Patent Description:
During ophthalmic surgery, fluid is typically infused into the eye and aspirated therefrom. To prevent damage to the eye tissue or collapse of the surgical site, aspiration and irrigation systems aim to maintain a stable pressure within the eye.

US patent publication <CIT> describes an ophthalmic surgical system comprising an irrigation line through which an irrigation fluid is delivered to the surgical site. The system also comprises an aspiration line, through which aspirated fluid and tissue can be evacuated from the surgical site. The flow of irrigation fluid from the infusion bottle/bag is controlled by the vacuum produced at the surgical site by the aspiration apparatus and/or pressurization of an irrigation fluid source, e.g. by squeezing a bag or bottle containing irrigation fluid.

US patent publication <CIT> discloses a method for intraocular pressure control using measured flow rate in a fluid line and a dual infusion chamber, with the intent to prevent too high a pressure in a patient's eye. From the measured flow rate, a predicted intraocular pressure is calculated, and depending on an operator input of desired pressure, infusion is adjusted. A dual infusion chamber is provided to allow continued fluid flow if one of the infusion chambers is (almost0 empty.

The present invention seeks to provide an improved surgical irrigation system, which provides for active irrigation of the surgical site by controlling the irrigation pressure.

According to the invention, there is provided an active irrigation system for controlling delivery of irrigation fluid to a surgical site, the irrigation system comprising: a chamber having at least one fluid port for introducing an irrigation fluid from a fluid source into the chamber and delivering the irrigation fluid to a surgical site; an irrigation pump configured to deliver irrigation fluid from the fluid source to the chamber; a variable pressure source in fluid communication with the chamber and configured to pressurize the chamber; a pressure sensor in fluid communication with the chamber configured to monitor the pressure in the chamber; a controller configured to adjust the pressure applied by the variable pressure source to maintain a desired irrigation pressure within the chamber, the controller operatively connected to the pressure sensor,wherein the chamber comprises a first compartment and a second compartment separated by an internal wall, the first compartment comprising the at least one fluid port and the second compartment comprising a fluid level indicator, and wherein the internal wall comprises at least one opening therein to allow the fluid level in the first compartment and the second compartment to equalize.

For illustrative purposes only and not being part of the claimed invention, there is provided a method for actively controlling irrigation pressure within a surgical irrigation system, the method comprising: moving an irrigation fluid from a fluid source through a fluid port into a chamber using an irrigation pump; pressurizing the chamber using a variable pressure source in fluid communication with the chamber via a pressure port by applying a predetermined pressure to move the fluid from the chamber, through the fluid port (or a dedicated outlet port); measuring the pressure within the chamber with a pressure sensor in fluid communication with the chamber; and adjusting the pressure applied by the variable pressure source in response to feedback from the pressure sensor to maintain a predetermined irrigation pressure within the chamber.

By actively controlling the irrigation pressure in the chamber with a variable pressure source, precise control of the pressure within the eye is possible, which may be even further improved by taking into account further (pneumatic) system parameters, such as tube and needle diameters. This reduces the risk of damage to delicate ocular tissue due to excessive pressure in the eye and minimizes the chance of the eye collapsing due to a lack of fluid at the surgical site.

Further embodiments are described in the claims as attached.

Exemplary embodiments of the present invention will now be described in detail. The skilled person will understand that devices described herein are non-limiting exemplary embodiments and that the scope of protection is defined by the claims. For example, although the present invention is described with respect to ophthalmic aspiration and/irrigation procedures, the skilled person will understand that the present invention may be used in other applications, for example in other aspiration and/or irrigation systems, e.g. fine needle aspiration procedures. The skilled person will also understand that the features illustrated or described in connection with one exemplary embodiment may be combined with features described in other exemplary embodiments. Such modifications and variations are included within the scope of the present disclosure.

An active irrigation system according to the present invention will now be described with reference to <FIG>. As shown in <FIG>, an irrigation system <NUM> comprises a cassette <NUM>, sometimes referred to as a surgical cassette, having a chamber <NUM>. The chamber <NUM> is configured to store a fluid F in a lower part 10b of the chamber <NUM> and air A in an upper part 10a of the chamber <NUM>, the upper part 10a being the remaining space at the top of the chamber <NUM>. The chamber <NUM> comprises at least one fluid port <NUM>; <NUM> for introducing an irrigation fluid F into the chamber <NUM> from a fluid source, e.g. an infusion bottle <NUM> into the chamber <NUM> and for delivering irrigation fluid F from chamber <NUM> to an irrigation tip (not shown) via an irrigation line <NUM>. The surgical irrigation tip can be used to deliver irrigation fluid to a surgical site, e.g. the eye <NUM>.

