Placement of the phaco probe and the chopper are critical to facilitating the phaco chop procedure. One of the big mistakes in learning chop is inappropriate placement of the instruments, both the phaco probe and the chopper.
The phaco probe should NOT be placed in the center of the nucleus because it leaves a much smaller distance for the chop maneuver. You should place the phaco probe just inside the subincisional capsulorhexis and aim it towards the optic nerve.
The chopper is placed at or under the nasal capsulorhexis edge, depending on the technique. For a horizontal chop, place it under the nasal capsulorhexis edge and around the equator of the nucleus. For a combo chop, place it just inside the nasal capsulorhexis edge and embed it into the nucleus there.
The phaco probe should hold the nucleus relatively still, while the majority of the movement is done by the chopper. Also remember that there is a finite window of just a second or two while the probe is holding the nucleus with high vacuum, in which to accomplish the chop. Once the chop has started, the two instruments are pulled apart to further propagate the separation of the nucleus into pieces.
click below to learn the phaco probe positioning in phaco chop: