Like most people, cataract surgeons need a good reason to alter something that works. Nearly seven in 10 surgeons still rely on some form of divide-and-conquer nucleofractis technique, and for the majority of their cases, do so quite effectively.
For many years, I've been a proponent of phaco chop, which I find is not only more efficient for standard cases, but is especially effective for complicated surgeries, such as those with small pupils, loose zonules, brunescent nuclei, or mature white lenses. When we face stressful surgical cases such as these, we always wonder if there is a better way. For me, the answer is phaco chop. I will review why I've adopted it as my preferred technique, and some of the ways that I've learned to maximize its effect.
|The horizontal chopper tip is passed beneath the capsulorhexis to hook the equator of the endonucleus within the capsular bag. |
The three most recent annual surveys of the American Society of Cataract & Refractive Surgery show an increasing interest in chopping: 11 percent specified it as their technique in 1997, 18 percent in 1998 and 23 percent in 2001.1
I see four advantages to phaco chop that may be driving that trend.
• Since chopping ultimately eliminates lens sculpting, we don't use ultrasound to divide up the nucleus. This results in a marked reduction in the phaco time and phaco energy that is otherwise needed for sculpting.
• In chopping, the stress placed on the zonules and the capsule during emulsification of a brunescent lens is greatly reduced. These firm, large lenses more directly transmit all of our instrument forces toward the capsular bag and zonules. In particular, when we sculpt this type of lens, it's really the capsular bag that is fixating the nucleus.
In contrast, in chopping a dense lens, we are always bracing and immobilizing the nucleus with the phaco tip, and the incoming mechanical force of the chopper is directed centripetally inward, toward the phaco tip, rather than outward toward the capsule.
|A close up of the horizontal chopper tip—modified Lieberman microfinger (Chang Combination Chopper, Katena Inc.)|
The phaco tip obtains its purchase by penetrating deep into the core of the brunescent material and utilizing high vacuum for holding power so that the piece doesn't become easily dislodged. Most phaco machines now offer burst mode, which, in a brunescent lens, avoids the coring away of material around the tip that occurs with continuous mode. The result is improved purchase and a much better seal around the tip, which is a prerequisite for attaining high vacuum.
• Chopping shares many of the same advantages of supracapsular phaco techniques. All of the emulsification is reserved for phaco-assisted aspiration of the fragments that, because they are small, have been elevated out of the capsular bag. This allows the emulsification to be done centrally in the pupillary plane at a safe distance from the posterior capsule.
However, unlike other supracapsular techniques, the all-or-none prerequisite of prolapsing the entire nucleus up through the capsulorhexis is avoided. The need to prolapse or flip the nucleus may be risky with a shallow chamber or when the capsulorhexis is much smaller than the diameter of the endonucleus.
|Closeup of vertical chopper tip (Chang Combination Chopper, Katena Inc.)|
• Finally, with phaco chop, it is the chopper that does most of the work. The phaco tip stays relatively immobile in the center of the pupil, providing an exit conduit for the fragmented lens material. Using a slender, versatile, manual instrument, instead of the phaco tip, to perform all of the most critical maneuvers means that most of the ultrasound and aspiration take place at the safest distance from the posterior capsule, and away from the edge of the pupil and capsulorhexis. This feature makes it less likely for the phaco tip to incise the CCC edge in small pupil cases.
By limiting how peripherally we can sculpt and diminishing the red reflex, small pupils complicate the sculpting of a deep, central trough. Because chopping is a more kinesthetic procedure, there is really no need to visualize the depth of the phaco tip. This is why chopping is advantageous with a poor or absent red reflex, as with small pupils and mature nuclear or cortical cataracts.
This reliance on the chopper is a great advantage if you have trouble rotating the nucleus for any reason. This can result from extremely loose zonules, or we may want to avoid rotation if there's a tear in the capsulorhexis. In the latter case, I believe it is rotation of the nucleus that is most apt to extend the capsulorhexis tear into the posterior capsule. In these situations, several chops can be made without any rotation by simply repositioning the chopper in different equatorial locations.
These same four universal benefits apply whether you use horizontal or vertical chop, and comprise the compelling advantages that chopping offers for difficult and complicated cases.2
In looking at the many variations of phaco chop, I've tried to simplify the classification by dividing them into two general categories of chopping: horizontal and vertical.3 Both share the same benefits of being able to fragment the nucleus manually, but they do so in different ways.
