For techniques such as stop-and-chop or divide-and-conquer, the phaco probe is used to sculpt a trench or groove in the middle of the nucleus. The instruments are placed in this groove and pushed apart so that the nucleus is cracked and split into smaller fragments.
In sculpting the initial groove, we must be careful to avoid going through the nucleus and hitting the posterior capsule like in the prior video shown here. The common thinking among newer surgeons is that the groove must be very deep and very long. But this is not the case — a short groove of just a few millimeters, and just deep enough to engage the central endonucleus, is enough.
click below to see that a short groove is sufficient to perform lens cracking: