Treatment device and method for controlling a fixation device for fixing a human or animal eye

Abstract

Method for controlling a fixation device (14) for fixing a human or animal eye (12) for treatment with a treatment device (10) by means of negative pressure, wherein after activation of the fixation device (14) a negative pressure is built up to a predetermined fixation negative pressure value, wherein a negative pressure build-up rate up to the fixation negative pressure value is limited by a pressure build-up algorithm below a predetermined rate value, wherein the rate value is based on a physiology of the eye (12), wherein the fixation negative pressure value is built up stepwise by the pressure build-up algorithm, wherein at each negative pressure level the negative pressure is kept constant for a predetermined waiting time.

Description

The invention relates to a method for controlling a fixation device for fixing a human or animal eye for treatment with a treatment device using negative pressure, and to a treatment device configured to carry out the method. Furthermore, the invention relates to a computer program comprising commands that cause the treatment device to perform the method steps, and a computer-readable medium on which the computer program is stored. In treatment with devices, particularly those featuring an ophthalmic laser, which can remove corneal tissue to treat refractive errors through ablation and / or photodisruption, suction devices, especially suction rings, are known to fix the eye in a treatment position. A vacuum pump creates a vacuum that holds the eye in this position. To prevent injury to the eye from the negative pressure, it is known to limit the negative pressure to a predetermined threshold, which is approximately 700 hectopascals (hPa). From DE 10 2006 053 098 A1, an ophthalmological device and an ophthalmological method for positioning a patient's eye in a predetermined target position are known.The ophthalmic device comprises a patient support device, an eye treatment device comprising a contact element for spatially fixing the patient's eye relative to the treatment device, and a positioning device for relative displacement of the support device and the contact element to each other in order to position the eye in a predetermined target position relative to the contact element before it is fixed by means of the contact element, wherein the ophthalmic device has a detection device that detects the eye of the patient located on the support device and, based on the detection, determines a relative displacement of the support device to the contact element that is necessary to bring the eye into the target position by means of the positioning device. A safety mechanism for a laser treatment device is known from EP 2 545 890 B1. From EP 1 970 034 B1, an apparatus for coupling an element to the eye is known. From DE 10 2020 208 679 A1, a UV laser-based system for refractive error correction and a contact interface are known. A safety mechanism for a laser treatment device is known from DE 10 2005 001 249 A1. The object of the present invention is to further increase safety in the fixation of the eye. The invention is based on the understanding that damage to the eye can occur not only by exceeding the maximum permissible negative pressure threshold or the fixation negative pressure value, which is approximately 700 hPa, but also if the rate of negative pressure build-up required to reach this value is too high. Therefore, pressure build-up algorithms are provided that control the rate of negative pressure build-up, taking into account the biology and / or physiology of the eye. The invention provides a method for controlling a fixation device for fixing a human or animal eye for treatment with a treatment device using negative pressure, wherein, after activation of the fixation device, a negative pressure is built up to a predetermined fixation negative pressure value, wherein a pressure build-up rate up to the fixation negative pressure value is limited below a predetermined rate value by a pressure build-up algorithm, wherein the rate value is based on the physiology of the eye. In other words, a vacuum can be created by a fixation device, which may include a vacuum pump. This vacuum can be transferred, for example, to a surface of the eye via a suction ring. For fixation of the eye, the maximum vacuum that occurs during a fixation can preferably be limited by a predetermined fixation vacuum value. The rate at which the vacuum builds up until this fixation vacuum value is reached can be limited according to a pressure build-up algorithm, particularly taking into account the physiology of the eye. This means that the rate at which the vacuum builds up is limited to prevent damage to or in the eye from an excessively rapid build-up of the vacuum.A minimum velocity value can be specified below which the vacuum build-up rate should remain. This velocity value can be defined by dividing the fixed vacuum value by the total time required to reach this value. Limiting this velocity value can be determined, in particular, from empirical data and / or simulations, especially using finite element simulation. Preferably, the vacuum build-up rate can be throttled by the pressure build-up algorithm, for example, by controlling a throttle valve, and / or a stepwise, time-controlled monitoring of the vacuum level can be implemented. The rate of vacuum build-up can