Kunihiro Nagahara's original technique is horizontal chopping. Here, you hook the nuclear equator with the chopper within the capsular bag, and basically trap the nucleus between the chopper and phaco tips. Since the chopper moves centrally toward the fixating phaco tip in the horizontal plane, I refer to this as horizontal chopping.
The horizontal technique depends on compressive force to fracture the nucleus. This takes advantage of a natural fracture plane in the lens created by the lamellar orientation of the lens fibers. The key skill to master is hooking the nuclear equator within the epinuclear space of the peripheral capsular bag.
In addition, a substantial amount of the endonucleus must lie within the path of the chopper. If the phaco tip is too superficial or too central, or the chopper tip is not kept deep enough as the chop is performed, it won't work. If the nucleus is very large in diameter, and extremely thick, the mechanics of trying to get as much of that nucleus as possible between the chopper and phaco tips is more difficult.
|A horizontal chop of a heminucleus. Note that high vacuum is utilized to increase the purchase of the phaco tip.|
Hideharu Fukasaku's "Snap & Split," and "Phaco Quick Chop," as taught by Vladimir Pfeifer and David Dillman, typify vertical chopping techniques. Here, the phaco tip is used to lollipop into the lens and fixate it, as a very sharp chopper tip penetrates into it and cleaves or chisels away a portion of it. Since the instrument descends from above and tends to move in a vertical direction, I call this vertical chopping. This technique imparts a shearing force to the nucleus in order to generate the fracture.Chopper Design
Since horizontal and vertical choppers work in dissimilar ways, their design is quite different.
Horizontal choppers feature a 1.5 to 2.0 mm long tip in order to be able to transect a relatively thick nucleus. The end of the tip is always dull, in case it ever contacts the posterior capsule. I prefer the curved shape of an elongated microfinger because it can wrap around the lens equator without tenting up the peripheral fornix of the bag.
Vertical choppers feature a shorter tip, but the point must be very sharp in order to penetrate dense nuclear material. If the tip is too dull, it will dislodge the nucleus off of the phaco tip rather than incising into it. I designed and use a combination chopper with vertical and horizontal choppers on opposite ends (Chang Combination Chopper, Katena Inc.).
Although I use both techniques with equal frequency, they are different and have complimentary advantages and disadvantages
As a snapping technique, vertical chop requires a certain brittleness to the nucleus. This makes it less effective for the softer end of the density spectrum, and I prefer horizontal chopping for these cases. In vertical chopping, adequate depth of the phaco tip is the critical factor. I start by impaling the nucleus first, spearing it as deeply as I can in the center with the phaco tip, before incising into it vertically with the sharp chopper. You may even want to lift the nucleus slightly as you're chopping downward to ensure that you are not pushing against the posterior capsule.
In contrast, horizontal chopping is more dependent on adequately deep placement of the chopper tip, so I insert that first. A large epinuclear space provides maximal room for placement of the chopper, and one should always transition to this technique with softer lenses at first.
Once I'm comfortable with the chopper placement, I'll brace the nucleus with the phaco tip. Rather than impaling the central nucleus, for a horizontal chop I try to bury the tip as deeply and proximally as possible in order to maximize the mass encompassed between the two tips. Because you need to repeatedly hook the nuclear equator in horizontal chopping, it becomes easier to do as you create more and more vacant space in the bag. Thus with horizontal chopping, I remove the pieces as soon as I've chopped them.
In addition to softer nuclei, I also prefer horizontal chopping when the anterior chamber is extremely deep. Here the steep angle of approach of the phaco tip hinders my attaining a strong enough purchase for vertical chop, but is less of a problem for horizontal chop. Horizontal chopping should not be utilized in the absence of an epinucleus since there will be insufficient space in the peripheral bag to accommodate the chopper. In addition, with such bulky, brunescent nuclei, the horizontal chop may not pass deeply enough to divide the leathery posterior plate.
Vertical for Brunescent Nuclei
Because vertical chop is more consistently able to fracture this posterior plate, it is my preference for denser nuclei. If you imagine using an axe to split an upright log, the blade only penetrates part way. Pushing the two halves apart is necessary in order to extend the split through the remainder of the log. The same is true for the initial horizontal or vertical phaco chop since it is impossible to position the phaco tip externally at the opposite pole of the nucleus.
