 |
Slide 1 |
Adapted from Chang DF. Converting to phaco chop: Why and how. Ophthalmic Practice. 1999;17(4):202-210.
Modern phaco strategies seek to subdivide the nucleus into small maneuverable pieces. This "disassembly" of the nucleus has two advantages: (1) The 10-mm wide nucleus can be removed through an intact 5-mm capsulorhexis. (2) The bulk of the nuclear material is emulsified near the center of the pupil and at a safe distance from the posterior capsule.
Hydrodissection separates the nucleus from the capsule and cortex so that it can spin within the capsular bag, but nucleus disassembly begins with hydrodelineation. Hydrodelineation cleaves away a thin epinucleus, leaving a remaining core of firm endonucleus. The larger the core endonucleus, the smaller the epinucleus will be. It is the endonucleus that is being chopped.
Most phaco surgeons use one of two basic strategies to fragment and subdivide the core nucleus. Cracking (as in four-quadrant divide and conquer) requires cutting a deep groove across the diameter of the nucleus. In brunescent nuclei, the groove must extend down almost to the posterior capsule. As with a log that has been sawed through to 90% depth, the nucleus can then be cracked into two pieces. Each heminucleus can similarly be cracked in half.1,2
At the 1993 American Society of Cataract and Refractive Surgery (ASCRS) meeting, Kunihiro Nagahara, MD, introduced the concept of phaco chop. While the nucleus is impaled and immobilized with the phaco tip, a "chopper" instrument hooks the equator of the nucleus and chops toward the phaco tip. The human lens fibers are arranged in lamellae oriented much like the grain of a piece of wood. Nagahara observed that because the chopping force is oriented parallel to these lamellae ("with the grain"), a natural cleavage plane is created. The nucleus is split into two pieces with surprisingly little force. In similar fashion, each heminucleus is chopped into two to four smaller pieces.
Paul Koch, MD, recognized that although the nucleus can be sliced into many parts, these pieces still fit tightly together within the capsular bag, like pieces in a jigsaw puzzle. The immobility of these pieces within the bag makes it difficult to aspirate them out. The process of making a groove for the cracking technique creates a working space within the capsular bag.
To create this desirable working space, Koch’s "stop and chop" technique begins with a central groove, which is used to crack the nucleus in half.3 One then stops cracking and chops the remaining sections. The initial grooved cavity provides enough space for the chopped pieces to be elevated out with the phaco tip.
I use the term "nonstop" chop to describe chopping techniques that eliminate all sculpting. There are two main variations of nonstop chopping. I call the classic Nagahara-style chopping horizontal chopping because the instrument tips move toward each other in the horizontal plane.
Hideharu Fukasaku, MD, introduced "phaco snap and split" at the 1995 ASCRS meeting. The "phaco crack" variation of chopping introduced at the 1996 ASCRS meeting by Vladimir Pfeifer, MD, and "stop, chop, and stuff" by Abhay Vasavada, MD, are also nonstop phaco chop techniques.4 (The Pfeifer technique has been renamed "phaco quick chop" by David Dillman, MD.) I call these variations vertical chopping because the instruments move toward each other in the vertical plane. Vertical chopping will be discussed later.
Both horizontal and vertical techniques use the manual energy of the chopper, instead of ultrasound energy, to section the nucleus into pieces. Ultrasound energy is reserved for the phaco-assisted aspiration of the individual nuclear fragments once they have been elevated out of the capsular bag. As with other "supracapsular" techniques, all of the emulsification in nonstop chop occurs, therefore, at a safe distance from the posterior capsule. I believe that nonstop phaco chop offers the same advantages (e.g., efficiency, safety, and reduced stress on the capsular bag) of supracapsular phaco flip without the danger and difficulty of prolapsing the entire nucleus out of the bag.
|
|
The first step of the horizontal phaco chop technique is dividing the nucleus in half without any sculpting. The chopping instrument passes peripherally beneath the anterior capsule and hooks the equator of the nucleus (Slide 1). I use a Lieberman microfinger for horizontal chopping because its slender, curved tip is ideally shaped for hooking around the lens equator (Slide 2). The central core of the nucleus is impaled proximally with the phaco tip and held with position 2. The chopping instrument is pulled toward the phaco tip, and, upon contact, the two tips are moved slightly apart (Slide 3). The initial chop cuts through the nucleus distal to the phaco tip. The separating motion continues the fracture along a natural cleavage plane through the proximal remainder of the nucleus (Slide 4).
|
|
The nucleus is rotated 30° to 45° clockwise, and the central core of the opposite heminucleus is impaled with the phaco tip. The bevel of the phaco tip is aligned parallel to and facing the surface it is about to impale. A small pie-shaped wedge is now created by the second chop (Slide 5). This first piece is the most difficult to remove. The strong holding force afforded by high vacuum usually will allow elevation of this first piece out of the bag. Alternatively, the curved tip of the microfinger can slip behind the equator of this nuclear piece in order to manually tumble it forward into the anterior chamber. The nucleus is rotated further, and the next piece is chopped and removed.
