the phaco machine

75

▪

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BASIC

PRINCIPLES

OFPOWER

GENERATIO

N

7Physical Principles Guiding

its OperationWilliam J. Fishkind,MD, FACS, Thomas F. Neuhann,MD,

Roger F. Steinert, MD

The Phaco Machine: The

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 oftendescribed, there is a tendency to overlook a basic aspect of thistype of surgery: the physics of closed-system surgery and how ittranslates into clinical performance.In addition, a basic knowledge of the principles of the physics

and engineering of the machines, the power generators, and flu-idics not only can assist in making a rational decision as to what

kind of equipment to use but also can promote the performanceof a surgical procedure that is more gentle and efficient, thusimproving outcomes and minimizing complications.All phaco machines consist of a computer to generate ultra-

sonic impulses and a transducer, usually piezoelectric crystals, toturn these electronic signals into mechanical energy. The energythus created is harnessed, within the eye, to overcome the inertiaof the lens and emulsify it. Once turned into emulsate, the fluidicsystems remove the emulsate and replace it with balanced saltsolution (BSS) in a closed, steady-state environment.

BASIC PRINCIPLES OF POWER
GENERATION▪The prerequisite for the removal of a cataract through a smallincision is a technique to break up the hard nucleus into emulsatefor aspiration. Inspired by the technique of dentistry to removetarter with a metal tip that oscillates longitudinally at frequenciesin the ultrasonic range, Kelman1–3 adopted this principle, com-bining the oscillating tip and the evacuation tube into a hollowneedle.4 Titanium is the material of choice for such applicationsbecause it resists the fragmentation that occurs with more brittlemetals. The mechanisms by which such an oscillating tip frag-ments the nucleus are examined in the following text.
TYPES OF TRANSDUCERS

Magnetostrictive Transducers

Magnetostrictive transducers are based on packs of ferromagneticlamellae surrounded by an electric coil. The magnetic fieldinduced by the high-frequency electric current flowing throughthe coil excites the oscillation.The advantages of magnetostrictive transducers include con-

tact-free excitation, thus avoiding deterioration at the junctionof the current and the transducer. These transducers, couplingelements, and the entire handpiece are rugged. They can with-stand mechanical injury and have a long life span. Their primarydisadvantage is a relative low grade of efficiency. Only a smallpart of the energy input is transformed into mechanical action;

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the majority becomes heat. Heating not only carries the risk oftissue burn but also makes the transducer lose efficiency withrising temperatures. Also, in the original design, the concentricaspiration 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 earthelements and engineering modifications that allow both the irri-gation and aspiration lines to be concentrically brought straightall the way through the tack to the tip. This not only avoids theclog-prone bends but also provides a double stream of constantlyflowing cooling fluid through all the elements of the vibratingsystem, thus obviating the need for a separate cooling system, aswas found to be necessary on the older handpiece.

▪
PIEZOELECTRIC TRANSDUCERS
These transducers are based on the reversal of the piezoelectricphenomenon. Certain crystals, on compression, produce electriccurrent. In reverse, electric current causes the crystal to contract.Applying current to a crystal at high frequency causes it tooscillate at that frequency.The crystal is mounted on the “horn.” This is a piece of tubing

of narrowing diameter eventually ending with the attachment ofthe phaco needle. The decreasing diameter tube acts as an ampli-fier to generate adequate power for emulsification.The advantages of piezoelectric crystals include a high grade of

efficiency and, therefore, little inherent heat generation, with noneed for extra cooling. Their low mass allows rapid movementand precise control. Newer machines use digital inputs to gener-ate power. Digital control is more precise and instantaneous.Many new handpieces use multiple crystals (usually two to foursets) to maximize responsiveness and provide adequate power toemulsify the mature hard nucleus. Disadvantages include the con-nection points between crystal and electric current, the connec-tions among the multiple layers of crystals that are necessary toprovide adequate stroke amplitudes, and the structural brittlenessof the crystal itself. These properties limit the longevity of suchtransducers. They are delicate and deteriorate both by accidentalmechanical injury and by the oscillation they produce.

TUNING▪Every material has an inherent frequency at which it vibrates nat-urally. This is called its resonant frequency. If excited to vibrate atthis frequency, the transformation into mechanical amplitude willbe optimal, and the creation of other forms of energy, principallyheat, will be minimized. The creation of balanced crystals, theirattachment to the horn, and the weight of the titanium phaconeedle are, therefore, carefully controlled during manufacturing.The phaco procedure itself is performed in a less rigidly con-

trolled environment. In the course of phacoemulsification, theneedle is passed through and inside material of inconsistent resis-tance. The aqueous humor is less resistant than a soft nucleus,and a soft nucleus less resistant than a mature one. Thus, forexample, as the phaco needle travels through BSS into a hardnucleus, the resonant frequency must be adjusted, to prevent inef-ficient emulsification. The result of inefficient emulsification is

prolonged phaco time, higher powers, and ensuing increased heatgeneration.Therefore, all modern phaco systems now have a built-in feed-

back loop constantly adjusting, or tuning, the oscillatingfrequency to an optimal resonance. This is a function of thecentral processing unit of the machine. It reads the change inresistance of the phaco needle and makes minute adjustments inthe stroke length or frequency, dependent on which phacomachine is utilized, thus maximizing effectiveness. The rate ofrepetition with which the machine makes these adjustments ismachine dependent. In the AMO Sovereign system, the tuningrate is 20 ms, in the Alcon Infiniti it is 100 times/s. It is intuitive,however, that the greater the frequency of these corrections, themore effective the emulsification.

