Abstract:
Systems and methods for controlling vacuum within phacoemulsification systems are described. The phacoemulsification system may include a handpiece having a needle coupled to a power source configured to cause the needle to be ultrasonically vibrated, and an aspiration source. The system further includes a footpedal that defines a first position and a second position and a computer program product, operatively coupled to the handpiece and the footpedal, having a non-transitory computer-usable medium having a sequence of instructions which, when executed by a processor, causes the processor to execute a process that controls power from the power source and vacuum from the aspiration source applied to the handpiece.

Description:
FIELD OF THE INVENTION 
     The field of the invention relates to systems and methods for cataract surgery, and more particularly to systems and methods for controlling vacuum within phacoemulsification systems. 
     BACKGROUND OF THE INVENTION 
     A number of medically recognized techniques are utilized for cataractous lens removal based on, for example, phacoemulsification, mechanical cutting or destruction, laser treatments, water jet treatments, and so on. 
     The phacoemulsification method includes emulsifying, or liquefying, the cataractous lens with ultrasonic power and then removing the emulsified material out of the eye. A phacoemulsification system  5  known in the art is shown in  FIG. 1 . The system  5  generally includes a phacoemulsification handpiece  10  coupled to an irrigation source  30  and an aspiration (or vacuum) pump  40 . The handpiece  10  includes a needle  15  at the distal tip (shown within the anterior chamber of the patient&#39;s eye  1 ) that is ultrasonically vibrated to emulsify the cataractous lens within the patient&#39;s eye  1 . The handpiece  10  further includes an irrigation port  25  proximal to the distal tip of the needle  15 , which is coupled to an irrigation source  30  via an irrigation line  35 , and an aspiration port  20  at the distal tip of the needle  15 , which is coupled to an aspiration pump  40  via an aspiration line  45 . Concomitantly with the emulsification, fluid from the irrigation source  30 , which is typically an elevated bottle of saline solution, is irrigated into the eye  1  via the irrigation line  35  and the irrigation port  25 , and the irrigation fluid and emulsified cataractous lens material are aspirated from the eye  1  by the aspiration pump  40  via the aspiration port  20  and the aspiration line  45 . Other medical techniques for removing cataractous lenses also typically include irrigating the eye and aspirating lens parts and other liquids. Additionally, some procedures may include irrigating the eye  1  and aspirating the irrigating fluid without concomitant destruction, alteration or removal of the lens, e.g., with ultrasonic power. 
     Aspiration can be achieved with a variety of different aspiration pumps  40  known in the art. The two most common types are (1) volumetric flow or positive displacement pumps (also referred to as flow-based pumps such as peristaltic or scroll pumps) and (2) vacuum-based pumps (such as venturi, diaphragm, or rotary-vane pumps). Each type has its own general advantages and disadvantages. Turning to  FIG. 2 , an example peristaltic flow pump  50  is illustrated. In this configuration, the aspiration line  45  is in direct contact with a rotating pump head  50  having rollers  52  around its perimeter. As the pump head  50  rotates clockwise, the rollers  52  press against the line  45  causing fluid to flow within the line  45  in the direction of the rollers  52 . This is referred to as a volumetric flow pump because the pump  50  directly controls the volume or rate of fluid flow. An advantage with this type of pump  50  is that the rate of fluid flow can be easily and precisely controlled by adjusting the rotational speed of the pump head  50 . 
     Turning to  FIG. 3 , an example vacuum-based pump  60  is illustrated. This type of pump indirectly controls fluid flow by controlling the vacuum within the fluidic circuit. For example, the vacuum-based pump  60  can be a pneumatic pump (e.g., a venturi pump) that creates a pressure differential in a drainage cassette reservoir  65  that causes the fluid to be sucked from the aspiration line  45  into the drainage cassette reservoir  65 . Thus, instead of pushing fluid through the aspiration line  45  like the flow pump  50 , the fluid is essentially pulled by vacuum through the line  45 . The rate of fluid flow generated by a vacuum-based pump is generally higher than the rate of fluid flow generated by a volumetric flow based pump because the vacuum-level is generally higher; however, the control of the rate of fluid flow generally involves a different control mechanism. 
