Ophthalmic surgical apparatus

Abstract

The invention relates to an ophthalmic surgical apparatus (1) comprising: - an irrigation fluid line (4), - an aspiration fluid line (10), - at least one first fluid pump (5), - at least one second fluid pump (11), - a first flow sensor (13), coupled to the irrigation fluid line (4), for detecting a flow of irrigation fluid in the irrigation fluid line (4), the first flow sensor providing a first flow signal (27), - a second flow sensor (14), coupled to the aspiration fluid line (10), for detecting a flow of aspiration fluid in the aspiration fluid line (10), the second flow sensor providing a second flow signal (28), and - a control unit (26) which is coupled to the flow sensors (13, 14) and to the fluid pumps (5, 11) and is designed to provide at least one first control signal (22) for the first fluid pump (5) and one second control signal (29) for the second fluid pump (11), wherein the control unit (26) is designed to compare the first flow signal (27) with the second flow signal (28) and to provide at least the second control signal (29) at least temporarily depending on the comparison.

Description

[0001] Ophthalmic Surgery Unit

[0002] The invention relates to an ophthalmic surgical device and a method for operating an ophthalmic surgical device according to the preambles of the independent claims.

[0003] Several surgical techniques exist for treating cataracts, a clouding of the eye's lens. The most widely used technique is phacoemulsification, in which a thin hollow needle of a handpiece is inserted into the lens capsule and vibrated using ultrasound. An irrigation fluid is introduced during this process. The vibrating needle emulsifies the lens in its immediate vicinity, allowing the resulting lens particles to be aspirated through the needle and an attached line, called the aspiration fluid line, using an aspiration pump. Once the lens has been completely emulsified and removed, a new artificial lens can be implanted into the empty capsule, restoring good vision to the patient. The phacoemulsification technique is now considered relatively safe.A corresponding ophthalmic surgical system is disclosed in document DE 10 2021 111 178 A1.

[0004] However, it has been observed that fluctuating intraocular pressure can occur during ophthalmic surgery, particularly phacoemulsification, which can be dangerous for the patient. If the intraocular pressure drops sharply, the cornea moves rapidly towards the iris, potentially altering the corneal surface, making it uneven, partially concave, and wavy. This can impair the surgeon's vision during the operation, making it unclear to the surgeon where the tip of a handpiece or hollow needle (hereinafter referred to simply as the hollow needle) is located. This increases the risk of the hollow needle inadvertently puncturing the posterior capsule. This is considered a serious injury for the patient, one that will not heal spontaneously or be treatable through medical intervention.With today's available technology, there are several safety mechanisms that attempt to prevent significant fluctuations in intraocular pressure. However, it has been reported that such fluctuations can occur despite these safety mechanisms, even in seemingly harmless situations. It has been shown that these fluctuations can be caused, among other things, by leakage at the point where the hollow needle is inserted into the capsular bag. This leakage can change during the phacoemulsification procedure.

[0005] In this context, EP 4 051 193 B1 discloses an ophthalmic surgical device that can reduce fluctuations in intraocular pressure. However, the teaching of EP 4 051 193 B1 is based on the ability to partially maintain intraocular pressure by controlling the irrigation fluid. Nevertheless, there is room for improvement because this results in increased consumption of irrigation fluid, or because physiological limits exist that prevent the irrigation pressure from being increased further, so as not to cause harm to a patient in the event of a malfunction.Since the irrigation fluid is usually provided using sterile containers with limited volume, one disadvantage is that increased consumption of irrigation fluid can lead to an undesirable reduction in the available time for performing phacoemulsification, because the irrigation fluid is usually provided in containers with a predetermined amount of content.

[0006] The object of the invention is to improve an ophthalmic surgical device and a method for its operation in such a way that fluctuations in intraocular pressure can be reduced with minimal effort during phacoemulsification.

[0007] The invention proposes a solution comprising an ophthalmic surgical device and a method as defined in the independent claims.

[0008] Advantageous further training opportunities arise from the characteristics of the dependent requirements.

[0009] With regard to a generic ophthalmic surgical device, the invention particularly proposes that the control unit is configured to compare the first flow signal with the second flow signal and to provide at least the second control signal at least temporarily depending on the comparison.

[0010] With regard to a generic method, the invention particularly proposes that the control unit compares the first flow signal with the second flow signal and provides at least the second control signal at least temporarily depending on the comparison.