POWER GENERATION▪Power is created by the interaction of frequency and strokelength. Frequency is defined as the speed of the needle move-ment. It is determined by the manufacturer of the machine. Pres-ently, most machines operate at a frequency of between 28,700cycles per second (c/s; or hertz [Hz]) to 45,000 c/s (Table 7-1).This frequency range is the most efficient for nuclear emulsifica-tion. Lower frequencies appear to be less efficient, and higherfrequencies create excess heat.5

Frequency is maintained constant by tuning circuitry designedinto the machine computer. As noted earlier, tuning is vitalbecause the phaco tip is required to operate in varied media.The computer recognizes the change in resistance by sensing achange in load. The appropriate response is then delivered tothe phaco tip by a minute change of frequency or stroke lengthdepending on the machine algorithm. The surgeon will subjec-tively appreciate good tuning circuitry by a sense of smoothnessand power.An innovative use of tuning circuitry software is found on the

Alcon Infinit Machine. This modification is called “SmartPulse” (Figure 7-1). When this proprietary programming isengaged, if the duration of the power stroke is less than 20 ms,a low power pulse, 1/2 of the programmed power (with a maxi-mum of power of 10%) is generated prior to the application ofthe commanded power stroke. The low power pulse is used tosense the resistance of the nuclear fragment (load) and adjustthe stroke length to provide the commanded power. This isimportant to allow maximum efficiency when ultrashort pulsesof 5 ms are utilized. Without this modification, by the time themachine tuned the pulse would be over!Stroke length is defined as the length of the needle movement

(Figure 7-2). This length is generally 2–6 mil (thousandths of aninch). Most machines operate in the 2–4-mil range. Longerstroke lengths are prone to generate excess heat. Much like ahammer striking a nail through a greater distance, the longerthe stroke length, the greater the physical impact on the nucleusand, in addition, the greater the generation of cavitational forces(Figure 7-3).Stroke length is determined by foot pedal excursion in position

three during linear control of phaco power. Although the frequencyis unchanged, the amplitude of the sine wave is increased in directproportion to the depression of the foot pedal (Figure 7-4).

▪

Conventional pulse

15 ms

5 ms 15 ms

60%

60%

10%

Smart pulse

Figure 7-1 Smart pulse diagram.

Figure 7-2 Stroke length.

Figure 7-3 According to the formula F ¼ MA (Force ¼ Mass � Acceleration),

as distance to the point of impact is increased, acceleration is increased,

resulting in increased force.

Amplitude 100%

Frequency (frequency = 47,000 times a secondthe needle moves back and forth)

Note: frequency does not change as amplitude is increased or decreased, continues at 47,000 Hz per second

Amplitude 10%

Figure 7-4 Frequency remains constant. The amplitude of the sine wave

increases. This increases stroke length and resultant jackhammer and

cavitational forces.

Table 7-1 AMO sovereign settings for phaco chop*

Phaco 1Hard chop

Phaco 2Mod. chop

Phaco 3Epinucleusunoccluded

Phaco 3Epinucleus occluded

Phaco 4Pre-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 (150 ms)

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 6/8¼14 BL 4/24¼28 BL 4/24¼28 BD 4/8¼12 CN 6/28¼34

CB 6/4¼10 CL 6/24¼30 CL 6/24¼30

DB 8/4¼12 BD 4/8¼12 BD 4/8¼12

CD 6/8¼14 CD 6/8¼14

*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.

7The Phaco Machine: The Physical Principles Guiding its Operation

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ENERGYATTHEPHACO

TIP

ENERGY AT THE PHACO TIP▪The actual tangible forces, which emulsify the nucleus, are ablend of the “jackhammer” energy and cavitation energy.1

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

1. Rapid forward acceleration of the phaco tip. This overcomesthe inertia of the nucleus penetrating it rather than driving itaway.

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Figure 7-6 A 30� tip. Enhanced cavitation shows ultrasonic wave focused

1 mm from the tip, spreading at an angle of 30�.

Figure 7-7 A 0� tip. Enhanced cavitation shows ultrasonic wave focused

0.5 mm in front of the tip, spreading directly in front of it.

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2. Close mechanical contact between the tip and the nucleus.Engineers call this force coupling. It is accomplished by pressingthe tip against the nucleus or by pressing the nucleus to the tip.

The jackhammer energy can bemaximized orminimized depend-ing 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 atultrasonic 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 tomicrobubbles (25.4�5 mm) in size. Forward tip movement createsan equally intense zone of high pressure. This produces compres-sion of the microbubbles until they implode. At the moment ofimplosion, the bubbles create a temperature of 7204�C and ashock wave of 75,000 PSI. Of the microbubbles created, 75%implode, amassing to create a powerful shock wave radiating fromthe phaco tip in the direction of the bevel with annular spread.However, 25% of the bubbles are too large to implode. Thesemicrobubbles are swept up in the shock wave and radiate with it.Utilizing high speed photography Dr. Teruki Miyoshi demon-

stated the development of cavitational energy in a video presentedat ASCRS in 2005 (Figure 7-5).1

The cavitation energy thus created can be directed in anydesired direction as the angle of the bevel of the phaco needlegoverns the direction of the generation of the shock wave andmicrobubbles.An artificial but educational method of visualizing these forces,

called enhanced cavitation, has been developed. Using this pro-cess, with a 45� tip, the cavitation wave is generated at 45� fromthe tip and comes to a focus 1 mm from it. Similarly a 30� tipgenerates cavitation at a 30� angle from the bevel, and a 15�

tip, 15� from the bevel (Figure 7-6). A 0� tip creates the cavita-tion wave directly in front of the tip, and the focal point is0.5 mm from the tip (Figure 7-7). The Kelman tip has a broadband of powerful cavitation, which radiates from the area of theangle in the shaft. A weak area of cavitation is developed fromthe bevel but is inconsequential (Figure 7-8).8,9

There is debate over the magnitude of the role of jackhammerand cavitation energy. Various investigators have found contrast-ing results on the subject of the power of cavitational energy.2

Analysis of their data indicates that Jackhammer energy is the more

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

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.

▪

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.


