Roger F. Steinert, MD
Contents
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Evolution of Phaco Chop |
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Detailed Technique of Phaco Chop |
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Chopping Instruments |
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The Phacoemulsification Needle |
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Transition to Phaco Chop |
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Complications of Phaco Chop |
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Conclusion |
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CHAPTER HIGHLIGHTS |
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In 1993, Kunihiro Nagahara introduced the concept of a new technique for nuclear disassembly during phacoemulsification. His insight was that natural cleavage planes existed in the nucleus that had not been used previously (Figure 17-1A). By impaling the nucleus with the phacoemulsification tip, and thereby stabilizing it, the second “chopping” instrument could be pulled from the equatorial side of the outer nucleus toward the center. The nucleus was split readily by the chopping instrument, taking advantage of these natural cleavage planes. Nagahara made an analogy to the technique of chopping or, more accurately, splitting a log of wood with a wedge, taking advantage of the wood's grain, or cleavage planes (Figure 17-1B).
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Figure 17-1 A, Nagahara's insight was to split the nucleus along its natural cleavage planes. B, The principle of chopping is the same as using a wedge to split a log along its natural planes. |
Evolution of phaco chop
Stop and chop
Several surgeons were stimulated by Nagahara's method and evolved techniques in an effort to improve on the reliability and repeatability of phaco chop. Paul Koch found that the initial chop, intended to bisect the nucleus, was the most difficult. He reverted to creating an initial deep trough with the phaco tip and then cracking the trough with lateral pressure from the phaco tip and a second instrument, identical to the beginning of the quadrant cracking technique. At this point, however, Koch stopped the quadrant cracking approach and then began chopping the remaining pieces of nucleus; he labeled this technique as “stop and chop.”[1] This technique (Figure 17-2) remains popular with many surgeons, and it is an important transition for almost anyone learning phaco chop because it eliminates the most difficult chopping step: the initial chop.
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Figure 17-2 A, Paul Koch's “stop and chop” technique begins with a groove and cracking of the nucleus into two halves, identical to the start of “divide and conquer” nuclear fracture. B, Nucleus is rotated 1 to 2 clock hours, and the surgeon stops the “divide and conquer” technique and begins to “chop.” |
Chop and debulk
To maximize the safety of the corneal endothelium and be able to continue to perform phacoemulsification in the posterior chamber and iris plane, the surgeon should create some central space to allow the chopping technique to be used in disassembling the nucleus posterior to the iris. Similar to a multipiece jigsaw puzzle, taking pieces apart becomes easier once the initial piece is removed. In addition, the majority of ultrasound power is used to phacoemulsify the central hard nucleus, not the periphery. Steinert[2] described a technique that began identically to Nagahara's with an initial phaco chop to bisect the nucleus. Although perhaps more difficult to master, this initial chop is a more efficient maneuver than the creation of a trough and then splitting it, as in the stop and chop technique. After the initial chop, however, the central hard nucleus is emulsified along the fault line of the initial crack before proceeding to chopping further pieces of nuclei. In softer nuclei, very little central material is removed at this step. In harder, larger nuclei, more central nucleus can be removed at this step; in very advanced cataracts, the center is bowled out to the midperiphery before beginning to chop further (Figure 17-3).
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Figure 17-3 A, Full phaco chop approach uses the chopper to split the nucleus into two halves. B, Space is created, and the hardest central portion of the nucleus is removed, leaving enough peripheral nucleus to gain purchase by the phaco tip with a small amount of ultrasound and high vacuum. C,nucleus is rotated clockwise (for a right-handed surgeon; a left-handed surgeon rotates counterclockwise and performs mirror-image maneuvers), and pie-shaped wedges are split off and removed with short bursts of ultrasound. |
Circumferential sequential disassembly
Both Koch and Steinert found that the chop technique was better applied as a method of the progressive chopping of small wedges in a circumferential direction, rather than the chopping of four full quadrants as originally described by Nagahara. The reason for this is that the progressive circumferential chopping of small wedges results in only one small piece being removed at any given time. Because of the bulk, the large nuclear pieces remain stable within the posterior capsular sac. Therefore, control of the phacoemulsification process is enhanced.
Howard Gimbel[3] earlier described several techniques of nuclear fracture whose principles have been incorporated in phaco chop as it has evolved. Gimbel pointed out the importance of debulking the central nucleus, forming a narrow trough for softer nuclei and a larger crater for hard nuclei. In addition, he demonstrated the ability to break off pieces of the peripheral nucleus with lateral separation movements after engaging them with the phacoemulsification tip, proceeding in a circumferential direction. Gimbel called this technique “nucleofractis.” In essence, a phaco chop is the nucleofractis technique, greatly facilitated by the second “chopping” instrument instead of relying on forceful lateral movements of the phacoemulsification tip.
