An actuator unit, a method and a computer program product

Abstract

An actuator unit, a method and a computer program product The invention relates to an actuator unit for operating an ophthalmic surgical phacoemulsification device. The actuator unit comprises a stack of driving piezo elements for driving a tip of the ophthalmic surgical phacoemulsification device. Further, the device comprises a driver circuit arranged for generating a driver signal for actuating the stack of piezo elements. In addition, the device comprises a probing circuit arranged for generating a probing signal for ultrasonically probing an environment of the tip. Furthermore, the device comprises a sensing circuit arranged for receiving a sensing signal resulting from probing the tip environment. The invention also relates to a computer program product.

Description

[0001] P138173NL00

[0002] Title: An actuator unit, a method and a computer program product

[0003] The invention relates to an actuator unit for operating an ophthalmic surgical phacoemulsification device.

[0004] Phacoemulsification is known as a process for disintegration of the lens of an eye utilizing an ophthalmic surgical phacoemulsification device vibrating at ultrasonic frequencies. Such phacoemulsification device includes a driver unit containing a piezoelectric module for actuating, via a sonotrode, a needle having a cutting tip which is vibrated at ultrasonic frequencies to disintegrate cataractic tissue in the eye.

[0005] Known phacoemulsification devices comprise a handpiece with a vibrating needle tip wherein the vibration of the needle tip is manually operated by a surgeon. Such known phacoemulsification devices are frequently operated by foot pedals. Manual operation and activation of the vibrating needle tip poses multiple risks in the field of phacoemulsification.

[0006] A first issue is the repulsion of a lens fragment in case a surgeon inadvertently activates the ultrasonic energy prior to making sufficient contact with a lens fragment. Then, the lens fragment is rapidly repelled away from the surgeon’s needle tip and away from the influence of the fluidics system’s aspiration flow, negatively impacting the surgeon’s workflow and therefore increasing the duration of the intervention.

[0007] Secondly, there is a risk of a particular iatrogenic injury whereby the surgeon can cause a posterior capsular break (a rupture of the posterior aspect of the anterior chamber), known to be one of the most severe surgical complications in cataract interventions. The possibility for this complication to occur is facilitated by the fact that phacoemulsification in known devices can be unintentionally activated against the posterior capsule layers, most frequently during the initial surgical steps of phaco lens chopping. Another major mechanism for said complication is a post-occlusion surge of aspiration pressure caused by a lens fragment.

[0008] It is an object of the present invention to provide an actuator unit for operating an ophthalmic surgical phacoemulsification device having a reduced risk of complications related to the repulsion of lens fragments and / or iatrogenic injury, more specifically a posterior capsular break.

[0009] Thereto, according to the invention, an actuator unit for operating an ophthalmic surgical phacoemulsification device is provided, comprising a stack of driving piezo elements for driving a tip of the ophthalmic surgical phacoemulsification device, a driver circuit arranged for generating a driver signal for actuating the stack of piezo elements, a probing circuit arranged for generating a probing signal for ultrasonically probing an environment of the tip and a sensing circuit arranged for receiving a sensing signal resulting from probing the tip environment.

[0010] The invention is at least partly based on the insight that complications occurring due to activation of phacoemulsification while the needle tip of the ophthalmic surgical phacoemulsification device is not in contact with a surface it is intended to be in contact with can be mitigated by activating phacoemulsification only when the needle tip is in contact with a surface it is supposed to be in contact with and by deactivating phacoemulsification when the needle tip is in contact with a surface it is not supposed to be in contact with.

[0011] By providing a design capable of detecting whether the needle tip of the ophthalmic surgical phacoemulsification device is in contact with a surface it is supposed to be in contact with, more specifically, ocular tissue, it is possible to activate or deactivate phacoemulsification based on the type of surface the needle tip is in contact with. Advantageously, the design is further adapted to distinguish and / or classify properties of the surface the needle tip is in contact with. A device comprising said detection capability allows for activation of phacoemulsification only in cases when the risk for complications is minimized, i.e. when the needle tip is in contact with a surface it is supposed to be in contact with. In addition, such device allows for deactivation of phacoemulsification if the operator encounters a situation posing a high risk for complications. The detection capability may be implemented as a safety system complementary to the manual operation system to be controlled by a surgeon.