Many different horizontal chopping instruments have been designed. Horizontal choppers usually feature an elongated, blunt-ended tip. The length is necessary to bisect thicker brunescent nuclei, and the inner cutting surface of the shaft may be sharpened for this purpose.
|
Horizontal chopping works by fracturing the nucleus along a natural cleavage plane defined by the orientation of the lens lamellae. It requires that the bulk of the endonucleus be sandwiched and compressed in between the two instruments—namely the chopper tip and the phaco tip (Slide 6). If positioned properly, the resulting compression force of instrument against instrument will result in the fracture taking place. The denser the nucleus, the more compression force is required.
|
As with all phaco methods, a given technique must be somewhat tailored according to the characteristics of the individual nucleus. Most surgeons mentally classify nuclei according to firmness. At the slit lamp, nucleus color progressing from yellow to gold to brown correlates with increasing firmness.
It is equally important to visualize or classify the size of the nucleus. The greater the diameter of the endonucleus, the greater the anterior-posterior thickness of the nucleus. While soft nuclei are always smaller, brunescent nuclei may range from small to large. At the slit lamp, some cataracts have a golden or brunescent fetal nucleus, but the peripheral nucleus is light yellow. This correlates with a small-diameter endonucleus and a generous epinucleus. Alternatively, the brunescence may extend all the way forward to the anterior capsule in another cataract. This indicates a huge endonucleus with a large diameter, greater a-p thickness, and minimal epinucleus. The key to differentiating between these two types is to examine the color and opalescence of the nucleus between the anterior capsule and the front edge of the fetal nucleus.
To crack a larger endonucleus, the sculpted trough must extend more peripherally and much deeper. This becomes obvious to anyone with experience with the four-quadrant divide and conquer (4Q D&C) method. The success of phaco chop in larger nuclei depends on understanding the implications of nuclei size and the ability to anticipate size variables. The chopper tip and phaco tip must penetrate deeper toward the posterior capsule, and the two instrument tips must initially be positioned farther apart from each other if the bulk of the larger nucleus is to be compressed in between them. If the two instrument tips are not deep enough prior to the start of the chop, only the anterior portion of the endonucleus will be compressed. The front surface will be scored, but a fracture will not result.
This excellent variation on chopping is based upon techniques described Dr. Hideharu Fukasaku of Japan, Dr. Abhay Vasavada of India, and Dr. Vladimir Pfeifer of Slovenia. It was renamed "phaco quick chop" by Dr. David Dillman. Having initially used a Sinskey hook, I believe that success with this wonderful technique requires using a sharper instrument such as the Maloney Quick Chopper (Storz). This chopper is configured like a Sinskey hook, but has a tip that is as sharp as a thumbtack, and was specifically designed by Dr. William Maloney for this technique (Slide 7).
|
|
Whereas the microfinger or Nagahara-style chopper moves from the periphery centrally toward the phaco tip, the vertical chopper is used like a spike from above to impale downward into the nucleus just anterior to the centrally buried phaco tip (Slide 8). The most important step is to bury the phaco tip as deeply into the endonucleus as possible. If done correctly, one should actually be able to lift the impaled, unsculpted nucleus upward toward the cornea. Depressing the sharp spiked tip downward while simultaneously lifting the nucleus slightly upward creates a shearing force that fractures the nucleus (Slide 9). Once the fracture begins to propagate, a slight sideways separation of the instrument tips extends the fracture deeper until the entire nucleus is cleaved in half (Slide 10).
|
|
Much like a chisel would be used with a block of ice or granite, the spike tip can be used to break the nucleus into multiple pieces of variable size. For this reason, I believe the name "phaco-spike" or "phaco-chisel" would have better conveyed the mechanics of this technique. Just like a fork and knife, the two instruments cut the nucleus into "bite-sized" pieces that are small enough to be efficiently eaten by the phaco tip. The sharp vertical chopper tip stays central to the capsulorhexis and does not need to pass underneath the equator and out to the equator. This is the only way, therefore, to chop a nucleus when there is little to no epinucleus present. Several different vertical choppers have been designed as well. Most employ a sharpened tip that can impale and penetrate the nucleus.
