Phacoemulsification (often referred to as phaco) makes use of ultrasound technology as well as vacuum (defined in the Glossary of Fluidics and Phacodynamics Terminology at the end of this chapter). Although there are several types of phaco machines, their major components are essentially the same: a handpiece, foot pedal, irrigation system, and aspiration pump.
The phaco handpiece (Fig 8-1) has been likened to a combination of a jackhammer, vacuum, and garden hose. The surgeon uses the handpiece to simultaneously emulsify and aspirate the crystalline lens while keeping the tip cool and maintaining anterior chamber depth. The mechanical energy of phacoemulsification is produced by the to-and-fro oscillation generated by piezoelectric crystals in the phaco handpiece. The amplitude of the movement, or stroke length, is variable and increases when the power is raised. As the phaco tip moves forward, compression of gas atoms in solution occurs; as the tip moves backward, expansion of gas atoms occurs, and bubbles of gas form (known as cavitation; see the Glossary of Ultrasonic Technology Terminology at the end of this chapter). The bubbles are subject to the same compression and expansion. When the bubbles implode, they release heat and shock waves, which disassemble the nucleus at the phaco tip. Nonaxial vibrations generated by a torsional or elliptical motion of the tip can augment the primary oscillation and aid the mechanical breakdown of nuclear material. These mechanisms are specific to the type of phaco machine used.
Figure 8-1 Illustration of the parts of a phaco handpiece. The smaller drawings depict the different tip bevels available.
(Illustration courtesy of Mark Miller.)
Mastering use of the phaco foot pedal is critical to successful phacoemulsification technique. All current phaco machines have foot pedal controls with at least 3 positions. Position 1 activates irrigation, with the infusion pressure determined by irrigation bottle height or its equivalent. Position 2 engages the aspiration or vacuum mode at a fixed or variable rate. Position 3 adds ultrasound power at a fixed or variable level. In the fixed power mode, the level may be set from 0% to 100%, and the chosen power level is delivered immediately when the foot pedal is depressed into position 3. With variable ultrasound, the surgeon controls the amount of phaco power delivered by varying the depth of depression of the foot pedal while it is in position 3.
Excerpted from BCSC 2020-2021 series: Section 11 - Lens and Cataract. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.