Vitrectomy surgical apparatus employing multisensor pressure feedback

A vitrectomy apparatus is provided, including a pressure source, a cut valve connected to the pressure source, the cut valve configured to be turned on and off to provide pressure to selectively extend and retract a vitrectomy cutting device, a plurality of sensors provided at a plurality of points between the pressure source and the vitrectomy handpiece, and a controller configured to employ a function correlating a desired cut rate with a pressure source duty cycle and employ a different function when one sensor of the plurality of sensors senses a pressure outside a predetermined pressure range.

BACKGROUND

Field of the Invention

The present invention relates generally to the field of surgical repair of retinal disorders, and more specifically to the efficient operation of pneumatic vitrectomy devices during ophthalmic surgical procedures.

Description of the Related Art

Vitrectomy surgery has been successfully employed in the treatment of particular ocular problems, such as retinal detachments resulting from tears or holes in the retina. Vitrectomy surgery typically involves removal of vitreous gel and may utilize three small incisions in the pars plana of the patient's eye. These incisions allow the surgeon to pass three separate instruments into the patient's eye to affect the ocular procedure. The surgical instruments typically include a vitreous cutting device, an illumination source, and an infusion port.

Current vitreous cutting devices may employ a “guillotine” type action wherein a sharp-ended inner rigid cutting tube moves axially inside an outer sheathing tube. When the sharp-ended inner tube moves past the forward edge of a side port opening in the outer sheathing tube, the eye material (e.g. vitreous gel or fibers) is cleaved into sections small enough to be removed through the hollow center of the inner cutting tube.

Vitreous cutters are available in either electric or pneumatic form. Today's electric cutters may operate within a range of speeds typically between 750-2500 cuts-per-minute (CPM) where pneumatic cutters may operate over a range of speeds between 100-2500 CPM. The surgeon may make adjustments to control the pneumatic vitrectomy surgical instrument cutting speed, i.e. controlling the cutting device using a surgical handpiece, in order to perform different activities during the corrective procedure. Corrective procedures may include correction of macular degeneration, retinal detachment, macular pucker, and addressing eye injuries.

The cutting device within a pneumatic handpiece requires precise control of applied pressure to overcome the internal spring return mechanism to assure the quality of each cutting stroke. Such systems have typically employed a fluid (typically air) reservoir or accumulator to collect fluid and from which fluid is drawn to effectuate the cut valve using pneumatic pressure. The frequency of opening and closing the pneumatic valve, i.e. the time interval between each opening cycle of the valve, is varied to achieve the desired cutting speed. In order to power the cut valve and cutter at a consistent pressure for an extended period of time, a relatively large fluid reservoir or accumulator is needed. A large fluid reservoir is undesirable in today's operating environment where smaller components are favored. Further, in this type of environment, inconsistent pressure can be provided to the cut valve in even the best of circumstances, and in the case of minor leaks, inconsistent pressure is practically a given. Even minor pressure inconsistencies can be highly undesirable.

Additionally, current systems employ calibration settings to account for changes in the operating room environment. Calibration settings can accommodate for relatively fixed environmental factors, such as altitude, but rapidly changing environmental factors such as temperature or electro-mechanical pump variations in virtually all situations cannot be adequately addressed using calibration techniques.

Based on the foregoing, it would be advantageous to provide a system that enables pneumatic cutting functionality at relatively consistent cutting pressures that reduce or eliminate the need for a relatively large fluid reservoir or accumulator. Such a system would have an ability to provide consistent cutting pressures under different conditions typically encountered in a vitrectomy surgical room environment.

SUMMARY

Thus according to one aspect of the present invention, there is provided a vitrectomy apparatus comprising a pressure source, a cut valve connected to the pressure source, the cut valve configured to be turned on and off to provide pressure to selectively extend and retract a vitrectomy cutting device, a plurality of sensors provided at a plurality of points between the pressure source and a vitrectomy handpiece, and a controller configured to selectively provide commands to change pressure source duty cycle according to a plurality of linear functions when one sensor of the plurality of sensors measures a pressure outside a predetermined pressure range.

According to another aspect of the present design, there is provided a method for controlling a vitrectomy system, comprising sensing pressure provided from a pressure source through a cut valve and to a vitrectomy handpiece using a plurality of sensors positioned between the pressure source and the vitrectomy handpiece, and controlling operation of the cut valve based on pressure measured by altering a function when measured pressure from one of the plurality of sensors is outside a predetermined pressure range.