To create the groove for cracking, the nucleus must be "sawed" from anterior to posterior. As pointed out by Nagahara, this cutting motion is directed perpendicular to the lens lamellae (against the grain). Like sawing through a log lying on its side, multiple passes—back and forth—are required. Phaco chop is analogous to placing the log upright on one end and chopping it with an axe. One strike, parallel to the grain, splits the log in half.
In addition to requiring less phaco power and time,5-7 chopping minimizes the stress placed on the zonules. For a phaco stroke to cut through the nucleus, the lens must be immobilized. Like a vise holding a piece of wood, it is the zonules and capsule that grip and fixate the nucleus as the groove is cut by the phaco tip. With phaco chop, however, it is the phaco tip that braces the nucleus against the force of the chopper. This manual energy, generated by one instrument pushing against the other, replaces the need for ultrasound energy to subdivide the nucleus. All forces are directed centrally inward and away from the zonules, rather than outward toward the zonules and capsule. This significant difference in zonular stress is readily appreciated when chopping and sculpting are compared from the Miyake-Apple viewpoint in cadaver eyes (K. Miyake, MD, presented at The 1999 Royal Hawaiian Eye Meeting, Waikoloa, Hawaii, January 1999).
Phaco Chop for Complicated Cases
The principles of decreased zonular stress and decreased phaco power define the indications for phaco chop. While advantageous for routine cases, the greatest value of phaco chop is in handling complicated phaco cases—those that entail greater risk of posterior capsule rupture or corneal decompensation.
Small Pupils
Small pupils complicate phaco for two reasons.8 First, working space in the pupillary plane is limited, making it harder to avoid
aspirating or phacoing the iris. Nonstop phaco chop eliminates the necessity of performing phaco behind the iris, because the phaco tip rarely moves
peripheral to the central 3 mm of the pupil. This decreases the chance of lacerating the capsulorhexis or pupillary margin with the phaco tip in these
eyes.
Secondly, visualization of the lens is impaired.9 The iris hides the lens periphery, and the intensity of the red reflex is significantly reduced with each reduced millimeter of pupil diameter. A poor red reflex makes it difficult to judge the depth at which the phaco tip is cutting. This is a problem for cracking techniques where an adequately deep central trough is essential. Phaco chop is a more kinesthetic technique in which visualization of the phaco tip depth is not important. It is only important to visualize that the chopper is passing beneath the anterior capsule as it hooks the equator of the nucleus.
Mature Cataracts
Mature white (cortical) and brown (nuclear) cataracts are challenging for many reasons.10 The capsulorhexis is difficult to
visualize because of the lack any red reflex and the liberation of cortical "milk" following the initial puncture. The excessive hydration of
these lenses promotes peripheral radial extension of the developing capsule tear. The lack of a red reflex also makes nuclear removal more
formidable. Without good visualization, the phaco tip or second instrument may inadvertently tear an intact capsulorhexis.
By far, the best solution is the use of indocyanine green (ICG) dye, as described by Horiguchi,11 or trypan blue dye, as described by Melles.12 Neither dye is approved by the US Food and Drug Administration (FDA); only ICG is available in the United States. Trypan blue creates a much darker staining and provides superior visualization when compared to ICG. Trypan blue staining also lasts longer and usually persists throughout the entire phaco step. Being able to see the capsulorhexis edge during sculpting or chopping is an advantage in these cases lacking a red reflex. Until trypan blue becomes available in the United States, ICG provides an adequate alternative.
A poor or missing red reflex makes it difficult to judge the depth at which the phaco tip is cutting. This is a problem for cracking techniques in which sculpting an adequately deep central trough is essential and where the appearance of an increasingly brighter red reflex is used to gauge the proximity of the posterior capsule. Unlike sculpting, phaco chop is a more kinesthetic technique in which visualization of the phaco tip depth is not important. Proper positioning of the chopper and phaco tips relies more on tactile rather than visual clues.