preferably remain below 340 hectopascals per second at all times until a fixation vacuum value of approximately 700 hectopascals is reached. The procedure can be controlled or monitored, for example, by a control unit of the treatment device, whereby a control unit is understood to be a device or device component that can control the fixation device and / or the treatment device, in particular a laser of the treatment device, by means of control data. The fixation or suction device can be provided as part of the treatment device. Alternatively, the fixation device can be provided separately from the treatment device. The treatment device preferably includes an ophthalmic laser for treating the eye, wherein the ophthalmic laser of the treatment device can preferably create optical breakthroughs in or on the cornea of ​​the eye by means of pulsed laser radiation in order to excise a volume to correct a refractive error. Alternatively or additionally, the method can also be used for lasers that achieve ablation, laser-induced refractive index change (LIRIC), and / or cross-linking. The invention offers the advantage of improving safety when fixing an eye for treatment with a treatment device. Furthermore, according to the invention, the pressure build-up algorithm provides for the fixation vacuum value to be built up in stages. In other words, the vacuum build-up rate can be limited by specifying a plurality of discrete vacuum levels and traversing these during the vacuum build-up until the last vacuum level reaches the fixation vacuum value. That is, the vacuum is increased stepwise. For example, two to five vacuum levels can be provided, which are traversed during the build-up of the fixation vacuum value. In addition, the invention provides that the negative pressure is kept constant for a predetermined waiting period at each negative pressure stage. This means that alternating periods of pressure build-up and subsequent waiting time, during which the negative pressure is kept constant, are provided for cycling through the negative pressure stages. This allows the eye to adapt to the new pressure conditions after the build-up up to each negative pressure stage. This has the advantage of reducing the risk of damage to the eye caused by an excessively rapid negative pressure build-up rate. The invention also includes embodiments that offer additional advantages. One design allows for a shorter waiting time for each subsequent negative pressure level than the waiting time for the preceding negative pressure level. In other words, the waiting time during which the negative pressure is kept constant at each negative pressure level can be shortened with each subsequent negative pressure level. For example, the waiting time can be halved with each subsequent negative pressure level. This is particularly useful because an initial change in the pressure situation at the eye has a more severe impact on physiology than subsequent changes. Furthermore, it is preferably provided that a specific, preferably different, vacuum build-up rate is defined between each vacuum stage. In other words, the vacuum build-up rate can differ between the respective vacuum stages. For example, in addition to a shortened waiting time for each subsequent vacuum stage, the vacuum build-up rate can also be varied between stages, preferably increasing with each subsequent stage. This allows the vacuum build-up to be limited below the specified rate until the fixing vacuum value is reached, while simultaneously accelerating the fixing process. Another embodiment provides that the pressure build-up algorithm limits the vacuum build-up rate to below 320 hectopascals per second (hPa / s), preferably below 225 hectopascals per second (hPa / s). These lower vacuum build-up rates have proven particularly advantageous in preventing eye damage. 320 hectopascals per second corresponds to approximately 240 millimeters of mercury per second, and 225 hectopascals per second to approximately 170 millimeters of mercury per second, the unit millimeters of mercury used by many fixation devices. This embodiment offers the advantage that the vacuum build-up rate can be particularly well adapted to the physiology of the eye. Another embodiment provides for a linear or exponential rate of vacuum build-up. In other words, the vacuum either increases constantly or builds up slowly and accelerates with increasing vacuum. This allows for preferred vacuum build-up rate profiles. A linear and / or exponential profile can also be provided between the aforementioned vacuum stages, with the type of profile potentially changing between these stages. Another embodiment involves dividing the vacuum build-up rate into at least three phases using the pressure build-up algorithm. In the first phase, at the beginning of the activation of the fixing device, and in the third phase, before reaching the fixing vacuum level, the vacuum build-up rate is lower than in the second phase, which occurs between the first and second phases. In other words, the vacuum can be built up slowly and then increased until, shortly before reaching the fixing vacuum level, the vacuum build-up rate is reduced again.This design offers the advantage that the eye can adapt to the changing vacuum conditions, particularly at the start of the vacuum build-up, allowing for a faster pressure increase after this adaptation phase. A slower rate towards the end prevents the vacuum from exceeding the fixation vacuum level due to an excessively rapid vacuum build-up, thus increasing safety. Another embodiment provides that the fixation device has a suction ring or suction ring segments through which the eye is fixed by means of negative pressure. In other words, the fixation device, which generates negative pressure, for example by means of a (vacuum) pump, can transmit the negative pressure to a surface of the eye via the suction ring or suction ring segments. Thus, the eye is held in position at the contact points of the suction ring or the contact points of the suction ring segments. Another design option involves predefining the velocity value depending on whether the fixation device is applied to the cornea or the sclera of the eye. Specifically, the pressure build-up algorithm can take into account the fixation position and thus the maximum permissible velocity for the vacuum build-up rate. In particular, the velocity value, and therefore the vacuum build-up rate, can be higher for the cornea than for the sclera, since the cornea is harder than the sclera and therefore less susceptible to high vacuum build-up rates. A further aspect of the invention relates to a treatment device, in particular with at least one ophthalmic laser for separating a lenticule with predefined interfaces from a human or animal eye by means of cavitation bubbles and / or for a laser-induced change in the refractive index, comprising a fixation device, wherein the treatment device is configured to carry out a method according to one of the preceding embodiments. In other words, the treatment device can comprise at least one ophthalmic laser, in particular with a beam deflection device, and a fixation device, wherein, for example, a control unit of the treatment device can be configured to carry out a method according to one of the preceding embodiments or to control a vacuum build-up according to the pressure build-up algorithm.The control unit or control device can be designed, for example, as a control chip, control unit, or application program ("app"). The control device can preferably include a processor and / or a data storage device. A processor is understood to be a device or device component for electronic data processing. The processor can, for example, include at least one microcontroller and / or at least one microprocessor. The optional data storage device can preferably contain program code for executing the method. The program code can be designed, when executed by a processor, to cause the control device to perform one of the described configurations of the method.The ophthalmic laser can be trained to separate corneal tissue using photoablation and / or photodisruption to treat refractive errors. Alternatively or additionally, the laser can be trained to perform laser-induced refractive index change (LIRIC). Preferably, the laser is capable of emitting laser pulses in a wavelength range between 300 nanometers and 1400 nanometers, preferably between 700 nanometers and 1200 nanometers, with a pulse duration between one femtosecond and one nanosecond, preferably between ten femtoseconds and ten picoseconds, and a repetition frequency greater than ten kilohertz, preferably between 100 kilohertz and 100 megahertz. Such a femtosecond laser is particularly well suited for the fabrication of volume structures within the cornea. The treatment device preferably includes a control device with at least one storage device for at least temporarily storing at least one control data set, wherein the control data set(s) comprise control data for positioning and / or focusing individual laser pulses into the cornea and / or control data for controlling the method for fixing the eye by means of the fixation device. The treatment device may further include at least one beam device for guiding and / or shaping and / or deflecting and / or focusing a laser beam. Further features and their advantages can be found in the descriptions of the aspects of the invention, whereby advantageous embodiments of each aspect of the invention are to be regarded as advantageous embodiments of the other aspect of the invention. Another aspect of the invention relates to a computer program comprising commands that cause the treatment device to perform process steps according to one of the preceding embodiments. According to the invention, a computer-readable medium is also provided on which the computer program according to the preceding aspect of the invention is stored. This offers the same advantages and possibilities for variation as the other aspects of the invention. Further features of the invention are evident 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 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 by the invention. 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. This shows: Figure 1 shows a schematic representation of a treatment device with a fixing device according to an exemplary embodiment; Figure 2 shows a schematic diagram for negative pressure curves. In the figures, identical or functionally equivalent elements are provided with the same reference symbols. Fig. 1 shows a schematic representation of a treatment device 10 with an ophthalmic laser 18 for the treatment of an eye 12, in particular a cornea of ​​the eye 12 by means of photodisruption and / or ablation and / or laser-induced refractive index change (LIRIC). In addition to the laser 18, the treatment device 10 can have a control unit 20, which can be configured to control the laser 18 by means of control data, so that it can emit pulsed laser pulses, for example, in a predefined pattern for the treatment of the eye 12. Alternatively, the control unit 20 can be an external control unit 20 with respect to the treatment device 10. Furthermore, Fig. 1 shows that the laser beam 24 generated by the laser 18 can be deflected towards the eye 12 by means of a beam deflection device 22, namely a beam deflection device, such as a rotary scanner. The beam deflection device 22 can also be controlled by the control unit 20 to direct the laser beam 24 to a predetermined position in the eye, in particular in the cornea of ​​the eye 12. The laser 18 is preferably a photodisruptive and / or ablative laser configured to emit laser pulses in a wavelength range between 300 nm and 1400 nm, preferably between 700 nm and 1200 nm, with a pulse duration between 1 fs and 1 ns, preferably between 10 fs and 10 ps, ​​and a repetition frequency greater than 10 kHz, preferably between 100 kHz and 100 MHz. The control device 20 optionally also includes a storage device (not shown) for at least temporarily storing at least one control data set, wherein the control data set(s) comprise control data for positioning and / or focusing individual laser pulses in a cornea of ​​the eye 12. The position data and / or focusing data of individual laser pulses can be generated based on predetermined control data, in particular from previously measured topography and / or pachymetry and / or morphology. Furthermore, the treatment device 10 can include a fixation device 14 designed to fix the eye 12 to be treated in a position for irradiation with the laser 18. The fixation device 14 can, for example, include a suction device 16, wherein the suction device 16 can be a vacuum pump that generates a vacuum at a suction ring or suction ring segments on a side of the fixation device 14 oriented towards the eye 12. In other words, the suction ring can be placed on the eye 12, and the suction device 16, in particular the vacuum pump, can hold the eye 12 in position by generating a negative pressure. To prevent injury to the eye 12 by the fixation device 14, particularly from excessively rapid vacuum build-up, a pressure build-up algorithm may be provided, for example, by the control device 20 and / or a control unit (not shown) of the fixation device 14. This algorithm limits the vacuum build-up rate to a fixation vacuum value below a predetermined rate. The fixation vacuum value is the maximum vacuum value that the fixation device 14 is intended to assume to fix the eye, and the rate value is preferably defined as the fixation vacuum value per unit of time required to build up to this fixation vacuum value. The pressure build-up algorithm can therefore provide strategies to prevent excessively rapid negative pressure build-up and thus damage to the eye 12. For example, the pressure build-up algorithm can define the negative pressure build-up rate linearly or exponentially, preferably limiting it to a rate below 320 hPa / s, and particularly preferably to 225 hPa / s. The rate limit can also depend on whether the fixation device 14 is applied to the cornea or the sclera of the eye 12, since the sclera is softer than the cornea and therefore a lower negative pressure build-up rate is required. Particularly preferably, the negative pressure build-up rate can be limited to approximately 265 hPa / s when the fixation device 14 is applied to the cornea and to approximately 135 hPa / s when applied to the sclera. In addition to limiting the vacuum build-up rate to a predetermined speed value, the pressure build-up algorithm can also specify a scheme for how the vacuum should be built up, with examples of curve progressions shown in Fig. 2. Figure 2 shows a schematic diagram of the negative pressure P on the ordinate (y-axis), where the magnitude of the negative pressure is represented. The abscissa (x-axis) represents time t. Furthermore, the fixation negative pressure value Pmax is shown on the y-axis, which provides a maximum negative pressure limit to be applied to the eye. The fixation negative pressure value Pmax can be, for example, 700 hPa (or -700 hPa). Alternatively, the fixation negative pressure value can also be chosen to be lower to provide increased safety for the eye 12. Figure 2 shows several exemplary curves for the build-up of the vacuum. These serve only as examples, and the characteristics of the individual curves can be combined. A first exemplary curve is shown by curve P1, in which the vacuum is built up in stages by the pressure build-up algorithm. This means that a vacuum is initially built up to a certain vacuum level at a preferably predetermined vacuum build-up rate, at which point the vacuum is held constant for a predetermined waiting period. This process can then be repeated until the maximum vacuum value, Pmax, is reached. The stages in curve P1 can each have the same slope and / or the same stage length or waiting period. The slope is shown linearly here, although it can also be exponential between the individual stages. The negative pressure curve P2 shows a similar step profile, where the slope between the individual steps can be the same with the specified waiting time, but the waiting time or step lengths can decrease with each subsequent step. This means that the negative pressure builds up slowly at the beginning, primarily due to the longer waiting