PHACODYNAMICSMade Easy

Gyanendra Lamichhane, MD

Phaco surgeon and Retina fellow

Lumbini Eye Institute

Bhairahawa,Nepal1

Definition

Study of the fundamental principles of inflow rates, outflow rates, vacuum, phaco power modulation along with microsurgical maneuvers with different types and grade of cataract.

true understanding of this will help in logical setting of the machine parameters in adaptation to different surgical techniques

Even the most modern machine will not give adequate results as compared to an older machine if the principles of phacodynamics are not well understood

KHOW THE PHACODYNAMICS …….LETS BECOME INDEPENDENT ………

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Foot pedal

Position 1----Irrigation( no aspiration ,no US)

Position 2---irrigation+aspiration( no US)

Position 3---irrigation +aspiration+ US

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Position 1

• to provide a source of fluid infusion into the eye during the surgery.

• There is no linear control of the infusion—the infusion is either turned on or turned off.

• The height of the infusion bottle determines the relative infusion pressure and flow rate during the surgery.

• To keep the eye inflated during surgery, we need to ensure that the fluid inflow rate is greater than the fluid outflow rate.

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Position 2

• There is a linear control of vacuum and flow, so that the top of foot position 2 provides less vacuum or flow than the middle or bottom range of the same foot position 2.

• To create the vacuum and the aspiration flow of fluid, the phaco machine must have a fluid pump. The most common types of fluid pumps are peristaltic and venturi,

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There are two primary sources of fluid outflow during phacoemulsification

• the outflow from the phaco probe created by the fluid pump (aspiration tube)

• and the leakage of fluid from the incisions.

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Foot Position 3: Ultrasound Energy

• There is linear control of the ultrasound energy level so that more the pedal is depreesd in position 3, more ultrasound energy, such as would be

needed for denser cataract.

• Note that if the pedal is in position 3, we are already engaging the full function of both positions 1 and 2. The irrigation is on, and the vacuum and

aspiration level is at its highest preset level. Ultrasound energy should only be applied once the tip of the phaco probe is in contact with part of the cataract.

• When we titrate the amount of ultrasound energy we place into the eye, we are keeping the frequency constant but we are increasing the stroke length and therefore, the total amount of energy.

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Hand Piece

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Silicon sleeve

80% of irrigating fluid enteres through this side port

20%

Irrigation(Inflow)

Aspiration( outflow)

USG POWER

• When we look at the phaco probe closely, we see that there are three lines attached:

(1) the infusion tubing carrying fluid into the eye,

(2) the outflow tubing that removes the fluid via flow that is created by the phaco machine’s fluid pump, and

(3) the line that carries the electrical signals to control the ultrasound energy at the tip of the phaco probe. These three lines correspond to the three phaco foot pedal positions.

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Concept of Fluidics

• The basic concept of fluidics is that the inflow of fluid must be greater than the outflow of fluid.

• By keeping a constant infusion pressure and limiting the outflow, we can ensure that the eye stays inflated and stable during surgery.

• If outflow > inflow, even for just a fraction of

a second -----surge

this can cause chamber instability, collapse of the eye, and aspiration of the posterior capsule.

The primary rule for phaco fluidics

INFLOW > OUTFLOW

Source of INFLOW

bottle of BSS

Source of OUTFLOW

Aspirated fluid via phaco probe

Leakage through incision11

fluidics

INFLOW

• . Approximately 11 mm Hg pressure (above ambient atmospheric pressure) is produced intraocularly for every 15 cm (6 inches) bottle height above the patient’s eye

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Aspiration Flow Rate

• The amount of fluid flowing through the tubing. This is reported in cubic centimeters per minute (cc/min). With a peristaltic pump, flow is determined by the speed of the pump. As flow increases the current in the anterior chamber increases how well particulate matter is attracted to the phaco tip.

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PARAMETRES

Flow rate( Aspiration)

how fast the things(cataract material,fluid) is coming to phaco tip.More flow rate---rapid movement of the material to tip

Vaccum

after occlusion of phacotip by nuclear material how strongly those material are held at tip. More vaccum -----more strong hold.