     As is well known, for these various surgical techniques it is necessary to maintain a stable volume of liquid in the anterior chamber of the eye, and this is accomplished by irrigating fluid into the eye at the same rate as aspirating fluid and lens material. For example, see U.S. Pat. No. 5,700,240, to Barwick et. al, filed Jan. 24, 1995 (“Barwick”) and U.S. Pat. No. 7,670,330 to Claus et. al, filed Mar. 21, 2005 (“Claus”), which are both hereby incorporated by reference in their entirety. During phacoemulsification, it is possible for the aspirating phacoemulsification handpiece  10  to become occluded. This occlusion is caused by particles blocking a lumen or tube in the needle  15  of the handpiece  10 , e.g., the aspiration port  20  or irrigation port  25 . In the case of volumetric flow based pumps, this blockage can result in increased vacuum (i.e. increasingly negative pressure) in the aspiration line  45  and the longer the occlusion is in place, the greater the vacuum. In contrast, with a vacuum-based pump, this blockage can result in a volumetric fluid flow drop off near the aspiration port  20 . In either case, once the occlusion is cleared, a resulting rush of fluid from the anterior chamber into the aspiration line  45  can outpace the volumetric flow of new fluid into the eye  1  from the irrigation source  30 . 
     The resulting imbalance of incoming and outgoing fluid can create an undesirable phenomenon known as post-occlusion surge or fluidic surge, in which the structure of the anterior chamber moves rapidly as fluid is replaced due to the dynamic change in the rate of fluid flow and pressure. Such post-occlusion surge events may lead to eye trauma. The most common approach to preventing or minimizing the post-occlusion surge is to quickly adjust the vacuum-level or rate of fluid flow in the aspiration line  45  and/or the ultrasonic power of the handpiece  10  upon detection of an occlusion. Many surgeons rely on their own visual observations to detect the occlusion; however, because of the unpredictable and time-sensitive nature of the problem, a reliable computer-based detection and response system is preferable. 
     For current systems with volumetric flow pumps  50 , if an occlusion occurs, the flow rate will decrease at the aspiration port  20  and the vacuum level within the aspiration line  45  between the pump  50  and the handpiece  10  will increase. Thus, a computer-based system (not shown) can utilize a vacuum sensor  55  placed on the aspiration line  45  to detect the vacuum increase and respond accordingly (an example of such a system is described in U.S. Pat. No. 5,700,240, to Barwick et. al, filed Jan. 24, 1995 and U.S. Pat. No. 7,670,330 to Claus et. al, filed Mar. 21, 2005). For current systems with vacuum-based pumps  60 , however, the vacuum level within the aspiration line  45  is tied to the vacuum power generated by the pump  60  and thus, may not be an effective indicator of whether an occlusion has occurred. Accordingly, an improved system and method for controlling the rate of fluid flow in vacuum based systems on the detection of occlusion within a fluid circuit is desirable. 
     SUMMARY OF THE INVENTION 
     The field of the invention relates to systems and methods for cataract surgery, and more particularly to systems and methods for controlling vacuum within phacoemulsification systems. In one embodiment, a phacoemulsification system may include a phacoemulsification handpiece having a needle. The needle is coupled to a power source configured to cause the needle to be ultrasonically vibrated during operation and an aspiration source. The system further includes a footpedal that defines a first position and a second position. The system also includes a computer program product operatively coupled to the phacoemulsification handpiece and the footpedal, the computer program product having a computer-usable medium having a sequence of instructions which, when executed by a processor, causes said processor to execute a process that controls power from the power source and vacuum from the aspiration source applied to the phacoemulsification handpiece. 
     The process includes the steps of providing the vacuum at a first vacuum level to the handpiece when the footpedal is at the first position; providing power to the handpiece when the footpedal is at the second position; and reducing the vacuum to a second vacuum level when the footpedal transitions from the first position to the second position. 
     Other systems, methods, features and advantages of the invention will be or will become apparent to one with skill in the art upon examination of the following figures and detailed description. It is intended that all such additional systems, methods, features and advantages be included within this description, be within the scope of the invention, and be protected by the accompanying claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In order to better appreciate how the above-recited and other advantages and objects of the inventions are obtained, a more particular description of the embodiments briefly described above will be rendered by reference to specific embodiments thereof, which are illustrated in the accompanying drawings. It should be noted that the components in the figures are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. Moreover, in the figures, like reference numerals designate corresponding parts throughout the different views. However, like parts do not always have like reference numerals. Moreover, all illustrations are intended to convey concepts, where relative sizes, shapes and other detailed attributes may be illustrated schematically rather than literally or precisely. 
         FIG. 1  is a diagram of a phacoemulsification system known in the art. 
         FIG. 2  is a diagram of a phacoemulsification system having a flow-based aspiration pump known in the art. 
         FIG. 3  is a diagram of a phacoemulsification system having a vacuum-based aspiration pump known in the art. 
         FIG. 4  is a functional block diagram of a phacoemulsification system in accordance with a preferred embodiment of the present invention; 
         FIG. 5  is a perspective view of a footpedal suitable for use with the present invention; 
         FIG. 6  is a diagram showing an exemplary configuration for the footpedal shown in  FIG. 5 . 
         FIG. 7  is a flowchart of a process in accordance with a preferred embodiment of the present invention. 
         FIG. 8 a    is another flowchart of a process in accordance with a preferred embodiment of the present invention. 
         FIG. 8 b    is chart illustrating an exemplary vacuum modulation in accordance with a preferred embodiment of the present invention. 
         FIG. 9  is another flowchart of a process in accordance with a preferred embodiment of the present invention. 
         FIG. 10  is another flowchart of a process in accordance with a preferred embodiment of the present invention. 
         FIG. 11 a    is a diagram of a phacoemulsification system having a venturi-based pump and a peristaltic-based pump known in the art. 
         FIG. 11 b    is another flowchart of a process in accordance with a preferred embodiment of the present invention. 
         FIG. 12  is another flowchart of a process in accordance with a preferred embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     As described above, phacoemulsification typically involves the interplay of three key elements: power (ultrasonic power), vacuum (or aspiration), and irrigation fluid. Turning to  FIG. 4 , an exemplary system  100  that allows for control of these elements during phacoemulsification is further illustrated in block diagram form. The system  100  has a control unit  105 , indicated by the dashed lines in  FIG. 4  that includes a source of ultrasonic power  107  coupled to a handpiece  104  via line  102 , a microprocessor computer  109  that provides control outputs to ultrasonic power level controller  111  that controls the ultrasonic power source  107 . Ultrasonic power is delivered to eye  106  via handpiece  104  as illustrated by line  117 . 
     The control unit  105  further includes an aspiration source  115 —which may be a vacuum-based pump, such as a venturi-based-pump described above, a flow-based pump, such as a peristaltic-based pump described above, or a combination of a vacuum-based pump and a flow-based pump. Fluid aspirated from eye  106  via handpiece  104  is illustrated by line  108 . The vacuum level of the aspiration source  115  applied to handpiece  104  via line  110  is controlled and monitored by computer  109 . The system  100  further includes an irrigation fluid source  101  that is fluidly coupled to the handpiece  104 . Irrigation fluid is delivered to eye  106  via handpiece  104  as illustrated by line  116 . The rate of fluid provided to the handpiece  104  is also controlled by computer  109  of the control unit  105 . 
     The block representation of the handpiece  104  includes a needle and electrical means (not shown), typically a piezoelectric crystal, for ultrasonically vibrating the needle. The handpiece/needle  104  is used to apply the elements above to a patient&#39;s eye, or affected area or region, indicated diagrammatically by block  106 . 
     The control unit  105  may further include a user interface console, such as a touch screen monitor (not shown), to the computer  109  to allow the surgeon/operator to preset various system parameters. User defined system parameters may include, but are not limited to, selecting pulse shape amplitude mode, setting maximum allowable vacuum from aspiration source, minimum pulse shape amplitude, maximum pulse shape amplitude and irrigation rates. 