[0012] The actuator unit may comprise a probing piezo element connected to the probing circuit for converting the probing signal into an ultrasonic interrogation signal, wherein the probing piezo element is further connected to the sensing circuit for generating a sensing signal from an ultrasonic response signal resulting from an interaction of the ultrasonic interrogation signal with the tip environment. The probing piezo element may further be placed in series with the stack of driving piezo elements. Then, a bespoke piezo for probing purposes is selected, having different intrinsic ceramic characteristics compared to the driving piezo elements, wherein said probing piezo characteristics are specifically geared towards a higher signal to noise ratio for sensing purposes.

[0013] Alternatively, the driving piezo elements are arranged for generating both the driving signal and the probing signal, and for receiving a sensing signal.

[0014] In an advantageous embodiment, the actuator unit comprises a superposition module for superimposing the driver signal of the driver circuit to the probing signal of the probing circuit for feeding the driving piezo elements. The driving piezo elements may further be arranged for converting the probing signal portion from the superimposed signal into an ultrasonic interrogation signal, and the driving piezo elements are connected to the sensing circuit for generating a sensing signal from the ultrasonic response signal resulting from an interaction of the ultrasonic interrogation signal with the tip environment from an interaction of an ultrasonic interrogation signal generated by the driving piezo elements with the tip environment. In this way, a stack of driving piezo elements, preferably all having identical intrinsic ceramic characteristics, is arranged to generate a mechanical displacement with an actuation function and a sensing function simultaneously, without the need for the stack to comprise dedicated probing piezo elements.

[0015] In a specific embodiment, the driver signal has a driver frequency, and the probing signal has a probing frequency that is larger than the driver frequency. The probing frequency may be higher than 40 kHz, preferably circa 60 kHz, circa 80 kHz, circa 100 kHz or circa 120 kHz, or higher than 120 kHz. Furthermore, the probing frequency may be centered around an odd harmonic or around multiple harmonics of the driver frequency. Additionally, the probing signal has a frequency spectrum, preferably a chirp spectrum. Then, analysis of the frequency domain of the sensing circuit output signal yields information which is influenced by the surface that is in contact with the needle tip, said influence may be analyzed to characterize the surface which is in contact with the needle tip.

[0016] Advantageously, the sensing circuit may be arranged for classifying the received sensing signal, based on a spectral behaviour of the sensing signal induced by any load in the tip environment. Additionally, the sensing circuit may be arranged for classifying a sensing signals as a first class of signals associated with tissue free tip environment, as a second class of signals associated with a lens fragment adjacent to the tip, and / or as a third class of signals associated with connective tissue adjacent to the tip. In this way, a specific profile observed in the frequency domain analysis of the sensing circuit output signal is mapped to characteristics of the surface that is in contact with the needle tip.

[0017] Optionally, the sensing circuit may be arranged for generating an auto-fire signal if an actual sensing signal is classified as a second class of signals. The sensing circuit may further be arranged for generating a safestop signal if an actual sensing signal is classified as a third class of signals. Then, the risk of complications is reduced significantly in case a surgeon encounters a situation wherein the needle tip is in contact with a surface it is not supposed to be in contact with, without the surgeon’s manual intervention to appropriately deactivate phacoemulsification depending on the situation. The risk of complications is further reduced by only allowing activation of phacoemulsification in case the needle tip is in contact with a surface it is supposed to be in contact with.

[0018] In addition, the invention relates to a method.

[0019] Further, the invention relates to a computer program product for operating an ophthalmic surgical phacoemulsification device with an actuator unit according to the invention. A computer program product may comprise a set of computer executable instructions stored on a data carrier, such as but not limited to a flash memory, a CD or a DVD. The set of computer executable instructions, which allow a programmable computer to carry out the method as defined above, may also be available for downloading from a remote server, for example via the Internet.

