The Phaco Machine :The Physical Principles Guiding its Operation

Cataract Surgery, 3rd Edition

PART II – Preparation

Chapter 7 – The Phaco Machine :The Physical Principles Guiding its Operation

William J. Fishkind, MD, FACS,
Thomas F. Neuhann, MD,
Roger F. Steinert, MD

Contents

	•	Basic Principles of Power Generation
	•	Tuning
	•	Power Generation
	•	Energy at the Phaco Tip
	•	Modification of Phaco Power
	•	Fluidics
	•	Vacuum Sources
	•	Surge
	•	Surge Modification
	•	Venting
	•	Tubing Compliance
	•	Irrigation and Aspiration
	•	Bimanual Irrigation and Aspiration
	•	Vitrectomy
	•	Phaco Machine Settings
	•	Conclusion

Chapter Highlights

		Generation of ultrasonic energy
		Mechanisms of lens disassembly
		Control mechanisms of ultrasound power and fluidics
		Anterior vitrectomy
		Settings

Although the surgical techniques of phacoemulsification are often described, there is a tendency to overlook a basic aspect of this type of surgery: the physics of closed-system surgery and how it translates into clinical performance.

In addition, a basic knowledge of the principles of the physics and engineering of the machines, the power generators, and fluidics not only can assist in making a rational decision as to what kind of equipment to use but also can promote the performance of a surgical procedure that is more gentle and efficient, thus improving outcomes and minimizing complications.

All phaco machines consist of a computer to generate ultrasonic impulses and a transducer, usually piezoelectric crystals, to turn these electronic signals into mechanical energy. The energy thus created is harnessed, within the eye, to overcome the inertia of the lens and emulsify it. Once turned into emulsate, the fluidic systems remove the emulsate and replace it with balanced salt solution (BSS) in a closed, steady-state environment.

Basic Principles of Power Generation

The prerequisite for the removal of a cataract through a small incision is a technique to break up the hard nucleus into emulsate for aspiration. Inspired by the technique of dentistry to remove tarter with a metal tip that oscillates longitudinally at frequencies in the ultrasonic range, Kelman^[1–3] adopted this principle, combining the oscillating tip and the evacuation tube into a hollow needle.^[4] Titanium is the material of choice for such applications because it resists the fragmentation that occurs with more brittle metals. The mechanisms by which such an oscillating tip fragments the nucleus are examined in the following text.

Types of Transducers

Magnetostrictive Transducers

Magnetostrictive transducers are based on packs of ferromagnetic lamellae surrounded by an electric coil. The magnetic field induced by the high-frequency electric current flowing through the coil excites the oscillation.

The advantages of magnetostrictive transducers include contact-free excitation, thus avoiding deterioration at the junction of the current and the transducer. These transducers, coupling elements, and the entire handpiece are rugged. They can withstand mechanical injury and have a long life span. Their primary disadvantage is a relative low grade of efficiency. Only a small part of the energy input is transformed into mechanical action; the majority becomes heat. Heating not only carries the risk of tissue burn but also makes the transducer lose efficiency with rising temperatures. Also, in the original design, the concentric aspiration line had to be brought out before the lamellar stack, necessitating two sharp bends that frequently clogged.

Recent improvements include considerably increased efficiency through sophisticated ferromagnetic metal alloys with rare earth elements and engineering modifications that allow both the irrigation and aspiration lines to be concentrically brought straight all the way through the tack to the tip. This not only avoids the clog-prone bends but also provides a double stream of constantly flowing cooling fluid through all the elements of the vibrating system, thus obviating the need for a separate cooling system, as was found to be necessary on the older handpiece.

Piezoelectric Transducers

These transducers are based on the reversal of the piezoelectric phenomenon. Certain crystals, on compression, produce electric current. In reverse, electric current causes the crystal to contract. Applying current to a crystal at high frequency causes it to oscillate at that frequency.

The crystal is mounted on the “horn.” This is a piece of tubing of narrowing diameter eventually ending with the attachment of the phaco needle. The decreasing diameter tube acts as an amplifier to generate adequate power for emulsification.

The advantages of piezoelectric crystals include a high grade of efficiency and, therefore, little inherent heat generation, with no need for extra cooling. Their low mass allows rapid movement and precise control. Newer machines use digital inputs to generate power. Digital control is more precise and instantaneous. Many new handpieces use multiple crystals (usually two to four sets) to maximize responsiveness and provide adequate power to emulsify the mature hard nucleus. Disadvantages include the connection points between crystal and electric current, the connections among the multiple layers of crystals that are necessary to provide adequate stroke amplitudes, and the structural brittleness of the crystal itself. These properties limit the longevity of such transducers. They are delicate and deteriorate both by accidental mechanical injury and by the oscillation they produce.

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Tuning

Every material has an inherent frequency at which it vibrates naturally. This is called its resonant frequency. If excited to vibrate at this frequency, the transformation into mechanical amplitude will be optimal, and the creation of other forms of energy, principally heat, will be minimized. The creation of balanced crystals, their attachment to the horn, and the weight of the titanium phaco needle are, therefore, carefully controlled during manufacturing.

The phaco procedure itself is performed in a less rigidly controlled environment. In the course of phacoemulsification, the needle is passed through and inside material of inconsistent resistance. The aqueous humor is less resistant than a soft nucleus, and a soft nucleus less resistant than a mature one. Thus, for example, as the phaco needle travels through BSS into a hard nucleus, the resonant frequency must be adjusted, to prevent inefficient emulsification. The result of inefficient emulsification is prolonged phaco time, higher powers, and ensuing increased heat generation.

Therefore, all modern phaco systems now have a built-in feedback loop constantly adjusting, or tuning, the oscillating frequency to an optimal resonance. This is a function of the central processing unit of the machine. It reads the change in resistance of the phaco needle and makes minute adjustments in the stroke length or frequency, dependent on which phaco machine is utilized, thus maximizing effectiveness. The rate of repetition with which the machine makes these adjustments is machine dependent. In the AMO Sovereign system, the tuning rate is 20μs, in the Alcon Infiniti it is 100 times/s. It is intuitive, however, that the greater the frequency of these corrections, the more effective the emulsification.

Power Generation

Power is created by the interaction of frequency and stroke length. Frequency is defined as the speed of the needle movement. It is determined by the manufacturer of the machine. Presently, most machines operate at a frequency of between 28,700 cycles per second (c/s; or hertz [Hz]) to 45,000c/s (Table 7-1). This frequency range is the most efficient for nuclear emulsification. Lower frequencies appear to be less efficient, and higher frequencies create excess heat.^[5]

Table 7-1 -- AMO sovereign settings for phaco chop⁎

Phaco 1 Hard chop	Phaco 2 Mod. chop	Phaco 3 Epinucleus unoccluded	Phaco 3 Epinucleus occluded	Phaco 4 Pre-occlusion
Vac. 315 Asp. 22 Power 30% Linear	Vac. 250 Asp.22 Power 25% Linear	Vac. 315 Asp. 22 Power 30% Thresh.150	Vac.150-315 Asp.22 Power 30%	Vac. 315 Asp. 22 Power 10%
0–25% CD 43%	0–25% BL 14%	0–25% BL 14%	4 long pulse (150ms) BD 33%	0–100% CN 18%
26–50% CD 43%	26–50% CL 25%	26–50% CL 25%
51–75% CB 60%	51–75% BD 33%	51–75% BD 33%
76–100% DB 67%	76–100% CD 43%	76–100% CD 43%
CD 6/8=14	BL 4/24=28	BL 4/24=28	BD 4/8=12	CN 6/28=34
CB 6/4=10	CL 6/24=30	CL 6/24=30
DB 8/4=12	BD 4/8=12	BD 4/8=12
	CD 6/8=14	CD 6/8=14

^⁎	With 2.8 mm temporal clear corneal incision, 19-gauge 0° tip. Letter designations indicate duty cycles, i.e. DB is 8 ms on and 4 ms off in a 12 ms duty cycle.