According to another aspect of the present design, there is provided a vitrectomy apparatus comprising a vitrectomy handpiece comprising a vitrectomy cutting device, a sensing arrangement comprising a plurality of sensors configured to sense pressure, tubing connecting the vitrectomy handpiece to the sensing arrangement, a cut valve connected to the sensing arrangement, a pressure source configured to provide pressure to the cut valve, and a controller configured to receive data from the sensing arrangement and selectively provide commands to change pressure source duty cycle according to a plurality of linear functions according to data received from the sensing arrangement.

Other features and advantages of the present invention should be apparent from the following description of exemplary embodiments, which illustrate, by way of example, aspects of the invention.

DETAILED DESCRIPTION

The following description and the drawings illustrate specific embodiments sufficiently to enable those skilled in the art to practice the system and method described. Other embodiments may incorporate structural, logical, process and other changes. Examples merely typify possible variations. Individual components and functions are generally optional unless explicitly required, and the sequence of operations may vary. Portions and features of some embodiments may be included in or substituted for those of others.

The present design provides a system and method for high-speed pneumatic vitrectomy control and operation that employs pressure feedback at various points in the pneumatic line, thereby reducing or eliminating the need for a fluid reservoir or accumulator space in a vitrectomy machine. Such a design enables more accurate and efficient cutting of the vitreous material.

The present design is directed to accurate, reliable, and efficient control of the cutting speed of the blade in a pneumatic vitrectomy handpiece used in a medical instrument system. The present design will be discussed herein with a particular emphasis on a medical or hospital environment where a surgeon or health care practitioner performs. For example, an embodiment of the present design is a phacoemulsification surgical system that comprises an integrated high-speed control module for the vitrectomy handpiece. The surgeon may adjust or set the cutting speed via a graphical user interface (GUI) module or a foot pedal switch to control the high-speed pneumatic vitrectomy handpiece.

FIGS. 1A and 1Bare high-level conceptual block diagrams illustrating a common vitrectomy system's pneumatic cutting mechanism located within a surgical handpiece provided for purposes of explaining the present invention.FIG. 1Ashows the pneumatic cutting mechanism in the “cut,” “closed port,” or “forward” position, whileFIG. 1Bshows the pneumatic cutting mechanism in the “initial,” “open port,” or “backward” position. Referring toFIGS. 1A and 1B, construction of pneumatic cutter devices typically involve a blade110positioned to work or operate against a spring120by inflating and deflating a bladder130configured to move blade110by ‘pushing’ blade110forward to a forward position175when bladder130is inflated and ‘pulling’ blade110backward using the energy stored in spring120to its resting position or initial position170when bladder130is deflated. The desired cutting speed may be realized by filling and emptying bladder130in a cyclical manner through an air passage140arranged for receiving a pressurized airburst in the direction indicated at point150. The received pressurized air burst is then evacuated or vented in direction160.

Current designs are generally configured to cyclically inflate and deflate bladder130to move blade110in a forward direction180and backward direction190, thus producing the desired cutting action. A combination input pressurized air supply and output air venting valve mechanism195, or valve, is represented inFIGS. 1A and 1B.

In order to control the speed of blade110, currently available pneumatic designs typically use a control signal to open and close valve195. Valve195may be configured to provide a pressurized airburst when the valve is open, filling bladder130and venting the air within bladder130when the valve is closed to empty the bladder. Increasing the frequency of the control signal cycling rate, which produces a shorter pressurized air burst time, generally results in an increased cutting speed, or an increased number of cuts-per-minute as observed at the knife or blade. A subsequent decrease in control signal cycling rate generally produces a slower or decreased cutting speed.

Previous designs have employed control signals to drive the cutter. One example control signal to instruct the opening and closing of valve195associated with air passage140is shown inFIG. 2A. The control signal illustrated inFIG. 2Amay cycle between valve-off (VO) at point210and valve-on (VE) at point220, or provide a valve-energized instruction at a predetermined cycling rate, thereby effectuating the desired cutting speed.FIG. 2Billustrates an example pressure waveform resulting from the application of the control signal shown inFIG. 2A. The waveform is shown to have a constant rise in pressure up to a peak pressure (PP) at230when the valve is energized. A subsequent drop in pressure to a residual pressure (PR) at point240occurs when the valve is de-energized. The cycling in pressure, for controlling the blade forward and backward reciprocating movements, as illustrated by the waveform shown inFIG. 2B, may produce a specific cutting speed for blade110in terms of cuts-per-minute.

Pneumatic cutter designs have been configured with a speed control device to select and vary the rate the blade mechanism moves forward and backward to effectuate cutting. In these designs, changing the speed of the blade may involve varying the time or duration of the control signal provided to the valve. By increasing the open period and closed period of valve195, the resultant blade speed is reduced. Likewise, decreasing the amount of time valve195is open and closed causes the blade speed to increase.

An example of a control signal for controlling the filling and emptying of air in bladder130with an increase in cycle time is illustrated inFIG. 2C. Before time t1at250, the control signal cyclic frequency is set at a lower rate than after time t1to illustrate the surgeon selecting an increase in cutting speed at time t1during a surgical procedure.FIG. 2Dillustrates an example pressure waveform resulting from the application of the control signal shown inFIG. 2C. This pressure waveform reflects the control signal change that occurred at time t1at250, and may drive blade110at a faster rate.

The pneumatic vitrectomy handpiece is used in connection with a phaco-vitrectomy module and may be part of a phacoemulsification machine. Such a handpiece may include a “guillotine” type cutter pneumatically driven to either an open or closed position. Opening and closing occurs via air pressure provided via a flexible line or delivery line between the cutter and a pneumatic driver. The pneumatic driver may include a pressure source, such as a pump, configured to fill a small reservoir or accumulator with compressed air at its maximum pressure capacity. As employed herein, the terms “accumulator” and “reservoir” are used interchangeably and are intended to mean the same fluid (typically air) buffering or holding device. The output of this reservoir is connected to a pressure regulator that may regulate the air pressure down to the level required by the cutter, as shown by peak PPand residual PRpressure inFIG. 2B. A smaller reservoir may be supplied or fed by the regulator output, forming the source for the delivery valve.

The cutter in the present vitrectomy embodiment is pneumatic, while the cut valve actuation is electrical. The pulsing discussed is an electrical signal transmitted from the control module. When the electrical pulse drops to a non-energized state, a vent is opened resulting in a drop in pressure that functions to enable the force of a spring to overcome the resultant pressure, and the cutter returns to an initial state.

The electronic controller may be connected to the delivery valve and may provide instructions to produce a pulse width (in time) of pressurized air when the valve is open. The controller may be arranged to provide fixed pulses of pressurized air within the flexible line in a manner that drives the cutter. The electronic controller may use a fixed pulse timing control signal to instruct the delivery valve to open and close. The fixed timing, or fixed duration, control signal instructs the delivery valve to open and close in a constant cyclical manner. When the flexible line is at zero or near zero pressure, for example refer to residual pressure PRshown inFIG. 2B, the cutter is biased toward the initial or resting position. The cutter closes when the air pressure in the cutter delivery line exceeds a predetermined value between PRand PP. When the delivery valve is off, the air in the cutter tubing is exhausted through the valve exhaust port. The cutter then returns to the initial position when the pressure in the delivery line decreases close to atmospheric pressure, i.e. PR.

The foregoing description generally discloses the components and control functionality of prior vitrectomy devices. Such control functionality can be characterized as “open-loop,” or without any type of feedback. Cutting speeds, etc. are simply set by a surgeon or user and effectuated, and changes in conditions or parameters in the environment are unaccounted for.

FIG. 3is a block diagram illustrating components and devices for a previous version of a pneumatic vitreous cutting module305integrated within a phacoemulsification machine300in accordance with the present design. Although depicted as an integral unit, module305functionality may be realized by using multiple devices to perform the functionality disclosed. FromFIG. 3, a compressed air source310and associated air check valve311may supply air pressure for pneumatic vitreous cutting module305. The compressed air source310typically comprises a pump (not shown) configured to both provide a pneumatic, typically a gas such as air, supply pressure to the cut valve and a vent mechanism to relieve pressure to atmospheric conditions. Compressed air source310thus provides a source of vacuum or pressure. Compressed air is provided by the pump via delivery line301illustrated between air check valve311and pre-regulator312. Check valve311is typically arranged with two ports and may allow air pressure to flow through in one direction, from compressed air source310to pre-regulator312. The pump may pump pressurized air into a high pressure chamber, not shown, which in turn provides high pressure air to pre-regulator312via delivery line301. The high-pressure chamber or compressed air source310may provide a stable source of air at a higher pressure than the working pressure of the cutter.