[0020] The computer program product comprises computer readable code for causing a circuit to perform at least one step of the method according to the invention.

[0021] It should be noted that the technical features described above or below may each on its own be embodied in a system or method, i.e. isolated from the context in which it is described, separate from other features, or in combination with only a number of the other features described in the context in which it is disclosed. Each of these features may further be combined with any other feature disclosed, in any combination.

[0022] The invention will be further elucidated on the basis of exemplary embodiments which are represented in the drawings. The exemplary embodiments are given by way of non-limitative illustration of the invention. In the drawings:

[0023] Fig. 1 shows a schematic cross-sectional view of a first embodiment of an ophthalmic surgical phacoemulsification device arranged to be operated by an actuator unit according to the invention;

[0024] Fig. 2 shows a schematic cross-sectional view of a second embodiment of an ophthalmic surgical phacoemulsification device arranged to be operated by an actuator unit according to the invention;

[0025] Fig. 3 shows a block diagram of a first embodiment of the actuator unit 19 for operating an ophthalmic surgical phacoemulsification device shown in Fig. 1;

[0026] Fig. 4 shows a block diagram of a second embodiment of the actuator unit for operating an ophthalmic surgical phacoemulsification device shown in Fig. 2;

[0027] Fig. 5a and Fig. 5b show a spectral output of the driver circuit and the sensing circuit, respectively, of the ophthalmic surgical phacoemulsification device shown in Fig. 1 and Fig. 2;

[0028] Fig. 6a, Fig. 6b and Fig. 6c show a spectral output of the sensing circuit of the ophthalmic surgical phacoemulsification device shown in Fig. 1 or Fig. 2 subjected to interference by varying system loads;

[0029] Fig. 7 shows a flow chart of a method for operating the ophthalmic surgical phacoemulsification device shown in Fig. 1 or Fig. 2;

[0030] Fig. 8 shows a partial flow chart of a first specific embodiment of the method shown in Fig. 7;

[0031] Fig. 9 shows a partial flow chart of a second specific embodiment of the method shown in Fig. 7, and

[0032] Fig. 10 shows a partial flow chart of a third specific embodiment of the method shown in Fig. 7.

[0033] In the figures identical or corresponding parts are represented with the same reference numerals. The drawings are only schematic representations of embodiments of the invention, which are given by manner of non-limited examples.

[0034] Fig. 1 shows a schematic cross-sectional view of a first embodiment of an ophthalmic surgical phacoemulsification device 1 arranged to be operated by an actuator unit according to the invention. The ophthalmic surgical phacoemulsification device 1 is used in modern-day cataract surgery that employs ultrasound energy for emulsifying the internal lens of the eye.

[0035] The ophthalmic surgical phacoemulsification device 1 is formed as a unit including an elongate housing 2 extending along a longitudinal axis A, forming a handpiece. The elongate housing 2 has a distal end 3 and a proximal end 4. Further, the ophthalmic surgical phacoemulsification device 1 includes a tip 5 mounted to the distal end 3 of the elongate house 2 and aligned with the longitudinal axis A. As shown in Fig. 1, the ophthalmic surgical phacoemulsification device 1 has a sonotrode 6 having a distal end 6a and a proximal end 6b, arranged for actuating the tip 5 and accommodated in the elongate housing 2. In operation, a stack of driving piezo elements 12, also accommodated in the elongate housing 2, is used for driving the tip 5 of the ophthalmic surgical phacoemulsification device 1. In addition, the ophthalmic surgical phacoemulsification device 1 is provided with a probing piezo element 15 for converting a probing signal into an ultrasonic interrogation signal. In the shown embodiment, the probing piezo element 15 is placed in series with the stack of driving piezo elements 12, in particular, at a distal end of the stack of driving piezo element 12. In other embodiments, the probing piezo element 15 is located elsewhere, e.g. at a proximal end of the stack of driving piezo elements 12.

[0036] The elongate housing 2 has an interior 8 accommodating the sonotrode 6. The interior 8 has a distal end 8a where the sonotrode 6 is placed such that the distal end 6a of the sonotrode 6 is positioned so as to actuate the tip 5. Further, the elongate housing interior 8 is provided with an elongate cavity 9, proximal to the sonotrode 6.

[0037] Generally, the sonotrode 6 and the cavity 9 may be provided in series, and aligned with the longitudinal axis A. The probing piezo element 15 may be placed in series with the stack of driving piezo elements 12. In other embodiment, different configurations may be considered.

[0038] Further, generally, the tip 5 and the sonotrode 6 are located such that ultrasound vibrations are transferred from the sonotrode 6 to the tip 5, e.g. by contacting each other.

[0039] In addition, the driver signal has a driver frequency and the probing signal has a probing frequency that is larger than the driver frequency. The probing frequency is preferably higher than 40 kHz, more preferably circa 60 kHz, circa 80 kHz, circa 100 kHz or circa 120 kHz, or higher than 120 kHz. The probing frequency is centered around an odd harmonic or around multiple harmonics of the driver frequency. In addition, the probing signal has a frequency spectrum, preferably a chirp spectrum. In other embodiments, different frequency configurations may be considered.

[0040] Fig. 2 shows a schematic cross-sectional view of a second embodiment of an ophthalmic surgical phacoemulsification device 1 arranged to be operated by an actuator unit according to the invention. The second embodiment shown in Fig. 2 is similar to the first embodiment of the ophthalmic surgical phacoemulsification device 1 shown in Fig. 1, however having another setup of piezo elements. In contrast to the stack of dedicated driving piezo elements 12 combined with the dedicated probing piezo element 15 of the ophthalmic surgical phacoemulsification device 1 shown in Fig. 1, the second embodiment of the device shown in Fig. 2 has a stack of driving piezo elements 12, all of which are arranged for performing an actuation function and a sensing function. In this way, the stack of driving piezo elements 12 is arranged to additionally provide the effect of the probing piezo element 15 of Fig. 1.

[0041] Further, the ophthalmic surgical phacoemulsification device 1 as shown in Fig. 2 comprises a superposition module for superimposing a driver signal to a probing signal for feeding the driving piezo elements 12.

[0042] Furthermore, in the second embodiment shown in Fig. 2, the driving piezo elements 12 are arranged for converting the probing signal portion from the superimposed signal into an ultrasonic interrogation signal. The driving piezo elements 12 are further connected to a sensing circuit, described below, for generating a sensing signal from the ultrasonic response signal resulting from an interaction of the ultrasonic interrogation signal with the tip 5 environment from an interaction of an ultrasonic interrogation signal generated by the driving piezo elements 12 with the tip 5 environment.

[0043] Generally, the actuator unit comprises a stack of driving piezo elements for driving a tip of the ophthalmic surgical phacoemulsification device. Further, the actuator unit comprises a driver circuit 11, a probing circuit 14 and a sensing circuit 17.

[0044] The driver circuit 11 is arranged for generating a driver signal for actuating the stack of driving piezo elements 12. The probing circuit 14 is arranged for generating a probing signal for ultrasonically probing an environment of the tip 5. Further, the sensing circuit 17 is arranged for receiving a sensing signal resulting from probing the tip environment.

[0045] Fig. 3 shows a block diagram of a first embodiment of the actuator unit 19 for operating an ophthalmic surgical phacoemulsification device 1 shown in Fig. 1. A controller 10 is provided which is connected to the driver circuit 11. The driver circuit 11 is arranged for generating a driver signal for actuating the stack of driving piezo elements 12. The tip 5 of the ophthalmic surgical phacoemulsification device 1, which is connected to the stack of driving piezo elements 12, is arranged to be driven by said stack of driving piezo elements 12. The stack of driving piezo elements 12 is further connected to a measurement circuit 13.

