STOP AND CHOP

Stop and chop is a technique of nuclear division started by Paul Koch and is very useful for beginner phaco surgeons. Stop and chop beautifully describes the essence of the technique - the surgeon begins with one technique (divide and conquer), stops after one groove and then continues with another technique (phaco chop). The stop and chop can be very effectively used as a launch pad for transitioning to direct chop techniques once the surgeon is comfortable with the standard divide and conquer technique.

TECHNIQUE

The technique starts with a good capsulorhexis, hydrodissection, hydrodelineation and nuclear rotation. Clear corneal incisions may be kept at 60 degrees to each other to enable easy cracking of the nucleus.

SCULPTING

Once nuclear rotation is verified, a longitudinal groove is sculpted in the nucleus. Moderate flow, low vacuum and continuous ultrasound power based on nuclear density is used. A combination of down-slope sculpting followed by up-slope sculpting is performed to follow the curve of the posterior capsule and to avoid accidental damage to the posterior capsule.

This technique of sculpting allows the groove to be deeper in the centre than in the periphery. The groove is made about one and a half phaco tips wide to allow access to the depth of the groove. It is also made about three phaco tips deep which leaves a thin posterior plate that can be cracked easily. The nucleus is rotated 180 degrees to allow the groove to be deepened equally on both sides.

CRACKING

The nucleus is then divided into two hemisections by cracking. The phaco tip and the second instrument are inserted into the depth of the groove and the posterior plate is cracked in half. Cracking can be accomplished as conventional cracking (both hands move towards ipsilateral sides to separate the nucleus) or by cross-cracking (both hands push towards contralateral sides). Alternatively, the cracking may also be performed using a pre-chopper such as the Akahoshi pre-chopper. Once the nucleus is separated into hemisections, it is time to stop and chop.

CHOPPING

The hemisections are rotated 90 degrees so that the two halves lie at six and 12 o clock. The settings are then changed to high vacuum, high flow rate and pulse or hyper-pulse phaco mode. The hemisection is embedded at mid-depth and chopped into two or more pieces. Each piece is then impaled, brought into the AC and emulsified. The other hemi-section is then rotated inferiorly, chopped and emulsified in a similar manner.

The number of pieces each hemisection is chopped into depends on the density and size of the nucleus. For moderately dense nuclei and when a good hydrodelineation has given a well-defined endonucleus, four quadrants are generally enough. Very dense cataracts may however be divided into more pieces. If desired, all the chopping may be completed first followed by piece removal. This is followed eventually by epinucleus removal, cortex aspiration and intraocular lens implantation. Chopping may be done either via a horizontal or vertical chopping technique.

ADVANTAGES OF STOP AND CHOP PHACOEMULSIFICATION

The creation of a groove before chopping is the main difference between stop and chop and the phaco chop as described by Nagahara. This longitudinal sculpting creates space for nuclear manipulation, unlike direct chop techniques where the pieces are closely wedged together like a jigsaw puzzle and are sometimes difficult to bring out of the capsular bag.

As compared to divide and conquer, the use of the chopper in the subsequent steps helps to decrease the use of phaco power that is used for sculpting, decreases phaco time and energy, as well as consequent endothelial damage. Manual chopping techniques break the nucleus into smaller pieces without the use of phaco power, thereby decreasing the need for ultrasound energy required for emulsification. Once the hard posterior plate of the nucleus is cracked, it becomes easier to subsequently chop it into smaller pieces as the sides of the groove are now available for an adequate purchase on the nucleus.

COMPLICATIONS

Care should be taken during sculpting to adjust the phaco power used according to the density of the nucleus. Grooving is difficult in a soft cataract. With inadequate power in a hard cataract, the nucleus may be pushed forward rather than being sculpted which can result in zonular stress. Grooving should be taken beyond the edges of the capsulorhexis only in deeper passes to avoid accidental damage to the capsular rim.

The groove should not be carried excessively into the periphery to avoid damage to the capsular bag. For the same reason, the curved contour of the bag should be followed during sculpting. Too thick a posterior plate may not get cracked. Posterior pressure should be avoided during the crack to avoid zonular dialysis and nucleus drop. The instruments should instead separate the hemisections with a horizontal and slightly upwards directed force. While chopping, the chopper should avoid tearing the anterior capsular rim accidentally. With soft cataracts, the chopper may end up cheese-wiring the nuclear hemisection instead of effectively separating it into quadrants. With hard cataracts, chopping may still be difficult for beginner surgeons.

To conclude, stop and chop nucleofractis is an effective technique and every phaco surgeon needs to have an adequate knowledge of all these basic techniques.

* 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