[0011] The invention is based, among other things, on the idea that the leakage can be determined by comparing the first flow signal with the second flow signal. In particular, the leakage can be determined based on the difference between the first and second flow signals. It can be taken into account that the flow rate of the aspiration fluid is generally no greater than the flow rate of the irrigation fluid. Therefore, a difference determined through this comparison can generally be attributed predominantly to a loss flow caused by the leakage.The invention can be applied not only to phacoemulsification but is equally suitable for use in other ophthalmic surgical procedures that are at least partially performed using hollow needles and involve both irrigation and aspiration, such as vitrectomy. Among other things, the invention makes it possible to better maintain a standardized pressure for the irrigation fluid by reducing the outflow of aspiration fluid, i.e., by reducing the flow of aspiration fluid in the aspiration line. For example, if the irrigation fluid pressure is already high, the pressure of the aspiration fluid can be reduced to minimize outflow and thus compensate for leakage.This allows for improved intended operation compared to the state of the art, even while adhering to technical limitations regarding the design of the ophthalmic surgical facility.

[0012] Preferably, the provision of the second control signal according to the invention occurs continuously, depending on the comparison. However, it can also be provided that the provision of the second control signal, depending on the comparison, occurs only for one or more predefined time periods and / or depending on events during the use of the ophthalmic surgical device. For example, this can be specified by a user of the ophthalmic surgical device.

[0013] The invention is based, among other things, on the understanding that fluctuations in intraocular pressure can occur not only when an occlusion at the tip of a hollow needle breaks down, causing a relatively high negative pressure to normalize very quickly in the aspiration fluid line. A fluctuation in intraocular pressure can also occur when there is no occlusion at the hollow needle. The inventors observed that irrigation fluid can constantly leak from the point where the hollow needle pierces the cornea. Such a puncture site is usually larger than the diameter of the hollow needle because another surgical instrument is often used to perform capsulorhexis before inserting the hollow needle, and this instrument typically requires a larger opening than the hollow needle.When the hollow needle is subsequently inserted through this opening, some leakage of irrigation fluid at this opening is almost unavoidable, for example, during phacoemulsification. Such a loss of irrigation fluid usually occurs irregularly because the surgeon repeatedly and unevenly moves the hollow needle at the insertion site during the phacoemulsification procedure. During phacoemulsification, the surgeon is primarily focused on successfully fragmenting the hard lens. However, it is difficult for them to ensure that little or a consistent amount of irrigation fluid leaks from the insertion site to prevent fluctuations in intraocular pressure.

[0014] The ophthalmic surgical device and method according to the invention can reduce, if not completely eliminate, this problem. A leak at the puncture site of the eye being treated, and thus the loss of irrigation fluid, can be detected by comparing the first flow signal, corresponding to the flow in the irrigation fluid line, with the second flow signal, corresponding to the flow in the aspiration fluid line. For this purpose, a first flow sensor is provided, which is preferably arranged in the flow direction between the first fluid pump and the handpiece and is configured to determine a first volumetric flow rate, i.e., the flow in the irrigation fluid line.Furthermore, a second flow sensor is provided, which is preferably arranged in the flow direction between the handpiece and the second fluid pump and is configured to determine a second volume flow or the flow in the aspiration fluid line. The flow sensors make it possible to detect the respective volume flow of a respective fluid and output a corresponding flow signal depending on the detected volume flow. The flow signal can preferably be an electrical signal.

[0015] The ophthalmic surgical unit includes a control unit coupled to the flow sensors and fluid pumps. The control unit is configured to provide at least one control signal for the first fluid pump and a second control signal for the second fluid pump. This allows the operation of the fluid pumps to be controlled in a predefined manner by the control unit. For this purpose, the control unit may, for example, include one or more electro-pneumatic and / or electrohydraulic transducers. The control unit may also include a comparator unit for performing the comparator function. The comparator unit may include an electronic hardware circuit, such as a differential circuit with a comparator. The differential circuit may be configured as a differential element.Using the comparison unit, a difference between the flow signals of the flow sensors can be determined and made available for further signal processing.

[0016] A comparison result can thus be used as an indicator of leakage. For example, if the difference between the first and second volume flow rates is zero, it can be concluded that there is no leakage at the eye insertion point. Conversely, if the difference deviates from zero, this may indicate a leakage in the area of ​​the opening or insertion point through which the hollow needle penetrates the cornea. The comparison result can, for example, be provided as a differential volume flow signal. According to the invention, this differential volume flow signal can be fed to a first input of the processing unit of the control unit, which is configured to receive a signal for a target irrigation fluid pressure at a second input.The processing unit processes, for example, the differential volume flow signal and the signal for an irrigation fluid setpoint pressure such that a signal for a drive pressure of a drive fluid is provided at an output of the processing unit in order to supply this to the respective fluid pump, preferably to at least one second fluid pump, particularly if it is designed as a diaphragm pump. Furthermore, the processing unit can also be configured to provide an electrical control signal for an electrically driven fluid pump or a hydraulic drive signal for a hydraulically driven fluid pump.