In some embodiments, the fluid inlet port <NUM> and fluid outlet port <NUM> are combined as a single fluid port directly connected to the chamber <NUM>. The fluid port <NUM>; <NUM> then splits into an input connection to a first conduit (such as infusion conduit <NUM> in the <FIG> embodiment), and an output connection to a second conduit (irrigation conduit <NUM> in the <FIG> embodiment). This is possible as the chamber <NUM> controls the flow of fluid into or out of the fluid port <NUM>; <NUM> by pressure control. In other embodiments, the chamber <NUM> is provided with a dedicated fluid inlet port <NUM> and a dedicated fluid outlet port <NUM>.

In other words, the chamber can be configured in two ways: in some embodiments, the at least one fluid port comprises a single fluid port configured to introduce fluid into the chamber from a fluid source and deliver fluid from the chamber to a surgical site. In alternative embodiments, the at least one fluid port comprises a first fluid port <NUM> configured to introduce fluid into the chamber <NUM> and a second fluid port <NUM> configured to deliver fluid F from the chamber <NUM> to the surgical site. In any event, the pressure control system controls the flow of fluid into and out of the chamber <NUM> via the fluid port(s).

An irrigation fluid pump <NUM> (e.g. a peristaltic pump) is configured to move fluid F from the (infusion) fluid source <NUM> to the chamber <NUM>. The irrigation pump <NUM> may be provided between the fluid source <NUM> and the chamber <NUM>, along infusion line <NUM>. A variable pressure source <NUM> is provided in fluid communication with the chamber <NUM> and is configured to pressurise the chamber <NUM>. A pressure sensor <NUM> is provided in fluid communication with the chamber <NUM> and is configured to measure the pressure within the chamber <NUM>. The pressure sensor <NUM> may be arranged to measure either the air pressure or the liquid pressure, and may be selected as any suitable pressure sensor, such as a diaphragm, piezo-resistive or a MEMS based pressure sensor.

A controller <NUM> is operatively connected to the pressure sensor <NUM> and the variable pressure source <NUM> and is configured to adjust the pressure provided by the variable pressure source <NUM> to maintain the pressure within the chamber <NUM> at a desired level.

Active control of the irrigation pressure within the surgical irrigation system <NUM> is achieved in the following manner. Before or during an irrigation procedure, a healthcare practitioner determines a suitable irrigation pressure and provides a pressure set-point(s) to the system <NUM> using a suitable user interface (not shown). The interface may by a digital interface such as a GUI, or it may be a foot pedal or dial. The user interface is not critical to the present invention.

Under the direction of the controller <NUM>, the irrigation pump <NUM> moves the fluid F from the (infusion) fluid source <NUM> through the fluid port <NUM> to the chamber <NUM>, partially filling the chamber <NUM> with fluid F. The lower part of the chamber <NUM> is filled with irrigation fluid F, the remaining space in the upper part of the chamber <NUM> is filled with air A. The variable pressure source <NUM> moves the fluid (F) from the chamber <NUM> to the fluid port <NUM> (or to a dedicated outlet port <NUM>), and eventually to a surgical site, by applying a positive pressure to pressurize the chamber <NUM> via the pressure port <NUM>. The flow of fluid through the system <NUM> is indicated by arrow F2.

The pressure sensor <NUM> measures the pressure within the chamber <NUM> and provides information regarding the actual pressure within the chamber <NUM> to the controller <NUM>. It will be appreciated that the actual pressure within the chamber <NUM> varies even when a constant pressure is delivered by the pressure source <NUM> due to variables that are outside the healthcare practitioner's control (e.g. temporary occlusions in the irrigation and aspiration lines used in a surgical procedure and the resultant sudden drop in pressure that follows the removal of such an occlusion).

To compensate for these variations, the pressure within the chamber <NUM> is adjusted by adjusting the pressure applied by the variable pressure source <NUM> in response to feedback from the pressure sensor <NUM> to maintain a predetermined irrigation pressure within the chamber <NUM>. The set-point for the pressure within the chamber <NUM> may be a constant irrigation pressure or it may be a varying pressure profile. The variable pressure source <NUM> selectively applies a positive or negative pressure through the pressure port <NUM> to correct an over- or under-pressurisation of the chamber <NUM> compared to the predetermined set-point. For example, if the pressure within the chamber <NUM> (as measured by the pressure sensor <NUM>) is too high, the pressure source <NUM> can be configured to apply a reduced (or negative pressure) to bring the pressure within the chamber <NUM> back within range.

By pressurising the chamber <NUM>, irrigation fluid F can be delivered to the eye <NUM> at a pressure determined by a medical practitioner, independent of the conditions at the surgical site. This allows the system <NUM> to compensate for fluctuations in irrigation pressure and/or flow due to temporary occlusion of aspiration or irrigation lines and the subsequent removal of those occlusions. This allows greater stability within the surgical site (e.g. the eye <NUM>). The arrangement shown in <FIG> also provides an advantage over systems in which the infusion fluid source is directly pressurised (e.g. where the infusion bottle is squeezed) since the pressure across the various infusion and irrigation lines and an intervening chambers in such systems is difficult to control.

The variable pressure source <NUM> is at least capable of applying a variable positive pressure to the chamber <NUM> to deliver fluid from the chamber <NUM> to the eye <NUM> via an irrigation line <NUM>. However, the variable pressure source <NUM> can be configured to selectively apply a positive pressure and a negative pressure to the chamber <NUM>. Such a configuration is advantageously versatile and can be used to quickly correct excessively high and/or low pressures within the chamber <NUM>. A variable pressure source <NUM> suitable for use in connection with the present invention is described with reference to <FIG> and <FIG>. However, the skilled person will appreciate that other variable pressure sources may be employed.

The irrigation system <NUM> shown in <FIG> may also comprise a fluid level indicator <NUM> arranged to measure the fluid level within the chamber <NUM> during operation. The fluid level indicator <NUM> can be arranged within the cassette <NUM> in which the chamber <NUM> is provided. The fluid level indicator <NUM> may be configured to measure the fluid level remote from the fluid/air interface W within the chamber <NUM>. In an exemplary embodiment, the fluid level indicator <NUM> may be a float based fluid level indicator, as described in more detail with refer to <FIG>. However, the skilled person will appreciate that other fluid level indicating arrangements are possible.

The controller <NUM> will now be described in more detail with reference to <FIG>, which shows a schematic of a controller <NUM> suitable for use in the irrigation system <NUM> of <FIG>. The controller <NUM> comprises a pressure controller <NUM> for maintaining a desired pressure within the chamber <NUM> and a fluid level controller <NUM> for controlling the fluid level within the chamber <NUM>, e.g. by maintaining the fluid level within a pre-determined range.

The pressure controller <NUM> receives pressure information from the pressure sensor <NUM> and adjusts the pressure delivered by the variable pressure source <NUM> to maintain the pressure within the chamber <NUM> at the desired level, as described above with reference to <FIG>. The pressure controller <NUM> can be programmed to provide a varying pressure profile or to maintain the pressure within the chamber <NUM> within a predefined range. As an example, if the pressure within the chamber <NUM> drops below a predetermined threshold (e.g. as a result of a spike in aspiration flow away from the surgical site), the pressure controller <NUM> adjusts the set-point for the variable pressure source <NUM> to increase the pressure within the chamber <NUM>, thereby increasing the flow of irrigation fluid to compensate for the sudden drop in pressure. Conversely, if the pressure controller <NUM> determines via the pressure sensor <NUM> that the pressure within the chamber <NUM> is too high (e.g. as a result of occlusion of the aspiration line), the pressure controller <NUM> instructs the variable pressure source <NUM> to supply a decreased pressure (or a negative pressure) to correct the over-pressurisation of the chamber <NUM>.

The controller <NUM> also comprises a fluid level controller <NUM> for controlling the fluid level within the chamber <NUM>, as shown schematically in <FIG>. The fluid level controller <NUM> is configured to maintain the fluid level W within the chamber <NUM> within a predefined range by adjusting the rate at which the irrigation pump <NUM> moves fluid from the fluid source <NUM> to the chamber <NUM> based on feedback from the fluid level indicator <NUM>. The fluid level controller <NUM> provides a set-point to a velocity controller <NUM>, which controls the rate at which irrigation pump <NUM> delivers irrigation fluid F to the chamber <NUM> from the infusion bottle <NUM>. As an example, if, based on feedback from the fluid level indicator <NUM>, the controller <NUM> determines that the fluid level within the chamber <NUM> is too low, the controller <NUM> adjusts the set-point of the velocity controller <NUM> to increase the rate/speed at which irrigation pump <NUM> delivers irrigation fluid from the infusion bottle <NUM> to the chamber <NUM>. Conversely, if the controller <NUM> determines that the fluid level within the chamber <NUM> is too high, the controller adjusts the set-point of the velocity controller <NUM> to decrease the rate/speed at which the irrigation pump <NUM> delivers fluid from the infusion bottle <NUM> to the chamber <NUM>.

Advantageously, the controller <NUM> shown in <FIG> can also allow for calculation of the flow rate to the eye <NUM> without the need for a flow sensor within the irrigation line <NUM>. The controller is configured to calculate the irrigation flow through the irrigation tip based on the fluid level measured by the fluid level indicator <NUM> and/or the infusion rate determined by the velocity controller <NUM>. Since the dimensions of the fluid port (s) <NUM>; <NUM>, the irrigation line <NUM> and the irrigation tip (not shown) are known, and the pressure within the chamber <NUM> is sensed by the pressure sensor <NUM>, the irrigation pressure and the irrigation flow rate at the irrigation tip can be calculated without direct measurement at the surgical site. This is advantageous because ophthalmic surgical systems often have small flow rates (as they comprise narrow gauge irrigation lines), for which accurate flow sensing can be challenging. It is noted that even without fluid level information, it is possible to only use the infusion rate determined by the velocity controller <NUM> (i.e. the actual velocity of a (peristaltic) pump <NUM>.

