DIRECT CHOPPING

Fig A: Horizontal chopping (A,B)- The blunt tipped horizontal chopper engages the equatorial nucleus and the phaco tip embeds the nucleus proximally (A); The chopper moves towards the phaco tip and then sideways to cleave the nucleus (B). Vertical Chopping (C,D)- The phaco tip is embedded deeply into the proximal nucleus and used to stabilize the nucleus upwards (C); The sharp tipped vertical chopper presses downwards next to the phaco tip and cleaves the nucleus into two (D).

Direct chopping techniques are essential for the cataract surgeon to know, as they help in performing surgery in difficult situations such as small pupil, zonulodialysis and mature cataracts.

Chopping techniques utilise manual forces to crack the nucleus with phaco power being utilised only to obtain a purchase on the nucleus. They utilise natural planes within the crystalline lenses to create lines of cleavage. In essence, the nucleus is grasped with the phaco tip and a chopping movement is used to crack the nucleus into two planes. It consists of the vertical and horizontal chops.

TECHNIQUE

An adequately sized rhexis, thorough hydrodissection, hydrodelineation and nuclear rotation are necessary before attempting to chop. Anterior cortex and epinucleus within the rhexis rim is aspirated to expose the nucleus. There are various choppers available. Horizontal choppers have a blunt tip and are long enough to reach the equator. They may have an inner cutting edge but this is not a must.

The Lieberman microfinger is a bent 1.5mm-long microfinger that follows the curve of the equator of the bag and is a very good instrument for horizontal chop. It can safely be used for rotation and for tumbling the quadrants out of the capsular bag. The Chang combo chopper, which has a modified Lieberman microfinger on one side and a sharp vertical tip on the other side, is also a good option. Other choppers available are the Nagahara karate chopper, which has a sharp spear tip with internal cutting edge, and the Agarwal chopper for moderately dense nuclei. The Agarwal chopper is mainly used for vertical chopping and has the advantage of being able to pass through a 26-gauge side port.

HORIZONTAL OR NAGAHARA CHOPPING

First described in 1993 by Nagahara, it is so-called as the instruments move towards each other in the horizontal plane. The horizontal chopper in the non-dominant hand slides under the rhexis rim and epinucleus, around the equator of the nucleus to hook it. The tip should pass under the rim and not above where it can tear the rhexis or get caught in the zonules and cause a zonulodialysis. Therefore, it should be made sure that the chopper touches the endonucleus before sliding it outwards under the epinuclear shell. An anterior capsule that has been stained with Trypan blue also helps in ascertaining the subcapsular position of the chopper. The phaco probe is then used to engage the nucleus close to the proximal edge of the capsular opening.

Burst mode phaco is applied angling downwards to obtain a deep purchase of the nucleus. The nucleus is then held using high vacuum, while simultaneously the chopper is moved towards the phaco probe and then horizontally in the form of a laterally reversed “L” to cleave the nucleus into two halves. The nucleus is rotated and the same manoeuvre repeated to chop it further into smaller fragments, which are then emulsified to create more working space in the bag for the remaining pieces.

VERTICAL CHOPPING

It is so-called as the movement between the two hands is in a vertical plane. A good purchase on the nucleus is much more important here than in horizontal chopping. In the latter, the nucleus is compressed between the two instruments moving towards each other, whereas in vertical chopping, forces act against each other as the phaco tip holds the nucleus up and the chopper depresses downwards into the nucleus to cleave it.

While embedding, it should be made sure that the phaco tip is completely occluded by the nucleus. This can be attained using traditional ultrasound with burst mode and high vacuum levels. A sharp chopper should be used to prevent a break of occlusion of the phaco tip.

In dense nuclei the crack may not propagate throughout and the nucleus needs to be rotated 180 degrees to repeat the chop from the other side. Each hemi-nucleus is then similarly chopped into smaller pieces. In hard brown cataracts, the posterior leathery plate has to be separated before the quadrants can be lifted out of the capsular bag. Vertical chopping is completed and the pieces are then lifted out one-by-one to be emulsified in the anterior chamber.

ADVANTAGES

Both horizontal and vertical chop techniques decrease the amount of phaco energy used within the anterior chamber as well as time taken for nuclear division while being more zonule friendly. As compared to divide and conquer, chopping decreases stress on zonules that is caused by sculpting.

However, during vertical chopping in hard nuclei, the tendency by beginner surgeons to push downwards and outwards to crack the nucleus should be avoided. Instead, the nucleus should be held firmly with an upward pull with the phaco tip using high vacuum while the second instrument is used to cleave the nucleus.

In comparison to phaco flip or tilt and tumble, chopping avoids the need for the entire nucleus to be prolapsed out of the capsular bag. It is therefore advantageous in harder cataracts and when the rhexis is not large enough to allow nucleus prolapse. Chopping is especially advantageous in small pupils where sculpting is difficult to perform and may result in damage.

Vertical chopping needs only the central portion of the nucleus exposed. Chopping may also be used in subluxated cataracts for nuclear disassembly.

DISADVANTAGES

Vertical chopping is not suitable for soft cataracts where the chopper can cheese wire through the soft nucleus without splitting it into two. It is however highly suited to brown cataracts. Similarly, horizontal chopping should be performed carefully in mature cataracts as the chopper passes very close to
the capsule.

CONCLUSION

As for all techniques, chopping techniques too have a learning curve, however they are an essential armament of every cataract surgeon and should be learnt in order to be prepared for difficult cases.

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