Ординатура / Офтальмология / Английские материалы / The Art and the Science of Cataract Surgery_Boyd, Barraquer_2000
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T H E A R T A N D THE S C I E N C E OF C ATA R A C T S U R G E R Y
need to convert to ECCE, it is important that he perform two relaxing incisions radially in the anterior capsule at 10 and 12 o'clock following the CCC, in order to facilitate the removal of the complete nucleus with a planned manual extracapsular. If these relaxing incisions in the anterior capsule are not done, the surgeon may confront serious problems in removing the nucleus (Fig. 37).
Hydrodissection
Once the surgeon is able to perform a circularcontinuouscapsulorhexis(CCC)without problems, he is ready to go into the next step, which is hydrodissection (Figs. 46, 47, 48). This step should not be undertaken before masteringthecapsulorhexis.Ifnot, tears inthe anterior capsule may extend towards the equator when performing the injection with fluid to do the hydrodissection. The surgeon should haveclearlyinmindtheanatomyofthecrystalline lens and what is it that he is after with hydrodissection (Fig. 1). With this maneuver, by using waves of liquid (Figs. 46, 47, 48) we wish to separate the anterior and posterior
capsules from the cortex (Figs. 46, 47) and the nucleus from the epinucleus (Fig. 48). When this is achieved, the nucleus is liberated so that it will be free for the ensuing maneuvers of rotation, fracture and emulsification, all of which will come as the next steps in the procedure (Figs. 55, 56). As long as the surgeon is not sure that the nucleus has been freed of its attachments through the hydrodissectionandwillrotateeasily, heshould not proceed to try to rotate it mechanically because this may lead to rupture of the zonules. Also, if the nucleus is not separated from the cortex by hydrodissection (Fig. 48), the surgeon should not proceed to apply the phaco ultrasound to the nucleus because he or she may well meet with complications by extending the effects of ultrasound not only to the nucleusbutperipherallytothecortex. Thiscan lead to the feared rupture of the posterior capsule. Instead, the surgeon should decide to convert to a ECCE. Although Fig. 47 shows hydrodissection through a corneal tunnel (surgeon's view), keep in mind that all maneuvers during the transition are done with a limbalincision, as shown in Figs. 40 A, 41, 42.
Figure46:Hydrodissection-Stage1 -SeparationoftheAnteriorandPos- terior Capsule from the Cortex - Cross Section View
A 25 gauge cannula is placed through the continuous circular capsulorhexis under the anterior lens capsule (A). Fluid is infused as shown by the pink arrows in order to separate the anterior capsule from the cortex. A wave of fluid shown by the pink arrows and identified as (W) extendsalongtheposteriorcapsule,separating the posterior capsule (P) from cortex (C).
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Figure 48 (below right): Hydrodissection - Stage 2 - Separation of Nucleus and Epinucleus and the Cortex
In this stage, the cannula is advanced beneath the cortex (C) and the infusion with BSS isstartedinorder toseparatethenucleus
(N) from the epinucleus (E). The pink arrows betweenthesetwostructures,nucleus(N)and epinucleus (E), show the flow of fluid. The gold "ring" of fluid separating the nucleus fromtheepinucleusishereidentifiedas(GR).
Figure 47 (above left): Hydrodissection of the Lens Capsule from the Cortex During Phacoemulsification - Surgeon's View
This is a surgeon's view of what is shown in figure 46 in cross section view. Following circular curvilinear anterior capsulorhexis,acannula(C)isinsertedintothe anterior chamber. The cannula tip is placed between the anterior capsule and the lens cortex at the various locations shown in the ghost views. BSS is injected at these locations (arrows) to separate the capsule from the cortex as showninFig.46.Theresultantfluidwaves(W) can be seen against the red reflex. These waves continue posteriorly to separate the posterior capsule from the cortex.
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THE MECHANISM OF THE
PHACO MACHINE
T H E A R T A N D THE S C I E N C E OF C ATA R A C T S U R G E R Y
patients. It must be achieved first in an experimental laboratory before attempting to operateonhumanswithseeingeyes,asemphasized by Centurion.
