US20060078448A1

US20060078448A1 - Phacoemulsification machine with post-occlusion surge control system and related method

Info

Publication number: US20060078448A1
Application number: US11/247,408
Authority: US
Inventors: Hugo Holden
Original assignee: HOLDEN PHACO PTY Ltd
Current assignee: HOLDEN PHACO PTY Ltd
Priority date: 2004-10-11
Filing date: 2005-10-11
Publication date: 2006-04-13

Abstract

A post-occlusion surge controller 90 for a phacoemulsification machine 30 is adapted to detect a post-occlusion surge in an aspiration conduit 41 of the machine 30, and to cause the conduit 41 to be vented in response to detecting the surge.

Description

FIELD OF THE INVENTION

The present invention relates generally to phacoemulsification machines which are used in cataract eye surgery to remove cataract-affected eye lenses and, in particular, to phacoemulsification machines which are adapted to control post-occlusion surges which sometimes occur during cataract eye surgery when such machines are used.
Although the invention will be described with reference to a particular type of phacoemulsification machine, it will be appreciated that this is by way of example only and that the invention may be used in connection with other types of phacoemulsification machines.

BRIEF DISCUSSION OF THE PRIOR ART

Phacoemulsification or phaco-machines are used in cataract eye surgery to remove cataract-affected eye lenses. FIG. 1 depicts a typical prior art peristaltic pump-based phaco-machine 30 which includes a hand-held probe 31 comprising a hollow infusion sleeve 32 surrounding a hollow phacoemulsification needle 33. Needle 33 projects from an end of the infusion sleeve 32 and is vibrated at ultrasonic frequencies by ultrasonic crystals 34 which reside inside the probe 31 and which are connected to a controller 35 which is operable to cause the ultrasonic crystals 34 to vibrate. The sleeve 32 of probe 31 is connected to an elevated and inverted bottle 36 which contains an infusion fluid 37 by a compliant infusion tube 38. The needle 33 is connected to an input port 39 of a peristaltic pump 40 by a length of aspiration tube 41.
The peristaltic pump 40 includes a rotatable rotor 42 which has a plurality of circumferentially-spaced rollers 43 secured thereto and is driven by a motor. A compliant pump tube 44 which is connected to the aspiration tube 41 extends around the circumference of the rotor 42 and is located between the rotor 42 and an arcuate wall 45 of the pump 40 such that the rollers 43 which are in contact with the tube 44 pinch the tube 44 between themselves and the wall 45. As the rotor 42 rotates about its axis, each of the rollers 43 progresses along the wall 45 so that the pinches in the tube 44 also progress along the wall 45. The rotor 42 rotates in a clockwise direction so that fluid is drawn through the tube 44 from the input port 39 of the pump 40 and is output from an output port 46 of the pump 40 into a collection bag 47.
The machine 30 also has a vacuum sensor 48 for sensing the vacuum which is produced inside the aspiration and pump tubes 41, 44 by the peristaltic pump 40. Vacuum sensor 48 is connected to the controller 35.
A compliant venting tube 49 interconnects the input and output ports 39, 46 of the pump 40, and a vent pinch valve 50 is operable by the controller 35 to selectively pinch the venting tube 49. When the venting tube 49 is released by the valve 50, the lumen of the aspiration and pump tubes 41, 44 are connected to atmospheric pressure by the venting tube 49.
Although the phaco-machine 30 vents to the output 46 of the pump 40, other phaco-machines may vent to air, the infusion bottle 36 or to a cassette system.
An infusion pinch valve 51 is operable by the controller 35 to selectively pinch the infusion tube 38 to prevent the infusion fluid 37 from flowing from the bottle 36 to the sleeve 32.
The operation of the peristaltic pump 40 is controlled by a foot-operated pedal 52 which is coupled to the controller 35. Depressing the pedal 52 by one-third causes the rotor 42 of the pump 40 to commence rotating. Further depression of the pedal 52 increases the speed of rotation of the rotor 42 in proportion to the amount by which the pedal 52 is depressed. When the pedal 52 is released the rotor 42 stops rotating so that the pump 40 stops aspirating. The pedal 52 is also used to control the vibration of the needle 33 and the infusion pinch valve 51 which controls the flow of infusion fluid 37 from the bottle 36 through the infusion tube 38 and from the sleeve 32. The needle 33 normally begins vibrating when the pedal 52 is depressed by two-thirds. When the pedal 52 is initially depressed, the infusion pinch valve 51 releases the infusion tube 38 during the initial one-third of the depression of the pedal 52 so that the infusion fluid 37 is able to flow from the bottle 36 through the infusion tube 38 and from the sleeve 32. The ultrasonic crystals 34 commence vibrating once the pedal 52 is depressed by more than two-thirds. In addition to stopping the pump 40, releasing the pedal 52 causes the ultrasonic crystals 34 to stop vibrating, and the infusion pinch valve 51 to pinch the infusion tube 38 so that the infusion fluid 37 stops flowing from the bottle 36 to the infusion sleeve 32. Releasing the pedal 52 may also cause the vent pinch valve 50 to release the venting tube 49 so that the aspiration tube 41 is vented to the collection bag 47. In general, the pedal 52 controls the three basic functions of fluid irrigation (infusion), aspiration, and vibrating of the needle (phacoemulsification). These functions can be allocated to any range of pedal depression by the user of the machine 30.
In use, the tip of the needle 33 is inserted into the anterior chamber of a patient's eye 53 by an eye surgeon such that the tip of the needle 33 is positioned adjacent to the cataract-affected lens in the eye 53 which is to be removed using the phaco-machine 30. The surgeon then depresses the pedal 52 so that the infusion fluid 37 flows from the bottle 36 and into the anterior chamber of the eye 53 from the infusion sleeve 32, and so that the peristaltic pump 40 commences aspirating, and the ultrasonic crystals 34 commence vibrating the needle 33. As the needle 33 vibrates at ultrasonic frequencies, the vibration breaks up the natural cataract-affected lens in the eye 53 and small particles of the lens are aspirated through the hollow needle 33 and into the aspiration tube 41 as a result of the vacuum produced within the lumen of the tube 41 by the operation of the pump 40. The particles then flow into the pump tube 44 from the aspiration tube 41 and then into the collection bag 47 for disposal. The object of the surgery is to leave the thin outer capsule of the lens behind to form a home for an artificial plastic lens which is inserted into the eye 53 to replace the cataract-affected lens. Infusion fluid 37 from the bottle 36 flows into the anterior chamber of the eye 53 from the sleeve 32 so as to maintain volume and pressure in the anterior chamber and to prevent the chamber from collapsing while the pump 40 is operating.
The vacuum sensor 48 of the machine 30 enables the controller 35 to continuously monitor the vacuum inside the aspiration tube 41 at a location which is adjacent to the input port 39 of the peristaltic pump 40. If the controller 35 determines that the vacuum inside the tube 41 has reached a predetermined maximum allowable level, such as a 300 to 500 mmHg vacuum, the controller 35 causes the peristaltic pump 40 to stop operating. Vacuums of 300 to 500 mmHg are usually only generated when the tip of the needle 33 is occluded by particles of the cataract or other tissue. In general, the vacuum in the aspiration tube 41 will not rise above 150 mmHg without a degree of occlusion as only modest vacuums of 0 to 100 mmHg are required in the un-occluded state to support the typically used 20 to 60 ml/minute fluid flow rates through the tube 41.
A post-occlusion surge will appear in the aspiration tube 41 if, after the vacuum in the aspiration tube 41 has reached the predetermined maximum level and the peristaltic pump 40 has stopped aspirating, the occlusion in the tip of the needle 33 suddenly breaks free. The post-occlusion surge is a result of the pump tube 44, vacuum sensor 48, and the aspiration tube 41, which are constructed from compliant materials, being compressed by atmospheric pressure just prior to the surge occurring so that they store potential energy. This is depicted in FIG. 2 where the various compliant components of the machine 30 are represented by a compliant chamber 54. When the occlusion breaks free, the pump tube 44, vacuum sensor 48, aspiration tube 41, and other compliant components connected thereto, expand and rapidly draw fluid into the aspiration tube 41. This causes a sudden rush of fluid from the anterior chamber of the eye 53 and into the needle 33 and aspiration tube 41 as depicted by the arrow 55 so that the compliant chamber 54 and aspiration tube 41 expand as depicted by the arrows 56. This sudden rush of fluid can cause the anterior chamber of the eye 53 to collapse and eye tissue to rush toward the tip of the needle 33. Eye tissue such as the lens capsule, corneal endothelium (which are important fragile cells on the inner surface of the cornea), or the iris may be engaged by the needle 33 at the time of the surge so that the surge causes significant damage to the tissue. The probability of the post-occlusion surge collapsing the anterior chamber of the eye 53 increases if there is fluid leakage from the anterior chamber around the instruments, probe 31, and manipulators which are inserted into the anterior chamber.
