The placement of the chopper is critically important to achieving division of the cataract nucleus with the phaco chop technique. The two primary principles are (1) to fixate the nucleus so it does not move during the chop maneuver and (2) to engage a sufficient amount of nucleus with the chopper so that we achieve a cleavage plan instead of simply scoring the surface.
The nucleus can be fixated and held still in two primary ways: using a high vacuum setting to engage the nucleus after it is impaled with the phaco tip or we can trap the nucleus between to opposing instruments so that it cannot move. By using both of these techniques in flip-and-chop, we virtually guarantee a successful chop and nucleus division.
Once the nucleus is prolapsed partially out of the capsular bag, a gap is created so that the chopper can be placed behind the central nucleus and directly opposite the phaco probe. This holds the nucleus securely so that the chopper can pull it into the chopper while the surgeon engages the phaco vacuum at the same time to give even more holding power. Now the chopper and phaco probe can be pulled apart, creating a complete division of the nucleus into two halves.
Click below to learn specifics about placing the chopper for flip-and-chop: