Since its introduction in 2002,1 microincision vitrectomy has been gaining in popularity amongst retinal surgeons for the surgical management of a wide variety of vitreoretinal disorders. MIVS allows for more efficient surgery, faster recovery times, reduced postoperative inflammation, and good visual outcomes compared to 20-ga. vitrectomy. The 2010 American Society of Retina Specialists’ Preferences and Trends survey reported that 72.5 percent of retinal surgeons have performed 23-ga. vitrectomy, while 60 percent have performed 25-ga. surgery.2 When performing MIVS it is important to be aware of the potential complications of this procedure, many of which are related to wound construction and closure. Here we review MIVS techniques to help avoid these wound complications.
Concerns About MIVS
Since MIVS is sutureless, there is a risk of hypotony, wound leak, choroidal hemorrhage and even endoph-thalmitis after surgery. Concerns about an increased risk of endophthalmitis after MIVS were voiced soon after the introduction of the technology. Two separate retrospective studies reported an increased rate of endophthalmitis after MIVS compared to 20-ga.3,4 However, other studies found no difference in the rates of endophthalmitis.5-8 A recently published meta-analysis reviewed the rates of endophthalmitis after MIVS.9 The authors reported rates of endophthalmitis after 20-ga.vitrectomy ranging from 0 percent to 0.07 percent compared to 0.03 percent to 0.84 percent following 25-ga. vitectomy. Partly because of the inherent heterogeneity of the individual studies and study populations in this meta-analysis, MIVS was not found to have a statistically significant higher rate of endophthalmitis than 20-ga. vitrectomy. To date, no prospective studies have addressed this issue.
There are several reasons why endophthalmitis may occur after MIVS, but most revolve around surgical technique especially wound construction and closure. Other factors that may play a role include post-surgery subconjunctival antibiotics, intraoperative use of corticosteroids, and whether or not a partial or complete air-fluid exchange was performed at the end of surgery. Incomplete removal of the peripheral vitreous skirt has also been hypothesized to result in bacterial in-growth,10 possibly predisposing the patient to endophthalmitis.
There are several steps that are important to follow to insure good wound construction during MIVS. First, the conjunctiva should be displaced using forceps, a foot-plate, or cotton-tipped applicator before inserting the trocar. Conjunctival displacement ensures that the conjunctival opening is away from the scleral incision. In case there is vitreous wick at the end of the case, conjunctival displacement minimizes the chance that the vitreous wick extends beyond the conjunctiva. Next, flatten the sclera before inserting the trocar. This ensures the longest possible chord length within the sclera, making it easier to close the wound when the cannulas are removed. Why is this? Since the sclera is curved, an incision through the sclera at a certain angle will give rise to a certain chord length. When the sclera is flattened and the same incision angle is used, the chord length will invariably be longer, making for better wound sealing. Various devices are commercially available to assist in flattening the sclera; these devices also assist in correct placement of the wound in the pars plana. Two such devices are the Dugel End Plate (Peregrine Surgical) and the toothed pressure plate (Dutch Ophthalmic USA).
Third, all MIVS incisions should be angled. Although vertical or straight incisions can be used especially with 25-ga. cannulas, angled or oblique incisions seal quicker, are more water-tight, and leak less. This is similar to the findings after clear corneal incisions for cataract surgery, where oblique or biplanar incisions have been shown to maintain a tighter seal under increasing intraocular pressure than perpendicular or vertical incisions.11 In one study looking at vertical versus angled sclerotomy incisions in New Zealand rabbit eyes, wound leakage was seen in 10.8 percent of straight incisions compared to 5.7 percent of angled incisions.12 Biplanar scleral wounds are difficult to create and result in inconsistent wound architecture.13 A single-plane oblique incision is, therefore, preferable and likely to help prevent wound complications. Using India ink, which mimics the size of bacteria, we have shown that straight incisions are more likely to have ink particles through the wound and into the eye regardless of gauge. However, oblique incisions did not have India ink within the wound or in the eye.14
Initial microsurgical sclerotomies were created using a needle-like blade. This was followed by a move to a beveled blade that resulted in improved wounds. Recently, a linear trocar blade has been released (EdgePlus, Alcon). Unlike the chevron incision of the beveled blade, linear incisions allow for better wound closure. An additional benefit of the new trocar blade is that less force is required to penetrate the sclera.
Closure of wounds is as important as wound construction. Adequate wound closure helps prevent postop wound leakage. The reported rates of postop hypotony with MIVS ranged from 3.8 to 16 percent.15-17 There are several steps that can help minimize this risk. Removing the cannula at an angle similar to the angle of entry helps maintain wound architecture. When removing the cannula, place a solid instrument into the wound first, like a light pipe, and then remove the cannula over this solid instrument. This is helpful to prevent suction and vitreous wick. Alternatively, the cannula can be removed with a plug in place.
Partial or complete air-fluid exchanges are another technique used by many surgeons to aid in sclerotomy closure. The different surface tension of air relative to fluid may play a role here, helping to seal the sclerotomy internally. Post-operative hypotony rates are less in eyes left with some degree of air fill relative to fluid-filled eyes.6,17 Improved sclerotomy site closure helps prevent entry of potential external fluids and contaminants, further decreasing the risk of endophthalmitis.
While their role in preventing endophthalmitis is unclear, postoperative subconjunctival antibiotics injected over the sclerotomy sites may help prevent vitreous wick by mechanically repositioning wick into the subconjunctival space.8 Note that this cannot be done with aminoglycoside antibiotics, which should never be injected over an open wound, and instead should be injected away from the wound to prevent intraocular migration of the antibiotic. Displacing the conjunctiva during wound construction, as above, will further help prevent vitreous wick extension past the conjunctiva.
MIVS has steadily gained popularity among vitreoretinal surgeons because it offers improved surgical efficiency, faster recovery times, reduced postoperative inflammation, and good visual outcomes. Avoiding complications such as wound leak, hypotony, choroidal detachment and endophthalmitis through optimal surgical technique is critical. Proper wound construction and closure are both necessary to ensure tight self-sealing wounds. Partial or complete air-fluid exchange, thorough peripheral vitrectomy, and subconjunctival antibiotics are supplemental steps that may also help ensure successful surgical outcomes.
Dr. Dhoot is a vitreoretinal fellow at the Cole Eye Institute, Cleveland Clinic. He has no financial interest in the subject matter. Dr. Kaiser is a professor of ophthalmology at the Cleveland Clinic Lerner College of Medicine and a vitreoretinal staff member of the Cole Eye Institute, Cleveland Clinic. Dr. Kaiser is a consultant for Alcon and Bausch + Lomb, and has received an unrestricted Lew R. Wasserman Award from Research to Prevent Blindness. Contact Dr. Kaiser at the Cole Eye Institute, 9500 Euclid Ave. Desk i3, Cleveland, OH, 44195. Phone: (216) 444-6702; fax: (216) 445-2226; e-mail:
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