A system and method for instructing removal of cataract tissue. Software generated vacuum signal (80) indicating vacuum force to be applied within the shaft of a phacoemulsification needle (120). Software responsive to a monitoring vacuum force signal reaching a threshold level (20) as a result of occlusion of the tip of the needle by cataract tissue (30). Said signal activates to and fro oscillation of needle tip (35), or application of ultrasonic power (37). Additional software instructions include; user-initiated oscillation, an ultrasonic termination signal (42), or the vacuum monitoring signal dropping below an activation threshold level (40).