High-vacuum phaco chop
In addition to his incorporation of central debulking techniques and use of progressive circumferential chopping steps, Steinert recognized that using high vacuum during chopping further improves nuclear control and reduces the total ultrasound energy required. High vacuum allows the surgeon to grasp and hold the nuclear wedges and draw them toward the central zone of safety before completing the emulsification. Moreover, the manual energy input from the phaco chop, combined with the energy input from the high vacuum, reduces the total amount of ultrasonic energy required. Overall, the technique appears to be safer and more controlled. Because of its efficiency, the nuclear disassembly step of phacoemulsification cataract surgery is generally substantially faster than alternative techniques such as quadrant cracking.[4–6]
Phaco quick chop (“vertical phaco chop”)
Vladimir Pfeifer of Slovenia is generally credited for originating the fundamental concept of vertical forces that also fragment the nucleus. This technique has been developed and taught by David Dillman and Louis Nichamin as “phaco quick chop.” Nagahara's fundamental concept is to stabilize the nucleus with the phaco tip and then pull the chopping instrument in the horizontal plane from the equator toward the center. Vertical chop differs by embedding the phaco tip deeply into the nucleus and then impaling a sharp-tipped chopping instrument into the anterior nucleus in front and adjacent to the phaco tip. The chopper pushes downward sharply while the phaco tip lifts upward (Figure 17-4A). Each instrument moves about one-half of the total amount of vertical separation needed to generate a fissure. As soon as the vertical (anteroposterior) split begins to develop, the two instruments also spread horizontally slightly to complete the cleavage of the two sections (Figure 17-4B). Vertical chop is then continued to break off smaller sections of nucleus for emulsification, progressing circumferentially, as in the technique described earlier (Figures 17-4C and D).
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Figure 17-4 A, In vertical phaco chop (“phaco quick chop”), the deeply buried phaco tip is lifted up while a sharp-tipped chopper presses downward. B, Once the endonucleus starts to split, the instruments are separated slightly laterally as well to enhance full cleavage of the two sections of nucleus.C, and D, Nucleus is rotated, and the vertical chop maneuver is repeated to create smaller nuclear fragments that can be removed with ultrasound and aspiration. (C, Side view; D, surgeon's view.) |
The principal advantage of vertical chopping is the elimination of the need to pass the chopper under the anterior capsule out to the equator of the nucleus. Because neither the anterior capsule edge nor the equator can always be seen, some surgeons dislike the necessity of relying on tactile feedback and judgment of distances under the iris. On the other hand, vertical chopping works best in moderate-density nuclei. It often fails in softer nuclei, where the phaco tip and chopper pull through the nucleus, or in hard nuclei, where so much force is required that, when cleavage does occur, the abrupt movement threatens the integrity of the posterior capsule and/or zonules.
The “complete” phaco surgeon should be comfortable with both horizontal and vertical chopping maneuvers, as each has its place.
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Detailed technique of phaco chop
The basic concept of horizontal phaco chop, as it is usually practiced, is illustrated in Figure 17-5. The nucleus is stabilized with the phacoemulsification tip, which is impaled with moderate vacuum (typically 50–80mmHg) and low ultrasonic power, in a position near the center, but off-center by about 1mm towards the incision. The irrigation sleeve should be retracted more than is customary for divide and conquer nuclear fracture, in order to permit the phaco tip to advance to the depth of midnucleus (1.5–2mm). While impaling the nucleus, the phaco handpiece is markedly tipped in the vertical direction, as if aiming for the optic disc. The chopping instrument is passed through a paracentesis that is about 1½ clock hours away from the incision. The chopper can assist the proper location of the impaling of the phaco tip by pressing lightly on the nuclear surface and shifting the nucleus gently (about 1mm) away from the incision.
