Comparison of Traditional Pars Plana Vitrectomy to a Transconjunctival Approach

MARC J. SPIRN, MD

Transconjunctival sutureless vitrectomy (TSV) was first introduced in 2002, using 25-gauge instruments through a trocar-based system. Prior to this date, the gold standard was the 20-gauge three-port pars plana vitrectomy, which was introduced nearly 30 years earlier. Since its inception, TSV has rapidly evolved. Many innovations have helped further its popularity and, as a result, the majority of vitreoretinal surgeons in the United States are now performing 25-gauge or 23-gauge surgery via a transconjunctival technique. In this article, I will discuss some of the reasons why transconjunctival surgery has gained in popularity over traditional 20-gauge surgery and some the advantages and disadvantages of each.

With standard 20-gauge techniques, a conjunctival peritomy is performed, an inferotemporal sclerotomy is made with a myringovitreoretinal (MVR) blade, and an infusion cannula is sewn in place 3.0 to 4.0 mm posterior to the limbus. Two additional sclerotomies are then made superotemporally and superonasally in a similar fashion.

Thirty-six years ago, when this technique was introduced, it was a major breakthrough over single-port vitrectomy, which previously had been introduced by Machemer using a multifunctional 17-gauge vitrector. With Machemer's original technique, the infusion was attached to the vitrector, so if the vitrector was removed from the eye, hypotony often ensued. By suturing the infusion cannula to the sclera, the 20-gauge three-port system minimized the likelihood of hypotony and its sequelae, such as choroidal hemorrhage. In addition, having a separate lightpipe and vitrector improved illumination and eventually set the stage for illuminated instruments, which were particularly helpful during difficult surgical repairs, such as complex tractional detachment repairs.

DISADVANTAGES OF TRADITIONAL 20-GAUGE OPENING

Despite the many advantages of 20-gauge over its predecessor, there are some disadvantages of 20-gauge surgery compared to 25- and 23-gauge. Opening and closing the conjunctiva invariably results in conjunctival scarring. This may be particularly troublesome in patients with advanced or worsening glaucoma, where filtering surgery may be imminent. In these patients, preservation of conjunctiva is paramount. Even in patients who do not have glaucoma, repeated opening and closing of the conjunctiva can result in severe scarring — and in extreme cases may eventually make it impossible to adequately close the conjunctiva over the sclerotomy at the end of the case.

A second disadvantage of traditional 20-gauge technique involves the size of the sclerotomy. Because it is made manually with an MVR blade, the size can vary. If it is too large, intraoperative hypotony may occur due to increased flow through the sclerotomy. During bullous rhegmatogenous retinal detachment repair, for example, this can increase the likelihood of retinal incarceration. Conversely, if the sclerotomy is too small, placing instruments in the eye may be difficult and time-consuming (as the surgeon searches repeatedly for the scleral opening). One of the more serious complications of a small wound is wound burn, which may occur when using a fragmenter through a small wound with limited flow around the instrument.

Another wound-related complication can occur during a reoperation, when placing a new sclerotomy next to a previous sclerotomy. If placed too close to the previous sclerotomy, extension of the new wound into the previous sclerotomy may occur, resulting in an extremely large wound. This can make wound closure more difficult, as well as result in intraoperative hypotony. When multiple reoperations are necessary, if the sclerotomies are placed circumferentially, the surgeon may eventually run out of locations to put a new sclerotomy. Due to the nature of wound construction with TSV, this is much less likely to occur.

The last disadvantage of 20-gauge surgery vs TSV relates to the suturing process. At the end of a traditional 20-gauge case, the sclerotomies must be sutured. Two suture passes are performed in a radial fashion, creating a figure eight. With this technique, meticulous attention must be paid to avoid wound leak. If the suture is improperly placed or not closed tightly enough, wound leak will occur. Conversely, if the sutures are cinched too tightly, postoperative astigmatism may result. In addition, if the conjunctiva is also closed with sutures (which is the norm), patients will frequently complain of some irritation or discomfort.

TRANSCONJUNCTIVAL SUTURELESS VITRECTOMY OPENING

As surgical technology evolves and patient expectations rise, demands for painless, seamless surgery also increase. Patients expect their eyes to look white and quiet the day after surgery. Increased patient demands helped drive the introduction of TSV. Unlike standard 20-gauge techniques, TSV does not involve a conjunctival peritomy. Rather, a trocar is inserted using a sharp blade through the sclera, after first displacing the conjunctiva. The conjunctiva is displaced so that the scleral and the conjunctival openings are in different locations, therefore theoretically diminishing the risk of bacteria traveling through both openings. The infusion cannula is then attached to the trocar and taped to the drape for stabilization purposes. The superotemporal and superonasal trocars are placed in a similar fashion.

ADVANTAGES OF A TRANSCONJUNCTIVAL APPROACH

There are several advantages to a transconjunctival approach. First, because the conjunctiva is only minimally manipulated, conjunctival scarring is limited. This is very helpful in patients with glaucoma, who either previously have had a trabeculectomy (and the surgeon wants to minimize the risk of a bleb leak) or who are likely to undergo filtering surgery in the future (and the surgeon wishes to minimize conjunctival scarring). Because sutures are often unnecessary, there is likely to be less astigmatism and decreased postoperative inflammation. Decreased postoperative inflammation ultimately means improved patient comfort. It is not unusual for a postoperative day one eye to look white and quiet, as if no surgery had been performed at all.

