POINT/COUNTERPOINT

The 23-g Preference Explained

JOHN S. POLLACK, MD

According to the 2007 American Society of Retina Specialists (ASRS) Preferences and Trends (PAT) Survey,¹ a clear trend exists toward the widespread adoption of sutureless vitrectomy surgery. The survey reports that only 20% of respondents plan on using 20-g systems as their primary vitrectomy system over the next 5 years due to plans for the adoption of 23-g and 25-g surgery.

In this article, I will discuss why I prefer 23-g vitrectomy systems and instruments to 25-g versions. It is not my intent to try to convince readers to use one brand over another. I have used both the Alcon (Fort Worth, Texas) and Dutch Ophthalmic USA (Kingston, NH) 23-g systems and they are both terrific. Bausch & Lomb (Rochester, NY) is working on a 23-g system for possible introduction Q1 2008 and I expect that their version will be excellent as well. My sole purpose is to explain to you why I believe 23-g vitrectomy systems are ideal for the vast majority of our vitrectomy surgeries. In my opinion, 23-g systems combine the instrument stiffness, reliability, and flow characteristics we have long enjoyed with 20-g with the well-known benefits of sutureless surgery that we, as well as our patients, have quickly come to appreciate.

WHY SWITCH TO 23-G SURGERY?

I was an early adopter and advocate of 25-g surgery soon after its introduction, performing approximately 80% my surgeries in this manner. However, approximately, 1 year ago, I switched to the new 23-g sutureless vitrectomy systems for almost 100% of my vitrectomy surgeries. I made this switch for 3 reasons: First, the instruments for 23-g are stiffer, second, the cutting ports are closer to the tip of the vitrectomy probes, and third, 23-g offers improved cutting rate and flow characteristics.

There is a widespread desire for sutureless vitrectomy systems that accommodate instruments stiffer than the current 25-g designs. According to the 2007 ASRS PAT Survey, 60% of respondents do not use 25-g instruments either due to "instrument flexibility" or because they feel that the "patient's pathology is not amenable" to 25-g.¹ This compares to only 16% of respondents reporting that they do not use 23-g instruments for these same reasons. It seems that most of us prefer for our instruments to "drive" the eye, not the other way around. We like easily attainable access to the most anterior aspects of the eye and we do not like having to compromise by pivoting instruments in cannulas to prevent having our instruments bend in directions opposite that of our intended path. All of these 25-g flexibility issues become nonissues with the stiffer 23-g systems.

GREATER CONTROL AND EFFICIENCY

I have found that the greater control afforded by the stiffer 23-g instruments translates into safer and more efficient vitrectomy surgery. Current 23-g instruments provide firm and reliable control of the eye and more importantly, excellent control of the instrument tips themselves. This represents a marked improvement over current 25-g instruments, despite recent attempts to mitigate 25-g flexibility. The 23-g instruments, like 20-g instruments, greatly facilitate our ability to rotate the eye far enough that we can easily inspect and treat the retinal periphery out to the ora serrata. This becomes particularly valuable when performing 360-degree anterior panretinal photocoagulation and dissecting anterior proliferative membranes.

A typical case where 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, which frees up both hands, allowing me to scleral depress with 1 hand while shaving back the vitreous base and lasering the anterior periphery with the other hand. In situations such as this I am particularly grateful for the improved firmness and control provided by 23-g instruments, as well as their ability to readily counteract the various vector forces resulting from scleral depression. Conversely, these maneuvers can be quite challenging when attempted 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 relatively deep orbits. I find the 23-g surgical experience to be virtually indistinguishable from the "feel" and efficiency I get working with my 20-g instruments, enabling me to use it with confidence in even the most challenging cases.

I was recently asked why I do not use 25-g for "easy" posterior pathology such as macular pucker and macular holes (where 25-g flexibility is less of an issue), and reserving 23-g for cases requiring stiffer instruments and better control (anterior membrane peeling, anterior laser treatment, repair of retinal detachments, and repair of tough diabetic membrane cases). The reason I prefer using 23-g surgery for all of my cases is similar to the reason I use all of my car's safety features for all driving conditions. I do not deactivate my car's skid control and airbag systems once I get off the highway because I want my family and myself protected by all of our cars control and safety features both on the streets around town as well as on the highways. Similarly, I want the optimal safety and efficiency that 23- systems provide for all of my patients.

PORT LOCATION

Another nice attribute of 23-g vitrectomy over 25-g is the availability of a 23-g vitrectomy cutting port (Alcon) that is 30% closer to the tip (.009 mm from tip) than 25-g vitrectomy probes (.013-.014, Alcon; B&L/MID Labs). I find the increased closeness to the tip of noticeable benefit over 25-g probes, particularly in delamination of diabetic fibrovascular membranes. It is now very uncommon for me to need scissors for diabetic membranes since I can usually remove them by simply excising them "head-on," or by "sitting" the probe tip directly over the point of adhesion between the membrane and the underlying retinal and allowing the edges of the membrane to fold back into the vitrectomy tip. In the most difficult diabetic cases with very tightly adherent diabetic membranes, I find that using a 25-g chandelier for illumination combined with a bimanual technique utilizing forceps one hand and the 23-g vitrectomy probe in the other is usually equally effective and more efficient than using scissors.

