Ultrasound energy is used in cataract surgery to divide the lens into smaller fragments, which can then be aspirated and removed from the eye.1 This technique, phacoemulsification, enables the surgeon to deal with small and self-sealing corneal or corneoscleral incisions. Besides the numerous benefits, some concerns remain; for example, the negative effects ultrasound energy can have on the human eye.2–8 Other effects, such as air bubbles or cavitation,4 are also related to the use of ultrasound. Usually, a hard nucleus demands more ultrasound time than a soft nucleus; thus it is expected that the endothelium in such an eye will be exposed to more damage. To facilitate the manipulation of hard nuclei and to shorten the use of ultrasound energy, as well as to minimize the infusion volume used during surgery in the eye, we developed the double phaco chop (DPC) technique and designed a new instrument called the Zirm phaco chop hook (Hans Geuder GmbH).
The end of the Zirm phaco chop hook (Figure 1) is longer than that of existing instruments, so the surgeon can reach deep layers of the lens. Since the bottom of the instrument is blunt, the risk of damage to the capsular bag is minimal. The cutting edge is marked with an arrow.
After entry to the eye's anterior chamber and 2 paracenteses at 2 and 10 o'clock are prepared, viscoelastic material is injected into the anterior chamber. A continuous curvilinear capsulorhexis (CCC)9 is performed in the anterior capsule of the lens. Hydrodissection of the cortex and nucleus, as well as aspiration of the anterior cortical material, follow. From here on, the double phaco chop technique differs from other approaches.
- Using the phaco tip with moderate ultrasound energy, a deep groove is created in the central nucleus and the phaco tip is removed and the right and left phaco chop hooks are inserted into the anterior chamber through the paracenteses.
- A hard nucleus can often be cracked by inserting the tips of the hooks deep in the central groove and tearing toward the paracenteses (Figure 2). The surgeon can then proceed with the DPC procedure. If this step fails or if the nucleus is not hard enough to provide enough resistance for the maneuver, the DPC technique continues as follows:
- While the left hook stabilizes the nucleus, the right hook is moved to the periphery of the lens, remaining close beneath the anterior capsule. The right hook is directed toward the left hook, using a pronating movement with the right hand (Figure 3).
- The nucleus is then rotated 180 degrees (Figure 4).
- The cutting is continued as previously described (Figure 5).
- The nucleus is rotated 90 degrees (Figure 6), and another cut is performed with the right hook (Figure 7); the nucleus is again rotated 180 degrees (Figure 8), and the fourth cut is made with the right hook (Figure 9).
The nucleus can be phacoemulsified and aspirated with minimal use of ultrasound energy and manipulation. After the cortex is aspirated and the capsule polished (optional), an intraocular lens can be implanted.
Phacoemulsification has become a widespread procedure.5,10 However, the surgeon should be aware of the possible complications. For example, phacoemulsification of the lens nucleus produces free radicals that may damage the corneal endothelium.6 This is supported by the findings of Ogino et al.,7,8 who showed that endothelial cell loss during phacoemulsification of hard nuclei is higher than that during extracapsular cataract extraction. Nuclear cracking techniques aim for shorter ultrasound time in the eye. Hayashi and coauthors3 report a significantly higher rate of damage to the corneal endothelium when undivided nuclei are emulsified. They found that a longer ultrasound time was associated with a greater decrease in endothelial cell counts and concluded that shorter ultrasound time resulted in less corneal endothelial damage.
Some techniques that aim to shorten ultrasound time have been described. As an alternative to Gimbel's parallel-split technique,11 Nagahara described an endocapsular nucleofractis technique, the phaco chop, in which hard nuclei are divided without central sculpting (K. Nagahara, MD, “Phaco-Chop Technique Eliminates Central Sculpting and Allows Faster, Safer Phaco,” Ocular Surgery News, International Edition, October 10, 1993, pages 12-13). Koch and Katzen12 introduced the stop and chop technique 1 year later. We introduce the DPC technique as a synthesis of these approaches. Our results have been promising: We found that the new instrument is useful not only with hard nuclei, but also with softer ones and other techniques such as the conventional phacochop procedures. To become familiar with the DPC technique, enough viscoelastic material should be applied into the central groove of the nucleus so one can operate in a deep anterior chamber that is stable, because the instruments are inserted through watertight paracenteses.
Mathias E. Zirm MD
Daniel J. Salchow BS
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