8 Divide-and-Conquer Technique and Complications The term divide and conquer was first used to describe a technique for removal of the cataractous lens nucleus using phacoemulsification by Gimbel in 1986. When applied in a thoughtful and careful manner (while keeping in mind the anatomy of the cataractous lens), this technique, which involves dividing the hard lens nucleus in half and then typically into quarters, enables the safe and efficient disassembly and removal of the cataract while preparing for lens implant insertion. The goal of the surgeon is to remove the cataract and be left with an intact lens capsule that is well supported by the lenticular zonules and that is without compromise of the capsulorrhexis edge. This gives us the opportunity to place the lens implant in the ideal location—the capsular bag. Even if there is a defect of the capsulorrhexis edge, the lens can still be removed safely with the divide-and-conquer technique as long as the surgeon is careful in applying forces within the lens in such a way as to minimize the risk that a tear of the anterior capsule will extend into the posterior capsule, necessitating additional procedures such as anterior vitrectomy and alternate methods of placement and fixation of the implant.1–3 The first step in successful divide-and-conquer lens removal is the creation of an adequate capsulorrhexis. The capsulorrhexis should be no larger than 5.0 to 6.0 mm, as round as possible, and centered on the visual axis. Having the patient look at the microscope light will help the surgeon determine the visual axis. The visual axis is not usually perfectly centered in the cornea or within the edges of the pupil. If a round capsulorrhexis is nicely centered around the visual axis, the lens implant will usually also tend to be well centered on the visual axis when implanted in an intact capsular bag. Keeping the capsulorrhexis diameter at 5.0 to 6.0 mm leads to easier cortical removal from under the anterior capsule, including the portion under the incision. Problems with forming too large a capsulorrhexis include tears into the periphery, which occur when the leading edge of the tear encounters anterior zonules and then tears into the periphery. When the capsulorhexis tear is showing signs of extending into the periphery, it can often be salvaged with careful redirection of the tearing force being applied to the anterior capsule. Folding the edge of the capsule being removed and then directing the force applied with the forceps toward the center, or even backward from the center of the tear with a slow, steady movement, can often redirect the edge of the tear back toward the center of the lens. If the edge extends too far, and cannot be brought back, a scissors can be used to cut the edge of the capsule and the forceps used to restart the edge tear in the desired direction. This may help salvage the integrity of the capsule and prevent extension of the tear into the posterior capsule. As long as the posterior capsule is intact and there is no vitreous prolapse, a three-piece posterior chamber lens implant can usually be placed in the posterior chamber with the haptics in the ciliary sulcus without the need for additional means of fixation. If there is compromise of the posterior capsule, but an intact anterior capsule with intact zonular support remains, the three-piece implant can again be safely placed in the posterior chamber, with the haptics anterior to the capsule, and with no additional fixation after ensuring no vitreous is prolapsed anteriorly. This may necessitate anterior vitrectomy prior to placement. If sulcus fixation is necessary, a one-piece intraocular lens (IOL) with square edged haptics should definitely not be used. It can result in several problems, including secondary glaucoma from pigment loss from chafing of the posterior surface of the iris, also resulting in late transillumination defects, inflammation, and sometimes hemorrhage, which can be recurrent, from erosion of the haptics into blood vessels and decentering of the optic due to its short length. If the anterior capsule edge is not intact, divide-and-conquer dismantling of the nucleus can still be accomplished, as described below, but care should be taken not to apply forces in a direction that will promote the further extension of a tear beyond the equator of the capsule; the forces should be applied only perpendicular to the axis of the tear. It is useful to think about the substance of the crystalline lens as actually being composed of three portions, or structures, of differing consistency, each of which is handled in a different way. The innermost and hardest portion of the cataractous lens is the nucleus. Depending on the grade of nuclear sclerosis, this can be smaller in a softer, less advanced cataract or represent a much greater portion of the lens in advanced nuclear sclerosis. The nucleus is the main target of the divide-and-conquer technique, as it requires phacoemulsification to be dismantled and removed. The next portion of the lens is the epinucleus, which surrounds the nucleus. This layer is not as hard as the nucleus but is best removed through the larger port of the phaco tip with irrigation and aspiration (I/A). It requires little or no phacoemulsification energy to facilitate its removal. Finally, the outermost portion of the lens is composed of the newest and softest fibers of the lens cortex. These fibers can be removed without phaco power, most safely using the smooth-tipped I/A handpiece (Fig. 8.1). In performing the divide-and-conquer technique, the surgeon needs to be cognizant of how his tools work together to safely remove the cataract. To protect the cornea and to maintain stability of intraocular structures, the anterior chamber is filled with a dispersive viscoelastic. The viscoelastic can be washed out and aspirated prematurely if the surgeon is not careful about the application of aspiration (foot pedal position 2 of 3). The surgeon should try to avoid application of aspiration (determined by the preset aspiration rate and maximum vacuum generated) unless there is lenticular material next to or in the tip of either the phaco or I/A handpiece and should be ready to back off to position 1 (irrigation only) once a given piece has been aspirated. Despite these precautions, it is likely that most of the viscoelastic will be aspirated along with the lens segments in the case of a relatively hard nucleus. For this reason, it is helpful to stop and add viscoelastic to continue to protect the corneal endothelium and minimize postoperative corneal edema in cases with denser nuclei. Fig. 8.1 Surgical anatomy of the crystalline lens. The next tool vital to lens removal has already been mentioned: the phacoemulsification handpiece. Early phacoemulsification (phaco) was often technically very difficult, especially in the case of an advanced, hard, nuclear sclerotic cataract. Because of the back-and-forth vibration path of the original straight-tip needles, nuclear segments were often pushed away from the tip even when varying levels of vacuum and aspiration (e.g., off/on cycles, higher vacuum and aspiration rates) were used. Strategies involving intermittent aspiration and vacuum were developed to make it easier and safer to remove the nucleus and worked well except in particularly hard nuclei. The development of the Kelman-style tip, bent at the end, significantly improved the ability to remove a hard nucleus. Later, the introduction of nonlongitudinal tip movement, combined with a bent-tip phaco needle, greatly improved the surgeon’s ability to safely remove a hard nucleus without having to resort to a large-incision extracapsular procedure. When presented with an advanced, hard nuclear sclerotic cataract, the surgeon should not hesitate to stop periodically during removal to add additional viscoelastic while also using techniques to minimize turbulence and avoid other complications such as wound burns by using only brief bursts of phaco energy and only when lens pieces are engaged by the tip of the handpiece. The next important tool is the second instrument. There are many types of manipulators and “choppers” available. These are designed to help divide the nucleus and bring the pieces to the phaco tip. To protect the posterior capsule from rupture, the tip of the chopper should not be sharp. We prefer a Rosen-type chopper, which is shaped like a hockey stick on the end, with rounded outside edges and tip. It also has a wedge-shaped edge on the inside distal end that can be used to further divide the pieces of the nucleus when they are between the phaco tip and the Rosen chopper or other manipulator. It also is useful to help feed nuclear pieces to the tip of the phaco handpiece quickly and efficiently in the center of the pupil away from the lens capsule and iris. In this case the phaco tip also serves the additional function of an “anvil” against which the chopper can be used to break up large nuclear pieces with the inner wedge-shaped edge (Fig. 8.2). There are additional intraocular aids for safe and efficient nuclear extraction. The epinucleus and the cortex both provide a barrier between the nucleus and the lens capsule. If possible, the epinucleus should not be removed until the entire nuclear portion of the lens has been emulsified and aspirated. The chopper can be used to hold the softer epinucleus away from the phaco tip, and it in turn serves as a scaffold to hold the lens capsule away and safe from engagement and damage from the sharp phaco tip. Additionally, the lens capsule and iris can be used as a counterforce to divide pieces of a relatively soft nucleus with a gentle upward movement of the chopper through the nucleus toward the lens–iris diaphragm, after which the pieces can easily be brought into the center of the eye for phacoemulsification with minimal power and duration of phaco energy. The pieces of the nucleus itself also work as barriers to forward prolapse and rupture of the capsule. Removing the pieces in front of remaining portions of the nucleus, in addition to maintaining a light foot on the pedal, keeps things from happening too quickly in the eye. As the surgeon approaches the last pieces of the nucleus for removal, it is also a good idea to slow down a bit and utilize only short, light bursts of phaco energy. This helps prevent collapsing of the chamber and forward bowing of the capsule when the aspiration rate increases as the pieces are aspirated. The chopper/manipulator should also be kept behind the phaco tip to hold the capsule gently back as the epinucleus is removed and to prevent rapid increases in the aspiration rate from drawing the capsule into the tip. After capsulorrhexis, the first step to prepare for removal of the nucleus is adequate hydrodelineation/hydrodissection. Using a cannula placed under the anterior edge of the capsulorrhexis, balanced salt solution (BSS) is directed toward the equator of the lens. The best clue to loosening of the lens is visualization of a fluid wave crossing behind the nucleus. To ensure loosening of the lens in the capsule, it is helpful to attempt to achieve dissection with fluid at multiple levels in the lens, indicated by viewing multiple fluid waves. Multiple waves can be obtained by infusing fluid not only close to the anterior capsule but also at deeper levels to separate the nucleus from the epinucleus and also the outermost cortex. It can also be helpful to irrigate from multiple locations around the lens. Gentle movement of the cannula tip anteriorly and posteriorly can facilitate the separation of those layers. However, irrigation with the hydrodissection cannula should not be initiated until the cannula is in position. Problems that can occur if the fluid is infused with too much pressure include rupture of the capsule posteriorly or premature delivery of the nucleus and epinucleus into the anterior chamber when pushed forward by the hydraulic effect of the posteriorly directed fluid in the presence of a large capsulorrhexis. The goal is to achieve easy rotation of the nucleus with the tip of the cannula within the capsular bag to facilitate its removal and to minimize stress on the zonules, which can occur when the connections between the different layers of the lens are not disrupted adequately.
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