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Figure 17-5 A, With a widely dilated pupil and small-to-moderate-sized endonucleus, hydrodelineation will create a separation of the endonucleus from the epinucleus, seen as a golden ring or a black ring, depending on the illumination and red reflex. B, The surgeon directs the chopper under the anterior capsule and down into the ring. C, If the pupillary dilation is smaller than the size of the endonucleus, the surgeon must advance the tip of the chopper without being able to see the equator. The surgeon, with experience, will have a good sense of how much the chopper must be advanced to reach the zone of the ring and will be able to feel when the chopper tip reaches this point and is able to drop. D, The phaco tip impales the nucleus and is advanced to the depth of the midnucleus. The chopper pulls toward the phaco tip, splitting the nucleus in half. E, The central, hardest portion of the nucleus is removed. The harder the nucleus, the larger the area sculpted. Enough nuclear material must remain that the phaco tip can engage and become occluded on the periphery, while the chopper breaks off pie-shaped wedges for removal (F). |
The chopper is advanced under the anterior capsule until it can pass around the equator of the nucleus at the nucleus–epinucleus border, about 180° opposite the paracentesis. If the nuclear equatorial border can be visualized as either a “golden ring” (smaller nucleus) or a dark ring (larger nucleus) as a result of effective hydrodelineation, the chopper can be placed into this ring under direct visualization (see Figures 17-5A and B). If the nucleus is very large or the pupil does not adequately dilate, the surgeon will nevertheless be able to feel the abrupt change as the chopper tip passes from the hard nucleus to the relatively soft epinucleus. The chopping instrument will shift posteriorly by at least 1mm when this border is encountered (see Figure 17-5C).
The chopping instrument is then drawn across the center of the nucleus, moving from opposite the paracentesis in the direction of the paracentesis (see Figure 17-5D). Once the center of the nucleus is approached or fully transected, the nucleus fractures readily. To successfully split the nucleus, the chopper tip should be at least at half depth in the nucleus anteroposteriorly, as well as chopping across half of the nucleus radially. The impaled phaco tip will also have weakened the central nucleus and contributes to a successful chopping hemisection of the nucleus. This basic chop maneuver works well in nuclei ranging from low to high density.
The next step is to debulk the center of the nucleus. If the lens has mild-to-moderate density, the debulking is restricted to a zone no larger than a conventional trough. In that manner, the peripheral nuclear pieces retain enough integrity for the circumferential peripheral chopping maneuvers. On the other hand, if the lens is firmer, a crater or bowl is phacoemulsified to further debulk the center (see Figure 17-5E). In all cases, it is important to leave sufficient firm peripheral nuclear material to allow the nucleus to be safely engaged and held by the phaco tip during the progressive circumferential chopping.
Circumferential peripheral nuclear chopping then proceeds. For a right-handed surgeon, the heminucleus being chopped should be located to the surgeon's left, and the nucleus rotated in a clockwise direction. The phacoemulsification tip engages the leading edge of the heminucleus, and then the chopper transects the peripheral wedge, leaving the wedge engaged in the phacoemulsification tip (see Figure 17-5F). For a left-handed surgeon, the maneuvers are performed in a mirror-image fashion, with the direction of the nuclear rotation counterclockwise.
The size of the pie-shaped wedges of nucleus to be chopped depends on the density of the nucleus. The harder the nucleus, the smaller the fragment should be. The pie-shaped pieces can be created in virtually any size. For 2+ nuclear density, only three wedges should be created in each heminucleus; for a very dense 4+ nucleus, six to eight wedges should be created. If a piece is chopped and appears to be too large, it can be chopped once again. The goal is to create “bite-sized” pieces that are appropriate for the phacoemulsification tip.
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Chopping instruments
A large number of chopping instruments have been developed. Although this can perplex a novice, the variety of chopping instruments gives the surgeon many options with which to solve technical problems. Once the surgeon becomes proficient with a specific design, however, there is little value in further change.
Original chopping instruments were fashioned out of Sinskey hooks, with the tip rebent to a length of approximately 1.5mm. This type of instrument is generally inadvisable, however. The very-fine-gauge wire of a Sinskey hook can cut through a nucleus, but the absence of any bulk in the wire prevents the full realization of the potential of phaco chop. Recall that Nagahara's fundamental principle was that the chopping instrument should act like a wedge. Most models of chopping instruments have a thicker gauge than the Sinskey hook, often with sharp internal cutting surfaces, thus obtaining the desired wedge-splitting effect.
Sharp cutting surfaces in chopping instruments may be on only one surface, generally directed along the shaft of the chopper, or two or three surfaces may be sharpened, allowing more successful “lateral chopping” maneuvers. The shaft may also be angled for right- or left-hand approaches.