Frequency is maintained constant by tuning circuitry designed into the machine computer. As noted earlier, tuning is vital because the phaco tip is required to operate in varied media. The computer recognizes the change in resistance by sensing a change in load. The appropriate response is then delivered to the phaco tip by a minute change of frequency or stroke length depending on the machine algorithm. The surgeon will subjectively appreciate good tuning circuitry by a sense of smoothness and power.

An innovative use of tuning circuitry software is found on the Alcon Infinit Machine. This modification is called “Smart Pulse” (Figure 7-1). When this proprietary programming is engaged, if the duration of the power stroke is less than 20ms, a low power pulse, 1/2 of the programmed power (with a maximum of power of 10%) is generated prior to the application of the commanded power stroke. The low power pulse is used to sense the resistance of the nuclear fragment (load) and adjust the stroke length to provide the commanded power. This is important to allow maximum efficiency when ultrashort pulses of 5ms are utilized. Without this modification, by the time the machine tuned the pulse would be over!



Figure 7-1 Smart pulse diagram.

Stroke length is defined as the length of the needle movement (Figure 7-2). This length is generally 2–6mil (thousandths of an inch). Most machines operate in the 2–4-mil range. Longer stroke lengths are prone to generate excess heat. Much like a hammer striking a nail through a greater distance, the longer the stroke length, the greater the physical impact on the nucleus and, in addition, the greater the generation of cavitational forces (Figure 7-3).



Figure 7-2 Stroke length.



Figure 7-3 According to the formula F = MA (Force = Mass × Acceleration), as distance to the point of impact is increased, acceleration is increased, resulting in increased force.

Stroke length is determined by foot pedal excursion in position three during linear control of phaco power. Although the frequency is unchanged, the amplitude of the sine wave is increased in direct proportion to the depression of the foot pedal (Figure 7-4).



Figure 7-4 Frequency remains constant. The amplitude of the sine wave increases. This increases stroke length and resultant jackhammer and cavitational forces.

Energy at the Phaco Tip

The actual tangible forces, which emulsify the nucleus, are a blend of the “jackhammer” energy and cavitation energy.^[1]

The jackhammer energy is the direct mechanical impact of the physical striking of the needle against the nucleus. The efficiency of this mechanism depends on two main prerequisites:

	1.	Rapid forward acceleration of the phaco tip. This overcomes the inertia of the nucleus penetrating it rather than driving it away.
	2.	Close mechanical contact between the tip and the nucleus. Engineers call this force coupling. It is accomplished by pressing the tip against the nucleus or by pressing the nucleus to the tip.

The jackhammer energy can be maximized or minimized depending on the tip selection as discussed in the text that follows.

The cavitation effect is more complex. The phaco needle, moving through the liquid medium of the aqueous humor at ultrasonic speeds, creates intense zones of high and low pressure. Low pressure, created with backward movement of the tip, literally pulls dissolved gases out of solution, thus giving rise to microbubbles (25.4⁻⁵mm) in size. Forward tip movement creates an equally intense zone of high pressure. This produces compression of the microbubbles until they implode. At the moment of implosion, the bubbles create a temperature of 7204°C and a shock wave of 75,000 PSI. Of the microbubbles created, 75% implode, amassing to create a powerful shock wave radiating from the phaco tip in the direction of the bevel with annular spread. However, 25% of the bubbles are too large to implode. These microbubbles are swept up in the shock wave and radiate with it.

Utilizing high speed photography Dr. Teruki Miyoshi demonstated the development of cavitational energy in a video presented at ASCRS in 2005 (Figure 7-5).^[1]



Figure 7-5 Miyoshi high-speed photograph of cavitation.

The cavitation energy thus created can be directed in any desired direction as the angle of the bevel of the phaco needle governs the direction of the generation of the shock wave and microbubbles.

An artificial but educational method of visualizing these forces, called enhanced cavitation, has been developed. Using this process, with a 45° tip, the cavitation wave is generated at 45° from the tip and comes to a focus 1mm from it. Similarly a 30° tip generates cavitation at a 30° angle from the bevel, and a 15° tip, 15° from the bevel (Figure 7-6). A 0° tip creates the cavitation wave directly in front of the tip, and the focal point is 0.5mm from the tip (Figure 7-7). The Kelman tip has a broad band of powerful cavitation, which radiates from the area of the angle in the shaft. A weak area of cavitation is developed from the bevel but is inconsequential (Figure 7-8).^[8],[9]



Figure 7-6 A 30° tip. Enhanced cavitation shows ultrasonic wave focused 1mm from the tip, spreading at an angle of 30°.



Figure 7-7 A 0° tip. Enhanced cavitation shows ultrasonic wave focused 0.5mm in front of the tip, spreading directly in front of it.



Figure 7-8 Kelman tip. Enhanced cavitation shows broad band of enhanced cavitation spreading inferiorly from the angle of the tip. A weak band of cavitation spreads from the tip.

There is debate over the magnitude of the role of jackhammer and cavitation energy. Various investigators have found contrasting results on the subject of the power of cavitational energy.^[2] Analysis of their data indicates that Jackhammer energy is the more potent force in emulsification. Cavitation augments the emulsification when lens material is very close to, or within, the lumen of the phaco tip.

Taking into consideration analysis of enhanced cavitation, it can be concluded that emulsification is most efficient when both the jackhammer energy and cavitation energy are integrated. To accomplish this, utilize a 0° tip. When using an angled tip, the bevel of the needle should be turned toward the nucleus, or nuclear fragment. This simple maneuver causes the broad bevel of the needle to strike the nucleus. This enhances the physical force of the needle striking the nucleus. In addition, the cavitational force is concentrated into the nucleus rather than away from it (Figure 7-9). This causes the energy to emulsify the nucleus and be absorbed by it. When the bevel is turned away from the nucleus, the cavitational energy is directed up and away from the nucleus toward the iris and endothelium (Figure 7-10). Finally, in this configuration, the vacuum force (discussed later in this chapter) can be maximally exploited as occlusion is encouraged.



Figure 7-9 Turning the bevel of the phaco tip toward the nucleus focuses cavitation and jackhammer energy into the nucleus.



Figure 7-10 When the bevel is turned away from the nucleus ultrasonic energy is directed toward the iris and endothelium.

Modification of Phaco Power

Modification of phaco power must be accomplished to harness these powerful forces for a controlled phaco surgical procedure.

Application of the minimal amount of phaco power intensity necessary for emulsification of the nucleus is desirable. Unnecessary power intensity is a source of heat with subsequent wound damage. Moreover, excessive cavitational energy is a cause of endothelial cell damage and iris damage with resultant alteration of the blood–aqueous barrier. Phaco power intensity can be modified by altering phaco power amplitude, phaco power duration, and phaco power delivery.

Alteration of Phaco Power Amplitude

Stroke length is determined by foot pedal excursion and, therefore, foot-pedal adjustment. When it is set for linear phaco, the depression of the foot pedal increases stroke length and, consequently, power.

Foot pedals, such as those found in the Allergan Sovereign and the Alcon Infiniti machines, permit surgeon adjustment of the throw length of the pedal in position 3. This can refine power application. The Bausch & Lomb (B&L) Millennium, and AMO Signature offer a dual linear foot pedal which permits the separation of the fluidic aspects of the foot pedal from the power elements, by adding a yaw movement to the foot pedal.

