phaco, cataract surgery

1. Jagdish Dukre

2. 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.

3. 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).

4. Phacomachine
The machine consists of the
Console,
Handpiece
Foot pedal,

5. 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.

6. 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.

7. Handpiece
There are two types of handpieces
1. Irrigation aspiration handpiece
2. Phaco handpiece

8. Irrigation-Aspiration (I-A) Handpiece
The 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.

9. Phaco Handpiece
The 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.

10. 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.

11. Piezoelectric Transducers
They 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.

12. 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.

13. Phaco Tip
The 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.

14. 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.

15. 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.

16. 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.

17. 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.

18. 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.

19. Foot gradient
Foot 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:

20. 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.

21. 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.

22. PHACODYNAMICS
The 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.

23. Power
Power 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

24. 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.

25. Mechanism of Emulsification
The 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.

26. Cavitation
The 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.

27. 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.

28. 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.

29. 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.

30. Control & Delivery of Power
There are various modes
Surgeon/linear mode
Panel mode
Pulse mode
Burst mode

31. 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.

32. 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.

33. Pulse Mode
In 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.

34. 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.

35. 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.

37. FLUIDICS
The fluidics of the machine refers to the integrated functions
performed by infusion and aspiration systems by which a
stable AC is maintained.