In our study we assessed preoperative cataract grades in manual and femtosecond laser–assisted cataract surgery and evaluated its influence on effective phacoemulsification times. For phacoemulsification the Infinity System was used (Alcon, Fort Worth, Texas, USA).
The effective phacoemulsification time (EPT) is determined by multiplying the phacoemulsification time (seconds) with the average phacoemulsification power (percent). In contrast to EPT, the cumulative dissipated energy (CDE) reflects the total U/S energy in footpedal position 3 and includes phaco and torsional times. At present, no phaco platform offers surgeons a direct or standard measure of the energy that is placed into the eye during cataract surgery in units such as Joules.
As mentioned by Drs Packer and Solomon, the Infinity system includes the OZil torsional technology, which features both longitudinal and torsional ultrasound delivery. OZil torsional technology produces a side-to-side motion of the phaco tip to break up the nucleus by shearing. We are aware that we did not describe this feature in our study settings, as it is a standard technique setting of the Infinity system. For our study purposes the average phaco power and phaco time was assessed in footpedal position 3 to calculate EPT, as EPT is commonly used in this context regardless of the type of power modulation or lens segmentation technique. The lens segmentation was undertaken in both treatment groups using a divide-and-conquer approach.
We agree that it is difficult to compare different phaco machines because manufacturers may use different algorithms to calculate EPT or CDE quantities.