Why (and When) I Prefer 25-g Vitrectomy
CARL C. AWH, MD
Let me begin my section of this "debate" by acknowledging the virtues of 23-g vitrectomy. The instruments are larger than 25-g instruments and are therefore stiffer and more durable. The inner diameter of a 23-g tube is larger than that of its 25-g counterpart, allowing greater flow or a larger working channel for multi-function devices. The wounds, when constructed properly, are watertight without sutures at the conclusion of surgery. In fact, were I forced to perform all my surgeries with a single system, and limited to either 25-g or 23-g, I would opt for a 23-g system because of those cases in which larger-diameter instruments are essential. Thankfully, I do not have to make such a choice, and here lies the basis of my argument in favor of 25-g vitrectomy.
|Carl C. Awh, MD, is an ophthalmologist in practice with Retina-Vitreous Associates, PC, of Nashville, Tenn. Dr. Awh reports the following minimal financial interests: Bausch & Lomb (consultant) and Synergetics (consultant).|
NO NEED TO COMPROMISE
In my opinion, there is no single system that ideally meets the needs of surgeons and patients. I choose to use either a 25-g or a 20-g system, depending upon the clinical situation. Here is where I differ with those who maintain that 23-g vitrectomy represents a perfect compromise between 25-g and 20-g vitrectomy. Rather, I find 23-g to be a weak compromise, lacking the major attributes of the other systems.
Let's consider the advantages of 25-g vitrectomy.
A PROVEN TECHNOLOGY.
Twenty-five–gauge vitrectomy (Figure), while revolutionary and somewhat controversial five years ago, is now a proven technology utilized worldwide. More than 125 000 25-g vitrectomy procedures have been performed in the U.S. since the introduction of this technology, with at least 50 000 of these procedures performed in 2006. The most recent American Society of Retina Specialists Preferences and Trends (PAT) Survey found that 70% of vitreoretinal surgeons use 25-g technology occasionally and 25% of surgeons use 25-g vitrectomy for more than 75% of their cases.1
Figure. 25-g vitrectomy.
The reasons for the successful adaptation of 25-g vitrectomy are apparent. It is effective, efficient, and reasonably safe. The ophthalmic literature is replete with articles which demonstrate the utility of 25-g vitrectomy in a variety of clinical settings. Despite reasonable and logical concerns about the potential increased risk of endophthalmitis associated with nonsutured wounds, published series do not identify postoperative infection as a particular problem. In a survey of 10 published retrospective series on the subject of 25-g vitrectomy, no cases of endophthalmitis were reported in a total of 700 surgeries.2 In my own experience of over 1100 25-g cases, I have had one case of post-operative bacterial endophthalmitis. Does this mean that the expected rate of endophthalmitis is 1 per 1800 cases? Probably not. Only a prospective, controlled clinical trial would reveal an accurate risk of endophthalmitis, but such a trial is unnecessary and impractical. As with sutureless cataract surgery, the advantages of sutureless vitrectomy, both for the patient and for the operating room staff, are obvious and have compelled a majority of conscientious and ethical physicians to adopt this technique when indicated.
AN IMPROVED TECHNOLOGY
Twenty-five–gauge vitrectomy in its present form is considerably different from the procedure first introduced over 5 years ago. Improved technology has eliminated the illumination limitations previously inherent to 25-g vitrectomy. New xenon and mercury-vapor light sources now provide levels of intraocular illumination greater than that achieved by the 20-g technology of just a few years ago.
Open the catalog of any major vitrectomy device manufacturer and you will find an exhaustive range of 25-g forceps, picks, scissors, cannulas, and laser probes.
Refined manufacturing techniques have resulted in stiffer and more durable instruments. Improvements in 25-g instrument stiffness and functionality will continue, allowing an increasingly larger percentage of cases to be effectively and efficiently performed with 25-g devices.
Until recently, the electric cutter from Bausch & Lomb (Rochester, NY) was the most effective 25-g vitreous cutter. However, because of resistance by some surgeons to the larger handpiece, many surgeons have only performed 25-g vitrectomy with first-generation 25-g pneumatic cutters. To these surgeons I say, "You haven't really tried 25-g vitrectomy until you've used a current-generation vitreous cutter."
A new generation of high-speed vitrectomy cutters now provides improved flow and stiffness. A clinical study by Tarek Hassan, MD, and laboratory analysis performed at the EyeConcepts Lab at University of Southern California both demonstrate that a new high-speed 25-g pneumatic cutter (the AVE cutter, B&L) has from 20% to 70% greater flow than the Alcon 25-g pneumatic cutter.3 Even more impressive is the fact that the AVE 25-g pneumatic cutter achieves this flow at a cut rate of 2500 cpm (66% faster than any other commercially available 25-g cutter), allowing increased flow with minimal vitreous traction. In fact, at 2500 cpm, the 25-g AVE cutter was found to have greater flow than the Alcon 20-g vitreous cutter at the same settings. And, as many surgeons will be pleased to learn, these performance advantages are packaged in a lightweight pneumatic handpiece virtually indistinguishable from traditional pneumatic cutters.
The smaller diameter of a 25-g cutter tip makes it an excellent device for dissection and delamination of epiretinal membranes, as in complex diabetic traction detachments. The stiffer AVE 25-g cutter can be manipulated anteriorly without the flex associated with first-generation vitreous cutters. This, combined with its ability to remove even large fragments of lens nucleus, makes it an excellent instrument for the management of dislocated lens fragments following complicated cataract surgery.
