To facilitate removal of the cataract nucleus with the phaco probe, it is helpful to divide it into quadrants or segments, which are more easily extracted. The original method of “one-handed” phaco used the ultrasound energy to “bowl out” the nucleus; however, this required a lot of energy and was rather slow and cumbersome. While there are still some surgeons who continue to perform one-handed phaco, using a method to mechanically disassemble the nucleus allows easier removal.
The phaco chop technique is one of the most effective, efficient, and safe nucleo-fractis techniques, but it has a learning curve that is not easy for beginning surgeons. For this reason, most of my ophthalmology residents start out by learning the divide-and-conquer technique which many credit to Howard Gimbel MD and his 1991 publication.
In the divide-and-conquer technique, the phaco probe is first used to sculpt grooves into the nucleus, and then a second instrument is used to crack the nucleus into pieces, which can then be easily removed.
For creating the groove, the phaco settings should be optimized for sculpting. Use a high pulse rate of 60 to 120 pulses per second, a duty cycle of 50% or more and a maximum power setting of 20% to 60%, depending on the density of the nucleus. If your phaco machine does not have the ability to do a high pulse rate and a variable duty cycle, then it is acceptable to use continuous phaco energy. Be aware that the continuous phaco energy mode will put more energy into the eye and may lead to a high rate of corneal endothelial cell loss. For fluidics, the goal is to simply keep the anterior chamber deep and well-formed while providing a small amount of flow and vacuum to aspirate the sculpted cataract material.
Sculpting the grooves
Start the grooves as close to the subincisional area as possible so that they have the longest length possible. Be careful not to hit the edge of the capsulorrhexis with the phaco probe, and continue to sculpt the grooves deeper into the lens material. With an average nucleus, there is a depth of about 4 mm centrally and less peripherally. You should have grooves that are at least half the depth of the nucleus in order to facilitate cracking. A softer nucleus may require a deeper groove compared to a denser nucleus in which propagation of the crack is facilitated.
Use the phaco probe and the second instrument to rotate the nucleus 90° and make a new groove. Once completed, the two intersecting grooves will form a plus sign and will segment the nucleus into four quadrants.
To crack the nucleus into quadrants, a second instrument is placed into the groove along with the phaco probe tip. If the instruments are placed too shallow, the crack will be incomplete and the pieces will not separate. The proper method is to place the instruments deep within the grooves, then pull apart. This will result in a complete crack with separation of the nucleus into distinct pieces.
Change phaco settings
Once the nucleus is fully cracked and separated into four quadrants, the phaco settings should be changed. The phaco power settings can be changed to a lower pulse rate, between 10 and 30 pulses per second, a somewhat lower duty cycle of 30% to 50% and a lower maximum power setting of about half of what was used for grooving. For fluidics, it is important to have more holding power, which means more vacuum. Depending on the phaco needle size, the vacuum level should be 300 mm Hg to 500 mm Hg, and the flow rate should be 30 cc/min to 50 cc/min. Make sure to raise the bottle height to ensure that the inflow of fluid into the anterior chamber exceeds the outflow of fluid in order to keep things stable.
Use the phaco probe’s vacuum to bring the pieces out of the capsular bag and to the iris plane. This is the ideal location, as it is far enough from the corneal endothelium and the capsular bag. Continue to bring the quadrants to the iris plane and phaco-aspirate them. This is the technique of divide-and-conquer for nucleus removal.
Click below to watch an instructional video of Divide-and-Conquer:
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