Mechanism of Phacoemulsification

1. PHACODYNAMICS
Dr. Arup Krishna Choudhury
FCPS, DO, MBBS
Vitreo-Retina Fellow ( IIEI&H)

2. Phacodynamics
The various functions of phaco machine and their
inter relationship is called phacodynamics

3. History
Dr. Charles Kelman –
father of phacoemulsification
In 1967 first performed
phacoemulsification in human eye
Dr. Barry seibal
Phacodynamics term first coined

4. Fundamental components
Ultrasound Energy (Power) Fluidics
Irrigation Aspiration

5. Phaco Machine
• Computerized ultrasound system
• Phaco Hand piece
• Foot pedal
• Irrigation Aspiration – Pump system

6. Phaco Hand Piece
Irrigation
Aspiration
US
80% irrigating fluid coming through side port
20% coming through head

7. Phaco tip
Phaco tip- Hollow titanium needle
Depending on the configuration of bevel- 0
0
, 15
0
, 30
0
, 45
0
, 60
0
tips

8. Phaco Sleeves
• Made of silicon material
• Provides cooling effect

9. Parameters
Aspiration flow rate
Vacuum
Power

10. Parameters
Aspiration flow rate – How fast materials coming to the tip
Vacuum – Amount of holding power
Power – Ability of the phaco handpiece to cut or emulsify cataract

11. Units
• Irrigation – cm
• Aspiration flow rate – cc/min
• Power – maximum 100%
• Vacuum – mm of Hg

12. Foot pedal
Position 1 Irrigation
Position 2 Irrigation +Aspiration
Position 3 Irrigation +Aspiration+ US

13. Power
• A computer to generate ultrasonic impulses
• A transducer – energy converter
• Piezo electric crystals that turn these electrical signals into
mechanical energy
The energy that is created used emulsify the lens

14. Power
(Frequency x Stroke length)
Power is created by an interaction between frequency and stroke
length
• Frequency – How fast phaco tip moves
• Stroke length – How far the phaco tip moves(back-and- forth
movement)
Power change means change in stroke length displayed in %
More power More stroke length More cracking power

15. Power
• 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 in % - Changeable
• Ex -If the stroke length of a machine is 3 mili inches
• 70% power means – 70% of 3 mili inches is forward out of the sleeve
• 30% power means – tip is moving forward by 30 % of its total length
Power 70% Power 30%

16. Motion of the tip
• Longitudinal
• Tortional
• Transverse / elliptical

17. Mechanism
• Jack Hammer effect – Direct mechanical effect
• Cavitational effect – Implosion of microbubbles
• Acoustic wave of fluid - Ultra Sonic wave propagation through water

18. Phaco delivery
Panal mode – Once get the position 3 ,the whole energy will be delivered to
the maximum.
Surgeon mode – at position 3 as we get pedal down gradually , the level of
energy will increase gradually.
c

19. Phaco ON
Ultrasound energy delivered
Heat is generated
Phaco OFF
No Ultrasound energy
Cooling effect

20. Phaco mode
Power can be given in different modulations
• Continuous mode
• Pulse mode
• Burst mode

21. Continuous mode
All the time ultrasound is on – No off time
Disadvantage – More power delivery

22. Pulse mode
Power is not delivered throughout
On time and off time present it is same throughout
Advantage – Less power

23. Pulse mode
• 2 pulse/sec 250ms 250ms
1s
• We Can adjust the pulses like 4,10 maximum 20/s
• It does not matter how many pulses but all the time we have 50%
sec US on and 50% sec US off.

24. Duty cycle
• Time during which power is on as % of cycle (traditionally 50%)
50:50
20:80

25. Burst mode
• Power is not delivered throughout
• On time and off time present but it is not the same
throughout
• i.e. off time decreases with depression of foot pedal 3 and
reaches preset value at end

26. Hyperpulse mode
Linear power with more “off” time
Up to 120 pps can be delivered
Hyperburst mode
Burst width 4 ms
Usually burst width 30 ms

27. Fluidics
• The basic concept of fluidics is that the inflow of fluid must be greater
than the outflow of fluid.
• Irrigation –
Source- Bottle of BSS
• Aspiration
Source - Aspirated fluid via phaco probe
Leakage through incision

28. Irrigation
• On foot position 1 – Fluids coming from the bottle into the A/C
• Pressure in the A/C is equivalent to the height of the bottle
11 mm Hg / 15cm bottle height

29. Aspiration
Flow of fluid which exits the eye through the aspiration port of the hand
piece and aspiration tubing into the waste bag.
• AFR low like 18 cc/min means that material will come to the tip slowly
• AFR high like 30 cc/min means that material will come quickly to the tip

30. Pump
Aspiration rate is determined by the speed of the pump
If the pump turns faster, it removes fluid from the eye faster & vice versa
• Flow pump-
The peristaltic pump
• Vacuum pumps –
The venturi pump
The diaphragm pump

31. Peristaltic pump
• Flow based
• Vacuum created on occlusion of tip
• Control by the movement of series of rollers
• Drains into a soft bag

32. Venturi pump
• Vacuum based
• Compressed gas generates vacuum
• Vacuum created instantly via pump by depress the foot pedal
• Drains into a rigid cassette

33. 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

34. Vacuum
When there is occlusion vacuum will start to build up
Vacuum provides the holding power to keep the nuclear material at
the phaco tip

35. Vacuum
Higher the preset vacuum level greater the holding power

36. Compliance of tubing
The change of volume of tubing when subjected to negative
pressure
High compliant tubing has a tendency to collapse on itself when
subjected to negative pressure
Low compliant tubing – i.e. rigid tube, does not have a tendency to
collapse on itself when subjected to negative pressure

37. Rise time
The amount of time required to reach a given vacuum preset,
assuming complete tip occlusion
• The diaphragm and venturi pumps have rapid rise times.
• The peristaltic pump has a slower rise time

38. Followability
Tendency of the nuclear fragments/cortical matter to come into the tip

39. Surge
Phaco needle occluded
Tubing collapses due to negative pressure
when occlusion breaks
Fluid sucked into the phaco tube from A/C due
to sudden expansion of the tubing
Shallowing of the A/C
Surge
Outflow> inflow

40. Surge
Surge

41. Surge Reduction
• Low AFR and vacuum
• Increase bottle height
• Non-compliant tubing
• Venting
• ABS
• Reducing tip size

42. Vent
Occlusion
vacuum created
Upto preset level(max vacuum)
Vent valve will open and some
Air /fluid will enter into the system
Equilibrium of pressure with
atmospheric level within tubing

43. Once occlusion is broken
Air or Fluid vent????
Air expands more in
Vacuum
Fluid
expands less
Air
contracts
more
Fluid
contracts
less

44. Aspiration bypass system
Small hole in metal part of phaco handpiece
so that in even under occlusion some fluid will
pass out through it . ABS will function only in
occluded state of tip. Also has cooling effect

45. Applications
• Sculpting
• Chopping
• Quadrant removal
• Epinucleus removal
• Cortex aspiration

46. Sculpting
Aspiration flow rate -
Vacuum -
Power -

47. Chopping
Aspiration flow rate -
Vacuum -
Power -

48. Quadrant removal
Aspiration flow rate -
Vacuum -
Power -

49. Take Home message
Using phaco power modulations and judicious use of irrigation
and aspiration
• Possible to reduce phaco time & energy
• Makes surgery safer
• Quicker post operative visual recovery

50. THANK YOU