13 Power Modulations

116

PHACODYNAMICS: STEP BY STEP

13

Power Modulations I HOWARD FINE, RICHARD S HOFFMAN, MARK PACKER (USA)

Power modulations were developed in the late 1980s and early 1990s and resulted in a modification in the delivery of phaco power, going from the delivery of continuous phacoemulsification to allowing milliseconds of rest between milliseconds of ultrasound activity. The ultimate advantage of these small periods of rest is to keep the phaco tip cooler and reduce the energy delivered into the eye, thereby avoiding tissue damage. It also results in better purchase of nuclear material since vacuum is continuous and the repulsive force of vibrations of the tip are intermittent. The first power modulation was pulsed phaco, which existed on most machines by the late 1980s. Pulse phacoemulsification was characterized by phacoemulsification energy being divided between phaco on and phaco off in equal durations, and the number of pulses per second (pps) was customizable on most machines from approximately 5 pps to 15 pps. With the addition of linear power, the on-off power option was further customized by the percent power being applied to nuclear material at any moment. The OMS Diplomax was the first to have an expanded menu of power modulations and had not only pulse phaco, but burst mode. Burst mode was a modulation in which there was panel control of power so that there was a loss of linear power, but the off interval between the bursts of phacoemulsification was customizable by the depression of the foot pedal in foot position three. At the initial entry of foot position three, there was a

two seconds pause between each burst. The duration of the burst was programmable and with depressions of the foot pedal, the pause increasingly shortened until the pause between bursts was equal to the duration of the burst, which was effectively pulse mode phaco. On full depression of the foot pedal in foot position three, one had basically continuous phacoemulsification. Pulse and burst modes were opposite sides of the same coin. Pulse mode had linear power and a set duration between pulses, while burse mode had fixed power of programmed duration and a linear interval between the bursts. Other power modulations on the Diplomax included an ability to go from power on, with an unoccluded tip, to zero power on occlusion of the tip. This was very useful for teaching residents so that during sculpting, which is a shaving rather than an occlusion technique, once occlusion took place, the power would turn off, thereby reducing the risk of posterior capsule rupture. There were other modulations achievable so that one could go from an unoccluded tip at one power setting to a completely different power setting on occlusion of the tip. This was what was later described as occlusion mode phacoemulsification. OMS was subsequently purchased by Advanced Medical Optics (AMO, Santa Ana, CA) and AMO has indeed been a leader in power modulations. AMO was the first to introduce microsecond intervals of power resulting in extremely short bursts of phacoemulsification. These extremely brief microsecond bursts,

POWER MODULATIONS

FIGURE 13.1: Demonstration of the cavitational energy of the AMO Sovereign with WhiteStar™

interrupted by rest periods, allowed us to independently program the burst length and the rest period between them as independent variables. This further reduced thermal energy and the total energy into the eye. The amount of time with power on, compared to the amount with power off for each burst or pulse, was called the duty cycle. We found that there were certain advantages to this. There was an alteration from stable cavitation, which occurs with continuous phaco, to transient cavitation, which resulted in extremely large energy cavitational bubble implosions compared to continuous phaco and stable cavitation (Fig. 13.1). Subsequently, AMO introduced WhiteStar™ ICE, which gave us an ability to alter the power profile during the microburst of ultrasound energy. This allows an added punch at higher power at the initiation of the burst to allow for creation of a microvoid between the occluded tip and the nuclear material, to allow fresh BSS in to cool the tip and to give us added ultrasonic and cavitational efficiency. We could customize the way in which this is delivered in a variety of ways, as seen in Figures 13.2 to 13.4. This gave us an improved cutting efficiency through accelerated cavitation and a reduction in reliance on mechanical manipulation of the nucleus during phacoemulsification. It also gave us some reduction in effective phaco time and improvements in followability. Alcon’s Infiniti™ (Alcon Laboratories, Fort Worth, TX) has given us several new options including short bursts of ultrasound energy. There is traditional ultrasound as well as NeoSoniX™, which adds rotational oscillations of the tip in the sonic frequency range to the

117

FIGURE 13.2: Demonstration of the possible customization of power modulations with increasing amplitude using the AMO Sovereign with WhiteStar™ ICE Technology

FIGURE 13.3: Demonstration of the possible customization of power modulations with decreasing amplitude using the AMO Sovereign with WhiteStar™ ICE Technology

FIGURE 13.4: Demonstration of the possible customization of power modulations with constant amplitude using the AMO Sovereign with WhiteStar™ ICE Technology

