Article Date: 1/1/2009

Overcoming Myths and Misconceptions in Small-gauge Vitreoretinal Surgery

Overcoming Myths and Misconceptions in Small-gauge Vitreoretinal Surgery

Recent enhancements have expanded the indications and improved outcomes.

J. FERNANDO AREVALO, MD, FACS · MARÍA H. BERROCAL, MD

Vitreous surgery became a reality in 1971 when Robert Machemer, MD, described pars plana vitrectomy.1 In the 1980s and ’90s, 3-port vitrectomy with 20-g instrumentation prevailed. In 2002, Eugene de Juan, MD, introduced 25-g transconjunctival sutureless vitrectomy (TSV).2,3 This system permits 3-port pars plana vitrectomy using microcannulas, trocars, and 25-g instrumentation, without requiring sutures to close the sclerotomies. Subsequently, Claus Eckardt, MD, developed a similar technique, but with 23-g instrumentation.4 Currently, the 2 most popular TSV techniques are performed utilizing 25-g and 23-g instrumentation. The objective of this article is to review the current status of small-gauge vitreous surgery.

INSTRUMENTATION

Transconjunctival sutureless vitrectomy consists of a 23-g or 25-g microcannular system and a wide array of vitreoretinal instruments specifically designed for this operating system. The microcannula consists of a thin-walled tube 4 mm in length. A collar is present at the extraocular portion and can be grasped with a forceps to manipulate the microcannula. The insertion trocar has a sharp tip that forms a continuous bevel with the microcannula, allowing ease to entry through the conjunctiva into the eye (Fig. 1). The 25-g infusion cannula consists of a small tube that fits securely and can be directly inserted into the cannula in the inferotemporal quadrant. A wide array of vitreoretinal microsurgical instruments complying with the 25-g standards has been designed. These include vitreous cutters, illumination probes, intraocular forceps, microvitreoretinal blades, tissue manipulator, aspirating picks, aspirators, soft-tip cannulas, curved scissors, extendable curved picks, intraocular laser probes, and diathermy probes.

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

J. Fernando Arevalo, MD, FACS, practices ophthalmology at the Retina and Vitreous Service, Clinica Oftalmológica Centro Caracas, Venezuela. María H. Berrocal, MD, is professor of ophthalmology at University of Puerto Rico in San Juan. Dr. Berrocal reports minimal financial interest in Alcon. Dr. Arevalo has no financial interests to report. Dr. Arevalo can be reached at arevalojf2020@gmail.com.

SURGICAL TECHNIQUE

Small-gauge vitrectomy is usually performed with the patient under local anesthesia. General anesthesia is only used in selected cases. Topical anesthesia with lidocaine 2% can also be performed, and intravenous sedation may also be helpful in selected cases. After appropriate anesthesia, the operative field is prepared using antiseptic solutions. Preoperatively, the eyelash margins are scrubbed with povidine-iodine solution. 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 tunnel and then a perpendicular tunnel are made parallel to the limbus through the conjunctiva and sclera, thus creating a self-sealing wound (Figure 1). After insertion of the first microcannula, the intraocular portion of the infusion cannula is directly inserted into the external opening of the microcannula.5,6 The other 2 microcannulas are inserted in the superotemporal and superonasal quadrants for a 3-port vitrectomy. At the completion of surgery, the microcannulas are simply removed by grasping the collar and withdrawing, with assessment of intraocular pressure and wound sites for any possible leak.

The 23-g system is a variation of the 25-g TSV system. The 23-g vitreous cutters have been improved with the placement of the cutter opening nearer to the end of the probe, which allows for a closer vitreous shave. This increases the safety near the retina (Figure 2). At the end of the vitrectomy, an adequate gas/air tamponade should be considered to reduce the risk of postoperative leakage and hypotony. However, in some cases, leakage still can occur, even in an air- or gas-filled eye, and the sclerotomy site can be closed with a single 7-0 or 8-0 vycril suture. The microcannulas can be simply removed by grabbing the external collar with a forceps at the end of the procedure. The last microcannula to be removed should be the one with the infusion line (Figure 3). Postoperative subconjunctival injection of antibiotic and steroid solutions can and should be administered similarly to standard vitrectomy. Endophthalmitis is extremely uncommon following vitreous surgery but there is a theoretical concern that 25-g sutureless surgery may result in an increased risk of endophthalmitis.7,8

Figure 2. New 23-g and 25-g vitreous cutters have the placement of the cutter opening nearer to the end of the probe.