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Power

Means change in stroke length..displyaed in %..% means how much % of length of tip is moving forward out of total length of tip.

eg if the stroke length of a machine is 3 milli inches( avarage phaco tip has lengh 2-4 mili-inches)s and if we use 100% phaco power means the whole 3 inches is moving forward out of sleeve but if power is 20% means the tip is moving forward by 20% of its total length i.e 0.6 mili-inch for that machine.

More power..more distance movement of tip …more cracking power

Longer stroke lengths are prone to generate excess heat. The longer the stroke length, the greater the physical impact on the nucleus, and the greater the generation of cavitation forces. Stroke length is determined by foot pedal excursion in position 3 during linear control of phaco.

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• APT—Absolute Phaco Time

Total amount of phaco energy used

APT= EPT X AVG

EPT----Elapsed Phaco Time

AVG----Avarage phaco power

• It makes sense that if you deliver 15 seconds of energy at 100% power, it is about the same as 30 seconds at 50% power, or 60 seconds at 25% power. This is because for each of these three examples, the APT (Absolute Phaco Time) is 15 seconds

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Decreasing USG energy uses(CAP)

• Important for corneal endothelial protection

1) Mechanically by using CHOP technique for nucleotomy.

2) Reducing AVG phaco power by

a) limiting the foot pedal depression in position three

b) by decreasing the maximum phaco power level on the machine.

3) Reducing phaco time by

a) applying the ultrasonic power when cataract pieces are at the phaco tip and are not aspirated by the vacuum forces alone

b) delivering smaller pulses or bursts of phaco energy instead of continuous ultrasound.

• With optimized ultrasonic phaco power parameters, it is possible to remove cataracts with less than 1 second of absolute phaco time, yielding immediate clear corneas and happy patients. 17

Power generation • Phaco needle movement creates mechanical power. Total power is a combination of

the frequency of the needle movement and stroke length.

Frequency • The speed of the needle movement. It is determined by the manufacturer of the

machine. Phacoemulsification needle move at a frequency of between 35,000 to 45,000 cycles per second (Hz)This frequency range is the most efficient for nuclear emulsification.

Lower frequencies are less efficient and higher frequencies create excess heat.

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Pump

• The part of the phaco machine which moves fluid through the aspiration tubing. The pump settings control the rate of movement of the fluid.

Flow Pump

• The primary example of the flow pump is the peristaltic pump. These pumps allow for independent control of both aspiration rate and aspiration level.

Vacuum Pump

• The primary example of the vacuum pump is the venturi pump. This pump type allows direct control of only vacuum level. Flow is dependent upon the vacuum level setting.

Vacuum

• Negative pressure measured in millimeters of Mercury (mm Hg). Vacuum determines how well, once occluded on the phaco tip, nuclear material will be held to the tip.(holding power)

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Peristaltic pump

Ventury pump

Peristaltic pump

rollers while moving

compress the phaco outflow tubing in a peristaltic manner

physically moves fluid and creates a continuous “milking” action on the fluid column

The phaco machine can directly control this flow level, hence the term flow based; however, the preset vacuum level is only achieved once there is occlusion of the outflow line, typically at the phaco needle tip with cataract material.

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Peristaltic pump

• At low speeds of rotation a vacuum is not produced unless the aspiration port is occluded. As the speed of rotation is increased( which is done only by increasing flow rate), vacuum is produced in the aspiration line without occlusion.

• N.B…in peristaltic pump vaccum can be produced both with or without occlusion of phaco tip depending upon whether the tip is occluded or not.

• .if you want to built vaccum without occlusion you have to increase flow rate and if you want to built vaccum at low flow rate you have to occlude the tip…

SO CALLED AD FLOW BASED PUMP

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As the occlusion of phacotip by catract material happens

the vacuum builds

the rollers slow down,

and the outflow level decreases

On complete occlusion

the rollers come to a stop

the outflow approaches zero, and the vacuum is at its highest level

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venturi

• The vacuum level is created within a rigid drainage cassette, to which the phaco aspiration tubing is connected . Since there is no milking of the aspiration line, the phaco tubing can be made rigid with low compliance

• The advantage of the venturi pump is that it is able to create the preset vacuum level without occlusion of the phaco needle tip

• . When the surgeon depresses the foot pedal, the preset vacuum level is immediately created, hence the term vacuum based

• Because venturi and diaphragm pumps have inherently higher flow rates, they build up vacuums in the aspirate line without occlusion of the aspiration

port. Once the tip is occluded, a vacuum builds uprapidly.

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• In the venturi pump Bernoulli’s principle is applied.

• When the speed of flow of a fluid is increased in a region, the pressure there is decreased.

• Compressed gas, such as air or nitrogen, flowing through pipe A reduces the pressure in the region just above the tube B and creates a partial vacuum in space C.

• There is no moving part in this pump.

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A B

C

Differences

• To create the preset maximum vacuum level with a peristaltic pump, there must be complete occlusion of the phaco needle with cataract material. To create the preset vacuum level with a venturi pump, the surgeon simply needs to depress the foot pedal.

• Currently in the United States, the most commonly used fluid pumps are of the peristaltic design.

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Peristaltic Venturi

Flow based Vaccum based

Vaccum created only when phacotip is occulded by catract material

--Vaccum created instantly via pump once surgeon press foot pedal

--No need of oclusion of phaco tip

Flow is constant until occlusion Flow varies with vaccum level

Drains into a soft bag Rains into a rigid cassette.

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• Peristaltic is DELUX CAR---SAFE AND RELIABLE

• Venturi is racing car----faster and dangerous

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Diaphragm pump

• In the diaphragm pump a flexible metal or rubber diaphragm moves up and down.

• This movement, along with the vertical motion of two valves,maintains the vacuum

• Clinically, diaphragm and venturi pumps are very similar

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• A peristaltic pump with a slower flow rate is useful for a beginner because it provides the largest safety margin in the event of a sudden capsule occlusion in the aspiration port.

• The slow rise time allows enough time for the surgeon to come back to position 1 of the foot pedal or even relax.

• The disadvantage of a peristaltic pump is that it results in a longer procedure. A peristaltic pump at a moderately high flow rate presents a good compromise between safety and efficiency.

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Rise time

• The amount of time required to reach a given vacuum preset, assuming complete tip occlusion

• The diaphragm and venturi pumps have rapid flow rates and rise times.

• The peristaltic pump has a slower rise time, which can be made more rapid by increasing the rotation of the wheel (i.e. at a higher flow rate).

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Compliance • Change of the tubing shape and volume when put under negative pressure.

• When the tip of the phaco needle is occluded, negative pressure will build in the tubing. The higher the compliance the more change in the tube’s volume. When negative pressure is created highly compliant tubing collapses on itself reducing its inner volume’s capacity.

• When occlusion breaks, the tubing returns to its original shape and a temporary imbalance of exists causing rapid exit of fluid from the anterior chamber. This is called Surge

The higher the compliance the greater the surge amplitude during occlusion break

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SURGE

• . phaco needle is occluded by nucleus matter and tubing collapses due to negative pressure.

• When occlusion breaks after eating that nuclear piece

• The negative pressure suddenly becomes off

• the rate of fluid sucked into the phacotube from the anterior chamber can be temporarily increased due to the sudden expansion of the tubing.

• This can cause temporary shallowing until the fluid is replaced by the infusion ( SURGE)

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Surge is the situation when the outflow of fluid from the eye exceeds

the inflow, even for just a fraction of a second.

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HOW TO REDUCE SURGE?

1) lower levels of flow and vacuum

2) Rigid noncompliant aspiration tubing.

3) venting.

Venting allows vacuum levels to be equilibrated to air or fluid into the aspiration line.

A system for venting exsits in all phaco machines.

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Minimizing surge

4) Increasing bottle height

5) Reducing tip size

6) ABS ( Aspiration Bypass Port) Port---small hole in metal part of phaco hand piece so that even under occlusion some fluid will pass out through it. ABS will function only in occluded state of tip.also has cooling effect

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VentLike Ventilation

Occlusion of phacotip by nuclear fragment

Vaccum created

When vaccum reached to the maximum preset level

Vent valve will open and some air or fluid will entres into the system (VENT)

this will happen to prevent exceeding vaccum from present level and no more vaccum will be there beyond preset level (ADVANTAGE OF VENT)

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Which vent is good????Air or Fluid????

