Microincision Vitrectomy Surgery For Diabetic Retinopathy

Current strategies and future perspectives.

Taku Wakabayashi, MD • Yusuke Oshima, MD, PhD

Since Robert Machemer, MD, pioneered the closed eye pars plana vitrectomy in 1968, followed by the introduction of a divided system with a three-port intravitreal approach in 1972, remarkable advances in the surgical techniques and technologies of pars plana vitrectomy with the threeport, 20-gauge (0.8 mm) system have been made in recent decades.¹

These advances have currently expanded the surgical indications of pars plana vitrectomy for a variety of vitreoretinal pathologies. Of these, traction retinal detachment (TRD) and combined traction and rhegmatogenous retinal detachment are among the most challenging scenarios related to advanced proliferative diabetic retinopathy (PDR). These cases are often complex because of thin ischemic retina adherent with fibrovascular membranes. They have historically been treated using 20-gauge instrumentation with a conjunctival peritomy for scleral access.

In the mid-2000s, transconjunctival microincision vitrectomy surgery (MIVS) with 23-g (0.6 mm) or 25-g (0.5 mm) instrumentation began to find surgeons' favor and gradually took over the 20-g system that had been the standard for decades.^2,3 In contrast to the 20-g ports, the smaller-gauge ports of 23-g and 25-g can be created transconjunctivally without the need for suture placement to close when angled incisions are applied. The advantages of MIVS include decreased operating time, less postoperative discomfort and inflammation and less surgically induced corneal astigmatisms, with potentially more rapid visual recovery after surgery.⁴ As of today, the majority of retina surgeons prefer to use transconjunctival MIVS with 23-g or 25-g instrumentation as a standard treatment of choice for not only simple vitreoretinal pathologies but also complex cases, including complications associated with advanced PDR.

THEORETICAL ADVANTAGES OF TRANSCONJUNCTIVAL MIVS FOR DIABETIC RETINOPATHY

Diabetic vitrectomy using either 25-g or 23-g instrumentation was initially recommended only for treating simple cases, such as diabetic macular edema associated with vitreoretinal adhesion and nonclearing dense vitreous hemorrhage. This was because of the limited design and fragility of the first-generation small-gauge instruments. Thanks to the recent development of rigid instrumentation, bright light sources (xenon or mercury vapor) with chandelier endoillumination, and new-generation vitrectomy machines, the indications for MIVS have been expanded to include extensive fibrovascular proliferation with TRD or combined traction and rhegmatogenous retinal detachment.

Recent studies have proved transconjunctival MIVS to have several advantages over conventional 20-g instrumentations for diabetic vitrectomy. The conjunctiva-preserving nature of MIVS allows repeated vitrectomy or filtering surgery that may be needed in patients with diabetes complicated with neovascular glaucoma, even after vitrectomy. The lesser postoperative inflammation associated with MIVS may contribute to reducing the chance of encountering reproliferation after surgery.

TECHNICAL ADVANTAGES OF SMALL-GAUGE INSTRUMENTS FOR DIABETIC VITRECTOMY

The critical limitations that surgeons experienced with MIVS in its early development phase were poor illumination, the fragility of small-gauge instruments, and low flow rates through the small-gauge lumen. Recently, however, powerful light sources, such as xenon and mercury vapor light, can offer superb brightness for endoillumination, not only with a 25-g single-optic fiber but also with 27-g or 29-g dual fibers.^5-7 The vitreous cutter has been improved in rigidity and can remove dense vitreous hemorrhage and fibrovascular tissues with excellent flow and cutting efficiency. Currently, the new-generation vitrectomy machines provide a new ultra-high-speed cutter with the cutting rate reaching 5,000 cpm, with the duty cycle maintained at 50%. There is a trend in Japan toward increasing use of the new vitrectomy machines with 25-g instruments rather than 23-g ones, because the smaller cannulas minimize fluid loss, and smaller wound size lowers the chance of suture placement.

Because the ports of 25- and 23-g vitreous cutters are small and the distances from the ports to the tips are shorter than those of a conventional 20-g vitreous cutter, the cutters can serve as multifunctional tools during diabetic vitrectomy (Figure 1). The surgical techniques for removing diabetic fibrovascular membranes during MIVS differ from those in conventional 20-g vitrectomy. The port of the 23- or 25-g cutters can be inserted readily between the fibrovascular membrane and retina, allowing successful membrane segmentation, dissection and removal using a 25- or 23-g vitreous cutter, instead of vitreoretinal scissors in most cases (Figure 2).⁸ The thickened fibrovascular membranes and/or large blood clots can also be engaged and cut off by the small-gauge cutter, along with the reduced cut rates. The cutter can be used as forceps to lift membranes and detach the posterior hyaloid with the application of suction. The cutter can also work as buckflash needle to aspirate or blow out blood in a proportional reflux mode with the new-generation machines.

Figure 1. The port of a 23-g vitreous cutter is small, and the distance from the port to the tip is shorter than that of a conventional 20-g vitreous cutter.

Figure 2. The port of a 25-g vitreous cutter is put at the elevated edge of a fibrovascular membrane, allowing successful membrane segmentation, dissection and removal, instead of using vitreoretinal scissors.

Thanks to the adjunctive use of vascular endothelial growth factor inhibitors, uncontrolled bleeding has become much less of an issue. Finally, even if the bleeding occurs during membrane removal, it stops in most cases with direct compression of the bleeding point with the blunt tip of the cutter. This technique is feasible and much easier using small-gauge instruments. Reducing the use of cautery to achieve hemostasis may eliminate coagulative damage to normal retinal vessels and time wasted in instrument exchanges.These performances with 23-g or 25-g will not be as easy as with the less delicate 20-g vitreous cutters. The lower chance of instrument exchange with MIVS helps efficiently save operating time, even in challenging diabetic cases.