Figure 3. After the cannula withdrawal, a cotton tip can be used to misalign both orifices.

ADVANTAGES OF SMALL-GAUGE VITRECTOMY

In general, TSV seems to be particularly advantageous for procedures that do not require extensive intraocular tissue dissection or manipulation. Experience has shown that 25-g surgery is a good approach for vitreous hemorrhages, rhegmatogenous retinal detachment, proliferative vitreoretinopathy, giant retinal breaks, and cases in which we combine vitrectomy and phacoemulsification with intraocular lens implantation. It is applicable for diabetic traction retinal detachment with moderate amounts of epiretinal membranes as well. However, if use of scleral buckling or silicone oil tamponade is anticipated, the standard 20-g vitrectomy system is preferred as its full capability may be required in those cases (Figure 4). Even in complex cases where we need a variety of scissors and forceps and/or injection of silicone oil, 25-g or 23-g sclerotomies can be used for the infusion and illumination probe, and a 20-g sclerotomy can be performed for instruments and the injection or removal of silicone oil at the end of surgery. This enables the surgeon to use 20-g instruments and reduce the costs of replacing all 20-g instruments.9

Figure 4. Intraocular lens implantation during 25-g combined vitrectomy surgery.

Another advantage is apparent on pediatric cases. Typically, newborn and premature eyes are significantly smaller than adult eyes and the use of standard vitreoretinal instruments may bring some technical difficulties related to the ocular size.10 Using TSV, the intraocular instruments are more compatible with the smaller pediatric eyes and are effective in select cases of persistent fetal vasculature, retinopathy of prematurity, uveitis, and some uncomplicated tractional or rhegmatogenous retinal detachments. In addition, TSV offers benefits in selected vitreoretinal cases because it is transconjunctival, and TSV-based surgery has the potential to reduce operative duration for a variety of procedures. It also reduces postoperative inflammation at sclerotomy sites, thus reducing patient discomfort after surgery and hastening postoperative recovery. Moreover, it avoids induced astigmatic changes, with a more rapid visual recovery.11

DISADVANTAGES OF SMALL-GAUGE VITRECTOMY

The disadvantages of this system include its learning curve to achieve maximum efficiency. However, the curve is short enough for the adaptable surgeon. Due to its smaller fiber-optic size, illumination is also reduced in 25-g surgery. However, illumination with current systems is adequate in most cases. A noticeable difference of the 25-g instruments is their increased flexibility.

There are some potential complications specifically related to the 25-g system, the most obvious being hypotony and the possible increase of the incidence of endophthalmitis with 25-g.7,8 The incidence of these complications can be reduced by building a tunnel or angular incision in a different plane to the conjunctiva and doing a fluid-air exchange at the end of the surgery. It is important to note that the incidence of hypotony is higher in eyes that have been previously vitrectomized.

In terms of prophylaxis, all patients undergoing 25-g vitrectomy have the standard meticulous preparation with povidine-iodine as well as postoperative injection of subconjunctival antibiotics. In addition, patients are instructed to remove the eye patch on returning home from surgery and to start topical antibiotics every hour while awake postoperatively.

For the surgeon who routinely performs 20-g vitrectomy, the transition to 23-g is easier than to 25-g. Rigidity, flow, and aspiration of the vitreous cutter are similar to 20-g, and the lighting is comparable. The instruments have stiffness similar to 20-g. The construction of the incisions must be meticulous with tunnel or angular incisions to reduce complications.

HOW RECENT ADVANCES HAVE ADDRESSED EARLY SMALL-GAUGE CONCERNS

Instrument Rigidity. Rigidity of instruments is a problem with 25-g, as instruments are more pliable and can bend and break, and moving the globe around can be cumbersome. This is not a problem with 23-g, as rigidity is similar to 20-g (Figure 5). In addition, several companies are making new 25-g instruments more rigid and/or reducing the length to achieve the same purpose.

Figure 5. Intraoperative surgical photograph of a diabetic tractional retinal detachment treated with 23-g instrumentation.

