VI. PURE CHOPPING TECHNIQUES
There are 5 important advantages to phaco chop:
- 1. Reduction in energy delivery
- 2. Reduction in stress on the zonules and capsular bag
- 3. Supracapsular emulsification
- 4. Decreased reliance on the red reflex
- 5. Greater reliance on the chopper than the phaco tip
A. Reduction in Energy Delivery
Pure chopping techniques eliminate lens sculpting. Ultrasound energy is not required to subdivide the nucleus and is reserved for the phaco-assisted aspiration of mobile fragments.The marked reduction in phaco power and energy is particularly important for brunescent nuclei where the risk of endothelial cell loss and wound burn is higher.
B. Reduction in Stress on the Zonules and Capsular Bag
The capsular bag fixates the nucleus during sculpting, which risks zonular trauma when dealing with a bulky brunescent nucleus. Unlike a soft nucleus that absorbs pressure like a pillow, a large firm nucleus directly transmits any instrument forces, such as sculpting, rotation, and cracking directly to the capsular bag and zonules. With chopping it is the phaco tip that braces and immobilizes the nucleus against the incoming mechanical force of the chopper (see Figure 14-1). The manual forces, generated by one instrument pushing against the other, replace the need for ultrasound energy to fragment the nucleus. In addition, these manual forces are directed centripetally inward away from the zonules, rather than outward toward the capsule. This significant difference in zonular stress is readily appreciated when both chopping and sculpting are compared from the Miyake-Apple viewpoint in cadaver eyes.
C. Supracapsular Emulsification
Chopping provides many of the same advantages of supracapsular phaco techniques.With phaco chop, virtually all of the emulsification is reserved for phaco-assisted aspiration of small fragments that have been elevated out of the capsular bag. This allows the emulsification to be performed centrally in the pupillary plane at a safe distance from the iris, posterior capsule, and endothelium. The phaco tip does not need to travel outside the central 2 to 3 mm zone of the pupil, which decreases the chance of incising the iris or capsulorrhexis edge in eyes with poor mydriasis. However, unlike with other supracapsular techniques, the all-or-none prerequisite of prolapsing the entire nucleus anteriorly out of the capsular bag and through the capsulorrhexis is avoided.
D. Decreased Reliance on the Red Reflex
The increasingly brighter red reflex at the base of the trough allows us to judge the depth of the phaco tip during sculpting. During chopping the maneuvers performed with the instruments are more kinesthetic and tactile. Because it is not necessary to visualize the exact depth of the phaco tip, chopping is advantageous with a poor or absent red reflex, such as with small pupils and cortical or mature nuclear cataracts.
E. Greater Reliance on the Chopper Than the Phaco Tip
Finally, with phaco chop, it is the chopper that executes the most important maneuvers. The phaco tip remains relatively immobile in the center of the pupil, providing an exit conduit for the fragmented lens material. Compared to the phaco tip, the chopper provides much greater maneuverability and freedom of motion. This is advantageous if the nucleus fails to rotate for any reason (eg, extremely loose zonules, unsuccessful hydrodissection, or the need to avoid hydrodissection, such as with polar cataracts). In these situations, sequential chops can be made without rotating the nucleus by simply repositioning the chopper in different equatorial locations and chopping toward the centrally impaled phaco tip. In addition to the improved efficiency of chopping techniques, safety is enhanced by these aforementioned attributes of reduced ultrasound power, reduced zonular stress, decreased reliance on the red reflex, and the supracapsular and central location of emulsification. These features universal to both horizontal and vertical chopping make them optimal techniques for difficult and complicated cases. The improved ability to handle brunescent nuclei, white cataracts, loose zonules, posterior polar cataracts, crowded anterior chambers, capsulorrhexis tears, and small pupils should be the primary motivation for a divide-and-conquer surgeon to transition to phaco chop.
VII. HORIZONTAL PHACO CHOP
Nagahara’s original technique is the classic horizontal chopping method. All subsequent variations make use of the same principle whereby the chopper hooks the endonucleus inside the capsular bag and chops centrally toward the fixating phaco tip in the horizontal plane. The horizontal chopping technique relies upon compressive force to fracture the nucleus. This exploits natural fracture planes in the lens created by the lamellar orientation of the lens fibers. The key first step is to hook the nuclear equator with the chopper tip within the epinuclear space of the peripheral capsular bag prior to initiating the horizontally directed chop (Figure 14-1A and 14-2A).
