Phacodynamics

128 PHACODYNAMICS: STEP BY STEP
15 Phacodynamics
A clear understanding of the physical and mechanical
principles that govern phacoemulsification can facilitate
usage of this technique for effective and efficient cataract
removal
It is essential to understand the basic principle of
phacodynamics. This is even more relevant to bimanual
microphaco and is mandatory for the evolution of this
technique.
Phacodynamics is defined as the study of the fundamental
principles of inflow rates, outflow rates, vacuum,
phaco power modulation along with microsurgical
maneuvers with different types and grade of cataract.
A true understanding of this will help in logical setting
of the machine parameters in adaptation to different
surgical techniques.
Even the most modern machine will not give adequate
results as compared to an older machine if the principles
of phacodinamics are not well understood.
Most of the surgeons use their equipment without
really understanding their machines or the basic values
which allow them to operate in great safety.
The most important parameters in microphacoemulsification,
in order to be performed well requires a
good understanding of fluid mechanics.
Basically the dynamics of phaco in both conventional
and microphaco remain the same In microphaco
irrigation is through the side port rather than through
the irrigation slevees (Fig. 15.1).
JEROME JEAN BOVET (SWITZERLAND)
With this one of the major problems encountered is
that not enough fluid is going into the eye through the
side port irrigating chopper. In conventional phaco the
silicon sleeve delivers up to 65 cc/min into the eye
whereas the best irrigating choppers of 20 G cannot
deliver more than 45 cc/min. keeping this basic fact in
mind one has to work around it in term of surgical
manoeuvers, fluid management, ultrasonics and type and
grade of cataract.
Some of the obvious advantages of bimanual microphaco
are decreased incision size, less astigmatism, good
anterior chamber maintenance if we understand the logic
of phacodynamic.
Because irrigation is separated from aspiration the
added advantage theoretically is that all fluids comes in
through one incision and exit through the other.We have
always to take in account some leak from the irrigation
sideport and from the aspiration sideport that’s we
demonstrate in our experimental set-up.
The irrigation fluid in conventional phaco has a
tendency to push the fragments away from the aspiration
tip.
With bimanual microphaco we are improved
followability, we are able to manipulate tissue with the
incoming stream of fluid and we have a much more stable
chamber because all of the fluid is entering through one
side of the eye and leaving through the other side so we
do not have competing currents of fluid aroud the phaco

FIGURE 15.1: Phaco overview
needle. Of course bimanual irrigation and aspiration
systeme of the cortex has been known for a long time to
be advantageous.
The fundamental principle of every cataract operation
is to improve the vision of the patient after surgery of
the cataract and not to diminish it.
The purpose of the stability of the anterior chamber
is to distance the endothelium and the posterior capsule
from the tip of the probe.
Consequently, in order to avoid any lesion of the
corneal endothelium, the consequence of which is
considerable corneal oedema with a risk of the need to
perform a graft, it is imperative to control the stability
and depth of the anterior chamber.
We must always bear in mind that the principal cause
of corneal grafts is the cataract operation.
The most important heading in phacodynamic that
will be discuss below are:
• Fluidic
• Surge
Phacoemulsification is a cataract surgery in a close
chamber, in a such close chamber ,one must monitor the
inflow (irrigation), the outflow (aspiration) and the leak.
There are three components of fluidics.
Irrigation
PHACODYNAMICS 129
For most machines irrigation is passive, i.e. it is determined
by the height of the perfusion and the diameter of
the tube. Most of these machines do not possess a
pressure control or a control of the flow rate of the liquid
entering the eye. Such a control would make it possible
to prevent the collapse of the anterior chamber. This is
the weak point of all of the phacoemulsification machines
and the bimanual microphaco technique.
There are two ways of increasing the flow rate of the
liquid in the anterior chamber:
• By increasing the pressure
Many authors have described theirs own methods to
increase the flow by increasing the pressure everybody
have forget the Poiseuilles law increasing the pressure
increase also the pressure inside the eye and affect the
endothelium
• By increasing the diameter of the perfusion probe
utilising a Duet handpieces design by Larry.Lacks of
Microsurgical technology in which the chopping
lumen of a 19 G tip deliver at least 60cc/min with a
pressure of 33 mm Hg
• An other way to increase inflow volume is to add an
anterior chamber maintener as has been described

130 PHACODYNAMICS: STEP BY STEP
by Michael Blumenthal, this device may be use in
addition to or instead of an irrigating second instrument,altough
it involves a third incision for access
to the anterior chamber.
Aspiration
outflow Rate
Outflow rate is defined as the volume of fluid by unit
that exit the anterior chamber that governs the speed of
the procedure and the danger to aspirated the iris or the
posterior capsule
Vacuum is what grips the nucleus which is occluding
the phacotip, this grip allow to decrease ultrasound and
aids chopping
Leak
In a conventional phaco the leak is a composant of the
surge and the instability of the anterior chamber. In a
bimanual microphaco with 19 G irrigation needle (that
mean at least a 60 cc/min of irrigation). The controled
leak is to cool done the phacotip without induce an
instability of the anterior chamber (Fig. 15.2).
The inflow rate has to be higher than the outflow
rate even with the maximum of vacuum with every type
of pump to avoid the surge.
FIGURE 15.2: Aspiration-irrigation leak: Microbimanual 19 G
FIGURE 15.3: Surge: Vacuum with a peristaltic pump
Surge
This phenomenon is produced when the phaco tip is
occluded by nuclear masses. The increase in the negative
pressure occurs up to the limit values that have been
predetermined. The greater the negative pressure and the
longer the time it is maintained, the larger will be the
volume of liquid to be replaced along the length of the
tubes at the time of the decompression. The vacuum will
be propagated up to the anterior chamber leading to its
collapse (Fig. 15.3).
The best way to avoid the problem is to increase the
flow rate upstream of the anterior chamber. In the case
of bimanual surgery, it is necessary to increase the
diameter of the irrigation probe to 19 G tip.
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