive flow meter monitors the infusion flow rate, calculates the pressure drop and adjusts the infusion pressure appropriately to maintain the set IOP.

The most important parameter for surgical safety inside the eye is cut rate. Advanced vitrectomy systems will have a cut rate of 5000 cuts a minute or faster. The faster the cut rate, the less the length of uncut vitreous aspirated into the port, the less the vitreous traction. Current spring-driven vitrectomy cutters are limited in the fastest cut rate by their very design. In order for a spring-driven cutter to work, a single pneumatic line will push air into a chamber and build enough pressure to push a diaphragm against a return spring, which will then close the vitrectomy port. The spring will then push the port open after the drive pulse is vented. However, this venting process is not instantaneous and requires a defined period of time. At ultrahigh cut rates, the venting time is simply insufficient and the port will remain closed longer than it remains open. In other words, with a spring-driver cutter, the duty cycle will decrease as the cut rate increases.

The inability of a spring return cutter system to control duty cycle can cause an reduction in flow. A revolutionary new cutter design is the dual pneumatic design. In this cutter design, there are 2 pneumatic lines: 1 dedicated to closing the port and 1 dedicated to opening the port. No springs are required; therefore, the duty cycle is controlled by adjusting the pneumatic drive pulses.

While many of the advancements mentioned above are also available in the 20-gauge system, the point is that microincisional vitrectomy surgery how has the ability to deliver all the flow advantages of the current 20-gauge system inside the eye while providing faster patient recovery, improved comfort, and increased surgical efficiency. I believe that the problems with instrument flexibility and intraocular fluidics have been overcome. The concerns regarding wound construction and subsequent endophthalmitis remain valid. Until a large perspective multicenter study is done, no definitive conclusion can be reached. However, it is my firm belief that our recent advances in wound-construction technology has made microincisional vitrectomy surgery at least as safe as a 20-gauge vitrectomy. As mentioned, recent studies are consistent with this observation.

I have known Dr. Arun Patel for over 2 decades. I know him to be one of the most gifted surgeons and one of the most intelligent physicians I have ever met. I respect his opinions and heed his concerns. There is no acceptable rate of increased endophthalmitis. There is no acceptable rate of increased blindness. However, good technology with the potential of benefitting patients must advance. Technology advances in steps and potential is only realized if dedicated physicians painstakingly address problems while keeping the goal of improved patient benefit in mind. Without such dedication and commitment, technology would never advance. Without such dedication and commitment, phacoemulsification would not currently be the standard of care. Indeed, even extracapsular cataract surgery would not have occurred. Consider the lost opportunity of providing better patient care.

While we should always question, we should never step backwards, but always continue to step forward. The ultimate litmus test in our field has always been, "Is this how you would treat your mother?" I can sincerely and without hesitation reply that, with what I know today, I would have no reservations regarding microincisional vitrectomy. RP

