CA2541845C

CA2541845C - Control of pulse duty cycle based upon footswitch displacement

Info

Publication number: CA2541845C
Application number: CA2541845A
Authority: CA
Inventors: Kenneth E. Kadziauskas; Paul W. Rockley
Original assignee: Abbott Medical Optics Inc
Current assignee: Johnson and Johnson Surgical Vision Inc
Priority date: 2003-10-06
Filing date: 2004-10-04
Publication date: 2013-09-10
Anticipated expiration: 2024-10-04
Also published as: US8195286B2; US7169123B2; EP1670402B2; US20040068300A1; AU2004281682A1; US20130131692A1; CA2541845A1; US9788998B2; EP1670402A1; WO2005037156A1; EP1670402B1; US20070073309A1; ATE515997T1; AU2004281682B2; JP2007507312A

Abstract

Phacoemulsification apparatus includes a phacoemulsification handpiece having a needle and an electrical circuitry for ultrasonic vibrating the needle. A power source provides pulsed electrical power to the handpiece electrical circuitry and an input is provided for enabling a surgeon to select an amplitude of dislighted pulses and a pulse width. A control system and pulse duty cycle is provided for controlling the off duty cycle to insure heat dissipation before a subsequent pulse is activated, including a foot pedal switch.

Description

CONTROL OF PULSE DUTY CYCLE
BASED UPON FOOTERITCH DISPLACEMENT
The present invention is generally directed to a method and apparatus for controlling the flow of fluid from a source to a patient and removal of fluids from the patient through a phacoemulsification handpiece as well as controlling power provided to the phacoemulsification handpiece.
The flow of fluid to and from a patient through a fluid infusion or extraction system and power control to a phacoemulsification handpiece is critical to the procedure being performed.
A number of medically recognized techniques has been utilized for lens removal and among these, a popular technique is phacoemulsification, irrigation and aspiration.
This -20 method includes the making of a corneal incision, and the ' insertion of a handheld surgical implement which includes .a needle which is ultrasonically driven in order to elmilsify:the eye lens.. Simultaneously with this emulsification, a fluid is inserted for irrigation of the emulsified lens and a vacuum provided for aspiration of the emulsified lens and inserted fluids.
Currently available phacoemulsification systems include a variable speed peristaltic = pump, a vacuum thensor, an 10. adjustable source of ultrasonic power and a 'programmable microprocessor with operator-selected presets and a footpedal for controlling aspiration rate, vacuum and ultrasonic power levels.' .
Many surgical instruments and controls in use today linearly control the vacuum or linearly control the flow of aspiration fluid.
This feature allows the surgeon to precisely "dispense" or control the "speed" at which he/she .emplOyp, 'either the vacuum or the flow, but not, both:.
However, there Often are times during surgery when the precise control of at least one of the variables (vacuum, aspiration rate, or ultrasonic power) is desired over another.
The experienced user, understanding the relationship between the vacuum and the flow, may manually adjust the preset 'variable appropriately at the console in order to obtair.l.an.acceptabl .
performance. However, if this adjustment is overlooked, then the combination of both high vacuum and high flow can cause undesirable fluidic surges at the surgical site with possible damage inflicted on the patient.

2 It should .be apparent that the control of handheld surgical instruments for use in phaco surgery is complex.
Phacoemulsification apparatus typically comprises a cabinet, including a power supply, peristaltic pump, electronic and associated hardware, and a connected, multi-function and handheld, surgical implement; or handpiece, including a hollow slender-like needle tube as hereinabove described, as well as =a footpedal, in order to perform the phacoemulsification of the cataractOus lens.
It should be appreciated that a surgeon utilizing the handheld implement to perform the functions hereinabove described requires easy and accessible control of these functions, as well as the ability to selectively shift or switch between at least some of the functions (for example, irrigation and irrigation plus aspiration) as may arise during phacoemulsification surgery.
In view of the difficulty with adjusting cabinet-mounted controls, while operating an associated handheld medical implement, control systems have been developed such as described in U.S. Patent No. 4,983,901 entitled "Digital Electronic Foot Control for Medical Apparatus and the Like".
=