Valve 50 of the machine 30 is used for venting purposes and generally pinches the venting tube 49 when the machine 30 is in use so that fluid is unable to flow through the venting tube 49. The vent pinch valve 50 may release the venting tube 49 at any time in order to neutralise any residual vacuum in the aspiration tube 41. For example, when the pedal 52 is released, the vent pinch valve 50 may release the venting tube 49 in order to neutralise the vacuum in the aspiration tube 41. The vent pinch valve 50 does not normally release the venting tube 49 during a post-occlusion surge.
FIG. 3 is a typical graph of the variation over time of the pressure in the aspiration tube 41 at a location therein which is adjacent to the vacuum sensor 48 immediately after an occlusion in the tip of the needle 33 breaks free, where the maximum allowable vacuum had been set by the user at 500 mmHg. It can be seen that the vacuum inside the aspiration tube 41 decreases from −500 mmHg to the positive pressure inside the eye 53 (which can be expressed pgh, where p is the density of the infusion fluid 37, g is the acceleration of gravity, and h is the height of the bottle 36 above the eye 53) which is above atmospheric pressure (i.e. 0 mmHg), and which is typically 51 mmHg with a 70 centimetre bottle height such that the vacuum halves after approximately 220 milliseconds. The actual amount of time required to halve the vacuum in the aspiration tube 41 is dependent on the compliance of the materials from which the compliant components of the machine 30 are fabricated as well as the geometry of those components.
FIG. 4 is a typical graph of the rate of flow of fluid through the aspiration tube 41 of the phaco-machine 30 immediately after the occlusion in the tip of the needle 33 breaks free. It can be seen that the flow of fluid peaks at approximately 100 millilitres per minute, or around five times the normal flow rate, approximately 220 milliseconds after the blockage in the needle 33 clears. The flow rate then gradually decreases to a normal flow rate. The flow peak depends on the vacuum in the aspiration system immediately prior to the start of the post-occlusion surge, and also the geometry of the needle 33 of the probe 31 and aspiration tube 41, and the compliance of the aspiration tube 41, vacuum sensor 48 and peristaltic pump tube 39.
FIG. 5 is a typical graph of the pressure inside the anterior chamber of the eye 53 immediately after the occlusion in the needle 33 breaks free. It takes approximately 220 milliseconds for the pressure to decrease from the positive pressure of the infusion fluid inside the anterior chamber of the eye 53 which is proportional to the height of the bottle 36, to around zero pressure at which point the anterior chamber collapses. As the flow rate of fluid through the aspiration tube 41 decreases, the pressure inside the anterior chamber steadily increases back to its former pressure. Unless the peristaltic pump 40 re-starts before the end of the surge, the pressure in the anterior chamber of the eye 53 will return to a value between pgh (i.e. the bottle pressure) and zero as depicted by the dotted line in FIG. 5.
The peak flow rate and pressure depicted in FIGS. 4 and 5 are proportional to the vacuum inside the compliant structures of the machine 30 just prior to the occlusion in the needle 33 breaking free. This vacuum is normally the maximum allowable vacuum set on the machine 30. The profile of the post-occlusion surge flow depicted in FIG. 4, and the anterior chamber pressure drop depicted in FIG. 5, and the loss of vacuum in the compliant system depicted in FIG. 3, are able to be determined by the mathematics and physics of damped simple harmonic motion. The stored energy in the compliant structures acts like a spring, this acts on the mass of the fluid being accelerated in the aspiration tube 41, and the resistance in this case is the resistance to fluid flow in the aspiration system. This resistance to fluid flow damps the oscillations. The surge flow profile therefore represents a half cycle of very damped oscillation.
Phaco-machine manufacturers have attempted to reduce the post-occlusion surge by reducing the compliance of the compliant components by using non-compliant aspiration tubing and by improving the flow of infusion fluid from the sleeve 32 and into the eye 53.
Another approach which has been used to reduce the amplitude of the post-occlusion surge has been to place what amounts to resistance in the aspiration tube 41 or in the tip of the needle 33. This can involve placing a small aperture in the aspiration tube 41 which fluid flowing through the tube 41 must pass through. The aperture may need to be filtered to prevent particles such as cataract particles from blocking the aperture.
Another technique for increasing the resistance involves decreasing the internal diameter of the tip of the needle 33 or otherwise modifying the needle 33 to create more turbulence and therefore resistance to the flow of fluid through the needle 33 and the aspiration tube 41.
Yet another method of increasing the resistance to the flow of fluid through the needle 33 and the aspiration tube 41 involves the use of tubing with a spiral lumen. This creates turbulent flow at higher flow rates which helps suppress the amplitude of the post-occlusion surge.
Although increasing the resistance of the aspiration tube 41 or other components of the aspiration system of the machine 30 does reduce the amplitude of the post-occlusion surge, it has the disadvantage of prolonging the duration of the surge. Adding resistance to the aspiration tube also has the significant disadvantage of reducing the flow rate, especially at vacuums below 150 mmHg. Also, as the probe needle 33 is cooled by the flow of infusion fluid, adding resistance results in an increase in probe temperature which increases the possibility of the probe needle 33 causing wound burns to the eye 53. Therefore, in the absence of any other means of reducing the post-occlusion surge, it is usually better to reduce the compliance of the compliant components as mentioned earlier rather than to increase the flow resistance in the aspiration pathways. However, there are limitations to the amount by which the compliance can be reduced because the compliant components of the machine 30 such as the pump tube 44 and the vacuum sensor 48 need to have some compliance in order for the machine 30 to operate properly. Also, the aspiration tube 41 needs to be flexible enough to handle easily and to be kink resistant, so it inevitably has to have some compliance.
Another known method of reducing the impact of the post-occlusion surge is to increase the elevation of the bottle 36 relative to the probe 31 so as to increase the rate of flow of infusion fluid into the anterior chamber of the eye 53 from the sleeve 32. However, if the bottle 36 is too high other problems result. For example, it is not widely known that increasing the height of the bottle 36 actually increases the magnitude of the post occlusion surge, and therefore the anterior chamber disturbance associated with it. This is because the surge is proportional to the sum of the absolute values of both the bottle pressure and the maximum vacuum prior to the surge. The maximum vacuum is the dominant value, and increasing the bottle height increases the anterior chamber pressure, moving the apex or peak of the surge away from zero pressure and therefore away from total chamber collapse. Therefore, the surgeon using the phaco-machine 30 is given the impression that the anterior chamber is more stable than it really is, despite the amplitude of the pressure drop of the surge being a little greater with the bottle being more elevated.
Although eye surgeons prefer their phaco-machines to have a relatively high predetermined maximum allowable vacuum level so as to improve their ability to efficiently remove lens fragments, they usually must compromise this with the maximum post-occlusion surge which they are prepared to tolerate since the post-occlusion surge is directly proportional to the maximum allowable vacuum level.
It would therefore be beneficial to have a phacoemulsification machine which has a relatively high predetermined maximum vacuum level so that lens fragments can be removed efficiently from the anterior chamber of an eye which is operated on using the machine, but which has a reduced post-occlusion surge.