times, and then becomes progressively faster as the waiting times decrease, until the maximum fixation negative pressure value Pmax is reached. A combination of the characteristics of stages P1 and P2 is shown in curve P3, in which there is initially a slow increase in negative pressure followed by a long waiting period. After the first waiting period, there is a rapid increase in negative pressure followed by a shorter waiting period than the first. Finally, the build-up of negative pressure can continue according to this scheme until the maximum fixation negative pressure value Pmax is reached. Another exemplary vacuum build-up profile is shown in curve P4, in which no discrete waiting times are provided, but this curve profile can essentially be divided into three velocity profile sections, wherein in a first velocity profile section at the beginning of the activation of the fixing device 14 a slow build-up of the vacuum takes place, which increases in a middle velocity profile section until it is slowed down again in a last velocity profile section and thus asymptotically approaches the fixing vacuum value Pmax. In summary, a gradual and controlled increase in vacuum can thus ensure not only that sufficient negative pressure is achieved to hold the eye 12 in place, but also that this negative pressure is built up in such a way that the biology / physiology of the eye 12 is not impaired. Furthermore, such a build-up of negative pressure also prevents any sudden reactive movements of the patient's eye 12 from being induced. This can be achieved, for example, by specifying a predetermined number of discrete negative pressure values ​​that are reached stepwise during a docking process, or by specifying, for example, a maximum flow rate that is compatible with the physiology of the eye and that does not allow the negative pressure to build up faster than a predetermined limit. For implementation, software measures can be provided, in particular a stepwise, time-controlled check of the vacuum level and the next vacuum setting, so that the eye 12 can adapt to the current state. Alternatively, hardware measures can be provided, for example, the use of a flow restrictor. A combination of software and hardware measures can also be provided. The time course of the vacuum level can be estimated in different ways, for example, linearly or physically as a time-exponential function or using detailed physical models. Overall, the examples show how the invention can achieve a gradual suction of the eye 12.

Claims

Method for controlling a fixation device (14) for fixing a human or animal eye (12) for treatment with a treatment device (10) by means of negative pressure, wherein after activation of the fixation device (14) a negative pressure is built up to a predetermined fixation negative pressure value, wherein a negative pressure build-up rate up to the fixation negative pressure value is limited by a pressure build-up algorithm below a predetermined rate value, wherein the rate value is based on a physiology of the eye (12), wherein the fixation negative pressure value is built up stepwise by the pressure build-up algorithm, wherein at each negative pressure level the negative pressure is kept constant for a predetermined waiting time. Method according to claim 1, wherein the waiting time for each subsequent vacuum stage is specified as being less than the waiting time of the preceding vacuum stage. Method according to one of claims 1 or 2, wherein a respective, preferably different, speed profile of the vacuum build-up rate is specified between respective vacuum stages. Method according to one of the preceding claims, wherein the pressure build-up algorithm limits the vacuum build-up rate below the rate of 320 hPa / s, preferably below 225 hPa / s. Method according to one of the preceding claims, wherein the vacuum build-up rate is linear or exponential. Method according to one of the preceding claims, wherein the pressure build-up algorithm divides the vacuum build-up rate into at least three rate profile sections, wherein in a first rate profile section at the beginning of the activation of the fixing device (14) and in a third rate profile section before reaching the fixing vacuum value the vacuum build-up rate is lower than in a second rate profile section which is located in time between the first and second rate profile sections. Method according to one of the preceding claims, wherein the fixing device (14) has a suction ring or suction-capable ring segments by which the eye (12) is fixed by means of negative pressure. Method according to one of the preceding claims, wherein the speed value is predetermined depending on whether the fixation device (14) is applied to a cornea or a sclera of the eye (12). Treatment device (10), in particular comprising at least one ophthalmic laser (18) for separating a lenticule with predefined interfaces from a human or animal eye (12) by means of cavitation bubbles and / or for a laser-induced refractive index change, comprising a fixation device (14), wherein the treatment device (10) is configured to perform a method according to one of the preceding claims. Computer program comprising commands that cause the treatment device (10) according to claim 9 to perform the process steps according to any one of claims 1 to 8. Computer-readable medium on which the computer program according to claim 10 is stored.

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