The above description of <FIG> relates to a pressure mode of operation, wherein a user can input a set point for the desired pressure to pressure controller <NUM>. This may be applied both when the present invention embodiments are used for controlling irrigation to the eye, and for controlling aspiration from the eye. In a further embodiment, specifically suited for aspiration purposes, the present invention embodiments are operated in a flow control mode. In the flow control mode, a set point for the desired aspiration flow is input to the velocity controller <NUM>, for controlling the speed of the drainage pump <NUM>. The fluid level controller <NUM> uses the input from the fluid level indicator <NUM> to provide a pressure set point to the pressure controller <NUM> that subsequently control the variable pressure source <NUM> to ensure the fluid level is controlled to an internal defined set point.

The controller <NUM> of <FIG> may also be employed to alert the user to an empty bottle condition (e.g. when the infusion bottle is empty/low of fluid). This minimizes the risk of air entering the irrigation line <NUM>, which can be dangerous.

An empty bottle warning system may issue a warning signal or alarm when a predetermined volume of irrigation fluid has been delivered by the velocity controller <NUM>. The extracted volume can be calculated based on the initial quantity of irrigation fluid in the infusion bottle <NUM> and the amount of the fluid delivered to the chamber <NUM> by the velocity controller <NUM>. A warning can be issued when the volume of fluid delivered approaches the total initial volume of the infusion bottle <NUM>.

However, the active irrigation system <NUM> described above also allows for an empty bottle warning system that does not require precise knowledge of the initial fluid volume contained within the infusion bottle <NUM>. Instead, the controller <NUM> can be configured to monitor the level of fluid within the chamber <NUM> during operation and issue a warning signal if the fluid level moves out of predefined range, e.g. falls below predefined threshold.

As described above, the fluid level controller <NUM> monitors the fluid level within chamber 10and adjusts the set-point of the velocity controller <NUM> to maintain the fluid level with the chamber <NUM> within the desired range. In an empty bottle condition, air will be transported into the chamber <NUM>. This will cause the fluid level within the chamber <NUM> to fall, even if the velocity controller <NUM> increases the rate at which pump <NUM> delivers fluid to the chamber <NUM>. This in turn causes the fluid level in the chamber <NUM> to drop out of range, which can trigger a warning signal or alarm to be issued, prompting the user to replace the infusion bottle <NUM>. This system is advantageous because it does not require prior knowledge of the volume of irrigation fluid in bottle <NUM> or the rate of flow of fluid into the chamber <NUM>. Moreover, by monitoring the level of fluid in the chamber <NUM>, a warning signal can be produced before the chamber <NUM> is empty, thereby minimizing the risk that air is delivered through the irrigation line <NUM> to the eye.

Referring now to <FIG>, in at least one embodiment, the irrigation system <NUM> described with reference to <FIG> can be modified to include a chamber <NUM> configured for air removal (e.g. minimizing the risk that air bubbles from the infusion line <NUM> can enter the irrigation line <NUM>).

As shown in <FIG>, the irrigation system <NUM> is generally similar to the irrigation system <NUM> described with reference to <FIG> and comprises an infusion bottle <NUM> and an irrigation pump <NUM> to deliver fluid from the infusion bottle <NUM> to a chamber <NUM> comprised in a surgical cassette <NUM> via an irrigation line <NUM>. A velocity controller <NUM> as shown schematically in <FIG> controls the rate of flow of fluid F from the infusion bottle <NUM> to the chamber <NUM>. A variable pressure source <NUM> and a pressure sensor <NUM> are in fluid communication with the chamber <NUM> via the pressure port <NUM>. A pressure controller <NUM> monitors the pressure within chamber <NUM> and controls the variable pressure source <NUM>, as described above, to maintain a desired irrigation pressure within chamber <NUM>. The surgical cassette <NUM> comprises a fluid level indicator <NUM> to monitor the fluid level with chamber <NUM>.

Whilst the chamber <NUM> described above with reference to <FIG> comprises a fluid (inlet) port <NUM> (connected to the infusion line <NUM>) in the lower part of the chamber <NUM> (i.e. below the fluid surface during normal operation), the chamber <NUM> shown in <FIG> comprises a fluid port comprising a fluid inlet port <NUM>, which is provided in an upper portion of the chamber <NUM>, such that the fluid inlet is provided above the fluid surface W within the chamber <NUM> during operation. By providing a fluid inlet port <NUM> above the surface W of the fluid F, air bubbles from the (infusion) fluid source <NUM> and the infusion line <NUM> are not introduced below the fluid surface W. This minimizes the risk of bubbles being introduced into the irrigation line <NUM> and bubbles forming beneath the surface on the float-based fluid level indicator <NUM>, which could adversely affect fluid level measurement. As the fluid level may actually change during use, the fluid inlet port <NUM> is positioned in the top half of the chamber <NUM>, e.g. in the top third of the chamber <NUM>. On the other hand, the fluid inlet <NUM> is also positioned or arranged to allow non-turbulent input of the fluid into chamber <NUM>, to prevent e.g. bubbles being formed in the fluid.