When Vaccum reached to preset level

Vent valve opens

Air or fluid entres the vaccum chamber ( air vent system/fluid vent system)……suppose stage 1

Bubbles of air/fluid expands .but air expands more in vaccum in comparion to water bubble stage 2

Once vaccum breaks( after emusification of nuclrear matter at phaco tip)and fluid enters inside

Expansion reverse …new stage 1

At this point the size of air bubble is less than water bubble( i.e air contracts more than water)

SURGE MORE WITH AIR VENT

Conclusion….FLUID VENT IS BETTER

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Surge is less with fluid VENT

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Air expands more in vaccum

Fluid expands

less

Air contracts

more

Fluid contracts

less

Once occlusion breaks

POWER(Frequency x stroke length)

• Each machine has fixed rate of vibration (35000-45000/sec )

FIXED

• When we change the phaco power we are changing stroke length of phaco

tip (CHANGEABLE) eg..

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Rate of vibration(fixed for particular machine)

10% phaco power

70% phaco power

Phaco mode

Continuous Mode

Pulse Mode

Brust Mode ----single VS multiple

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Continuous mode

• All the time ultrasound is ON at gradual manner (LINEAR) depending upopn foot pedal position 3 …….no OFF

• In Every second……. all second is full with ultrasound

Disadvantage……More USG power delivery as there is no gap

uses—for scuplting

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Pulse mode

• Phaco is not on throughout all part of 1 second

• With in 1 second …in part of second phaco is ON and in another part of second phaco is OFF….there is pause in ultrasound

• Less energy---ADVANTAGES

• Adjustable like 2 pulses/sec

4 pulses/sec

10 pulses/sec

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What does it mean????

• Eg..1

If we have 2 pulses/sec…

Means in 1 sec 2 on cycle and 2 off cycle ( i.e total 4 cycle)

So each pulse is of 250 millisec..( 1sec= 1000 millisec)

Eg 2 if we have 4 pulse/sec

4 pulses/sec = 4 oncycle and 4 offcycle/sec =total 8 cycle= 1000/8m =each pulse is of 125 millisec

End Result— in all …50% of second USG is ON and 50% of sec USG OFF…doesn’t matter what pulse u have set..

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• Pulse of energy are delivered at definite rate of pulses per second(pps),which is the number of cycles per second

• The defult cycle for pulse mode is to have phaco energy on and off for equal period(50:50),thus giving a duty cycle of 50%

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Phaco can be delivered in

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• Panal mode

• Surgeon mode

PANAL MODE……When you introduce your foot pedal to stage 3 the whole energy will be delivered to maximum (i.e from beging of stage 3 to end of stage 3 constant power)

SURGEON MODE or LINEAR MODE..…when you push foot pedal to stage 3..the phaco enery will be deliver gradually

Eg.. When you set phaco power of 60%

in Panal mode …when you go to stage 3 in foot pedal whole 60% will be delivered at a time but in ( it doesn’t matter whether you are in beginning or end of stage 3)

surgeon mode the power will built up gradually like 10%...20%....30 %....40%.....50%....60%... As you gradullay push the pedal…ie 10% as you enter in beginning of stage 3 and increasing finally reaching to your preset level of 60% when your foot pedal is at end of stage 3

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Panal mode

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60% 60%

Foot pedal in position 3 early stage Late stage of foot pedal 3

SURGEON or LINEAR MODE

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10%

60%

Between 2 pulse interval is equal

Linear mode pulse

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Hyperpulse

• Hyperpulse allows the surgeon to choose from new, higher-range pulse settings that can exceed 100 pulses per second (compared with traditional pulse, which had a maximum of 20 pulses per second).

• The surgeon does not change the amount of phaco energy used by using more pulses per second because each short phaco pulse is followed by a short phaco-off time.

• The increased frequency of phaco-off periods does, however, reduce the amount of heat generated

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BRUST MODE

Ultrasound……long period of no ultrasound….ultrasound

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USG USG

BRUST WIDTH30----500 milli Sec

If you are in early stage of foot pedal 3…there will be off period( interval between pulses) of 2.5 milisec.

As the foot pedal goes down the off period will be shortens

At the end there will be no off periode…brust mode will become continuous mode.

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For brust mode

If foot pedal is in late stage of position 3

As phaco will convert to continuous mode…no off…used for sculpt

If foot pedal is in mid stage of position 3

now some interval between phaco pulse develop …quardrant removal

If foot pedal is in early stage of position 3( pedal just pressed in 3)

Long gap between……epinucleus removal,chop,bringing material in centre

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Single Vs Multiple brusts

• Single burst delivers just one single burst of energy, for burying the phaco probe into a nucleus for chopping. (not preferrable)….doesn’t matter whether you are in early or late stage of foot pedal position 3….one and only 1 brust …then finished

• multiple burst mode delivers one single burst by just entering foot position 3, and still have the ability to deliver many more bursts at varying intervals with further foot pedal depression

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• Because the phaco foot pedal now controls the rest interval between identical bursts, we do not have linear control of the phaco power level.

• For this reason, it is important to use a lower phaco power setting when using burst mode as compared to pulse or continuous modes.

• When the foot pedal is maximally depressed, the rest interval between bursts is zero and the phaco probe essentially delivers continuous energy

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• For my technique of quick chop, I typically use just one phaco setting:

multiple burst mode with a burst time of 20 milliseconds, a power of 10% and an endpoint duty cycle of 50%

• . This means that I can give 50 of these identical bursts in 1 sec at 10% power which is equivalent to doing phaco in continuous mode of 1 sec at 10% power

• This low energy delivery in burst mode makes surgery safer by minimizing heat production and by minimizing endothelial cell damage from the ultrasound power.

• This translates to clear corneas immediately after surgery, better visual outcomes, and most important, higher patient satisfaction. I encourage you to try burst mode.

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Hyperpulse and Hyperbrust

• The concept of pulse and brust has been more modified in new machine.

• Old machine had maximum pulse of 20 pps but new has upto 120 pps.

• Old machine had brust width as narrow as 30milisec whereas new has 4 ms.

• advantage of this upgraded range of programmability is the smoothness and precision of power delivery

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Hyperburst

• Hyperburst technology allows you to use burst durations as short as 4 ms (compared with traditional burst, which had a minimum of 80 ms max 600).

• These "microbursts" are very small amounts of phaco energy that reduce the total amount of energy used, and the "microrests" allow for dissipation of

thermal energy.

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• . If we want to harness the sculpting and cutting ability of the phaco hand-piece for grooving of the cataract nucleus, it makes sense that a knife with a

smooth blade would cut well.

• A coarsely serrated knife with large, widely spaced serrations would not cut as smoothly.

• However if we use a very finely serrated knife, it would likely cut the best of all. Using a very high pulse rate of 100 or more pulses per second results in the cutting ability of a very finely serrated knife, yet delivers half of the energy of continuous phaco power.

ADVANTAGE…we get continous phaco effect delivering half energy

NB..by changing PPS we cant can’t change the APT.

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NB..in continuos and in pulse phaco energy is increasing linearly but no linear in brust…that’s brust

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• Phaco ON Ultrasound energy delivered

Jack Hammer repulsion effect

Heat generated

Phaco OFF Aspiration of nuclear fragments

Cooling effect

No ultrasound energy

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Repulsive Vs Attractive forces

When power on….Repulsive force acts ( emulsification + heat generation)

When power off…

attractive force acts

brings the nuclear matter to phaco tip

Vaccum builds up

Mechanical removal of material,no heat and surge occur during attractive force

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Phaco ON—repulsionPhaco OFF--attraction

Vaccum and bottle height

VACCUM (mm/Hg)

BOTTLE HEIGHT (In Centimeters)

150 65

200-250 85

250-300 110

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Use of pulse

Long OFF(or short ON) eg…2 pulse/sec

attractive force come on play for long time…used for chopping or to bring material to central area before removing

Short off (or long ON) eg…6 pulses/sec

for sculpt and quadrant removal

So long OFF for better hold and short OFF just to clear materials.

