1. Phacodynamics
Nakhleh E. Abu-Yaghi, MD

2. Phacodynamics Studying the fundamentals of : Inflow rates
Outflow rates
Vacuum
Phacopower modulation
Micorsurgical maneuvers in dealing with different types/grades of cataract

3. Charles Kelman ( )

4. Devised the cryo-probe (1962)
Introduced extracapsular cataract extraction
Introduced phacoemulsification (1967)
Most influential IOL designer (1975)
Lasker award (highest award in medical science)

6. Overview
The machine
The ultrasound energy
The fluidics

7. Understanding the machine

8. The phaco machine The console The foot pedal The hand piece
The connections

9. The console Computer controlling functions Setting and parameters
Display foot pedal signals and input information and display modes

10. The hand piece Tip Sleeve Body
3 ports (Aspiration, irrigation, Ultrasound)

11. The body contains piezoelectric crystals (acting as a transducer) that contract or expand converting electric energy into mechanical energy causing movement of the tip.
This is temperature dependent (Curie temperature)

12. Silicone sleeve for phaco tip:
Insulates corneal wound and provides fluidic pathway for irrigation
Infusion flows between the tip and sleeve and exits from two openings perpendicular to the tip bevel

13. Tip Outer diameter: wound size (1.1) (0.9- microtip)
Inner diameter: aspiration flow rate (0.9 mm) (0.7mm- microtip) G?

14. The tip is from titanium
Angle of standard tip is from 0-60 degrees
The less the angle: the better the holding but the poorer the cutting action
Tip selection depends on hardness of nucleus and technique
30 degree tip is a good compromise between trenching and chopping
End configurations: round, ellipsoid, bent or flared
Occludability: is the tendency of the tip to get occluded
The smaller the tip angle the higher the occludability
Your garden hose is zero angle

15. Variations on the tips
Microseal, microflow tips (to reduce incisional burns)
Kelman and Kobra tips (to improve cutting efficiency)

16. I/A port
Straight
45 degrees
90 degrees

17. Foot pedal

18. Excursions and dentations
Feel the resistance at dentations/positions (mode changes)
Tactile feedback
Auditory feedback

19. Excursion I Irrigation is on No gradient in this step
Going back to excursion 1 and stopping at D1 prevents collapse of AC
Nuclear rotation/manipulation of nuclear fragments, require a formed AC without aspiration

20. Excursion IA A linear control of vacuum and flow
Top of foot position 2 provides less vacuum or flow than middle or bottom
The vacuum and flow effect is created by a peristaltic or venturi pump
Sources of fluid outflow during phaco:
1. Aspiration tube
2. Leakage from incisions

21. Excursion IAP IAP0= phaco energy is zero
IAP max= energy at maximum preset
Phaco power is linear in surgeon and pulse mode
In panel or burst mode, maximum preset energy is delivered
In IAP, irrigation is on and aspiration is at maximum preset

22. Foot gradient (FG)
The excursion of foot pedal in mm to produce unit power of phaco energy
If total foot excursion (from IAP0 to IAPmax is 10 cm (100mm),and the maximum preset phaco energy is 100%, hence FG:
FG= 100mm/100=1 unit power per 1mm of excursion
If maximum preset phaco is changed to 50%:
FG=100/50= 1unit power per 2mm of excursion more FG more foot control
Phaco maximum should be set at the minimum power required for that particular step

23. Side kick function
Reflux function
Not a linear function

24. Continuous infusion
Foot is off pedal but irrigation is still on

25. Fluidics

26. Main concepts
Maintain space (prevent collapse of AC by balancing inflow and outflow rates)
Create currents (bring cataract pieces to phaco probe and remove them)
Keep it cool (prevent thermal injury)

27. Fluidics parameters Mechanical Infusion Aspiration and leakage Vacuum
Clinical
Incision size
Vitreous pressure

28. Inflow/infusion BSS flows from bottle to irrigation port
Infusion is passive by gravity
Bottle height above patient creates a pressure gradient
Approximately 11 mmHg (above ambient atmospheric pressure produced intraocularly) for every 15 cm of bottle height above the patients eye

29. outflow Aspiration and leakage (ml/min)
Affected by diameter of phaco tip, tubing and vacuum
Wound leakage

30. Aspiration flow rate (AFR)
Measured in ml/min
Is determined by speed of pump
As flow increases :
current in AC increases: this determines how well particulate matter is attracted to the tip
Optimum rate is cc/min