In any event, the fluid inlet port <NUM> is configured such that when the fluid level is within the desired range, the fluid inlet port <NUM> is above the fluid surface (i.e. the air/liquid interface), when the fluid level is within the normal operating range. This configuration ensures that any air bubbles introduced into the infusion line <NUM> are not introduced below the surface W of the fluid F within the chamber <NUM>, which could lead to bubbles being introduced into the irrigation line <NUM> or disturbances at the fluid/air interface W that could adversely affect fluid level measurement.

To prevent falling droplets impacting the fluid level indictor <NUM>, the chamber <NUM> comprises a first compartment <NUM> and a second compartment <NUM> separated by an internal wall <NUM>. The first compartment <NUM> comprises the fluid port <NUM>; <NUM> and the second compartment <NUM> comprises the fluid level indicator <NUM>. The internal wall <NUM> comprises at least one opening <NUM> therein to allow the fluid level in the first compartment <NUM> and the second compartment <NUM> to equalize. By providing separate compartments for the fluid port <NUM>; <NUM> and the fluid level indictor <NUM>, surface ripples formed by fluid droplets hitting the fluid surface W within the first compartment <NUM> from cannot propagate into the second compartment <NUM> due to internal wall <NUM>. This ensures minimum disturbance in the fluid surface in the second compartment <NUM>, where fluid level measurements are made. This may allow for more accurate fluid level measurement.

Furthermore, the internal wall <NUM> will also prevent any splashing of fluid originating from the fluid inlet <NUM> onto the outer surface of the float which is part of the fluid level indicator <NUM> as drawn in the embodiment of <FIG>. This will prevent a possibility of the float sticking at the inside of the second compartment <NUM>, which might also influence proper operation of the fluid level indicator <NUM>.

In any event, the first opening <NUM> should be positioned such that it is below the fluid surface when the fluid level is within the normal operating range. The specific location of the first opening <NUM> can be determined by the skilled person based on the operating parameters of the system. the first opening <NUM> is positioned below the fluid port <NUM>, which would prevent any possible bubbles being formed to reach the float of the fluid level indicator <NUM>. In an even further embodiment, the first opening <NUM> may be even at the bottom side of the chamber <NUM>, and would then (as in the other positions described above) also act as a dampening element for the fluid level in the second compartment <NUM>.

In some embodiments, the internal wall <NUM> comprises a second opening <NUM> in the upper part of the chamber <NUM> to allow the air pressure in the first compartment <NUM> and the second compartment <NUM> to equalize. The second opening <NUM> can be formed as a bore through an internal wall <NUM> that extends all the way to the top of the chamber <NUM>. Alternatively, the internal wall may stop short of the upper wall of the chamber <NUM>, thereby providing an opening <NUM> at the upper end of the chamber <NUM>.

In any event, the second opening <NUM> should be positioned such that it is above the fluid surface when the fluid level is in range. The specific location of the first opening <NUM> can be determined by the skilled person based on the operating parameters of the system. The specific location of the second opening <NUM> can also be determined by the skilled person based on the operating parameters of the system.

As shown in <FIG>, in some embodiments a dedicated fluid outlet port <NUM> can be provided in the second compartment <NUM>. This further reduces the risk of disturbances/bubbles produced by fluid droplets entering the chamber <NUM> from entering the irrigation line <NUM>. However, the skilled person will recognize that the fluid outlet port <NUM> may be provided in the first compartment <NUM> (or possibly combined in a single port with the fluid inlet, as described above), leaving the fluid level sensor <NUM> with a dedicated compartment <NUM>. As the fluid in the chamber <NUM> with the application to irrigation only will originate only from the fluid source, there will be virtually no debris present in the fluid in chamber <NUM> during use, and hence the fluid outlet port <NUM> may be positioned in the bottom part of chamber <NUM>, possibly even at the bottom.

Furthermore, by selecting a position of the fluid outlet port <NUM> and/or first opening <NUM> away from the float of the fluid level indicator <NUM>, any possible sideways flow of the fluid in the vicinity of the float is prevented, which will improve the accuracy and proper operation of the fluid level indicator <NUM>.

The fluid level indicator <NUM> shown in <FIG> (and described in more detail with respect to <FIG>) is a float based fluid level sensor. However, the skilled person will appreciate that the advantages of a divided chamber may also be realized in systems with alternative fluid level sensing means. For example, minimizing disturbances in the fluid surface may also be advantageous in direct fluid level measurement systems, e.g. systems in which optical or electrical sensors detect the position of the air/fluid interface.

Optionally, to further minimize pressure disturbances in the chamber <NUM> caused by falling droplets, the fluid inlet port <NUM> may open onto a inclined surface <NUM> down which droplets from the fluid inlet port <NUM> can glide into the fluid F. This will also further minimize the chance of bubbles being formed in the fluid F by falling droplets from the fluid inlet port <NUM>.