Once the partial split is made by the chopper, it is the sideways separation of the instrument tips that extends the fracture along the natural lamellar cleavage plane through the remaining nucleus. In horizontal chop, the developing fracture moves in the horizontal plane toward the surgeon. It will not tend propagate more and more posteriorly. In contrast, with vertical chop, as we pry the two halves apart the developing fracture moves downward in the vertical plane until it eventually extends through the posterior plate.
With an ultra-brunescent lens, I also alter the angle of my vertical chop slightly. Instead of incising straight down like a karate chop striking a board, my chop approaches the phaco tip more diagonally. This provides more of a horizontal vector to push the nucleus against the tip as the vertical vector initiates the downwardly directed fracture. This "diagonal" chop therefore combines the advantages of both strategies. Another option is to sculpt a small central pit into the bottom of which the phaco tip is maximally impaled. Retracting the irrigation sleeve allows the phaco tip to penetrate deeply enough to approach the center of these unusually thick nuclei.
Unlike with horizontal chopping, I don't remove the vertically chopped pieces until the entire nucleus is fragmented. This is because the presence of the adjacent interlocking pieces gives better immobilization of the section that I'm chopping. Once I start to elevate the loose fragments out of the capsular bag, I often find that they are still quite sizable. In order to subdivide them into smaller pieces, I then switch to the microfinger tip on the opposite end of my combination chopper for horizontal chopping.
While it is hard to adequately immobilize these mobile pieces for a vertical chop, horizontal sub-chopping is easily accomplished by crushing the large fragment between the chopper and phaco tips. This is why I advise mastering both chopping variations. Not only do they allow me to better handle the entire spectrum of nuclear density, but I can also employ both techniques for different stages of the same case.
The Learning Curve
Compared to divide-and-conquer, phaco chop is more difficult to learn because the most difficult skills are performed with the non-dominant hand. This is one of the reasons why the learning curve may be longer than people anticipate.
To achieve a successful chop, there are five interdependent conditions that must simultaneously occur: proper placement of the chopper; proper placement of the phaco tip; stabilization of the nucleus with high vacuum; keeping the chopper tip deep during the actual chop; and proper orientation of the chopper shaft at the limbus. In this coordination of positions and motions, the dexterity of the non-dominant hand is very critical. For instance, inadvertently depressing the paracentesis site with the chopper shaft will impede proper movement of the chopper tip and may compromise visibility and chamber stability.
For this reason, I recommend that you first start using the chopper as a second instrument for your divide-and-conquer technique until you are comfortable working with it in your non-dominant hand. Once the nucleus has been cracked into quadrants, you can practice hooking the equator and tumbling the quadrant out of the bag with the horizontal chopper. You can also chop a mobilized quadrant or heminucleus while holding it in the center of the pupil under direct visualization. These component skills can therefore be developed and rehearsed while still performing a divide-and-conquer or stop-and-chop procedure.
While you can't be wildly aggressive with chopping techniques, neither can you be timid and hesitant. There is a certain pace and timing to doing these maneuvers which you can learn by observing other surgeons.
Once you finally achieve that first successful chop, you will forever remember and recognize how it is supposed to look and feel. This is similar to the quantum leap in your learning curve that occurred after you successfully cracked a grooved nucleus in half for the first time. After you've mastered the horizontal or vertical chopping maneuver, you simply repeat the same step over and over again as you fragment the remainder of the lens. In addition, whether you master horizontal or vertical phaco chop first, learning the second variation becomes infinitely easier, because you already have a good understanding of the mechanics of chopping.
Dr. Chang is a clinical professor of ophthalmology at the University
of California, San Francisco and in private practice in Los Altos, California. Contact him at 650-948-9123, or firstname.lastname@example.org. He has no financial interest in any instruments or products mentioned.
1. Leaming D. Practice styles and preferences of ASCRS member—2001 Survey. J Cataract Refract Surg 2002;28:1681-1688.
2. Chang, DF. Prevention Pearls and Damage Control. Chapter 31 in Complications in Phacoemulsification, edited by W. Fishkind, Thieme, 2002
3. Chang, DF: Converting to Phaco Chop: Why and How. Ophthalmic Practice 17:4,1999
4. Chang DF. Mature Cataracts—Capsular Dye and Phaco Chop. Chapter 17 in Phako, Phakonit and Laser Phako: A Quest for the Best, edited by S. Agarwal, A. Agarwal, A. Agarwal. Highlights of Ophthalmology. 2002.