Steinert designed a curved chopping instrument (Figure 17-6; Rhein Medical, Tampa, Fla.) to incorporate all of these principles and also to facilitate keeping the chopper engaged in the center of the nucleus. The curved distal element acts in the same manner as a cat's claw or a farmer's hoe. The chopper naturally engages the curved equator of the nucleus, which can be felt by the surgeon. The claw configuration then keeps the chopper engaged deeply into the nucleus, avoiding the tendency for straight choppers to rise up and out of the nucleus as they pass toward the center.
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Figure 17-6 Steinert double-ended claw chopper. One end is 1.5mm in length, for chopping most nuclei; the other end is 1.75mm length, for chopping large, hard nuclei. (Courtesy Rhein Medical.) |
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The phacoemulsification needle
For many years, phacoemulsification instrument manufacturers progressively increased the angle of the phacoemulsification tip to gain increased “cutting power.” The phaco chop technique has reversed that trend, however. The greater the angle of the phacoemulsification tip, the larger the cross-sectional area of the phaco tip port. With a greater tip angle, more of the tip must be buried into the nuclear fragment to obtain occlusion, which is necessary for stabilizing the nucleus before the initial phaco chop and for engaging and controlling the peripheral circumferential wedges. In fact, Nagahara returned to a true 0° phacoemulsification tip. The 0° tip greatly facilitates obtaining occlusion of the circumferential nuclear fragments and their manipulation.
Why does this not reduce ultrasound power unacceptably?
Phacoemulsification handpieces have greatly increased in power over recent years. More importantly, however, better understanding of ultrasonics had led to manipulations in the configuration of the phacoemulsification tip to improve the efficiency of ultrasonification of the nucleus through the creation of cavitation. For example, Nagahara's 0° tip has an internal bevel that vastly improves ultrasound power through internal cavitation, as well as reducing the cross-sectional area of the phacoemulsification needle tip.
Some surgeons use a bent needle phaco tip, a design originally introduced by the late Charles Kelman. The bent tip is necessary for the action of torsional phaco. However, obtaining occlusion at the tip in order to build high vacuum levels and then manipulate a wedge of nucleus becomes more difficult.
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Transition to phaco chop
The surgeon should first become proficient in anterior capsulorrhexis, hydrodissection, and hydrodelineation; the nucleus must be freely mobile to allow easy rotation once chopping begins. An intact and well-defined circular-tear anterior capsulotomy provides a clear landmark for the surgeon, as well as the capsular strength for extra manipulation.[7]Hydrodelineation frees the nucleus from the epinucleus, which is necessary for chopped fragments to be removed, as well as disclosing the location of the nuclear equator.
The surgeon wishing to learn phaco chop should begin by chopping the second half of the nucleus in a case where the first half of the nucleus is removed with a conventional divide and conquer quadrant technique (Figure 17-7A). The second half of the nucleus is usually quite mobile at that point, and the basic technique and tactile feel of phaco chop can be appreciated within several cases by chopping the second half of the heminucleus (Figure 17-7B).
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Figure 17-7 A, To begin learning phaco chop, the first half of the nucleus is removed using standard divide and conquer technique; the second heminucleus remains undivided. B, The second half of the nucleus can now be chopped with good direct visualization. |
Once the surgeon feels comfortable with chopping the second heminucleus, the next step is to perform the stop and chop technique for both halves of the heminucleus, while still retaining the initial trough and split hemisection of the traditional divide and conquer technique (see Figure 17-2).
The last step in the progress to full phaco chop is to bisect the nucleus with the phaco chopper (see Figures 17-3A and 17-5D). Although some surgeons have found this to be the most challenging step in the technique, it also is the most rewarding. Full phaco chop markedly improves the efficiency of the disassembly of the nucleus, particularly because of the elimination of the multiple steps of rotation and trough creation in the standard quadrant cracking techniques.
Challenges in phaco chop
Small Pupils
A novice will be insecure about the inability to visualize the periphery during chopping maneuvers. Small pupil cases should only be undertaken with phaco chop after the surgeon has gained reasonable comfort in more straightforward cases with large pupils and moderate-density nuclei. However, once this basic skill is achieved, chopping is preferred over the quadrant cracking or the divide and conquer techniques because chopping does not require peripheral passes with the ultrasound tip, and it is not dependent on a good red reflex.[8–10]
The 4+ nucleus
Chopping a 4+ hard nucleus can be particularly difficult, both because a hard nucleus is also a thick nucleus and because of the physical properties of a hard brunescent nucleus.[10]Nevertheless, chopping offers distinct advantages in the phacoemulsification of very advanced cataracts.[11] Because the nucleus is thick, a standard 1.5mm phaco chopper will not have adequate length to pass through the center of a nucleus (Figure 17-8A). As a result, a superficial vertical split will occur, but the deeper layer of the nucleus will tend to split in a more lateral fashion, creating a posterior plate (Figure 17-8B). If this occurs, the surgeon must identify which half of the heminucleus is above the plate and which half is attached to the plate. The half of the nucleus that is above the plate should be removed first, which allows the larger fragment to be mobilized and chopped. Several chopping instruments are now available with longer tips, in the order of 1.75–2mm, which greatly facilitates successful chopping of these thicker nuclei. These choppers, although longer, are still well short of endangering the posterior capsule, considering that a brunescent nucleus is at least 3.5mm thick (Figure 17-8C).
