Jagdish Dukre

Introduction

Introduced by Dr. Charles Kelman in 1962,

phacoemulsification machines have undergone constant

improvement, ever increasing both their complexity and

safety.

All phaco machines consist of a computer to generate

electrical signals and a transducer to turn these electronic

signals into mechanical energy.

The energy thus produced is passed through a hollow

needle and is controlled within the eye to overcome the

inertia of the lens and emulsify it.

Once turned into emulsate, fluidic systems remove the

emulsate, replacing it with balanced salt solution (BSS).

PhacomachineThe machine consists of the

Console,

Handpiece

Foot pedal,

CONSOLE

The console consists of a

computer which controls all the

functions of the machine.

The computer generates

ultrasonic waveform and sends

it to the transducer in the form

of electronic signals.

The setting for the various parameters, i.e. power, vacuum

and flow rate are fed in here.

These settings represent the maximum level of the

parameter that will be achievable

Settings for different types of cataract can also be fed into

the memory.

HandpieceThere are two types of handpieces

1. Irrigation aspiration handpiece

2. Phaco handpiece

Irrigation-Aspiration (I-A) HandpieceThe I-A tip differs from the phaco tip in being smooth and rounded with a single aspiration port on the side of the tip and not at the end.

The aspirating port at one side usually 0.75 mm to 1.5 mm away from the tip.

The opening can be in a diameter of 0.2, 0.3, 0.4, or 0.5 mm.

The angulations of the I-A handpiece can be straight, 45° bent, or has a 90° bend.

Phaco HandpieceThe phaco handpiece contains the

piezoelectric crystal, which is in

contact with the tip.

The tip is covered by a silicon

sleeve.

The infusion fluid flows between the

tip and the sleeve cooling the

former.

There are two openings on the sleeve for the exit of this

fluid, which should be kept perpendicular to the tip bevel.

The proximal end of hand piece is connected to the console

with an electric cord.

There are two more connections: one each for the irrigation

tubing and for connecting the aspiration system.

Piezoelectric TransducersThey are based on the reversal of the piezoelectric

phenomenon.

Certain crystals, on compression, produce electric current.

In reverse, electric current causes the crystal to contract.

The crystal is mounted on a piece of tubing of narrowing

diameter eventually ending with the attachment of the phaco

needle.

The decreasing diameter tube acts as an amplifier to

generate adequate power for emulsification.

There may be 2–6 crystals, 6 giving more stroke length

and more power.

Phaco TipThe phaco tip is made of titanium and is hollow with the

distal opening functioning as the aspiration port.

The acoustic energy produced along the ultrasonic handpiece

is then transmitted onto the phaco tip.

The angulation of the tips may vary from 0–60°.

Tips with 60°, 45°, 30°, 15° and 0° angulation are available.

The commonly used tips are 30° and 45° phaco tips.

More the angulation, the lesser the

holding power but the cutting

power is more.

e.g. 60° tip is a sharper tapered tip

making occlusion difficult. But is

useful for grooving hard cataracts.

Entering into the anterior chamber

is easy with the 60° tip and

progressively harder with a 15° or a

0° tip.

Foot Pedal

Foot pedal control is the most important

aspect of phaco.

Though the foot pedal of each machine

may have a different design, it essentially

consists of main central part and side

kicks.

The main part of the foot pedal controls

infusion, aspiration and phaco power.

The entire distance that the foot pedal traverses is divided

by 2 dentations into 3 excursions-

I (irrigation only),

IA (infusion and aspiration) and

IAP (infusion, aspiration and phaco).

In the I excursion, the pinch valve

opens and irrigation is switched on.

There is no gradient in this step and

the irrigation is either switched fully on or off.

The function of this dentation is to dissociate infusion from

irrigation-aspiration.

As foot is brought back from IA/IAP excursion, stopping at

this dentation will keep the infusion on preventing the

collapse of anterior chamber.

Many steps like nuclear rotation, manipulation of nuclear

fragments, epinuclear plate etc. require a formed AC without

any aspiration.

From dentation 2 to full depression is the phaco or the ‘IAP’

excursion.

At IAP0 phaco energy delivered will be zero and at IAPmax

the energy will be maximum preset.

The delivery of phaco energy is linear both in the surgeon and

the pulse mode.

However, in panel or burst mode, as soon as foot clears IAP0,

maximum preset energy is delivered.

Foot gradientFoot gradient is the excursion of foot pedal in mm to

produce unit power of phaco energy.

If the total foot excursion, from IAP0 to IAPmax is 10 cm

i.e. 100mm and the maximum preset phaco energy is 100%,

then the foot gradient (FG) becomes:

Decreasing the maximum preset

power on console increases the

foot gradient and hence the foot

control.

Therefore, phaco maximum

should be set at the minimum

power which is required for a

particular step in that grade of

cataract.

Side kick functions of foot pedal

The most important sidekick function of foot pedal is reflux.

On kicking the side switch, aspiration flow rate is inverted

and the material aspirated is expelled into the AC.

Since it is not a continuous function, for further reflux, the

switch needs to be kicked again.