Although the exemplary irrigation system described with reference to <FIG> is advantageous, the skilled person will appreciate that the split level chamber <NUM> described above with reference to <FIG> may also be employed in an irrigation system in which the fluid inlet port <NUM> is provided toward the bottom of the chamber <NUM>, i.e. below the fluid surface. The internal wall <NUM> may limit the passage of air bubbles introduced at the fluid inlet port <NUM> in the first compartment <NUM> to into the second compartment <NUM>, thereby minimizing the risk of bubble formation around the fluid level indicator <NUM> (which could cause the float to stick to the sides of the chamber <NUM>). The two-chamber arrangement may also limit bubble formation at the fluid surface, which can adversely affect the accuracy of fluid level measurement.

In some exemplary embodiments of the irrigation system <NUM>, <NUM>, the fluid level indicator <NUM> is a float-based fluid level indicator. Referring now to <FIG>, the float-based fluid level indicator <NUM> comprises at least one float <NUM> configured to rise and fall with the fluid level W within the chamber <NUM>. As shown in <FIG>, the cassette <NUM> comprises a chamber <NUM> having a channel <NUM> extending therefrom.

The float <NUM> comprises a float body <NUM>, which is disposed within the chamber <NUM>, and a float stem <NUM>, which is disposed at least partially within the channel <NUM>. The float body <NUM> and the float stem <NUM> are arranged such that they are free to move within the chamber <NUM> and channel <NUM> respectively, as the fluid level W rises and falls. The cassette <NUM> is configured so that the position of the float stem <NUM> within the channel <NUM> can be measured by a sensing system that detects the position of the float stem <NUM> within the channel <NUM>. The fluid level W within the chamber can thus be determined by measuring the position of the float stem <NUM> within the channel <NUM>. The position of the float stem <NUM> within the channel <NUM> can be sensed with means known to the person skilled in the art, e.g. optically, acoustically, electronically, etc..

By measuring the position of the float stem <NUM> within the channel <NUM>, the level of the fluid F within the chamber <NUM> can be made indirectly, i.e. remote from the air/liquid interface W within chamber <NUM>. This is advantageous because such a measurement is generally insensitive to changes in liquid properties within the chamber which may affect the liquid surface, e.g. disturbances in the fluid surface due to fluid ingress from the infusion bottle <NUM>. It also allows fast and reliable fluid level sensing, which allows fine control of the fluid level within the chamber <NUM> by the controller <NUM>, as described above with reference to <FIG>.

The float based fluid level sensor <NUM> is described above with reference to a chamber <NUM> having a single compartment. However, the skilled person will appreciate the float-based fluid level indicator described with reference to <FIG> can also be employed in a multi-compartment chamber, such as chamber <NUM>.

A variable pressure source <NUM> suitable for use in the active irrigation system according to the present invention will now be described with reference to <FIG> and <FIG>.

<FIG> and <FIG> each depict an embodiment of a variable pressure source <NUM> that comprises a pump unit <NUM> having a negative pressure source <NUM> (e.g. a vacuum source) and a positive pressure source <NUM> (e.g. a compressor). In an embodiment, the negative or positive pressure source <NUM>, <NUM> may be a membrane pump for example, although the skilled person will appreciate that other positive and/or negative pressure sources could be employed. The terms negative and positive pressure are being used herein with respect to an ambient pressure. As an alternative implementation one of the pressure sources <NUM>, <NUM> could be actually at the ambient pressure.

The pump unit <NUM> is further provided with an adjustable valve arrangement <NUM>, wherein the valve arrangement <NUM> comprises a vacuum port 25a connected to the negative pressure source <NUM> and a pressure port 25b connected to the positive pressure source (<NUM>). The adjustable valve arrangement <NUM> also comprises a main port 25c in fluid communication with the vacuum port 25a and/or the pressure port 25b. The main port 25c is configured to connect to an upper part 10a of a chamber <NUM> for storing air A and exchanging the air A with the pump unit <NUM>. The chamber <NUM> comprises a bottom part 10b for storing a surgical fluid F to be irrigated or aspirated.

The adjustable valve arrangement <NUM> is adapted to control the flow of air to/from the chamber <NUM> through the main port 25c corresponding to the intensity at which the vacuum source <NUM> and/or the pressure source <NUM> is/are active. Since the valve arrangement <NUM> shown in <FIG> and <FIG> couples the chamber <NUM> to a negative pressure source <NUM> as well as a positive pressure source <NUM>, the pump unit <NUM> is able to provide fast, dynamic pressure control within chamber <NUM> and with remarkable precision rather than solely relying on a vacuum source to vary the pressure within the chamber <NUM>. The valve arrangement <NUM> of the present invention is thus configured to provide virtually any pressure required at the main port 25c below or above atmospheric pressure with any desired speed and accuracy.