Getting Ready to Use Phaco During Transition
We have already emphasized the crucial importance of understanding how the phaco machine works in order for the surgeon to performphacoemulsificationsuccessfully. This is a task every cataract surgeon must undertake when contemplating the use of phaco in his/her
Figure 49-A: The Principles of How the
Phaco Machine Works
Thisconceptualviewshowsthethree main elements of most phaco systems. (1) The irrigation (red): Intraocular pressure is maintained and irrigation is provided by the bottleofbalancedsaltsolution(B)connected via tubing to the phaco handpiece (F). It is controlled by the surgeon. Irrigation enters the eye via an infusion port (H) located on the outersleeveofthebi-tubephacoprobe. Height of the bottle above the eye is used to control the inflow pressure. (2) Aspiration (blue):
(I) enters through the tip of the phaco probe, passes within the inner tube of the probe, travels through the aspiration tubing and is controlled by the surgeon by way of a variable speed pump (J). The peristaltic type pumpisbasicallyamotorizedwheelexerting rotating external pressure on a portion of the flexible aspiration line which physically forces fluid through the tubing. Varying the speed of the rotating pump controls rate of aspiration. Aspirated fluid passes to a drain
(L). (3) Ultrasonic energy (green) is provided to the probe tip via a connection (M) to the unit. All three of these main phaco functions are under control of the surgeon by way of a multi-control foot pedal (N).
Optimal Use of the Phaco
Machine
The Rationale Behind It -
Main Functions
Edgardo Carreño, M.D., one of South America's top phaco surgeons and teacher, describes the three main functions of the
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Figure 49-B (previa Fig. 1-1, p.3 libro Seibel on Phacodynamics): The Rationale Behind the Phaco Machine
In this diagramatic figure from Seibel's excellent book on Phacodynamics, you can clearly observe the mechanical workings and rationale behind the function of the phaco machine, as explained in Fig. 49-A, its figure legend and the text. The ultrasound energy coming from the handpiece emulsifies the cataract (Fig. 50-B) so that a 10 mm cataract may be removed by the aspiration port and line through a 3 mm or smaller incision. A fluidic circuit counteracts the heat build up caused by the ultrasonic needle and removes the fragmented or "emulsified" lens material via the aspiration port and aspiration line while maintaining the anterior chamber. The fluid is supplied via the irrigation port and line by the elevated irrigatingbottle,whichiscontrolledbythesurgeonelevatingitorloweringit. Thisfluidcircuitisregulatedbytheaspiration pump. (After Seibel, B.S., Phacodynamics, 3rd Ed., 1999, p. 3, Slack, as modified by HIGHLIGHTS).
phaco machine: 1) irrigation; 2) aspiration; and 3) fragmentation of nucleus. This is clearly shown in Figs. 49-A and 49-B. Irrigation is done with the irrigation bottle, aspiration with the aspiration pump and fragmentation with ultrasonic energy through the titanium needle present in the
phaco tip of the hand piece (Figs. 50-A and 50-B). Many types of phaco tip shapes have been created to more efficiently handle nuclear extraction, as shown in Fig. 51. A command pedal, which is controlled by the surgeon’s foot, guides the machine into the following four positions: 0 (zero) which is at
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Figure 50 A (above left): The Phaco Handpiece
This diagramatic figure clearly shows the different components of the phacoemulsification handpiece. The phaco needle is manufactured with variousdegreesofbevel,angulationsandshapes,as shown in Fig. 51. The probe tip is hollow with the distal opening functioning as the aspiration port. Irrigation fluid flows through two ports located 180º apart on the silicone irrigation sleeve. The irrigation sleeve hub shown here in blue threads the sleeve onto the handpiece body outer casing. The phaconeedlethreadsdirectlyintotheinternalmechanism of the handpiece containing the ultrasound generator. The ultrasound power oscillates between 25.000 and 60.000 times a second (Hz). This energy is transmitted along the handpiece into the phaco needle in such a way that the primary oscillation is axial.(After Seibel, B.S., Phacodynamics, 3rd Ed., 1999, p. 99, Slack, as modified by HIGHLIGHTS).
Figure50B(belowright): MechanismofAction
of Phacoemulsification Probe Tip
Phacoemulsification involves the use of a probe tip (T) which vibrates very rapidly and acts as a jackhammer and emits heat to break up lens material (L) into fragments (F). Fragments are aspirated from the eye via the center of this probe tip which is hollow (black arrow). An outer sleeve
(S) provides for passage of infusion fluid. Fluid enters the eye (white arrow) via infusion ports (P) in this outer sleeve. The infusion fluid constantly replaces any aspirate removed from the eye to maintain a stable intraocular pressure.