Inadvertent aspiration of wrong tissue (iris, capsule) can be

released by this function especially by beginners.

PHACODYNAMICSThe various functions of the phaco machine and their inter

relationship is called phacodynamics.

The basic functions of the machine are two, which include

ultrasonic power for emulsification

irrigation-aspiration for safe suction of the emulsified

material.

Irrigation-aspiration system and the parameters on which it

depends together are called fluidics.

PowerPower is created by an interaction between frequency and

stroke length.

The frequency is variable from 29–60 kHz in different

machines.

Higher frequency ensures a better cutting action but more

heat is generated.

However, in each machine, the frequency remains fixed and

power is varied by varying the stroke length

Stroke length is defined as the length of the needle movement.

Most machines operate in the 2 to 4 mil range. (1 mil = 25µ)

Therefore, most phaco needles travel a distance of 50 to 100 µs.

The longer the stroke length, the greater the generation of

cavitation energy.

Longer stroke lengths tend to generate extra heat.

Stroke length is determined by foot pedal excursion in position 3

during linear control of phaco.

Mechanism of EmulsificationThe actual mechanism of emulsification is a combination of

Jack-hammer and

Cavitation phenomenon

The jackhammer effect is the physical striking of the needle against the nucleus.

The Jack-hammer action requires that the nucleus should be fixed as for the bombarding action to be effective.

This is the action that is primarily used during trenching.

CavitationThe phaco needle, moving through a liquid medium at ultrasonic speeds, gives rise to intense zones of high and low pressure.

Low pressure, created with backward movement of the tip, pulls dissolved gases out of solution, thus producing micro bubbles.

Forward tip movement then creates an equally intense zone of high pressure.

This initiates compression of the micro bubbles until they implode.

At the moment of implosion, the bubbles create a

temperature of 7204˚C degrees and a shock wave of

5,171,100 mbar.

Of the micro bubbles created, 75% implode, amassing to

create a powerful shock wave radiating from the phaco tip in

the direction of the bevel with annular spread.

The energy created by cavitation exists for no more than 4

milliseconds and is present only in the immediate vicinity of

the phaco tip and within its lumen.

Additionally, cavitation is instrumental in clearing nuclear fragments

within the phaco needle, preventing repetitive needle clogging.

The angle of the bevel of the phaco needle governs the direction of

the generation of the shock wave and micro bubbles.

The disadvantage of this wave is that it may push nuclear pieces

away if the hold is not good and thus decrease the Jack-hammer

effect.

Phacoemulsification is most efficient when both the jackhammer

effect and cavitation energy are combined.

To accomplish this, the bevel of the needle should be turned

toward the nucleus or nuclear fragment.

This simple maneuver will cause the broad bevel of the

needle to strike the nucleus.

In addition, the cavitation force is then concentrated into the

nucleus rather than away from it.

Also, in this configuration, the vacuum force can be

maximally exploited as occlusion is encouraged.

Control & Delivery of PowerThere are various modes

Surgeon/linear mode

Panel mode

Pulse mode

Burst mode

Surgeon/Linear Mode

The power delivery varies from 0 to the maximum that one

sets on the panel, by varying the foot pedal in phaco mode.

At pedal position 2, i.e. at the start of phaco mode (P0) the

power will be 0 and at full depression (Pmax) power will be

the maximum that has been pre-set.

Thus the excursion of the foot in phaco mode will determine

the amount of power being delivered.

Panel Mode

As soon as surgeon depress the foot pedal into the phaco

mode (P0), he will immediately reach the maximum power

that has been set on the panel.

Here, there is no variation and full power is delivered.

The only probable indication for the use of panel mode is in a

very hard cataract where the nucleus is uniformly hard

requiring more or less uniformly high power for

emulsification.

Pulse ModeIn pulse mode each pulse of energy is followed by a gap of

equal duration.

For effective power delivery, the nuclear fragment has to be

held, so the interval between the pulses of phaco allow the

vacuum to build up and thus a good hold is developed.

Pulse mode is a variant of linear phaco mode where the

frequency of the pulses is fixed and the phaco energy

delivered in each pulse will depend on the amount the pedal

is pressed.

Thus the power is delivered at pre-set intervals, the frequency

of which is pre-set and decided by the surgeon.

Most machines have from 0–12 pulses.

The use of the pulse mode in phaco aspiration almost halves

the power use, as the vacuum build up between the pulses

ensures efficient emulsification and aspiration.

Newer machines have softwares which can have pulses in

hundreds and thousands, called the hyperpulse mode.

Burst Mode

Burst mode is where maximum power is delivered at intervals which vary with the amount you depress the foot pedal.

Burst mode is a variant of panel mode where the energy is fixed and the frequency of phaco bursts will increase with increasing depression of the foot pedal in phaco mode.

At P0 there will be one burst per second and at full depression (Pmax) the power delivery is continuous.

The duration of the burst can be selected and is usually 100 msec.

FLUIDICSThe fluidics of the machine refers to the integrated functions

performed by infusion and aspiration systems by which a

stable AC is maintained.