The classical “Divide and Conquer” and Phaco-Chop techniques enable the practitioner to break up nuclei of different degrees of hardness. When transitioning to bimanual phaco, it is advisable not to change one’s nuclear fracture strategy: Surgeons accustomed to the Divide and Conquer technique should begin with this strategy to familiarise themselves with microincisions and the use of a separate irrigation probe before moving on to the Phaco-Chop technique, which remains more difficult to learn as it requires performing more delicate manoeuvres with the non-dominant hand.
The Divide and Conquer technique
The manipulator-irrigator has two openings and is introduced into the anterior chamber through the incision with the left hand if the practitioner is right-handed, and inversely if left-handed. It is recommended to activate the continuous irrigation mode and always to keep in mind that this irrigation probe must not be withdrawn before the US probe in order to avoid problems leading to the collapse of the anterior chamber, with consequences that could be fatal for the endothelium and the posterior capsule.
A first deep, narrow and abrupt groove is created with the phacoemulsification tip, using low vacuum and ultrasound levels. The length of this groove should not exceed the limits of the epinucleus, in practice those of the capsulorhexis. Its depth must allow the surgeon to reach 90 % of the thickness of the nucleus, or approximately three times the diameter of the phaco probe. It helps provide light to determine the pupillary reflex. The width of the groove must be 1.5 to 2.0 times that of the phaco probe to enable the irrigation and phacoemulsification probes to be introduced into the bottom of the groove. Cracking takes place by moving the phaco tip horizontally away from the infusion probe when both are placed at the bottom of the groove. Then, after rotating the nucleus, a second groove is created at the same depth as the first one, which then enables the initial nuclear fracture to be carried out. By repeating the same manoeuvre, the nucleus is split into four quarters of equal size. The irrigation handpiece is used to lift and direct the crystalline quarters towards the US probe, which emulsifies each in turn using more aspiration power.
However, the narrow gauge of the microincisions renders cracking more difficult than in coaxial phaco, as the horizontal movements of the instruments when pulling away from each other are limited. It is better to use the instruments in the axis of the microincisions; the phaco probe in the axis of the groove stabilises the nucleus, while the irrigation probe, which is positioned perpendicularly to it, pushes onto the half of the nucleus facing it to create the fracture line. A variant exists used in the shape of the Cobra® probe, whose ladder-step end enables it to hook perpendicularly into the wound wall. Exercising traction towards 12 o’clock with the Cobra® probe hooked into the upper edge of the groove, associated with a push towards 6 o’clock with the phaco probe on the opposite wound edge facilitates cracking.
In the event of difficulties it is possible to perform cracking with two micro-manipulators after having filled the anterior chamber with viscous agent and withdrawn the bimanual phaco instruments.
The advantage of this technique lies in the simplicity of the intracameral manoeuvres required. On the other hand, with hard nuclei it is time consuming and requires higher ultrasound power levels than the Phaco-Chop technique.
Horizontal Phaco-Chop
Nagahara’s 20 G diameter Duet® chopper has an infusion opening, a soft foam tip and a cutting lateral edge; it is introduced into the anterior chamber through the incision with the left hand if he or she is right-handed, and inversely if left-handed. It is recommended to activate the continuous irrigation mode and always to keep in mind that this irrigation instrument must not be withdrawn before the US probe in order to avoid problems leading to the collapse of the anterior chamber.
The US tip with the bevel directed upwards aspirates the anterior cortex and the epinucleus from the anterior dome of the crystalline lens and then penetrates deeply into the proximal portion of the nucleus by means of an ultrasound burst. In maintaining strong aspiration, the crystalline nucleus remains firmly impacted in the US probe.
The Nagahara chopper is inserted horizontally into the epinucleus, opposite the US probe. When it reaches the equator of the nucleus, it is brought back into vertical position and driven into the capsular bag towards the US probe which continues to hold the nucleus at its end. This horizontal chop manoeuvre enables the nucleus to be split into two halves. It is repeated once the nucleus has been rotated in order to obtain four, six or more fragments, depending on the hardness of the nucleus, which will subsequently be emulsified.
The advantage of this technique is its time-effectiveness and the use of much lower ultrasound power levels than the Divide & Conquer technique when fragmenting firm nuclei. On the other hand it necessitates intracameral manoeuvres that are more difficult to carry out with the non-dominant hand, and requires a certain learning curve.
Vertical Phaco-Chop
The US tip with the bevel directed upwards aspirates the anterior cortex and the epinucleus from the anterior dome of the crystalline lens and then penetrates deeply into the proximal portion of the nucleus by means of an ultrasound burst. In maintaining strong aspiration, the crystalline nucleus remains stabilised by the US probe. Aspiration power is greater in vertical chop than in horizontal chop.
Fine’s 20 G diameter Duet® chopper has an infusion opening and a cutting tip; it is placed at the centre of the nucleus, penetrating into the depths of the nucleus while the US probe carries out an upward lever movement, bringing about a vertical fracture in the nucleus. The two instruments are then moved away from each other laterally to complete the division of the nucleus into two sections. This is facilitated by the strong irrigation of the chopper placed inside the nucleus.
The advantage of this technique is its time-effectiveness and the use of much lower ultrasound power levels than the Divide & Conquer technique when fragmenting hard nuclei. On the other hand it necessitates intracameral manoeuvres that are more difficult to carry out with the non-dominant hand, and a certain learning curve. It requires a large capsulorhexis and a specific learning curve.
Stop-and-Chop
There is a variant that associates the Divide & Conquer and Chop techniques, described by Paul Koch under the name of Stop-and-Chop. A first groove is created as in Divide & Conquer in order to split the nucleus in two; then, STOP Divide. Each heminucleus is then fragmented by means of the CHOP technique.
This technique can be an excellent transition method between Divide and Chop. It circumvents the difficulties encountered with Chop on a whole nucleus. Placing the US probe on a heminucleus is facilitated by the central groove.
Which chop technique should I use for what type of nucleus ?
In many cases, the subtle manoeuvres of the chopper can be alternatively horizontal and vertical, thus mixing the advantages of the two techniques to facilitate fragmentation of the nucleus.
For a relatively soft nucleus, both Divide and Vertical Chop would be inappropriate and difficult as the lack of firmness would hinder the nuclear cracking procedure. On the other hand, Horizontal Chop would be the technique of choice.
In strongly myopic or vitrectomised eyes with a large anterior chamber, it is easier to perform Horizontal Chop.
In cases of zonular fragility (a small dehiscence or capsular pseudo-exfoliation), Horizontal Chop is the author’s preferred technique.
On the other hand, very hard nuclei, brunescent (N5 in LOCS III) or white cataract are easily fragmented with Vertical Chop.
In the absence of an epinucleus, Horizontal Chop is contraindicated, as in these cases it involves an increased risk of capsular rupture.