[0017] The second fluid pump allows the flow rate of the aspiration fluid in the aspiration fluid line to be adjusted so that the loss of irrigation fluid due to corneal leakage essentially does not result in fluctuating or changing intraocular pressure. This can be achieved, for example, by reducing the pressure of the aspiration fluid or increasing the magnitude of the aspiration fluid pressure. The effort required for using flow sensors, processing the resulting differential signal, and controlling the second fluid pump accordingly is minimal.Since normal operation without occlusion at the hollow needle accounts for a large proportion of the time spent during phacoemulsification, the device according to the invention allows fluctuations in intraocular pressure to be minimized or avoided during this time, representing a significant improvement compared to conventional phacoemulsification devices. Furthermore, irrigation fluid consumption can be kept low. A reduced flow volume with respect to the aspiration fluid, achieved through lower suction pressure, can at least partially, and preferably substantially completely, compensate for an increase in fluid leakage in the area of ​​the leak. This largely prevents a drop in intraocular pressure.The invention thus makes it possible to achieve at least partial compensation for leakage and thereby maintain essentially constant intraocular pressure. Furthermore, the invention can largely avoid a significant reduction in service life due to high consumption of irrigation fluid in relation to compensating for leakage.

[0018] The processing unit can, for example, include a multiplication element configured to receive the differential flow rate signal at one input and output a drive pressure signal at one output. The multiplication element is preferably configured to convert the differential flow rate signal into a pressure signal. Additionally, the processing unit can include an adding element configured to receive a signal for the aspiration fluid setpoint pressure at a first input, the differential pressure signal at a second input, and to supply a drive pressure signal for the drive fluid of at least one second fluid pump to the output of the control unit. The adding element can thus process and add two pressure values. The signal for the aspiration setpoint pressure can be supplied by an input device such as a foot pedal.The sum of the two pressures can then be supplied as the drive pressure to at least one second fluid pump in the aspiration fluid line.

[0019] According to an advantageous further development, it is proposed that the control unit be configured to additionally provide the first control signal depending on the comparison. This makes it possible not only to control the discharge of the aspiration fluid depending on the leakage, but also, additionally, to control the supply of the irrigation fluid depending on the leakage. For example, it is possible to control the supply of the irrigation fluid depending on the comparison if the discharge of the aspiration fluid should not be reduced further. It can be provided, for instance, that in an initial operating state only the supply of the irrigation fluid is controlled depending on the comparison, and only when a maximum predefinable value for the supply of the irrigation fluid is reached is the discharge of the aspiration fluid then controlled depending on the comparison.Overall, further improvements can be achieved in terms of the use of the ophthalmic surgical facility.

[0020] It is further proposed that the ophthalmic surgical device include a setpoint unit configured to specify at least one flow setpoint for the irrigation fluid or one flow setpoint for the aspiration fluid. The flow setpoint can, for example, be a starting value that can be preset at the beginning of use of the ophthalmic surgical device. The setpoint can be a fixed, predefined value or a value specified by the user. The setpoint can, for example, be selected based on a specific, predefined irrigation volume to be achieved during use of the ophthalmic surgical device. The setpoint can also be selected based on a specific use of the ophthalmic surgical device by the user, particularly depending on the design or application of the handpiece or similar factors.

[0021] Furthermore, it is proposed that the control unit be configured to provide the second control signal only if a difference between the first and second flow signals, determined by the comparison, persists for longer than a predefined change period. This allows for improved stability in the intended operation of the ophthalmic surgical device, as a particularly short difference need not trigger a response. For example, a difference with a change period of less than approximately 50 ms, preferably less than approximately 10 ms, can be disregarded. It is specifically proposed that the change period be shorter than 4.5 ms, particularly shorter than 3.5 ms. In this case, the second control signal can be provided essentially independently of the comparison.

[0022] Furthermore, it is proposed that the control unit be designed to provide the second control signal only when the difference between the first and second flow signals, determined by comparison, exceeds a certain flow comparison value. This allows for increased stability during the use of the ophthalmic surgical device. The flow comparison value can be predefined, for example, based on the type of use, the design of the handpiece, or similar factors. This predefined value can be set by the user, or the ophthalmic surgical device can automatically detect the type of use or the handpiece and predefine the flow comparison value accordingly.