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Changing the PPS doesnot change the absolute phaco time

in both of 2pps and 4 pps 50% of time phaco is ON and 50% of time phaco OFF .what ever the pulse we keep total phaco ON time will be 500ms and OFF time will be 500ms…….so by changing pps the APT will remain constant .

That’s why if you want to reduce or increase phaco time you have to change the duty cycle not the pps

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250ms 250250ms

250 ms

125 125 125125

2PPS

4 PPS

Changing duty cycle can change APT

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50%

20%

50% duty cycle

20% duty cycle

50%

80%

Both has 4 pps but duty cycle in 1 is 50% and 2 is 20%

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250ms 250 ms

2PP250ms 250ms

100ms

100ms 2PP

400ms 400ms

Ratio ON to OFF is 50:50,hence 50% duty cycle

Ratio ON to OFF is 20:80,hence 20% duty cycleIn 1 sec total on 200ms and total off 800 ms .

The amount of phaco energy affects corneal endothelial cells so the goal is to use just enough ultrasound

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How ??????

1) Use mechanical division

D& Q,Chop

2) Use high vaccum

3) The phaco tip used

4) Use pulse or brust mode not continuous

5) Modify US delivery

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Phaco tip

Standard tip (19 guage)

Outer diameter(OD)----1.1 mm

Inner Diameter( ID)-----0.9 mm

Micro tip( 21 guage)

OD---0.8mm

ID----0.6mm

ADVANTAGE of Microtip

Smaller incision

DISADVANTAGE

Less holding force for same power setting

Less amount of material/time73

Modifying US Delivery• By changing duty cycle

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ON

OFF

ON

INTERVAL ( Between 2 on part)

CYCLE TIME

PULSE DURATION PULSE DURATION

• Frequency—number of pulse/sec

• Duty Cycle---time during which power is on as % of cycle (traditionally 50%)

i.e 50% time USG ON…50% OFF

• Pulse duration- time of phaco power on (PYRAMID)

• Interval duration —time from one pulse to another

• Cycle time —pulse duration+interval duration

N.B--- in cycle time pluse duration is added to interval where as in interval we exclude pulse duration

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Change in duty cycle

• Duty cycle 50%....means 50% time USG on…50% time no USG

• Duty cycle 20%---20% time Phaco ON…80% time OFF

• 2 Pulse /sec---means 1 sec is divided in 2 part• 4 Pulse/sec---means 1 sec is divided in 4 parts

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Duty cycle

phaco-on time

phaco-on time + phaco-off time

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Changing duty cycle

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50% duty cycle

20on

20% duty cycle

50:50

20:8080% off

Both duty cycle have 3 pulses/sec in upper fig.50% time phaco on whereas in lower 20%

time

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80

250ms 250 ms

2PP250ms 250ms

100ms

100ms 2PP

400ms 400ms

Ratio ON to OFF is 50:50,hence 50% duty cycle

Ratio ON to OFF is 20:80,hence 20% duty cycleIn 1 sec total on 200ms and total off 800 ms .

• For example, if I am using 10 pulses per second and I’d like to slightly reduce the ultrasound energy,

• I can decrease it from a 50% duty cycle to a 40% duty cycle. This can be done by dropping the duty cycle ratio as seen on the control panel of the phaco platform

• . Alternatively, I can delineate the specific on and off periods for each cycle, with an on-time of 40 milliseconds followed by an off-time of 60 milliseconds, I will achieve the same result—a total cycle time of 100 milliseconds, with 10 pulses per second and a 40% duty cycle.

• NB..if i change the PPS I cant reduce APT as explained before so I have to reduce duty cycle

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When do we want higher or lower duty cycles?

• The answer depends on the phase of surgery.

• For sculpting such as with the technique of divide-andconquer, we need to deliver sufficient energy to be able to cut the grooves. This requires a duty cycle of about 40-60%. (MORE DUY CYCLE)

• Once we have the grooves placed in the nucleus and we have cracked it into quadrants, we can use a lower duty cycle during the phaco-assisted aspiration of the quadrants.

