Several different variations of the chopping technique have evolved since Kunihiro Nagahara, MD, gave his original presentation at the 1993 ASCRS meeting. Conceptually, these can be divided into two main categories.1 I call the classic Nagahara technique horizontal chopping, because the instrument tips move toward each other in the horizontal plane during the chop. In vertical chopping, the two instrument tips move toward each other in the vertical plane in order to create the fracture. Although David Dillman, MD, later popularized the name “phaco quick chop,” the “phaco snap and split” technique, developed by Hideharu Fukasaku, MD, was the first incarnation of this concept. All chopping techniques utilize manual instrument forces to segment the nucleus, thereby replacing the ultrasound power otherwise needed to sculpt grooves. Such energy efficiency is possible because the lamellar orientation of the lens fibers creates natural fracture planes within the hardened nucleus that are exploited by the chopping maneuver.The surgeon eventually elevates these smaller nuclear segments into the supracapsular space for phaco-assisted aspiration at a safe distance from the posterior capsule.
I believe that phaco chop provides the same advantages as supracapsular phaco flip—efficiency, safety, and reduced stress on the capsular bag—without the difficulty of prolapsing the entire nucleus out of the bag in one piece.
ADVANTAGES FOR CHALLENGING CASES
During sculpting, the capsular bag fixates the nucleus. In comparison, chopping applies much less force against the zonules because the phaco tip secures the nucleus, and the manual instrument forces are directed centripetally against each other. This difference in zonular stress is particularly evident when comparing chopping and sculpting from the Miyake-Apple viewpoint in cadaver eye surgery.
During chopping, the critical instrument maneuvers are primarily kinesthetic, and are performed with the chopper tip. The surgeon does not need the red reflex to visually gauge the depth of the instrument tips, which is advantageous when dealing with mature cataracts. Because the phaco tip is relatively stationary and always remains in the central 2- to 3-mm pupillary zone, phaco chop is an excellent technique for small pupil cases.
In addition to improved efficiency, the features of reduced phaco power, reduced zonular stress, decreased reliance on the red reflex, and the supracapsular location of emulsification all serve to enhance safety. These universal benefits of both horizontal and vertical phaco chop are particularly important for complicated cases such as brunescent nuclei, white cataracts, loose zonules, capsulorhexis tears, and small pupils.
HORIZONTAL PHACO CHOP
Following the capsulorhexis and hydrodissection, hydrodelineation is performed in order to define and separate the epinuclear shell. After the surgeon fragments and removes the endonucleus, he aspirates and flips the remaining epinuclear shell as the final step. In horizontal chop, the chopper tip must hook the equator of the endonucleus peripherally beneath the anterior capsule. Several steps and principles that help the surgeon to properly place the chopper tip are discussed in the following paragraphs.
There are numerous horizontal chopper designs, but all feature an elongated tip, which is blunt to avoid capsule perforation. A relatively long tip is necessary in order to transect thicker, brunescent nuclei, and the inner cutting surface of the tip may be sharpened for this purpose. I prefer a modified Lieberman Microfinger (the Chang Combination Chopper; Katena Products, Inc., Denville, NJ) for horizontal chopping because its slender, curved tip is ideally shaped for hooking and cupping the lens equator (Figure 1A). Typical right-angled chopper tips do not conform as well to the natural contour of the equator and can result in more distention of the peripheral capsular bag.
The surgeon first aspirates the central anterior epinucleus with the phaco tip in order to better estimate the size of the endonucleus and the amount of separation between the endonucleus and the capsular bag. The chopper tip touches the central endonucleus, and maintains contact as the surgeon passes it peripherally beneath the capsulorhexis edge. This ensures that the tip stays inside the bag as it descends and hooks the endonucleus peripherally (Figure 1B). Because the chopper tip drops into and occupies the epinuclear space, it does not overly distend or stretch the capsular bag fornix. Although not approved for use in the US, capsular dye improves visualization of the capsulorhexis for this step and is a useful teaching adjunct.2,3
Once it has hooked the nuclear equator, the surgeon may use gentle palpating motions with the chopper to confirm that the tip is internal and not external to the capsular bag. Next, the surgeon deeply impales the nucleus with the phaco tip. The phaco tip should be directed downward and positioned as proximally as possible in order to maximize the nuclear mass encompassed between the two instrument tips. The surgeon pulls the chopper tip directly toward the phaco tip, and upon contact, moves the two tips slightly apart (Figure 1C and 2A). This separating motion propagates the fracture across the entire nuclear diameter.