[0023] According to a further training, it is proposed that the control unit be configured to provide the second control signal in such a way that the flow of aspiration fluid in the aspiration fluid line is greater than a predefinable minimum flow rate. This minimum flow rate ensures a minimum rinsing effect, for example, to guarantee sufficient removal of lens particles when using the ophthalmic surgical device. Furthermore, the minimum flow rate prevents the aspiration fluid flow from being undesirably reduced. It is particularly advantageous if, for example, when the minimum flow rate is reached and the difference between the flow rates of the irrigation fluid and the aspiration fluid increases, the flow rate of the irrigation fluid is increased by adjusting the first control signal.

[0024] It is further proposed that the at least one first fluid pump and the at least one second fluid pump be designed as diaphragm pumps, with the diaphragm pumps serving as flow sensors. This eliminates the need for separate flow sensors. The control unit can be designed to detect the diaphragm movements of the diaphragm pumps and thereby determine the respective flow rate of the respective fluid.

[0025] It is further proposed that the ophthalmic surgical device include at least one pressure sensor capable of detecting at least the irrigation pressure in the irrigation fluid line or the aspiration pressure in the aspiration fluid line. The pressure sensor need not be located near the handpiece. It can, for example, be located near a console of the ophthalmic surgical device, particularly in conjunction with a cassette that can be detachably connected to the console. The pressure sensor can, for example, be a combination of a force sensor on the console and a membrane on the cassette, wherein the membrane contacts the fluid, particularly the irrigation fluid, with a first surface and the force sensor with a second surface opposite the first surface.

[0026] The advantages and effects stated for the ophthalmic surgical device according to the invention naturally apply equally to the method according to the invention and vice versa.

[0027] Further features of the invention will become apparent from the claims, the figures, and the description of the figures. The features and combinations of features mentioned above in the description, as well as those subsequently mentioned in the description of the figures and / or shown in the figures alone, are not only usable in the combinations specified, but also in other combinations without departing from the scope of the invention. Thus, embodiments of the invention that are not explicitly shown and explained in the figures, but which can be derived and generated from the explained embodiments by separate combinations of features, are also to be considered as encompassed and disclosed. Embodiments and combinations of features that do not exhibit all the features of an originally formulated independent claim are also to be considered disclosed.Furthermore, embodiments and combinations of features, in particular those set out above, are to be considered disclosed which go beyond or deviate from the combinations of features set out in the cross-references of the claims.

[0028] The figures show:

[0029] Fig. 1 shows a schematic block diagram of an ophthalmic surgical facility, and

[0030] Fig. 2 schematic diagrams of volume flow curves and pressure curves depending on time during use of the ophthalmic surgical equipment.

[0031] Fig. 1 shows a schematic representation of an embodiment of an ophthalmic surgical device 1. The ophthalmic surgical device 1 has an irrigation fluid line 4, which has a first line end for fluid coupling to an irrigation fluid source and a second end for fluid coupling to a handpiece 6. The irrigation fluid source is formed in this case by an irrigation fluid reservoir 2 containing an irrigation fluid 3, for example, a BSS solution, which is conveyed through the connected irrigation fluid line 4 to a first fluid pump 5 of the ophthalmic surgical device 1, which in this case is designed as a diaphragm pump. The first fluid pump 5 is fluid-connected to the irrigation fluid line 4 and is designed to pump the irrigation fluid through the irrigation fluid line 4 to the handpiece 6.In alternative configurations, a different type of pump can of course be used. From the first fluid pump 5, the irrigation fluid 3 can flow along the irrigation fluid line 4 to the handpiece 6 for phacoemulsification and reach the lens of an eye 9 to be treated through a hollow needle 7, which is pierced through a cornea 8. An opening 30 is created in the cornea 8 at the point of insertion.

[0032] The ophthalmic surgical device 1 further comprises an aspiration fluid line 10, which has a first line end for fluid coupling to an aspiration fluid sink in the form of a collection container 12 and a second end for fluid coupling to the handpiece 6. The ophthalmic surgical device 1 also comprises a second fluid pump 11, which is fluid-connected to the aspiration fluid line 10 and is designed to pump the aspiration fluid from the handpiece 6 through the aspiration fluid line 10. When the second fluid pump 11, which is designed as a diaphragm pump and is a suction pump, is in operation, emulsified lens particles and fluid can pass through a channel within the hollow needle 7 and the handpiece 6 along the aspiration fluid line 10 to the second fluid pump 11.The lens particles and the fluid, i.e. the aspiration fluid in total, are transported by the second fluid pump 11 along the aspiration fluid line 10 to the collection container 12.

