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Slide 1 |
Reprinted with permission from Koch PS. Stop & chop. Chapter 13. In: Koch P, ed. Simplifying Phacoemulsification. Thorofare, NJ: Slack; 1997.
The phaco chop technique was a revolutionary addition to the advancement of cataract surgery. However, one difficulty with the technique was the creation of the intracapsular jigsaw puzzle and the limitation of first-piece elimination. The problem seemed to lie in the lack of space for manipulation in the middle of the cataract.
For many years, cataract surgeons performed Dr. Howard Gimbel’s divide and conquer nucleofractis technique. The first step in this technique was the creation of space within the cataract, which is imporant because the nuclear rim fragments can be pulled away from the fornix and emulsified easily below the level of the anterior capsule.
Surgeons had evolved from the divide and conquer technique to in situ fracture because of the challenge of breaking the nuclear rim according to Gimbel’s parallel instrument fracture method. The in situ fracture technique offered a simpler way to break apart the nuclear rim. I combined it with the preparation step of the divide and conquer technique to create a surgery that was easier to perform.
The technique combining Gimbel’s nucleus preparation and Nagahara’s chop to break up the nuclear rim is called stop and chop phacoemulsification. This tutorial outlines the steps involved in stop and chop phaco.
First, thorough hydrodissection is performed. I do not usually perform hydrodelineation for stop and chop phaco because I am able to chop the nucleus into bite-sized pieces. And, because I constantly pull pieces into the middle of the capsular bag, I do not need the cushion of epinucleus. In addition, creating an epinucleus adds an additional step at the end of the procedure — removal of epinucleus.
Following hydrodissection, the nucleus is sculpted, creating either a trench in patients with soft cataracts or a crater in hard cataracts. The posterior plate is shaved until it is very thin because we want to break the posterior plate before proceeding any further. Once the posterior plate is broken into two pieces, the rest of the nucleus can easily float away from the fornix into the middle of the bag (Slide 1).
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The chopper is introduced into the groove through a side-port incision and placed against the left-hand wall of the groove. The phaco tip is pressed against the right-hand wall. Both instruments are placed deeply in the groove, so that the separation effort is as close to the posterior plate as possible. The chopper is pulled gently to the left, while the phaco tip is pushed gently to the right. If the posterior plate has been shaved thin enough, it will separate easily and the nucleus will be broken into two halves (Slide 2).
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If the posterior plate does not break easily, more of the plate must be sculpted out to make it thin. If it were one cell-width thick, it would break apart easily, so the thickness of the plate is critical to its separation. For a surgeon who does not want to be extremely aggressive in shaving the posterior plate, I recommend putting the tip and the chopper as deep into the groove as possible to get the best leverage on the posterior plate for separation. If the instruments are too high up in the groove, they can actually impede separation rather than assist it (Slide 3, Slide 4, Slide 5, Slide 6, Slide 7, Slide 8, Slide 9, Slide 10, Slide 11 and Slide 12).
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Sometimes the groove can be made deeper and the posterior plate fractured without any nuclear rotation. Other times, the surgeon must rotate the nucleus 180°, complete the trench, and then fracture the posterior plate. The former technique is faster, but not always successful. The latter is slightly slower, but always successful. Time and experience dictate which of these techniques is easiest to perform in a case. The nucleus is rotated in approximately 20% of cases.
The next step is choppng the nucleus. The nucleus is rotated 60° to 90° and the aspiration on the phaco machine increased. The phaco tip is placed in the lower heminucleus about one-third of the way from right to left. It is buried fairly deeply in the nuclear half, at least halfway to the posterior plate. This is the densest part of the cataract and the location where there is the most control. The phaco tip will bury in firm tissue and will fulfill its function as a chopping block. It is buried using emulsification and, once set, held in place using aspiration. This effectively impales the nucleus on the phaco tip.
The chopper is placed in the peripheral nucleus as far out as you can comfortably go, usually at the edge of the capsulotomy. It is plunged into the nucleus right up to its bend, which is about 1.5 mm. This is safe, because the nucleus is 2.0 mm to 2.5 mm thick. The phaco tip is held still while the chopper is pulled toward it. This is the chopping block analogy described by Nagahara. The phaco tip is the block, the nucleus is the log, and the chopper is the axe.
When the instruments reach each other, they are separated, pulling the chopper to the left and pushing the phaco tip to the right. This chops off a wedge of nucleus tissue. This piece is already impaled on the phaco tip and can be emulsified without any further manipulation (Slide 13).
