Microincision vitrectomy surgery has rapidly gained increased popularity. It is associated with many advantages, but there have been some reports of disadvantages such as a significantly higher incidence of endophthalmitis postoperatively, though more recent reports do not substantiate this conclusion. Advances in the technology likely will facilitate safer and more efficient vitrectomy.
"The adoption of microincisional surgery, that is, of 23-gauge and 25-gauge vitrectomy surgery, has been remarkably rapid," said Dr. Dugel, managing partner, Retinal Consultants of Arizona, Phoenix. "The recent survey of the American Society of Cataract and Refractive Surgery showed that 71% of respondents will use microincisional vitrectomy over the next 5 years. Many case series reported worldwide have shown increased patient satisfaction and decreased surgical time."
Despite this, however, and other advantages associated with MIVS, such as the smaller incision size, reduced conjunctival scarring, and increased patient comfort, the rate of endophthalmitis has been reported to have increased by 12-fold after 25-gauge vitrectomy over that associated with conventional vitrectomy, an increase that is both statistically significant and "sobering," according to Dr. Dugel. He is also in private practice in Phoenix.
Possible mechanisms for the increased risk, he pointed out, were discussed in a paper by Jay Stewart, MD, and co-workers published in Retina (2008;28:553-557), in which the investigators cited how India ink used to simulate bacterial contamination traveled through a poorly constructed wound. This study followed one in which Peter McDonnell, MD, and associates showed how hypotony with a clear corneal incision surgery can cause internal and external wound gape that creates a suction effect that allows microbial contamination; the investigators pointed to this as the mechanism for increased infection rates in clear corneal incision surgery, Dr. Dugel said.
Following this, Omesh Gupta, MD, and colleagues conducted the Microincision Pars Plana Vitrectomy Study, reported in the American Journal of Ophthalmology (2008;146:193-197), which was designed to determine the short-term safety and efficacy of a 23-gauge MIVS system. In this nonrandomized, retrospective surgical case series, 128 consecutive patients underwent pars plana vitrectomy to treat a variety of retinal diseases such as epiretinal membrane, vitreous hemorrhage, macular hole, and retinal detachment. Dr. Dugel said that the wound construction was strictly controlled; the primary outcome measures included visual acuity, IOP, and intraoperative and postoperative complications, with particular attention to hypotony and wound leaks. The study did not have sufficient power to detect a difference in the rate of endophthalmitis.
"The results indicated that the visual recovery was remarkably fast," he said. "Within 7 days after surgery, almost all patients had recovered their baseline visual acuity level or had achieved improved vision. The recovery of IOP was likewise remarkably fast."
Interestingly, no cases of endophthalmitis developed. Six cases of hypotony, defined as IOP less than 6 mm Hg, developed by day 1 postoperatively; by day 7 postoperatively five of the six cases resolved spontaneously.
"The study had a short follow-up, but it showed a remarkable improvement in the visual acuity as well as stable IOP and a low incidence of hypotony that resolved spontaneously," Dr. Dugel said.
The issue of wound construction and its relationship to the incidence of endophthalmitis has received attention. A linear blade, designed by Carl Awh, MD, and Stan Rizzo, MD, should facilitate safer wound construction, according to Dr. Dugel.
In addition, newer vitrectomy machines, such as a proprietary system featuring efficiency components (Constellation, Alcon), that will allow better control of the cut rate, the vacuum, and the duty cycle also are expected to facilitate safer and more efficient surgery.
"Safety is related to vitreous traction that in turn is related to the length of collagen pull. This is described in the formula: the length of collagen pull equals the flow rate divided by the lumen area divided by the cut rate," he said.
"Newer instruments will allow transformation of the relatively simple equation into a triad of surgeon-controlled parameters that will allow the highest cut rate, the lowest vacuum, and a closed bias duty cycle," Dr. Dugel continued. "The movement of the port closer to the tip of the probe (port optimization) will allow for more effective vitrectomy using the least flow possible to get the job safely done.
"Microincisional surgery is the wave of the future. Microincisional surgery has revolutionized retinal surgery and will continue to do so," he concluded. "Concerns regarding wound closure and endophthalmitis need to be scientifically and critically addressed. Major technologic advances will allow surgeons to perform safer and more efficient vitrectomies."