[0033] The ophthalmic surgical device 1 further comprises a first flow sensor 13 coupled to the irrigation fluid line 4 for detecting a flow of the irrigation fluid in the irrigation fluid line 4, which provides a first flow signal 27 depending on the detected flow. In addition, the ophthalmic surgical device 1 comprises a second flow sensor 14 coupled to the aspiration fluid line 10 for detecting a flow of the aspiration fluid in the aspiration fluid line 10, which provides a second flow signal 28 depending on the detected flow. The flow signals 27, 28 are analog electrical signals. In particular, if the fluid pumps 5, 11 are designed as diaphragm pumps, the diaphragm pumps can, in alternative configurations, also additionally perform the function of the flow sensors 13, 14, so that separate flow sensors can potentially be eliminated.

[0034] The first flow sensor 13, coupled to the irrigation fluid line 4, is arranged as a first volumetric flow rate determination device in the flow direction between the first fluid pump 5 and the handpiece 6, with which a first volumetric flow rate Q1 in the irrigation fluid line 4 can be determined. Preferably, the first volumetric flow rate Q1 can be determined indirectly, for example, by detecting the position of a diaphragm or float of the first fluid pump 5 and calculating the volumetric flow rate from this. A separate first flow sensor 13 can thus be omitted.The second flow sensor 14, coupled to the aspiration fluid line 10, is arranged as a second volume flow determination device in the flow direction between the handpiece 6 and the second fluid pump 11, by means of which a second volume flow Q2 in the aspiration fluid line 10 can be determined. Preferably, the second volume flow Q2 can also be determined indirectly by means of the second flow sensor, for example by detecting the position of a diaphragm or a float of the second fluid pump 11 and calculating the volume flow from this. A separate second flow sensor 14 can thus be omitted.

[0035] In this configuration, the ophthalmic surgical device 1 has a control unit 26 to which the flow sensors 13 and 14 and the fluid pumps 5 and 11 are connected. The control unit 26 is designed as an electro-pneumatic control unit, which, among other things, can receive and process the electrical flow signals 27, 28. Furthermore, in this configuration, the control unit 26 is designed to provide corresponding pneumatic signals in the form of respective drive pressures for the fluid pumps 5, 11, which are designed as diaphragm pumps. Compressed air serves as the drive fluid.

[0036] The fluid pumps 5 and 11 are designed as diaphragm pumps. Each diaphragm pump has a pump chamber that is fluidly sealed off from a drive chamber by means of an elastic separating element. The pump chamber is pressurized with the fluid to be pumped, i.e., the irrigation fluid 3 or the aspiration fluid. The drive chamber is pressurized with the drive fluid, which is supplied by the control unit 26 at a drive fluid pressure. A change in the drive fluid pressure results in a corresponding change in the position of the separating element, which leads to a pumping effect with respect to the fluid to be pumped. In this case, a pneumatic drive pressure is therefore supplied by the control unit 26 for the intended operation of the diaphragm pump.

[0037] The control unit 26 processes the signal of the first volume flow Q1 and the signal of the second volume flow Q2, i.e., the flow signals 27, 28, such that these are directed to a differential element 15 as a comparison unit. The differential element 15 is configured to calculate a difference between the first volume flow Q1 and the second volume flow Q2, or the flow signals 27, 28, in order to generate a signal 16 corresponding to a differential volume flow DQ. The signal 16 is thus the difference of Q1 minus Q2, or the difference of flow signal 27 minus flow signal 28.

[0038] This signal 16 is fed to a first input 171 of a processing unit 17 and passes to a multiplication element 18, which is configured to receive signal 16 at one input and output a signal 19 for a differential pressure at one output. The processing unit 17 also has an adding element 20, which is configured to receive a signal 21 for the irrigation fluid setpoint pressure at a first input and the signal 19 for the differential pressure at a second input. The adding element 20 processes these two signals 19 and 21 such that their sum is calculated, in order to feed a signal 22 for a pneumatic drive pressure to the output of the processing unit 17 at one output of the adding element 20. The drive pressure signal 22 is then fed to the first fluid pump 5, which changes the pressure of the irrigation fluid 3 in the irrigation fluid line 4 accordingly.This allows a predetermined flow of the irrigation fluid 3 to be achieved in the irrigation fluid line 4.

[0039] Furthermore, signal 16 is fed to a first input 311 of a further processing unit 31 and passes to a further multiplication element 32, which is configured to receive signal 16 at one input and output a signal 34 for a differential pressure at one output. The further processing unit 31 additionally has an adding element 33, which is configured to receive a signal 35 for the aspiration fluid setpoint pressure at a first input and to receive signal 34 for the differential pressure at a second input. The adding element 33 processes these two signals 34 and 35 such that their sum is calculated in order to supply a signal 29 for a pneumatic drive pressure to the output of the further processing unit 31 at one output of the adding element 33.It should be noted that signal 35 for the aspiration fluid setpoint pressure has a negative signal value because there is a negative pressure at least between the second fluid pump 11 and the handpiece 6.