Alteration of Phaco Power Duration-Burst, Pulse, Micro-Pulse

The duration of application of phaco power has a dramatic effect on overall power delivered to the anterior segment. This is the use of power modulations. Power modulations include the use of burst, multiburst, and pulsed phaco. For example, if continuous power is employed for 1min, the effective phaco time is 1min. If the power is pulsed at 10 pulses per second, the effective phaco time is 30seconds. The effective power delivered to the anterior segment is half of the continuous amount.

There are three different types of noncontinuous power modulations: burst, pulse, and hyperpulse, phaco.

In pulse phaco there is a fixed period of power with a fixed period of no power (aspiration only). The phaco power progressively increases as the foot pedal is depressed in position 3.

In burst phaco there is a fixed power with a reduced duration of the period of power on and power off (aspiration only) until there is continuous power.

Hyperpulse phaco has extremely short periods of power on and power off. Where a standard short pulse might be 50ms a micropulse might by 5ms.

Burst mode in the Allergan Sovereign (parameter is machine dependent) is characterized by 80 or 120ms periods of power combined with variable short periods of aspiration only. Pulse mode uses fixed pulses of power of 50 or 150ms with variable short periods of aspiration only. Phaco techniques such as phaco chop use minimal periods of power in pulse mode to reduce power delivery to the anterior chamber. In addition, the use of pulse mode, or hyperpulse mode, to remove the epinucleus provides an added margin of safety. When the epinucleus is emulsified, the posterior capsule is exposed to the phaco tip and may move forward toward it because of surge. Activation of pulse phaco mode creates a deeper anterior chamber to work within. This occurs because each period of phaco energy is followed by an interval of no phaco energy. During the interval of absence of energy the epinucleus is drawn toward the phaco tip, producing occlusion, interrupting outflow. This allows inflow to deepen the anterior chamber immediately before onset of another pulse of phaco energy. The surgeon will recognize the outcome as operating in a deeper, more stable anterior chamber.

Recent innovations by Alcon, AMO, B&L, and Staar have resulted in new forms of power modulation.

Cavitational Modifications of Software

Abbott Medical Optics (AMO) introduced the WhiteStar System of hyperpulse phaco. In this modification, extremely short bursts of power are interspersed with similar, extremely short periods of aspiration. The relationship of these on/off periods are called a “duty cycle” (see Figure 7-13).



Figure 7-13 A duty cycle is the combined burst and rest time.

In a duty cycle pulse, the on time for ultrasonic energy is active for only a percentage of the total time of the pulse. For example, with a duty cycle of 50% the pulse on time/off time could be 4ms on/8ms off or 6ms on/12ms off. In the first example the pulse duration is 12ms and in the second 18ms. It can be seen with similar duty cycles the time of power on or off may be vastly different.

The duty cycle is selected by the surgeon. Using the AMO Sovereign there are many choices for on/off time and duty cycle (Table 7-2). The Alcon Infiniti system may generate up to 100 pps with programmable duty cycle between 5 and 95%. The B&L Millennium can generate up to 120 pps with duty cycles between 10 and 90%.

Table 7-2 -- Alcon Infinity: torsional phaco⁎

	Sculpting	Quadrant removal	Epinucleus/cortex removal
Irrigation (cm H₂O)	95	95	95
Aspiration rate (cc/min)	24	38	33 linear
Vacuum limit (mm Hg)	120	360	300 linear
Torsional amplitude	100% linear	100% linear	100% linear

^⁎	20 gauge, 15° Kelman ABS Tip.

Pulse Contouring

The newest variation of phaco energy is the modification of the contour of the ultrasonic waveform. This is helpful in emulsification of cataract fragments. The traditional ultrasonic waveform is square (Figure 7-11). The B&L Millennium employs “rounded waveform” (Figure 7-11). This modulation changes the contour of the ultrasonic pulse so that within the duty cycle the pulse begins at low power and intensifies rapidly to the maximum preset power. The low power enhances the movement of the fragment toward the phaco tip enhancing occlusion. The higher power provides for the emulsification of the fragment.



Figure 7-11 The B&L Stellaris square waveform compared to the rounded waveform.

The AMO Sovereign and Signature approach the problem of improved followability from a different perspective. They have engineered a pulse of ultrasonic power with a short burst of increased energy at the beginning of each ultrasonic waveform (Figure 7-12); this is named ICE (increased control and efficiency). The amplitude of this “kicker” can be programed up to 12% of the total power of the pulse. It can increase, decrease, or remain the same as the phaco power is increased. The concept is to drive the fragment a microscopic distance from the phaco tip as the tip is energized. The fragment is then available for emulsification without occlusion.



Figure 7-12 AMO ICE – a 1 ms “kicker” at the beginning of the pulse (not to scale).

The change in phaco duty cycles leads to enhanced followability by altering the tendency for phaco power to repel cataractous material and modifying the fluidic characteristics of the pre-occlusion/post-occlusion cycle (discussed below). The end result is shorter phaco power on times, less delivery of total phaco energy to the anterior segment, and increased anterior chamber stability resulting is decreased incidence of ruptured posterior capsules and vitrectomy. In addition, the off time allows effective cooling of the phaco tip, minimizing the likelihood of wound burn, even during emulsification of a hard nucleus.

Wound Burn

The prevention of wound burn is an important feature of this software modification. Studies have shown that the wound will show the first signs of a wound burn at 45°C and frank signs of burn at 50°C. With WhiteStar, the maximal wound temperature at 100% power was measured at 28°C.^[11] Therefore, the phaco tip can be placed though the wound without the cooling sleeve. Whenever there is decreased outflow through a phaco tip, especially when the wound is tight surrounding the tip compressing the sleeve or tip shaft, wound burn is possible. The greater the energy setting the greater the risk of wound burn. The surgeon must be vigilant to monitor bubbles around the tip wound interface or striae in the clear cornea over the phaco tip. Any suggestion of these phenomena mandates immediate cessation of phaco energy.

Bimanual Microincisional Phaco

Micropulse phaco allows for the performance of a bimanual, microincisional, phacoemulsification procedure. The irrigation is provided by a 20-gauge irrigating chopping instrument through a 1.4mm clear cornea incision. The 20-guage, 15° or 30° phaco tip without the irrigation sleeve is inserted through a 20-gauge clear cornea incision 90–100° away (21-gauge instrumentation with 1.1mm incisions can also be utilized). The nucleus is emulsified by either a vertical or horizontal chopping procedure. The wound remains cool and the efficiency of the procedure is enhanced as the separate irrigation tends to wash fragments into the phaco tip.

Coaxial Microincisional PhacoMicropulse phaco also allows for another variation of microincisional phaco. This is coaxial phaco utilizing micro phaco tip of 20 gauge (Alcon Infiniti) and a thin-walled rigid infusion sleeve through a 2.4mm. Torsional phaco (discussed below) is another excellent modality for coaxial microincisional phaco.

Employing similar modification to tip and sleeve the B&L Stellaris is capable of passing through a 1.8 mm incision for coaxial microincisional phaco.

Alteration of Phaco Power Delivery

The amplitude of phaco energy is modified by tip selection. Phaco tips can be modified to accentuate: (1) power intensity, (2) flow, or (3) a combination of both.

Power intensity is modified by altering bevel tip angle. As noted previously, the bevel of the phaco tip focuses power in the direction of the bevel. The 0° tip focuses both jackhammer and cavitational force directly in front of it. The 30° tip focuses these forces at a 30° angle from the phaco tip (see Figures 7-6, 7-7, 7-9, and 7-10). The Kelman tip produces broad powerful cavitation directed away from the angle in the shaft (see Figure 7-8). This tip is excellent for the hardest of nuclei.