The more brunescent and sizable a mature nucleus, the greater the risk of complications. By necessitating increased phaco power and time, the potential for wound burn and endothelial cell loss is increased.13 In addition, because of the excessive bulk, density, and size of these nuclei, all of the instrumentation forces are directly transmitted to the capsular bag. The increased capsular and zonular stress induced by maneuvers such as rotation, sculpting, and cracking makes posterior capsule rupture much more likely. The ability of phaco chop to reduce the amount of nuclear sculpting, the total phaco time and energy, and the stress on the zonules are particular advantages in these high-risk eyes.14 If a can-opener capsulotomy is necessary, outward cracking motions should be minimized as much as possible, in favor of chopping maneuvers.
Loose Zonules
Cataracts with loose zonules are among the most challenging to remove.15-18 Predisposing factors include exfoliation, advanced age,
trauma, retinopathy of prematurity, and previous intraocular surgery (e.g., some postvitrectomy or trabeculectomy patients). Loose zonules pose
three sets of problems for the phaco surgeon. First, the nucleus, epinucleus, and cortex do not easily separate from a capsule that is not firmly
anchored. Thus, it may be hard to rotate the nucleus. Later, aspirating epinucleus and cortex may pull the anterior capsule centrally together
with the lens material.
Secondly, the zonules rupture more easily.19,20 Aspirating the anterior capsule or adherent lens material may dehisce the zonules in that region. Pushing the nucleus against the capsular bag (as with sculpting) or forceful nuclear rotation may shear zonules 180° away. Finally, less centrifugal tension by the zonules allows the flaccid central posterior capsule to trampoline forward. The phaco or irrigation and aspiration (I&A) instruments may aspirate folds of redundant posterior capsule.
Phaco chop greatly reduces the stress placed on the zonules and capsule by replacing sculpting and cracking forces with the manual forces of one instrument pushing against another.21 Unlike cracking, these manual forces are directed centripetally inward, rather than outward toward the zonules.
Problems with Capsulorhexis or Hydrodissection
Any surgeon, regardless of experience, can encounter problems with these steps. Failure to properly complete these preliminary maneuvers greatly
complicates the ensuing phaco step. An inadvertent radial tear during capsulorhexis may result because of poor technique, chamber shallowing,
loose zonules, poor visualization, or patient movement. A radial tear may also be created by phacoing the capsulotomy edge. A capsulorhexis is more
difficult to achieve with poor visualization of the red reflex (e.g., mature nuclei, anterior cortical spokes, hazy cornea), shallow anterior chambers
(e.g., very narrow angles), increased capsule elasticity (e.g., pediatric cataracts), or pseudoelasticity (e.g., loose zonules).
A capsulorhexis renders the capsular bag very resistant to tearing.22 Like an elastic waistband, a capsulorhexis stretches with forces such as cracking without tearing. A single radial tear is precarious because all of the stress placed upon the capsule is transmitted to that single weak point. Enough stress will cause an anterior radial tear to extend around the equator into the posterior capsule. Nuclear cracking stretches the capsulotomy and is particularly risky with a single radial tear. Nonstop phaco chop eliminates the need for this step and is the technique of choice when a radial tear has developed.
Hydrodissection to enable rotation of the nucleus is a prerequisite for safe cracking techniques. However, it may not be possible to rotate a very soft nucleus or a nucleus in a patient with loose zonules. Phaco chop can "slice" the initial wedges of nucleus for removal without the need for rotation. These pie-shaped wedges can then be tumbled out using the chopping instrument.
Nuclear cracking and phaco chop are excellent techniques for routine phaco cases. Nonstop phaco chop provides the following additional benefits: less phaco time and energy, less stress on the zonules and capsule, and the ability of the phaco tip to remain in the central 3 mm of the pupil. It is a kinesthetic technique with less reliance on visualization of the phaco tip’s depth. Therefore, phaco chop is an advantage particularly in complicated cases that carry increased risk of posterior capsule rupture or corneal decompensation.
Common Pitfalls in Learning Phaco Chop
1) Not hooking the nucleus equator with the chopper. The chopper should pass below the capsulorhexis edge and into the epinuclear space. The novice is afraid that fully inserting the chopper tip under the anterior capsule and around the lens equator will overly distend and tear the capsulorhexis. This should not occur, as long as there is an epinucleus present. The maneuver is contraindicated in a giant, brunescent nucleus with no epinucleus for this reason. If the chopper tip never starts deep enough, it will simply deflect over the anterior nucleus rather than penetrate into it.
