Do the Advantages of 25-Gauge Vitrectomy Outweigh the Disadvantages?
One surgeon explains why his answer is yes.
CARL C. AWH, MD

Vitrectomy using 25-gauge instrumentation, introduced in 2002 by Eugene de Juan, MD, and co-workers,¹ is now considered by many to be a useful, and occasionally superior, alternative to the conventional 20-gauge procedure. In its present form, 25-gauge vitrectomy is made possible by thin-walled, transconjunctival cannulas inserted with a trocar system. The resulting conjunctival and scleral wounds are small and typically do not require sutures to close.

I have been performing 25-gauge vitrectomy for more than 2 years, and as an "early adopter" am aware of both its advantages and its limitations. One limitation at this time is that the selection of compatible instruments is limited. Another is that the small lumen of the instruments makes the removal of rigid materials (e.g., organized blood clot) impractical. Also, 25-gauge instruments are more flexible and delicate than 20-gauge instruments. Relative to 20-gauge instruments, flow is somewhat reduced, scissors make shorter incisions, and forceps grasp a smaller amount of tissue. And, finally, while insertion and removal of the transconjunctival cannulas takes less time than creating and closing peritomies and sclerotomies, for certain pathologies 25-gauge cases take longer than 20-gauge cases.

So, given the limitations, why do I believe that the advantages of 25-gauge surgery outweigh the disadvantages? Because the elimination of the opening and closing of the conjuctiva and sclera reduces trauma to the eye, which results in improved outcomes for our patients.

BETTER OUTCOMES ARE THE ADVANTAGE

The major advantages of 25-gauge vitrectomy are:

Figure 1. A consecutive series of eyes photographed from 1 to 5 days following 25-gauge vitrectomy.

Reduced inflammation and discomfort. One of the more common postoperative complaints of patients who undergo conventional vitrectomy is discomfort related to the sutured sclerotomy sites. Sutures cause foreign-body sensation, localized inflammation and occasionally a granulomatous reaction.

These suture-related problems are eliminated in 25-gauge vitrectomy (Figure 1). Patients who have had both 20- and 25-gauge vitrectomy consistently report a significant reduction in postoperative discomfort following 25-gauge surgery. Additionally, the improved appearance of the eye during the immediate postoperative period is of real value to many patients.

Preservation of the conjunctiva. The ability to address posterior segment pathology with minimal trauma to the conjunctiva is of particular importance for patients with keratoconjunctivitis sicca or glaucoma. In addition to those patients with existing filtering blebs, a number of patients who require vitrectomy have underlying conditions that put them at risk for difficult-to-control glaucoma. Preserving the conjunctiva maintains future therapeutic options (Figure 2, Figure 3).

	Figure 2. Transconjunctival cannulas for 25-gauge surgery can be precisely placed to minimize disruption of a filtering bleb.

At the upcoming meeting of the American Society of Retina Specialists, Brandon Busbee, MD, Jeffrey Heier, MD, and I will present a retrospective series of 10 eyes of patients with functioning glaucoma filtering blebs who underwent 25-gauge vitrectomy. A functioning trabeculectomy was maintained in each case, as was postoperative control of intraocular pressure.

More rapid rate of visual acuity improvement. Both surgeons and patients have observed that visual acuity (VA) improves more rapidly following 25-gauge vitrectomy. At the 2003 annual meeting of the American Society of Retina Specialists, I presented a retrospective case series comparing the outcomes of 20- and 25-gauge vitrectomy and membrane stripping for eyes with macular epiretinal membranes and no other intraocular pathology.² In this series of 22 eyes, there was no difference in the baseline visual acuity, the final degree of visual acuity improvement (about 3 Snellen lines), or in the number of postoperative complications (none). However, the rate of visual acuity improvement was significantly different.

Among the 25-gauge cases, 10 of 11 eyes achieved better than the preoperative VA by 1 week (5 to 8 days) after surgery. One eye did not achieve better than the pre-op VA until 11 weeks after surgery. The average time to better-than-pre-op VA for all eyes in the 25-gauge group was 2.1 weeks. Among the 20-gauge cases, 3 of 11 eyes achieved better than the pre-op VA by 1 week after surgery. The average time to better-than-pre-op VA for all eyes in the 20-gauge group was 10.4 weeks (range 1 to 30 weeks).

The difference in the percentage of eyes achieving better-than-pre-op VA by 1 week after surgery (91% vs. 27%) was statistically significant, as was the average number of weeks to achieve better-than-pre-op VA (2.1 vs. 10.4 weeks).