• For this quadrant removal, a lower duty cycle of 20-40% can be used since the principal force for nucleus removal is the fluidics and not the ultrasound.( LOWER DUTY CYCLE)

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The concept to remember is that a higher duty cycle results in better cutting

power but increased heat generation and more energy- related damage to the corneal endothelium.

Using the lower duty cycle allows more fluidic aspiration of nuclear fragments while minimizing heat and phaco power, resulting in clear corneas immediately after surgery.

And we all know that clear corneas on post-op day one make for good visual acuity and very satisfied patients.

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• For grooving and sculpting of the nucleus, the work is being done by the ultrasonic energy and thus the flow and vacuum settings are quite low – just enough to aspirate the nuclear material removed from each forward stroke of the phaco probe.

• A vacuum level of less than 100mmHg and a flow rate of less than 30cc/min is sufficient for this purpose

• For quadrant removal, a moderate amount of holding power is required to bring each quadrant into the phaco tip. Using a higher vacuum level of 200-300mmHg and a flow rate of 30-50cc/min, depending on the needle size, is typically sufficient for this purpose.

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• For phaco chop, holding power of the nucleus is important in order to securely fixate it while using the chopper to mechanically disassemble the nucleus.

• This requires a relatively high vacuum, such as 200-250 mmHg with the 1.1mm needle, or 300-400mmHg with the 0.9mm needle.

• Once the nucleus has been broken into smaller fragments, the speed at which the fragments are attracted to the phaco tip is determined by the peristaltic flow rate, with 20cc/min being very slow and 50cc/min being very fast.

• The same vacuum and flow rate settings can be used for the entire nucleus removal procedure during phaco chop.

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Variable rise time and custom setting

• To reduce the repulsive force of phaco we can decrease the phaco power, but this isn’t always the best answer, particularly when a nucleus is dense and requires more phaco power for emulsification.

• Instead, if we initially attack the nucleus with lower power, then hold on to it with the vacuum fluidics of the phaco machine, we can ramp up the power to a higher level.

• The new phaco power modulation software on most platforms allows this automatically, with millisecond precision. Burst and pulse modes deliver square-wave

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clear corneal Incision

• Easy to construct

• Good assess to cataract

• Seal well

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SCULPT

• high pulse mode (80 PPS or more), with a 40-60% duty cycle,

• maximum phaco power of 40-60%.

• The fluidics should allow for a low vacuum and low flow setting to simply evacuate any emulsified cataract bits from the excavated trench.

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CHOP

• To chop each half, we need to change the phaco and fluidic settings:

• here a burst mode is my preference as it affords using very little energy.

A short burst width of 4-20 milliseconds and a power of 10-40% works well.

For those surgeons preferring a pulse mode,

try 10-20 PPS (pulses per second), 30-50% duty cycle, and a maximum power of 20-50%.

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• The fluidics must also be changed to increase the holding power of the nucleus.

• Try using a higher vacuum level (200-400 mmHg depending on your phaco needle size), and a higher flow rate (30-50 cc/min) with a corresponding higher bottle height to ensure that the inflow is greater than the outflow

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UltraSound Power

Fixed Machine setting

• The variable that is controlled is set and when the foot pedal is pushed the machine produces the preset amount of ultrasound power or aspiration flow rate. (this can be used when referring to power and aspiration flow rate.)

Surgeon Controlled Machine setting

• The amount of ultrasound and or aspiration is controlled by the surgeon by pushing down the foot pedal. Also referrerd to as variable control.

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Typical Power Modulation Settings

• The following are a few typical settings on the Alcon Infiniti Vision System:

sculpting,

a maximum preset power of 60 percent with 60 pulses per second and a duty cycle of 50 percent

quadrant removal, a maximum preset power of 40 percent with 10 pulses per second and a duty cycle of 35 percent

epinucleus, a maximum preset power of 20 percent with 10 pulses per second and a duty cycle of 25 percent

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LETS ENJOY THE CHARM OF PHACO

THANK YOUMeet me-- yourgyanu@gmail.com

Facebook—gyanu raja

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