[0046] The controller 10 is further connected to the probing circuit 14 which is arranged for generating a probing signal for ultrasonically probing an environment of the tip 5. The probing circuit 14 is connected to the probing piezo element 15 for converting a probing signal into an ultrasonic interrogation signal. The probing piezo element 15 is further connected to the sensing circuit 17 for generating a sensing signal from an ultrasonic response signal resulting from an interaction of the ultrasonic interrogation signal with the environment of the tip 5. In the shown embodiment, the sensing circuit 17 comprises a low noise measurement circuit arranged to detect a resulting measured electrical signal, which may be subject to interferences such as noise signals.

[0047] Fig. 4 shows a block diagram of a second embodiment of the actuator unit 19 for operating an ophthalmic surgical phacoemulsification device shown in Fig. 2. A controller 10 is provided which is connected to the driver circuit 11. In addition, the probing circuit 14 is connected to the controller 10. The driver circuit 11 as well as the probing circuit 14 are connected to a superposition module 18 for superimposing a driver signal to a probing signal for feeding the stack of piezo elements 12 arranged to generate a mechanical displacement with an actuation function as well as a sensing function, simultaneously. Therefore, the stack of piezo elements 12 shown in Fig. 2 is also referred to as the stack of driving and probing piezo elements 12. In the shown embodiment, the driver circuit 11 is arranged for generating a driver signal for actuating the stack of piezo elements 12, whereas the probing circuit 14 is arranged for generating a probing signal for ultrasonically probing an environment of the tip 5. The stack of piezo elements 12 is arranged to convert a probing signal into an ultrasonic interrogation signal. The tip 5 of the ophthalmic surgical phacoemulsification device 1 which is connected to the stack of piezo elements 12 is arranged to be driven by said stack of piezo elements 12.

[0048] The superposition module 18 and the stack of piezo elements 12 are further connected to a measurement circuit 13. In addition, the stack of piezo elements 12 is connected to the sensing circuit 17. Then, the measurement circuit 13 as well as the sensing circuit 17 are arranged to measure an identical output of the stack of piezo elements 12, e.g. at an identical potential. The sensing circuit 17 is arranged to generate a sensing signal from an ultrasonic response signal resulting from an interaction of the ultrasonic interrogation signal with the environment of the tip 5. The sensing circuit 17 comprises a low noise measurement circuit 16 arranged to detect a resulting measured electrical signal, which may be subject to interferences.

[0049] Figures 5a-b show a spectral output, also referred to as a graphical representation of the frequency domain of the output of the driver circuit 11 and the sensing circuit 17, respectively, of the ophthalmic surgical phacoemulsification device 1 shown in Fig. 1 and Fig. 2. In the shown embodiment, the sensing circuit 17 is provided with a low-noise amplifier to filter the noise sidebands created by a frequency-shift keying modulated pseudo-chirp. By filtering the noise sidebands created by a frequency-shift keying modulated pseudo-chirp, information indicative of a specific material present at the tip 5 is obtained, as the interference caused by different system loads influences said noise sidebands.

[0050] In Fig. 5a, a magnitude 35 of the spectral output of the driver circuit 11 is shown as a function of frequency 36. The first seven harmonics of the output signal of the driver circuit 11 are shown. More specifically, a first harmonic 40, a harmonic 41, a third harmonic 42, a fourth harmonic 43, a fifth harmonic 44, a sixth harmonic 45 and a seventh harmonic 46 of the output signal of the driver circuit 11 are shown. In addition, a spectral bandpass filter 39 filtering out everything except the first harmonic 40 is shown.

[0051] In Fig. 5b, a magnitude 37 of the spectral output of the sensing circuit 17 is shown as a function of frequency 38 . Here, spectral output of the sensing circuit 17 includes spectral sideband signals 48, 49, 50, 51, 53, 54, 55 and 56 induced by a probing signal 52 having a frequency spectrum or spectral behaviour, also shown, generated as a frequency-shift keying modulated pseudo-chirp signal. Further, the spectral output of the sensing circuit 17 includes a response of the first harmonic 57 of the output signal of the driving circuit 12 . It is noted that the probing signal 52 is centered at the third harmonic 42 of the driver signal of the driving circuit 11. In addition, a spectral high pass filter 47 filtering out the first harmonic 57 is shown.