     A foot pedal  120  coupled to the computer  109  may be utilized to enable a surgeon/operator to control the irrigation source  101 , the power source  107 , and the aspiration source  115 . Turning to  FIG. 5 , an exemplary foot pedal  120  is shown, which is described in U.S. patent application Ser. No. 12/613,562, U.S. Publication No. 2011/0098721 A1, filed Nov. 6, 2009, for “Adjustable Foot Pedal Control for Ophthalmic Surgery”—incorporated herewith in its entirety. The foot pedal  120  includes a platform or footswitch  54  mounted to a base  52 . The base  52  has an undercarriage  58  arranged to lie flat on a ground surface and also a carrying handle  56 . Footswitch  54  mounts on the base  52  to provide a movable control surface for the user. In one embodiment, footswitch  54  may be mounted for rotational yaw or horizontal movement relative to the base  52 , as seen by the movement arrows in  FIG. 5 . Alternatively, the footswitch  54  may be mounted for pivoting movement in a vertical plane (pitch), as in a standard car accelerator-type pedal or as shown in  FIG. 5 , or may be a dual-control footswitch capable of both yaw and pivoting movement. As is known in the art, the computer  109  may include a computer-usable medium having a sequence of instructions which, when executed by a processor, causes said processor to execute a process that controls the elements above based on the displacement of the foot pedal  120 . For example,  FIG. 6  shows typical relative pitch displacement functions of the footswitch  54  communicatively coupled to computer  109  in which 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. Further description of the operation of the foot pedal  120  can be found in U.S. patent application Ser. No. 11/560,333, U.S. Publication No. 2007/0073309 A1, filed Nov. 15, 2006, for “Control of Pulse Duty Cycle Based Upon Footswitch Displacement”—also incorporated herewith in its entirety. 
     As mentioned above, for phacoemulsification systems  100  using vacuum-based pumps such as venturi, diaphragm, or rotary-vane-based pumps as aspiration sources  115 , the vacuum level within the aspiration line  110  is tied to the vacuum power generated by the source  115 , and thus, may not be an effective indicator of whether an occlusion has occurred. As a result, surgeons tend to use lower vacuum levels to avoid post-occlusion, use a smaller gauge phaco tip to restrict the inflow of fluid, immediately release the footswitch  54  following the application of power to reduce the maximum allowable vacuum level, and/or use flow restrictors. Though each of these action items may be able to reduce the risk of post-occlusion surge, each one can undesirably lengthen the time of surgery and still allow for human error. 
     One approach to address this issue is shown in  FIG. 7 , which illustrates a process  1000  that may be executed within computer  109 . Starting with the footswitch  54  displaced at foot position  2  (starting block  1010 ), if the user displaces or transitions the footswitch  54  to foot position  3  (decision block  1020 ), as described above, not only is vacuum applied to the handpiece  104 , but ultrasound power is delivered as well (action block  1060 ). As one of ordinary skill in the art would appreciate, an experienced surgeon would depress the footswitch  54  from foot position  1  to foot position  2  to apply vacuum to grab hold of a particular piece of cataract particle at the tip of the needle  104  to emulsify and remove. Often, the control is set up such that the vacuum level linearly rises as the surgeon depresses the footswitch  54  from the foot position  1 / 2  transition to the foot position  2 / 3  transition until the maximum allowable vacuum level (“Max Vac”) is reached (e.g., 300 mm Hg), and vice versa. For example, see U.S. Pat. No. 7,670,330 to Claus et. al, filed Mar. 21, 2005. Additionally, the control may be set up such that a transition from the foot position  1 / 2  to the foot position  2 / 3  linearly raises the vacuum level from a non-zero value (e.g., 100 mm Hg). When the tip of the needle of the handpiece  104  makes contact with the particle and is able to grab hold of it (with the help of the aspiration source  115 ), the surgeon would then further transition the footswitch  54  into foot position  3 , to apply the ultrasonic power that would emulsify the particle for aspiration. Subsequently, an actual occlusion may occur or the existence of an occlusion at the handpiece needle  104  can be inferred if the surgeon stays in foot position  3  for a period of time. 