As used herein, the term “pressure source” or the “compressed air source” means any device or arrangement that is configured to provide a source of pressure or vacuum, including but not limited to a pump or Venturi device, compressed air supply, compressed air inlet supply, or any device provided within a vitrectomy machine or originating from an external source that provides pressure or vacuum, such as a pressure source provided through a wall of a building, e.g. via a wall mounted nozzle or device, an external pressure source such as an external pump, or otherwise. The terms are therefore intended to be interpreted broadly.

Pre-regulator312may provide a workable steady air pressure stream from which compressed air source310may supply air pressure for pressure regulator313via delivery line302. Pressure regulator313may be preset to a desired pressure and may be configured to provide air to accumulator314at a low,-steady, and safe operating pressure. Pressure regulator313may connect directly to compressed air source310, typically a pump, but alternately a high pressure chamber, by a delivery line and input high pressure and regulate the air pressure to a lower value consistent with the operating pressure of the cutter handpiece.

Accumulator314may operate as a working pressure chamber, and may receive pressurized air at specific pressure and volume from pressure regulator313via delivery line303. Accumulator314may provide a specific amount of air pressure at a predetermined volume to cut valve316via delivery line304such that no excess pressure is forced into the delivery line307.

Controller320, which may provide a graphical user interface, computes a cut rate based on physician input (programmed and/or the footpedal position) or the pre-programmed maximum cut rate and/or the footpedal position and electronically provides a desired or computed cut rate to cut valve316via communications control line306. The controller320may take different forms, including comprising a PCBA (printed circuit board assembly), or may be part of a PCBA, ASIC, or other hardware design. A storage unit (not shown) may be provided to store certain values used by the controller320during the vitrectomy procedure, including settings desired by the surgeon and other relevant data. Cut valve316may open and close in response to the control signal provided from controller320. Controller320electronically controls the valves operating the regulated pressure and/or vacuum air sent to the cutter. The handpiece blade motion may move in a forward and backward reciprocating motion in response to the pressure waveform provided via delivery line307.

During operation, controller320may operate cut valve316to deliver a pulse of regulated air pressure to delivery line307and the cutter (not shown). While the surgeon or practitioner may select variations in the pulse repetition frequency, once the selection is made, the system seeks to attain the desired cutting rate.

Cut valve316is electronically controlled by controller320to transmit pressure, and cut valve316opens and closes at a precise time to allow air at a specific pressure and volume to fill the delivery line307and operate the cutter. Cut valve316may connect to atmospheric pressure for purposes of venting air received from delivery line307. Controller320may provide an electronic indication to cut valve316that originates with a user selected switch, such as a switch on the handpiece, graphical user interface, or a foot switch. Line308represents the electrical connection between controller320and compressed air source310.

The present design employs pressure feedback at multiple points in the line between the compressed air source310and valve195, and feedback of the pressures at the various points is employed in a specific manner to control cut pressure.

FIG. 4illustrates an embodiment of a vitrectomy device according to the present design. A number of components inFIG. 4are identical to those ofFIG. 3. As shown inFIG. 4, sensors401,402, and403are provided, where sensor401is provided at the cut valve195, sensor402is provided between the compressed air source310and the pre-regulator312, and sensor403is provided between pressure regulator313and accumulator314. Each of sensors401,402, and403provide signals to controller320, typically in the form of current pressure sensed.

Thus, the present design includes a vitrectomy apparatus having a compressed air source such as a pump, a cut valve connected to the pump, the cut valve configured to be turned on and off to provide pressure to selectively extend and retract a vitrectomy cutting device, a plurality of sensors configured to sense pressure provided along the line between the pump and the vitrectomy cutting device, and a controller configured to control the duty cycle of the pump based on a linear function selected based on pressure sensed by the plurality of sensors. The pressure source comprises a pump having a pump core and a pressure regulator configured to control pressure supplied from the pump core.

FIG. 5presents an alternate embodiment of the present design.FIG. 5shows compressed air source501, regulator502, accumulator503, and cut valve504in a single line and connected as shown. Pressure sensor511measures or senses (collectively, “measures”) pressure at cut valve504, while pressure sensor513measures pressure at a point between regulator502and accumulator503. Pressure sensor512measures the pressure between compressed air source501and regulator502. As shown, each of sensors511,512, and513feeds information to controller520, which then controls compressed air source501based on information received from the sensors.