A. Initial Placement of the Chopper Tip
Hydrodelineation is particularly important for horizontal chopping be- cause it decreases the diameter of the endonucleus that must be peripherally hooked and divided by the chopper. In addition, the separated soft epinucleus provides a working zone for the chopper where it can be manipulated peripheral to the endonuclear equator without overly distending or tearing the capsular bag.
Prior to placing the chopper, the central anterior epinucleus should be aspirated with the phaco tip. This allows one to better visualize and estimate the size of the endonucleus and the amount of separation between the endonucleus and the surrounding capsular bag. The chopper tip touches the central ante- rior endonucleus and maintains contact as it passes peripherally beneath the opposing capsulorrhexis edge. This ensures that the tip stays inside the bag as it descends and hooks the endonucleus peripherally. Although some surgeons tilt the chopper tip sideways to reduce its profile as it passes underneath the capsular edge, this is generally unnecessary unless the capsulorrhexis diameter is small. The elongated horizontal chopper tip can be kept in an upright and vertical orientation because the capsulorrhexis will stretch like an elastic waistband without tearing.
Once it reaches the epi/endonuclear junction, the chopper tip should be vertically oriented as it descends into the epinuclear space alongside the edge of the endonucleus (see Figure 14-1A and 14-2A). The smaller the endonucleus, the larger the epinucleus, and the easier this step will be. Slightly nudging the nucleus with the chopper confirms that it is alongside the equator and that it is within, rather than outside, the bag. Trypan blue capsular dye improves visualization of the anterior capsule for this step and is a useful teaching adjunct.Another helpful measure for transitioning surgeons is to inject a dispersive ophthalmic viscosurgical device (OVD), such as Viscoat, beneath the nasal capsulorrhexis edge. This further separates the anterior capsule from the endonucleus and displaces any overlying cortex and epinucleus to afford optimal visualization of these anatomic relationships.
B. Executing the First Chop
Next, one must deeply impale the nucleus with the phaco tip. The phaco tip should be directed vertically downward and positioned as proximally as possible in order to maximize the amount of nucleus located in the path of the chopper (see Figure 14-1A). If the depth of the phaco tip is too shallow, sufficient compression of the central nucleus cannot occur. Once impaled, the phaco tip holds and stabilizes the nucleus with vacuum in foot pedal position
The chopper tip is pulled directly toward the phaco tip, and upon contact, the 2 tips are moved directly apart from each other (Figure 14-2B). This separating motion occurs along an axis perpendicular to the chopping path, and propagates the fracture across the remaining nucleus located behind the phaco tip (Figure 14-2C). The denser and bulkier the endonucleus, the further the hemisections must be separated in order to cleave the remaining nuclear attachments. Thanks to the elasticity of the capsulorrhexis, a wide momentary separation of large nuclear hemisections will not tear the capsular bag.
In order for the initial chop to succeed, a substantial amount of the central endonucleus must lie within the path of the chopper. Particularly if the anterior epinucleus has not been removed, it is easy to misjudge the depth of the 2 instrument tips. If the phaco tip is too superficial or too central, or the chopper tip is not kept deep enough throughout the chop, the nucleus will not fracture.Instead, the chopper will only score or scratch the anterior surface. The larger and denser the nucleus is, the more difficult proper positioning of the 2 instrument tips becomes. Fear of perforating the posterior capsule creates a counterproductive, but natural tendency to elevate the chopper tip during the chop.
The ergonomics and tactile “feel” of the horizontal chop will vary signifi- cantly as one advances along the spectrum of nuclear density. A soft nucleus has the consistency of soft ice cream and no resistance is felt as the chop- per is moved. With a medium density nucleus, the chopper encounters slight resistance, indicating that some compression is taking place. This resistance becomes much greater when chopping a dense nucleus, where the compressive force is followed by a sudden snap as the initial split occurs. To develop sufficient compressive force, one must move the chopper tip directly toward the phaco tip until they touch before commencing the sideways separating motion. Veering the chopper tip to the left as it approaches the phaco tip prevents the instruments from touching. However, this limits the compressive force and causes the nucleus to swivel and turn.