     As illustrated in  FIG. 7 , in light of the above, a feature can be added to the control in computer  109  that allows for a pre-determined or user-chosen “chamber stabilization” (“CS”) setting to be enabled. If the CS setting is enabled, the process  1000  may proceed as follows. An actual occlusion may occur or the existence of an occlusion can be inferred if the footswitch  54  transitions into foot position  3  and stays in foot position  3  for a certain programmable period of time, e.g., in the hundreds of milliseconds range (a timer is compared in decision block  1030 , labeled as “counter limit reached?” and the timer is updated in action block  1040 , labeled as “run counter”), In one embodiment, this programmable period of time is between 100 ms and 5000 ms. In response, the maximum allowable vacuum level, Max Vac, from the aspiration source  115  can immediately be adjusted and dropped to a lower, safer value, in the event that the occlusion clears before the surgeon expects it to (action block  1050 ) (e.g., from 300 mmHg to 200 mmHg). During this period of time, there has been no change in the surgeon&#39;s footswitch  54  position, nor has an assistant been required to modify any setting on the system. Accordingly, the process  1000  provides the advantage of reducing manual input and accordingly enables the physician to concentrate on the procedure. This lower vacuum level should be sufficient to maintain the hold of the particle to allow the surgeon to continue to apply power or use another instrument to manipulate the particle and clear the occlusion. 
     After the occlusion has cleared, the surgeon may release the footswitch  54  from foot position  3  (decision block  1020 ) to disable the application of ultrasonic power. To disable the CS feature, if the aspiration source  115  is linearly controlled as described above and if the surgeon releases the footswitch  54  to a point where the vacuum level drops below a certain threshold (“down threshold”), e.g., 100 mmHg, for example at a point near the middle or beginning of foot position  2  (decision block  1070 ) then Max Vac is reset to the programmed level, e.g., 300 mmHg in the example above (action block  1080 ). In the alternative, or additionally, the surgeon may simply reset Max Vac through another trigger, e.g., the yaw movement of footswitch  54  relative to base  52 . 
     Turning to  FIG. 8   a , another process  2000  that provides for chamber stabilization in a vacuum-based phacoemulsification system  100  is shown Like with process  1000 , process  2000  starts with the transition of the footswitch  54  from foot position  2  to foot position  3  (starting block  2010  and decision block  2020 ). As described above, this transition applies both vacuum and ultrasonic power to handpiece  104  (action block  2060 ). Also, an actual occlusion may occur or the existence of an occlusion can be inferred if the footswitch  54  transitions into foot position  3  and stays in foot position  3  for a certain programmable period of time, e.g., in the hundreds of milliseconds range (a timer is compared in decision block  2030 , labeled as “counter limit reached?” and the timer is updated in action block  2040 , labeled as “run counter”). In one embodiment, this programmable period of time is between 100 ms and 5000 ms. In response, the vacuum source can reduce the Max Vac and modulate between two programmable lower vacuum levels, e.g., between 200 mm Hg and 100 mm Hg (action block  2050 ). This modulation will allow for the grasping of the particle at the higher level (e.g., 200 mm Hg) and reduce the risk of surge at the lower level (e.g., 100 mm Hg), and the modulation will further create a “shear” force to help break up the occlusion. Additionally, the application of power (in foot position  3 ) will create movement of the particle to allow inflow of irrigation fluid into the aspiration line  110 , contributing to a balanced and stable anterior chamber of the eye  106 . 
     In addition to programming the lower vacuum levels, the cycles between the modulation also can be programmed, as illustrated in  FIG. 8 b   . For instance, the time that a particular vacuum level is maintained, t 1  and t 2 , can each be programmed. For example, the time t 2  at the higher vacuum level v2 (e.g., 200 mm Hg) can be maintained for 2 seconds whereas the time t 1  at the lower vacuum level v1 (e.g., 100 mm Hg) can be maintained for 2 seconds. In yet another example, the time t 2  at the higher vacuum level v2 (e.g., 200 mm Hg) can be maintained for 5 seconds whereas the time t 1  at the lower vacuum level v1 (e.g., 100 mm Hg) can be maintained for 2 seconds. As noted above, in a vacuum-based system, the modulation of vacuum levels at times t 1  and t 2  can enable the system to control particle movements for enhanced destruction (i.e., emulsification) of an occlusion. What is shown in  FIG. 8 b    is an exemplary square wave pattern; however, as one of ordinary skill in the art can appreciate, the process  2000  may be configured to provide modulation in a sine, triangle, or sawtooth wave pattern and/or a combination thereof. 