Power intensity and flow are modified by using a 0° tip. This tip focuses power directly ahead of the tip and enhances occlusion caused by the smaller surface area of its orifice.

Flare tips direct cavitation into the opening of the bevel of the tip. Thus random emission of phaco energy is minimized. The wide opening of the tip makes it easier to minipulate the fragment. The narrow “neck” of the tip functions as a flow restrictor by increasing the resistance to flow and reducing the tendency to create surge (Figure 7-14). Designer tips such as the “flathead” designed by Barry Seibel and power wedges designed by Douglas Mastel offer the ability to fine tune the focus of phaco energy as well as modify the aspiration flow dependent upon the configuration and diameter of the phaco tip. The rounded tip designed by Steven Dewey is interesting as it will maximize cavitational energy but is “capsular friendly.” Thus, if the capsule should be aspirated by the phaco tip while energized, tearing the capsule is less likely.



Figure 7-14 Flare tip focuses power at the tip secondary to the flare and acts as a flow restrictor secondary to the narrowing at the “neck.” (Courtesy Micro Technology Inc.)

Small-diameter tips, such as 21-gauge tips, change fluid flow rates. Although they do not in reality change the power intensity, they appear to have this effect, as the nucleus must be emulsified into smaller pieces for removal through the smaller diameter tip.

The Alcon aspiration bypass system (ABS) tip modification is available with many tip configurations. The tip type is a modification of power intensity, and the ABS is a flow modification. In the ABS system a 0.175mm hole in the needle shaft permits a variable flow of fluid into the needle, even during occlusion (Figure 7-15). The amount of flow through the shaft hole is variable and depends on the vacuum level. The higher the vacuum level, the greater the flow. This flow adjustment serves to reduce postocclusion surge (discussed below).



Figure 7-15 A 0.175mm hole drilled in the shaft of the ABS tip provides an alternate path for fluid to flow into the needle when an occlusion occurs at the phaco tip.

Alteration of Phaco Power, Duration and Configuration – please see Pg 92 for an update to this section

Torsional Phaco

A new development in phaco is the harnessing of lateral or ocillatory movement of the phaco tips developed by Alcon in the Infiniti Machine. The OZiL torsional handpiece has both a longitudinal movement and torsional movement. The longitudinal movement, like a standard phaco needle is at 40 kHz. The torsional movement is at 32 kHz with 1° arc of motion (Figure 7-16). The torsional movement may be used alone or in combination with the longitudinal movement with many variations of timing. It requires an angled “kelman” tip of 15° or 30° to be effective. It appears to be most efficient when using a mix of longitudinal and torsional movement. This modification, as well as needle configurations, is presently under modification. The final parameters for its use are yet to be determined. The torsional movement will emulsify with minimal chatter and improved followability. However, occasionally the low power phaco will cause chunks of nucleus to occlude the phaco needle lumen. Longitudinal movement is then used to emulsify the material present in the needle bore.



Figure 7-16 Torsional needle.

Torsional phaco is noteworthy for its efficient removal of nuclear material due to the propensity of torsional movement to favor pre-occlusion phaco (see below).

Phaco power intensity is the energy that emulsifies the lens nucleus. The phaco tip must operate in a cool environment and with adequate space to isolate its actions from delicate intraocular structures. This portion of the action of the machine is dependent on its fluidics.

Fluidics

The fluidics aspect of all machines is fundamentally a balance of fluid inflow and fluid outflow. The resultant balance of these two influences will be the maintenance of a constant intraocular volume and, therefore, a stable and deep anterior chamber. In addition, the intraocular pressure must be maintained within physiologically compatible limits.

Infusion

Inflow (infusion) is the pressure gradient, which drives the infusion flow. In a gravity feed system, the bottle height above the eye of the patient creates an infusion pressure. When infusion pumps are employed, the amount of infusion pressure programmed into the pump will be responsible for the generation of infusion pressure. With temporal surgical approaches, the eye of the patient may be physically higher than in the past. This requires that the irrigation bottle be adequately elevated. In addition, when the machine flow rate is increased, increased fluid evacuation from the anterior chamber requires increased inflow to maintain the steady-state system. Therefore, when the machine flow rate is increased, the bottle height should also be increased. A shallow, unstable anterior chamber results otherwise.

Infusion tubing diameter and elasticity do not play a significant role in infusion volume control because high pressures and rapid pressure fluxes rarely occur on the irrigation bottle side of the system.

Outflow

Control of outflow is notably more complex because many factors influence both volume and speed of fluid outflow during the phaco procedure. Among these variables are incision size, phaco tip diameter and sleeve diameter, pump type and settings, and tubing diameter and compliance. In addition, computer software design plays a significant role in regulating both outflow volume and speed.

Incision

The incision size is an important variable in the determination of fluid outflow. This is actually a controlled leak determined by the sleeve–incision relationship. The incision length selected should create a snug fit with the phaco tip and sleeve selected. This results in minimal controlled wound fluid outflow with resultant increased anterior chamber stability.

If the incision is too large for the selected phaco tip and sleeve combination, the excessive fluid outflow will necessitate increased fluid inflow to maintain a deep anterior chamber. The increased infusion volume not only is deleterious to the health of the endothelium but usually cannot sustain the sudden changes in volume that occur during the procedure. This leads to considerable chamber instability with increased risk of rupturing the posterior capsule.

If the incision is too small, crimping of the sleeve will lead to decreased inflow with resultant chamber shallowing. In addition, decreased inflow is the origin of decreased cooling and may produce wound burns.

Aspiration Settings

Aspiration rate, or flow, is defined as the flow of fluid, in cubic centimeters per minute (cc/min), through the aspiration tubing. With a peristaltic pump this rate is determined by the speed of the pump. Flow is the fluidic force that determines how well particulate material is attracted to the phaco tip. Flow adjustments act to speed up or slow down events in the anterior chamber. Therefore, if events appear to be occurring too rapidly, the flow rate is slowed. Alternatively, if events are occurring too slowly, the flow rate is increased.

Aspiration level, or vacuum, is a level and measured in millimeters of mercury (mmHg). It is defined as the magnitude of negative pressure created within the tubing. Vacuum is the fluidic force determinant of how well, once occluded on the phaco tip, particulate material will be held to the tip.

Flow, therefore, is the setting that controls how well material is attracted to the phaco tip. Vacuum is the setting that determines how well material is held against the tip once occlusion occurs.

Vacuum Sources

The origin for the development of vacuum is the vacuum pump. The three categories of vacuum sources or pumps are: (1) flow pumps, (2) vacuum pumps,^[3] and (3) hybrid pumps.

The prototype example of the flow pump is the peristaltic pump (Figure 7-17). This pump consists of a series of rotating rollers that successively compress the aspiration tubing, moving fluid within the tubing and creating vacuum. The speed of rotation of the pump head governs the flow rate. One important advantage of this class of pumps is the ability to allow independent control of both aspiration rate and aspiration level.



Figure 7-17 Peristaltic pump uses a rotating wheel with rollers to pinch off segments of the aspiration tubing, thereby moving separate columns of fluid through the tubing at a controlled rate of aspiration or flow. The vacuum limit is set separately and independently, limiting the maximal vacuum that is tolerated in the condition of complete occlusion of the aspiration line. The collection chamber, located after the vacuum limit chamber and the aspiration pump, is open to atmosphere.