FLOW CHARACTERISTICS

New 23-g vitrectomy systems now provide flow rates (at 2500 cpm) that are actually comparable to 20-g surgery (at 2500 cpm) and significantly greater than flow rates attainable with 25-g probes (at 2500 cpm). Alcon's 23-g probe has flow rates of 7 cc/min at 450 mm Hg aspiration and 9 cc/min at 600 mm Hg aspiration, which is virtually the same as 20-g flow rates (150 mm Hg) (Alcon). Dutch Ophthalmic reports that their probe achieves flow rates of 13 mm Hg at a cut rate of 2500 cpm (aspiration not reported). Both of these probes provide a much broader range of available flow rates than are achievable with 25G vitrectomy probes at 2500 cpm, which have been reported to be between 4 cc/min (aspiration not provided; B&L/MID Labs) and 4.5 cc/min (at 600 mm Hg aspiration; Alcon).² That said, while it is nice to have enough flow to perform vitrectomy efficiently, I believe that it is important to keep in mind that "more flow" isn't always better. If we increase flow too high — out of proportion to 2500 cpm — then we increase the risk of dragging vitreous and causing iatrogenic retinal tears and retinal detachments. Thus, I do not believe that infinitely higher flow rates are a goal to which we should aspire unless the increased flow is paired with a proportional increase in cut rates greater than 2500 cpm. In fact, in circumstances such as shaving cortical vitreous over detached retina, lower flow rates in the setting of 2500 cpm are preferable if we wish to reduce the risk of iatrogenic retinal breaks. Clearly, different types of retinal pathology call for different flow rates and 23-g systems provide a broader range of flow rates at 2500 cpm than 25-g systems. Therefore, flow characteristics are the third reason that I prefer 23-g surgery to 25-g surgery.

Figure 1. Biplanar 5°/30° Insertion Technique: 30° vitreous entry.

Figure 2. Biplanar 5°/30° Insertion Technique: 5° scleral tunnel.

BIPLANAR 5°/30° INSERTION TECHNIQUE

Having experimented with several different single-step 23-g trocar insertion techniques (Alcon 23-g system), I have developed the Biplanar 5°/30° Insertion Technique and have found that it most easily produces the most reliably leak-free wounds. Leak-free wounds are critical to minimizing the risk of endophthalmitis and there are many potential insertions techniques for sutureless vitrectomy cannulas. It is important to use the technique that most reliably produces leak-free wounds in our own hands. I presented a study of the first 50 patients on whom I performed the Biplanar 5°/30° Insertion Technique at the 2007 ASRS Annual Meeting in Palm Springs, CA. The PowerPoint presentation with audio and embedded video demonstration of this technique will be available for viewing at www.asrs.org in early 2008. I outline the technique (Figure 1 and 2) here.

■ Ocular Fixation

1. Firmly grasp sclera with 0.12 forceps at location you want trocar to internally enter vitreous cavity (Tip: Check and be sure all 3 teeth of forceps are present because the sclera cannot be grasped with only 2 teeth)
2. Rotate eye into a position that provides easy access to desired insertion site (allows very flat insertion of trocar).
3. Use tip of trocar to displace conjunctiva towards limbus (reduces risk of endophthalmitis)
4. Start insertion superior to forceps and aim towards tips of forceps (parallel to limbus).

■ Biplanar Insertion

1. Hold trocar bevel up with tip at ~ 5° angle to sclera (virtually flat on sclera).
2. Insert trocar until approximately three-quarters of the bevel disappears into scleral tunnel
3. Raise handle until trocar shaft at ~ 30°angle to sclera and complete insertion
4. Self-sealing clear corneal cataract wound principles are the rationale behind this technique.

■ Cannula Removal

1. Remove cannulas at same 5° angle as insertion
2. 2. Remove cannulas with plugs in place and pressure ~ 30 mm Hg (intraocular pressure should "collapse" the internal aspect of tunnel
3. Collapse "roof " of scleral tunnel with Q-tip (Tip: If wound leaks, briefly increase IOP while pressing on roof of tunnel with Q-tip. If the wound was constructed using the °/30° technique, this should always collapse the tunnel and eliminate the leak).

CHOICES IMPROVE SURGICAL OUTCOMES

In conclusion, these are good times for vitreoretinal surgeons. In addition to our conventional 20-g vitrectomy "workhorse" systems, we now have several different gauge vitrectomy systems that can be used in a potentially suture-less manner. I believe that the ideal sutureless vitrectomy system is one that provides us with all the instrument stiffness we need to safely and efficiently achieve our surgical goals, through reliably leak-free, pressureresistant wounds. Based on my experience thus far, 23-g vitrectomy systems deliver this combination of features better than 25-g systems. RP

REFERENCES

1. 2007 American Society of Retina Specialists Patterns and Trends Survey. Poster presented at the 2007 Annual ASRS meeting; December 1-5, 2007; Palm Springs, CA.
2. Upgrading to the latest generation of 25-gauge vitrectomy. Retina. 2007;27(7):(Suppl).