SUMMARY OF THE INVENTION

It is an object of the present invention to overcome, or at least ameliorate, one or more of the deficiencies of the prior art mentioned above, or to provide the consumer with a useful or commercial choice.
Other objects and advantages of the present invention will become apparent from the following description, taken in connection with the accompanying illustrations, wherein, by way of illustration and example, a preferred embodiment of the present invention is disclosed.
According to a first broad aspect of the present invention there is provided a post-occlusion surge controller for a phacoemulsification machine, wherein the controller is adapted to detect a post-occlusion surge in an aspiration conduit of the machine, and to cause the conduit to be vented in response to detecting the surge.
By detecting the post-occlusion surge in an aspiration conduit of the phacoemulsification machine, and venting the conduit in response to detecting the surge, the post-occlusion surge controller is able to limit the duration and the amplitude of the post-occlusion surge in the conduit. Limiting the duration and amplitude of the post-occlusion surge reduces the risk of injuring an eye which is being operated on with the machine when the post-occlusion surge occurs.
The post-occlusion surge controller may be adapted to be used with any type of phacoemulsification machine. For example, the post-occlusion surge controller may be adapted to be used with a peristaltic pump-based phacoemulsification machine. In a particular preferred form the post-occlusion surge controller is adapted to be used with a peristaltic pump-based phacoemulsification machine which includes an aspiration tube connected to a peristaltic pump, a venting tube connected to the aspiration tube, and a vent pinch valve operable to pinch the venting tube to prevent venting of the aspiration tube through the venting tube.
Preferably, the post-occlusion surge controller is adapted to detect the onset of the post-occlusion surge, and to cause the conduit to be vented in response to detecting the onset of the surge. This enables the conduit to be vented early on during the surge so that the amplitude and duration of the surge may be minimised.
The post-occlusion surge controller preferably includes a detector for detecting the onset of a post-occlusion surge in the aspiration conduit of the phacoemulsification machine, and a valve controller for controlling a vent valve of the machine in response to the detector detecting the onset of the surge.
The detector preferably includes a differentiator for differentiating the output of a vacuum sensor of the machine which senses the vacuum inside the aspiration conduit of the machine, and a comparator for comparing the output of the differentiator with a reference value and for outputting a trigger signal depending upon the outcome of the comparison.
The valve controller preferably includes a timer for outputting a vent valve control signal in response to receiving the trigger signal from the detector, and a vent valve driver for driving the vent valve of the phacoemulsification machine to vent the aspiration conduit in response to the timer outputting the vent valve control signal.
Preferably, the valve controller also includes a high voltage pulse generator for outputting a high voltage pulse signal to a solenoid of the vent valve in response to the timer outputting the vent valve control signal.
It is also preferred that the valve controller includes a vent valve pre-energiser for pre-energising the solenoid of the vent valve to reduce the time required for the vent valve to respond to the high voltage pulse signal which is output to the solenoid by the high voltage pulse generator.
According to a second broad aspect of the present invention there is provided a method of controlling a post-occlusion surge in an aspiration conduit of a phacoemulsification machine, the method comprising the steps of:

- (i) detecting the post-occlusion surge; and
- (ii) venting the conduit in response to detecting the surge.

Preferably, the step of detecting the post-occlusion surge involves detecting the onset of the surge, and the step of venting the conduit is done in response to detecting the onset of the surge so that the amplitude and duration of the surge is minimised.
The step of detecting the onset of the surge preferably includes determining whether the negative of the rate of change of the vacuum in the conduit with respect to time is greater than or equal to a constant value. If the rate of change is greater than or equal to the constant value, this indicates that the variation in the vacuum is a result of a post-occlusion surge.
It is preferred that the step of venting the conduit involves operating a vent valve of the machine to vent the conduit. The vent valve may vent the conduit for a predetermined period of time.