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potent force in emulsification. Cavitation augments theemulsification 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 boththe jackhammer energy and cavitation energy are integrated. Toaccomplish this, utilize a 0� tip. When using an angled tip, thebevel of the needle should be turned toward the nucleus, ornuclear fragment. This simple maneuver causes the broad bevelof the needle to strike the nucleus. This enhances the physical forceof the needle striking the nucleus. In addition, the cavitationalforce is concentrated into the nucleus rather than away from it(Figure 7-9). This causes the energy to emulsify the nucleus andbe absorbed by it. When the bevel is turned away from the nucleus,the cavitational energy is directed up and away from the nucleustoward the iris and endothelium (Figure 7-10). Finally, in thisconfiguration, the vacuum force (discussed later in this chapter)can be maximally exploited as occlusion is encouraged.

MODIFICATION OF PHACO POWER▪Modification of phaco power must be accomplished to harnessthese 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. Unneces-sary power intensity is a source of heat with subsequent wounddamage. Moreover, excessive cavitational energy is a cause ofendothelial cell damage and iris damage with resultant alterationof the blood–aqueous barrier. Phaco power intensity can be mod-ified 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, there-fore, foot-pedal adjustment. When it is set for linear phaco, thedepression of the foot pedal increases stroke length and, conse-quently, 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 powerapplication. The Bausch & Lomb (B&L) Millennium, andAMO Signature offer a dual linear foot pedal which permitsthe separation of the fluidic aspects of the foot pedal from thepower elements, by adding a yaw movement to the foot pedal.

ALTERATION OF PHACO POWERDURATION-BURST, PULSE, MICRO-PULSE

The duration of application of phaco power has a dramatic effecton overall power delivered to the anterior segment. This is the useof power modulations. Power modulations include the use ofburst, multiburst, and pulsed phaco. For example, if continuouspower is employed for 1 min, the effective phaco time is 1 min.If the power is pulsed at 10 pulses per second, the effective phacotime is 30 seconds. The effective power delivered to the anteriorsegment is half of the continuous amount.There are three different types of noncontinuous power modu-

lations: 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 progres-sively 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 thereis continuous power.Hyperpulse phaco has extremely short periods of power on and

power off. Where a standard short pulse might be 50 ms a micro-pulse might by 5 ms.Burst mode in the Allergan Sovereign (parameter is machine

dependent) is characterized by 80 or 120 ms periods of powercombined with variable short periods of aspiration only. Pulsemode uses fixed pulses of power of 50 or 150 ms with variableshort periods of aspiration only. Phaco techniques such as phacochop use minimal periods of power in pulse mode to reducepower delivery to the anterior chamber. In addition, the use ofpulse mode, or hyperpulse mode, to remove the epinucleus pro-vides an added margin of safety. When the epinucleus is emulsi-fied, the posterior capsule is exposed to the phaco tip and maymove forward toward it because of surge. Activation of pulse

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Conventional

Fixed duty cycle

Advanced power modulation with CCS

Variable duty cycle (10–100%)

– To prevent continuous phaco energy even w/maximum pedal depression

Fixed rise time Variable rise time (waveform pulse)

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phaco mode creates a deeper anterior chamber to work within.This occurs because each period of phaco energy is followed byan interval of no phaco energy. During the interval of absenceof energy the epinucleus is drawn toward the phaco tip, produc-ing occlusion, interrupting outflow. This allows inflow to deepenthe anterior chamber immediately before onset of another pulseof phaco energy. The surgeon will recognize the outcome asoperating in a deeper, more stable anterior chamber.Recent innovations by Alcon, AMO, B&L, and Staar have

resulted in new forms of power modulation.

Unique to millennium technology

– less energy during nuclear removal– less heat build-up; less total energy

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

waveform.

CAVITATIONAL MODIFICATIONS OF SOFTWARE

Abbott Medical Optics (AMO) introduced the WhiteStar Sys-tem of hyperpulse phaco. In this modification, extremely shortbursts of power are interspersed with similar, extremely shortperiods of aspiration. The relationship of these on/off periodsare called a “duty cycle” (see Figure 7-13).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 4 mson/8 ms off or 6 ms on/12 ms off. In the first example the pulseduration is 12 ms and in the second 18 ms. It can be seen withsimilar duty cycles the time of power on or off may be vastlydifferent.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 to100 pps with programmable duty cycle between 5 and 95%.The B&L Millennium can generate up to 120 pps with dutycycles between 10 and 90%.

PULSE CONTOURING

The newest variation of phaco energy is the modification of thecontour of the ultrasonic waveform. This is helpful in emulsifica-tion of cataract fragments. The traditional ultrasonic waveform issquare (Figure 7-11). The B&L Millennium employs “roundedwaveform” (Figure 7-11). This modulation changes the contourof the ultrasonic pulse so that within the duty cycle the pulse

Table 7-2 Alcon Infinity: torsional phaco*

Sculpting Quadrantremoval

Epinucleus/cortexremoval

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.

begins at low power and intensifies rapidly to the maximumpreset power. The low power enhances the movement of thefragment toward the phaco tip enhancing occlusion. The higherpower provides for the emulsification of the fragment.The AMO Sovereign and Signature approach the problem of

improved followability from a different perspective. They haveengineered a pulse of ultrasonic power with a short burst ofincreased energy at the beginning of each ultrasonic waveform(Figure 7-12); this is named ICE (increased control and effi-ciency). The amplitude of this “kicker” can be programed up to12% of the total power of the pulse. It can increase, decrease,or remain the same as the phaco power is increased. The conceptis to drive the fragment a microscopic distance from the phaco tipas the tip is energized. The fragment is then available for emulsi-fication without occlusion.The change in phaco duty cycles leads to enhanced followabil-

ity by altering the tendency for phaco power to repel cataractousmaterial and modifying the fluidic characteristics of the pre-occlusion/post-occlusion cycle (discussed below). The end resultis shorter phaco power on times, less delivery of total phacoenergy to the anterior segment, and increased anterior chamberstability resulting is decreased incidence of ruptured posterior

Pow

er p

erce

ntag

e

5

10

15

20

25

30

35

40

45

Time

Constant amplitude

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

scale).