Pearl: Insert the chopper tip first. This optimizes visualization for the most intimidating step of the chop and allows one to test whether the chopper tip is adequately deep. As you slightly pull with the chopper, the nucleus moves if the chopper tip has hooked the equator. This tap test also confirms that the chopper is inside the bag, rather than outside the bag and into the zonules.
2) Elevating the chopper tip as the chop is performed. If this occurs, the core of the endonucleus will not be compressed during the chop motion. The chopper tip will only scratch or score the anterior surface of the nucleus, rather than driving through the central core. This tendency comes from fear of puncturing the posterior capsule with a deeply positioned chopper tip.
Pearl: It is usually more than 4.5 mm from anterior to posterior capsule. Even allowing for removal of the anterior epinucleus, this is a long way for a 1.5-mm to 2.0-mm long chopper tip to be able to reach the posterior capsule. To best convince yourself of this, pause the next time you have removed an endonucleus but while the epinucleus is still present. Insert your favorite chopper, and see how far posteriorly it must travel before it can touch the posterior epinucleus. This will help you visualize with confidence how much room you truly have.
3) Chopper shaft presses down on limbus during the chop motion. Leaning on the limbal side port incision causes corneal striae, displaces the globe, and may increase "posterior pressure." Chopping is an advanced maneuver of the non-dominant hand. It presupposes dexterity and comfort in bimanual maneuvers that are best acquired in techniques such as 4Q D&C.
Pearl: Prior to performing the critical initial chop, take some "practice" chops by moving the chopper within the anterior chamber, just above the nucleus. This will verify proper position of the non-dominant hand and the side port incision so that optimal orientation of the chopping instrument can be achieved. Also, if you have never used a large chopper-like second instrument, start using one with your standard divide and conquer cases. This will help you adapt to handling such a second instrument in a more comfortable setting.
4) Chopper placed outside the anterior capsule into the zonular space. This is more likely to happen with poor visualization of the anterior capsule and with a deficient epinuclear space (e.g., small pupils and large brunescent nuclei). The chopping attempt will result in a local zonular dialysis and appearance of a peripheral area of clear red reflex.
Pearl: Position the chopper tip before using the phaco tip. Start by aspirating some of the anterior epinucleus. This improves visualization of the underlying endonucleus. At the center of the pupil, place the chopper tip directly on the anterior endonuclear surface. By maintaining this contact as the chopper tip moves peripherally, it will pass beneath the capsulorhexis rim prior to hooking the equator of the endonucleus. As long as the chopper tip maintains contact with the endonucleus, the anterior capsule cannot come in between. If uncertain, test the chopper position by gently moving the nucleus toward you. The anterior capsule shouldn’t move.
5) Phaco tip is too superficial and central. With firm nuclei of increased diameter, the phaco tip must be deep and proximal in order to sandwich as much of the core nucleus between the two instrument tips as possible. Sculpting habits give rise to an incorrect tendency to advance the phaco tip centrally and superficially while in position 3. If so, the ensuing chop will only compress the anterior third of the endonucleus and will fail to fracture the nucleus.
Pearl: With large, firm nuclei, keep the phaco tip just within the proximal capsulorhexis edge, and aim it toward the optic nerve. Avoid letting it drift toward the center of the pupil in such nuclei. With brunescent lenses, burst mode can facilitate deeper penetration while maintaining a tight seal around the tip.
6) Inability to remove the first piece. With firm, large nuclei, the pieces fit tightly within the bag like pieces in a wooden jigsaw puzzle. Insufficient holding force by the phaco tip results in the piece getting knocked back off before it is fully lifted out.
Pearl: The larger and firmer the nucleus is, the smaller the first piece should be. High vacuum and larger phaco tips increase holding force. Burst mode (if available) can enhance the phaco tip’s purchase of a firm nuclear piece. As an alternative, the microfinger can be used to manually tumble the piece out. Although the pie-shaped piece somersaults forward, it is pivoting upon its apex. This prevents the sharp apical tip of the fragment from getting close to the posterior capsule.
Strategies for Converting to Phaco Chop
Learning any new phaco technique is simplified and facilitated by optimal case selection. Large pupils with softer and smaller endonuclei are important, along with avoidance of problem characteristics (e.g., exfoliation, long axial length, poor corneal clarity, deep-set eyes, uncooperative patients, etc.). A larger capsulorhexis and a well-hydrodissected, rotating nucleus make phaco chop easier. Vigorous hydrodelineation facilitates visualization of the endonucleus and placement of the chopper just around its equator. I advocate learning horizontal chop first, if possible. This technique is excellent for soft – medium nuclei, which are the preferable densities when trying a new technique. Because horizontal chopping seeks to divide the endonucleus, hydrodelineation is an important step for this procedure.