[0052] A frequency-shift keying modulated pseudo-chirp signal is a wideband electrical signal exploiting a spectral Ventage’ that occurs if we deploy the probing signal as a chirp. The theoretical bandwidth of a chirp can be defined in frequency domain as f(t) =fo + Kt. In practice this means that for an up-chirp we will sweep from an initial frequency ( fo ) up to an end frequency (fo + KT), where K corresponds to the rate of change of frequency (speed) of the chirp and T corresponds to the time duration of the chirp. The theoretical bandwidth of such a chirp would be just Af =KT. However, depending on the speed K and duration T, a chirp will actually create a very large ‘tail’ of sideband noise, this noise is normally undesirable in electrical design, however in the present application serving a purpose a purpose of retrieving rich information of the characteristics of the load.

[0053] It appears that a step change in frequency, effectively an FSK modulation with a chirp-like bandwidth, enables maximum power delivery of the noise sidebands 48-51, 53-56.

[0054] Generally, the frequency of the probing signal is higher than circa 40 kHz, preferably circa 60 kHz, circa 80 kHz, circa 100 kHz or circa 120 kHz, or higher than 120 kHz. As an example, the frequency of the probing signal is centered around an odd harmonic or around multiple harmonics of the driver frequency, such as around the third harmonic, shown in Fig. 5b, or around the fifth harmonic.

[0055] The sensing circuit 17 is arranged for classifying the received sensing signal, based on a spectral behaviour of the sensing signal induced by any load in the tip 5 environment. In the shown example, the sensing circuit 17 is arranged for classifying a sensing signals as a first class of signals associated with tissue free tip environment, as a second class of signals associated with a lens fragment adjacent to the tip, such as a hard lens, and / or as a third class of signals associated with connective tissue adjacent to the tip.

[0056] It is noted that the sensing circuit 17 may be arranged to classify the sensing signals into the three classes mentioned above, or into a subset of the three classes, e.g. two classes or one class only. As an example, the sensing circuit 17 may be arranged to identify a sensing signal to belong to either the first class, or the second class or the third class. As another example, the sensing circuit 17 may be arranged to identify a sensing signal to belong to either the first class or the second class, or to belong to either the second class of the third class. As yet another example, the sensing circuit 17 may be arranged to identify a sensing signal to belong to the first class. Further, the sensing circuit 17 may be arranged to classify the sensing signals in even more than three classes, e.g. four or five classes.

[0057] Furthermore, the sensing circuit 17 is arranged for generating an auto-fire signal if an actual sensing signal is classified as a second class of signals and / or for generating a safe-stop signal if an actual sensing signal is classified as a third class of signals.

[0058] Figures 6a-c show a spectral output of the sensing circuit 17 of the ophthalmic surgical phacoemulsification device 1 shown in Fig. 1 and Fig. 2 subjected to interference by different system loads. Each of the frequency domain representations corresponds to a situation wherein a specific material is in touching or near or contact with the tip 5 of the device 1.

[0059] Knowledge of how a specific material present near the tip 5 may influence the spectral behaviour of the received sensing signal received by the sensing circuit 17 of the ophthalmic surgical phacoemulsification device 1 allows to construct a database with classifier profiles 58a-c. Each classifier profile 58a-c may correspond with a specific frequency domain profile, from which the material present at the tip 5 can be deduced. Mapping 61 a measured spectral behaviour to a specific material present at the tip 5 by using said database of classifier profiles 58a-c may be performed by means of artificial intelligence, preferably by means of machine learning, more preferably by means of analysis using a support vector machine 59 specifically trained on said classifier profiles 58a-c or other hardware component arranged for classifying such as a processing unit or rule based machine. In Fig. 6a-c, it is shown that the spectral responses 58 are fed 62 into the support vector machine 59 for comparison and classification, resulting in an output 61 reflecting a classification.

