The bimanual vitrectomy technique is designed to take advantage of the fluidics that are best for vitrectomy, which may differ from the fluidics that are ideal for phacoemulsification and for I/A. When most cataract surgeons were trained to perform vitrectomy, they were taught that if they encountered a broken capsule, to immediately switch from using a phaco instrument to using a vitrectomy instrument with a coaxial irrigation system, which means that the fluid would be going around the vitrectomy needle. The bimanual technique tries to separate those two instruments so that the vitrectomy probe is inserted through a different incision than the irrigation probe (Figure 1).
It is important to have a protocol established in the event of a bimanual vitrectomy so that the staff knows what to do and is able to assemble the vitrectomy equipment quickly. One of the best preparations that I've seen is the vitrectomy kit advocated by Louis Nichamin, MD, from Brookville, Pennsylvania. In addition, being prepared for the event of a vitrectomy can have a certain calming effect on the surgery staff, which can translate to the patients.
Managing the Complication
One nice thing about bimanual vitrectomy is that it does not require a large financial outlay for equipment; surgeons are basically using the same equipment they already have available, only splitting up the two instruments for the procedure. There are two important points to remember. First, the surgeon should not extract the phaco tip as soon as he or she suspects a problem. Rather, it is best to continue irrigating because the tear can expand on its own if hypotony is present. Secondly, in order to continue to reduce the possibility of hypotony, the surgeon keeps his or her foot on the foot pedal and injects a viscoelastic through the side port incision before removing the phaco tip. This would replace the BSS with the viscoelastic as the surgeon removes the phaco instrument, and would subsequently maintain the stability of the anterior segment. The surgeon would then be able to reassess the situation.
Preparing for the Vitrectomy
If a vitrectomy is indicated, the surgeon must decide whether the size of the existing side port incision is adequate to accommodate an irrigator and/or a vitector—often, it is too small. For this reason, one of the items surgeons should include in their vitrectomy kit is an MVR blade, or a 15º blade—something that could expand an incision size just enough to allow for an irrigator or vitrector. The surgeon must then make a new incision opposite the side port. Before doing so, however, it is often necessary to hydrate the phaco wound so that other incisions can be made without collapsing the anterior chamber.
In order to perform the vitrectomy portion of the procedure, the surgeon must abandon the phaco wound and depend on the two side port incisions. The next step depends on where the surgeon is in removing the lens. If the circumstance requires a phaco glide in order to remove any residual chunks of nucleus, the surgeon should use a phaco glide (Bobbitt; BD Ophthalmic Systems, Waltham, Massachusetts) that can be placed through the existing phaco incision. However, the surgeon may have to expand the incision from 3.0 to 3.2 mm before inserting the phaco glide, assuming that there is no significant amount of vitreous in the anterior chamber. If there is vitreous in the anterior chamber, then the surgeon must address that before removing the residual nuclear material (the vitreous material may be surrounding the nuclear material). It is best not to phaco the vitreous, so to speak. If there are remaining fragments of nucleus in the anterior chamber, they are best removed by inserting a phaco glide beneath the nuclear material and then carefully removing the remaining nuclear material under the viscoelastic while trying to avoid engaging vitreous material. At this point, the surgeon should lower the irrigation bottle to reduce intraocular pressure so as to prevent the rent from expanding in the capsule.
Removing Cortex
After the nucleus is removed, the rent in the posterior capsule still remains. The next step is to remove the cortex and ready the posterior chamber for implanting a posterior chamber lens. The surgeon injects viscoelastic through the sideport incision before removing the phaco tip, and then extracts the lens glide and proceeds with bimanual vitrectomy. The vacuum rates and the cutting rate of the vitrector will depend on the tissues being removed. It may be easier to aspirate the cortex by switching the two hand pieces so that the vitrectomy hand piece is in the fellow hand where it can more easily attract material on the other side of the eye.
Once the vitreous is removed, it is possible to remove any remaining cortex with the same instrument by turning it on I/A mode, and the surgeon can switch back and forth from I/A to vitrectomy as indicated. In some cases, it is best to perform a posterior sclerotomy for posterior vitreous aspiration by using the same irrigating device as for a standard vitrectomy, and introducing the vitrector probe through the sclera. Again, the surgeon first injects viscoelastic into the anterior chamber before performing the posterior sclerotom. The surgeon then makes a conjunctival peritomy either in the superior or inferior temporal quadrant, and measures 3.5 mm from the limbus with a caliper to make a sclerotomy incision with an MVR blade. Cautery can be performed prior to placing the blade. The surgeon then carefully places the blade through the pars plana to allow for the vitrector through this separate incision. Using this method can prevent the vitreous from continually leaking into the anterior chamber—I sometimes prefer it, depending on the ocular conditions and how much vitreous is present in the anterior chamber.
Once the surgeon performs the posterior vitrectomy, he or she closes the sclerotomy with a nylon suture in an X-fashion. The peritomy can also be closed with a 6–0 plain suture, which allows for nice cosmetic results. This technique may seem a little foreign to some surgeons because most cataract surgeons are not used to making sclerotomy incisions, but I would say that in terms of standard of care, this technique is in the best interest of the patient.
A Better Choice for patients
Using this bimanual system avoids hydrating the vitreous, which tends to increase the difficulty of performing the procedure. There is a lot of interest in this right now, and many questions have been raised about bimanual vitrectomy at several recent meetings. One of the challenges in performing this procedure is finding a good irrigation tip; it is not uncommon to find that the irrigation is not adequate in these procedures. One company that does supply a good irrigation tip is Duckworth & Kent (Hertfordshire, England). The irrigation hand piece of their bimanual I/A system can be coupled with a vitrectomy system to allow the surgeon adequate irrigation for bimanual vitrectomy.