The most difficult steps of "nonstop" phaco chop are the initial ones—the first chop through the entire diameter of the nucleus and the creation and removal of the first piece. Each subsequent step in the procedure becomes progressively easier. Therefore, it would be ideal if one could learn the steps in a reverse order—starting with the easiest maneuvers first.
My game plan for teaching residents is as follows:
Step 1: Learn and master four-quadrant divide and conquer technique. Cracking is easier to master than chopping. Sculpting a deep trough is, in essence, a lamellar by lamellar dissection of the nucleus. Experience with 4Q D&C, therefore, teaches us the dimensions and relative density of all varieties of nuclei. Furthermore, if a chopping attempt fails, one needs a backup technique upon which to rely.
Step 2: Become familiar with the larger profile of the chopper by using this as a second instrument during 4Q D&C. When performing 4Q D&C, try using a microfinger or chopper to tumble one of the quadrants out. As mentioned earlier, this maneuver can be used to tumble chopped fragments out of the bag. It also provides practice hooking the equator of the endonucleus with the chopper.
Step 3: When performing 4Q D&C, aspirate and elevate one quadrant into the pupillary plane. Instead of simply emulsifying it, chop it in half. With visualization of the entire piece and no anterior or posterior capsule to worry about, one can concentrate on the positioning of the chopper and the "feel" of the chopper cutting through nuclei of different density. Use the second quadrant to similarly experiment with the orientation of the chopper tip as it chops.
Step 4: After removing two quadrants, don’t sculpt a groove into the remaining heminucleus. Instead, impale and aspirate the center of the heminucleus, and carry it to the center of the pupil. One can now proceed to chop it into thirds with full visualization of the equator and without having to pass the chopper tip peripherally beneath the anterior capsule.
Step 5: Learn and master "stop and chop." Sculpt an adequately deep and long groove in order to crack the nucleus in half. Then "stop" sculpting, rotate slightly, and chop the remaining halves. This requires learning to place the chopper peripherally underneath the anterior capsule and around the nucleus equator. This is still much easier than chopping the full endonuclear diameter for three reasons. First, one is chopping across a shorter distance (equivalent to the radius rather than the diameter). Secondly, proper position and depth of the phaco tip is virtually guaranteed. By placing the phaco tip into the trough and up against the side of the heminucleus, the nucleus is now sandwiched between the phaco tip and a properly placed chopper tip. Finally, the trough provides vacant space into which to slide out the first chopped fragment.
Step 6: One is now ready to do the full "nonstop" or "pure" Nagahara chop in which the entire nuclear diameter is chopped in half without any sculpting or groove. Softer and smaller endonuclei should be mastered before progressing to firmer and larger endonuclei. Luckily, if the initial chop is unsuccessful, one can simply start to sculpt a trough and convert to the "stop and chop" technique.
Comparison of Horizontal and Vertical Chopping (Classic Nagahara vs. Quick Chop)
I employ and am comfortable using either chopping technique. Although they work according to different principles, they both provide the same universal advantages:
Because they both have relative merits, I believe it is worth learning both variations. A comparison of the two methods follows.
Difficulty: These are both advanced techniques with a greater learning curve than 4Q D&C. Learning one of these techniques will make it easier to learn the other. Because Nagahara-style chopping can be learned on softer and smaller nuclei, I believe that it is easier to learn this method first.
Risks: Like all phaco techniques, both methods entail some risk of capsular or zonular rupture. Because Nagahara-style chopping requires peripheral placement of the microfinger or chopper, there is the risk of going anterior to the capsulorhexis and causing a localized zonular dehiscence. The risk of vertical chopping is that a firm nucleus can be pushed so posteriorly that it ruptures the posterior capsule. This can occur if the firm nucleus is not fully impaled and supported from below by the phaco tip. The downward pushing force of the chopper must be borne by the phaco tip and not the posterior capsule.