3 a.
To further illustrate' the compleXity of the control system, reference is also made to U.S. Patent No., 5;268,624 entitled "Footpedal Control with User Selectable Operetional 'Ranges".
It should thus be apparent, in view of the complex nature of the control system of fluids and ultrasonic power in the case of phacoemulsification procedures, that it is deeirable for a surgeon to have a system which is programmab1e.to serve both the needs of the surgical procedure and particular techniques of the surgeon, which may differ depending on the experience and ability.oftbe surg9on.
Phacoemulsification systems typically include a handpiece having an ultrasonically vibrated hollow needle and an .electronic control therefor.
?is well. known. in the art, the =phacoemulsificetion handpiece is interconnected with a control console by an electric cable for powering and controlling the piezoelectric transducer and tubing for providing irrigation, fluid to the eye and withdrawing aspiration fluid from an eye through the handpiece.

4 CA. 02541845 2011-06-10 The hollow, needle of the handpiece is typically driven or excited along its longitudinal axis by the piezoelectric effect in crystals created by an AC voltage applied thereto.
The motion of the driven .crystal is amplified by a mechanically resonant .system within the handpiece, such that the motion of the needle connected thereto is directly la. dependent upon the frequency at which the crystal is driven, with a maximum motion occurring at .a resonantfrequency. =
The resonant frequency is dependent, in part upon the mass of the needle intercohnected.therewith, which is vibrated 15 by the crystal...
For pure capacitive circuits, there is a 90-degree phase angle between a sine wave representing the voltage applied to .
the handpiece and the resultant current into the handpiece..
. . .
20 This is expressed by the angle fis equaling -90 degrees. For a purely inductive circuit, the phase angle equals + 90 degrees and, of course, for purely resistive circuits (5 = 0.
A typical range of frequency used for phacoemulsification 25 handpiece is between about 30 kHz to about 50 kHz.
A
. =
frequency window exists forõeach phacoemulsification.handpiece that can be characterized by the handpiece impedance and phase.

This frequency window is bounded by an upper frequency and a lower cutoff frequency.
The center of this window is =

,typically defined as the point where the handpiece electrical phase reaches a maximum value.
At frequencies outside of this window, the electrical phaSe.
,5 of the handpiece is equal to. -90 .degrees.
Handpiece power transfer efficiency is given by the formula (V*I)(COS 6).
This means that the most efficient handpiece operating point occurs when the phase is closest to :0 degrees..
In order to maintain .optimum handpiece power transfer efficiency, it is important to .control the 'frequency to achieve a phase value as close to zero degrees as possible.
This goal is complicated by the fact that the phase angle of the ultrasonic handpiece is also dependent on the loading of the transducer which occurs through the mechanically resonant system which includes the needle.
That is, contact with the needle with tissue and fluids .within the eye create a. load on the piezoelectric crystals with concomitaht change in the operating phase angle.
Consequently, it is important to determine and.measure the phase angles at all times during operation of the handpiece in order to adjust the driving circuitry to achieve an optimum Phase angle in order to effect constant energy transfer into the tissue ,by, the phacp handpiece, regardless. of '.loading effects.
Thus, it is important to provide automatic tuning of the handpiece during its use in phacoemulsification tissue and withdrawing same from an eye.
This auto tuning is accomplished by monitoring the handpiece electrical signals and adjusting' the frequency to maintain consistency With . .selected parameters.
In any event, control circuitry for phacoemulsification 'handpiece can include circuitry for measuring the phase .between the voltage and the 'current, tyPicallyidentified'as a phase detector. However, problems arise in the measurement of the phase shift without dependence on the operating frequendy Of the phacoemulsification handpiece. That is, because; as hereinabove noted, the phase shift is depenaent on the operating frequency of the handpiece and time. .delay' in the measurement thereof requires complex calibration circuitry in' order to compensate to provide for responsive tuning of the handpiece.
The ultrasonically driven needle in a phaco handpiece becomes waLitt during use and such generated, heat is :for the most part dissipated by the irrigation/aspiration fluids passing through the needle. However, care must be taken to .
.avoid 'overheating .of eye tissue during phacoemulpl,ficat,i.on;
Interrupted power pulse methods have been developed. in order to drive the needle with reduced heating to avoid overheating and burning of tissue.
The present invention improves this power pulse method, and allows an operator to .rpodulat.e.,involved power. settings with .a -foot .pedal 'switchi inter alia.
=

SUMMARY OF THE INVENTION
In accordance with the present invention, phacoemulsification apparatus generally includes a = 5 phacoemulsification handpiece having a needle and an electrical means for ultrasonically vibrating the needle. The power source provides a means for ,Supplying pulsed electrical power to the handpiece electrical means and a means for providing irrigation to the eye and aspirating fluid from the handpiece needle is also incorporated in the present invention.
Input means is provided for enabling a surgeon to select an amplitude of the electrical pulse and separately a pulse duty cycle provided to the handpiece, the input means may include a 'switch such as, for example, a footpedal.
Control means, controls an off duty cycle in order to ensure heat- dissipation = before a subsequent pulse is activated. The control means provides a pulse repetition rate of between about 25 and about 2000 pulses per second, with other factors taken into account in having surgeon or power modulated triggering of the off duty cycle inherent in the present invention.
A method in accordance with the present invention for operating a phacoemulsification system which includes a phacoemulsification handpiece, and an ultrasonic power source, a vacuum source, a source of irrigating fluid, and a control ' unit having a vacuum sensor for controlling the aspiration of the irrigating fluid from the handpiece. .The method inCl.p.des the steps of placing ' the handpiece in an .operative ' relationship with an eye for phacoemulsification procedure. and .
supplying irrigation fluid from the irrigation fluid source into the eye.
Pulsed ultrasonic power is provided from the ultrasonic power source to the handpiece for ,performing .the-phacoemulsification procedure. Preferably the pulsed power is at a repetition rate of between 25 and about 2000 pulses per second.
A vacuum is applied from the vacuum source to the handpiece to aspirate the irrigating fluid from the eye through the handpiece at a selected rate.
An input is provided enabling manual selection of power pulse amplitude and pulse duty cycle of power supplied to the handpiece.
Variable control of the power includes varying an off duty cycle of the supply power.
The present invention comprises at least two ways to accomplish this. In addition = 25_ the surgeon's selection. of a pulse ..cluty,cycle, by. switching and having a preset parameter to address this issue, control means known to those of skill may be readily substituted. By controlling the pulse duty cycle with an inherent Off duty . cycle in order to ensure heat dissipation before a Subsequent pulse is actuated tissue insult is mitigated or precluded.
Likewise,., there is provided novel enhanced ophthalmic lens . extraction apparatus .which comprises a, phacoeMUlsification handpiece having p. needle and electrical means for ultrasonically vibrating Said needle, apower source .
' means for providing pulsed electrical power to the handpiece .electrical means, an input means for enabling a' surgeon to ,select an amplitude of the alectridal pulses, means for providing irrigation fluid to the eye and aspirating flUid,, from the. handpiece needle; and a Control means, further , comprising at least a switch for controlling a pulse duty cycle of power supplied to the handpiece, an off duty cycle being controlled to ensure heat dissipation before a subsequent pulse is activated.¨

.
BRIEF DESCRIPTION OF THE .DRAWINGS
The advantages and features of the present invention will be better understood by the following description when considered in conjunction with the accompanying drawings in which:
.25 Figure 1 is a functional block diagram of a phacoemulsification system in accordance with the present invention;
=

Figure 2 is a functional block diagram of an alternative embodiment of 'a phacoemulsification system in accordanCe With .the present invention which includes apparatus for .providing irrigation fluid at more than one pressure to a handpiece'; =
=
Figure 3 is a flow chart illustrating the operation of the occluded-unoccluded mode of the phacoemulsification system . with variable aspiration rates; =
= Figure 4 is 4 flow chart illustrating the operation of the occluded-unoccluded mode of the phacoemulsification system with variable ultrasonic power levels; .
Figure 5 is a flow chart illustrating the operation, of the variable duty cycle pulse function of the phacoemulsification system;
Figure 6 is a flow chart illustrating the operation of .the occluded-unoCclucled mode pf the.phcoemulSification.systemh.
. .
with variable irrigation rates;
Figure 7 is a plot of the 90-degree phase shift between the sine wave representation of the voltage applied to a piezoelectric phacoemulsification handpiece and the resultant =
, current into the handpiece; . , =
Figure 8 is a plot of the phase relationship and the impedance of a typical piezoelectric . phacoemulsification handpiece;

Figure 9 is .a block sdiagram of improved phase detector circuitry' suable for performing a method in accordance with the present invention;
:5 Figure 10 is a plot of phase relationship as a function ' of frequency for various handpiece/needle loading;=
= Figure 11 is a function block diagram of a pilase control .10 phacoemulsification system utilizing phase angles to control handpiece/needle.parameters with max phase mode operation;
=
Figure 12. is a function block control diagram of a phase control phacoemulsification system utilizing phase angles to 15 control handpiece/needle parameters with a load detect method;
Figure 13 is a function block control diagram of a pulse control phacoemulsification system;
20 Figure 14 is a perspective view of a footpedal suitable for use with the present invention; and Figure 15 is a diagram showing functional use of the footpedal.
DETAILED DESCRIPTION OF THE DRAWINGS
Turning now to the drawings, and particularly to Figure 1 thereof, there is shown, in functional block diagram form, a phacoemulsification system indicated generally by the reference numeral 10.
The system, has a control Unit -.12, .indicated by the dashed lines in Figure i which 'includes a Variable speed peristaltic .pump 14, which provides a vaCuum.
source, a source of pulsed ultrasonic power ,16,. .alad a microprocessor computer 18 that provides control outputs to pump speed controller 20 and ultrasonic.power'level controller . 22.
A vacuum sensor 24 px.ovides, an input to computer ,18 = .representing the vacuum level on the putput. side. of.
peristaltic pump 14. Suitable venting is provided by' vent 26..
. .
As hereinafter described in greater 'detail, a phase detector 28 provides an input to computer 18 representing a phase shift between a sine wave representation of the Voltage applied to a handpiece/needle 30 and the resultant Current into the handpiece 30. The block representation.of.the. handle 30 includes a typical handpiece having a needle and electrical means, typically a piezoelectric crystal, for ultrasonically vibrating the needle.' ' 20 The control unit 12 supplies ultrasonic power on line 32 to a phacoemulsification handpiece/needle 30. An irrigation fluid source 34 is fluidly coupled to handpiece/needle 30 through line 36. The irrigation fluid and ultrasonic power are applied by handpiece/needle 30 to.a.patient'.s eye :which is indicated diagrammatically by block 38. Aspiration of the eye 38 is achieved by means of the control unit peristaltic pump 14 through lines 40 and 42.

A switch 43 disposed on the handpiece 30 may be.utilized as a means for enabling a surgeoh to select' an amplitude and/or pulse 'duty cycle of electrical pulses to the handpiece via the computer 18, power level controller 22 and ultrasonic

-5. power source 16 as hereinafter discussed. =
It should. be appreciated that-any suitable input means, .
such as, for example, a footpedal 43A, see Figure 14, may be .utilized in lieu of the switch 43.. 'Further description of the footpedal operation for controlling pulse duty =cycle will be presented hereinafter.
The computer 18 responds to preset vacuum levels in output line 42 from peristaltic pump 14 by means of signals frOm the previously mentioned vacuum sensor 24. Operation of the contrbl unit in response to the occluded-unoccluded condition of handpiece 30 is shown in the flow diagram of Figure 3.
As shown in Figure 3, if the handpiece aspiration line 40 is occluded, the vacuum level sensed by vacuum sensor 24 will increase.
The computer 18 has operator-settable limits for aspiration rates, vacuum levels and ultrasonic power levels.
As illustrated in Figure 3, when the vacuum level sensed by vacuum sensor 24 reaches,a'predetermined=level as a result of:
occlusion of the handpiece aspiration line 40, computer 18 instructs pump speed controller 20 to change the speed of the peristaltic pump 14 which, in turn, changes the aspiration rate.
It will be appreciated that, depending upon the

6 = characteristics of the material occluding handpiece/needle 30, the speed of the peristaltic pump 14 can either be *increased . or decreased. When the occluding Material' is broken up, the =
vacuum sensor 24 registers .a drop in Vacuum level, cauSing compUter 18 to change the speed of peristaltic pimp 14 to an. .
unoccluded Operating speed.
In addition to changing the phacoemulsification parameter . of aspiration rate by varying the speed of the 4peristaltic ,pump 14, the power level of the ultrasonic power Source 16 can be varied as a function of the occluded or unodcluded condition of handpiece 30.
Figure 4 illustrates in .flow diagram form the control of the ultrasonic power source power level by means of computer 18 and power level controller 22.
It will be appreciated that the flow diagram of Figure 4 .
corresponds to the flow diagram of Figure 3 but varies the phacoemulsification parameter of the ultrasonic power level.
With reference to Figure 5, there is shown a flow diagram depicting the control of the ultrasonic power source 16 to produce varying pulse duty cycles as a function of selected power levels. The pulse duty cycles may also be controlled via the footpedal 43A.
As shown in Figure 5, and by way of. illustration 33% pulse duty cycle is run until the power level exceeds a preset threshold; in this case, 33%. At that point, the pulse duty cycle is increased to 50% until the ultrasonic power level exceeds a 50% threshold, at which point the pulse duty , cycle is increased to 66%.. When the ultrasonic power level exceeds 66% threshold, the power Source is run continuously, i.e., a l00% duty cycle. Although the percentages of 33, 50 ' and 66 have been. illustrated in Figure 5, it should be ' 5 understood that other percentage levels can be selected by the =
footpedal 43A to define different duty cycle shift. points. =
With reference to Figure 13,, when the computer 18 has ' -been enabled for pulse mode operation by an amplitude input via the switch .43, the use of thermal tissue damage Is reduced.' In accordance with the present invention, very rapid pulse duration is provided with adequate energy to cut the tissue with 'kinetic or. mechanical energy but then the pulse is 'turned off long enough to eliminate the thermal BTU's before the next pulse, is activated. A surgeon may vary the pulse amplitude in a linear manner via the switch 43. and the .control unit in response to the selected pulse amplitude, irrigation and aspiration fluid flow rates and pulse duty cycle controls . =
. an off' duty ¨Cycle to ensure'. heat .(11.spipation .before a.
=== .=- '..=..."
subsequent pulse is activated.
In this, way, increased amplitude will increase tip acceleration and thus BTU's for tissue damaging heat generation. That is, the surgeon can use linear power control to select. the correct acceleration necessary . to Cut through.
the tissue density while the control unit provides a corresponding variation in pulse width and "Off Time" to prevent tissue de-compensation from heat. The control unit is programmed depending on the phaco handpiece chosen (total CA. 02541845 2011-06-10 wattage) or the phaco tip (dimensions, weight). This: use of rapid pulsing is similar to how lasers operate with .very short duration pulses. Pulses may have a repetition rate of between about 25 and 2000 pulses per second.
Turning back to Figure 2, there is shown an alternative embodiment 50 of a phacoemulsification system, in accordance with the present invention, and which incorporates all ofthe =elements of the system. 10 shown in Figure 1, with' identical reference characters identifying' components, As '-shown in Figure .1.
In addition to the irrigation fluid source 34, a second irrigation fluid source 35 is provided with the sources '34, .35 being connected to the line 36 entering the handpiece/needle 30 through lines 34a, 35a, respectively, and to a, valve 59 .
The valve 59 functions to alternatively connect line 34a and source 34 and line 35a and source 35 with the handpiece/needle .30:in response to a Signal :from power. evel conr,61:1= 22 through a line 52.
As shown, irrigation fluid sources 34, 35 are disposed at different heights above the handpiece/needle 30 providing a means for introducing irrigation fluid to the handpiece at a plurality of pressures, the head of the fluid in the container =
being greater than the head of fluid in the container 34.
A harness, including lines of different lengths 44, 46, when connected to the support 48, provides a means for disposing CA. 02541845 2011-06-10 the containers 34, 35 at .different heights over the handpieCe/needle 30.
The use ..of. containers .for irrigation fluids at the various heights ,is representative of the means for providing irrigation fluid at different .pressures, and alternatively,.
separate, pumps may be provided with, for example, separate circulation loops (not shown) '.which also can provide .irrigation, fluid at discrete pressures to the handpiece/needle 30 upon a coMmand.from the power controller 22.
With reference to Figure 5, if the handpiece .aspiration line 38 is 'occluded, the vacuum level sensed by the. .vacuum sensor 24 will. increase.
The, computer 18 has operator-settable limits for controlling which of the irrigation fluid supplies X35 will be connected to "thehandpiece 30. It should be appreciated that while two irrigation fluid sources!
or Containers 34,35 are shown, any number of containers may be utilized.
As shown in Figure 6, when the vacuum level by the vacuum sensor 24 reaches a predetermined level, as a result of occlusion of the aspiration handpiece line 38, the computer controls the valve 59 causing the valve to control fluid communication between each of the containers 34, 35 and the handpiece/needle 30.
It should be appreciated that, depending upon the characteristics of the material occluding the handpiece/needle 30, as hereinabove described and the needs and techniques of the physician, the pressure of irrigation fluid provided the handpiece may be increased or decreased.. As occluded material 24, the vacuum sensor 24 registers a drop in the vacuum.
level causing the valve 36 to switch to a container 34, 35, providing pressure at an unoccluded'level.
As noted hereinabove, it should be appreciated that more than one container may be utilized in the present 'Invention, as an additional example, three containers (not shown) with the. valve interconnecting to select irrigation fluid from any of the three containers, as hereinabove described in connection with the Figure 2 container system.
In addition to changing phacoemulsification handpiece/needle 30 parameter as a .function of vacuum, the occluded or unoccluded state of the handpiece can be determined based on a change in load sensed by a handpice/needle:by Way Of.a¨change in phase shift qr shape'o'f:
the phase curve.
The typical range of frequencies used for phacoemulsification handpiece 30 is between about 30 kHz and about 50 kHz. When the frequency applied to the handpiece is significantly higher, or lower than.resonancy, it. responds electrically as a capacitor.
The representation of this dynamic state is shown in Figure 7 in which curve 60 (solid line) represents a sine wave corresponding to handpiece 30 =

= =

. current, and. curve. 62 (broken line) represents a sine wave corresponding to handpiece 30 voltage.
The impedance of the typical phacoemulsification ' .5 handpiece 30 varies with frequency, i.e., it is reactive. The dependence of typical handpiece 30phase and impedance as a =
functicin, of frequency is shown in Figure 8 in which curve 64 . represents the phase difference between, current and voltage of .the handpieces function frequency. and 'curve -66 shows the change in impedance of the ,handpiece as a function of frequency. The impedance exhibits a low at "Fr" and a high ' "Fa" for a typical range of frequencies.
Automatic tuning of the handpiece, as hereinabove briefly noted, is typically accomplished by monitoring the handpiece electrical signals and adjusting the frequency to maintain a consistency with selected parameters.
In order to compensate for 'a load occurring at the tip; of the phacoemulsification handpiece, the drive voltage to the handpiece can be increased while the load is detected and then decreased when the load is removed. This phase detector is typically part of the controller in this type of system.
. A block diagram 70 as shown in Figure 9 is x.epresentative.
of an improved phase detector suitable for performing the method in accordance with the present invention. Each of the function blocks shown comprises conventional state-of-the-art circuitry of typical design and components for producing the function represented by each block as hereinafter described., =
= The voltage input . 72 and Current 74 from *a.
phacoemulsification handPiece . 30 is converted to . an appropriate signal using an attenuator 76 on the Voltage' signal to the phacoemulsification handpiece, and a current . sense resistor 78 and fixed gain amplifier for the handpiede -30 current.
.
Thereafter, an AC voltage signal 80 and AC, current signal 82* is passed to comparators 84, 86 which convert the analog representations of the phacoemulsification voltage, and current to logic level clock signals.
.
The output from the comparator .84 is fed into a D flip flop integrated circuit 90 configured as a frequency divide by 2. The output 92 of the integrated circuit 90 is fed into an :operational- amplifier .configured as an integrator :94., ....The:
= . . . . .
=
output 96 of the integrator 94 is a sawtooth waveform of which the final amplitude is inversely proportional to the handpiede frequency. A timing generator 98 uses a clock synchronous with the voltage signal to generate AID converter timing, as well as timing to reset the integrators at the end' of each cycle.
This signal is fed into the voltage reference of an AID
converter via line 96.