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

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.)


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capsules and vitrectomy. In addition, the off time allows effectivecooling of the phaco tip, minimizing the likelihood of woundburn, even during emulsification of a hard nucleus.

Wound Burn

The prevention of wound burn is an important feature of thissoftware modification. Studies have shown that the wound willshow the first signs of a wound burn at 45�C and frank signsof burn at 50�C. With WhiteStar, the maximal wound tempera-ture at 100% power was measured at 28�C.11 Therefore, thephaco tip can be placed though the wound without the coolingsleeve. Whenever there is decreased outflow through a phacotip, especially when the wound is tight surrounding the tip com-pressing the sleeve or tip shaft, wound burn is possible. Thegreater the energy setting the greater the risk of wound burn.The surgeon must be vigilant to monitor bubbles around the tipwound interface or striae in the clear cornea over the phaco tip.Any suggestion of these phenomena mandates immediatecessation of phaco energy.

BIMANUAL MICROINCISIONAL PHACO

Micropulse phaco allows for the performance of a bimanual,microincisional, phacoemulsification procedure. The irrigation isprovided by a 20-gauge irrigating chopping instrument througha 1.4 mm clear cornea incision. The 20-guage, 15� or 30� phacotip without the irrigation sleeve is inserted through a 20-gauge clearcornea incision 90–100� away (21-gauge instrumentation with1.1 mm incisions can also be utilized). The nucleus is emulsifiedby either a vertical or horizontal chopping procedure. The woundremains cool and the efficiency of the procedure is enhanced as theseparate irrigation tends to wash fragments into the phaco tip.Coaxial Microincisional PhacoMicropulse phaco also allows for

another variation of microincisional phaco. This is coaxial phacoutilizing micro phaco tip of 20 gauge (Alcon Infiniti) and athin-walled rigid infusion sleeve through a 2.4 mm. Torsionalphaco (discussed below) is another excellent modality for coaxialmicroincisional phaco.Employing similar modification to tip and sleeve the B&L

Stellaris is capable of passing through a 1.8 mm incision forcoaxial 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 inthe direction of the bevel. The 0� tip focuses both jackhammerand 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 powerfulcavitation directed away from the angle in the shaft (see Figure7-8). 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 occlusioncaused 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. Thewide opening of the tip makes it easier to minipulate the fragment.The narrow “neck” of the tip functions as a flow restrictor byincreasing the resistance to flow and reducing the tendency tocreate surge (Figure 7-14). Designer tips such as the “flathead”designed by Barry Seibel and power wedges designed by DouglasMastel offer the ability to fine tune the focus of phaco energy aswell as modify the aspiration flow dependent upon the configura-tion and diameter of the phaco tip. The rounded tip designed bySteven Dewey is interesting as it will maximize cavitational energybut is “capsular friendly.” Thus, if the capsule should be aspiratedby the phaco tip while energized, tearing the capsule is less likely.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 emulsifiedinto 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 modifi-cation of power intensity, and the ABS is a flow modification. Inthe ABS system a 0.175 mm hole in the needle shaft permitsa variable flow of fluid into the needle, even during occlusion(Figure 7-15). The amount of flow through the shaft hole is var-iable and depends on the vacuum level. The higher the vacuumlevel, the greater the flow. This flow adjustment serves to reducepostocclusion surge (discussed below).

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▪Figure 7-15 A 0.175 mm 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.

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ALTERATION OF PHACO POWER, DURATION ANDCONFIGURATION – please see Pg 92 for an updateto this section

Torsional Phaco

A new development in phaco is the harnessing of lateral or ocilla-tory movement of the phaco tips developed by Alcon in the InfinitiMachine. The OZiL torsional handpiece has both a longitudinalmovement and torsional movement. The longitudinal movement,like a standard phaco needle is at 40 kHz. The torsional movementis at 32 kHz with 1� arc of motion (Figure 7-16). The torsionalmovement may be used alone or in combination with the longitu-dinal movement with many variations of timing. It requires anangled “kelman” tip of 15� or 30� to be effective. It appears tobe most efficient when using a mix of longitudinal and torsional

Oscillation at incision

Action at the tip end – 90 microns

Figure 7-16 Torsional needle.

movement. This modification, as well as needle configurations, ispresently under modification. The final parameters for its use areyet to be determined. The torsional movement will emulsify withminimal chatter and improved followability. However, occasionallythe low power phaco will cause chunks of nucleus to occlude thephaco needle lumen. Longitudinal movement is then used toemulsify the material present in the needle bore.Torsional phaco is noteworthy for its efficient removal of

nuclear material due to the propensity of torsional movement tofavor 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 andwith adequate space to isolate its actions from delicate intraocularstructures. This portion of the action of the machine is dependenton its fluidics.

FLUIDICS▪The fluidics aspect of all machines is fundamentally a balance offluid inflow and fluid outflow. The resultant balance of these twoinfluences will be the maintenance of a constant intraocularvolume and, therefore, a stable and deep anterior chamber. Inaddition, the intraocular pressure must be maintained withinphysiologically compatible limits.

INFUSION

Inflow (infusion) is the pressure gradient, which drives the infu-sion flow. In a gravity feed system, the bottle height above theeye of the patient creates an infusion pressure. When infusionpumps are employed, the amount of infusion pressure pro-grammed into the pump will be responsible for the generationof infusion pressure. With temporal surgical approaches, theeye 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, increasedfluid evacuation from the anterior chamber requires increasedinflow to maintain the steady-state system. Therefore, whenthe machine flow rate is increased, the bottle height should alsobe increased. A shallow, unstable anterior chamber resultsotherwise.Infusion tubing diameter and elasticity do not play a significant

role in infusion volume control because high pressures and rapidpressure fluxes rarely occur on the irrigation bottle side of the system.