In general, pressure sensor511measures pressure and in conjunction with the controller520determines whether the peak value during a period of time is between a first set minimum and maximum allowable value. These components also determine whether the measured value of pressure sensor513is between a third set of minimum and maximum values, while pressure sensor512and controller520determine whether the pressure at the pressure sensor512is between a second set of minimum and maximum values.

Sensors inFIG. 5are illustrated as separate from the line, i.e. not specifically in line, while sensors inFIG. 4are shown in line. Sensors can be positioned either in line or separate, but in either situation the sensor functions to determine the air pressure in the positions shown. In one embodiment, each sensor comprises a passage configured to monitor pneumatic pressure at a point between the compressed air source and the vitrectomy cutting device, and the controller comprises circuitry configured to provide signals to control the pump duty cycle based on a linear function selected based on pressure sensed or measured by the plurality of sensors.

Further,FIG. 4illustrates the sensor402provided between the compressed air source310and the pre-regulator312, however in an embodiment the sensor may be placed elsewhere, such as between pre-regulator312and pressure regulator313.

FIG. 6is a simplified view of the present design reflecting certain maximum and minimum predetermined pressure values employed in a particular arrangement. Numbers presented are generally representative but may change depending on circumstances and equipment employed. FromFIG. 6, compressed air source601provides pressure to regulator602in an expected range of between about 25 and 45 psi. Pressure between regulator602and cut valve603is expected to be between about 21 and 27 psi. Pressure at cut valve603is expected to have a trough, or lowest, value of between zero and three psi, with a peak between 14 and 22 psi, irrespective of cut speed. Again, these are representative values and actual values may differ, but the values may differ between the three sensors as far as acceptable pressure ranges. While three sensors are shown in this embodiment, it is to be understood that any number of sensors may be employed that is typically greater than one.

In operation, the controller such as controller320inFIG. 3, employs a function, typically a linear function, to drive the speed of the compressed air source310or pump601to deliver a relatively steady source of pressure to the cut valve. Controller320monitors the sensors, typically at a very rapid rate such as in the tens of milliseconds. If the pressure at any sensor of the multiple sensors varies outside the expected range, the system changes the function (e.g. linear function) employed. In an embodiment, if the pressure at any sensor of the multiple sensors varies outside the expected range, the system changes the function employed by increasing or decreasing a linear function constant depending upon whether greater or lower pressure is required.

Employing this type of design, including regulating compressed air source pressure, enables the design to employ an accumulator or reservoir that is measurably smaller than accumulators previously employed. Further, in certain instances, the need for an accumulator may be eliminated entirely.

FIG. 7illustrates representative duty cycle graphs or curves according to one aspect of the present design. The y axis ofFIG. 7represents the motor duty cycle, i.e. the speed of the motor driving the compressed air source, while the x axis represents the cut rate. Again, these curves are representative of expected curves and values in a typical setting, but the values may differ for different settings, components, and/or circumstances, and any number of curves may be employed. InFIG. 7, eight curves are shown as an example, and each of the curves701a-hmay be employed depending on circumstances. In one instance, a default curve may be employed and a different curve employed as time progresses, e.g. a curve above or below the default curve may be selected depending on pressures encountered. One example curve may be provided as:
F(x)=( 1/100)x+(MinDuty−1)  (1)

From Equation (1), x represents the cut rate desired, or provided by the surgeon or operator. As an example, the requested cut rate may be 1200 CPM. MinDuty is the minimum acceptable duty cycle, in percent, and a number as low as 10 is not unusual in certain operations. For an example minimum duty cycle of 10 percent, Equation (1) would provide ( 1/100)*1200+(10−1), or a value of 21 for the motor duty cycle.

The value 1/100, or the slope of the function or curve, is generally calculated as the maximum duty cycle minus the minimum duty cycle desired for performance over the range divided by the maximum cut rate minus the minimum cut rate expected for the device. Thus while numbers may vary depending on circumstances including cut range and pump duty cycles, a number such as 1/100 may be appropriate in certain instances.

Cut rate in certain pneumatic applications may be, for example, between 100 and 1200 CPM. In this particular application, duty cycle varies based on the pump motor employed, but in some circumstances, a minimum duty cycle of 10 percent and a maximum duty cycle of 45 percent is not unexpected. The present design switches between functions, in this embodiment between linear functions, when one of the three sensors senses a pressure above a highest value or below a lowest value, the controller320changes the function to adapt to changes in environment. Such a design may serve to maintain or improve cut pressure even when a leak is present in the system or more specifically in the line.