Instrumentation Availability. Although initially instrumentation was limited to forceps in small gauge, at present a full armamentarium of instruments is available in small gauges, including extrusion cannulas for silicone oil injection and removal, scissors, dual-bore cannulas for per-fluorocarbon injection, diathermy, multidirectional laser probes, chandeliers, and 40-g cannulas for subretinal injections. In essence, at present the same range of instruments used in 20-g is available in 23- and 25-g, with the exception of a fragmatome. Nevertheless, several companies are working on developing a 23-g fragmatome to address dislocated nuclei.

Illumination. Since the number of light fibers is reduced, particularly in 25-g procedures, brighter light sources are needed such as the Photon (Synergetics Inc., O'Fallon, MO) and Xenon (Alcon Labs., Fort Worth, TX). Alcon's new Constellation system has a light that is much brighter than the actual Xenon, and Baush & Lomb (Rochester, NY) uses the Photon, so light is not an issue any longer.

Cutting Efficiency. Slow vitreous removal is a problem with 25-g at present but this challenge is addressed in the new Constellation machine. The new 25-g probe has a bigger opening and a longer duty cycle (amount of time the port is open). This allows for increased aspiration rate while having high-speed cutting rates. The 23-g system will benefit from the same duty cycle improvement. Plus the probe is different, and it does not have a spring mechanism to open it so it can stay open longer during each cut, allowing greater aspiration. Thus, the rapidity of vitreous removal with 23- and 25-g will be markedly improved. Cutting rates of up to 5000 cpm are available with Constellation, allowing for shaving of the vitreous base and safer vitrectomy even in detached retinas.

Wound Architecture. Achieving proper wound architecture is the most important aspect of small-gauge surgery, as complications of endophthalmitis and retinal breaks are associated with the wounds. Initially, wounds were made in 25-g procedures by direct entry, which is potentially a cause of hypotony and other potential problems, including increased endophthalmitis rates. Displacement of the conjunctiva and 2 plane wounds with fluid-air exchange at the end of the procedure allow for reduced wound leaks and less risk of endophthalmitis and hypotony. The DORC (Zuidland, The Netherlands) 23-g and the new Alcon 23-g TSV systems will have a flat-blade trocar system that will produce a slit wound, which closes better than the actual chevron wound made by the round trocar blade system. Wound construction in our view is the most important aspect of this surgery and the most important aspect of the learning curve, but if in doubt, just suture. Our threshold to suture a sclerotomy tends to be lower in complicated cases where silicone oil needs to be used.

Surgical Outcomes. Outcomes are excellent. Benefits include astigmatic neutral surgery, important in this age of refractive surgery, shortened time, and less inflammation and patient discomfort. We truly believe that the increased incidence of endophthalmitis is technique-dependent. With adequate preoperative povidone preparation, good wound construction in 2 steps with a partial or total fluid-air exchange at the end of the procedure, and subconjunctival antibiotics, the complications of hypotony and endophthalmitis can be kept to a minimum.

Learning Curve. The learning curve for wound construction and for 25-g at present is due to lack of rigidity. The TSV 23-g system has less of a learning curve, as instruments feel just like 20-g. In a nutshell, 23-g has been more user-friendly due to the light (comparable to 20-g), rigidity, and increased flow through the instruments (aspiration rates like 20-g) (Table 1). With the new improvements of the 25-g system, at least with the Constellation system, 25-g surgery will feel more like 23-g as rigidity, aspiration, and light will be increased significantly.

SUMMARY

Cataract surgery was revolutionized by the introduction of phacoemulsification and foldable IOLs. This technology enabled a reduction in the size of the incision and avoided the necessity of using sutures. This transition shortened surgical time, reduced complications, and increased the satisfaction and comfort of the patient.

The same transition is occurring in vitreous surgery. Both vitrectomy techniques, either 25-g or 23-g, have been improving with time, experience, and the introduction of better instrumentation. The surgical indications are expanding with experience and availability of new technology. To perform minimally invasive surgery has many advantages for both the surgeon and the patient. The reduced surgical time creates more efficiency and reduces complications and surgical trauma. The postsurgical recovery is more rapid, since there is less hassle-induced inflammation. Technological developments, more efficient vitreous cutters, and more varied 23-g and 25-g instruments have made small-gauge vitrectomy the gold standard. RP

REFERENCES

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Retinal Physician, Issue: January 2009