OUTFLOW

Control of outflow is notably more complex because many factorsinfluence both volume and speed of fluid outflow during thephaco procedure. Among these variables are incision size, phacotip diameter and sleeve diameter, pump type and settings, andtubing diameter and compliance. In addition, computer softwaredesign plays a significant role in regulating both outflow volumeand speed.

Incision

The incision size is an important variable in the determination offluid outflow. This is actually a controlled leak determined by the

▪


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VACUUM

SOURCES

sleeve–incision relationship. The incision length selected shouldcreate a snug fit with the phaco tip and sleeve selected. Thisresults in minimal controlled wound fluid outflow with resultantincreased anterior chamber stability.If the incision is too large for the selected phaco tip and sleeve

combination, the excessive fluid outflow will necessitate increasedfluid inflow to maintain a deep anterior chamber. The increasedinfusion volume not only is deleterious to the health of the endo-thelium but usually cannot sustain the sudden changes in volumethat occur during the procedure. This leads to considerable cham-ber 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 mayproduce wound burns.

Aspiration Settings

Aspiration rate, or flow, is defined as the flow of fluid, in cubiccentimeters per minute (cc/min), through the aspiration tubing.With a peristaltic pump this rate is determined by the speed ofthe pump. Flow is the fluidic force that determines how well par-ticulate material is attracted to the phaco tip. Flow adjustmentsact to speed up or slow down events in the anterior chamber.Therefore, if events appear to be occurring too rapidly, the flowrate is slowed. Alternatively, if events are occurring too slowly,the flow rate is increased.Aspiration level, or vacuum, is a level and measured in milli-

meters of mercury (mm Hg). It is defined as the magnitude ofnegative pressure created within the tubing. Vacuum is the fluidicforce 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 determineshow well material is held against the tip once occlusion occurs.

Aspiratio

Vacuum Limit Chamber

Atmospheric Pressure

Figure 7-17 Peristaltic pump uses a rotating wheel with ro

moving separate columns of fluid through the tubing at a cont

separately and independently, limiting the maximal vacuum th

aspiration line. The collection chamber, located after the vacu

atmosphere.

VACUUM SOURCES▪The origin for the development of vacuum is the vacuum pump.The three categories of vacuum sources or pumps are: (1) flowpumps, (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 rotatingrollers that successively compress the aspiration tubing, movingfluid within the tubing and creating vacuum. The speed of rota-tion of the pump head governs the flow rate. One importantadvantage of this class of pumps is the ability to allow indepen-dent control of both aspiration rate and aspiration level.The primary example of the vacuum pump is the Venturi pump

(Figure 7-18). In the Venturi pump, compressed gas is passedthrough a Venturi, which creates a vacuum. The Venturi isattached to a rigid reservoir that is attached to the aspirationtubing. The velocity of the compressed gas passage through theVenturi creates greater or lesser vacuum that is then transferredthrough the reservoir to the aspiration line. This results in varyingamounts of vacuum.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 noindependent setting of aspiration flow.Modern modifications of the basic pump types have prompted

the creation of a new pump category, the hybrid pump. Thesepumps are interesting in that they can act like either a vacuumor flow pump, independent of their original design, dependingon their programming. They are the most recent supplement topump types. They are universally controlled by digital inputs,producing extraordinary flexibility and responsiveness.The primary example of the hybrid pump is the Allergan Sov-

ereign peristaltic pump (Figure 7-19) or the B&L Concentrixpump (Figure 7-20).12

Pump

n (mL/min)

Open Collection Container

llers to pinch off segments of the aspiration tubing, thereby

rolled rate of aspiration or flow. The vacuum limit is set

at is tolerated in the condition of complete occlusion of the

um limit chamber and the aspiration pump, is open to

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83

▪

Atmospheric Pressure

Vacuum Limit Chamber

Vacuum

Venturi Chamber

Valve Aspiration RateAdjustment (mL/min)

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.

Figure 7-19 AMO Sovereign hybrid peristaltic pump.

ii Preparation

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SURGE

84

Recognizing that surgeon preference over pump types may playa role in surgeon machine purchase, some new machines offerboth types of pumps. The AMO Signature with Fusion Technol-ogy and the B&L Stellaris offer this option. The challenge to thesurgeon is to balance the effect of phaco power intensity, whichtends to push nuclear fragments away from the phaco tip, withthe effect of flow, which attracts fragments toward the phacotip, and vacuum, which holds the fragments on the phaco tip.Generally, low flow slows down intraocular events, and high flowor vacuum speeds them up. Low or zero vacuum is helpful duringsculpting of a hard or a large nucleus. In this circumstance, thelarge, hard endonucleus may cause the surgeon to phacoemulsifynear or under the iris, or anterior capsule, with a high-powerintensity. With normal aspiration the phaco tip may aspirate

the iris. The high power will cause immediate, severe damageto the iris. Therefore, zero (or very low) vacuum will preventinadvertent aspiration of the iris or capsule, preventing significantmorbidity.

SURGE▪A principal limiting factor in the selection of high levels of vac-uum or flow is the development of surge. When the phaco tipis occluded, flow is instantly interrupted, and vacuum rapidlybuilds to its preset maximum level (Figure 7-21). Emulsificationof the occluding fragment then clears the occlusion. Flow instan-taneously begins at the preset level in the presence of the highvacuum level. In addition, if the aspiration line tubing is not rein-forced to prevent collapse (tubing compliance), the tubing willhave constricted during the occlusion. It then expands on occlu-sion break. The expansion is an additional source of brisk vacuumproduction. These factors cause a rush of fluid from the anteriorsegment into the phaco tip (Figure 7-22). The fluid in the ante-rior chamber may not be replaced by infusion rapidly enough toprevent its shallowing. Therefore, subsequent, rapid anteriormovement of the posterior capsule occurs. Often the cornea col-lapses. The violent snapping of the posterior capsule, or abruptforceful stretching of the bag around nuclear fragments, may bea cause of capsular tears (Figure 7-23). In addition, the posteriorcapsule can be literally sucked into the phaco tip, tearing it. Themagnitude of the surge is contingent on the presurge settings offlow and vacuum.The phaco machine manufacturers help to decrease surge by

providing noncompliant aspiration tubing. This does not con-strict in the presence of high levels of vacuum.Most manufacturers have created algorithms in their software

that emulate the anterior chamber, moment to moment, duringthe phaco procedure. These algorithms can anticipate changes

▪

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 7-20 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.