31. Followability
Tendency for structures within the AC to move towards the phaco tip
It is a function of AFR
Positive pressure of infusion and negative pressure of aspiration create pressure gradient at the tip that leads to Eddy currents from the infusion orifice to the phaco tip. This area is known as zone of followability

32. Vacuum Create holding power to keep material in phaco tip
Created by a pump:
Peristaltic pump: vacuum develops slowly
Venturi pump: rapid rise in vacuum
Trenching: low to no vacuum
Segment removal: moderate vaccum
Chop: high vacuum

33. Holdability
Ability of the phaco tip to hold onto the material occluding its tip
It is a function of Vacuum
1st generation machines: max vacuum 120mmHg
2nd generation machines: max vacuum 250mmHg
3rd generation vacuum up to 650mmHg

34. AFR Vs Vacuum
AFR is the rate at which fluid and emulsified nuclear particles are removed from the eye when the phaco tip is not occluded
Vacuum is the negative pressure that builds up when the tip is occluded
They are separate components that work hand in hand during outflow
At low flow rates: gradual build up of vacuum (safe but slow)
At high flow rates: faster vacuum build up (but less safe)

35. Pump Main function is to move fluid through the aspiration tubing
Pump settings control rate of movement of fluid
Peristaltic pump (Flow based)
Allows independent control of aspiration rate and vacuum level
Venturi pump (Vacuum based)
Allows direct control of only vacuum level. Flow is dependent on vacuum level setting

36. Peristaltic pump

37. Rollers move
Compress the outflow tubing in a peristaltic manner
“milking” action on fluid column
The machine can control the flow level (flow based)
A preset vacuum level is achieved once there is occlusion of outflow line (at low speed of rotation)
By increasing the flow rate, vacuum is produced in the aspiration line without occlusion
To build up vacuum without occlusion, you need to increase the flow rate (flow based pump)

38. Venturi pump
Vacuum is created within a rigid drainage cassette connected to the aspiration tubing
No milking of the aspiration line phaco tubing can be made rigid with low compliance
Main advatage is the ability to create the preset vacuum level without occlusion of the phaco tip needle
As the surgeon depresses the pedal, the preset vacuum is immediately created (vacuum based)
Venturi and diaphragm pumps have inherently higher flow rates high build up of vacuum

39. Only the vacuum can be controlled
Only the vacuum can be controlled. The flow rate is fixed and is a function of the vacuum
Vacuum is directly transmitted from a closed chamber to the tip ensuring a better followability

40. Peristaltic pump Venturi pump
Flow based vacuum based
Vacuum created on occlusion instantanous
of phaco tip
Flow constant until occlusion Flow varies with vacuum
Drains into a soft bag Drains into a rigid cassette

41. The slow flow rate is useful for beginners (high safety margin in case of sudden capsule occlusion in the port)
Slow rise time allows time to come back to position 1 or even relax
At a moderately high flow rate it is a good compromise between safety and efficiency

42. Vacuum rise time
The amount of time taken by the system to reach maximum vacuum setting once occlusion takes place
Peristaltic pumps have a slower rise time (can be made faster by increasing the rotation of the wheel)

43. Other pump modalities Concentrix (millennium)
(flow mode and Vacuum mode)
Rotary vane- Chiron’s catalyst
(vacuum based)
Diaphragm

45. Clinical Parameters Incision size: affects: Leakage Infusion
AC stability
Depends on external diameter of phaco tip
Small incision causes infusion flow obstruction: squeezing of infusion sleeve AC instability and build up of heat at the tip
Big incision more leakage and more astigmatism

46. Vitreous pressure
Patient dependent
Affects AC depth during phaco
Compensate with increased bottle height

47. AC stability Inflow=outflow
AC pressure has to be greater than vitreous pressure and atmospheric pressure (positive IOP)
Under pressurization : collapse of AC forward movement of iris and lens and posterior capsule  rupture
One indicator of AC pressure imbalance is bouncing movement of iris and lens
Over pressurization can lead to deepening of AC and zonular stress

48. Compliance and Surge
Property or ability of the tubing to collapse or deform under pressure
High compliance means more surge
Surge is a temporary fluid imbalance:
When the phaco tip is occluded negative pressure builds in the tubing collapse of the aspiration tube occlusion breaks after eating the nucleus piece  tube returns to original shape surge (sudden sucking effect of fluid with AC shallowing (until infusion fluid compensates)