[0060] Fig. 6a represents the spectral output of the sensing circuit 17 of the ophthalmic surgical phacoemulsification device 1 in case the tip 5 does not make contact with any kind of material. In this case, a first classifier profile 58a resembles an upside-down V shape. Furthermore, Fig. 6b shows the spectral output of sensing circuit 17 of the ophthalmic surgical phacoemulsification device 1 in case the tip 5 is in contact with lens tissue 63. In this case, a second classifier profile 58b resembles an upside-down V shape, wherein the right leg of the upside-down V shape is flattened or higher compared to the right leg of the first classifier profile 58a shown in Fig. 6a. Fig. 6c shows the spectral output of sensing circuit 17 of the device 1 in case the tip 5 is in contact with capsular tissue 64. In this case, the third classifier profile 58c resembles an upside-down V shape, wherein the right leg of the upside-down V shape is lower compared to the right leg of the first classifier profile shown in Fig. 6a.

[0061] Figure 7 shows a flow chart of a method for operating the ophthalmic surgical phacoemulsification device 1 shown in Fig. 1 or Fig. 2. The method 130 comprises a step 31 of providing an actuator unit 19 as described above for operating an ophthalmic surgical phacoemulsification device, a step 32 of generating a driver signal for actuating the stack of piezo elements, a step 33 of generating a probing signal for ultrasonically probing an environment of the tip 5, and a step 34 of receiving a sensing signal resulting from probing the tip 5 environment.

[0062] Fig. 8 shows a partial flow chart of a first specific embodiment of the method shown in Fig. 7. Here, the first specific embodiment of the method 28 is also referred to as auto-fire, and comprises additional steps, including a step 21 of, based on the sensing signal, detect if the sensing signal is indicative of lens tissue being present at the tip 5, i.e. classify the sensing signal as a first class of signals associated with tissue free tip environment. The first specific embodiment of the method 28 further comprises a step 22 checking whether an activation switch is enabled. Said switch may be implemented as a foot pedal to be operated by a surgeon. The first specific embodiment of the method 28 further comprises a step 23 of activating phacoemulsification only if the detection step 21 indicates that lens tissue is present at the tip 5 and if the activation switch is enabled.

[0063] Fig. 9 shows a partial flow chart of a second specific embodiment of the method shown in Fig. 7. Here, the second specific embodiment of the method 29 is also referred to as safe-stop, and further comprises a step 24 of detecting if the tip 5 during use transitions from lens tissue to posterior capsule layers tissue by means of the sensing circuit 17, i.e. classify the sensing signal as a third class of signals associated with connective tissue adjacent to the tip. The second specific embodiment of the method 29 further includes a step 25 of stopping phacoemulsification if the tip 5 during use transitions from lens tissue to posterior capsule layers tissue.

[0064] Fig. 10 shows a partial flow chart of a third specific embodiment of the method shown in Fig. 7. Here, the third specific embodiment of the method 30 is also referred to as occlusion- pre-emption, and comprises a step 26 of detecting if a large fragment of lens is present at the tip 5 by means of sensing circuit 17, i.e. classify the sensing signal as a second class of signals associated with a lens fragment adjacent to the tip. The third specific embodiment of the method 30 further includes a step 27 of stopping phacoemulsification if a large fragment of lens is present at the tip 5.

[0065] The method for operating an ophthalmic surgical phacoemulsification device can also at least partially be performed using a computer program comprising instructions for causing a an actuator unit or a circuit thereof to perform at least one step of the method according to the invention. All (sub)steps can in principle be performed on a single processor. However, it is noted that at least one (sub)step can be performed on a separate processor. A processor can be loaded with a specific software module. The circuit may comprise a driver circuit, a probing circuit and / or a sensing circuit. In further embodiments, there may be a multiple number of circuits, wherein each of the circuits may comprise a driver circuit, a probing circuit and / or a sensing circuit. It is noted that embodiments comprising a multiple number of circuits may be arranged as a distributed system of circuits.

[0066] The invention is not restricted to the embodiments described herein. It will be understood that many variants are possible.