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.)

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.)


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SURGEMODIFICATIO

N

per microsecond in the real anterior chamber and make appropri-ate pump adjustments to minimize surge.

SURGE MODIFICATION▪Surge is undoubtedly an unwanted event. The trampolining ofthe posterior capsule caused by surge has the effect of creatingdismay 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 endo-thelium unnecessary trauma, the astute surgeon will considerwhat changes in fluidics are necessary to prevent surge.

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ii Preparation

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VENTING

86

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

Preocclusion

Historically, the only way to modify surge was to select lowerlevels of flow and vacuum. This category would be a modificationin preocclusion (Figure 7-24). At present, many other methodsexist to decrease surge. Another approach to surge management,in all phases of occlusion, is the use of an anterior chamber main-tainer. The constant flow of this device acts to deepen the cham-ber in all phases of phacoemulsification. Constant infusion,when available, is another preocclusion modification, althoughits benefits are not significant.The most powerful modification of fluidics to allow emulsifica-

tion in the pre-occlusion phase is not a fluidic modification but apower modification. The development of micro pulse phaco (dis-cussed earlier), a patented development of AMO, found origi-nally in the Sovereign with Whitestar, and now available in allmachines by all manufacturers, is an evolutionary change in creat-ing a more stable anterior chamber during emulsification. Theextremely short bursts of energy followed by a variable period ofno energy and aspiration only, serves to hold a nuclear fragmentvery near, but not occluded on, the phaco tip. Therefore, the frag-ment is emulsified with a combination of jackhammer and cavita-tion energy without ever totally occluding the tip. If there isno occlusion, there cannot be surge. Therefore, the phaco isperformed 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, discussedearlier, has a 0.175 mm hole drilled in the shaft of the phaconeedle (see Figure 7-15). When occlusion occurs at the tip, fluidflows into this hole. The amount of flow depends on the vacuumand flow settings. For example, the flow through this hole is4 cc/min at a vacuum of 50 mm Hg and 11 cc/min at a vacuumof 400 mm Hg. Because some flow always exists, in reality thereis never complete occlusion. This prevents the rise of highvacuum levels and thus diminishes postocclusion surge. This modi-fication must be used with the high vacuum tubing or it does notfunction properly.The second, as employed by AMO Sovereign/Signature, B&L

Mellennium/Stellaris with the peristaltic pump (AdvancedFluidics System), and the Infinit (ALCON) with the dynamicrise time option, is a variable rise time. By slowing the pumpspeed during occlusion, the generation of high vacuum levels isdecelerated, 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 onlycan be selected. Utilizing linear vacuum the vacuum level can beincreased to the exact amount to cause occlusion, but not higher,minimizing the post occlusion surge when phaco power isapplied. This method of vacuum control changes both the occlu-sion and post occlusion function.

Postocclusion

Once occlusion has occurred, decreasing the vacuum or flowinstantaneously to dramatically decrease flow into the phaco tipis 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 samplevacuum and flow parameters 50 times a second, creating a“virtual” anterior chamber model. At the moment of surge, themachine computer senses the increase in flow and instantaneouslyslows or reverses the pump to stop surge production. Pump man-agement, rather than venting, is the mechanism to control surge.In addition, this device has a programmable occlusion thresh-

old setting. When the vacuum reaches this threshold, a new flow,as well as a new power modulation, can be programmed. There-fore, if a hard nucleus is being emulsified, when the vacuumreaches 80 mm Hg, for example, the flow, which might havebeen set at 350 mL/min, can now be automatically decreased to100 mL/min. The result will be a noteworthy decrease in surge.Moreover, the pulse rate can be simultaneously slowed to furtherstabilize the anterior chamber.Ever improving digital control is demonstrated in the Sover-

eign/Signature (AMO) with a fluidic modification they havenamed CASE (Chamber Stabilization Environment) technology.With this software the surgeon sets a vacuum threshold and timefor an extremely fast, 26 ms, drop in vacuum to a pre-set new,lower vacuum. This drop occurs so fast that there is not enoughtime for vacuum to build and thus prevents the surge fromoccurring.Another solution to this problem is demonstrated in the B&L

Millennium/Stelaris machine. The dual linear foot pedal can beprogrammed to separate both the flow and vacuum from power.In this way, flow or vacuum can be lowered before beginningthe emulsification of an occluding fragment. The emulsification,therefore, occurs in the presence of a lower vacuum or flow sothat surge is minimized.Finally, the Starr Wave machine solves this problem in another

manner. The patented coiled aspiration tubing acts as a flowresistor. At low flow settings, up to 50 mL/min, the tubing actslike normal tubing. When flow exceeds this level, turbulence inthe tubing inhibits further increases in flow. This dampens thefluid outflow, and subsequent vacuum rise. The result isdecreased surge.An add-on tubing restrictor, also manufactured by Starr, is

called “cruise control.” It is a dual sleeved tubing. The outer tub-ing creates the cartridge shell, and the inner tubing is fenestratedand is a filter (Figure 7-24A). The cartridge is inserted into theaspiration orifice of the handpiece and then connects to the aspi-ration tubing. Where it connects the cartridge narrows to 1 mmdiameter. The inner cartridge filters emulsate particulates to pre-vent clogging at the flow restrictor, the 1 mm narrowing of thetubing. Thus a powerful flow restrictor decreases surge andstabilizes the anterior chamber insulating against fluid fluxes.

