phacodynamics

1. PHACOEMULSIFICATION
PART -II
BY- DR. PRIYANKA RAJ

2. FLUIDICS
• The fluidics of the machine refers to the integrated functions
performed by infusion and aspiration systems by which a stable AC is
maintained.
• It consists of :
1. Infusion system
2. Aspiration System

3. Concept of Fluidics
• The inflow of fluid must be greater than the outflow of fluid
INFLOW > OUTFLOW
BSS ASPIRATED FLUID via phaco probe
LEAKAGE through incision
• By keeping a constant infusion pressure and limiting the outflow
• If outflow > inflow  surge  cause chamber instability  collapse of the eye and
aspiration of the posterior capsule.

4. Infusion System
1. Bottle height provides the gradient for
flow.
2. Tubing  run through a pinch valve
which is controlled by the foot pedal.
• Bottle height 3 ± 1 ft maintains a safe
IOP with sufficient fluid entering the eye.
• In addition, when the machine flow rate is
increased, increased fluid evacuation from
the anterior chamber requires increased
inflow to maintain the steady-state system.
• Therefore, when the machine flow rate is
increased, the bottle height should also be
increased.
• Raising the bottle height too much can
have undesirable effects due to repeated
iris prolapse, especially if the pupil is small
and wound is large.

5. Aspiration System
• The two functions of the aspiration system
 lavage of the anterior chamber governed by the flow rate
 creation of a hold for emulsification or crushing of the nucleus by vacuum generated by
the system
• Therefore there are two types of aspiration systems (pumps):

6. PUMPS
Flow pumps
• AFR and vacuum limit are set by
surgeon
• AFR is maintained while vacuum varies
with fluidic resistance (occlusion of tip)
up to the maximum set limit
1. Peristaltic pumps
2. Scroll pumps
Vacuum pumps
• Surgeon controls the vacuum
1. Venturi pumps
2. Diaphragmatic pumps
3. Rotary vane pumps

7. Flow rate (FR)
• Volume of fluid removed from eye per minute.
• Flow rate therefore helps in bringing the material towards the tip
• Measured in cc/min.
• Determined by pump speed, compliance, venting and tubing
• With a peristaltic pump, flow is determined by the speed of the pump.
• Normally between 20-36 cc/min
• Low FR
 when working near the capsule
 Slow surgery and flowability to the tip is decreased
• High FR 
 swifter removal of lens matter with less power
 Surgery will be uncontrolled and cataract pieces may slip away as the rollers may
slip from the tubing decreasing the effectiveness

8. Vacuum
• Vacuum level is the difference in pressure between atmospheric pressure and the
pressure inside the aspiration tubing.
• This is a negative suction pressure that is created by the pump.

9. PERISTALTIC SYSTEM
• Aspiration is generated by a series of
rollers at regular intervals on a
rotating cylinder.
• Appreciable vacuum values reached
only when the tip of handpiece is
occluded.
• As the tip is occluded, vacuum
builds, the rollers slow down, and
the outflow level decreases.
• On complete occlusion, the rollers
come to a stop, and the vacuum is at
its highest level.

10. Advantages of Peristaltic Pump
• In this system, vacuum will be built up
only after the tip is occluded.
• There is a large safety margin in this
pump as it is slower in building up
vacuum.
• There is no inadvertent pull on the
ocular structure since vacuum builds up
only on occlusion
• Flow rate and vacuum can be set
independently in a peristaltic system.
Disadvantages of Peristaltic
Pump
• The vacuum build-up is in a stair-
stepped pattern causing more
pulsations in the anterior chamber.
• The vacuum build-up is directly
related to the density of occlusion
which in turn would depend upon
the bevel angle of the titanium tip.
• One has to mechanically approach
the nuclear or cortical matter to first
achieve occlusion for vacuum to build
up in order to aspirate the tissue.

11. SCROLL PUMP
• Contains two circular elements: Mobile &
Fixed.
• The mobile element has a mound while
the fixed element has a channel and
there is a space between the two.
• Its action is split in three phases:
• Filling Phase: the liquid aspirated
through an orifice on the fixed
element enters the space between
mound and channel.
• Isolation Phase: the mobile element
proceeds along its orbit and
displaces the space and the liquid it
contains, so that they are no longer
in communication with the entrance
orifice.
• Emptying Phase: the bag of liquid
comes into communication with the
exit orifice and flows to the outside.

12. • Advantages of a scroll pump:
• The compliance, hence the surge
is reduced.
• No problems of leakage along the
aspiration line.
• Can work either in a “flow” or
“vacuum” dominant mode.