CHANDELIER ENDOILLUMINATION AND WIDE-ANGLE VIEWING SYSTEM INCREASE THE SAFETY AND EFFICIENCY OF MIVS FOR CHALLENGING CASES

The current widespread use of chandelier endoillumination, combined with a wide-angle viewing system, offers additional advantages to diabetic vitrectomy with small-gauge instrumentation (Figure 3). The diffuse illumination from the chandelier fiber provides an easy overview of the fundus with more thorough identification of the areas with fibrovascular traction, thereby reducing the chance of creating iatrogenic retinal breaks and the advancement of retinal detachment during surgery.

Figure 3. A 29-g dual chandelier endoillumination system combined with a wide-angle viewing system offers im proved ability to perform bimanual intraocular manipulation for diabetic vitrectomy with small-gauge instrumentation.

Under panoramic viewing, we no longer need to move the globe with small-gauge instruments to see the periphery; thus, there are far fewer feelings of frustration over the fragility of the small-gauge instruments during vitrectomy. Chandelier illumination allows the surgeon to have one hand free to manipulate and depress the globe. This may facilitate quicker, safer and more extensive removal of the peripheral vitreous and dense hemorrhages than scleral depression performed by a surgical assistant in diabetic vitrectomy, regardless of gauge size.

In addition, the largest advantage of chandelier endoillumination is the improved ability of performing bimanual intraocular manipulation for challenging cases. In patients with combined traction and rhegmatogenous retinal detachment with extensively adhesive fibrovascular membranes, we usually use a membrane forceps with a 25-g vitreous cutter to grasp and dissect the broad sheet of fibrovascular membranes. Under panoramic viewing, the membrane forceps allows us to engage easily the edge of the membrane to introduce more easily the blunt tip of the cutter into the tight spaces between the detached retina and adherent membranes (Figure 4). The combination of forceps with curved scissors can be another option for creating spaces between the fibrovascular membrane and its tightly adhered detached retina (Figure 5).

Figure 4. Bimanual dissection of a fibrovascular membrane. The membrane forceps allows us to engage easily to the edge of the membrane to introduce more easily the blunt tip of the cutter into the spaces between the detached retina and adherent membranes.

Figure 5. The combination of forceps with curved scissors can be another option for creating the spaces between the fibrovascular membrane and the detached retina when the membrane is tightly adhered to the detached retina.

Intraoperative bleeding is the most troublesome complication during diabetic vitrectomy. Even if prominent bleeding cannot be stopped with the above-described simple technique with a small-gauge cutter, it is now very easy to manage bimanually under chandelier illumination. This allows us to use a small-gauge back-flush needle or cutter in one hand and diathermy for hemostasis in the other.

After membrane dissection and removal, with bleeding controlled, endolaser panretinal photocoagulation up to the anterior retina can be applied using an extendable laser probe, without the need for scleral depression. Under wideangle viewing with diffuse chandelier illumination, retinal breaks, whether pre-existing or iatrogenic, can be easily identified and treated with laser photocoagulation, followed by fluid-air exchange. The glare from chandelier illumination after fluid-air exchange is the only drawback of chandelier illumination. However, this glare can be resolved by dimming the illumination or using a coaxially illuminated laser probe for endolaser photocoagulation.

SURGICAL OUTCOMES AND FUTURE PERSPECTIVES IN MIVS FOR DIABETIC RETINOPATHY

In a retrospective study,⁹ we found that MIVS in conjunction with preoperative bevacizumab shortened surgical time with less need to use scissors and fewer intraoperative bleeding-related complications, as compared with 20-g systems. We thus obtained favorable anatomic and visual recovery in patients with TRD resulting from severe PDR (Table 1). However, adequate wound construction and closure are very important for diabetic vitrectomy with smallgauge instruments.

If leakage is noted through a scleral wound, suture placement should be undertaken to obtain complete wound closure. Otherwise, postoperative hypotony will easily occur with postoperative bleeding and the potential risk of endophthalmitis in diabetic cases. In actuality, the incidence of bacterial endophthalmitis with MIVS was reported as higher than that with 20-g in the early phase of MIVS. These results were possibly associated with inadequate wound construction and closure. In a recent multicenter survey conducted by the Japan MIVS Study Group, with a retrospective review of the patients' charts for more than 43,000 pars plana vitrectomies, the incidence of postvitrectomy endophthalmitis was low, with no significant differences between MIVS (0.08%) and 20-g vitrectomy (0.03%).¹⁰ The Pan-American Collab o rative Study Group also recently reported similar results, with no differences in the rates of endophthalmitis between 23-g, 25-g, and 20-g vitrectomies.¹¹ To enhance the advan tages and eliminate the necessity of complex techniques for adequate wound closure and the potential complications associated with 23-g or 25-g MIVS, diabetic vitrectomy with 27-g instrument systems may be the least invasive style for next-generation MIVS in the very near future.¹²

SUMMARY

MIVS for PDR appears to simplify surgical procedures, reduce surgical time and lower the chances of encountering complications. MIVS may improve anatomical and visual outcomes, even in challenging cases. Currently, improved 25-g instrumentation with new-generation vitrectomy machines and illumination techniques offers the best surgical options. In the near future, much smaller-gauge systems will be available for even less invasive MIVS procedure. RP

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