All chopping techniques rely on the principle of lens “disassembly,” in which the firm nucleus is divided into smaller maneuverable pieces. As a result the 10-mm wide nucleus can be removed through a 5-mm diameter capsulorrhexis, and the majority of the nucleus is emulsified near the center of the pupil at a safe distance from the iris, posterior capsule, and corneal endothelium.
II. CHOPPING PREREQUISITES
The capsulorrhexis preserves the bag-like anatomy of the capsule.It provides secure fixation and centration of the intraocular lens (IOL), and its continuous edge renders the capsular bag much more resistant to tearing during nuclear emulsification. Hydrodissection separates the nucleus from the capsule and cortex so that it can spin within the capsular bag.It also loosens the capsular-cortical attachments, which facilitates cortical cleanup.
The hydrodelineation wave cleaves a thin epinuclear shell apart from the firm endonucleus, reducing the dimensions of the central mass that must be chopped, fragmented, and emulsified. In addition, the bulk of the epinuclear shell blocks the exposed posterior capsule from trampolining toward the phaco tip as the final endonuclear fragments are emulsified.
III. CLASSIFICATION OF CHOPPING TECHNIQUES
Since Kunihiro Nagahara first introduced the concept of phaco chop in 1993, many different chopping variations have been described.This diverse array of modifications can be confusing to transitioning surgeons. For simplification, this author first proposed that all chopping methods be conceptually divided into 2 general categories: horizontal and vertical.Both share the same benefit of fragmenting the nucleus manually but accomplish this objective in different ways. The classic Nagahara technique exemplifies horizontal chopping because the instrument tips move toward each other in the horizontal plane during the chop (Figure 14-1A). In vertical chopping, the 2 instrument tips move toward each other in the vertical plane in order to create the fracture (Figure 14-1B).
IV. PHACO PRECHOP
Takayuki Akahoshi and Jochen Kammann pioneered methods of prechopping the nucleus prior to insertion and use of the phaco tip. In the case of a denser lens, one manual instrument must generally hook the equator (as with horizontal chopping) so that the penetrating and chopping forces are not transmitted directly to the capsular bag and zonules.
One potential problem with prechop techniques is that there is no phaco tip to aspirate the lens debris liberated after the initial chop. This may impair visibility for subsequent steps. Another problem is that prechop techniques and instrumentation are designed to create 4 nuclear quadrants. For denser and larger nuclei, it is more desirable to create multiple smaller pieces. With dense nuclei it is also difficult to judge how deeply the splitting instrument has penetrated. Over-penetration risks posterior capsule perforation. Finally, prechopping requires additional steps and instrumentation that are avoided when the phaco tip itself is utilized for the chopping technique. By prechopping and softening the nucleus the femtosecond laser further reduces the amount of ultrasound or manual instrument energy needed to remove the lens. As would be expected, the denser the nucleus the greater the reduction in ultrasound energy and time afforded by femtosecond laser nucleotomy is.
V. STOP AND CHOP
Paul Koch’s “stop and chop” method is a hybrid of divide-and-conquer and horizontal chopping. A deep, central groove is first sculpted in order to crack the nucleus in half. One then stops the divide-and-conquer method, and chops the heminuclei. Although this method utilizes some horizontal chop- ping, this author coined the term nonstop chop to differentiate and designate pure chopping techniques that eliminate all sculpting.
The advantage of “stop and chop” is that it avoids the difficult first chop. As a result, one only chops across the radius, rather than the full diameter of the nucleus. Second, unlike with the initial nonstop chop, the phaco tip can be positioned within the trough up against the side of the heminucleus that is to be cleaved. Finally, the presence of the trough facilitates removal of the first fragment because it is not tightly wedged inside the capsular bag. While chopping the heminuclei does reduce total ultrasound energy, the majority of sculpting during divide-and-conquer is used to create the first groove. Thus, “stop and chop” does not provide the full benefits of nonstop chopping listed next.
*Dikutip dari Buku Essentials Of Cataract Surgery 2nd Ed, halaman 135-137