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Figure 17-8 A, Thick, advanced nuclear cataract will not chop well with a standard chopping instrument because the length of the tip is inadequate to split the center of the nucleus. B, If the thick nucleus splits at all, a short-tip chopper will tend to split the upper portion of the nucleus, but the fracture line will lateralize, leaving a posterior nuclear plate attached to one portion of the two pieces of nucleus. C, A longer length chopper will have a better likelihood of cleanly splitting the nucleus. The extra length of the chopper tip is far from the posterior capsule. D, In advanced nuclear sclerosis, “leathery” posterior nuclear strands will bridge across a chopped wedge and interfere with its removal, particularly at the posterior apex. E, Chopper can be rotated 90°, parallel to the posterior capsule, and used to snap across these strands and free the nuclear wedge. |
A very hard brunescent nucleus also tends to have a posterior “leathery” quality. Chopped fragments have posterior bridging strands that keep nuclear fragments attached to each other. These posterior strands represent posterior epinucleus that has partially hardened, with strong adhesion to the posterior nucleus and with a tough, strandlike quality. When these strands occur, they are seen against the red reflex as they bridge between two chopped nuclear fragments (see Figure 17-8D). The surgeon can rotate the phaco chopper 90° in his or her fingers, then carefully pass the chopper posterior to the nuclear fragment and transect the bridging fibers (see Figure 17-8E). This maneuver has led to variations of phaco chop generally known as “posterior cracking.” Techniques for phacoemulsification of the dense brunescent cataract are discussed in detail in Chapter 28.
Zonular abnormalities
Once experience is gained with phaco chop, it is the preferred technique in the presence of weak or missing zonules. This situation occurs most commonly in pseudoexfoliation syndrome or after trauma.[12–15] It is because horizontal chopping creates opposing forces between the two instruments that it minimizes forces on the zonules.[16]
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Complications of phaco chop
Multiple incomplete chops
A surgeon inexperienced at phaco chop often tends to “scratch” the nucleus without accomplishing front-to-back cleavage. This usually occurs for two reasons. The first is because the chopper is not passed far enough into the periphery in order to allow the chopper to “hook” and engage the equator. The surgeon can test whether the chopper is around the equator by gently pulling on the chopper and verifying that the nucleus moves with it. The second is because the chopper is allowed to ride up and out of the nucleus. The claw-shaped chopper was designed by Steinert to resist this tendency. For all chopper styles, the surgeon must learn to maintain appropriate posterior pressure on the chopping instrument.
When fragmented and incomplete chops do occur, the most important step is for the surgeon to remain patient. He or she should continue rotating and attempt to chop a new area, concentrating on proper technique. In addition, the chopper can act as a “finger” to hook around the equator of a fragment and help bring it toward the phaco tip in the central zone. This maneuver is particularly helpful when the vacuum is inadequate or complete occlusion cannot be achieved, and the nuclear fragment keeps “falling back,” away from the phaco tip.
Posterior capsule rupture
The most feared complication for novice surgeons with phaco chop is the rupture of the posterior capsule with the chopper. In fact, this is rare and should not occur at all with adherence to the principles of phaco chop. The phaco chop instrument is typically only 1.5mm long and, even with phaco chop instruments that have been elongated for dealing with a 4+ nucleus, the length never exceeds 2mm (see Figure 17-8A and C). The conventional lens is thicker than this in the periphery and increases to between 3mm and 4mm centrally (and sometimes even thicker). As a result, the phaco chopping instrument is well away from the posterior capsule. Many of the phaco chopping instruments have a blunted tip, which is also less likely to engage the posterior capsule.