The primary example of the vacuum pump is the Venturi pump (Figure 7-18). In the Venturi pump, compressed gas is passed through a Venturi, which creates a vacuum. The Venturi is attached to a rigid reservoir that is attached to the aspiration tubing. The velocity of the compressed gas passage through the Venturi creates greater or lesser vacuum that is then transferred through the reservoir to the aspiration line. This results in varying amounts of vacuum.



Figure 7-18 In a Venturi pump system, the flow of gas passed through tubing with increasing diameter creates a vacuum. The collection chamber is, therefore, a closed system. A separate valve can control the aspiration rate. A separate vacuum limit can be set, but a continuous internal vacuum is necessary to drive the aspiration of the fluid.

Additional examples of this pump type are the rotary vane and diaphragmatic pumps.

Vacuum pumps allow direct control of only vacuum level. Flow control is dependent on the vacuum level setting. There is no independent setting of aspiration flow.

Modern modifications of the basic pump types have prompted the creation of a new pump category, the hybrid pump. These pumps are interesting in that they can act like either a vacuum or flow pump, independent of their original design, depending on their programming. They are the most recent supplement to pump types. They are universally controlled by digital inputs, producing extraordinary flexibility and responsiveness.

The primary example of the hybrid pump is the Allergan Sovereign peristaltic pump (Figure 7-19) or the B&L Concentrix pump (Figure 7-20).^[12]



Figure 7-19 AMO Sovereign hybrid peristaltic pump.



Figure 7-20 A, The scroll pumps' emptying phase is flow based, analogous to a peristaltic system. B, During the inflow phase, the male scroll opens like a bellows, creating vacuum response similar to a Venturi system.

Recognizing that surgeon preference over pump types may play a role in surgeon machine purchase, some new machines offer both types of pumps. The AMO Signature with Fusion Technology and the B&L Stellaris offer this option. The challenge to the surgeon is to balance the effect of phaco power intensity, which tends to push nuclear fragments away from the phaco tip, with the effect of flow, which attracts fragments toward the phaco tip, and vacuum, which holds the fragments on the phaco tip. Generally, low flow slows down intraocular events, and high flow or vacuum speeds them up. Low or zero vacuum is helpful during sculpting of a hard or a large nucleus. In this circumstance, the large, hard endonucleus may cause the surgeon to phacoemulsify near or under the iris, or anterior capsule, with a high-power intensity. With normal aspiration the phaco tip may aspirate the iris. The high power will cause immediate, severe damage to the iris. Therefore, zero (or very low) vacuum will prevent inadvertent aspiration of the iris or capsule, preventing significant morbidity.

Surge

A principal limiting factor in the selection of high levels of vacuum or flow is the development of surge. When the phaco tip is occluded, flow is instantly interrupted, and vacuum rapidly builds to its preset maximum level (Figure 7-21). Emulsification of the occluding fragment then clears the occlusion. Flow instantaneously begins at the preset level in the presence of the high vacuum level. In addition, if the aspiration line tubing is not reinforced to prevent collapse (tubing compliance), the tubing will have constricted during the occlusion. It then expands on occlusion break. The expansion is an additional source of brisk vacuum production. These factors cause a rush of fluid from the anterior segment into the phaco tip (Figure 7-22). The fluid in the anterior chamber may not be replaced by infusion rapidly enough to prevent its shallowing. Therefore, subsequent, rapid anterior movement of the posterior capsule occurs. Often the cornea collapses. The violent snapping of the posterior capsule, or abrupt forceful stretching of the bag around nuclear fragments, may be a cause of capsular tears (Figure 7-23). In addition, the posterior capsule can be literally sucked into the phaco tip, tearing it. The magnitude of the surge is contingent on the presurge settings of flow and vacuum.



Figure 7-21 Immediate presurge. The nuclear fragment has occluded the phaco tip. Flow instantaneously drops to zero. Vacuum begins to rise toward the maximum preset. The aspiration tubing begins to collapse. The chamber is deep. (Courtesy Thieme Publications, New York.)



Figure 7-22 Early surge. Phaco power has partially emulsified the fragment. Flow is about to resume and instantaneously rise to the preset maximum. Vacuum, at maximum, is about to precipitously drop. The tubing is expanding. Outflow is exceeding inflow. The chamber is beginning to collapse. The posterior capsule is beginning to bulge around the remaining heminucleus. (Courtesy Thieme Publications, New York.)



Figure 7-23 Midsurge. Flow is now at preset maximum. Vacuum is zero. The anterior chamber is markedly shallowed. The posterior capsule has snapped around the heminucleus, causing a tear. The cornea has collapsed. (Courtesy Thieme Publications, New York.)

The phaco machine manufacturers help to decrease surge by providing noncompliant aspiration tubing. This does not constrict in the presence of high levels of vacuum.

Most manufacturers have created algorithms in their software that emulate the anterior chamber, moment to moment, during the phaco procedure. These algorithms can anticipate changes per microsecond in the real anterior chamber and make appropriate pump adjustments to minimize surge.

Surge Modification

Surge is undoubtedly an unwanted event. The trampolining of the posterior capsule caused by surge has the effect of creating dismay among surgeons. In an effort to prevent capsular tears, they move the nucleus anteriorly, closer to iris and endothelium. To promote a more safe procedure and to spare the iris and endothelium unnecessary trauma, the astute surgeon will consider what changes in fluidics are necessary to prevent surge.

If the defining instant in the generation of surge is the occlusion break, the entire episode can be divided into: preocclusive, occlusive, and postocclusive segments.

Preocclusion

Historically, the only way to modify surge was to select lower levels of flow and vacuum. This category would be a modification in preocclusion (Figure 7-24). At present, many other methods exist to decrease surge. Another approach to surge management, in all phases of occlusion, is the use of an anterior chamber maintainer. The constant flow of this device acts to deepen the chamber in all phases of phacoemulsification. Constant infusion, when available, is another preocclusion modification, although its benefits are not significant.