I would like to emphasize that the more peripheral the chopper can go, the easier the chop is to perform. Although it is physically possible to make a chop by placing the chopper a millimeter or two away from the phaco tip, it requires too much work and effort to separate the pieces. This can translate to stress on the bag or zonules, leading to breakage (Slide 14).
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If the chopper can be placed to the full width of the capsulotomy (or even beyond), that longer pass will make a smoother and more gentle chop. If the capsulotomy is small, the chopper can be placed on the nucleus within the capsulotomy and pushed gently out of the periphery. The anterior capsule will retract in front of the chopper and a long chop can be made.
I am often asked how to avoid poking the chopper through the anterior capsule. This is a difficult question to answer. Poking the chopper through the anterior capsule is a concern only with a small capsulotomy. Many times, the anterior capsule can be seen easily and so this is not a problem even with a small opening. Sometimes, because of epinucleus disruption, it is difficult to see the edge of the capsule even with a large capsulotomy. Therefore, it is possible to poke the chopper through it.
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Once that first wedge is emulsified, the surgeon should rotate the nucleus further 30° or 40°, re-engage the middle of the remaining nuclear half with the phaco tip, put the chopper in the periphery, and pull it toward the tip. The next steps are chopping and separating the nucleus, which results in a wedge of nucleus impaled on the phaco tip. It can be emulsified without any further manipulation (Slide 15).
One piece of the nuclear half remains to the left side of the capsular bag. This can be nudged toward the phaco tip, engaged, and emulsified easily without any further chopping (Slide 16). The second nuclear half is rotated approximately 180° and is removed exactly the same way as the first half (Slide 17 and Slide 18).
The technique I have described involves chopping the cataract into six pieces. Soft cataracts can be emulsified easily by chopping them into only four pieces, whereas dense cataracts may need to be chopped into a dozen or more pieces. If a piece is chopped off and it seems too big for easy emulsification, that piece can be chopped in half, creating two smaller pieces.
It is important to have pieces that are adequately small so they enter the emulsification tip smoothly without contacting the inside the eye. Simple and gentle removal of the pieces improves the quality of the surgery and outcome.
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Stop and chop is one of the safest nuclear disassembly procedures. Until the introduction of stop and chop, each technique had an outward movement as its primary nucleus separation force. Each piece of nucleus was separated by pushing outward against the capsular bag. This can cause capsule or zonule ruptures.
With the stop and chop technique, the outward force is limited to the separation of a deeply sculpted trench or crater. If the posterior plate is sufficiently thin, this force is negligible.
Other maneuvers used to break the nucleus are directed inward toward the middle of the bag. Surgeons aspirate and hold the nucleus piece, pulling it to the tip and away from the fornix. The chopper is pulled toward the middle of the bag. Even the separation movement is performed in the previously sculpted area, so it is performed in open space without any contact with the bag.
When we first developed the stop and chop technique in 1993, we compared phaco times used to remove cataracts in a series of 147 eyes (Table 1). For soft cataracts, we compared stop and chop to spring surgery and in situ fracture. We found a reduction in phaco times of 28% to 55% (average 41%).
What if we can’t bury the phaco tip in the first place? The tip should be able to get deeply into the nucleus. Sometimes you will find that the sleeve impedes progress. If this happens, adjust the sleeve so more of the tip is showing. You will need 1 mm to 2 mm of exposed tip to get a good grip.
Do we pull the nucleus out of the fornix prior to chopping? If so, we’re having a problem, because we seem to be pulling our phaco tip out of the nucleus instead.
We should be able to pull the free pieces of nucleus, but an entire hemi-nucleus is held rather firmly in the fornix by its shape and size. These can stay in place as we chop them into smaller pieces. When we try to chop, the nucleus falls off the phaco tip. What’s the problem?
The phaco tip is buried too far up on the nucleus. When you plunge the chopper, you nudge the phaco tip through the anterior nucleus and into the epinucleus, which is not firm enough to support the tip. The phaco tip should be buried deep in the nucleus, at least two-thirds of the way down. Try to get it impaled right in the densest part of the cataract.
Table. Phaco Time Comparison
In situ Fracuture/Spring Surgery (1992) |
Stop and Chop (1993) | ||||
Cataract Density | Number |
MPT | Number |
MPT | Reduction (%) |
1+ | 7 |
1.33 | 11 |
0.59 | 55.6 |
2+ | 27 |
1.45 | 30 |
1.04 | 28.2 |
3+ | 36 |
2.15 | 30 |
1.27 | 40.9 |
4+ | 3 |
ECCE | 3 |
3.41 | n/a |
Total | 73 |
— | 74 |
— | |
Average | 41.6 |
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MPT=mean phaco time |