[0040] The signal 29 for the drive pressure is then supplied to the second fluid pump 11, which changes the pressure of the aspiration fluid in the aspiration fluid line 10 accordingly. This allows a predetermined flow rate of the aspiration fluid in the aspiration fluid line 10 to be achieved.

[0041] In one embodiment, it is provided that if a leak L occurs, the flow rate of the irrigation fluid 3 is initially increased up to a predetermined maximum value for the irrigation fluid 3. If the leak L becomes larger than this, the flow rate of the aspiration fluid is then reduced accordingly.

[0042] Below the specified maximum value for the irrigation fluid 3, the following operating mode is initially provided: If the difference between the first and second volume flow rates is zero, the differential pressure signal 19 is also zero, and the first fluid pump 5 does not experience any additional change in its control signal beyond the change caused by the irrigation fluid setpoint pressure signal 21. However, if the differential flow rate signal 16, which corresponds to the differential flow rate DQ, is not zero and is usually greater than zero, the first fluid pump 5 experiences an additional change in its control signal due to signal 22, thus altering the pressure of the irrigation fluid 3 in the irrigation fluid line 4. This counteracts the unwanted outflow of fluid from the eye 9 through a leak L.

[0043] Above the specified maximum value for the flow rate of the irrigation fluid 3, the following operating mode is provided: If the difference between the first and second volumetric flow rates is zero, the signal 34 for the differential pressure is also zero, and the second fluid pump 11 does not experience any additional change in its control. However, if the signal 16 is not zero and is usually greater than zero, the second fluid pump 11 experiences an additional change in its control due to the signal 29 for a pneumatic drive pressure, thus changing the pressure of the aspiration fluid in the aspiration fluid line 10. This also counteracts the unwanted drop in intraocular pressure caused by fluid leaking from the eye 9 through a leak L by reducing the flow rate of the aspiration fluid.

[0044] The ophthalmic surgical device 1 additionally features a first timer 23, which is configured to define the target irrigation fluid pressure over time. The first timer 23 is coupled to a second input 172 of the processing unit 17, whereupon the signal 21 for the target irrigation fluid pressure is supplied to the adding element 20. The first timer 23 is coupled to a foot pedal 24, which receives a control signal for the target irrigation fluid pressure when actuated by a surgeon.

[0045] The foot pedal 24 is additionally coupled to a second timer 25, to which a control signal for a target aspiration fluid pressure can be supplied when the corresponding foot pedal 24 is actuated. The second timer 25 is configured to define the profile of the target aspiration fluid pressure as a function of time. The second timer 25 is coupled to a second input 312 of the further processing unit 31, whereupon the signal 35 for the target aspiration fluid pressure is supplied to the adding element 33. With the timers 23 and 25, a time profile of the respective target pressure can be provided.

[0046] Fig. 2 shows several schematic diagrams of volume flow curves and pressure curves as a function of time for the operating mode above the specified maximum value for the irrigation fluid 3.

[0047] Diagram 100 shows the time course of an irrigation fluid flow rate Q(IRR). Up to time t1, no irrigation fluid flows through irrigation fluid line 4 (see 101 in Diagram 100). This also applies to the aspiration fluid in aspiration fluid line 10 (see 201 in Diagram 200), which shows the time course of the aspiration fluid flow rate Q(ASP). Up to time t1, a steady pressure p1 prevails in irrigation fluid line 4 (see 401 in Diagram 400), which shows the time course of the irrigation fluid pressure p(IRR). In aspiration fluid line 10, the aspiration pressure is zero until time t1, see 601 in diagram 600, which shows the aspiration fluid pressure p(ASP) as a function of time. The intraocular pressure p(IOP) as a function of time is shown in diagram 500.This shows that up to time t1 the intraocular pressure is greater than zero, which corresponds to the normal state of the eye.

[0048] It is assumed that at time t1 the foot pedal is pressed, causing the first fluid pump 5 and the second fluid pump 11 to each pump fluid. The irrigation fluid flow rate increases (see 102) and reaches a steady-state value (see 103 in Diagram 100). Simultaneously, the aspiration fluid flow rate also increases (see 202) and likewise reaches a steady-state value (see 203 in Diagram 200). Since irrigation fluid 4 flows in the irrigation fluid line and aspiration fluid in the aspiration fluid line 10, a corresponding fluid pressure builds up in these lines. The irrigation fluid pressure p(IRR) increases, see 402, and reaches a steady-state value, see 403 in Diagram 400. Similarly, the aspiration fluid pressure increases, see 602, and reaches a steady-state value, see 603 in Diagram 600.If the first time constant T1 for the increase in irrigation fluid pressure and the second time constant T2 for the increase in aspiration fluid pressure differ by no more than 200 ms, there will be only a slight or no decrease in intraocular pressure, see 502 in Diagram 500.

