Choosing Your Chop Technique
The pros and cons of the most popular approaches.
BY TERRY KIM, M.D. AND KUNAL KANITKAR, M.D.

Phacoemulsification surgery has evolved dramatically since its inception. In terms of surgical technique, the nucleus removal portion of the procedure continues to be rapidly refined, with resulting improved safety and efficiency. During the 1980s, Howard Gimbel, M.D.'s, divide and conquer method was the prevailing approach to phacoemulsification nucleus removal.

At the 1993 meeting of the American Society of Cataract and Refractive Surgery, Kunihiro Nagahara, M.D., presented a technique known as phaco chop. Within the past decade, the chop technique and its various incarnations have become popular choices among cataract surgeons. These techniques have been shown to remove the lens nucleus with minimal energy and maximum speed. In experienced hands, these techniques have excellent safety profiles. Over the years, a number of adaptations to Dr. Nagahara's original chopping technique have been described and have gained popularity.

Chopping Basics

Chopping techniques are so named because they are analogous to chopping wood. Much as a wooden log has a plane in which a wedge can easily cause splitting, so does the lens nucleus have its own cleavage planes. The direction of splitting follows the lens fibers, which course from equator to equator through the center of the lens nucleus. All chopping techniques rely on the lens to split easily when forces are applied in certain directions. Most chopping techniques rely on the phacoemulsification handpiece to stabilize the nucleus, while a second instrument (called a chopper) cleaves and pulls apart pieces of the lens. Dozens of choppers have been designed for various purposes. Ultrasound energy is conserved by the chopper's application of manual energy, which is more localized and less likely to cause endothelial damage than ultrasound energy. Disassembly of the lens nucleus into fragments allows these larger pieces to be aspirated, further decreasing ultrasound energy delivery.

All chopping techniques are dependent on good wound construction, relatively large continuous curvilinear capsulorrhexis, and good hydrodissection. Necessary instruments include a phacoemulsification handpiece with sufficient tip exposure and a chopping instrument. Some of the more popular chopping techniques are described in this article.

Phaco Chop (Horizontal Chop)

Dr. Nagahara's chopping technique, also known as horizontal chop, has been practiced since 1993. The phacoemulsification tip is initially buried in the direction of the center of the nucleus. The lens nucleus is held in position using relatively high vacuum, while the chopping instrument is passed under the distal edge of the anterior capsulotomy and around the lens equator. The tip of the chopper is then drawn through the lens nucleus toward the phaco handpiece in the horizontal plane, cleaving the lens. The phaco tip and chopper are then separated laterally, breaking the nucleus into two pieces. The nucleus is then rotated 90 degrees, and the same procedure is performed on each of the lens halves. The nucleus is broken into four or more pieces, depending on the density of the lens (more pieces for denser lenses). The lens fragments are then removed and emulsified.

The benefit of phaco chop is that the nucleus can be rapidly disassembled, resulting in significantly decreased use of ultrasound energy. Phaco chop makes the time and energy spent on creating grooves, as in divide and conquer, unnecessary. Since the force vectors in horizontal phaco chop are pointed centrally, less stress is placed on the zonular fibers and capsular bag, which makes this technique preferable in situations of loose or broken zonules (i.e., pseudoexfoliation) and anterior-capsule tears. The primary limitation is the difficulty in removing the initial segment following separation of the nucleus into pieces. Little room for maneuvering remains, with the pieces interlocking like a puzzle. Additionally, there exists a steep learning curve for phaco chop. Increased risk of capsular tears and zonular dehiscence exists for inexperienced surgeons.

Quick Chop (Vertical Chop)

Quick chop is a variant of the phaco chop technique in which the chopper is not passed horizontally around the lens equator, but rather enters the nucleus vertically near the center of the lens. The phaco tip is initially exposed, with the silicone sleeve withdrawn approximately 2.5 mm. The tip is buried into the center of the nucleus, and the nucleus is held in place with vacuum. Next, the chopper is placed slightly in front of the phaco tip, and the chopper tip is embedded as deeply as possible into the lens. Force is placed laterally and downward with the chopper to split the lens into two halves. The nucleus is rotated, and a similar procedure is performed on each lens half. The benefits of this procedure are the good visualization of the chopper throughout, and the avoidance of proximity to the capsular bag, resulting in increased safety. Quick chop is an important technique for small pupil cases or cases where the capsulorhexis is small. A chopper with a thinner, sharper blade is often necessary for quick chop. However, this procedure may be limited in dense cataracts where the chopper can have difficulty initially embedding onto the lens nucleus.

