Drill-and-prechop technique: modification of the drill-and-crack technique for mature cataracts

Complete splitting of the nucleus into two hemispheres is an essential step in accomplishing uneventful coaxial microincision phacoemulsification of mature cataracts. Endothelial cell loss was initially increased in MICS, especially in eyes with increased nuclear density because of increased cumulative dissipated energy, aspiration time, and volume of balanced salt solution used [14]. Some advanced phacoemulsification techniques may also decrease energy use. However, the techniques including various prechop techniques quite often does not succeed, resulting in incomplete nuclear segmentation and intact posterior plate, or require additional special prechop instruments.

The consecutive drilling combined with phaco chop technique introduced by Chen D et al. [6] to remove hard cataracts in MICS involves 3–4 holes consecutively drilled into the endonucleus. The nucleus is deeply impaled with the last drilling and firmly engaged with high vacuum, and then chopped with chopper centripetally from the lens equator. The chopper and phaco tip are spread apart laterally after they approach at the centre of the nucleus. It combines the advantages of phaco-chop and phaco-drill [15]. Rotary chop introduced by Ifantides C et al. [7] created two or more partial thickness pilot holes around the periphery of the nucleus by the phaco tip. Then, tackle the nucleus with the chopper and phaco tip in two holes in a meridian. At least two holes need to be created in the technique. Moreover, drilling holes with high ultrasound energy may increase the risk of complications such as corneal burn and corneal endothelial damage in mature cataracts in MICS.

The drill-and-crack technique, introduced by Hwang HS et al. [13] involves a deep hole in the central nucleus with the phaco tip and divides the nucleus with the prechopper inside the hole. Different from the consecutive drilling combined with the phaco chop technique [6] and rotary chop [7], it only drills one deep, narrow hole near the geometric centre of the endonucleus which could decrease the ultrasound energy. It offers easy and effective nuclear disassembly in patients with a hard nucleus cataract. However, it needs an Akahoshi prechopper [8, 10]. In microincisional cataract surgery, especially in 1.8 or 2.2 mm incision surgery, it is difficult to fully deploy the prechopper near the main incision and completely separate the posterior plate.

We adopted the drill-and-prechop idea from the drill-and-crack technique [13] and the cystotome-assisted prechop technique [16]. After digging a narrow, deep hole near the centre of the endonucleus, we used the Nagaharra chopper and the modified capsulorhexis forceps to split the nucleus. It can be considered a prechop technique. No phaco energy is wasted in the prechop procedure. We made a new capsulorhexis forceps which can perform the capsulorhexis and prechop. The modified capsulorhexis forceps (Fig.1) has a sharp triangular forceps head similar to a bow of a warship when it closes. Because of this feature, the nucleus is easily split into two unconnected hemispheres.

In the cystotome-assisted prechop technique [16], after the capsulorhexis, the surgeon-bent cystotome is inserted into the lens while the Nagahara chopper is set around the lens equator. The cystotome and the chopper are then brought together in the centre to create a bisecting crack in the nucleus, dividing it into two hemispheres. The nucleus of grade 3 according to Emery-Little classification is easy to split, but when splitting the grade 4 or 5 nucleus, the nucleus may rotate or cannot completely split the posterior plate. We replace the cystotome with our modified capsulorhexis forceps to do the prechop. When we firstly dig a hole in the endonucleus, the hardest part of the nucleus was wrecked. Then the counterforce of the chopper and the capsulorhexis forceps can totally split the nucleus.

We performed the bisection without hydrodissection. Xu Chen et al. [16] made the point that after hydrodissection, the endonucleus may be rotatable, which makes holding and bisecting it difficult or impossible in the manual prechop technique. The surgeon can also choose to perform additional hydrodissection after the nucleus bisection procedure. Then, the hemispheres are rotated by the chopper and divided into quadrants.

Like other prechop technique, no phaco energy is wasted in drill and prechop procedure. It is not necessary to build the occlusion in the endonucleus with precise pedal control and a high vacuum, which eliminates the difficulty in the chopping procedure and reduce use of the ultrasound energy.

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