C. Removing the First Chopped Fragment
Upon completion of the initial chop the nucleus should be bisected in half. After rotating the bisected nucleus 30 to 45 degrees in a clockwise direction, the opposite heminucleus is impaled with the phaco tip in a central location. Repeating the same steps of hooking the equator and chopping toward the phaco tip creates a small, pie-shaped fragment. The strong holding force afforded by high vacuum facilitates elevation of this first piece out of the bag. Insufficient holding force may be the result of inadequate vacuum settings or failure to completely occlude the tip. Single burst mode can enhance the phaco tip’s purchase of a firm nuclear piece by better preserving the initial seal around the opening.
Every subsequent chop is a repetition of these steps, and each wedgeshaped piece is emulsified as soon as it is created. Once half of the capsular bag is vacated, the phaco tip can impale and carry the remaining heminucleus toward the center of the pupil. This allows the horizontal chopper tip to be positioned alongside the outer edge under direct visualization and without having to pass it beneath the anterior capsule.
One advantage of horizontal chopping is that larger nuclear pieces can be subdivided into smaller and smaller fragments. The size of the pieces should be kept proportional to the size of the phaco tip opening. Poor followability and excessive chatter of firm fragments engaged by the phaco tip may indicate that they are too large. Because of their greater overall dimensions, brunescent nuclei will need to be chopped many more times than soft nuclei.
VIII. VERTICAL PHACO CHOP
Hideharu Fukasaku’s “phaco snap and split” and Vladimir Pfeifer’s “phaco crack” (renamed “phaco quick chop” by David Dillman) are examples of vertical chopping because when the chop is first initiated, the instruments move toward each other in the vertical plane (see Figure 14-1B).Whereas the horizontal chopper moves inward from the periphery toward the phaco tip, the vertical chopper is used like a spike or blade from above to incise downward into the nucleus just anterior to the centrally impaled phaco tip (Figure 14-3A). Depressing the sharp spiked tip downward, while simultaneously lifting the nucleus slightly upward imparts a shearing force that fractures the nucleus (see Figure 14-1B). This contrasts with the compressive force produced by horizontal chopping. After initiating a partial thickness split, the embedded instrument tips are used to pry the 2 hemisections apart (Figure 14-3B). Just as with horizontal chopping, this sideways separation of the instrument tips extends the fracture deeper and deeper until the remainder of the nucleus is cleaved in half.
Whereas the depth of the chopper tip is key for horizontal chopping, adequate depth of the phaco tip is the most crucial factor in vertical chop.This is because the centrally impaled phaco tip must completely immobilize the nucleus against the incoming sharp chopper tip in order to generate enough shearing force to fracture it. Slightly elevating the impaled phaco tip also prevents the descending chopper tip from pushing a firm nucleus against the posterior capsule. The need for a strong purchase is also why high vacuum and single burst mode are more critical for vertical than for horizontal chop.
Much like a chisel with a block of ice, the vertical chopper tip can be used to cleave the nucleus into multiple pieces of variable size. The vertically chopped edges may appear sharp, like pieces of broken glass, because there is none of the crushing force that characterizes horizontal chop involved. The sharp vertical chopper tip generally stays central to the capsulorrhexis. Thus, in contrast to horizontal chopping, it is always visualized and does not pass underneath the anterior capsule or behind the iris. For each of the 2 different chopping techniques, one should position the more important instrument first. For horizontal chop, this means hooking the nucleus with the chopper tip first. With vertical chop, the nucleus should first be impaled with the phaco tip.
IX. COMPARING HORIZONTAL AND VERTICAL CHOP—WHICH TECHNIQUE?
Although the author uses both techniques with equal frequency, they employ different mechanisms that have complimentary advantages and disadvantages. It is worth learning and utilizing both variations for this reason. Vertical chopping requires a nucleus that is brittle enough to be snapped in half. A lack of firmness explains the difficulty of performing vertical chop or divide-and-conquer techniques in soft nuclei. The ability of the chopper tip to easily slice through a soft nucleus instead of fracturing it makes horizontal chopping an excellent method for these cases.
Horizontal chopping is more advantageous for eyes with deeper-than- average anterior chambers, where the phaco tip must approach the nucleus from an extremely steep angle.
In such eyes, one must take measures to prevent or reverse lens-iris diaphragm retro-displacement syndrome (LIDRS). The momentary pupillary block can be reversed or prevented by lifting the pupil edge off of the anterior capsule, so that irrigation fluid can flow into the posterior chamber.