Indications for Horizontal Chopping
1) Soft and smaller nuclei. Vertical chopping relies on a shearing force to snap the nucleus in half. Like cracking, this is difficult with soft nuclei, which are not firm or brittle enough. This is why one can break a cracker in half, but not a piece of bread. The microfinger or Nagahara-style chopper literally cuts through the soft nucleus, rather than chopping it, which makes horizontal chopping the method of choice for these cases.
2) Extremely deep anterior chambers (e.g., high myopes, post-vitrectomy eyes). The phaco tip does not need to be quite as deep with horizontal chopping as it does with vertical chopping. This is particularly true in the case of softer and medium density nuclei. With horizontal chopping, it is more important for the chopper tip to be as deep as possible. In these eyes where the nucleus drops so far posteriorly, it may be difficult to get the phaco tip deep enough to accomplish the initial vertical chop of phaco quick chop. The ergonomics of the microfinger or Nagahara-style chopper allow them to be placed deeply enough even in these eyes.
3) Very small pupils. Firmer and larger nuclei require that the vertical chops be performed more peripherally. Because the sharp vertical chopper tip cannot pass through the anterior capsule or iris, a very small pupil or small capsulorhexis may therefore limit use of this maneuver. Unlike with phaco quick chop, horizontal Nagahara chopping does not require visualization of the chopper tip during the chop maneuver. Being more kinesthetic than visual, it may be performed blindly behind the iris, as long as initial placement of the chopper tip underneath the capsulorhexis edge is confirmed.
Indications for Vertical Chopping
1) Difficulty visualizing the capsulorhexis edge (e.g., anterior cortical spokes, poor corneal visualization). It is crucial that the microfinger or Nagahara-style chopper pass beneath the anterior capsule edge. If this can’t be visually confirmed, it is safer to perform phaco quick chop, in which the chopping instrument does not need to be placed peripherally into the fornix of the capsular bag.
2) Brunescent nuclei. For brunescent nuclei, I find that vertical chopping works best. The denser the lens, the sharper the tip should be. The Chang chopper (Katena) is maximally sharpened to better penetrate the firmest nuclei. The most important step is to bury the phaco tip as deeply into the central nuclear core as possible. A beveled, micro phaco tip has a slim profile that is best suited for penetrating a dense lens. Retracting the infusion sleeve and employing burst mode are also helpful.
Compared to horizontal chopping, quick chop is more likely to divide the leathery posterior plate of a thick lens because the fracture propagates vertically from the anterior nuclear surface toward the back. With Nagahara-style chopping, the fracture propagates in the horizontal direction, from one equatorial side to the other, and may not extend deeply enough to bisect the posterior plate. As with chiseling a block of ice, vertical chopping can be used to create very small fragments. This versatility is useful when dealing with a large and bulky dense nucleus where smaller pieces must be created for maximal emulsification efficiency.
3) Little or no epinucleus. Because the microfinger or Nagahara-style chopper passes into and occupies the epinuclear space, the thinner the epinucleus, the more difficult this maneuver is. By avoiding the need for instrumentation in the peripheral fornices of the capsular bag, vertical chopping may be preferable for progressively larger and denser nuclei (see #2 above). Indeed, lack of a sufficient epinucleus is a contraindication to horizontal chopping.
By reducing phaco power and zonular stress, "nonstop" phaco chop provides enormous advantages for complicated and higher risk cases. This justifies its inclusion in our surgical armamentarium. Mastering the steps in reverse order and understanding the principles and common pitfalls facilitate the transition to phaco chop. Horizontal and vertical chopping are complementary variations offering different advantages but common benefits.
Machine settings should be individualized for each surgeon depending on his or her equipment, technique, and experience. Copying someone else’s settings may not be appropriate. For example, experienced surgeons may work at a more rapid pace than would be recommended for a novice. The following concepts should guide someone making the transition to phaco chop using a peristaltic pump system.
Of the two components that determine the overall suction provided by foot position 2, flow rate governs the "speed" of the procedure. If things are happening too rapidly, decrease the flow rate. Vacuum determines the strength with which the phaco tip grips nuclear material occluding its opening. Increase the vacuum if you can’t hold on to the nucleus.
With both horizontal or vertical phaco chop, there are three sequential phaco maneuvers used to remove the endonucleus. The first step is the chopping of the nucleus into progressively smaller fragments. Secondly, the phaco tip is used to elevate and carry these fragments out of the capsular bag into the pupillary plane. Finally, free-floating pieces are emulsified in the "supracapsular" location at a safe distance from the posterior capsule. This can be thought of as "phaco-assisted aspiration." For the first two maneuvers, we want our machine to deliver holding power. With the last maneuver, followability and surge elimination are the primary goals.