Anterior capsule/zonular rupture
A more common complication is misjudging the location of the anterior capsule, such that the phaco chopper is anterior to the peripheral anterior capsule rather than within the capsular bag (Figure 17-9A). This mistake can be avoided by placing the phaco chopping instrument against the nucleus centrally within the capsulorrhexis, and keeping a small amount of posterior pressure against the nucleus as the chopper is passed peripherally. In a very hard nucleus with almost no anterior cortex, little space is present between the anterior capsule and the nucleus. In this case, the surgeon should rotate the phaco chopping instrument 90° within the surgeon's fingers so that it can slip under the anterior capsule in a “flat” position (Figure 17-9B). As the chopper passes out to the edge of the endonucleus, it is rotated back 90° to the vertical chopping position (Figure 17-9C).
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Figure 17-9 A, The surgeon must be careful to avoid passing the chopper over the anterior capsule instead of under it. This error is more likely in a large, dense cataract where little anterior cortex remains to separate the anterior capsule from the anterior nucleus. B, By rotating the chopper 90°, in a horizontal position parallel to the iris plane, the tip can pass easily between the anterior capsule and the nucleus. C, As the chopper tip is advanced out to the level of the equator of the nucleus, the tip is then rotated back 90°, from horizontal back to vertical, where it will pass around the nuclear equator and be positioned for chopping. |
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Conclusion
With careful attention to detail in following the progressive learning technique that was suggested earlier, any two-handed phacoemulsification surgeon should be able to master the maneuvers of phaco chop. Phaco chop is faster, and, as a result, ultrasound time is reduced, with a reduction in corneal endothelial damage and the potential for rupture of the posterior capsule.
Moreover, because phaco chop is a technique that involves stabilizing the nucleus with a phaco instrument centrally and then applying centripetal forces with the phaco chopper against the ultrasound tip, there is much less zonular stress than in standard cracking techniques. After phaco chop is mastered, it becomes a central element in the phacoemulsification surgeon's technique.
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References
[1]. Koch P.S., Katzen L.E.: Stop and chop phacoemulsification. J Cataract Refract Surg 1994; 20:566-570.
[2]. Steinert R.F.: Phaco chop. In: Steinert R.F., ed. Cataract surgery: technique, complications, and management, Philadelphia: WB Saunders; 1995.
[3]. Gimbel H.V.: Divide and conquer nucleofractis phacoemulsification: development and variations. J Cataract Refract Surg 1991; 17:281-291.
[4]. Pirazzoli G., D'Eliseo D., Ziosi M., et al: Effects of phacoemulsification time on the corneal endothelium using phacofracture and phaco chop techniques. J Cataract Refract Surg 1996; 22:967-969.
[5]. DeBry P., Olson R.J., Crandall A.S.: Comparison of energy required for phaco-chop and divide and conquer phacoemulsification. J Cataract Refract Surg 1998; 24:689-692.
[6]. Ram J., Wesendahl T.A., Auffarth G.U., et al: Evaluation of in situ fracture versus phaco chop techniques. J Cataract Refract Surg 1998; 24:1464-1468.
[7]. Gimbel H.V., Neuhann T.: Development, advantages, and methods of the continuous circular capsulotomy technique. J Cataract Refract Surg 1990; 16:31-37.
[8]. Lumme P., Laatikainen L.T.: Risk factors for intraoperative and early postoperative complications in extracapsular surgery. Eur J Ophthalmol 1994; 4:151-158.
[9]. Joseph J., Wang H.S.: Phacoemulsification with poorly dilated pupils. J Cataract Refract Surg 1993; 19:551-556.
[10]. Hayashi K., Nakao F., Hayashi F.: Corneal endothelial cell loss after phacoemulsification using nuclear cracking procedures. J Cataract Refract Surg 1994; 20:44-47.
[11]. Vasavada A., Singh R.: Step-by-step chop in situ and separation of very dense cataracts. J Cataract Refract Surg 1998; 24:156-159.
[12]. Lunne P., Laatikainen L.: Exfoliation syndrome and cataract extraction. Am J Ophthalmol 1993; 116:51-55.
[13]. Osher R.H., Cionni R.J., Gimbel H.V., et al: Cataract surgery in patients with pseudoexfoliation syndrome. Eur J Implant Refract Surg 1993; 5:45-50.
[14]. Fine I.H., Hoffman R.S.: Phacoemulsification in the presence of pseudoexfoliation: challenges and options. J Cataract Refract Surg 1997; 23:160-165.
[15]. Moreno J., Duch S., Lajara J.: Pseudoexfoliation syndrome: clinical factors related to capsular rupture in cataract surgery. Acta Ophthalmol 1993; 71:181-184.
[16]. Masket S.: Consultation section. J Cataract Refract Surg 1998; 24:1289-1298.