49. Surge
Here the outflow fluid from the eye exceeds the inflow fluid (even for a split second)

50. How to reduce surge? Lower levels of flow and vacuum
Rigid (low compliance) aspiration tubing
Venting
Increased bottle height
Reduce tip size
Aspiration bypass port (ABS)

51. Venting
The machine has a sensor that detects occlusion breaks and releases fluid/air into the system fill the volume for the re-expanding tubing, preventing outflow of fluid from the AC
(vent valve senses a maximum vacuum level)
Fluid venting is better (less surge) because air bubbles contract more when expansion of tubing reverses
Fluid expands less and contracts less than air

52. Aspiration bypass port
A small hole in the metal part of phaco hand piece that functions when the tip is occluded. It also has a cooling effect

53. Central safe zone
A conceptual area within the capsulorhexis margin bounded vertically by the cornea on top and the posterior capsule from the bottom
In contrast to the peripheral unsafe zone (corneal curvature is in play)

54. Ultrasound power

55. Ultrasound power
It is the conversion of electrical energy into mechanical one by ultrasound vibrations of the Quartz crystal in the transducer/ vibrator of the hand piece
Depends on frequency (29-60Hz) and Stroke length (2-6mm)
The higher the frequency the more the cutting action and heat
The longer the stroke length the greater the action and the heat

56. PHACO POWER= STROKE LENGTH X FREQUENCY
Frequency: number of longitudinal vibrations per second
Stroke length: distance the tip displaces in the axial direction during phaco
Phaco power is indicated as a percentage: at 100% the stroke length is the maximum permissible for the machine. When the power is decreased, the stroke length decreases (frequency is fixed per machine)

57. Piezoelectric crystals
Converting electrical energy to mechanical energy

58. Mechanism of phacoemulsification
The Jackhammer effect: physical striking of needle against nucleus by to and fro movement (transverse or elliptical)
Cavitation effect: formation of micro-bubbles which at moment of implosion create 7204 C temperature and shock wave of 75000psi which can be directed away from cornea according to angle of tip.

60. Phaco power variables
Too little power: pushes nucleus instead of carving it zonular stress and extension of posterior capsular (PC)tears
Too much power: pierces nucleus rent in PC
Safest phaco is with appropriate power not with low power
This depends on :
Nuclear density
Amount of tip that is engaged
Linear velocity of tip during phaco

61. Control and delivery of power
Linear (surgeon mode): progressive pressing of foot pedal control leads to gradual rise in phaco power from 0 to preset level
Panel mode: parameter reaches the preset panel maximum on pressing the foot pedal without any linear pedal control
(useful in very hard cataract with uniformly hard nucleus)

63. Phaco mode
Continuous: power is delivered constantly and is either linear or panel controlled
(more ultrasound power- good for sculpting)
Pulse mode: power is delivered as pulses of energy followed by a gap of equal duration of pulse free period
(there is a pause in ultrasound)
(duty cycle concept)
The more the pedal is pressed, the higher the power in linear mode
Burst mode: maximum power is delivered at intervals which vary with amount of depression of foot pedal
(burst width is less the more the surgeon steps on the pedal, full pedal gives continuous burst i.e zero burst width)

65. Q
Will phaco energy increase by using more pulses per second?

67. No
Each short phaco pulse is followed by a short phaco-off time

68. Duration of on and off time can be set by operator and is called duty cycle
This can reduce heat generation and increase followability
This is all programmable and affects smoothness and precision of power delivery

69. Duty cycle Phaco on time/ phaco on time +phaco off time
Higher duty cycle results in better cutting power but increased heat generation
Lower duty cycle allows more fluidic aspiration of nuclear fragments while minimizing heat and phaco power

70. tips Pulse mode: Holding the lens Chopping
Bringing material to central area
More pulses per second: sculpting and removing quadrants

71. Burst
Wide burst time: epinucleaus (when you want to hold lens material you need an off phaco mode)
Narrower: quadrants
Full burst: sculpting

72. Different settings Trenching (hi power, low vacuum)
Chopping (hi vacuum, moderate power)
Quadrant removal (hi vacuum, moderate power)
Epinucleus removal (high vacuum, no or low phaco)
Cortex aspiration (high vacuum)

73. Final words Understand your machine to become a more efficient driver
Proper knowledge harnesses hidden advantages
Check your machine

75. Basic principles?
There are none!