[0067] It is noted that the actuator unit may be provided with a single probing piezo element or a multiple number of probing piezo elements, e.g. arranged in series.

[0068] These and other embodiments will be apparent for the person skilled in the art and are considered to fall within the scope of the invention as defined in the following claims. For the purpose of clarity and a concise description features are described herein as part of the same or separate embodiments. However, it will be appreciated that the scope of the invention may include embodiments having combinations of all or some of the features described.

Claims

Claims1. An actuator unit for operating an ophthalmic surgical phacoemulsification device, comprising:- a stack of driving piezo elements for driving a tip of the ophthalmic surgical phacoemulsification device;- a driver circuit arranged for generating a driver signal for actuating the stack of piezo elements;- a probing circuit arranged for generating a probing signal for ultrasonically probing an environment of the tip, and- a sensing circuit arranged for receiving a sensing signal resulting from probing the tip environment.

2. An actuator unit according to claim 1, comprising a probing piezo element connected to the probing circuit for converting the probing signal into an ultrasonic interrogation signal, wherein the probing piezo element is further connected to the sensing circuit for generating a sensing signal from an ultrasonic response signal resulting from an interaction of the ultrasonic interrogation signal with the tip environment.

3. An actuator unit according to claim 2, wherein the probing piezo element is placed in series with the stack of driving piezo elements.

4. An actuator unit according to claim 1, comprising a superposition module for superimposing the driver signal of the driver circuit to the probing signal of the probing circuit for feeding the driving piezo elements.

5. An actuator unit according to claim 4, wherein the driving piezo elements are arranged for converting the probing signal portion from the superimposed signal into an ultrasonic interrogation signal, and wherein the driving piezo elements are connected to the sensing circuit for generating a sensing signal from the ultrasonic response signal resultingfrom an interaction of the ultrasonic interrogation signal generated by the driving piezo elements with the tip environment.

6. An actuator unit according to any of the preceding claims, wherein the driver signal has a driver frequency, and wherein the probing signal has a probing frequency that is larger than the driver frequency.

7. An actuator unit according to claim 6, wherein the probing frequency is higher than 40 kHz, preferably circa 60 kHz, circa 80 kHz, circa 100 kHz or circa 120 kHz, or higher than 120 kHz.

8. An actuator unit according to claim 6 or 7, wherein the probing frequency is centered around an odd harmonic or around multiple harmonics of the driver frequency.

9. An actuator unit according to any of the preceding claims 6-8, wherein the probing signal has a frequency spectrum, preferably a chirp spectrum.

10. An actuator unit according to any of the preceding claims, wherein the sensing circuit is arranged for classifying the received sensing signal, based on a spectral behaviour of the sensing signal induced by any load in the tip environment.

11. An actuator unit according to claim 10, wherein the sensing circuit is arranged for classifying a sensing signals as a first class of signals associated with tissue free tip environment, as a second class of signals associated with a lens fragment adjacent to the tip, and / or as a third class of signals associated with connective tissue adjacent to the tip.

12. An actuator unit according to claim 11, wherein the sensing circuit is arranged for generating an auto-fire signal if an actual sensing signal is classified as a second class of signals.

13. An actuator unit according to claim 11 or 12, wherein the sensing circuit is arranged for generating a safe-stop signal if an actual sensing signal is classified as a third class of signals.

14. A method for operating an ophthalmic surgical phacoemulsification device, comprising the steps of:- providing an actuator unit according to any of the preceding claims for operating an ophthalmic surgical phacoemulsification device; - generating a driver signal for actuating the stack of piezo elements;- generating a probing signal for ultrasonically probing an environment of the tip; and- receiving a sensing signal resulting from probing the tip environment.

15. A computer program product for operating an ophthalmic surgical phacoemulsification device with an actuator unit according to any of the preceding claims, the computer program product comprising computer readable code for causing the actuator unit to perform the steps of:- generating a driver signal for actuating the stack of piezo elements;- generating a probing signal for ultrasonically probing an environment of the tip; and- receiving a sensing signal resulting from probing the tip environment.

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