The voltage .leading edge to ,Current trailing edge.' detector 100 uses a P flip flop integrated circuit in order to isolate the ,'.1eading edge of the handpiece voltage signal.
= This signal is.used as the initiation signal to start the . .5 timing process between the handpiece 30 voltage and handpiece 30 current. , The output 102 of the leading detector 100 is a pulse .that is proportional to the time difference in occurrence of the leading edge of the handpiece, 30-voltage waveform and the falling edge of the handpiece current waveform.
Another integrator circuit 104 is used for the handpiece *
phase signal 102 taken from the detector 100. The output 106 of the integrator circuit 104 is aosawtooth waveform in which . the peak amplitude is proportional to the time difference in . the onset of leading edge of the phacoemulsification voltage and the trailing edge of the onset of the handpiece current .waveform. The output 106 of.the:integrator.cirouit 104 is fed *into the analbg input or an AID (analog to digital converter) integrated circuit 110.
Therefore, the positive reference input 96 to the AID
converter 110 is a.voltage that is inversely proportional to the frequency of operation. The phase voltage signal 96 is proportional to the phase difference between the leading edge of the voltage onset, and the trailing edge of the current onset, as well as inversely proportional to the frequency of operation. In this configuration, the two signals Frequency voltage reference 96 and phase voltage 46 track each other over the. range of frequencies, so that the output. sof the: A/D .
. converter. 110 produces the phase independent of the .frequency ' of operation.
The advantage of utilizing this approach is 'that the 'system computer 18 (see Figures 1 and 2) is provided with a real time digital phase signal that 0 to 255 'count's, will . 'consistently represent 0 to 359 degrees of phase.
.
The significant advantage is .that no form of calibration is necessary since .the measurements are consistent despite, the frequencies utilized.
=
For example, .using AMPs operation frequencies of "38' kHz and 47 kHz and integrator having a rise time of 150x 101V/2 and an 8 bit A/D converter having 256 counts, a constant ratio is maintained and variation in frequency does not, affect the results. This is:shoWn...in the following examples-.
EXAMPLE 1 - 38 KHz OPERATION:
=
Period of 1 clock cycle = 1/F @ 38KHz=26.32 x 10-6S
Portion of one period for I
= 90 degrees = 26.32 x 10-6S /4=6.59 x 10-6S
- Integrator output for one reference'cycle = (150 x 10-3 V/S)x(26.32 x 10-6S)=3.95 Volts Integrator output from 90 degree cycle duration = (150) x 103 V/S)x(6.59 x 10-6S)= .988 Volts .
Resulting Numerical count from A/D converter = 3.95 Volts/256 counts = .0154 Volts per count , .
. Actual Number of A/C counts for 90 degrees at 38 KHz =
EXAMPLE' 2- 47 KHz OPERATION:
. 5 Period of 1 clock cycle- 1/F @ 47KHz=21.28 x Integrator output for one reference cycle =
= (150 x 103 V/S) x (21.28 x 10-6S) = 3.19 Volts = Integrator output from 90 degree cycle duration = (150 x 103 V/S)x(5.32 x 1010-6S) = .798 Volts Resulting Numerical count from A/D converter 3.19 Volts/256 counts = .0124 Volts per count .Actual 'Number of A/D counts for 90 degrees at 47 KHz =.798/:0124=64 counts =
=
1.5 A.plot of phase angle as a function of frequency is shown in Figure 10 for various handpiece 30 loading, a.no load (max . phase), light load, medium load and heavy load.
With reference to Figure 11, representing max phase mode .operation, the actual phase is determined and compared to the Mak.phase. 1f-.theactual.phase is equal' tO,-or%greater-than;
the max phase, normal aspiration function is performed.
If the actual phase is less than the max phase, the aspiration rate is changed, with the change being proportionate to the change in phase.
-Figure 12 represents -operation at less than max 'load in which load (see Figure 10) detection is incorporated into the operation, a method of the present invention.

. As represented in Figure 11, representing max. phase Imdie operation, if the handpiece aspiration line 40 is. Oollided, . .the phase sensed by phase detector sensor 28 will. decrease (see Figure 10). The computer 18 has Operator-settable limits , for aspiration rates, vacuum levels and ultrasonic s.power levels. As illustrated in Figure 11, when the phase.serised by phase detector 28 reaches a predetermined level as a result of occlusion of the handpiece aspiration line 40, .computer 18 instructs pump speed controller 20 to change the speed of.the . peristaltic pump 14 .which,. in turn, changes the -aspiration rate.
It will be appreciated that, depending upon the characteristics of the material occluding handpiece/needle 30, the speed of the peristaltic pump 14 can either be increased or decreased. When the occluding material is broken.up, the phase detector 28 registers an increase in. phase angle, causing computer 18 to change the speed of peristaltic pump 14 to an upoccIuded operating: speed.
In addition to changing the phacoemulsification parameter of aspiration rate by varying the speed of the peristaltic pump 14, the power level and/or duty cycle of the ultrasonic power source 16 can be varied as a function of the occluded or unoccluded condition of handpiece 30.
Turning to Figure 14, there is shown the footpedal 43A
hereinbefore referenced, which is suitable for controlling irrigation/aspiration and both linear control of ultrasound power. delivery and/or duty cycle, as hereinabove noted. .The footpedal 43A is= described in U.S. 6,452,123.
Briefly, the footpedal 43A. includes a depressible platform or footswitch 60 mounted -to. a base. 62.
The depressible platform 60 .may be used in lieu of the switch 43 hereinabove described. Alternatively side switches 64, 66 may also be utilized for controlling duty cycle, as hereinabove described.
In A cataract delivery modality where very rapid pulses of ultrasonic energy are used to deliver energy to the lens of an eye, as hereinabove described, further control pulse delivery is desired by a user. This function is provided by .
the footpeda1.4iA:.
As hereinabove describe, while the delivery of rapid pulses of energy accompanied by appropriate rest periods for enabling heat dissipation further surging control of the pulse duty cycle and delivery is desired.
Accordingly, the controller 22 includes an algorithm in which displacement of the footswitch 60 or sideswitch 64,66 in the delivery of ultrasonic energy can be further subdivided to allow for multiple, "rapid pulse" delivery options.