     Turning back to  FIG. 8 a   , after the occlusion has cleared, the surgeon may release the footswitch  54  from foot position  3  (decision block  2020 ) to disable the application of ultrasonic power. To disable the chamber stability feature described above, when the footswitch  54  travels back to foot position  2 , the Max Vac is set to 100 mm Hg for a certain period, e.g., 1 second (action block  2070 ), and the linear control of the aspiration source  115  is returned with the vacuum level dependent on location of the footswitch in foot position  2  (action block  2080 ). 
     Turning to  FIG. 9 , another process  3000  that provides for chamber stabilization in a vacuum-based phacoemulsification system  100  is shown Like with process  1000 , process  3000  starts with the transition of the footswitch  54  from foot position  2  to foot position  3  (starting block  3010  and decision block  3020 ). As described above, this transition applies both vacuum and ultrasonic power to handpiece  104  (action block  3060 ). Also, an actual occlusion may occur or the existence of an occlusion can be inferred if the footswitch  54  transitions into foot position  3  and stays in foot position  3  for a certain programmable period of time, e.g., in the hundreds of milliseconds range (a timer is compared in decision block  3030 , labeled as “counter limit reached?” and the timer is updated in action block  3040 , labeled as “run counter”). In response, the computer  109  and aspiration source  115  can reduce the Max Vac to a lower level, e.g., 200 mm Hg (action block  3050 ). Further, if the footswitch  54  is further depressed (decision block  3055 ), the vacuum level is further reduced concomitantly with the depression of the footswitch  54  until it reaches a base vacuum level, e.g., 100 mm Hg (action block  3057 ). 
     After the occlusion has cleared, the surgeon may release the footswitch  54  from foot position  3  (decision block  3020 ) to disable the application of ultrasonic power. To disable the chamber stability feature described above, the surgeon can release the footswitch  54  to a point where the vacuum level drops below a certain threshold (“down threshold”), e.g., 100 mmHg, for example at a point near the middle or beginning of foot position  2  (decision block  3070 ) then Max Vac is reset to the programmed level, e.g., 300 mmHg in the example above and linear control of the aspiration source  115  is returned (action block  3080 ). In the alternative, or additionally, the surgeon may simply disable the CS feature through another trigger, e.g., a switch on the handpiece  104  (not shown) or the yaw movement of footswitch  54  relative to base  52 . Moreover, the release described in process  2000  may be utilized, i.e., when the footswitch  54  travels back to foot position  2 , the Max Vac is set to 100 mm Hg for a certain period, e.g., 1 second, and linear control of the aspiration source  115  is enabled with the vacuum level dependent on location of the footswitch in foot position  2 . 
     Turning to  FIG. 10 , another process  4000  that provides for chamber stabilization in a vacuum-based phacoemulsification system  100  is shown Like with process  1000 , process  4000  starts with the transition of the footswitch  54  from foot position  2  to foot position  3  (starting block  4010  and decision block  4020 ). As described above, this transition applies both vacuum and ultrasonic power to handpiece  104  (action block  4060 ). Also, an actual occlusion may occur or the existence of an occlusion can be inferred if the footswitch  54  transitions into foot position  3  and stays in foot position  3  for a certain programmable period of time, e.g., in the hundreds of milliseconds range (a timer is compared in decision block  4030 , labeled as “counter limit reached?” and the timer is updated in action block  4040 , labeled as “run counter”). In response, the vacuum source can reduce the Max Vac to a base level, e.g., 100 mm Hg (action block  4050 ). Further, if the footswitch  54  is further depressed (decision block  4055 ), the vacuum level increases concomitantly with the depression of the footswitch  54  until it reaches an adjusted max vac level, e.g., 200 mm Hg (action block  4057 ). 
     After the occlusion has cleared, the surgeon may release the footswitch  54  from foot position  3  (decision block  2020 ) to disable the application of ultrasonic power. The CS feature may also be released as well (action block  4070 ). In the alternative, or additionally, the surgeon may simply disable the CS feature through another trigger, e.g., a switch on the handpiece  104  (not shown) or the yaw movement of footswitch  54  relative to base  52 . 
