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Horizontal phaco chop makes cataract surgery more efficient with less ultrasonic energy
Learning phaco chop is a straightforward transition for experienced surgeons who use the divide-and-conquer technique.
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More than 20 years ago, Dr. Kunihiro Nagahara described the technique of phaco chop, which transformed cataract surgery by making it more efficient. His idea was simple: Use mechanical energy to break the cataract nucleus into smaller pieces instead of using the standard divide-and-conquer technique. Phaco chop requires less ultrasonic energy to disassemble the nucleus, and that means less damage to the delicate corneal endothelial cells, which makes for less inflammation and a faster postoperative recovery.
About phaco chop
Although the technique seems difficult, it is actually surprisingly simple to learn. Despite this reasonable learning curve, many cataract surgeons have not adopted this technique. During the course of the past 15 years, I have taught phaco chop to resident surgeons as part of their surgical training. Surgeons who currently use the divide-and-conquer technique are already adept at having a second instrument in the eye for the cracking portion of the nucleofractis technique. Learning phaco chop is a straightforward transition for these experienced surgeons.
The classic Nagahara technique is a horizontal chop, which means that the principal plane of movement is horizontal, parallel to the iris and lens surface. This is different from a vertical chop technique, whereby the goal is to propagate a crack vertically, toward the posterior capsule. For this article we will focus on the horizontal chop, which is suited to a wide range of nuclear densities and works well with most chopping instruments.
The only additional instrument that is needed is the chopper. This instrument has a tip that is just a few millimeters long in order to avoid touching the posterior lens capsule when the chopper is placed at the nucleus equator. The phaco platform settings must be adjusted so that the phaco probe is able to securely hold the cataract nucleus as the chopper divides it. This means that the vacuum level should be increased to 300 mm Hg to 500 mm Hg, depending on the size of the phaco tip, with a larger tip requiring less vacuum pressure than a smaller one. The flow rate and the bottle height/infusion pressure should be balanced and at a moderate range in order to facilitate nuclear fragment removal. Ultrasonic phaco power depends on the density of the nucleus, with a denser nucleus requiring more power.
Horizontal phaco chop. The chopper is placed under the capsulorrhexis (yellow dashed line) and moved toward the lens equator (a). The chopper tip drops as it hooks the lens equator, indicating that it is in the correct position (b). The phaco probe is buried into the nucleus to stabilize it while the chopper is brought toward the probe and then apart in order to fracture the nucleus (c). The chopper and probe are pushed apart in order to fully propagate the fracture so that two separate nuclear halves are created (d).
Image: Devgan U
The technique
Once the capsulorrhexis is created and hydrodissection is performed to mobilize the nucleus, the first move, which is also the most critical, is the proper placement of the chopper. This instrument needs to be placed around the lens equator, under the capsulorrhexis edge, and this view may be obscured by the iris if it is not maximally dilated. For beginners, I suggest sliding the chopper along the anterior surface of the lens and then pushing the capsulorrhexis edge until the chopper tip reaches the lens equator. At this point, the chopper will slightly drop as it reaches the lens equator and the capsulorrhexis will snap back into position. This is the correct placement of the chopping instrument, and it can be placed before impaling the nucleus with the phaco probe.
More experienced surgeons will simply tilt the chopper tip on its side and then pass it toward the lens equator, and once there, they will straighten the chopper so that it is in position. In order to chop the nucleus, we must fixate and stabilize it. This is done by burying the phaco tip into the nucleus and using the high vacuum level to hold it still. Now the chopping maneuver takes place by bringing the chopper toward the phaco probe to start a fracture in the lens nucleus. Then, the force vector shifts by about 90°, and the chopper is used to pull the two nuclear pieces apart. The fracture propagates through the entire nucleus, and two clean halves are created. At this point, the nucleus halves can be further chopper into quadrants or sextants.
As surgeons become more adept at this maneuver, a few subtle improvements can be incorporated. These include placing the chopper at the same time as the phaco probe impales the nucleus; chopping during the initial application of power as the phaco tip is being buried in the nucleus; using the phaco probe to push one nuclear half away from the other to facilitate the propagation of the nuclear split; and angling the phaco probe during sub-chops so that nucleus rotation can be minimized.
While we now have femtosecond lasers that can also divide the cataract nucleus into fractions, the horizontal phaco chop technique can achieve the same results more efficiently with less time and with a small degree of mechanical energy. This is a technique that has stood the test of time and has made cataract surgery more efficient and more enjoyable for the surgeon as well as the patient who gets the benefit of a minimally invasive technique and excellent visual results.
For more information:
Uday Devgan, MD, is in private practice at Devgan Eye Surgery, Chief of Ophthalmology at Olive View UCLA Medical Center and Clinical Professor of Ophthalmology at the Jules Stein Eye Institute, UCLA School of Medicine. He can be reached at 11600 Wilshire Blvd. #200, Los Angeles, CA 90025; email: devgan@gmail.com; website: www.DevganEye.com.Disclosure: Devgan has no relevant financial disclosures.