BRIEF DESCRIPTION OF THE ILLUSTRATIONS

In order that the invention may be more fully understood and put into practice, an embodiment thereof will now be described with reference to the accompanying illustrations, in which:
FIG. 1 illustrates a prior art peristaltic pump-based phaco-machine for use in cataract eye surgery;
FIG. 2 illustrates a portion of the prior art phaco-machine depicted in FIG. 1 with the pump tube and vacuum sensor thereof represented by a compliant chamber;
FIG. 3 is a typical graph of the variation over time of the vacuum in the compliant chamber of the prior art phaco-machine depicted in FIGS. 1 and 2 immediately after an occlusion in the probe tip of the machine is removed;
FIG. 4 is a typical graph of the variation over time of the flow of fluid through the aspiration tube of the prior art phaco-machine illustrated in FIG. 1 immediately after an occlusion in the probe tip of the machine is removed;
FIG. 5 is a typical graph of the variation over time of the pressure inside the anterior chamber of an eye which is treated with the prior art phaco-machine illustrated in FIG. 1 immediately after an occlusion in the probe tip of the machine is removed;
FIG. 6 is a schematic block diagram of a post-occlusion surge detector of a post-occlusion surge controller for the phaco-machine depicted in FIG. 1;
FIG. 7 is a schematic block diagram of a valve controller of the post-occlusion surge controller for the phaco-machine depicted in FIG. 1;
FIG. 8 is a graph of the variation over time of the voltage signal output by the vacuum sensor of the prior art phaco-machine depicted in FIG. 1 immediately after an occlusion in the probe tip of the machine is removed;
FIG. 9 superimposes the graph depicted in FIG. 3 on a graph of the variation over time of the vacuum sensed by the vacuum sensor of the prior art phaco-machine depicted in FIG. 1 immediately after an occlusion in the probe tip of the machine is removed when the machine is equipped with the post-occlusion surge controller;
FIG. 10 superimposes the graph depicted in FIG. 9 with a graph of the variation over time of the pressure inside the anterior chamber of an eye which is treated with the prior art phaco-machine depicted in FIG. 1 immediately after an occlusion in the probe tip of the machine has been removed when the machine is equipped with the post-occlusion surge controller;
FIG. 11 is a schematic block diagram of another post-occlusion surge controller;
FIG. 12 is a graph of the variation over time of the vacuum sensed by the vacuum sensor of the prior art phaco-machine depicted in FIG. 1 immediately after the removal of an occlusion in the probe tip of the machine when the machine is equipped with the post-occlusion surge controller depicted in FIG. 11;
FIG. 13 is a graph of the trigger signal which is output by the post-occlusion surge detector of the post-occlusion surge controller depicted in FIG. 11;
FIG. 14 is a graph of the signal which is output by the vent valve driver of the post-occlusion surge controller depicted in FIG. 11;
FIG. 15 is a graph which depicts the timing of the operation of the vent valve of the prior art phaco-machine depicted in FIG. 1 when the machine includes the post-occlusion surge controller depicted in FIG. 11;
FIG. 16 is a graph of the variation over time of the pressure inside the anterior chamber of an eye which is treated with the prior art phaco-machine illustrated in FIG. 1 immediately after the removal of an occlusion in the probe tip of the machine when the machine is equipped with the post-occlusion surge controller depicted in FIG. 11;
FIG. 17 superimposes the graphs depicted in FIGS. 3 and 4 with the graphs depicted in FIGS. 12, 15, and 16;
FIG. 18 is a schematic circuit diagram of the vent valve controller depicted in FIG. 7;
FIG. 19 is a schematic circuit diagram of the timer of the vent valve controller depicted in FIG. 7; and
FIG. 20 is a schematic circuit diagram of the post-occlusion surge detector depicted in FIG. 6.