THE SIMPLEST, MOST RELIABLE WOUND
Twenty-five–gauge cannulas are easily inserted and the ability to create a water-tight wound is far less techniquedependent than the current generation of 23-g sutureless systems. Whether hollow or solid core, the major 25-g and 23-g single-step systems utilize a trocar that is round in cross-section, and which create a crescent or chevronshaped incision. Such scleral wounds are not inherently watertight. Could you imagine a cataract surgeon ever using a 3-mm diameter needle to create a corneal wound?
During the development of 25-g vitrectomy, animal studies demonstrated that a 25-g needle wound was the largest that would reliably heal without sutures.4 This was critical to the selection of 25-g as the critical dimension for transconjunctival sutureless vitrectomy as described by de Juan et al. In my opinion, the incidence of post-operative wound leaks with 23-g vitrectomy will prove to be substantially greater than with 25-g.
Listen to any lecture or read any article about sutureless vitrectomy with larger-than-25-g systems and you will be instructed about the critical importance of fixating the globe, entry angle, and beveling. Failure to construct the wound properly will almost always result in a leaking sclerotomy. Not so with 25-g, where even "straight in" wounds are generally watertight and where an angled incision is easily performed and may add a measure of security.
Although some surgeons choose to enter the eye obliquely with 25-g cannulas, this is an option, not a strict requirement as with 23-g or 20-g sutureless entry systems. The ability to create water-tight wounds with minimum disruption to the conjunctiva and sclera makes 25-g vitrectomy ideal for surgery on eyes with glaucoma filtering blebs. In a study presented by my colleague Brandon Busbee, MD, at the 2004 Annual Meeting of the ASRS, we demonstrated the ability to preserve 100% of functioning glaucoma filtering blebs in a series of nine eyes operated on with 25-g vitrectomy.5 Many of these eyes had extremely limited locations in which the cannulas could be safely inserted without traumatizing the filtering bleb and I doubt that similar results could have achieved with a larger-gauge system requiring long, oblique wounds.
NO NEED TO COMPROMISE
There is no effective fragmatome smaller than 20-g. There will always remain a need for large gauge instruments to remove dense scar tissue, organized hemorrhage, and intraocular foreign bodies. In such cases, I prefer to use the largest instruments available. 20-g instruments and the systems developed for them remain the most economical and durable of the available options.
In the most difficult of cases the avoidance of sutures is usually a non-issue. However, those who wish to perform sutureless vitrectomy but remain uncomfortable with the more flexible nature of 25-g instruments have the option of performing sutureless 20-g vitrectomy. For over a decade, innovative surgeons have described a number of techniques for sutureless 20-g vitrectomy. However, these techniques generally require conjunctival incisions and meticulous wound construction and have not been widely adopted.
More recently, I have helped develop a new system for 20-g sutureless vitrectomy from Synergetics (O'Fallon, MO). This system combines the merits of flexible polyamide cannulas with the superior wound characteristics of a flat blade incision. The trocar has at its tip a razoredged blade that is actually wider than the diameter of the preloaded polyamide cannula. The trocar-cannula is inserted, similar to 23-g systems, oblique to the scleral surface. The outer corner of the blade is rounded, allowing the flexible cannula to deform into an oval shape as the trocar is withdrawn. The cannula then returns to a round cross-section through which conventional 20-g instruments can be easily introduced. The wounds created by the 1-step 20-g cannulas, by virtue of the razor-edged blade, are sutureless. Recalling my earlier reference to cataract surgery, consider that 3-mm wide sutureless incisions are routinely created with flat blades. The architecture of a wound created with a flat blade is superior to that created with the hollow or solid needle typical of one-step 23-g systems.
There are potential economic advantages to the 20-g 1-step cannulas. Surgeons have access to virtually all of the 20-g instruments already present in their operating rooms, most notably the fragmatome (unavailable in 23-gauge). A standard 20-g vitrectomy pack is considerably less expensive than a 23-g or 25- g pack, even when considering the additional cost of the 20-g cannulas. Finally, 20-g instruments are more durable than their 25-g or 23-g counterparts.
ONE SIZE DOES NOT FIT ALL
The ease and reliability of 25-g sutureless wound construction remains unmatched, and improvements in technology allow surgeons to perform operations of increasing complexity both efficiently and effectively. Our patients benefit from a continued effort to simplify and minimize the trauma associated with vitreoretinal surgery. I predict that office-based vitrectomy will one day become a reality. Imagine being able to effectively operate with a 27-g or 30-g system! We should push forward, not step backward.
For those who prefer the "feeling of 20-g," or who require the capabilities of a larger-diameter system, my recommendation is to use a 20-g system. Sometimes only the largest and most robust instruments will do. Quite frankly, avoiding scleral and conjunctival sutures is a non-issue in our most difficult cases. Why seek the best of both worlds when you can use both worlds? RP
- 2007 American Society of Retina Specialists Patterns and Trends Survey. Poster presented at: 2007 Annual ASRS meeting; December 1-5, 2007; Palm Springs, CA.
- Awh CC. Why I prefer 25-gauge vitrectomy. Paper presented at: 2007 Annual AAO meeting; November 10-13, 2007; New Orleans, LA.
- Fujii GY, De Juan E Jr, Humayun MS, et al. A new 25-gauge instrument system for transconjunctival sutureless vitrectomy surgery. Ophthalmology. 2002;109: 1807-1812.
- Fang SY, DeBoer CMT, Humayun MS. Performance analysis of new-generation vitreous cutters. Graefes Arch Clin Exp Ophthalmol. 2008;246:61-67.
- Busbee BG, Awh CC. Transconjunctival, sutureless 25-gauge vitrectomy: an effective technique for glaucoma patients with a filtering bleb. Paper presented at: 2007 ASRS Meeting; August 16-24, 2004; San Diego, CA.