Chop procedure is the principal step for phacoemulsification. Many methods can be used to crack a nucleus such as phaco-chop, stop-and-chop, and divide-and-conquer.4,9 But all of them involve occlusion, using high vacuum to stabilize the nucleus, and ultrasound power to create the initial groove or fracture.
Among these methods, phaco-chop technique is the most appropriated method for moderate to hard nuclei.2,7 However, it is very difficult to achieve the occlusion and high vacuum required to cleave a soft nucleus. For soft nucleus even in occlusion, holding is difficult, because the phaco tip tends to aspirate the soft nuclear matter. Alternatively, flipping technique and phaco rolling technique have been described to remove soft nucleus. However both of them represent a certain risk to the endothelium, particularly in eyes with shallow anterior chambers.10,11 Therefore, we invented the power-free-chop technique, which was a modified phaco-chop technique, can be used to mechanically cleave soft nucleus into distinct fragments without occlusion and ultrasound power participation. In clinical applications, we found power-free-chop technique is suitable for not only soft nucleus but also moderate nucleus.
As both power-free-chop and phaco-chop techniques could be used to cleave moderate nucleus. We compared 2 techniques for handling moderate nucleus in our study. The results showed that in the power-free-chop group CDE was significantly lower. In the postoperative follow-up period, compared with the phaco-chop group, corneal edema was significantly lower and the healing period was shorter in the power-free-chop group.
Compared with phaco-chop technique, occlusion and holding tightly are not necessary in the power-free-chop technique. In the chop procedure, the phaco tip just needs lean against the nucleus as deep as possible in I/A gear. Therefore, no ultrasound power is wasted in the chop procedure. As a contrast, phaco-chop technique requires ultrasound power to bury the phaco tip into the nucleus deeply. In the chop procedure, the using of the chopper is the same for these 2 techniques. The chopper needs to be placed beyond the edge of the nucleus and move to the phaco tip. Moreover, since without ultrasound power involved, the phaco tip will not penetrate the nucleus during the chopping process in the power-free-chop technique. Therefore, this also can protect the posterior capsule and avoid the occurrence of posterior capsule rupture (PCR).
Another significant benefit of the power-free-chop technique is that this technique do not need to build the occlusion in the nucleus with precise pedal control. This can eliminate the difficulty in the chopping procedure especially for the phaco beginners. Therefore, power-free-chop technique is easier to be learned and controlled compared with phaco-chop and other manual prechop techniques such as cystotome-assisted prechop technique.12
The power-free-chop technique also has disadvantage. It is effective for soft to moderate nucleus (Emery-Little classification, grade 1 to 3) only. We have tried to use this technique on hard nucleus, but it did not succeed. If encounter hard nucleus, power-free-chop technique can be easily switched to phaco-chop technique in the operation.