[0049] If a loss of irrigation fluid occurs due to a leak L at the eye, the control unit 26 activates the second pump 11 such that the aspiration fluid pressure in the aspiration fluid line 10 between the second pump 11 and the hollow needle 7 increases, causing the second pump 11 to provide a larger, i.e., less negative or, in terms of magnitude, smaller, aspiration fluid volume flow rate (see 204). Thus, a smaller amount of aspiration fluid is aspirated. The irrigation fluid volume flow rate remains unaffected and constant (see 104). The ophthalmic surgical device 1 according to the invention determines a difference between the irrigation fluid volume flow rate and the aspiration fluid volume flow rate, which is greater than zero (see 304 in diagram 300), which represents a differential volume flow rate DQ as a function of time.The adding element 33 receives a signal 35 for the aspiration fluid setpoint pressure and a signal 34 for the differential pressure, so that a correspondingly increased, i.e., lower, aspiration fluid control pressure acts on the second fluid pump 11 (see 604) to aspirate the smaller quantity of aspiration fluid. Thus, while irrigation fluid leaks from a leak L at the eye 9, a higher aspiration fluid pressure prevails in the aspiration fluid line 10. As a result, the intraocular pressure remains unchanged during this time (see 504).

[0050] If the leakage rate L decreases again, for example due to a change in the position of the hollow needle 7, and thus the unwanted outflow of irrigation fluid from the eye also decreases, the second fluid pump 11 can maintain the usual irrigation fluid pressure with a lower, that is, a larger, volume flow rate (see 205). Therefore, more aspiration fluid may be drained than with pump 204. Thus, the differential volume flow rate is reduced (see 305). The aspiration fluid pressure then returns to the target pressure (see 605), which corresponds to the pressure according to 603. The intraocular pressure remains unchanged (see 505). The pressure in the irrigation fluid line 4 is unaffected (see 405).

[0051] The fluctuation in aspiration fluid volume flow can also be relatively high, see 206, resulting in a higher value for the differential volume flow DQ, see 306. This leads to a greater change in aspiration fluid pressure, see 606, so that the intraocular pressure may remain unchanged, see 506.

[0052] When the foot pedal is no longer pressed, the first fluid pump 5 and the second fluid pump 11 are no longer activated, so that the irrigation flow rate and the aspiration flow rate settle at zero, see 107 and 207. Then the pressure in the irrigation fluid line 4 and a certain amount of the pressure in the aspiration fluid line 10 also decrease, see 407 and 607.

[0053] The exemplary embodiments serve solely to illustrate the invention and are not intended to limit it.

[0054] Reference symbol list

[0055] 1 ophthalmic surgical unit

[0056] 2 irrigation fluid containers

[0057] 3 Irrigation fluid

[0058] Irrigation fluid line

[0059] 5 first fluid pump ophthalmic surgical handpiece

[0060] 7 Hollow needle

[0061] cornea

[0062] Eye

[0063] 10 Aspiration fluid line

[0064] 11 second fluid pump

[0065] 12 collection containers, first flow sensor

[0066] 14 second flow sensor

[0067] 15 Difference element

[0068] 16 Signal for the differential volume flow

[0069] 17 processing units

[0070] 18 Multiplication element

[0071] Differential pressure signal

[0072] 20 Adder element

[0073] 21 Signal for the irrigation fluid setpoint pressure

[0074] 22 Signal for pneumatic drive pressure

[0075] 23 first time element

[0076] 24 Foot pedal second time element

[0077] 26 Control unit

[0078] 27 first flow signal

[0079] 28 second flow signal

[0080] 29 Signal for pneumatic drive pressure

[0081] 30 Opening

[0082] 31 Processing unit 32 Multiplication element

[0083] 33 Adder element

[0084] 34 Signal for differential pressure

[0085] 35 Signal for the aspiration fluid setpoint pressure

[0086] 171 first input of the further processing unit

[0087] 172 second entrance of the further

[0088] Processing unit

[0089] 311 First input of the processing unit

[0090] 312 Second input of the processing unit DQ Differential volume flow L Leak

[0091] P print

[0092] P(ASP) Aspiration fluid pressure p(IRR) Irrigation fluid pressure p(IOP) Intraocular pressure

[0093] Q1 first volume flow

[0094] Q2 second volume flow

[0095] Q(ASP) Aspiration fluid volume flow rate Q(IRR) Irrigation fluid volume flow rate t Time

