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Chop techniques for brown cataracts

Everything you ever wanted to know about brown 
cataract phacoemulsification – Part 2

Soosan Jacob

Posted: Friday, September 1, 2017

Fig: Terminal chop technique: A: The phaco probe embeds at the equator superficially; B: The blunt olive-tip chopper performs a horizontal chop (Images courtesy Rajendra Prasad, MD). Stop and Chop: C: An initial trench is created and chopped; D: The nucleus is rotated and the crack is completed from the other side. Smaller fragments are then directly chopped

Hard cataracts require various means to chop them, and the final choice is dependent on surgeon skill, experience, comfort level as well hardness of nucleus. This article is the second instalment of a two-part series on brown cataract phacoemulsification, and deals with various chop techniques that can be used for nuclear disassembly.

Divide and Conquer:
Described by Shepherd and Gimbel, after nuclear rotation, two cross-grooves are created by sculpting using moderate flow, low vacuum, and continuous ultrasound power. Harder nuclei require higher power to avoid zonular stress. Downslope sculpting is followed by upslope sculpting until a clear red reflex is seen. A groove depth of approximately three phaco tips is generally adequate. Once both grooves are created, the nucleus is cracked into four quadrants, either by conventional cracking, when incisions are at an acute angle to each other, or by cross cracking when, incisions are at 90 degrees to each other. Each quadrant is then emulsified.

Crater-and-chop:
Described by Vanathi M et al for large, hard, leathery brown nuclear cataracts, a large, approximately 6.0mm diameter crater is first created, leaving an outer nuclear rim. The edge of the crater is held using high vacuum, and small wedge-shaped pieces are created with a chopper. These small pieces are then emulsified in the endocapsular space created by the crater.

No vacuum chop:
Described by Pezzola, similar to the crater and chop technique, a central crater is first created to obtain a peripheral ring of nucleus. Horizontal chop is then done without using vacuum to hold the nucleus. The peripheral rim is impaled between the phaco probe and the horizontal chopper and chopped using mechanical forces. Avoiding vacuum obviates loss of occlusion and surge.

Prechop:
Described by Akahoshi, the prechopper is utilised to split the nucleus in two, thereby decreasing the amount of phaco power used within the eye. However, in hard nuclei, burial and separation can be difficult, and excess stress may be translated by this manoeuvre to the zonules. Though a supporting instrument may be introduced to hold the nucleus at the equator, if excessive resistance is felt during insertion of the prechopper, the pre-chop should be abandoned.

Nagahara’s horizontal chop:
Described by Nagahara, the phaco tip is embedded into the nucleus in the superior half, and a long chopper is used to score and crack the nucleus by moving it upwards from around the equator at 
6 o’clock position towards the phaco tip. Once it reaches close to the phaco tip, it is moved laterally towards the non-dominant hand to split the nucleus into two halves. This is repeated to get smaller fragments. A blunt chopper such as the Chang modified microfinger can be used for this.
Though this technique can be performed with hard nuclei, care should be taken as the amount of epinuclear cushion for the chopper is less or absent, depending on the density of the nucleus. Inadvertent placement of the chopper in the supracapsular plane can damage the capsulo-zonular apparatus, and care should be taken to ascertain that the chopper has been placed below the anterior capsule.

Stop and Chop:
Described by Douglas Koch, a longitudinal groove is created using settings for sculpting as previously described, and the nucleus is divided into two. This initial sculpting and the crack formed creates space within the capsular bag, making further disassembly of the nucleus easier. The surgeon is then able to get a deep enough grasp of the heminucleus to make subsequent nuclear disassembly by chopping easy.

Choo Choo chop and flip:
Described by Howard Fine, this uses burst mode to impale the endonucleus, thus reducing cavitation around the phaco tip and giving a better hold. The chopper is then used to perform a horizontal chop. After nucleus removal, the remaining epinucleus is flipped out of the bag and removed.

Vertical chop:
Described by Fukasaku and Dillman, the phaco tip embeds and holds the nucleus up while a sharp chopper depresses into the nucleus to cleave it. In dense nuclei, if the crack has not propagated through the other side, the nucleus is rotated 180 degrees and chopped from the opposite side.

Woodcutter technique:
Described by Vikas Mahatme, the chopper is buried into the nucleus near the rhexis margin at 6 o’clock. With phaco on in continuous mode, the phaco probe is moved towards the stationary chopper. As the phaco tip reaches near the chopper, the nucleus splits in two, similar to a woodcutter hammering the axe towards a chisel that has been wedged in at one end of the log.

Step-by-step chop in situ 
and lateral separation:
Described by Vasavada et al, a trench or crater is created following which a vertical chop manoeuvre is performed after embedding the phaco probe in the depth of the trench at 6 o’clock. The initial partial crack produced is made full thickness by repositioning the chopper deeper, and this is repeated all along the length of the crack to get a complete separation. The phaco probe holds the nucleus all through the chopping manoeuvres.

Terminal chop technique:
Described by Rajendra Prasad, this variant of horizontal chop impales the phaco probe superficially, just within the equator. The equator of the nucleus is then slightly drawn within the capsulotomy edge and a specially designed wedge-shaped blunt olive-tip chopper is used to perform a horizontal chop. It generates tension at the sides of the groove and initiates a full-thickness nuclear crack, which propagates to the equator on the other side, breaking the nucleus in two on laterally separating both instruments.
It has the advantage of bypassing central trenching, drilling and cratering, which require high-intensity phaco forces and stressful manipulation. In hard cataracts, it should be done with care, and capsulo-zonular damage should be avoided.

• See Part 1

Dr Soosan Jacob is Director and Chief of Dr Agarwal’s Refractive and Cornea Foundation at Dr Agarwal’s Eye Hospital, Chennai, India: dr_soosanj@hotmail.com