118

PHACODYNAMICS: STEP BY STEP

FIGURE 13.5: The physical principles of torsional phacoemulsification on the Alcon Infiniti™ and the differences from traditional phacoemulsification

ultrasonic vibrations of the tip with programmable oscillations, up to a two degree arc, which become activated at a programmed percent power level of the ultrasonic vibrations. This gives improved occlusion management by repositioning the material at the tip as well as enhanced cutting. The use of NeoSoniX™, compared to stated ultrasound with power modulations, in our experience, gave us an 87 percent reduction in effective phaco time and a 57 percent reduction in average phaco power. The newest ultrasound modulation on the Infiniti™ involves torsional phaco, which allows for torsional movements of a bent tip at ultrasonic frequencies. This gives us a type of cutting independent of the repulsive force of the vibrating tip, which provides dramatic improvements in followability. The elimination of the repulsive effect is an extremely efficacious benefit because it further protects the corneal endothelium, the trabecular meshwork, intraocular structures, and has added efficiency (Fig. 13.5) The STAAR Phacoemulsification (STAAR Surgical, Monrovia, CA) system gives us a new option: the ability to have the tip vibrate in the sonic range, in addition to ultrasound, both of which allow power modulations of both pulse and burst mode. The foot pedal is programmed so that one can go back and forth between sonic and ultrasonic vibratory frequencies of the phaco tip in the same case, thereby allowing greater customization of energy delivered to the eye in any particular part of the case, and the complete elimination of heat in sonic mode. Bausch and Lomb (San Dimas, CA) has recently added Customized Control Software (CCS) to their

Millennium™ system, which allows for hypercool settings by having extremely short bursts, or pulses, of energy. There can be up to 120 pulses per second, which leads to more effective cutting with less heat. The hyperburst mode allows us to move from 80millisecond bursts to bursts of energy as short as 4 milliseconds, again with reduction in energy and heat build-up. We also have a variable duty cycle from 10 to 100 percent and a variable rise time in the waveform pulse, which again reduces energy in the eye and heat build-up, and allows for further customization in the delivery of energy to the nucleus (Figs 13.6 and 13.7). We have found this to be extremely efficacious in addressing harder cataracts. Our initial study on the use of power modulations was published in 20011 and allowed us to reduce both effective phaco time and average power. Subsequently, we achieved further reductions as we added the new power modulations as new technology was added (Tables 13.1 to 13.3).2 In summary, the use of power modulations allows the customization of the delivery of energy to the nucleus as we read the nuclear density and followability. Power modulations have allowed us to achieve dramatic reductions in energy delivered to the eye resulting in almost immediate visual rehabilitation to excellent levels of visual acuity. The reduction of heat was the precursor of bimanual microincision phacoemulsification, which has many fluidic advantages along with minimized incision sizes, which will be advantageous once microincision intraocular lenses (IOLs) become available.

POWER MODULATIONS

119

FIGURE 13.6: Comparison of the Custom Control Software (CCS) on the Bausch & Lomb Millennium™ Phacoemulsification System to standard power modulations

FIGURE 13.7: Variable duty cycle and rise time using the Bausch & Lomb Millennium™ Phacoemulsification System with CCS

Table 13.1: Effective phaco time (EPT) and average phaco power compared with previously reported data for four phacoemulsification systems with new power modulation modalities

Table 13.3: Percentage of eyes with 20/40 or better uncorrected visual acuity (UCVA) at the first postoperative visit (2 to 24 hours)

Technology*

EPT (seconds)

Average Phaco Power (%)

Legacy NeoSoniX

11.51 1.50

15.0 6.5

Millennium Phaco Burst

5.44 3.10

13.0 8.8

STAAR Wave Sonic Wave

2.85 3.95

7.2 7.6

Sovereign WhiteStar

2.65 1.55

2.0 1.8

Technology*

Percentage (%)

Legacy NeoSoniX

70 96

Millennium Phaco Burst

91 100

STAAR Wave Sonic Wave

79 74

Sovereign WhiteStar

81 94

*New technology appears under old technology in column 1

*New technology appears under old technology in column 1 Table 13.2: Percentage of clear corneas at the first postoperative visit (2 to 24 hours) Technology*

Percentage (%)

Legacy NeoSoniX

90 98

Millennium Phaco Burst

91 100

STAAR Wave Sonic Wave

95 95

Sovereign WhiteStar

88 100

*New technology appears under old technology in column 1

The DVD accompanying this chapter will show the use of each of these modalities without narration. We are just demonstrating that you can achieve adequate bimanual microincision chopping with any of these systems and the parameters are evident in almost all of them on the video overlay.

REFERENCES 1. Fine IH, Packer M, Hoffman RS. Use of power modulations in phacoemulsification: choo-choo chop and flip phacoemulsification. J Cataract Refract Surg; 27:188-97. 2. Fine IH, Packer M, Hoffman RS. Power modulations in new technology: improved outcomes. J Cataract Refract Surg 2004;30:1014-9.