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Figure 51: New Phaco Tips
Many types of phaco tip shapes have been created in an attempt to more efficiently handle nuclear extraction. Different types include various degrees of bevel, angulations, and shapes of the tip. Examples include: A-straight round tip, B- 15º bevel, C-30º bevel, D-45º bevel, E-bent 45º tip, F-rectangular tip, G- enlarged bevel tip, and H-another enlarged bevel tip. The beveled tips provide an oval shaped aspiration opening with gradually increasing areas of contact (areas shown in blue) to nuclear material. Angled or bent tips attempt to allow access of the tip to more peripheral locations within the capsular bag.
rest; position 1 for irrigation, position 2 for irrigation-aspiration and position 3 for irrigation, aspiration and phacoemulsification (Figs. 52 and 53).
The first function (irrigation) controlled by the foot pedal is provided by a bottle with BSS. The liquid flows by gravity. The amount of liquid that reaches the anterior
chamber depends on the height of the bottle, the diameter of the tubing and the pressure already existing in the anterior chamber (Figs. 49-A, 49-B, 54). The flow rate into the eye is determined by the balance of the pressure in the tubing - regulated by the height of the bottle, and the back pressure in the anterior chamber. When the two are
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Figure 52 (above left): Basic Phaco Foot
Pedal Functions
The foot pedal controls inflow, outflow, and ultrasonic rates. With the foot pedalintheundepressedposition,theinflow valve is closed, the outflow pump is stationary, and there is no ultrasonic energy being delivered to the phaco tip. With initial depression of the pedal (1), the irrigation line from the raised infusion bottle is opened. Further depression of the pedal (2), starts and gradually increases the flow rate of the aspiration pump to a maximum amount preset by the surgeon. Further depression of the pedal (3) turns on increasing ultrasonic power to the phaco tip for lens fragmentation.
Figure 53 (below right): New Dual Linear-
Lateral Pedal Control
A new pedal control separates the in- flow-outflow and ultrasonic power functions. The inflow (1) - outflow (2) function is controlled by pedal depression, with increasing outflow availability incurred with increasing pedal depression. Inflow will match outflow rates. Increasing ultrasonic power is applied by doinga lateralrotationofthefootpedal(3). The lateral rotation of the foot pedal (3) is shown in the ghost view. Separating these functions allows the surgeon to apply varying amounts of ultrasonic power with varying inflow-outflow rates. With the depression only type pedal, ultrasonic power is only engaged with maximum inflow and outflow. There are phacoemulsificationmaneuverswhenthisisnot desirable. A low inflow-outflow rate, for instance, may be desired when engaging ultrasound.
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equal, there is no flow. If there is leakage or aspiration of fluid from the anterior chamber, the pressure there drops, and fluid in the tubing flows in to restore the pressure in the AC, and, indirectly thereby, the volume. The tubing is purposely made wide enough so that it impedes the flow of the BSS only slightly under normal rates of flow. It does limit maximum flow - during anterior chamber collapse for example, unfortunately, however.
Figure 54: Irrigating Bottle Height Related to Flow Rate - Hydrostatic and Hydrodynamic Stages
Bottle height (C) has the important function of providing constant chamber pressure during all phases of surgery, including during times of sudden changes in outflow rates. Maintenance of safe intraocular pressure is important in both "hydrostatic" (A - no fluid moving within the fluidic circuit) and "hydrodynamic" situations (B - fluid moving within the circuit). A bottle height of 45cm above the eye will provide an approximate 30mmHg of intraocular pressure (I) when no fluid is moving in the circuit (hydrostatic state A) when there is no aspiration taking place and the aspiration pump (E) is off. When the aspiration pump (J-arrows) is turned on, (hydrodynamic state B), the intraocular pressure (M) will go down, for example to 20mmHg, depending on the outflow rate. Arrows depict fluidic inflow (red) and outflow (blue) in the system. This is because the intraocular pressure decreases proportionallyastheflowrateincreases(Bernoulli'sequation).Therefore itisimportantto maintain aconstantIOP,toincreasethebottle height when using a high phaco outflow rate. Likewise, the bottle height should decrease when the aspiration (outflow) rate is decreased. The black arrows on the tube (J) indicates drainage.