VENTING▪Often during the performance of phacoemulsification, or irriga-tion and aspiration (I&A), undesirable material is aspirated onthe phaco tip. This could be posterior capsule or a piece of

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.

(Continued)


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VENTING

87

Figure 7-24, cont’d 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 500 mm Hg

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.

ii Preparation

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VENTING

88

nucleus that is too large for efficient emulsification. Often theaspiration of these structures requires hasty release. Venting isthe mechanism for this release by neutralizing vacuum in theaspiration 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 aban-doned by most manufacturers. When the aspiration line is ventedto air, bubbles form in the aspiration tubing. When the foot pedalis again depressed, the development of vacuum is slowed becausethe air in the line must first be aspirated before vacuum can oncemore rise.

▪

▪

▪

▪


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VITRECTOMY

The preferred venting material is, therefore, fluid. Mostmachines use fluid from the infusion bottle for this purpose.The fluid flows into the aspiration tubing, neutralizing vacuumand permitting the release of unwanted material. Because no airhas been introduced into the system, when the foot pedal is againengaged, there is brisk redevelopment of flow and vacuum. Thistechnique produces a more responsive system.In some machines, venting also occurs when the selected vac-

uum level is attained. Controlled venting stops further generationof vacuum and maintains the commanded vacuum level.

TUBING COMPLIANCE▪The thickness and rigidity of the tubing, as well as the innerlumen diameter, contribute to the ability of the tubing to collapseand expand during the fluid fluxes which accompany phaco-emulsification. The greater the tubing compliance, the less of atendency it has to collapse when the phaco tip is occluded andvacuum rises. Generally, if the tubing collapses at high vacuum,it will expand when emulsification occurs, and vacuum suddenlydrops to zero. This sudden expansion of the tubing is an addi-tional factor in post-occlusion surge.

IRRIGATION AND ASPIRATION▪Fluidic management techniques used in the phaco mode are nowapplied to the I&A segment. Therefore, surge managementsystems function to prevent surge when a large or “sticky” pieceof cortex is aspirated.Most I&A tips use a 0.3 mm orifice. They are now available in

straight and angled configurations. Soft or hard metal sleeves arealso offered to provide coaxial fluid inflow. Soft sleeves are nowpreferred to provide a tighter uniform seal within the surgicalwound. This lessens superfluous outflow and leads to a morestable anterior chamber. Silicone I&A tips are also available andare, reportedly, less likely to tear the capsular bag.

BIMANUAL IRRIGATION AND

-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
ASPIRATION▪
Introduced in Europe by Dr. Peter Brauweiler, the use of separatecannulas for I&A has been widely accepted. In this technique, smallparacentesis-like incisions are made for placement of the cannulas.The small incisions and smaller cannulas offer controlled inflowand outflow, which promotes anterior chamber stability. The abilityto more easily reach recalcitrant cortex provides surgeons with atechnique that simplifies I&A. The relative positions of the cannu-las 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, theadditional control of aspiration cannula placement, as well asthe decreased anterior chamber fluid fluctuations, minimizes therisk of rupturing the vitreous face with subsequent necessity forvitrectomy. In addition, in cases of zonular dehiscence, the addedflexible placement and maneuverability of the aspiration cannulaprovide a margin of safety removing cortex without further dis-ruption of zonules.

VITRECTOMY▪All current machines have vitrectomy capability. Generally thesame I&A tubing is used. They are attached to the vitrectomyhandpiece. In the vitrectomy mode the foot pedal controls irriga-tion and aspiration and activates the vitrectomy handpiece cutter.If the cutter is actuated by compressed air, it must be connectedwith the dedicated compressed air tubing to the machine attach-ment 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 per-

pendicular to the long axis of the aspiration tube. They have theadvantage of being self-sharpening and, therefore, perform excel-lent cutting when in proper working order. They are often actu-ated electrically. The potential problem with these cutters occurswhen the blades are dull from extensive usage or are out of align-ment. The rotatory movement of the blades then has the capabil-ity of pulling the vitreous into the instrument without cutting it.The result is “spooling” of the vitreous, which is often the causeof postoperative vitreous traction with subsequent cystoid macularedema or retinal detachment.Oscillatory cutters function similarly to rotary cutters, but

rather than spinning in 360� circles, they rotate 180� and thenreverse direction. They can be self-sharpening. They are electri-cally driven. Because they do not completely spin, they cannotspool the vitreous and are, therefore, safer to use. They requireperiodic 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 longaxis of the aspiration tube. These blades cannot be self-sharpen-ing because of their design. Therefore, these instruments are usu-ally disposable rather than reusable. This feature offers the benefitof well-lubricated, sharp blades each time they are used. They areactuated by compressed air. The higher the compression the morepowerful the cutting downstroke. When compressed air flowstops, a spring forces the blade to open. These cutters removevitreous cleanly, without spooling.There have been recent improvements in vitrectomy instrumen-

tation. First is the high speed vitreous cutter, cutting at 400–800cuts/min. The second is the 23 ga and 25 ga vitrectomy instru-ments. These are available presently on the B&L Millennium,and the Alcon Infinity and Acuris machines. They will be availableon the AMO Signature and B&L Solaris.