If the surgeon has not positioned the phaco and chopper tips deep enough, the chop will not succeed. The thicker and denser the endonucleus, the deeper the chopper tip must pass. The tendency to elevate the chopper tip during the chop arises from a fear of perforating the posterior capsule. Instead of dividing the nucleus, this may merely score the superficial nuclear surface.
The surgeon rotates the nucleus in a clockwise direction and repeats the maneuver in order to create a pie-shaped fragment. He then elevates this fragment out of the bag using high vacuum (Figure 2B). Once he chops and evacuates the first heminucleus, there is enough room to pull the second heminucleus to the center of the bag. The surgeon can then perform subsequent chops without having to place the chopper beneath the anterior capsule.
VERTICAL PHACO CHOP
In the case of denser nuclei, a horizontal chopper must exert a greater compressive force in order to fracture the nucleus along its natural lamellar cleavage plane. In contrast, vertical chopping utilizes a shearing force to split the nucleus into pieces. The vertically chopped edges appear sharp, like pieces of broken glass, because there is no crushing force involved.
Whereas a horizontal chopper moves centripetally inward from the periphery, the surgeon uses the vertical chopper like a spike to impale downward into the nucleus just anterior to the centrally buried phaco tip. This action creates the fracture line that is propagated farther posteriorly when he separates the embedded instrument tips (Figure 3B, C, and D). All vertical chopper designs have a short, sharpened tip that is able to penetrate the nucleus (Figure 3A). If the chopper tip is too dull, it will displace the fragment from the phaco tip instead of incising into it.
The key to a successful vertical chop is to impale the phaco tip as deeply into the central nucleus as possible (Figure 3B). Like spearing a potato, the tip must gain enough purchase to be able to lift the entire nucleus upward. By immobilizing the nucleus against the incoming sharp chopper tip, the surgeon generates enough shearing force to fracture the material. High vacuum is invaluable for vertical chop, which requires a maximally strong purchase. With brunescent lenses, burst mode helps to maintain a tight seal around the phaco tip, which is a prerequisite for accessing high vacuum.
COMPARING CHOPPING TECHNIQUES
In horizontal chop, sequentially removing each newly created fragment provides the chopper with increased working space within the capsular bag. Because there is no need to hook the equator with vertical chopping,
Vertical chopping requires a nucleus that is brittle enough to be snapped in half. Therefore, horizontal chopping is better suited for the softer nucleus. I prefer vertical chopping for brunescent nuclei because it is more consistently able to fracture through the leathery posterior plate. However, if mobile brunescent pieces must be subdivided, horizontal chopping is more effective as this maneuver traps and compresses the fragment between the two instrument tips (Figure 2C).
Horizontal and vertical chopping are complementary variations offering different advantages but common benefits. I utilize both chopping techniques routinely depending on the nuclear density. With dense lenses, I may employ both strategies during the same case, and I designed the Chang double-ended combination chopper (Katena Products, Inc.) to provide both tips on a single instrument.David F. Chang, MD, is a clinical professor of ophthalmology at the University of California, San Francisco, and is in private practice in Los Altos, California. He has no financial interest in any product mentioned herein. Dr. Chang may be reached at (650) 948-9123; firstname.lastname@example.org.
1. Chang DF: Converting to Phaco Chop: Why? Which technique? How? Ophthalmic Practice. 1999; 17(4):202-210.
2. Horiguchi M, Miyake K, Ohta I, Ito Y: Staining of the lens capsule for circular continuous capsulorhexis in eyes with white cataract. Arch Ophthalmol. 1998; 116:535-537.
3. Melles G, de Waard P, Pameyer J, Beekhuis W: Trypan blue capsule staining to visualize the capsulorhexis in cataract surgery. J Cataract Refract Surg. 1999; 25:7-9.