13. VENTURI SYSTEM
• Driven by the compressed gas which
generates vacuum.
• The production of vacuum is related
to the flow of gas, regulated by a
valve.
• The vacuum built up is
instantaneous and does not depend
on the occlusion of the aspirating
port.
• Venturi Effect: The flow of gas
creates vacuum proportional to the
rate of flow of the gas

14. Advantages of Venturi Pump
• The vacuum build-up is linear.
• There is a consistent increase in the
vacuum from zero to the preset level on
depressing the foot switch.
• Nuclear and cortical material can be
attracted towards the probe on
depressing the foot pedal.
Disadvantages of Venturi Pump
• least safety margin.
• The incidence of iris trauma and
posterior capsular rents have been
reported to be much higher
• In the venturi system only the level
of vacuum can be controlled and not
the flow rate.
• The flow rate is a fixed fraction of
the vacuum. However, the change in
vacuum level doesn’t always lead to
a proportionate change in the flow
rate since port size and resistance in
the passage also modify flow rate.

15. Diaphragmatic pump
• A flexible membrane within cassette
is used to generate the vacuum.
• It has a slow rise time but vacuum
builds up in exponential manner
after occlusion.
• This makes it unsafe, however lens
material can be aspirated without
having to mechanically approach it

16. Advantages of Diaphragm pump
• The flow rate and aspiration rate are
faster
• Greater control with the diaphragm
pump during posterior segment surgery
Disadvantages of Diaphragm
pump
• Lesser safety margin as it is a faster
pump.
• Foot –pedal depression does not have a
very good graded control over vacuum
build up.
• Vacuum build up reaches preset level
even without occlusion leading to
inadvertent pull on ocular tissue
resulting in a higher complication rate.

17. Rotatory Vane Pump
• Essential element is a rotor fitted
eccentrically inside a cylinder.
• A series of lamellae are suspended inside
the rotor & they run forwards and
backwards.
• Centrifugal force pushes the lamellae
outward and traps a certain amount of air.
• Air is compressed and released through a
specific outlet.
• This movement is exploited to evacuate air
from the drainage tank, inside of which
negative pressure is created which is
subsequently transmitted to the aspiration
line.

18. • PUMP IS AFFECTED BY
1. Flow rate
2. Vacuum and occlusion
3. Venting
4. Reflux

19. Rise Time (RT)
• The rise time is the time taken by machine to
reach maximum preset vacuum after occlusion
has been achieved.
• Speed with which the maximum value of
vacuum is reached, once the aspiration port is
occluded
• Venturi systemRT is fast, linear and
dependent upon the highest preset vacuum.
• Peristaltic pumpRT depends on the FR of the
machine.
• The higher the FR, the lesser the RT though the
relationship is not absolutely linear.
• Rise time ∝ AFR ∝ Pump speed

20. ZONES OF ASPIRATION
• Central safe zone (CSZ) - central area within the
capsulorhexis margin
• Peripheral unsafe zone (PUSZ) - capsular fornices
and angle of anterior chamber
SMALLER CSZ LARGER CSZ
Hypermetropia Myopes
Narrow pupil Zonular stress syndromes
Small capsulorrhexis Vitrectomized eyes

21. Followability
• The tendency of the nuclear fragments/cortical matter to come into the tip.
• The positive pressure due to the infusion and the negative pressure created
by the aspiration pump are responsible for the creation of a pressure
gradient at the tip.
• This in turn leads to eddy currents from the infusion orifice to the phaco
tip.
• The area encompassed by these eddy currents is known as the zone of
followability.
• There are some areas of no followability. Here the positive pressure from
the infusion pushes the pieces out of the eye.

22. Zones of followability
• Zone of good (highest) followability - area
around the phaco tip
• Zone of poor followability - near angle of
AC and capsular fornices
• Zone of no followability - area around main
and side port incisions and near dome of
cornea
POOR
GOOD
NO

23. Surge
• Sudden withdrawal of fluid from AC after occlusion breaks is called
surge.
• extra fluid aspiration when occluded phaco tip with built up vacuum
is suddenly dis-occluded
• Occlusion High vacuumOcclusion broken Fluid gushes into
Phaco tipExceeds inflow capacity of irrigation lineSHALLOW AC

24. • EFFECTS OF SURGE
1. Anterior chamber collapse
2. Damage to iris and cornea
3. Posterior capsular rupture
• FACTORS CONTRIBUTING TO SURGE
1. Compliance of tube
2. High vacuum level
3. High AFR
• Critical limit: Upper limit of AFR at which AC remains stable for a fixed
bottle height and fluid leakage
At critical limit
AFR + Wound leakage = Infusion