DETAILED DESCRIPTION OF THE ILLUSTRATIONS

The prior art phaco-machine 30 depicted in FIG. 1 can be modified to include a post-occlusion surge controller which includes a post-occlusion surge detector 60 which is depicted in FIG. 6, and a valve controller 61 which is depicted in FIG. 7.
The post-occlusion surge detector 60 includes a vacuum sensor input 62 for connecting the detector 60 to the output of the vacuum sensor 48 of the phaco-machine 30 so that the electrical signal which is output by the sensor 48 can be monitored and processed by the detector 60. The electrical signal which is output by the sensor 48 is a positive voltage which is proportional to the vacuum in the interconnected compliant components of the machine 30 which is sensed by the sensor 48. The output of the vacuum sensor 48 may, for example, be 10V/500 mmHg vacuum.
The detector 60 may include, for example, an operational amplifier configured as a differentiation amplifier, or a microcontroller. The detector 60 is configured to differentiate the electrical output of the sensor 48 with respect to time and to compare the differentiated output with a positive predetermined constant value so as to determine whether the negative of the rate of change with respect to time of the voltage output by the vacuum sensor 48 is greater than or equal to a positive predetermined constant value. This can be expressed mathematically in the form: $- \frac{ⅆ V}{ⅆ t} \geq K,$
where: V is the voltage output by the sensor 48 expressed in volts, t is the time in seconds, and K is the positive predetermined constant value having the units volts/second. This is proportional to directly differentiating the pressure sensed by the sensor 48 with respect to time, taking the negative of the differential, and then determining whether or not the result is greater than or equal to a positive predetermined constant value of variation of pressure with respect to time, or: $- \frac{ⅆ P}{ⅆ t} \geq X,$
where: P is the pressure sensed by the sensor 48 expressed as mmHg vacuum (and is a negative value), t is the time in seconds, and X is the positive predetermined constant value having the units mmHg/second (and is a positive value). X may, for example, be 1000 mmHg/second. The value of X may be adjusted between 100 to 5000 mmHg/second to alter the sensitivity of the detector component 60. The value of X may be displayed on a control panel of the phaco-machine 30 and may be adjusted to the sensitivity that suits the preference of the surgeon who uses the machine 30.
If the negative of the differentiated output of the sensor 48 is greater than or equal to the positive predetermined constant value, a trigger signal 63 is output from a trigger signal output 64 of the detector 60 to an input of the valve controller 61 as depicted in FIGS. 6 and 7. The trigger signal 63 is an inverted step function in which the output of the detector 60 changes abruptly from +10V to 0V. The trigger signal 63 is output less than 1 millisecond after the detector 60 detects that the rate of change of the vacuum sensor output voltage is greater than or equal to the value of K. The detector 60 detects this shortly after an occlusion in the tip of the probe 31 of the phaco-machine 30 breaks free because the vacuum inside the aspiration tube 41 of the machine 30 is falling very rapidly at this stage but more slowly at other times during operation of the machine 30. This is depicted in FIG. 8 where it can be seen that the positive voltage output of the sensor 48 which is proportional to the vacuum inside the aspiration tube 41 decreases rapidly after the occlusion breaks free such that the negative of the rate of change of the voltage at the start of the illustrated waveform exceeds or is equal to the positive predetermined constant value. The portion of the voltage waveform depicted in FIG. 8 which is below 0V is represented by a dotted line because the vacuum sensor 48 is only able to output a positive voltage.
The detector 60 includes an input 98 for disabling the operation of the detector 60 for experimental purposes such as for making experimental recordings of the reduced performance of the machine 30 when the detector 60 (and, therefore, the post-occlusion surge controller) is disabled. The detector 60 has an input 65 for enabling the detector 60 to operate only if the machine 30 is being operated in a high vacuum mode where the predetermined maximum allowable vacuum inside the aspiration tube 41 and other compliant components has been reached. Moreover, the detector 60 has an input 67 for enabling the detector 60 to operate only when the vacuum inside the aspiration tube 41 and other compliant components has reached 70% of the predetermined maximum allowable vacuum, or any other preset value.
The valve controller 61 illustrated in FIG. 7 includes a timer 70 whose input is connected to the output 64 of the post-occlusion surge detector 60, and which outputs an ON vent valve control signal 71 to a vent valve driver 72 and a high voltage pulse generator 73 for a predetermined period of time immediately after receiving a trigger signal 63 from the detector 60. The valve controller 61 also includes a vent valve pre-energiser 74. The vent valve driver 72 and the high voltage pulse generator 73 energise a solenoid of the vent pinch valve 50 of the phaco-machine 30 while receiving the vent valve control signal 71 from the timer 70 so that the vent pinch valve 50 opens and thereby vents the inside of the aspiration tube 41 to fluid or air which has a higher pressure than that inside the tube 41. Venting the aspiration tube 41 in this manner causes the vacuum inside the tube 41 and other compliant components to rapidly decrease and reduces both the amplitude and duration of the post-occlusion surge. Once the timer 70 times out, the vent valve driver 72 ceases energising the solenoid of the vent pinch valve 50 so that the valve 50 pinches the venting tube 49 of the phaco-machine 30 to prevent further venting of the aspiration tube 41 through the venting tube 49. The machine 30 is then able to resume normal operation. Upon receiving the vent valve control signal 71, the high voltage pulse generator 73 outputs a high voltage signal 75 which times-out prior to the vent valve control signal 71 in all cases. The pre-energiser 74 switches off on account of the vacuum in the aspiration tube 41 falling to a value which is lower than the value which enables the pre-energiser 74.
The high voltage pulse generator 73 can be regarded as a current source drive to the solenoid of the vent pinch valve 50 which functions to rapidly establish an opening current in the solenoid coil of the vent pinch valve 50. The coil is inductive, and therefore opposes a rapid rate of change in current. A rapid increase in the current can be achieved with either the application of a high voltage pulse, which attempts to generate a rapid increase in current, or a current source equivalent circuit which attempts to apply a constant current through the solenoid, and also therefore generates a high voltage pulse in the process of doing so. The net effect of either a high voltage pulse, or a current source drive, is equivalent.
When the solenoid of the vent pinch valve 50 is energised by the driver 72 or high voltage pulse generator 73 it is important that the valve 50 opens as quickly as possible to minimise the delay in arresting the post-occlusion surge and to reduce the possibility of damaging the eye 53 which is being treated with the phaco-machine 30. The delay in opening the vent pinch valve 50 can be reduced if the vent pinch valve 50 is a normally closed electromechanical pinch valve which is maintained in the closed position by a spring when the solenoid of the valve 50 is not energised. This enables the solenoid of the valve 50 to be pre-energised prior to being opened such that the valve 50 is on the verge of opening. This reduces the electromechanical delay in opening the valve 50. It has been found that pre-energising the solenoid of the valve 50 in this manner results in valve opening times of 30 to 40 milliseconds being achieved as opposed to valve opening times of over 100 milliseconds when the valve 50 is not pre-energised. Driving the valve 50 with a high voltage pulse further reduces the delay to 20 milliseconds.
The vent valve 50 is pre-energised by the pre-energiser 74. The output of the pre-energiser 74 is connected to the solenoid of the vent pinch valve 50 by the driver 72 and, when enabled, the pre-energiser 74 applies a pre-energising voltage across the solenoid so that the vent pinch valve 50 is on the verge of opening. The pre-energiser 74 includes an input 76 for disabling its operation when the machine 30 is used in a low vacuum mode where the predetermined maximum allowable vacuum inside the aspiration tube 41 is set to a relatively low level. The pre-energiser 74 also has an input 77 for enabling its operation when the vacuum inside the aspiration tube 41 exceeds 70% of the predetermined maximum allowable vacuum level or some other preset level of measured aspiration tube vacuum. The pre-energiser 74 may also have a switch for disabling its operation for purposes such as making experimental recordings.
FIG. 9 depicts a graph 80 of the variation over time of the vacuum inside the aspiration tube 41 of the machine 30 fitted with the post-occlusion surge controller which includes the detector 60 and the valve controller 61 immediately after an occlusion in the tip of the needle 33 of the machine 30 is removed. Around 40 milliseconds after the occlusion is removed (i.e., around 40 milliseconds after t=0 seconds), the valve controller 61 has opened the valve 50 after receiving a trigger signal 63 from the surge detector 60 so that the rapidly opened vent valve 50 causes the vacuum inside the aspiration tube 41 to rapidly decrease beyond zero to the eye pressure due to bottle height, pgh, which in turn reduces the amplitude and duration of the post-occlusion surge. The oscillations in the graph 80 of the vacuum are a result of low resistance in the pathway to the vent valve 50. In a system of damped simple harmonic motion, reducing the resistance encourages oscillations. Note that the positive pressure values of the graph 80 depicted in FIG. 9 would not be sensed by the sensor 48 because the sensor 48 can only sense vacuum and not positive pressure. For comparative purposes, the graph depicted in FIG. 3 is superimposed on the graph 80 and is represented by a dotted line.