This involves the pre-programming of a combination: of , .alternative duty ,cycles and pulse rates by the controller 22.
=
It should be appreciated that previous approaches. have been constrained by the fact that the pulse control '(pulse duration) of less than 20 milliseconds was not possible. In .accordance with the present. invention, this control is 1121A7 feasible and the micro-processor control of surgical systems allows for the footpedal 43A programming which allows the ability of the user to customize the energy delivery profile based upon input received from the user.
=
In general, at least three sub-zones of energy delivery can be defined based upon footswitch 60 displacement: The duty cycles for these zones do not necessarily need to =
progress in a linear fashion based upon footswitch 60 displacement (for example: 16%, 243%, 260% 233%) see Figure 15.' It should be appreciated that the amplitude of energy delivery may be either kept constant or varied as a function, of footswitch 60 displacement.
Figure 15 shows relative displacement functions .of. the footswitch 60 in which a foot position 1 controls the irrigation, foot position 2 controls irrigation/aspiration and foot position '3 provides for control of ultrasound power delivery; and/or duty cycle.

Although there has been hereinabove described-a.pe4fic .control of pulse duty cycle based upon footswitch displacement ' in accordance with the present inventioh for the purpose of, illustrating the manner in which the invention may, be used to advantage, it should be appreciated that the invention is not 'limited thereto. That is, the present .invention may suitably . comprise, consist of, or consist essentially of the recited elements. Further, the invention illustrativelY. disclosed herein suitably may be Practiced in the absence of.any.element which.is not specifically disclosed herein. Accordingly, any and all modifications, variations or equivalent arrangements which may occur to those skilled in the art, should be considered to be within the. scope .of the present invention as defined in the appended claims.

Claims

WHAT IS CLAIMED IS:

1. Ophthalmic lens extraction apparatus comprising:
a phacoemulsification handpiece having a needle configured to ultrasonically vibrate the needle;
a power source for providing pulsed electrical power to an electrical transducer;
an irrigation source for providing irrigation fluid to the eye and an aspiration source to provide aspiration of the eye; and a footswitch for enabling a surgeon to select an amplitude of electrical pulses and also select a duty cycle of the electrical pulses.

2. The lens extraction apparatus according to claim 1, wherein the electrical pulses further comprise an off duty cycle

3. The lens extraction apparatus according to claim 1, wherein the footswitch is further configured to control at least one of aspiration flow and irrigation flow.

4. The lens extraction apparatus according to claim 1, wherein a control means provides a pulse repetition rate of between about 25 and about 2000 pulses per second.

5. The lens extraction apparatus according to claim 1, further comprising an input to enable a linear selection of pulse amplitude.

6. The lens extraction apparatus according to claim 1, wherein continued linear footswitch displacement enables activation of a series of pulse duty cycles of power supplied to the handpiece.

7. The lens extraction apparatus according to claim 1, wherein the apparatus is responsive to a selected pulse amplitude and a selected duty cycle for controlling an off duty cycle to ensure heat dissipation before a subsequent pulse is activated.

8. The lens extraction apparatus according to claim 1, wherein the footswitch is configured such that duty cycles are selected in a non-linear fashion based upon footswitch displacement.