25. CONTROL OF SURGE
• Improvisation in the phaco machine
• Surgeon’s measures to control surge

26. Improvisation in the phaco machine
• Reduce compliance
1. Biocompliant tubing - more compliant tubing at point of pump rollers and less
compliant tubing between pump and handpiece (Alcon Legacy)
2. Sealed rigid cassettes with stiff polymer membrane (Fluid Management
System, Alcon Infiniti)
3. Software control algorithms to compensate for leakage (Advanced Flow System,
Bausch and Lomb) Increase inflow
• High infusion phaco sleeve (provides more inflow potential to keep AC formed)
• Second irrigation bottle
• Pressure transducer and logarithmically control of pump
Logarithmically decrease the pump speed as vacuum approaches maximum preset
When pressure transducer senses an occlusion break, there is delay in starting the
pump by a second or so Speed is increased again logarithmically rather than
abruptly tip

27. • ABS tip
 The tip has a 0.175 mm hole drilled in the shaft of the phaco needle.
 When occlusion occurs at the tip, fluid flows into this hole.
 The amount of flow depends on the vacuum and flow settings.
 Because some flow always exists, in reality there is never complete
occlusion.
 This modification must be used with the high vacuum tubing or it does not
function properly.

28. • Venting
• Breaking of vacuum.
• The machine has a sensor which
detects occlusion break and releases
fluid into the system to fill the
volume of the reexpanding tubing.
• This prevents fluid being drawn out
of the AC.
 AIR VENTING
 FLUID VENTING
• Fluid-venting is superior to air-
venting - air is compressible,
increases compliance of tubing

29. AIR FLUID
• high time delays for detecting
vacuum change
• low time delays detection for
vacuum change
• Responds slowly to compensate
vacuum surge
• Responds faster to compensate
vacuum surge
• Air venting increases compliance
of the system, which increases
surge
• Compliance is less in a system
with fluid vents with lesser surge
as a result

30. • Cruise control
 Disposable flow restrictor - attached between phaco handpiece and
aspiration tubing
 Internal diameter = 0.3 mm
 Placed behind a mesh filter that traps emulsified nucleus to prevent the
flow restrictor from getting clogged
 Allows use of higher flow rates and vacuums
• Differential AFR and vacuum settings before and after occlusion
 Immediately after the occlusion breaks, the AFR and vacuum are
decreased for a short period to prevent the surge
 After the nuclear piece has been aspirated, the settings revert back to
higher values to allow a better grip of the next nuclear piece

31. Vacuum Surge Suppressor
• As vacuum increases, the VSS constricts, thereby limiting fluid
outflow and maintaining a deep and stable anterior chamber

32. Surgeon’s Control of Surge
• More resistive phaco needle (Micro-flow or Flare tip)
• More resistive tubing set (Alcon Max Vac)
• Augment inflow by using high infusion sleeves (Alcon) or anterior chamber
maintainer (ACM)
• Proper wound construction Leaky wound disturbs equilibrium of AC - even
small amount of fluid withdrawn on break of occlusion can cause surge
Tight wound or long tunnel reduces inflow & disturbs equilibrium of inflow
vs. outflow - surge
• Increase bottle height
• Lower vacuum setting
• Decrease AFR

33. • Partial-Occlusion Phacoemulsification
 In partial-occlusion phaco, micro-pulse phaco is used to avoid total
occlusion to prevent surge.
 The nuclear fragment is brought close to the phaco tip with a 4-millisecond
period of aspiration until the fragment partially occludes it.
 With the onset of a 4-millisecond burst of phaco energy, the fragment is
emulsified before it can totally occlude the phaco tip.
 Therefore, flow never falls to zero and vacuum never builds to maximum,
thus preventing surge.
• Good foot control
• Partial occlusion of tip with another nuclear fragment before the occlusion
breaks and the occluding piece is aspirated
• Viscoelastic substances - decrease effective flow rate, as viscous fluid
increases resistance and does not flow out easily

34. • Reflux
• creates positive pressure in aspiration line to invert the flow
and release the material that has already been aspirated.
• This is achieved by:
 Inverting the direction of pump.
 Blocking the infusion line and opening a 2nd infusion line.
• Carries increased risk of contamination.

37. CENTRAL
SCULPTING
AND TRENCH
DIGGING
CHOPPING QUADRANT
REMOVAL
EPINUCLEUS
REMOVAL
CORTEX
ASPIRATION
AFR 20-25 cc/min 25-30 cc/min 25-30 cc/min 30-35 cc/min 25-30 cc/min
VACUUM 0-15 mm Hg 100-200 mmHg 100 mm Hg 70-100 mmHg 400 mm Hg
POWER 60-70% 50-60% 50% 10%
BOTTLE
HEIGHT
65 cms above
eye level
75 cms above eye
leve
65cms above
eye level
75 cms above eye
level
65 cms above eye
level
TIP 30-45 degrees 0-30 degrees 30 degrees 30 degrees
OR- 0.5 mm I/A
tip for epinucleus
removal
0.3 mm I/A tip

38. THANK YOU