The variation over time of the pressure inside the anterior chamber of an eye 53 treated with the post-occlusion surge controller equipped version of the machine 30 is depicted in FIG. 10 by the waveform 81. Waveform 81 depicts the variation of the eye pressure immediately after an occlusion in the probe tip of the machine 30 is removed. In comparison to the eye pressure graph depicted in FIG. 5, the peak of the drop in eye pressure depicted by the waveform 81 has been significantly attenuated. Moreover, the duration of the waveform 81 has been significantly reduced in comparison to the duration of the waveform depicted in FIG. 5. The attenuation in the peak drop in eye pressure and the reduced duration of the drop in eye pressure correspond to a reduction in the post-occlusion surge. Waveform 81 is superimposed over a graph of the variation over time of the vacuum in the aspiration tube 41 of the same machine 30 over the same period of time when the machine 30 includes the post-occlusion surge controller. The portions of the graph of the variation over time of the vacuum in the aspiration tube 41 which are above zero pressure are depicted by dotted lines because vacuum levels above zero (i.e., positive pressures) are not sensed by the vacuum sensor 48 which only outputs a positive voltage for a vacuum.
A schematic block diagram of a different post-occlusion surge controller 90 is illustrated in FIG. 11. For convenience, features of the controller 90 which correspond to features of the previously described post-occlusion surge controller are referenced using the same reference numbers.
Post-occlusion surge controller 90 is identical to the previously described post-occlusion surge controller except that the high voltage pulse generator 73 and pre-energiser 74 of the controller 90 are only enabled when the measured vacuum in the aspiration tube 41 is greater than 150 mmHg. The high voltage pulse generator 73 and the pre-energiser 74 respectively include an input 91 and an input 92 for receiving an enable signal which enables the generator 73 and the pre-energiser 74.
At the beginning of the post-occlusion surge, fluid enters the probe end of the aspiration tube 41, and the wall of the aspiration tube 41 begins to expand to its original geometry, prior to compression by atmospheric pressure. The expansion of the aspiration tube 41 progresses along the length of the tube 41 (which is typically 2 metres long) from the probe towards the pump 40 at 360 kilometres per hour. When this reaches the vacuum sensor 48 there is an abrupt drop in vacuum. This assists the detector circuit 60 to detect the start of the post-occlusion surge.
Moreover, the pre-energiser 74 of the post-occlusion surge controller 90 does not have a disable switch and does not include separate inputs for enabling it when the vacuum is greater than 70% of the maximum allowable vacuum, and for disabling it when the machine 30 is being used in a low vacuum mode.
The valve driver 72, vent valve 50, and pre-energiser 74 of the controller 90 are powered by a 12V supply voltage, while the generator 73 is powered by a 40V supply voltage. Also, the vent valve control signal 71 which is output by the timer 70 has a reduced duration of 50 milliseconds to reduce the time that the valve 50 is open which reduces oscillations of the vacuum in the aspiration tube 41 of the machine 30 from those depicted in FIG. 9 to those depicted in FIG. 12.
The timer 70 includes an input 93 for controlling the standard functioning of the timer 70. Additional information in relation to the input 93 is provided further on in relation to FIG. 18.
FIG. 11 depicts a high voltage pulse timing waveform 95 which is generated by the high voltage generator 73 coincident with the rising edge of the vent valve control signal 71, the timing relationship between the waveform 95 and the signal 71 is also depicted.
FIG. 11 also depicts an output signal 96 which is output by the vacuum sensor 48 during the post-occlusion surge.
The timing of the trigger signal output by the detector 60, the output signal 71 of the timer 70, and the opening time of the vent valve 50 relative to the waveform depicted in FIG. 12, is provided in FIGS. 13 to 15. Due to the compliance of the aspiration tube 41, there is a 20 millisecond delay, t₁, between the start of the surge in the eye and a response by the vacuum sensor 48 of the machine 30. The 20 millisecond delay, t₁, adds to the 20 millisecond delay, t₃, to deploy the valve 50. The valve 50 therefore mechanically deploys approximately 40 milliseconds after the actual surge in the eye starts. This delay is short enough to allow the surge neutralisation to be effective as depicted in FIG. 16. There is also a short delay, t₂, which is attributable to the detector 60 but which is insignificant.
Referring to FIG. 17, the graphs depicted in FIGS. 3 and 4 are represented by dotted lines and are superimposed on the graphs depicted in FIGS. 12, 15, and 16. The representation in FIG. 17 of the graphs depicted in FIGS. 12, 15, and 16, are an actual recording of the performance of the machine 30 when equipped with the controller 90.
FIG. 18 is a schematic circuit diagram of the valve controller 61 which belongs to the post-occlusion surge controller 90. The timer 70 includes an input 97 which is connected to the output 64 of the post-occlusion surge detector 60, and an input 93 for controlling the timer 70 so that the valve controller 61 is also able to control the vent pinch valve 50 to vent the aspiration tube 41 at times other than when a post-occlusion surge is detected by the detector 60. The timer 70 also includes an input 98 for disabling the timer 70.
The output of the timer 70 from which the vent valve control signal 71 is output is connected to a first input of an AND logic gate 99 and to the base of a Darlington transistor T1 via a 5.1 kΩ resistor R1. An override input 100 is also connected to the base of the Darlington transistor T1 via a 5.1 kΩ resistor R2.
An input 101 for enabling the high voltage pulse generator 73 and the vent valve pre-energiser 74 is connected to an input of an AND logic gate 102. Another input of the AND gate 102 is connected to the output of an AND logic gate 103. An input of the AND logic gate 103 is connected to the output of an AND logic gate 104. Gate 104 is connected to a first low level disable input 105 and a second low level disable input 106, while an input of the gate 103 which is not connected to the output of the gate 104 is connected to a third low level disable input 107. The output of the gate 102 is connected to an input of the gate 99. The output of the gate 102 is also connected to the base of a Darlington transistor T2 via a 10 kΩ resistor R3. The base of the transistor T2 is also connected to ground via a 47 kΩ resistor R4. The output of the gate 102 is also connected to input 65 of the detector 60. The output of the gate 102 is high when the high voltage pulse generator 73 and the vent valve pre-energiser 74 are enabled and low when the high voltage pulse generator 73 and the vent valve pre-energiser 74 are disabled.
The output of the gate 99 is connected to the base of a transistor T3 via a 10 kΩ resistor R5. The emitter of the transistor T3 is connected to ground, while the collector of the transistor T3 is connected to the base of a Darlington transistor T4 via a 4.7 kΩ resistor R6. The base of the transistor T4 is connected to the emitter thereof via a 47 kΩ resistor R7.
The emitter of the transistor T1 is connected to ground. The collector of the transistor T1 is connected to the collector of the transistor T4 via a diode D1. A normally closed 12V vent valve solenoid 108 is connected across the diode D1. The collector of the transistor T1 is also connected to the collector of the transistor T2 via a 2 Watt 39Ω resistor R8.
The emitter of the transistor T4 is connected to ground via a 5600 μF capacitor C1. A positive terminal of the capacitor C1 is connected to a +40V power supply via a 2 Watt 470Ω resistor R9. The positive terminal of the capacitor C1 is also connected to a +12V power supply via a diode D2. The +12V power supply is also connected to the collector of the transistor T4 via a diode D3. The high voltage pulse 95 is output from the collector of the transistor T4.
The 0V reference outputs of the +40V and +12V power supplies are connected to ground.
The relative timing of the trigger signal 63, vent valve control signal 71 and the high voltage pulse 95 are also depicted in FIG. 18.
During standard vent valve deployment, the vent valve solenoid 108 is activated via input 93 to the timer 70, the output of which drives the Darlington transistor T1. When T1 is conducting, current flows from the 12V supply, via diode D3, through the solenoid coil 108 and transistor T1 to ground.
Diode D1 absorbs the EMF (voltage spike) generated by the solenoid 108 when T1 ceases to conduct at the end of the timing cycle when the field in the solenoid 108 collapses. This protects T4, T1 and T2 from being damaged. This completes the circuit, and the valve 50 of the machine 30 opens for the duration specified by the valve control signal 71 which is output by the timer 70.
However, in this usual mode, depending on the particular solenoid 108, there is a delay of 80 to 150 milliseconds between the time that the timer 70 gives the command to open before the actual valve 50 opens, because it takes time to establish the opening current in the solenoid coil 108 and time to move the mass of the armature or moving core of the solenoid 108. In addition, once the valve 50 opens and the infusion fluid 37 starts to flow there is a further delay of around 40 milliseconds before the effects of venting are realised in the anterior chamber of the eye 53. In usual operation this delay is not a concern. However, if the valve 50 is to be used as a “post-occlusion surge neutralisation device”, it must have accelerated operation, as a typical surge has already peaked at 200 milliseconds after it begins.
The valve controller 61 is also capable of controlling the vent valve 50 when the vent valve solenoid 108 is of the normally closed type (i.e. closed with a spring) and opened with the application of electrical drive to the solenoid 108.
Post-occlusion surges occur in high vacuum modes during phaco-emulsification, typically over 100 to 150 mmHg, and in some modes of phaco-machine use, for example low vacuum mode or irrigation/aspiration (IA) mode surges are not as troublesome and the function of surge neutralisation is not needed. Therefore, the vent controller circuit 61 includes inputs to enable or disable the specialised operations.
As mentioned previously, the vent controller circuit 61 includes AND logic gates 99, 102, 103, and 104 which are standard dual input logic AND gates where both inputs need to be high to enable or give a high output. For the output of gate 102 to be high, all inputs, 101, 105, 106, and 107, must be high. Taking any of those inputs low takes the output of gate 102 low.
Input 101 is high only when the vacuum sensed in the aspiration tube 41 is over 150 mmHg (or any other level specified), and surges are anticipated, and is otherwise low to disable the function. The other inputs 105, 106, 107 can be taken low to disable the function at any time. For example, input 105 can be taken low in IA mode or 106 taken low in low vacuum mode and 107 could be used to deactivate the specialised operation on command.
