VITRECTOMY UPDATE
Are You Performing 25-Gauge Vitrectomy?
These systems offer better patient comfort and shorter opening and closure times.

There are advantages and inherent limitations to 25-gauge vitrectomies. By understanding which patients make the best candidates and how we can use the system effectively, we can improve our patients' comfort and reduce surgery time.

ABOUT 25-GAUGE SYSTEMS

The 25-gauge vitrectomy system has become a viable alternative to standard vitrectomy approaches. In appropriate cases, vitrectomies performed with a 25-gauge system result in less postoperative discomfort from incisions and sutures, less intraocular inflammation and shorter operating time. In some instances, visual recovery may be faster due to the absence of incision or suture-related ocular surface disturbances.

All 25-gauge systems have about a 23.5-gauge scleral opening. The wound is usually, but not always, self-sealing, often requiring a small amount of residual peripheral vitreous to plug the incision. Also, a small-caliber infusion cannula may not keep up with aspiration; it requires high infusion pressures to maintain flow. As a result, equilibrated intraocular pressure (IOP) is higher than the IOP when intraocular aspiration is occurring. We reduce the infusion pressure to 30 mm Hg to 40 mm Hg during membrane dissection or laser.

Recent advances in 25-gauge systems include lower trocar insertion forces; reduced vitrectomy probe flexure; tapered, self-retaining trocar plugs; forceps, picks, diathermy, scissors; and brighter illumination systems. In addition, the tapered trocar plugs (Alcon) allow scleral depression and indirect laser, since they are self retaining and do not pop out when the sclera is depressed. Stiffer 25-gauge vitrectomy probes allow the surgeon to remove more peripheral vitreous and gives more stable ductions of the probe tip when the eye is rotated.

CANDIDATES FOR 25-GAUGE VITRECTOMY

Who might benefit from 25-gauge vitrectomy? This is an important question because the procedure has both suitable and unsuitable candidates. Good candidates include patients with:

• Macular epiretinal membranes
• Macular holes
• Diabetic vitreous hemorrhage or limited traction retinal detachment with focal adhesions only
• Terson's syndrome
• Endophthalmitis
• Coexistent filtration bleb.

Due to the limitations of the instrumentation, a standard 20-gauge sclerotomy may be required for cases requiring larger bore instruments or numerous instrument exchanges. A procedure using only the 25-gauge cannula/trocar system is currently not well-suited for:

• Dislocated lens nuclear fragments
• Silicone oil injection
• Conditions in which moderate or severe bleeding may occur (such as in diabetics)
• Proliferative vitreoretinopathy
• Any long or complex vitrectomy case.

Some surgeons use 25-gauge vitrectomy for rhegmatogenous retinal detachment. Currently, my preference is to use a standard 20-gauge approach in these cases because of the need for a more thorough peripheral vitrectomy, and the more numerous instrument exchanges that can sometimes be required.

MANAGING PERIPHERAL VITREOUS

Vitreous always incarcerates in the wound, even when we perform a "complete" peripheral vitrectomy¹. With an endoscopic camera, Koch (unpublished data) showed that retention of a large skirt of peripheral vitreous results in retinal traction to the wound and that a more "complete" vitrectomy limits traction to the ciliary body region. Wound closure of the sclerotomy with the vitreous "plug" still occurs, but retinal traction is less likely. Thus, a thorough vitrectomy during 25-gauge surgery is probably a good idea. If a complete fluid-gas exchange is planned, it may also reduce the risk of postoperative retinal breaks from a large gas bubble exerting traction on the vitreous base.

Wound leaks are more common in reoperations because of preexisting vitreous contraction. You can reduce wound leaks by using sclerotomies as a fulcrum as opposed to stretching them. Charles (unpublished data) recommends partial fluid-air exchange to 50%. This may allow surface tension to functionally close very small leaks, allowing for spontaneous closure in the immediate postoperative period. If I get a wound leak, I place a single scleral suture with an 8-0 vicryl stitch transconjunctivally. If necessary, I open conjunctiva to make the wound closure if it cannot be visualized through the conjunctiva.

ADVANTAGES FOR THE FUTURE

In the future, steadily improving instrumentation will lead to increased use of 25-gauge systems. Better patient comfort, shorter opening and closure times, and possibly faster visual recovery from ocular surface disturbances are already exciting advantages of 25-gauge vitrectomy.

Dr. Han is the Jack A. and Elaine D. Klieger Professor of Ophthalmology and Director of Vitreoretinal Service at the Medical College of Wisconsin in Milwaukee.

References

1. Koch FH, Kreiger AE, Spitznas M, et al. Pars plana incisions of four patients: histopathology and electron microscopy. Br J Ophthalmol. 1995;79:486-493.