     Turning to  FIG. 11 b   , another process  5000  that provides for chamber stabilization in a vacuum-based phacoemulsification system  100  is shown. This process is based on a dual pump system  200 , as shown in  FIG. 11 a   . In a dual pump system  200 , two types of aspiration sources are included, a vacuum based source, such as a venturi-based aspiration source  115 , and a flow-based source, such as a peristaltic-based source  215 . The computer  109  can serve as a switch to determine which aspiration source  115 / 215  is applied to aspiration line  110  and the handpiece  104 . The foot pedal  120  may also be used to trigger the switch between one aspiration source and the other  115 / 215 , e.g., the yaw movement of footswitch  54  to the left of base  52  to operate pump  115  and the yaw movement of footswitch  54  to the right of the base  52  to operate second pump  215 . In one embodiment, the ramp-up/start-up of the newly employed aspiration source will typically start before the ramp-down of the previously used source has completed. Thus there is no time delay between switching of the sources and/or significant change (increase or decrease) in vacuum or flow rate during the switching. Accordingly, switching between these two different types of aspiration flow may occur “on-the-fly” without halting of a corresponding irrigation flow, and without awaiting input from the system operator regarding that particular flow change. Further detail about an exemplary dual pump system  200  and the switch mechanism is described in U.S. patent application Ser. No. 12/614,093, U.S. Publication No. 2010/0280435 A1, filed Nov. 6, 2009 for “Automatically Switching Different Aspiration Levels and/or Pumps to an Ocular Probe,” which is hereby incorporated by reference. 
     Turning back to  FIG. 11 b   , like with process  1000 , process  5000  starts with the transition of the footswitch  54  from foot position  2  to foot position  3  (starting block  5010  and decision block  5020 ). If the footswitch  54  transitions into foot position  3  (decision block  5020 ), then the aspiration source can be switched from a vacuum-based aspiration source  115  to a flow-based pump  215  (action block  5030 ). This allows a vacuum sensor (not shown) coupled to aspiration line  110  to provide a reading indicating whether an occlusion exists or not based on measured vacuum level in the aspiration port of the handpiece/needle  104 . In response, the system  200  may control at least one of: the supply of irrigation fluid, vacuum level, aspiration rate, and power applied to the handpiece  104 . Specifically, the vacuum level may be controlled by lowering a maximum level of vacuum allowed during an occluded state of a surgical procedure. Such a system is described in U.S. Pat. No. 7,670,330 to Claus et. al, filed Mar. 21, 2005 and U.S. Pat. No. 7,785,336 to Staggs, filed Aug. 1, 2006, which are incorporated by reference in their entirety. 
     The peristaltic pump  215  can be preset to a maximum vacuum or a ratio of the maximum venturi-based source  115 . As ultrasonic power is being applied (action block  5040 ), particle movement will cause vacuum level to fluctuate. If the vacuum level increases to a high threshold (decision block  5050 ), e.g., 300 mm Hg, the handpiece/needle  104  may be occluded with a particle. In that situation, large particles tend to be more readily emulsified when the particle is moved away from the handpiece/needle  104  tip. Therefore, it may then be desirable to determine whether additional energy is required to bump or move a large particle away from the tip of needle  104 . As described in U.S. Pat. No. 7,670,330 to Claus et. al, filed Mar. 21, 2005 and U.S. Pat. No. 7,785,336 to Staggs, filed Aug. 1, 2006, increasing ultrasonic power proportional to an increase in a sensed aspiration vacuum pressure (e.g., increasing duty cycle or amplitude of the pulsed ultrasonic energy) allows for more effective emulsification of large and small particles (action block  5055 ). If, on the other hand, the particle is released or completely emulsified, the vacuum level will quickly drop, thus signifying completion of the emulsification process (decision block  5060 ). At this point, less or no ultrasonic power is needed to enable the particle to be drawn to the needle tip (action block  5065 ). If the user maintains the foot switch  54  in foot position  3  (decision block  5020 ), the peristaltic source  215  is still utilized (action block  5030 ) and thus, if an occlusion occurs again, the vacuum sensor may detect it (decision block  5050 ) and automatically increase power again (action block  5065 ). This process allows for less foot pedal  54  activity by the user with faster reaction time. The user can also transition back to foot position  2  (decision block  5020 ), thereby causing the system  200  to switch its aspiration source back to the venturi source  115  (action block  5070 ). Furthermore, the CS feature may also be released as well, e.g., through another trigger, e.g., the yaw movement of footswitch  54  relative to base  52 . 