Figure 7-24 The dynamics of vacuum and flow, with particular emphasis on the phenomenon of surge. The values shown are illustrative and not necessarily those of any particular commercial system or surgical technique. A, In traditional peristaltic technology, flow ideally can be set at a relatively high rate just below that which would flatten the anterior chamber. In a nonoccluded system, the flow can be high, and the vacuum level at the phaco tip is nearly zero. When the tip is occluded, the aspiration rate rapidly falls to zero. The vacuum level rises correspondingly. The more rapid the flow rate, the more quickly the vacuum level rises. The vacuum level continues to build up to the preset limit, after which fluid is bled into the aspiration line, limiting the maximum vacuum. When occlusion is relieved, the vacuum then rapidly falls back to a near zero level at the tip. The stored potential energy in the aspiration line causes a momentary “surge” in the fluid flow before the flow stabilizes at the original level determined by the rotation of the peristaltic pump. If the potential energy causes a surge of fluid flow greater than the combined rate of irrigation fluid inflow and wound leak, flattening of the anterior chamber results. B, One mechanism for compensating for surge is to reduce flow. When flow or aspiration rate is reduced, two effects are seen. First, after occlusion is obtained, the rate at which the vacuum rises is slower. Ultimately, however, the vacuum still builds to the preset level. Second, after occlusion break, the height of the fluid surge is the same as in panel A. However, the surge is relative to the baseline level of nonoccluded flow. Because the flow has been reduced, the overall surge level may be at or below the level of a momentary flattening of the anterior chamber. C, An alternative compensation for surge is to reduce the vacuum level. Because the flow rate is unchanged, the speed at which the maximum vacuum is achieved is unchanged compared with the buildup of vacuum seen in panel A. After the occlusion is relieved, the amount of surge is reduced because the stored potential energy is reduced through the lower vacuum level. Because of the high flow rate, however, even this reduced amount of surge may exceed the level at which flattening of the anterior chamber is seen. D, In common clinical practice, both the flow and vacuum levels are reduced below the theoretical maximum to guard against surge. As illustrated, the reduction in flow rate and maximal vacuum level reduced the surge below the level at which the anterior chamber flattens. Through these compromises, safe phacoemulsification can be clinically performed. The dynamics of vacuum and flow are shown, with particular emphasis on the phenomenon of surge. The values shown are illustrative and not necessarily those of any particular commercial system or surgical technique. E, In a Venturi or diaphragm pump, flow and vacuum are intrinsically linked. The potential vacuum within the system caused by the Venturi and diaphragm pump is the principal determinant of the flow level. As illustrated in the left side of the figure, one attribute of the Venturi system is the rapid response time of the flow rate achieved by varying the potential vacuum within the system. After total occlusion occurs clinically, however, the performance at the phaco tip is similar to that of the peristaltic pump. The vacuum level at the tip rises to the preset level of the internal pump while the flow rate drops to zero. When occlusion is relieved, the vacuum at the tip once again drops to nearly zero. The stored potential energy in the system is translated into the clinical phenomenon of surge, just as in a peristaltic system. After the surge phenomenon, the flow rate stabilizes at the level determined by the internal vacuum of the Venturi pump. F, To compensate for surge and to maintain the anterior chamber, typically maximum potential vacuum and flow rate are reduced. Because of the intrinsic linkage of flow and vacuum in a Venturi or diaphragm pump system, reduction of the internal potential vacuum necessitates a reduced flow rate. By reducing both the flow and maximum vacuum, the surge level can be reduced below the level of flattening of the anterior chamber. G, New technology offers enhanced control over the surge phenomenon. As a result, phacoemulsification can be performed at vacuum levels that were previously highly unsafe. As illustrated, a microprocessor peristaltic pump control system may allow vacuum levels to build up to 500mmHg or more. After a break in the occlusion, the microprocessor delays the action of the pump by delaying its onset. In this manner, combined with other steps, such as reducing the compliance of the vacuum tubing, the phenomenon of surge is reduced to clinically tolerable levels, and high vacuum can be employed as a clinical tool without danger of collapse of the anterior chamber.

The most powerful modification of fluidics to allow emulsification in the pre-occlusion phase is not a fluidic modification but a power modification. The development of micro pulse phaco (discussed earlier), a patented development of AMO, found originally in the Sovereign with Whitestar, and now available in all machines by all manufacturers, is an evolutionary change in creating a more stable anterior chamber during emulsification. The extremely short bursts of energy followed by a variable period of no energy and aspiration only, serves to hold a nuclear fragment very near, but not occluded on, the phaco tip. Therefore, the fragment is emulsified with a combination of jackhammer and cavitation energy without ever totally occluding the tip. If there is no occlusion, there cannot be surge. Therefore, the phaco is performed on the pre-occlusive side of the pattern.

Occlusion

Only a few modifications take place at the moment of occlusion. The first is the use of the ABS tip (Alcon). This tip, discussed earlier, has a 0.175mm hole drilled in the shaft of the phaco needle (see Figure 7-15). When occlusion occurs at the tip, fluid flows into this hole. The amount of flow depends on the vacuum and flow settings. For example, the flow through this hole is 4 cc/min at a vacuum of 50mmHg and 11cc/min at a vacuum of 400mmHg. Because some flow always exists, in reality there is never complete occlusion. This prevents the rise of high vacuum levels and thus diminishes postocclusion surge. This modification must be used with the high vacuum tubing or it does not function properly.

The second, as employed by AMO Sovereign/Signature, B&L Mellennium/Stellaris with the peristaltic pump (Advanced Fluidics System), and the Infinit (ALCON) with the dynamic rise time option, is a variable rise time. By slowing the pump speed during occlusion, the generation of high vacuum levels is decelerated, and surge is diminished.

A third method is demonstrated by the Signature (AMO), and Mellennium/Stellaris (B&L) with the dual linear foot pedal. Employing this device, by yawing the foot pedal, aspiration only can be selected. Utilizing linear vacuum the vacuum level can be increased to the exact amount to cause occlusion, but not higher, minimizing the post occlusion surge when phaco power is applied. This method of vacuum control changes both the occlusion and post occlusion function.

Postocclusion

Once occlusion has occurred, decreasing the vacuum or flow instantaneously to dramatically decrease flow into the phaco tip is a powerful method of diminishing surge.

The model for this type of surge modification is found in the AMO Sovereign unit. In this machine, microprocessors sample vacuum and flow parameters 50 times a second, creating a “virtual” anterior chamber model. At the moment of surge, the machine computer senses the increase in flow and instantaneously slows or reverses the pump to stop surge production. Pump management, rather than venting, is the mechanism to control surge.

In addition, this device has a programmable occlusion threshold setting. When the vacuum reaches this threshold, a new flow, as well as a new power modulation, can be programmed. Therefore, if a hard nucleus is being emulsified, when the vacuum reaches 80mmHg, for example, the flow, which might have been set at 350mL/min, can now be automatically decreased to 100mL/min. The result will be a noteworthy decrease in surge. Moreover, the pulse rate can be simultaneously slowed to further stabilize the anterior chamber.

Ever improving digital control is demonstrated in the Sovereign/Signature (AMO) with a fluidic modification they have named CASE (Chamber Stabilization Environment) technology. With this software the surgeon sets a vacuum threshold and time for an extremely fast, 26ms, drop in vacuum to a pre-set new, lower vacuum. This drop occurs so fast that there is not enough time for vacuum to build and thus prevents the surge from occurring.

Another solution to this problem is demonstrated in the B&L Millennium/Stelaris machine. The dual linear foot pedal can be programmed to separate both the flow and vacuum from power. In this way, flow or vacuum can be lowered before beginning the emulsification of an occluding fragment. The emulsification, therefore, occurs in the presence of a lower vacuum or flow so that surge is minimized.

Finally, the Starr Wave machine solves this problem in another manner. The patented coiled aspiration tubing acts as a flow resistor. At low flow settings, up to 50mL/min, the tubing acts like normal tubing. When flow exceeds this level, turbulence in the tubing inhibits further increases in flow. This dampens the fluid outflow, and subsequent vacuum rise. The result is decreased surge.

An add-on tubing restrictor, also manufactured by Starr, is called “cruise control.” It is a dual sleeved tubing. The outer tubing creates the cartridge shell, and the inner tubing is fenestrated and is a filter (Figure 7-24A). The cartridge is inserted into the aspiration orifice of the handpiece and then connects to the aspiration tubing. Where it connects the cartridge narrows to 1mm diameter. The inner cartridge filters emulsate particulates to prevent clogging at the flow restrictor, the 1mm narrowing of the tubing. Thus a powerful flow restrictor decreases surge and stabilizes the anterior chamber insulating against fluid fluxes.

Venting

Often during the performance of phacoemulsification, or irrigation and aspiration (I&A), undesirable material is aspirated on the phaco tip. This could be posterior capsule or a piece ofnucleus that is too large for efficient emulsification. Often the aspiration of these structures requires hasty release. Venting is the mechanism for this release by neutralizing vacuum in the aspiration line.

When the surgeon lifts the foot pedal from position 2 or 3, the venting mechanism is engaged. This allows air or fluid to flow into the aspiration line. Generally, venting to air has been abandoned by most manufacturers. When the aspiration line is vented to air, bubbles form in the aspiration tubing. When the foot pedal is again depressed, the development of vacuum is slowed because the air in the line must first be aspirated before vacuum can once more rise.