[0096] time constant

Claims

Patent claims 1. Ophthalmic surgical unit (1) with: - an irrigation fluid line (4) which has a first line end for fluid coupling of an irrigation fluid source (2) and a second end for fluid coupling of a handpiece (6), - an aspiration fluid line (10) which has a first line end for flow coupling of an aspiration fluid sink (12) and a second end for flow coupling of the handpiece (6), - at least one first fluid pump (5) which is fluidically connected to the irrigation fluid line (4) and which is designed to pump the irrigation fluid through the irrigation fluid line (4) to the handpiece (6), - at least a second fluid pump (11) which is fluidically connected to the aspiration fluid line (10) and which is designed to pump the aspiration fluid from the handpiece (6) through the aspiration fluid line (10), - a first flow sensor (13) coupled to the irrigation fluid line (4) for detecting a flow of the irrigation fluid in the irrigation fluid line (4), which provides a first flow signal (27) depending on the detected flow, - a second flow sensor (14) coupled to the aspiration fluid line (10) for detecting a flow of the aspiration fluid in the aspiration fluid line (10), which provides a second flow signal (28) depending on the detected flow, - a control unit (26) coupled with the flow sensors (13, 14) and the fluid pumps (5, 11), which is configured to provide at least a first control signal (22) for the first fluid pump (5) and a second control signal (29) for the second fluid pump (11), characterized in that the control unit (26) is configured to compare the first flow signal (27) with the second flow signal (28) and to provide at least the second control signal (29) at least temporarily depending on the comparison.

2. Ophthalmic surgical device according to claim 1, characterized in that the control unit (26) is configured to additionally provide the first control signal (22) depending on the comparison.

3. Ophthalmic surgical device according to one of the preceding claims, characterized by a setpoint unit (23, 25) which is configured to specify at least one flow setpoint for the irrigation fluid or a flow setpoint for the aspiration fluid.

4. Ophthalmic surgical device according to one of the preceding claims, characterized in that the control unit (26) is configured to provide the second control signal (29) only when a difference between the first and second flow signal (27, 28) determined by means of the comparison is present for longer than a predefinable change period.

5. Ophthalmic surgical device according to claim 4, characterized in that the change period is shorter than 4.5 ms, in particular shorter than 3.5 ms.

6. Ophthalmic surgical device according to one of the preceding claims, characterized in that the control unit (26) is configured to provide the second control signal (29) only when the difference between the first and second flow signal (27, 28) determined by means of the comparison is greater than a flow comparison value.

7. Ophthalmic surgical device according to one of the preceding claims, characterized in that the control unit (26) is configured to provide the second control signal (29) such that the flow of the aspiration fluid in the aspiration fluid line (10) is greater than a predefinable minimum flow of the aspiration fluid.

8. Ophthalmic surgical device according to one of the preceding claims, characterized in that the at least one first fluid pump (5) and the at least one second fluid pump (11) are designed as diaphragm pumps, wherein the diaphragm pumps serve as flow sensors (13, 14).

9. Ophthalmic surgical device according to one of the preceding claims, characterized by at least one pressure sensor by means of which at least one irrigation pressure in the irrigation fluid line or one aspiration pressure in the aspiration fluid line can be detected.

10. Method for operating an ophthalmic surgical device (1) comprising an irrigation fluid line (4) having a first line end for fluid coupling of an irrigation fluid source (2) and a second end for fluid coupling of a handpiece (6), and an aspiration fluid line (10) having a first line end for fluid coupling of an aspiration fluid sink (12) and a second end for fluid coupling of the handpiece (6), wherein at least one first fluid pump (5), fluidly connected to the irrigation fluid line (4), pumps the irrigation fluid through the irrigation fluid line (4) to the handpiece, and wherein at least one second fluid pump (11), fluidly connected to the aspiration fluid line (10), pumps the aspiration fluid from the handpiece (6) through the aspiration fluid line (10).wherein a flow of the irrigation fluid in the irrigation fluid line (4) is detected by means of a first flow sensor (13) coupled to the irrigation fluid line (4), which provides a first flow signal (27) depending on the detected flow, wherein a flow of the aspiration fluid in the aspiration fluid line (10) is detected by means of a second flow sensor (14) coupled to the aspiration fluid line (10), which provides a second flow signal (28) depending on the detected flow, wherein a control unit (26) coupled to the flow sensors (13, 14) and the fluid pumps (5, 11) provides at least a first control signal (22) for the first fluid pump (5) and a second control signal (29) for the second fluid pump (11), characterized in that the control unit (26) compares the first flow signal (27) with the second flow signal (28) and provides at least the second control signal (29) at least temporarily depending on the comparison.

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