High vacuum increases our holding power. Prior to making a chop, a more solid purchase of the nucleus will prevent the chopper tip from simply dislodging the nucleus from the phaco tip. This is particularly important for vertical chopping. The maximum holding power afforded by higher vacuum levels also allows one to pull a chopped fragment out of the capsular bag into the pupillary plane.
This latter characteristic is equally important in removing a quadrant created by the divide and conquer technique. Therefore, for chopping, simply start with your "quadrant setting" and a low flow rate initially. For the first two maneuvers, I like to work at the highest vacuum level I can. The limit is determined by the phenomenon of post-occlusion surge. Rigid, low compliance tubing, smaller diameter phaco tip and tubing lumens, occlusion mode settings, smart pumps, pressure sensors, and the ABS tip are all examples of strategies used by manufacturers to reduce the amount of surge. Other universally available adjustments include raising the bottle height and decreasing the flow rate.
To determine the maximum vacuum level you can safely use with your machine, impale a sizable nuclear fragment, hold it in the pupillary plane, a nd allow the maximum vacuum level to be reached (accompanied by beeping tone). Gauge the amount of posterior capsule bounce as the piece is then pulled through the tip. During this testing, you should have a significant amount of nucleus remaining in the bag to keep the capsule from approaching the phaco tip. If there is no surge, increase the maximum vacuum setting.
By repeating this step, one will eventually experience an unacceptable degree of surge, at which point the "safe" vacuum level has just been exceeded. To reduce the surge, you can raise the bottle height, decrease the flow rate, or reduce the maximum vacuum setting. I am willing to tolerate some chamber bounce during the first two maneuvers, because there is still plenty of nuclear material present to hold the posterior capsule back.
Solid purchase of nuclear material also requires a tight seal around the tip because high vacuum levels cannot be achieved if the tip does not remain occluded. With dense nuclei, a continuously vibrating phaco tip tends to core out a small cavity around the tip, eroding the seal. In contrast, burst mode or low frequency pulse mode allow us to better embed the tip into firm nuclei without loss of the seal.
The final maneuver is the evacuation of the chopped, free-floating fragments. By increasing the force by which material is pulled through the tip, higher vacuum levels can actually decrease the requirement for phaco energy during this step. Flow rate plays a more important role here, by attracting the progressively smaller fragments to the tip, particularly because the occlusion is only intermittent. Ideally, pieces should gravitate toward a stationary and centrally held phaco tip. If one has to chase pieces into the periphery, or if it is taking too long for the piece to be phaco-aspirated, the flow rate should be increased.
As the last two to three fragments are removed, there should be no trampolining of the posterior capsule, for obvious reasons. One might switch to a different memory setting employing a lower vacuum level (to decrease surge) and a slightly higher flow rate. I find that the use of pulse mode also improves the efficiency and followability during this step. The same settings will usually be appropriate for the epinucleus.
Another very effective way to reduce surge is to use a smaller diameter phaco tip (e.g., 20 gauge). Smaller phaco tips are easier to maneuver, and easier to occlude, reduce the incidence of clogged tubing, and more easily penetrate into dense nuclei. However, although microtips and lower flow rates allow us to use higher vacuum, they slow the rate by which chopped fragments can be phaco-aspirated from the eye.
Below, I use my own settings for the Sovereign (Allergan) to illustrate how I use high vacuum parameters to maximize holding power and aspirating force (#1, #2), and lower vacuum setting to maximize followability and minimize surge (#3). Burst mode is inappropriate for softer nuclei, and therefore "Phaco 1" is primarily used for firm nuclei. "Phaco 3" is for the last two to three nuclear fragments, very soft nuclear f ragments, and epinucleus. I don’t need a sculpting setting for nonstop chop.
| AMO Sovereign [20-gauge tip] |
Chop 3+NS "Phaco 1" |
Followability "Phaco 2" |
Surge Elimination "Phaco 3" |
| Vacuum (mm Hg) Max Vacuum Occlusion Threshold |
400 | 320 250 |
200 100 |
| Aspiration (cc/min) Unoccluded Occluded |
18 | 28 24 |
38 34 |
| Phaco Power (%) Unoccluded Mode Occluded Mode |
35 Burst Burst |
30 Continuous Short Pulse |
25 Continuous Short Pulse |