REFERENCES

1. Kunimoto DY, Kaiser RS; Wills Eye Retina Service. Incidence of endophthalmitis after 20- and 25-gauge vitrectomy. Ophthalmology. 2007;114:2133-2137.
2. Scott IU, Flynn HW Jr, Dev S, et al. Endophthalmitis after 25-gauge and 20-gauge pars plana vitrectomy: incidence and outcomes. Retina. 2008;28:138-142.
3. Singh RP, Bando H, Brasil OF, Williams DR, Kaiser PK. Evaluation of wound closure using different incision techniques with 23-gauge and 25-gauge microincision vitrectomy systems. Retina. 2008;28:242-248.
4. Singh A, Chen JA, Stewart JM. Ocular surface fluid contamination of suture-less 25-gauge vitrectomy incisions. Retina. 2008;28:553-557.
5. Hagemann LF, Marques LE, Kuppermann BD. Comparison of wound leakage between straight and tunnel scleral incisions after 25-gauge vitrectomy. Paper presented at: 44th Annual Meeting Association for Research in Vision and Ophthalmology; April 30-May 4, 2006; Fort Lauderdale, FL.
6. Mason JO 3rd, Yunker JJ, Vail RS, et al. Incidence of endophthalmitis following 20-gauge and 25-gauge vitrectomy. Retina. 2008 Jul 28. [Epub ahead of print].
7. Gupta OP, Weichel ED, Regillo CD, et al. Postoperative complications associated with 25-gauge pars plana vitrectomy. Ophthalmic Surg Lasers Imaging. 2007;38:270-275.
8. Tewari A, Shah GK, Fang A. Visual outcomes with 23-gauge transconjunctival sutureless vitrectomy. Retina. 2008;28:258-262.
9. Rizzo S, Belting C, Cresti F, Genovesi-Ebert F. Sutureless 25-gauge vitrectomy for idiopathic macular hole repair. Graefes Arch Clin Exp Ophthalmol. 2007;245:1437-1440.
10. Okamoto F, Okamoto C, Sakata N, et al. Changes in corneal topography after 25-gauge transconjunctival sutureless vitrectomy versus after 20-gauge standard vitrectomy. Ophthalmology. 2007;114:2138-2141.
11. Magalhães O Jr, Maia M, Maia A, et al. Fluid dynamics in three 25-gauge vitrectomy systems: principles for use in vitreoretinal surgery. Acta Ophthalmol. 2008;86:156-159.

Counterpoint

Minimally Invasive Surgery?

A Stitch in Time Saves Nine.

ARUN PATEL, MD

When 25- and subsequently 23-gauge instruments arrived, my partners and I converted from 20-g with enthusiasm. The truth is that I had fun doing these cases; easy-in and you get going right away, and easy-out once you're finished. Having done 7,000 cases without infection previously, I was dismayed when a routine diabetic membranectomy (my 210th sutureless small-gauge) patient developed endophthalmitis, and despite aggressive management, progressed to phthisis and NLP. I abandoned sutureless surgery. Within 6 months, despite using all current techniques such as carefully angled wound construction, conjunctival displacement, etc., 3 of my partners each had a case of endophthalmitis with sutureless small-gauge vitrectomy. We have all now either returned to 20-g surgery or are suturing our smaller incision wounds closed.

Small-gauge (especially 25-g) lacks the full spectrum of instruments that we sometimes need to use. Despite some case series' by very talented surgeons, the use of 25-/23-g instruments is limiting for most of us in more difficult cases where lensectomy and/or more extensive membranectomy, etc., is required. Commonly recognized complications that are increased with sutureless small-gauge surgery are endophthalmitis, wound leak, hypotony, and choroidals.

Sutureless eye surgery began with our cataract surgery colleagues and as retinal surgeons, we noted that we were being referred more endophthalmitis cases; these cases often had a delayed onset and we had to suture closed the leaking clear corneal incision in almost every case. Numerous lines of evidence including examination of Medicare data, other epidemiologic studies, controlled clinical trials, and large series convincingly demonstrate that clear corneal sutureless cataract surgery has a 2.5 to 3x increased risk of endophthalmitis.¹ The American Society of Cataract and Refractive Surgeons published a White Paper stating that "…the bulk of the recent literature suggests that post-cataract endophthalmitis is more likely with corneal incisions." Five case reports (12 eyes) of intraocular ointment following sutureless cataract surgery have been published. Experimental studies in the lab of Peter McDonnell, MD, explained a mechanism: the ingress of contaminated fluid in the tear film through the unsutured incision that can occur with ocular manipulation, low IOP, or even just when blinking.