When the output of gate 102 is high, this is the enable signal which enables the post-inclusion surge controller 90 in anticipation of a post-occlusion surge, and the NPN Darlington transistor T2 is able to conduct. A current, determined by the value of R8, flows from the 12V power supply, via D3, through solenoid 108, and then via R8 and T2 to complete the circuit. The value of R8 is selected so the current flowing through the solenoid 108 is close to but below the current required to open the vent valve 50. This reduces the time it takes to increase the current to the value which will cause the vent valve 50 to open. This is the pre-drive current, applied in anticipation of the need for a rapid valve deployment. The enable signal which is output by the gate 102 is also used to enable the surge detector 60 that generates the trigger signal 63 that drives the timer 70.
Pre-drive current is present therefore prior to a post-occlusion surge and when the surge is detected by the detector 60 (i.e. is a rapid rate of change of vacuum in the aspiration tube 41) the trigger signal 63 is generated and fed to input 97 of the timer 70. This triggers the timer 70 so that the output of the timer 70 goes high for the opening period. At this point, a number of things occur.
One thing which occurs is that T1 conducts, and the current flowing through the solenoid coil 108 starts to increase above the pre-drive value. The output of the timer 70 is passed via gate 99 to NPN transistor T3 which conducts, turning on PNP Darlington transistor T4.
Also, T4 is connected to C1, a capacitor charged to the potential of the +40V power supply, via a charging resistor R9 so that approximately 4.5 Joules of energy is stored in the capacitor C1. Moreover, diode D2 is reverse biased and is not conducting. At the moment T4 conducts, the capacitor C1 is switched to the uppermost terminal of the vent valve solenoid 108, and the lower terminal of the vent valve solenoid 108 is at ground potential as T1 is conducting also during the timing period. Capacitor C1, via transistor T4, immediately applies the +40V to the solenoid 108 and this rapidly increases the current to the opening value.
At the time T4 is conducting (i.e. during the time that the timer 70 is high), the uppermost terminal of the solenoid 108 spikes to +40V and diode D3 is reverse biased, decoupling the standard +12V drive from the upper terminal of the solenoid 108. The width of the high voltage pulse 95 is shorter than the period of the vent valve control signal 71, and decays away as capacitor C1 rapidly discharges into the solenoid 108. This prevents the solenoid 108 from overheating from excessive drive. Only an initial impulse is required for the rapid opening. The diode D2 prevents capacitor C1 discharging below 11.3V. Therefore, after the initial rapid pulse occurs at the opening time, the solenoid current returns to its standard value.
After the timing period T3, T4 and T1 turn off. Due to the post-inclusion surge controller 90 having controlled the vent valve 50 to vent the aspiration tube 41 of the machine 30, the vacuum in the aspiration tube 41 is very low or positive from the pressure of the infusion fluid 37 in the bottle 36, and the input 101 falls low because the vacuum in the aspiration tube 41 is below 150 mmHg. T2 also turns off and the pre-drive current is now zero. With no current flowing through the solenoid coil 108, the spring of the vent valve 50 causes the valve 50 to close. At this time, C1 also recharges to the 40V supply potential via R9. When the vacuum in the aspiration tube 41 later climbs above 150 mmHg, the pre-drive current returns and the system is “armed” again ready to neutralise another post-inclusion surge.
FIG. 19 is a schematic circuit diagram of the timer 70 of the valve controller 61 which belongs to the post-occlusion surge controller 90.
Timer 70 includes a 555 timer integrated circuit IC1 which includes pins P1, P2, P3, P4, P5, P6, P7, and P8. Pin P1 is connected to ground, and pin P5 is connected to ground via a 0.01 μF capacitor C2. Pins P7 and P6 are connected to ground via a 1 μF capacitor C3, and to pin P8 via a 47 kΩ resistor R10. Pin P3 is connected to resistor R1 and gate 99 which are depicted in FIG. 18. Pin P4 of the timer IC1 is connected to input 98 which is depicted in FIG. 18.
A diode D4 and a 100 kΩ resistor R11 are connected to each other in parallel and across pins P2 and P8. The vent valve control signal 71 is output by the timer IC1 on pin P3. The duration of the signal 71 is 51.7 milliseconds and is calculated by multiplying the product of the capacitor C3 and the resistor R10 by 1.1.
Pin P8 is connected to a +10V power supply and to ground via a 10 μF capacitor C4. The 0V reference output of the +10V power supply is connected to ground.
Pin P2 of the IC1 is connected to a diode D5 and a diode D6 via a 0.1 μF capacitor C5. Pin P8 is connected to the diodes D5 and D6 via a 100 kΩ resistor R12. Diode D5 is connected to input 93 of the timer 70, while diode D6 is connected to input 97 of the timer 70.
Timer 70 can be disabled, for example in the machine setup mode by the input 98. The vent valve 50 can be opened at any time, for example in the machine setup mode to assist insertion of the aspiration tube 41 into the head of the valve 50, by the override input 100 depicted in FIG. 18. Timer 70 is a standard circuit. Timer 70 may be implemented in either software or hardware.
FIG. 20 is a schematic circuit diagram of the post-occlusion surge detector 60 which belongs to the post-occlusion surge controller 90.
Vacuum sensor 48 of the phaco-machine 30 includes a sensor component 109 whose input is connected to the lumen of the aspiration tube 41 of the machine 30, and an amplifier component 110 which amplifies the electrical signal which is output by the sensor component 109. The output of the amplifier component 110 is able to vary between 0 to 10V which corresponds to a vacuum variation in the lumen of the aspiration tube 41 of 0 to −500 mmHg. Thus a 50 mmHg variation in vacuum corresponds to a 1V variation in the output of the amplifier component 110.
The output of the amplifier component 110 of the vacuum sensor 48 is connected to the negative input of an operational amplifier IC2 via a 1 kΩ resistor and 1 μF capacitor C6 which are connected in series to each other. The negative and positive inputs of IC2 are connected to each other by a pair of parallel diodes D7, D8. The positive input of IC2 is also connected to ground. The negative input and output of IC2 are connected to each other via a resistor R14 which is typically a 300 kΩ resistor. The output of IC2 is connected to the negative input of an operational amplifier IC3 and to the collector of a transistor T5 via a 5.1 kΩ resistor R15. IC2 is powered by a +10V power supply.
The base of the transistor T5 is connected to a +10V power supply via a 9.1 kΩ resistor R16, and to the collector of a transistor T6. The emitter of transistor T6 is connected to ground, and the base of transistor T6 is connected to an enable input 65 of the controller 61 via a 20 kΩ resistor R17.
A positive input of the operational amplifier IC3 is connected to a +6V reference voltage. The output of IC3 is connected to the input 97 of the valve controller 61. IC3 is powered by a +10V power supply.
Operational amplifier IC2 is configured as a differentiator and is used to monitor the output from the amplifier component 110 of the vacuum sensor 48. The output of IC2 is fed into the operational amplifier IC3 which is configured as a comparator and which is referenced to the fixed +6V reference voltage. The trigger signal 63 is generated by IC3 when the negative rate of change of the voltage output of the amplifier component 110 is greater than or equal to the +6V reference divided by the product of resistor R14 and capacitor C6. This corresponds to the voltage output by the operational amplifier IC2 being greater than or equal to the +6V reference voltage. In a worked example with R14 having a value of 300 kΩ and C6 having a value of 1 μF, dividing the +6V reference voltage by the product of the resistor R14 and the capacitor C6 gives 20V/second (50 mmHg corresponds to 1V from the amplifier component 110). This corresponds to a rate of change of vacuum of 1000 mmHg/second, to generate the trigger signal 63. The threshold for the trigger signal 63 as determined by the reference voltage and product of C6 and R14 sets the “sensitivity” of the detector 60 and can be adjusted to any value, for example, between 100 and 5000 mmHg/second. Significant post-occlusion surges have higher rates of change of vacuum associated with them, so the sensitivity can be set so that the venting does not excessively interrupt the course of the cataract extraction. Diodes D7 and D8 allow for rapid recharging of differentiator capacitor C6. T5 and T6 are used to disable the detector when the output of gate 102 is low, or in the disabled state. The surge detector 60 may be implemented in hardware or in software.
The above techniques shorten the opening time of the vent valve to 20 milliseconds after the trigger signal 63 is presented. The trigger signal 63 is generated 20 milliseconds after the surge begins in the eye 53, so there is an overall latency of 40 milliseconds. Another 40 milliseconds delay is encountered prior to any measurable effect of the venting at the machine 30, near the vent valve 50, reducing the surge in the eye 53. The deployment of the vent valve 50 therefore occurs significantly sooner than when the unaltered surge would have otherwise peaked at around 200 milliseconds. The result is a post-occlusion surge of significantly lower amplitude and duration. This reduced surge has approximately one-third of the area below the curve of pressure versus time compared to any existing machine.
The vent valve solenoid 108 is preferably constructed with the lowest possible mass armature or moving core so as to reduce the inertia of the vent valve 50 by as much as possible.
Plain transistors, Darlington transistors, power MOSFETS, or IGBT's or similar can be used to implement the circuit configuration.
The present invention allows for early detection and arrest of the post-occlusion surge such that both the amplitude and duration of the surge are reduced. This enables a phaco-machine which is equipped with the invention to be used with high maximum vacuums whilst the amplitude and duration of any post-occlusion surges which may occur remain within acceptable limits.
It will be appreciated by those skilled in the art that variations and modifications to the invention described herein will be apparent without departing from the spirit and scope thereof. The variations and modifications as would be apparent to persons skilled in the art are deemed to fall within the broad scope and ambit of the invention as herein set forth.

