Phaco prechop, or prephaco chop to be exact, is a nuclear fracture technique that is performed under viscoelastic material prior to phacoemulsification. Using this simple procedure, the surgeon can divide the nucleus without grooving or sculpting, which significantly facilitates phacoemulsification. I first introduced this technique in 1993; however, due to fear of breaking a posterior capsule or ciliary zonules, many surgeons hesitated to attempt this procedure, or tried but abandoned the technique before acquiring the necessary level of skill. The most common questions I have been asked about this procedure are (1) which prechopper should be used? and (2) which direction and at what depth should the prechopper be inserted? To answer these questions, a Combo Prechopper (ASICO, Westmont, IL) was developed. The karate prechop technique is performed with this new instrument; using a single prechopper, most of the cataract nucleus can be processed quite easily and safely.
The karate prechop technique is used for treating relatively soft nuclei with intact ciliary zonules. In Tokyo, presently more than 67% of the cataract cases have a relatively soft nucleus, between grade 1 and 2+. Accordingly, most of these cases can be managed by this technique. Harder nuclei are also prechopped before phacoemulsification; however, the nucleus should be supported with a second instrument during insertion of the prechopper. This is another prechop technique called counter prechop, which is performed with a Universal Prechopper (AE-4282, ASICO) and a Nucleus Manipulator (AE-2530, ASICO). In the presence of weak ciliary zonules such as in cases of pseudoexfoliation syndrome, trauma, and after vitreoretinal surgery or incomplete capsulorhexis, the counter prechop technique is indicated, and should not be performed without supporting the nucleus.
The Combo Prechopper (AE-4284) has a sharp angled edge on one side of the blade and a rounded blunt edge on the other side. The angled blade is usually used for the initial insertion (Figure 1A) and for rotating the bisected nuclear fragments. The rounded blade is used not only for prechopping very soft nuclei, but also for ascertaining the complete nuclear division close to the posterior capsule (Figure 1B). The rounded edge is so blunt that it is safe even if it touches the posterior capsule. Making a complete nuclear division is the key principle of the prechop technique. The blunt side of the blade is used most safely in confirming a complete division and thus leads to a successful prechop.
There are three important prerequisites for the karate prechop technique: (1) creating a complete continuous curvilinear capsulorhexis without tears or notches; (2) performing sufficient hydrodissection so that the nucleus rotates freely in the capsular bag; and (3) protecting the corneal endothelium with dispersive viscoelastic material. The prechop procedure itself will never damage the corneal endothelium; however, to protect the endothelial cells during phacoemulsification, a soft-shell technique should be applied using Viscoat (Alcon Surgical, Fort Worth, TX) and ProVisc (Alcon Surgical).
After making a complete continuous curvilinear capsulorhexis, sufficiently hydrodissect using an AE-7636 cannula (ASICO). Fill the anterior chamber with ProVisc again so that it removes the anterior cortex and exposes the nuclear surface. When performing the prechop technique for the first time, I suggest removing the anterior cortex with an irrigation-aspiration tip or ultrasound tip first, and then filling the anterior chamber with ProVisc. This will improve visualization of the nucleus, and make it easy to see how the prechopper blade is inserted and how the nucleus is divided. Once you have become accustomed to this technique, you will no longer need to perform cortical preaspiration.
Place the sharp angled edge of the Combo Prechopper blade at the center of the nucleus. Insert the closed prechopper directly into the nucleus by pushing downward (Figure 1A). Open the prechopper blades slowly while pushing the nucleus downward. If you apply the proper force, the nucleus will be cracked completely by a single action. It is important that the blade is always inserted along the direction of the lens fibers. If unable to achieve bisection, I suggest placing the closed blades at the deepest portion of the nuclear crack, and reopen.
COMPLETE NUCLEAR DIVISION
Once the nucleus is completely divided, the inner surface of the posterior capsule will be observed between the bisected nuclear fragments. The most important point of the prechop technique is to break the posterior plate completely. Merely creating a crack in the nucleus is not adequate. The nucleus must be completely divided from top to bottom. In order to confirm complete nuclear division, use the rounded side of the prechopper blade. When complete division has been achieved, the nuclear crack will become A-shaped rather than V-shaped in the lateral view. Perform complete nuclear division from the anterior to the posterior surface and from the proximal to the distal end of the nucleus.
Before rotating the nucleus, restore the bisected nuclear fragments to their original position to reduce the resistance of rotation caused by the expanded nuclear volume. By pushing the distal end of the nucleus with the angled blade, rotate the nucleus exactly 90º. Using the sharp and blunt blades of the Combo Prechopper alternately, divide each bisected nuclear fragment in the same way. If any viscoelastic material leaks during the procedure, inject an additional amount in order to maintain the anterior chamber depth. The additional viscoelastic material will improve the visibility of the nucleus, which can be decreased by the cortex. Divide the nucleus completely into four pieces as shown in Figure 1B.
The surgeon phacoemulsifies the prechopped nuclear fragments using high-vacuum and high-flow settings. Choosing a first-rate machine that can maintain a stable anterior chamber at a higher vacuum is important. I recommend the Legacy version 3.12 (Alcon Laboratories) with a specially modified standard flared aspiration bypass system tip attached to the MaxVac (Alcon Laboratories, Inc.) cassette, and a high infusion irrigation sleeve. With a vacuum pressure of 500 mm Hg+ and a flow rate of 60 mL/min at a bottle height of 110 cm, the prechopped nucleus can be phacoemulsified quite easily and rapidly by a single-handed technique. For relatively soft nuclei such as those that can be prechopped by the karate prechop technique, a 15-Hz AdvanTec (Alcon Laboratories, Inc.), pulse mode is used.
For harder nuclei, the AdvanTec burst mode is most effective with a NeoSoniX (Alcon Laboratories, Inc.) handpiece. To activate oscillation of the ultrasound tip, the threshold is set at 0% and the amplitude at 100% for the AdvanTec burst mode, while the threshold and amplitude are both at 100% for the AdvanTec pulse mode. The ultrasound tip is used with its bevel directed down toward the nucleus, so that it makes direct and complete contact with the nuclear surface. Complete occlusion of the ultrasound tip can produce a higher vacuum pressure and removes the nucleus more efficiently. Compared with the conventional divide-and-conquer technique, the karate prechop technique can reduce ultrasound time to less than 10% for each nuclear grade by employing phaco prechop and ultrahigh vacuum phacoemulsification.Takayuki Akahoshi, MD, is Director of Ophthalmology at the Mitsui Memorial Hospital in Tokyo, Japan. He does not hold a financial interest in any of the materials mentioned herein. Dr. Akahoshi may be reached at +81 (0) 3 3862 9111; firstname.lastname@example.org.
Reprinted with permission from Akahoshi T: The Karate Prechop Technique. Cataract & Refractive Surgery Today. 2002;2:63-64.
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