In my opinion, the more rapid improvement in visual acuity is due to the elimination of astigmatism typically caused by scleral sutures, as well as a reduction in postoperative inflammation. More rapid visual acuity recovery is a real benefit to our patients, some of whom require vision in the operative eye for activities of daily living, and all of whom appreciate a more rapid improvement. This benefit is analogous to that of small-incision cataract surgery, which has supplanted extracapsular surgery as the predominant technique largely on the basis of more rapid visual acuity improvement and reduced surgical trauma.

Figure 3. Preservation of a trabeculectomy bleb 1 day after 25-gauge vitrectomy.

Equipment problems are being solved. Although advertising campaigns often emphasize the "cut rate" of the vitrectomy probe as a measure of "speed," I find this to be misleading. The clinically relevant "speed" is "flow," the amount of vitreous that can be safely removed in a given amount of time. The flow of a 25-gauge cutter, because of its smaller lumen, can be expected to be less than that of its 20-gauge counterpart. At the advent of 25-gauge vitrectomy, an obvious concern was that if vitreous removal were too time-consuming, the potential benefits of eliminating the opening and closing steps of the case would be negated.

Therefore, we conducted in-vitro studies of the flow of various pneumatic and electric vitreous cutters.³ I found that a 25-gauge electric cutter is surprisingly effective, with flow approaching that of a conventional 20-gauge pneumatic cutter. My clinical experience has confirmed what the studies suggested: In most cases, a 25-gauge cutter removes vitreous with sufficient flow to make the use of small sutureless sclerotomies practical. Furthermore, many cases require little, if any, vitreous removal (e.g., stripping of an epiretinal membrane in an eye that has undergone a previous vitrectomy).

Light sources were initially a problem because 25-gauge instruments have far smaller cross-sectional areas than their 20-gauge counterparts. This resulted in lower levels of illumination through the smaller diameter optical fibers; however, this problem has been eliminated with the development of new light sources (Figure 4). The Photon light source from Synergetics, for example, delivers the amount of light typically transmitted by a 20-gauge endoilluminator through a 25-gauge endoilluminator or even through a 25-gauge illuminated laser probe.

Brighter light sources also allow for a smaller optical fiber to be used in the light pipe. Therefore, the walls of the metal tubing can be made thicker, resulting in a substantially stiffer light pipe. This eliminates the flexion of the light pipe that makes manipulation of the globe more difficult in 25-gauge cases.

Moreover, stiffer materials are being evaluated for use in a variety of 25-gauge instruments. In my opinion, the issue of instrument flexibility is a solvable technical problem, and not a fundamental limitation of the technique.

	Figure 4. Bright light sources for 25-gauge vitrectomy have already been developed.

A WELCOME ADVANCE

The role of 25-gauge vitrectomy in our practices is evolving and expanding, although it is unlikely to supplant 20-gauge vitrectomy in the foreseeable future. Issues of potential postoperative hypotony (typically avoidable in my experience) and the yet-to-be-determined comparative risks of postoperative infection or retinal tears may prevent some surgeons from adopting this technique. However, thousands of 25-gauge cases have been performed worldwide in the past 2 years, with no reports of a significant difference in the rate of post-op complications. The ability to perform effective, efficient, minimally traumatic vitreous surgery with 25-gauge instruments is a true advantage.

The discussion engendered by this technology has redirected our attention to aspects of vitreous surgery that have remained largely unchanged for 30 years. In the past year, I've heard presentations about 23-, 27-, and 30-gauge vitreous surgery devices! What is the ideal size? Only time will tell. However, I believe that the advantages of smaller-port vitreous surgery already outweigh the disadvantages.

For a different perspective on this question, see the next issue of Retinal Physician, which will be published in October.

From Retina-Vitreous Associates PC in Nashville, Tenn. Dr. Awh is a surgical consultant to Bausch & Lomb and Synergetics. 

Address correspondence to: Carl C. Awh, MD, Retina-Vitreous Associates, PC, 2011 Murphy Ave., Suite 603, Nashville, TN 37203.Telephone: (615) 320-7911. Fax: (615) 320-8911. E-mail: cawh@aol.com.

REFERENCES

1 Fujii GY, de Juan E, Humayun MS, Pieramici DJ, Chang TS, Awh CC, Ng E, Barnes A, Wu SL. A new 25-gauge instrument system for transconjunctival sutureless vitrectomy surgery. Ophthalmol. 2002;109(10): 1807-1813.

2. Awh CC. Rate of visual acuity improvement after transconjunctival sutureless 25-gauge vitrectomy. Paper presented at: annual meeting of the American Society of Retina Specialists; August 2003; New York, NY.

3. Awh CC. Objective comparison of high speed vitreous cutters. Presented at: Vitreous Society annual meeting; December 2002; San Juan, Puerto. Rico.