In an embodiment, the adjustable valve arrangement <NUM> is a proportionally adjustable valve arrangement allowing smooth and continuous changes in air pressure and air flow across the main port 25c. The proportionally adjustable valve arrange is capable of switching between and/or "blending" the negative and positive pressure sources <NUM>, <NUM>, so that any desired pressure and air flow across the main port 25c can be achieved with great speed and precision. As an alternative implementation, a pulse width modulation (PWM) controlled on/off valve arrangement may be applied.

In an exemplary embodiment as shown in <FIG>, the adjustable valve arrangement <NUM> comprises a first adjustable valve R1 connected between the vacuum port 25a and the main port 25c and a second adjustable valve R2 is connected between the pressure port 25b and the main port 15c. This allows virtually any amount of negative pressure from the negative pressure source <NUM> and any amount of positive pressure from the positive pressure source <NUM> to be accurately controlled at the main port 25c, so that any desired net pressure and air flow across the main port 25c can be achieved with great accuracy and speed (within the negative and positive pressure ranges of the vacuum source <NUM> and/or pressure source <NUM>).

In an advantageous embodiment, the first adjustable valve R1 is a first proportional valve and the second adjustable valve R2 is a second proportional valve. Each of the proportional valves R1, R2 allow for fast, continuous control to further increase speed and accuracy of the net pressure and air flow across the main port 25c.

Controlling the first and second adjustable/proportional valves R1, R2 with e.g. a current source can be advantageous because current controlled valves may be less insensitive for temperature variations, when compared to voltage controlled valves. Alternatively, the first and second adjustable/proportional valves R1, R2 are position controlled valves.

In a further embodiment, the first and second adjustable/proportional valves R1, R2 are biased with a first current to allow a bias flow in the flow path between negative pressure source <NUM> and positive vacuum source <NUM>, whilst maintaining a net zero flow through the main port 25c (keeping pressure in the chamber <NUM> at a constant level). In general, the current/flow characteristic of such a valve includes a threshold current below which the valve remains closed. Biasing the first and second adjustable/proportional valves R1, R2 with a current at least equal to this threshold current allows to have a faster response time when further opening one of the valves R1, R2 during control.

To allow control and proper setting of the adjustable valve arrangement <NUM>, the pressure control unit may further comprise a flow sensor <NUM> arranged in a bias flow path between the negative pressure source <NUM> and the positive pressure source <NUM>. The bias flow path comprises the direct connection parts between the negative pressure source <NUM> and the positive pressure source <NUM> in any of the exemplary embodiments described herein. the flow sensor <NUM> is arranged between the positive pressure source <NUM> and the pressure port 25b or between the vacuum source <NUM> and the vacuum port 25a. The flow sensor <NUM> can be any suitable flow sensor, e.g. an in-line flow sensor.

The flow sensor <NUM> may be connected to the controller <NUM> (or to a dedicated controller), and may be implemented as a mass flow sensor or as a volumetric flow sensor (e.g. a differential pressure based flow sensor which allows measuring a volumetric flow rate by measuring a differential pressure over a (fixed) restriction). The measurement data from the flow sensor <NUM> can then be used in a secondary control loop which actively controls the flow in the bias flow path (without affecting flow through the main port 25c).

Referring to <FIG>, in an alternative embodiment, the adjustable valve arrangement <NUM> is a three-way valve arrangement T, which may be seen as a single, unitary valve manifold having three connecting ports 25a, 25b, 25c and a valve insert for controlling/dividing air flow through these connecting ports. For example, the three-way valve arrangement <NUM> comprises the vacuum port 25a, the pressure port 25b, and the main port 25c, wherein the valve insert allows accurate control of the degree in which the vacuum port 25a or the pressure port 25b is in communication with the main port 25c.

As with the first and second adjustable/proportional valves R1, R2, the three-way valve arrangement T may be current controlled, thereby reducing or avoiding temperature dependent valve sensitivities. Note that the skilled person will of course appreciate that voltage control may still be effectively used to control the adjustable valve arrangement <NUM>, in particular the first and second adjustable/proportional valves R1, R2 as well as a three-way valve arrangement T as described above.

In order to monitor the pressure within the chamber <NUM> during operation, an embodiment is provided wherein the pump unit <NUM> comprises a pressure sensor <NUM> in communication with the main port 25c. For example, in an embodiment the pressure sensor <NUM> is connected to a conduit arranged between the main ports 25c and the upper part 10a of chamber <NUM>. Note that in an embodiment a controller can be provided and configured to adjust the adjustable valve arrangement <NUM> to maintain a desired pressure in the chamber <NUM> in response to the pressure measured by the pressure sensor <NUM>.