In general, if the pressure at any of the sensed points is less than the corresponding threshold, the linear function constant is incremented resulting in the duty cycle being incremented if not already at an upper limit. If pressure at any of the sensors is greater than the corresponding threshold, the linear function constant is decremented resulting in the duty cycle being decremented if not already at a lower limit. The result is a new function, i.e. a new linear function when pressure is outside an expected range, when the linear function is not already at an upper or lower limit.

FIG. 8is a general flowchart depicting operation of the controller based on sensed pressures. FromFIG. 8, operation begins at point801and runs through low pressure evaluation and adjustment. Note that the particular functions depicted inFIG. 8may occur in any order or in different groupings than shown. For example,FIG. 8shows making low pressure assessments and adjustments before high pressure assessments and adjustments, but these may reversed, and/or ordering of the sensors evaluated and pressures addressed may differ from the depiction shown. At point801, the system assesses the cutter sensor, e.g. first sensor511inFIG. 5, and determines if the peak value is less than or equal to a predetermined value, shown as 14 psi in this embodiment. If the peak value sensed is less than or equal to this predetermined value, operation progresses to point804, but if not, operation progresses to point802. At point802, the system determines whether pressure sensed at, for example, third sensor513inFIG. 5, and the pressure is evaluated as being less than or equal to a predetermined level, in this embodiment 21 psi. Again, if the pressure is less than or equal to, operation transitions to point804, but if not, operation passes to point803, wherein pressure sensed at second pressure sensor512inFIG. 5, is evaluated. If the pressure at second pressure sensor512is less than or equal to a predetermined amount, such as 25 psi, operation transitions to point804. If not, this indicates that every sensor has sensed a pressure above the requisite minimums, and operation transitions in this embodiment to high pressure sensing and adjustment.

Point804indicates that the minimum duty cycle is increased to less than or equal to a desired value, such as 34 psi, and the maximum duty cycle is also increased to less than or equal to a desired value, such as 45 psi. Point805evaluates whether the peak value has been less than an acceptable value for a predetermined amount of time. If not, there is no current issue, and processing progresses to high pressure assessment and adjustment. If so, a low pressure error exists, which may be any number of problems including but not limited to a severe break in the line(s). In this failure situation, failure processing may occur, including providing warnings and/or shutting down operation in a safe and approved manner.

At point810, the system assesses the cutter sensor, e.g. first sensor511inFIG. 5, and determines if the trough value is greater than a predetermined value, shown as 3 psi in this embodiment. If the trough or lowest value sensed is greater than this predetermined value, operation progresses to point814, but if not, operation progresses to point811. At point811, the system determines whether the peak value is greater than a predetermined value, in this embodiment greater than 22 psi. If so, operation progresses to point814, and if not, operation progresses to point812. At point812, the pressure sensed at, for example, second sensor512inFIG. 5, is evaluated as being greater than a predetermined level, in this embodiment 45 psi. Again, if the pressure is greater, operation transitions to point814, but if not, operation passes to point813, wherein pressure sensed at third pressure sensor513inFIG. 5, is evaluated. If the pressure at third pressure sensor513is greater than a predetermined amount, such as 27 psi, operation transitions to point814. If not, this indicates that every sensor has sensed a pressure below the established maximums, and operation is complete for this functionality.

Point814indicates that the minimum duty cycle is decreased to a value of greater than or equal to a desired value, such as 10 psi, and the maximum duty cycle is also decreased to greater than or equal to a desired value, such as 21 psi. Point815evaluates whether the trough value has been greater than a predetermined value for a certain amount of time. If not, there is no current issue, and processing ends. If so, a high pressure error exists. In this failure situation, failure processing may occur, including providing warnings and/or shutting down operation, again in a safe and approved manner.

Thus the present design takes pressure readings from multiple positions along the line and alters functions when the pressures sensed are above or below predetermined values. In this manner, a more robust maintenance of cutting pressure, either at a high cutting speed or a low cutting speed, is maintained without the need for a large accumulator. Sensor measurements may be evaluated at an appropriate rate, such as in the tens of milliseconds, e.g. from between 10 to 100 milliseconds. Advantages may be gained by evaluating at different points along the path before others; for example, if concern is great regarding pressure at the cut valve, the cut valve sensor may be evaluated first. If concern is greatest regarding compressed air source pressure, the sensor closest to the compressed air source may be evaluated first. Evaluations may be done in parallel or in any order desired, and operation is not in any way limited to the depiction provided inFIG. 8.

