Editing Phacoemulsification (section)

===Ultrasound===
The ultrasound component is used to break the lens down into particles small enough to be aspirated through the suction passages around the tip, which allows a very small incision for access. The incision is small enough that sutures are not needed for closure, and very little astigmatism is caused by healing of the wound in the cornea.

The phacoemulsification handpiece has a tip which vibrates longitudinally at a frequency in the range of 27 to 60&nbsp;kHz, with a stroke length of 60 to 150 micrometres. Power is adjustable by the operator as a percentage of full power, and indicates a variation in nominal stroke length. Actual stroke length may vary slightly depending on the density of the material it contacts, though some instruments use feedback to maintain nominal stroke by adjusting current, voltage or frequency. Nominal frequency is not adjustable. Both efficiency and heat generation are increased with higher frequency, and 40&nbsp;kHz is considered a good compromise and is in common use.<ref name="Yow and Basti 1997" />

Most handpieces use [[piezoelectric crystal]]s and the rest use [[Magnetostriction|magnetostrictive material]]s to generate the vibration.<ref name="Yow and Basti 1997" />

The handpiece is hollow and usually accommodates an aspiration line, and the vibratory transducer components are sealed into it. The handpiece is designed and constructed to be autoclaved between uses.<ref name="Yow and Basti 1997" />

The phaco tip is available in a variety of configurations, including a selection of tip angles to suit lens removal technique. Standard tip angles range between straight and 60 degrees, and more complex tips may have [[compound angle]]s. The end of the tip may be round, ellipsoid, bent or flared. A variety of designs are intended to enhance cooling and irrigation, and to prevent burns.<ref name="Yow and Basti 1997" />

There are three hypothesised mechanisms of how the nuclear material is emulsified. One proposes that the tip acts as a chisel and removes material on the forward stroke, another proposes that ultrasonic energy is somehow involved,{{clarify|how is "ultrasonic energy" hypothetically "involved"?|date=May 2023}} and the third proposes that the tip causes [[Cavitation|microcavitation]] bubbles on the retraction stroke, which collapse to exert high pressures on the materials very close to the bubble, which cause them to disintegrate.<ref name="Yow and Basti 1997" />