The preferred venting material is, therefore, fluid. Most machines use fluid from the infusion bottle for this purpose. The fluid flows into the aspiration tubing, neutralizing vacuum and permitting the release of unwanted material. Because no air has been introduced into the system, when the foot pedal is again engaged, there is brisk redevelopment of flow and vacuum. This technique produces a more responsive system.

In some machines, venting also occurs when the selected vacuum level is attained. Controlled venting stops further generation of vacuum and maintains the commanded vacuum level.

Tubing Compliance

The thickness and rigidity of the tubing, as well as the inner lumen diameter, contribute to the ability of the tubing to collapse and expand during the fluid fluxes which accompany phacoemulsification. The greater the tubing compliance, the less of a tendency it has to collapse when the phaco tip is occluded and vacuum rises. Generally, if the tubing collapses at high vacuum, it will expand when emulsification occurs, and vacuum suddenly drops to zero. This sudden expansion of the tubing is an additional factor in post-occlusion surge.

Irrigation and Aspiration

Fluidic management techniques used in the phaco mode are now applied to the I&A segment. Therefore, surge management systems function to prevent surge when a large or “sticky” piece of cortex is aspirated.

Most I&A tips use a 0.3mm orifice. They are now available in straight and angled configurations. Soft or hard metal sleeves are also offered to provide coaxial fluid inflow. Soft sleeves are now preferred to provide a tighter uniform seal within the surgical wound. This lessens superfluous outflow and leads to a more stable anterior chamber. Silicone I&A tips are also available and are, reportedly, less likely to tear the capsular bag.

Bimanual Irrigation and Aspiration

Introduced in Europe by Dr. Peter Brauweiler, the use of separate cannulas for I&A has been widely accepted. In this technique, small paracentesis-like incisions are made for placement of the cannulas. The small incisions and smaller cannulas offer controlled inflow and outflow, which promotes anterior chamber stability. The ability to more easily reach recalcitrant cortex provides surgeons with a technique that simplifies I&A. The relative positions of the cannulas are simply exchanged to reach new areas of cortex.

Bimanual techniques are especially suited to removal of cortex in difficult situations. When the posterior capsule is torn, the additional control of aspiration cannula placement, as well as the decreased anterior chamber fluid fluctuations, minimizes the risk of rupturing the vitreous face with subsequent necessity for vitrectomy. In addition, in cases of zonular dehiscence, the added flexible placement and maneuverability of the aspiration cannula provide a margin of safety removing cortex without further disruption of zonules.

Vitrectomy

All current machines have vitrectomy capability. Generally the same I&A tubing is used. They are attached to the vitrectomy handpiece. In the vitrectomy mode the foot pedal controls irrigation and aspiration and activates the vitrectomy handpiece cutter. If the cutter is actuated by compressed air, it must be connected with the dedicated compressed air tubing to the machine attachment port.

Vitrectomy Instruments

The three types of vitrectomy handpieces are rotary, oscillatory, and guillotine cutters.

Rotary cutters have a sharp blade, or blades, which rotate perpendicular to the long axis of the aspiration tube. They have the advantage of being self-sharpening and, therefore, perform excellent cutting when in proper working order. They are often actuated electrically. The potential problem with these cutters occurs when the blades are dull from extensive usage or are out of alignment. The rotatory movement of the blades then has the capability of pulling the vitreous into the instrument without cutting it. The result is “spooling” of the vitreous, which is often the cause of postoperative vitreous traction with subsequent cystoid macular edema or retinal detachment.

Oscillatory cutters function similarly to rotary cutters, but rather than spinning in 360° circles, they rotate 180° and then reverse direction. They can be self-sharpening. They are electrically driven. Because they do not completely spin, they cannot spool the vitreous and are, therefore, safer to use. They require periodic maintenance because they are usually reusable.

Guillotine cutters are presently the most popular form of vitrectomy handpiece. The blade moves up and down in the long axis of the aspiration tube. These blades cannot be self-sharpening because of their design. Therefore, these instruments are usually disposable rather than reusable. This feature offers the benefit of well-lubricated, sharp blades each time they are used. They are actuated by compressed air. The higher the compression the more powerful the cutting downstroke. When compressed air flow stops, a spring forces the blade to open. These cutters remove vitreous cleanly, without spooling.

There have been recent improvements in vitrectomy instrumentation. First is the high speed vitreous cutter, cutting at 400–800 cuts/min. The second is the 23ga and 25ga vitrectomy instruments. These are available presently on the B&L Millennium, and the Alcon Infinity and Acuris machines. They will be available on the AMO Signature and B&L Solaris.

Vitrectomy Technique

When vitrectomy is necessary it can be performed from the limbus or pars plana. In either case a bimanual vitrectomy technique is preferred. If present the irrigation sleeve is removed from the vitrectomy handpiece and discarded. The main incision is closed. If not self-sealing, it should be sutured. The paracentesis incision is used for infusion. A 23-gauge cannula attached to the infusion bottle is inserted through the paracentesis. The infusion bottle is lowered to an adequate height to maintain the anterior chamber without excessive outflow. A new 2mm paracentesis is created in a comfortable position. The vitrectomy handpiece, without the infusion sleeve, is placed through this incision. The machine is set to low vacuum (100–300mmHg). If a peristaltic pump is used, a flow of 20–30mL/min will provide adequate generation of vacuum without excessive turbulence. The cutting speed should be high (400–800 cuts/min) so that the aspirated vitreous is cut before the vitreous strands are allowed to place traction on the vitreous base.

The tip of the cutter is placed into the anterior vitreous, and the vitrectomy is performed until vitreous is removed to the level of the posterior capsule (Figure 7-25). In this way the vitreous is literally shelled out of the posterior segment without disturbing the vitreous base at the pars plana or the vitreous connections to the macula or optic nerve. This approach minimizes the risk of postoperative cystoid macular edema and retinal detachment.



Figure 7-25 The vitrector, with the Charles Sleeve removed is placed through a paracentesis into the vitreous. Irrigation is provided by a 23-gauge cannula placed through another paracentesis. The vitreous is drawn back into the posterior segment and removed to the level of the posterior capsule. (Courtesy Thieme Publications, New York.)

If performed from the pars plana, similar settings are used. The vitrectomy instrument is introduced through an incision created precisely 3.0–3.5mm posterior to the limbus with a microvitreoretinal (MVR) blade. Under direct visualization the vitrector is placed into the anterior vitreous with the aspiration port up, and vitrectomy is performed as noted previously (Figure 7-26).^[13]



Figure 7-26 Vitrectomy through the pars plana. After an incision is made 3.5mm posterior to the limbus with an MVR blade, the vitrectomy instrument is placed into the anterior vitreous under direct observation. (Courtesy Thieme Publications, New York.)

Alternatively, a 25-gauge, self-sealing, transconjunctival approach can be used. A trocar-cannula system is used to enter the pars plana passing directly through the conjunctiva and sclera. After removing the trocar, the entry alignment cannula remains in place. The vitrector is placed through the cannula into the vitreous and the vitrectomy is performed carefully watching the vitrector tip. When the vitrectomy is judged to be adequate, the vitrector is removed and a plug is placed in the cannula. The cannula is removed when it is evident that no further vitrectomy is assumed. No sutures are necessary.

Phaco Machine Settings

Currently, many new-generation sophisticated machines are available. Each of these controls the balance of power generation and fluidic features by different methods. In addition, surgeons now can tailor the machine parameters not only to their style of surgery, but also to each individual segment of the phaco procedure. Therefore, a listing of different settings for each procedure is beyond the scope of this chapter. However, a representative listing of different parameters for three surgeons using the same machine is illustrated in Tables 7-2–7-4. These tables show how power, flow, and vacuum vary from surgeon to surgeon and for each phase of phacoemulsification.