Vitrectomy Performance

FIG. 9illustrates closed loop control of the compressed air source or pump according to an embodiment of the present design.FIG. 9illustrates the vitreous cutter running continuously and stepped from a low value to a high value, in one embodiment from 100 CPM to 1200 CPM. Pump motor duty cycle, labeled as Speed inFIG. 9, shows that compensation follows the same basic stepping pattern as the requested cut rate, labeled as Cut-Rate inFIG. 9. While the duty cycle follows the stepping pattern of the requested cut rate, the peak pressure, labeled Peak, as well as the pump pressure (PS2) and the regulator pressure (PS3) are consistent in amplitude.

FIG. 9specifically represents one embodiment, with PS2 (line901) being pump pressure in psi, ranging from 21 to 45 psi, PS3 (line902) being regulator pressure in psi, from 21 to 25, Peak (line903) being a peak pressure level, from 14 to 22 psi, Trough (line904) being a trough or low pressure between 0 and 3 psi. Speed (line905) represents the speed of the compressed air source motor, while Cut Rate (line906) represents the cut rate. The x axis ofFIG. 9represents time, while the y axis is motor duty cycle, or pressure in psi, or cut rate divided by 100 depending on the variable. These values and conditions represent a single embodiment, and different readings, parameters, values, speeds, and so forth may be encountered while still within the scope of the present invention.

FIG. 10shows an example vitreous cutter making repeated single cuts. In this embodiment, the data shows the effect of the compensating closed-loop software control of the duty cycles of the pneumatic pump, i.e. the effect of the linear functions. The corresponding data for the pump motor duty cycle (Speed, line1005) shows the compensation for each single cut remains consistent as does peak pressure, labeled as Peak (line1003), pressure at the pump, labeled PS2 (line1001), and pressure at the regulator, labeled PS3 (line1002). As withFIG. 9,FIG. 10represents a particular embodiment, with PS2 (line1001) being pump pressure in psi, ranging from 21 to 45 psi, PS3 (line1002) being regulator pressure in psi, from 21 to 25, Peak (line1003) being a peak pressure level, from 14 to 22 psi, Trough (line1004) being a trough or low pressure between 0 and 4 psi. Speed (line1005) represents the duty cycle of the compressed motor source. The x axis ofFIG. 10represents time, while the y axis is motor duty cycle or pressure in psi depending on the variable. Again, these values and conditions represent a single embodiment, and different readings, parameters, values, speeds, and so forth may be encountered while still within the scope of the present invention.

Though discussed herein with respect to a surgical device and more specifically a vitrectomy cutter, the present approach may be used to control any pneumatic device wherein pressures vary or need to be varied over time. Pneumatic devices driven by varying pressures may include devices used for cutting, hammering, or lifting.

Thus the present design includes a vitrectomy apparatus, comprising a pressure source, a cut valve connected to the pressure source, the cut valve configured to be turned on and off to provide pressure to selectively extend and retract a vitrectomy cutting device, a plurality of sensors provided at a plurality of points between the pressure source and the cut valve, and a controller configured to employ a function correlating a desired cut rate with a pressure source duty cycle and employ a different function when one sensor of the plurality of sensors senses a pressure outside a predetermined pressure range.

Alternately, the present design is a method for performing a vitrectomy procedure, comprising sensing pressure provided from a pressure source through a cut valve and to a vitrectomy handpiece using a plurality of sensors positioned between the pressure source and the vitrectomy cutting device, and controlling operation of the cut valve based on pressure sensed by altering a function when sensed pressure from one of the plurality of sensors is outside a predetermined pressure range.

Another embodiment of the present design is a vitrectomy apparatus, comprising a vitrectomy handpiece comprising a vitrectomy cutting device, a sensing arrangement comprising a plurality of sensors configured to sense pressure, tubing connecting the vitrectomy handpiece to the sensing arrangement, a cut valve connected to the sensing arrangement, a pressure source configured to provide pressure to the cut valve, and a controller configured to receive data from the sensor arrangement and selectively provide commands to change pressure source duty cycle according to a plurality of linear functions according to data received from the sensor arrangement.