Unfortunately, as retinal surgeons, our track record with sutureless vitrectomy is far worse. A meta-analysis of 5 large clinical series (35 523 eyes) with sutured 20-g vitrectomy has demonstrated the risk of endophthalmitis is approximately 1/3000. A similar analysis of 3 large series (4841 eyes from Wills,² BP/Hershey,³ and Wilmer) with sutureless 25-g cases resulted in an infection in 1/255 cases. This represents a 12x increased risk! A recent report from Japan shows no difference in endophthalmitis rates between 20-g and 25-g surgery (3592 and 3343 eyes respectively). It is difficult to translate these results to the US experience since all patients were hospitalized for several days, and had preop, intraop and postop intravenous fluroquinolone. Furthermore, intraop sutures were placed in 1.6% of eyes, and 30% of the vitreous was exchanged with air or gas in 94.4% of eyes. The Retina Consultants of Alabama have observed no significant difference in infection in 1906 consecutive 25-g vs 2642 consecutive 20-g cases.⁴ They closely inspected their wounds, and utilized suture closure (unspecified %) if needed. The 23-g Micro-incisional Vitrectomy Prospective Trial (121 subjects) had wound blebs in 17% and hypotony in 6.5% on postop day #1, despite gas fill in 27% of eyes.⁵

The experimental data and mechanism appears similar to cataract surgery. Jay Stewart, MD, at the University of California, San Francisco, has shown India ink penetration in the majority of straight-incision unsutured sclerotomy sites in 25-g cadaver eyes, with or without conjunctival displacement.⁶ More recently, they have shown inconsistent wound architecture and internal disruption of oblique-entry incisions, reducing the effective distance between the ocular surface and the intraocular cavity. Human cadaveric eyes studied at Wills demonstrated India ink along the entire incision length in 1 of 2 23- and 25-g eyes, and partially along the incision length in 1 of 2 beveled 25-g incision eyes. In Peter Kaiser's lab, rabbit eyes with angled incisions "demonstrated less wound opening overall and somewhat better wound apposition under high verses low IOP" (as opposed to straight incision which demonstrated open wounds), and there was no penetration of India ink into angled incision wounds. However, they point out that "significant manipulation of the sclerotomies via moving of instruments in extreme awkward and extreme directions … can change the wound architecture from its original construction and deem the wound relatively unstable and unpredictable."

Figure 1. Endophthalmitis following a vitreoretinal procedure.

Clinically, as in cataract cases, the onset of the infection appears delayed, making timely diagnosis challenging as most of us examine the patient on the first postop day, and then a week or so later. This in turn obliges the surgeon, staff and patient to maintain a heightened level of suspicion of infection following surgery, and makes prompt examination of any suspicious symptom mandatory. Furthermore, it is my impression that in vitrectomized eyes, the disease course appears to be more aggressive, with a worse prognosis.

How have we addressed this problem? The ASCRS convened a panel and recommended careful lid draping, chemoprophylactic antisepsis, and careful wound construction. The ESCRS (European cataract) endophthalmitis study demonstrated a 5-fold reduction in infection with the use of intraocular cefuroxime. Retinal surgeons have also convened The Micro-Surgical Safety Task Force and emphasized wound construction techniques. To prevent wound leak and hypotony/choroidals, others have advocated a routine air-fluid exchange.

Although a completely appropriate, worthwhile and laudable effort, when we change angled wound construction techniques (initially start 10° — enter 90°, now start 10° — enter 30°), it is difficult to ascertain whether this makes any difference, since infection is a relatively low-risk event. As an aside, one of my mentors always asked me why surgeons could change techniques at will with no evidence other than case series, but medical retina has the burden of masked controlled clinical trials before treatments are considered acceptable?

The idea of doing an air-fluid exchange routinely in these cases seems to introduce another complicating element, with the risk of new retinal tears, slower visual recovery and the inability of the patient to travel to elevations, not to mention the annoyance to the patient. Injecting intraocular antibiotics routinely also has the added risk of dosing errors, resistance and contamination. Martidis & Chang and Williams, in editorials, have reminded us that a definitive answer is not possible without a prospective controlled clinical trial, but in my opinion, such a large trial is highly unlikely to be undertaken.