Table 7-3 -- Alcon Infinity

Traditional phaco settings
Cataract density	1	2	3	4
Irrigation (cm H₂O)	110	110	110	110
Aspiration rate (cc/min)	40	40	40	40
Vacuum limit (mm Hg)	400	400	400	400
Dynamic rise	Off	2	2	2
Phaco power limit	15	30	50	70
On time (ms)	30	20	20	20
0.9 mm. Kelman ABS Tapered Needle.
Cataract grading system to limit repulsive forces and energy dissipation of traditional ultrasound.
Dynamic rise increases ability to hold tissue during energy activation.

Torsional phaco settings
	Initial Chop	Fragments
Irrigation (cm H₂O)	110	110
Aspiration rate (cc/min)	40	40
Vacuum limit (mm Hg)	400	350
Dynamic rise	2	Off
Phaco power limit	Longitudinal 50 Torsional Off	Longitudinal 100	Torsional Amplitude 100
On Time (ms)	20	5	100
0.9 mm. Kelman ABS Tapered Needle.
Initial chop using OZil Handpiece with traditional longitudinal burst.
Quadrant removal for all other segments use 5 ms linear traditional and 100 ms linear torsional burst for all cataract grades.
Dynamic rise is not utilized due to deceased repulsion.

Table 7-4 -- Bimanual Alcon Infinity

Ozil	0.9 microtip½ silver/1/2prpl (dewey-or-all purple, sharp: bent, no ABS)	Bimanual	Choose Grade 2
Grade 2
CHOP – Ozil Pulse
Power			Torsional amplitude %		Irrig (bottle)
limit	% on	pps	limit	% on	142
40 (linear)	30	10	0	NA	142
vac	320 (fixed)		asp rate	30 (fixed)
Dynamic rise 1

QUAD – Ozil burst
Power		Torsional amplitude %		Irrig (bottle)
limit	% on	limit	msec on	msec off	142
0		100% (linear)	35	50	142
vac	350 (fixed)	asp rate	33 (fixed)
Dynamic rise 1

EPI – Ozil continuous
Power		Torsional amplitude %		Irrig (bottle)
limit	% on	limit	% on	142
0		25 (linear)	na	142
vac	300 (fixed)	asp rate	32 (fixed)
Dynamic rise 0

IA
Cortex				Irrig (bottle)
vac	600 (linear)	asp rate	50 (linear)	110
Viscoat removal
vac	650 (linear)	asp rate	50 (fixed)	110
Dynamic rise 0

Vit cut I–A
Cut rate	800	Vac (linear)	250	Asp	20 (linear)	Irrig (bottle)	60
Dynamic rise 0

Conclusion

It has been said that the phaco procedure is blend of technology and technique. Awareness of the principles that influence phaco machine settings is required to perform a proficient and safe operation. In addition, often during the procedure, the initial parameters must be modified. A thorough understanding of fundamental principles will enhance the surgeon's capability to respond appropriately to this requirement.

It is a fundamental principle that through relentless evaluation of the interaction of the machine and the phaco technique, the skillful surgeon will find innovative methods to enhance technique. “The road to success is always under construction.”

References

[1]. Kelman C.D.: Phaco-emulsification and aspiration. Am J Ophthalmol 1967; 64:23-35.

[2]. Kelman C.D.: History of emulsification and aspiration of senile cataracts. Trans Am Acad Ophthalmol Otolaryngol 1974; 78:35-38.

[3]. Kelman C.D.: Phacoemulsification in the anterior chamber. Ophthalmology 1979; 86:1980-1982.

[4]. Kratz R.P., Colvard D.M.: Kelman phacoemulsification in the posterior chamber. Ophthalmology 1979; 86:1983-1984.

[5]. Cimino W.W., Bond L.J.: Physics of ultrasonic surgery using tissue fragmentation. II. Ultrasound Med Biol 1996; 22:101-117.

[6]. Miyoshi T.: Ultra-high-speed images of the phaco tip under different power modes. ASCRS Film Festival Grand Prize Winner, Annual Meeting Spring, 2005.

[7]. Fishkind W.J.: Pop goes the microbubbles. Video Film Festival ASCRS 1998, Grand Prize winner ESCRS, 1998.

[8]. Schafer M.: Quantifying the impact of cavitation in phacoemulsification. Presentation ASCRS Annual Meeting, Best Paper of Session, Spring, 2006.

[9]. Zacharias J.: Jackhammer or cavitation: the final answer. ASCRS Film Festival Grand Prize Winner, ASCRS Annual Meeting. Spring, 2006.

[10]. Serafano D.: Upgrades to phaco system give surgeons more options. Ophthalmol Times 2001; 26:16-17.

[11]. Soscia W., Howard J.G., Olson R.J.: Microphacoemulsification with WhiteStar. A wound-temperature study. J Cataract Refract Surg 2002; 28:1044-1046.

[12]. Seibel B.S.: Section 1. In Phacodynamics, mastering the tools and techniques of phacoemulsification surgery, 3rd ed.. Thoroughfare, NJ, Slack Inc, 1999.

[13]. Nichamin L.D.: Prevention pearls. In: Fishkind W.J., ed. Complications in phacoemulsification, New York: Thieme; 2001:260-270.

Bibliography

Chang D.F.: Phaco chop, mastering techniques, optimizing technology and avoiding complications, New Jersey, Slack Inc, 2004.

In: Fishkind W.J., ed. Complications in phacoemulsification, avoidance, recognition and management, New York: Thieme; 2001.

Garg A., Fine I.H., Ali J.L., et al: Mastering the phacodynamics, New Delhi, India, Jaypee Publishers, 2007.

Seibel B.S.: Phacodynamics, mastering the tools and techniques of phacoemulsification surgery, 3rd ed.. Thoroughfare, NJ, Slack Inc, 2004.

Non-Longitudinal Phaco: Modification of Fluid Control by Power Modulations

Torsional Phaco (Alcon Infinity)

A new development in phaco is the harnessing of lateral or ocillatory movement of the phaco tips developed by Alcon in the Infiniti Machine. The OZiL Torsional Handpiece has both a longitudinal movement and torsional movement. The longitudinal movement, like a standard phaco needle is at 40 kHz. The torsional movement is at 32 kHz with 1 arc of motion (Figure 7-16). The torsional movement may be used alone or in combination with the longitudinal movement with many variations of timing. It requires an angled “Kelman” tip of 15° or 30° to be effective. It appears to be most efficient when using a mix of longitudinal and torsional movement. This modification, as well as needle configurations, is presently under modification. The final parameters for its use are yet to be determined. The torsional movement will emulsify with minimal chatter and improved follow-ability. However, occasionally the low power phaco will cause chunks of nucleus to occlude the phaco needle lumen. Longitudinal movement is then used to emulsify the material present in the needle bore.

Elliptical Phaco (AMO Signature)

In this system the longitudinal movement of the phaco tip at 38 kHz is combined with a transversal motion at 26 kHz. The resultant movement of the needle can be described as prolate-spheroid (shaped much like an egg cut in half). Elliptical power can be generated with any type of phaco tip.

While the longitudinal phaco cores the nuclear material, the non-longitudinal phaco shaves the nuclear material. Therefore this mode of needle movement is a noteworthy variation from other technology, since by its very movement, it generates partial occlusion phaco and therefore lessens the risk of surge.

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Contents

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Cataract Surgery, 3rd Edition

PART II – Preparation Chapter 7 – The Phaco Machine :The Physical Principles Guiding its Operation

PART II – Preparation

Chapter 7 – The Phaco Machine :The Physical Principles Guiding its Operation