A second major advantage of TSV revolves around the use of the trocar. The trocar-based system has many advantages. First and foremost, it creates a uniform, reproducible wound. It is unlikely that the wound will be too large or too small, thereby minimizing the complications noted above. Because the trocar sticks out of the eye, it is easy to visualize the wounds, so the surgeon does not waste time looking for sclerotomies (which frequently happens during 20-gauge surgery). The trocars make it easy to enter and exit the eye. As a result, the trocar-based system likely results in less overall manipulation of the vitreous base, which may lead to fewer sclerotomy tears. The difference in opening and closing with TSV, as well as the increased efficiency of entering and exiting the eye, often results in greatly reduced operative times, which may have obvious advantages for both the surgeon and the patient.

DISADVANTAGES OF TRANSCONJUNCTIVAL APPROACH

Although TSV has many advantages, there are some concerns and obstacles still to overcome. Initially, postoperative hypotony was an issue. Early on, sclerotomies were made in a straight single-plane fashion. To combat hypotony, which frequently resulted, techniques evolved and now include a biplanar entry, as well as a partial air fill at the end of the case whenever possible. The biplanar entry results in a longer scleral tunnel than a straight entry and makes it more likely that the sclerotomy will stay closed. Partial air or gas fills have also been shown to decrease hypotony rates, as the air interface may press up against the internal surface of the sclerotomy and facilitate closure.

Another rare, but potentially devastating, complication of the transconjunctival approach is its increased risk of intraoperative choroidal effusion or hemorrhage. With 25- or 23-gauge transconjunctival techniques, the infusion line is snapped into the trocar and is ultimately taped to the drape. Unlike the 20-gauge system, where the infusion is sewn to the sclera, the trocar-based infusion can sometimes partially extrude during surgery. I have found that this is most likely to occur during scleral depression, either from excessive depression by an assistant or by accidentally catching the depressor on the infusion line and pulling it out. If the infusion is totally removed, immediate hypotony can result. If the infusion is only partially extruded, the infusion line can infuse directly into the suprachoroidal space. Although this can be remedied by moving the infusion line quickly to one of the superior trocars, it still may result in an unwanted complication.

The most important concern, however, about transconjunctival surgery is the observation that it may be associated with a higher rate of endophthalmitis than 20-gauge surgery. Early on, endophthalmitis rates with 25-gauge surgery were shown to be much higher than with traditional 20-gauge techniques. Although limited by their retrospective nature, Kunimoto et al. showed a 12-fold increased rate of endophthalmitis with 25-gauge compared to 20-gauge PPV.¹ Similarly, Scott et al. showed a near 28-fold increased rate with 25-gauge compared to 20-gauge.² More recently, however, Hu et al.³ and Parolini et al.⁴ found similar rates with small-incision (25- or 23-gauge) compared to traditional 20-gauge surgery.

Two factors likely play a role in any case of endophthalmitis: vitreous wick and hypotony. Either alone can lead to endophthalmitis, but together their roles are synergistic. To decrease vitreous wick, meticulous attention should be paid to the vitreous near the sclerotomies. Limiting the vitreous near the sclerotomies will subsequently diminish the chance of vitreous prolapsing through the wound and acting as a wick. As mentioned above, making a biplanar incision and placing air or gas to tamponade the wounds may diminish hypotony and vitreous wick and subsequently reduce the risk of endophthalmitis.

Whenever possible, I like to leave the pressure at the higher end of the physiologic spectrum, usually between 20 and 25. To inspect the sclerotomy in an air- or gas-filled eye, I find it useful to sprinkle balanced salt solution (BSS) on the wound. If there is a wound leak, bubbling will occur at the wound site, where the BSS and air interface. This is a similar technique used by mechanics looking for a small leak on a car tire. Whenever there is any doubt about the integrity of a wound, I prefer to place a single 8-0 vicryl suture through both the conjunctiva and the sclera, being careful to make the scleral bite partial thickness (since the full-thickness bite can act as a conduit for bacterial passage into the eye).

In addition to securely closing the wound, the vicryl suture causes a localized inflammatory reaction (Figure 1). Suturing the wound brings inflammatory cells to the sclerotomy site, which both quickens wound healing and may act as an added site of defense against invading bacteria. It does, however, cause some discomfort until the suture dissolves, which takes approximately six weeks. Unlike figure-eight sutures, which are typically used to close 20-gauge sclerotomies (and are often placed radially), the single pass for closing the transconjunctival sclerotomy is often circumferential. As a result, there should be less induced astigmatism.

Figure 1. A single 8-0 vicryl suture securely closes the wound, causing a localized inflammatory reaction.

CONCLUSION

In conclusion, TSV is becoming increasingly popular. The reasons for its rise in popularity include greater patient comfort, decreased postoperative astigmatism, and reduced operative times. As techniques and instrumentation improve, nearly all surgical indications can be performed using either 25- or 23-gauge vitrectomy with a transconjunctival approach. However, despite heralded progress, there are still some limitations. Hypotony is more likely, and rates of endophthalmitis must be clarified and limited. Ultimately, with both traditional 20-gauge and TSV, one case of endophthalmitis is too many. Efforts must continue to focus on ways to prevent endophthalmitis. RP

REFERENCES

1. Kunimoto D Y, 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. Hu AY, Bourges JL, Shah S P, et al. Endophthalmitis after pars plana vitrectomy a 20- and 25-gauge comparison. Ophthalmology. 2009;116:1360-1365.
4. Parolini B, Romanelli F, Prigione G, Pertile G. Incidence of endophthalmitis in a large series of 23-gauge and 20-gauge transconjunctival pars plana vitrectomy. Graefes Arch Clin Exp Ophthalmol. 2009;247:895-898.