When I review the benefits of small-gauge vitrectomy, the most meaningful one, in my opinion, is better instrument tip design to allow us to cut and delaminate membranes without the need for scissors. Moving the cutting tip towards the end of the instrument has been advantageous and I urge the leading instrument manufacturers to do this with their 20-g probes.

In my opinion, the claim of shorter surgery time is exaggerated and unimportant. It take only a few minutes to close incisions with sutures. If one is a slow surgeon, sutureless surgery is not going to make one a fast surgeon. If the goal is to finish one's cases faster, for most of us, the most effective intervention would be to shorten our turnover time between cases, where far more time than we can imagine or make up for in the OR, is wasted.

I agree that patients are more comfortable postop and recover vision faster with small-gauge surgery, but this is only relevant for simple cases such as pucker removal. For macular hole surgery, retinal detachment or any other case where gas is used, or for diabetic vitrectomy, retained lens, etc., where visual recovery is limited by the underlying or co-existent disease (macula detached pre-op, ischemia, corneal edema, CME), the difference in visual recovery time is not determined by the absence or presence of sutures, and associated minor corneal astigmatism.

Recent reports of doing increasingly complex cases using small-gauge sutureless techniques are pushing the envelope further and skilled surgeons are to be commended on their prowess. However, the absence of sclerotomy sutures does not contribute anything to retinal reattachment rates and the patient does not derive some inherent unspoken benefit because no sclerotomy sutures were used on their eye for their advanced retinal surgical disease.

I have no doubt that there are very highly skilled retinal surgeons (and cataract surgeons) who can do any case with sutureless small-gauge surgery and will rarely, if ever, develop a complication. In my opinion, this is not the true test of a technique or instrument; rather, its widespread use by the average surgeon should determine its utility and safety profile, because most of us, by definition, are average surgeons. In this regard, I feel that sutureless small-gauge surgery has come up short so far.

In transitioning from 20-g to small gauge, we must learn to angle our incisions (the current trend is start 10° then 30° entry), not excessively manipulate this incision intraop, convert a few cases to 20-g for larger instruments, examine the wound and suture it closed if leaking, possibly subject all patients to a partial air-fluid exchange, and be extra vigilant about delayed infection postop with more prompt office examination if necessary. Also, how should our informed consent and patient education change with regards to infection risk, need to call the office with symptoms, and safer alternatives?

The data with regards to infection rates are compelling. I cannot, on behalf of my patients, accept the increased risk of a blinding complication, even if there are significant benefits, when there is a perfectly acceptable safer alternative available. A suture is such a simple step, even if one wishes to use small-gauge instruments. I completely agree with the editorial by Hillel Lewis, MD, in which he states "we should not sacrifice possible safety for the potential reward of saving a few minutes in the OR or of avoiding mild ocular discomfort because of the presence of conjunctival sutures." Remember: "A stitch in time saves nine." RP

REFERENCES

1. Taban M, Behrens A, Newcomb RL, et al. Acute endophthalmitis following cataract surgery: a systematic review of the literature. Arch Ophthalmol. 2005;123:613-620.
2. Kunimoto DY, Kaiser RS; Wills Eye Retina Service. Incidence of endophthalmitis after 20- and 25-gauge vitrectomy. Ophthalmology. 2007;114:2133-2137.
3. Scott IU, Flynn HW Jr, Dev S, et al. Endophthalmitis after 25-gauge and 20-gauge pars plana vitrectomy: incidence and outcomes. Retina. 2008;28:138-142.
4. Mason JO 3rd, Yunker JJ, Vail RS, et al. Incidence of endophthalmitis following 20-gauge and 25-gauge vitrectomy. Retina. 2008 Jul 28. [Epub ahead of print].
5. Gupta OP, Weichel ED, Regillo CD, et al. Postoperative complications associated with 25-gauge pars plana vitrectomy. Ophthalmic Surg Lasers Imaging. 2007;38:270-275.
6. Singh A, Chen JA, Stewart JM. Ocular surface fluid contamination of sutureless 25-gauge vitrectomy incisions. Retina. 2008;28:553-557.