     As discussed above, upon a transition back to the venturi source  115  (action block  5070 ), the vacuum level of peristaltic source  215  may be controlled while the venturi source  115  is ramping/starting-up to affect an “on-the-fly” transition. Accordingly, as one of ordinary skill in the art would appreciate, system  200  controls the vacuum level of both aspiration sources  115 / 215  to maintain a stable vacuum level and to alleviate any spike in vacuum level occurring during the transition. In one embodiment, a transition from the peristaltic source  215  to the venturi source  115  may cause dips in the patient&#39;s eye if there is a mismatch in flow rate between the two sources  115 / 215 . To avoid the mismatch in flow rate and to maintain a stable chamber, system  200  can adjust the vacuum level of the venturi source  115  to the actual vacuum measured while using the peristaltic source  215  prior to the transition. Following the transition, the venturi source  115  is allowed to ramp up to a setting that has been configured in the system  200  and the system  200  resumes normal operation. 
     In the event the system  200  transitions back from venturi source  115  to peristaltic source  215 , the system  200  also provides a stable vacuum level during operation. This similarly requires maintaining constant flow rate between the two aspiration sources  115 / 215 . However, as discussed above, while using venturi source  115 , the vacuum level may not give an accurate indication of flow rate of the aspiration fluid. Nevertheless, it is possible to measure the flow rate of the fluid without contamination by measuring the air flow rate from the vacuum port using, e.g., an air flow sensor placed on the aspiration port  110 . Accordingly, in one embodiment, as the air flow is proportional to the flow rate of the fluid, the flow rate of the aspiration fluid can be measured using air flow and the flow rate of the peristaltic source  215  can be similarly made to match the actual calculated vacuum while using the venturi source  115  prior to the transition. Following the transition, the peristaltic source  215  is allowed to ramp up to a setting that has been configured in the system  200  and the system  200  resumes normal operation. 
     Turning to  FIG. 12 , a more general process  6000  that provides for chamber stabilization in a vacuum-based phacoemulsification system  100  is shown. The previous embodiments are based on the foot pedal  120  having a configuration as shown in  FIGS. 5 and 6 . However, other configurations may be utilized. For example, a hand controlled switch (not shown) may also be utilized. In yet another example, a voice command controller (not shown) may also be utilized. Turning back to  FIG. 12 , like with process  1000 , process  6000  starts with the application of vacuum (action block  6010 ). If the user initiates the application of power (decision block  6020 ), and applies power for a certain programmable period of time, e.g., in the hundreds of milliseconds range (a timer is compared in decision block  6030 , labeled as “counter limit reached?” and the timer is updated in action block  6040 , labeled as “run counter”), the existence of an occlusion can be inferred or an actual occlusion occurs. In response, the maximum allowable vacuum level, Max Vac, from the aspiration source  115  can immediately be adjusted and dropped to a lower, safer value, in the event that the occlusion clears before the surgeon expects it to (action block  6050 ) (e.g., from 300 mmHg to 200 mmHg). 
     After the occlusion has cleared, the surgeon may elect to disable power (decision block  6020 ). To disable the CS feature, if the aspiration source  115  is linearly controlled as described above and if the surgeon releases the vacuum controlled switch to a point where the vacuum level drops below a certain threshold (“down threshold”), e.g., 100 mmHg (decision block  6070 ), then Max Vac is reset to the programmed level, e.g., 300 mmHg in the examples above (action block  6080 ). In the alternative, or additionally, the surgeon may simply reset Max Vac through another trigger, e.g., the yaw movement of footswitch  54  relative to base  52  in the case where a foot pedal  120  is used. 
     In the foregoing specification, the invention has been described with reference to specific embodiments thereof. It will, however, be evident that various modifications and changes may be made thereto without departing from the broader spirit and scope of the invention. For example, the reader is to understand that the specific ordering and combination of process actions described herein is merely illustrative, and the invention may appropriately be performed using different or additional process actions, or a different combination or ordering of process actions. For example, this invention is particularly suited for vacuum-based phacoemulsification systems, such as venturi-based systems; however, the invention can be used for any phacoemulsification system. Additionally and obviously, features may be added or subtracted as desired. Accordingly, the invention is not to be restricted except in light of the attached claims and their equivalents.