VITRECTOMY TECHNIQUE

When vitrectomy is necessary it can be performed from the lim-bus or pars plana. In either case a bimanual vitrectomy techniqueis preferred. If present the irrigation sleeve is removed from thevitrectomy handpiece and discarded. The main incision is closed.If not self-sealing, it should be sutured. The paracentesis incisionis used for infusion. A 23-gauge cannula attached to the infusionbottle is inserted through the paracentesis. The infusion bottle islowered to an adequate height to maintain the anterior chamberwithout excessive outflow. A new 2 mm paracentesis is created

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▪

Figure 7-26 Vitrectomy through the pars plana. After an incision is made

3.5 mm 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.)

ii Preparation

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CONCLUSIO

N

90

in a comfortable position. The vitrectomy handpiece, without theinfusion sleeve, is placed through this incision. The machine isset to low vacuum (100–300 mm Hg). If a peristaltic pump isused, a flow of 20–30 mL/min will provide adequate generationof vacuum without excessive turbulence. The cutting speedshould be high (400–800 cuts/min) so that the aspirated vitreousis cut before the vitreous strands are allowed to place traction onthe vitreous base.The tip of the cutter is placed into the anterior vitreous, and

the vitrectomy is performed until vitreous is removed to the levelof the posterior capsule (Figure 7-25). In this way the vitreous isliterally shelled out of the posterior segment without disturbingthe vitreous base at the pars plana or the vitreous connectionsto the macula or optic nerve. This approach minimizes the riskof postoperative cystoid macular edema and retinal detachment.If performed from the pars plana, similar settings are used.

The vitrectomy instrument is introduced through an incisioncreated precisely 3.0–3.5 mm posterior to the limbus with amicrovitreoretinal (MVR) blade. Under direct visualization the vit-rector is placed into the anterior vitreous with the aspiration portup, and vitrectomy is performed as noted previously (Figure 7-26).13

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

▪

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.)

PHACO MACHINE SETTINGS▪Currently, many new-generation sophisticated machines areavailable. Each of these controls the balance of power generationand fluidic features by different methods. In addition, surgeonsnow can tailor the machine parameters not only to their style ofsurgery, but also to each individual segment of the phaco proce-dure. Therefore, a listing of different settings for each procedureis beyond the scope of this chapter. However, a representativelisting of different parameters for three surgeons using the samemachine is illustrated in Tables 7-2–7-4. These tables showhow power, flow, and vacuum vary from surgeon to surgeonand for each phase of phacoemulsification.

CONCLUSION▪It has been said that the phaco procedure is blend of technologyand technique. Awareness of the principles that influence phacomachine settings is required to perform a proficient and safeoperation. In addition, often during the procedure, the initialparameters must be modified. A thorough understanding offundamental principles will enhance the surgeon's capability torespond appropriately to this requirement.It is a fundamental principle that through relentless evaluation

of the interaction of the machine and the phaco technique, theskillful surgeon will find innovative methods to enhance tech-nique. “The road to success is always under construction.”

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 ChooseGrade 2

Grade 2

CHOP – Ozil Pulse

Power Torsional amplitude % Irrig (bottle)

limit % on pps limit % on 142

40 (linear) 30 10 0 NA

vac 320 (fixed) asp rate 30 (fixed)

Dynamic rise 1

QUAD – Ozil burst


limit % on limit msec on msec off 142

0 100% (linear) 35 50


Dynamic rise 1

(Continued)


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CONCLUSIO

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91

Table 7-4 Bimanual Alcon Infinity—cont’d

EPI – Ozil continuous


limit % on limit % on 142

0 25 (linear) na


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

ii Preparation

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CONCLUSIO

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92

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1979;86:1983–1984.[5] Cimino WW, Bond LJ. Physics of ultrasonic surgery using tissue fragmentation. II. Ultrasound

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Festival Grand Prize Winner. Annual Meeting Spring; 2005.[7] Fishkind WJ. Pop goes the microbubbles. Video Film Festival ASCRS 1998, Grand Prize winner

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

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2001;26:16–17.

[11] Soscia W, Howard JG, Olson RJ. Microphacoemulsification with WhiteStar. A wound-tempera-ture study. J Cataract Refract Surg 2002;28:1044–1046.

[12] Seibel BS. Section 1. In Phacodynamics, mastering the tools and techniques of phacoemulsifica-tion surgery. 3rd ed. Thoroughfare, NJ: Slack Inc; 1999.

[13] Nichamin LD. Prevention pearls. In: Fishkind WJ, editor. Complications in phacoemulsification.New York: Thieme; 2001. p. 260–270.

Bibliography

Chang DF. Phaco chop, mastering techniques, optimizing technology and avoiding complications. NewJersey: Slack Inc; 2004.Fishkind WJ, editor. Complications in phacoemulsification, avoidance, recognition and management.New York: Thieme; 2001.Garg A, Fine IH, Ali JL, et al. Mastering the phacodynamics. New Delhi, India: Jaypee Publishers;2007.Seibel BS. Phacodynamics, mastering the tools and techniques of phacoemulsification surgery. 3rd ed.Thoroughfare, NJ: Slack Inc; 2004.

NON-LONGITUDINAL PHACO: MODIFICATION OFFLUID CONTROL BY POWER MODULATIONS

Torsional Phaco (Alcon Infinity)

A new development in phaco is the harnessing of lateral or ocil-latory movement of the phaco tips developed by Alcon in theInfiniti Machine. The OZiL Torsional Handpiece has both alongitudinal movement and torsional movement. The longitudi-nal movement, like a standard phaco needle is at 40 kHz. Thetorsional movement is at 32 kHz with 1 arc of motion (Figure7-16). The torsional movement may be used alone or in combi-nation with the longitudinal movement with many variations oftiming. It requires an angled “Kelman” tip of 15� or 30� to beeffective. It appears to be most efficient when using a mix of lon-gitudinal and torsional movement. This modification, as well asneedle configurations, is presently under modification. The finalparameters for its use are yet to be determined. The torsionalmovement will emulsify with minimal chatter and improved

follow-ability. However, occasionally the low power phaco willcause chunks of nucleus to occlude the phaco needle lumen. Lon-gitudinal movement is then used to emulsify the material presentin the needle bore.

Elliptical Phaco (AMO Signature)

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

non-longitudinal phaco shaves the nuclear material. Thereforethis mode of needle movement is a noteworthy variation fromother technology, since by its very movement, it generates partialocclusion phaco and therefore lessens the risk of surge.

the phaco machine

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