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The second function, which is aspiration, is provided by a pump, which creates a difference in pressure between the aspiration line and the anterior chamber. The pumps may be a peristaltic pump, a Venturi pump, a diaphragm pump, a rotary vane pump, or a scroll pump. The peristaltic pump has become the most widely known and used.
Many feel it is safer. Just like inflow, a base level of suction occurs whenever the pump is activated, depending on how hard the pump is working. When there is occlusion of the tip with the foot pedal in the aspiration position (position 2), the pump will continue to pump and crate more and more suction until the material which is provoking the occlusion is aspirated, or until the suction in the tubing reaches the maximum that the surgeon has preset on the control panel (Figs. 59, 60, 61). This latency period before reaching maximum suction level provides a greater security margin allowing the surgeon to take immediate action in case the tip grasps (and sucks in) the iris or the posterior capsule instead of grasping the lens mass. In order to perceive what happens to the fluid dynamics when the phaco tip is not occluded, please see Figs. 57, 58. The reason for limiting the maximum suction pressure is to limit the rush of fluid out of the eye the moment the fragment which occluded the tip is aspirated. This provides the surgeon the opportunity to stop aspiration and avoid collapse of the anterior chamber.
The third function of the phaco machine - the production of ultrasonic vibrations leading to fragmentation of the lens - is carried out by a crystal transducer located in the handpiece, which transforms high frequency electrical energy into high (ultrasonic) frequency mechanical energy. The crystal drives the titanium tip of the phaco unit to oscillate in its anterior-posterior axis.
It is precisely the anteroposterior oscillation of the phaco tip which produces the emulsification (Figs. 50-B, 55, 56, 67, 68).
Parameters of the Phaco Machine
What are the phacoemulsification machine parameters? How are they utilized? These parameters need to be set and reset
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surgeon must solve. These parameters are:
1)the amount of ultrasonic energy applied to the nuclear material for its emulsification. It is expressed as a percentage of the phaco machine’s available power and it determines the turbulence which is generated in the anterior chamber during surgery. It is ideal to use the least amount of power possible during the operation. This is possible by combining other functions of the machine and maneuvers within the nucleus to facilitate fracture and emulsification of the lens. The use of excess phaco energy may result in damage to structures beyond the nucleus, such as the posterior capsule and the endothelium.
2)The aspiration flow rate. This measures the amount of liquid aspirated from the anterior chamber per unit of time. In practical terms, this determines the speed with which the lens material is sucked in into the phaco tip. This is synonymous with the power of "attraction" or suction of the lens fragments into the irrigation-aspiration handpiece (Fig. 61). High maximum flow rates may result in collapse of the anterior chamber if the irrigation cannot keep up.
3)The third parameter measures the vacuum or negative pressure created in the
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Figure 55: Varying Ultrasonic Settings While Proceeding Through a Nucleus of Varying Density During the Creation of a Furrow or Groove
Under surgeon control via the foot pedal, the ultrasonic power can be varied during creation of a trans nuclear groove to accommodate the varying density of the nucleus encountered at each location. For example, when beginning the furrow (A) 30% power is all that is required initially in the low density peripheral portion of the nucleus (P). Note slight depression (arrow) of the foot pedal
(1) to obtain this power setting. As the phaco tip is progressed toward the central nucleus, ultrasonic power may be increased to 60% asitencountersmoredenseepinuclearmaterial(E). Noteincreasedfootpedaldepression(arrow)toincreasepower(2). Whenthephaco enters the densest central portion of the nucleus (N), ultrasonic power may be increased up to 90-100% by further depression (arrow) of the foot pedal (3). As the phaco tip again encounters less dense material on the distal side of the nucleus near the epinucleus (E), ultrasonic power is again reduced to perhaps 60% to efficiently remove that material. The foot pedal depression is reduced to lower the power (4). Varying the power to just the minimum level required at each stage avoids excessive intraocular ultrasonic power, provides for a safer extraction, and avoids possible abrupt engagement of the tip with epinucleus and nearby the posterior capsule.
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