Horizontal chop is also this author’s preference for weak zonule cases, such as traumatic cataracts. Because of the inwardly directed, compressive instrument forces, horizontal chop produces the least amount of nucleus movement or tilt. Finally, horizontal chop is more effective for subdividing smaller, mobile nuclear fragments—particularly if they are brunescent. Because small mobile pieces are hard to fixate adequately, attempting to vertically shear such fragments with a chopper will often dislodge the small piece instead. Trapping and then crushing the fragment between the horizontal chopper and the phaco tip will immobilize and divide it most effectively.
The limitation of horizontal chopping is in its relative inability to transect thicker, brunescent nuclei. Indeed, horizontal chopping should never be utilized in the absence of an epinuclear shell since there will be insufficient space in the peripheral bag to accommodate the chopper. Frequently, the horizontally directed path of the chopper is not deep enough to sever the leathery posterior plate of an ultra-brunescent nucleus. If this occurs, the partially chopped pieces will still be connected at their apex, like the petals of a flower. In such cases, it is best to try injecting a dispersive OVD through one of the incomplete cracks in the posterior plate to distance it from the posterior capsule. Since a dispersive OVD resists aspiration, the surgeon can attempt to carefully phaco through the remaining connecting bridges that have been visco-elevated away from the posterior capsule.
Because vertical chop is more consistently able to fracture the leathery posterior plate, it is well suited for denser nuclei.6 In horizontal chop, this propagating fracture continues horizontally toward the surgeon, but it will not tend to advance further and further posteriorly. In contrast, with verti- cal chop, as the 2 halves are pried apart, the advancing fracture propagates downward in the vertical plane until it eventually transects the posterior-most layer. With an ultra-brunescent lens, the vertical chopper should approach the embedded phaco tip more diagonally. This provides more of a horizontal vector that pushes the nucleus against the phaco tip, while the vertical vector initiates the downward fracture. This “diagonal” chop therefore combines the mechanical advantages of both strategies. With denser nuclei, one should also begin by sculpting a small, deep pit centrally. By entering at the base of the pit, the phaco tip can impale more deeply than would have been possible without this preliminary de-bulking. Retracting the irrigation sleeve further maximizes penetration of the phaco tip.
A. Comparison of Horizontal and Vertical Choppers
Horizontal choppers feature an elongated, but blunt-ended tip. A tip length of 1.5 to 2.0 mm length is necessary in order to transect thicker nuclei, and the inner cutting surface of the shaft may be sharpened for this purpose of incising denser lens material. The very end of the tip is always dull to dimin- ish the risk of posterior capsule perforation. The author prefers the curved shape of an elongated microfinger because it can wrap snuggly around the lens equator without distending or stretching the peripheral fornices of the capsular bag (see Figure 14-1A).The microfinger design also allows one to cup the nucleus equator so that it cannot slip away as the compression begins. Vertical choppers feature a shorter tip that has a sharpened point in order to penetrate denser nuclei (see Figure 14-1B). If the tip is too dull, it will tend to knock the nucleus off of the phaco tip rather than incising into it. In contrast to horizontal choppers, the length of the vertical chopper tip is less important since it never encompasses one side of the nuclear segment.
The 3-dimensional motions required of the chopper are much simpler with vertical chop. Compared to horizontal chop, the chopper tip is not placed as peripherally and simply incises downward into the nuclear mass. The tip is kept vertically oriented and is always visible until it descends into the nucleus. In contrast, the horizontal chopper tip is much longer, must execute a far more difficult set of motions, must pass underneath the capsulorrhexis, and must be blindly positioned behind the peripheral iris before initiating the chop. The side-port incision should always serve as the motionless fulcrum for the chopper shaft. In order to avoid displacing or distorting the side-port incision, somewhat counterintuitive movements must be made with the horizontal chopper in particular.
Horizontal and vertical chopping are variations that rely upon different mechanisms to provide complementary advantages and common benefits. The author utilizes both chopping techniques routinely depending on the nuclear density.With dense lenses, one may employ both techniques during the same case, and the Chang double-ended combination chopper (Katena Products, Inc) was designed to provide both a horizontal and a vertical chopper on a single instrument (see Figures 14-1 to 14-3). This also allows the surgeon using a sharp vertical chopper to easily switch to the blunt-tipped horizontal chopper for epinuclear manipulation and removal. The Seibel vertical chopper tip has the profile of a rounded blade with no sharp point that could contact the posterior capsule. For this reason, transitioning surgeons often prefer the Chang horizontal/Seibel vertical chopper as their first combination chopper.
*Dikutip dari Buku Essentials Of Cataract Surgery 2nd Ed, halaman 137 – 146