Prechop

Prechop is a method of nucleus removal in which the nucleus is broken into fragments prior to placing the phacoemulsification handpiece into the eye. Use of a prechopper is required, such as the micro combo prechopper popularized by Takayuki Akahoshi, M.D. A prechopper is an instrument with two flat blades, which are apposed during entry into the nucleus, but can separate once inside the nucleus. After hydrodissection is complete, the prechopper tip is inserted toward the center of the lens nucleus. If resistance to entry of the prechopper is encountered, a second instrument can be used to stabilize the nucleus and provide counter-traction. As the prechopper blades are separated, the nucleus starts to crack. The prechopper tip is then advanced deeply into the crack, and the splitting of the nucleus progresses. This procedure continues until the nucleus is fully cracked. The prechopper is then used to spin the nucleus and split it in a perpendicular direction. After the nucleus is broken into fragments, the phacoemulsification handpiece is used to remove the fragments (with or without the use of a second instrument). Benefits of the prechopping technique include the ease of use, the quick splitting of the nucleus, and the elimination of grooving or sculpting with the phaco handpiece. Prechopping can also neatly divide very soft lenses, which may be difficult to split by other methods. The prechopping technique does require a soft-to-medium density nucleus. For denser lenses, the prechopper will have difficulty initially entering the lens.

Stop and Chop

Stop and chop is a variant of the horizontal chop technique in which the nucleus is divided into two pieces before chopping begins. In the same way as in the initial step of the divide and conquer method, a central groove is made through the lens nucleus. The chopper and phaco tip are placed together in the groove and then separated to divide the nucleus into halves. Each individual half is then chopped in a manner identical to phaco chop. This method may take slightly more time than phaco chop, and it likely will use more ultrasound energy. However, the benefit of stop and chop is that more maneuvering room is created within the capsular bag. Thus, the first nuclear segment is easier to remove from the capsular bag or to emulsify in-situ than with traditional phaco chop. Due to the minimum of outward force on the capsular bag, stop and chop is also a very safe technique. Because this technique is simpler to learn than phaco chop, many surgeons learn stop and chop as a bridge between the divide and conquer and phaco chop techniques.

Bimanual Chop

Bimanual phacoemulsification is an interesting refinement of cataract surgery that is growing in popularity. Two small incisions (1.2 mm or less) are placed in the cornea in order to allow entry of a sleeveless phacoemulsification handpiece and a separate irrigating chopper. Chopping then proceeds in any of the methods described above. The difference is that the irrigation port is on the chopping instrument. The risks and benefits of bimanual chop are due more to the nature of the small incisions and the sep-

arated irrigation and aspiration than the specific chopping technique. Bimanual chop requires different equipment and adjusted technique compared with standard coaxial phaco. Disadvantages of this technique include insufficient irrigation pressures causing chamber instability during fragment removal and tight incisions that can cause oarlocking of instruments.

Currently, intraocular lenses that can be implanted through such small incisions are not available in the United States, but are under investigation. In its favor, bimanual microincision phacoemulsifiction can offer astigmatically neutral incisions. The wounds are more likely to self-seal and can theoretically offer a reduction in endophthalmitis rates. Separating the irrigation from the phaco/aspiration can also improve followability. In addition, removal of subincisional cortex is facilitated by this technique.

A Chop for All Cases

Since its introduction, phacoemulsification surgery has undergone tremendous advances in instrumentation and technique. One of the most important advancements in technique is the development of phaco chop. Chopping offers improved speed and safety, thus increasing operating room efficiency and improving patient outcomes. The various refinements of phaco chop increase its applicability in various clinical situations. The continuing advancement of chopping techniques also accompanies and stimulates advancements in IOL technology.

Terry Kim, M.D., is associate professor of ophthalmology at Duke University School of Medicine and associate director of cornea and refractive surgery at Duke University Eye Center, Durham, N.C. Dr. Kim can be reached at (919) 681-3568. Kunal Kanitkar, M.D., is affiliated with the cornea department at Duke University Eye Center, Durham, N.C. Neither author has financial interest in the information contained in this article.

References

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