During a surgical procedure, also discussed above with reference to <FIG> as pressure sensor <NUM>, the pressure sensor P as depicted in <FIG> can provide feedback to a controller <NUM> for adjusting the valve arrangement <NUM> to maintain the pressure within chamber <NUM> at a desired level. For example, if the sensed pressure within the chamber <NUM> is lower than the desired pressure, the pressure can be quickly increased by adjusting the valve arrangement <NUM> to deliver pressurised air from the positive pressure source <NUM> to the main port 25c and thus to the chamber <NUM>. Should the sensed pressure within the chamber <NUM> be higher than the desired pressure, the pressure can be quickly decreased by adjusting the valve arrangement <NUM> such that a negative pressure is applied to the main port 25c and thus to the chamber <NUM>. This allows for rapid adjustment of the pressure within the chamber <NUM> e.g. to compensate for non-linearities and valve hysteresis as well as blockages and leaks within the system or at the surgical site.

In an embodiment, the controller <NUM> controls the first and second adjustable/proportional valves R1, R2 such that if the desired pressure set-point is achieved, the steady state air consumption is minimized to meet the flow capacity of the compressor and the vacuum source.

According to the present invention the adjustable valve arrangement <NUM> allows for rapid and accurate control of negative and positive air pressure within the chamber <NUM>. To allow this fast pressure changes, short term mass flow rates are required. To be capable of providing these flow rates that might not match the flow capacity of the internal system pressure sources <NUM>, <NUM>, a vacuum buffer 28a and a pressure buffer 28b are used. Furthermore, fast changes in air pressure can induce short bursts of relatively high mass flow rates and pressure ripples through the pump unit <NUM>. To provide dampening of such high mass flow rates and pressure ripples there is provided an embodiment wherein the pump unit <NUM> further comprises a vacuum buffer 28a arranged between the negative pressures source <NUM> (i.e. vacuum source) and the vacuum port 25a. In another embodiment a pressure buffer 28b may be provided and arranged between the positive pressure source <NUM> and the pressure port 25b. Of course, in an advantageous embodiment the pump unit <NUM> comprises both the vacuum buffer 28a and the pressure buffer 28b, so that short bursts of high mass flow rates to and from the chamber <NUM> are dampened. The vacuum buffer 28a and the pressure buffer 28b each provide capacitance to momentary absorb some of the high mass flow rate from/to the chamber <NUM> and in doing so also provide dampening of pressure ripples through the pump unit <NUM> and in the chamber <NUM>. It is noted that either the vacuum buffer 28a and/or the pressure buffer 28b may alternatively or additionally be formed by using the air volume within the pneumatic tubing between the negative/positive pressure sources <NUM>, <NUM> and the main port 25c.

As mentioned above, the adjustable valve arrangement <NUM> allows for rapid changes in air pressure within the chamber <NUM> for optimizing irrigation and/or aspiration during an ophthalmic procedure. For safety purposes when high pressure pulses occur during operation of the pump unit <NUM> (e.g. in case of failure of the control unit <NUM> or one or more of the pneumatic components), the adjustable valve arrangement <NUM> may further comprise on or more safety valves.

The variable pressure source <NUM> is described above with reference to a chamber <NUM> having a single compartment. However, the skilled person will appreciate the variable pressure source <NUM> described with reference to <FIG> and <FIG> can also be employed in a multi-compartment chamber, such as chamber <NUM>.

Claim 1:
An active irrigation system for controlling delivery of irrigation fluid to an ophthalmic surgical site, the active irrigation system comprising:
a chamber (<NUM>, <NUM>) having at least one fluid port (<NUM>; <NUM>) for introducing an irrigation fluid (F) from a fluid source (<NUM>) into the chamber (<NUM>, <NUM>) and for delivering the irrigation fluid (F) to a surgical site;
an irrigation pump (<NUM>) configured to deliver irrigation fluid (F) from the fluid source (<NUM>) to the chamber (<NUM>, <NUM>);
a variable pressure source (<NUM>) in fluid communication with the chamber (<NUM>, <NUM>) and configured to pressurize the chamber (<NUM>, <NUM>);
a pressure sensor (<NUM>) in fluid communication with the chamber (<NUM>, <NUM>) configured to monitor the pressure within the chamber (<NUM>, <NUM>);
a controller (<NUM>) configured to adjust the pressure applied by the variable pressure source (<NUM>) to maintain a desired irrigation pressure within the chamber (<NUM>, <NUM>), the controller (<NUM>) operatively connected to the pressure sensor (<NUM>),
wherein the chamber (<NUM>) comprises a first compartment (<NUM>) and a second compartment (<NUM>) separated by an internal wall (<NUM>), the first compartment (<NUM>) comprising the at least one fluid port (<NUM>; <NUM>) and the second compartment (<NUM>) comprising a fluid level indicator (<NUM>) arranged to indicate the fluid level within the chamber (<NUM>, <NUM>) during operation, and wherein the internal wall (<NUM>) comprises at least one opening (<NUM>) therein to allow the fluid level in the first compartment (<NUM>) and the second compartment (<NUM>) to equalize.