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  • Vitrectomy for the Anterior Segment Surgeon

    Cataract/Anterior Segment
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    Recent refinements in phaco and IOL surgery have led to a myriad of patient benefits including the reduction of pre-existing refractive error, improvement in the quality of vision through the use of aspheric implants and most recently by the introduction of new multifocal and pseudo-accommodating lenses.1 At the heart of these advances, however, is the remarkable reproducibility of the procedure and amazingly low rate of complications.

    Nonetheless, on occasion, be it due to "pilot error" or unavoidable ocular characteristics and anatomy, problems will be encountered. Arguably, the single most significant complication still faced by today's phaco surgeon continues to be rupture of the posterior capsule and vitreous loss.2 Fortunately, in the setting of small-incision surgery, if the surgeon adheres to certain fundamental principles and employs proper instrumentation and surgical technique, the vast majority of these complicated eyes will enjoy an outcome that differs little from that of an uncomplicated case.3

    The key components to the management of this condition include quick recognition of the problem, avoidance of hypotony, and maintenance of a truly closed-chamber environment. These are predicated on the use of watertight incisions. As such, a much lower rate and volume of infusion may be used, thereby reducing intraocular turbulence. To further enhance control of the intraocular environment and reduce vitreoretinal traction, a separated or bimanual vitrectomy should be used. In this way, the location and vector force of the infusion is displaced from the point where one is attempting to delicately remove vitreous. A reasonable approach is to place both instruments through limbal incisions (Figure 1).

    Skip Nichamin; CI Module 4 2008
    Figure 1. Bimanual vitrectomy performed through limbal incisions.

    The author would submit, however, that a much more efficient and potentially safer approach is to perform the vitrectomy through a pars plana incision (Figure 2). This allows the surgeon to "pull down" prolapsed vitreous from the anterior chamber, markedly reducing the amount of vitreous that is removed from the eye. When working from the limbus and bringing vitreous up, it is much more difficult to find an "end point," and one often unintentionally removes a considerable portion of the vitreous body and must then deal with a hypotonus eye.

    Skip Nichamin, CI 2008 mod 4
    Figure 2. Bimanual vitrectomy with vitreous cutter placed through the pars plana.

    Another significant advantage to working through a pars plana incision is the enhanced access one has to residual lens material. Cortex, epinucleus, and even medium density nuclear material may be removed with the vitrector by gradually increasing vacuum and reducing the cutting rate. When addressing vitreous, the highest cut rate is used with the lowest possible vacuum that will permit vitreous aspiration. In this way, a more complete "clean-up" may be achieved, reducing secondary complications such as increased intraocular pressure (IOP), inflammation, and cystoid macular edema (CME).

    • It goes without saying that care and effort must be directed toward the learning and acquisition of any new surgical technique, but in reality the pars plana approach is quite straightforward. Typically, one first takes down the conjunctiva and applies light cautery at the site of the intended sclerotomy, although some surgeons incise directly through the conjunctiva.
    • The cardinal meridia should be avoided due to increased vascularity.
    • Given that the posterior capsule is open, infusion may be placed through a limbal paracentesis incision or a second pars incision. A useful infusion cannula for this technique is available from Stortz (Figure 3).
    • The clock hour of the vitrectomy incision should be selected to best access remaining lens material.
    • The pars plana is anatomically located between 3.0 and 4.0 mm posterior to the limbus, so most commonly the incision is placed 3.5 mm from the limbus, though an adjustment may be made for unusual axial lengths.
    • Depending on surgeon preference, wounds are created to accommodate either 19- or 20-gauge instruments. A dedicated disposable microvitreoretinal (MVR) blade should be used to create properly sized and therefore watertight incisions for both pars plana and limbal incisions.
    • In creating the pars incision, the MVR blade is held perpendicularly to the scleral surface and usually oriented in a limbal-parallel fashion. The blade is directed toward the center of the globe with a simple in-and-out motion.

    Skip Nichamin, CI mod 4 '08
    Figure 3. Infusion Cannula #E4421-S21 (Stortz).

    As mentioned, when removing vitreous, the highest possible cut rate is used along with the lowest possible vacuum setting. One can titrate up with vacuum and down on the cutting rate to remove remaining lens material. Attention is paid to preserve as much capsule as possible, especially the anterior capsular rim, to facilitate implant placement. Infusion is kept at a minimum-only enough to maintain adequate intraocular pressure. Generous use of appropriate (often several different) viscoelastic agents aids in volume maintenance, further decreasing the need for infusion. A dispersive agent works best to tamponade the hyaloid face, and a more cohesive viscoelastic is used to maintain space.

    Care should be taken in both cleaning and closing the pars plana incision. Choices for suture closure would include 9-0 nylon or 8-0 vicryl. Recently, 25-gauge instrumentation has become available that, in some settings, may allow for sutureless surgery. Insertion, however, requires a firm globe. These instruments can still be used in a complicated setting by first creating small incisions with a sharp blade as opposed to the usual trochar system. One downside to 25-gauge instruments is their lack of tensile rigidity, and therefore, an ability to manipulate the position of the globe.

    Prudence would dictate that a pars plana vitrectomy should not be performed for the first time while under duress during a live complication, but rather carefully studied and first practiced in a lab setting. By abiding to these surgical principles, the author firmly believes that a salutary outcome may be obtained despite the occurrence of what remains one of the most troublesome complications of cataract surgery.

    References

    1. Nichamin LD. Mastering Refractive IOLs: The Art and Science. Thorofare, NJ: SLACK Incorporated; 2008.
    2. Wu MC, Bhandari A. Managing broken capsule. Curr Opin Ophthalmol. 2008; 19(1):36-40.
    3. Nichamin LD. Posterior capsule rupture and vitreous loss: advanced approaches. In: Chang DF, ed. Phaco Chop: Mastering Techniques, Optimizing Technology and Avoiding Complications. Thorofare, NJ: SLACK Incorporated; 2004:199-202.

    Author Disclosure

    Dr. Nichamin has no financial relationship with the manufacturer of any product discussed in this article or with the manufacturer of any competing product.