Claims

1. A post-occlusion surge controller for a phacoemulsification machine, wherein the controller is adapted to detect a post-occlusion surge in an aspiration conduit of the machine, and to cause the conduit to be vented in response to detecting the surge.

2. The post-occlusion surge controller of claim 1, wherein the controller is adapted to detect the onset of the surge, and to cause the conduit to be vented in response to detecting the onset of the surge.

3. The post-occlusion surge controller of claim 2, wherein the controller includes a detector for detecting the onset of the surge, and a valve controller for controlling a vent valve of the machine in response to the detector detecting the onset of the surge.

4. The post-occlusion surge controller of claim 3, wherein the detector includes a differentiator for differentiating the output of a vacuum sensor of the machine, and a comparator for comparing the output of the differentiator with a reference value and for outputting a trigger signal depending upon the outcome of the comparison.

5. The post-occlusion surge controller of claim 4, wherein the valve controller includes a timer for outputting a vent valve control signal in response to receiving the trigger signal, and a vent valve driver for driving the vent valve to vent the aspiration conduit in response to the vent valve control signal.

6. The post-occlusion surge controller of claim 5, wherein the valve controller includes a high voltage pulse generator for outputting a high voltage pulse signal to a solenoid of the vent valve in response to the vent valve control signal.

7. The post-occlusion surge controller of claim 6, wherein the valve controller includes a vent valve pre-energiser for pre-energising the solenoid.

8. A method of controlling a post-occlusion surge in an aspiration conduit of a phacoemulsification machine, the method comprising the steps of:

(i) detecting the post-occlusion surge; and

(ii) venting the conduit in response to detecting the surge.

9. The method of claim 8, wherein the step of detecting the surge involves detecting the onset of the surge and the step of venting the conduit is done in response to detecting the onset of the surge.

10. The method of claim 9, wherein the step of detecting the onset of the surge includes determining whether the negative of the rate of change of the vacuum in the conduit with respect to time is greater than or equal to a constant value.

11. The method of claim 8, wherein the step of venting the conduit involve operating a vent valve of the machine to vent the conduit.

12. The method of claim 11, wherein the vent valve vents the conduit for a predetermined period of time.