METHOD FOR PROVIDING TAX DATA FOR AN OPHTHALMIC ABLATION LASER, TAKING INTO ACCOUNT LASER PULSE POSITIONING INACCURACY, TAX DEVICE, TREATMENT DEVICE, COMPUTER PROGRAM AND COMPUTER-READABLE MEDIUM

Abstract

The invention relates to a method for providing control data for an ophthalmic ablation laser (12) of a treatment device (10). The method comprises determining a laser pulse positioning inaccuracy based on a predetermined statistic of eye movements and a predetermined processing latency, wherein the processing latency comprises a latency of a camera device (24), a beam deflection device (22), and the ablation laser (12); determining an ablation volume (14) for correcting a refractive error as a function of the determined laser pulse positioning inaccuracy; and providing the control data for controlling the ablation laser (12), which includes the determined ablation volume (14).

Description

The invention relates to a method for providing control data for an ophthalmic ablation laser of a treatment device. The invention further relates to a control unit configured to carry out the method, a treatment device with such a control unit, a computer program comprising commands that cause the treatment device to execute the method, and a computer-readable medium on which the computer program is stored. Treatment devices and methods for controlling ophthalmic lasers to correct refractive errors and / or pathologically or abnormally altered areas of the cornea are known in the prior art. For example, pulsed lasers and a beam deflection device can be configured such that laser pulses cause an optical breakthrough in corneal tissue, in particular an ablation, to remove the corneal tissue. Typically, the eye is not fully fixed during ablation laser treatment. To prevent eye movements from interfering with the treatment, it is common practice to track the eye during the procedure using a camera system, known as eye tracking. A camera captures an image of the eye, and an image processing unit locates the pupil and calculates the eye's position. This positional information is then provided to the laser or a beam deflection device, such as adjustable mirrors or a rotary scanner, allowing the laser beam to be repositioned and compensated for. A problem with this approach is that image acquisition, image processing, and the beam deflection device's response all take time and therefore cannot keep up precisely with rapid eye movements. Systems and methods for correcting higher order aberrations in laser refractive surgery are known from US patent 2013 / 0190736 A1. From DE 10 2005 025 462 A1, a method and a device for reducing latency in eye tracking are known. The method comprises, based on a measurement of past eye positions, calculating a future eye position and using the calculated prediction of a future eye position to reduce the latency effect of the eye position measurement system. Therefore, the object of the invention is to improve laser pulse positioning. This problem is solved by the independent patent claims. Advantageous embodiments of the invention are disclosed in the dependent patent claims, the present description, and the figures. The invention is based on the idea that rapid eye movements, such as saccades or vestibular movements, are statistically determined, and that, in addition, a laser pulse positioning inaccuracy is calculated based on a predetermined processing latency of a camera device, a beam deflection device, and the ablation laser. The laser pulse positioning inaccuracy can represent a positioning error tolerance of individual pulses or of the entire treatment area, whereby a statistical error or probability can be specified regarding the area in which a laser spot strikes or how the initially planned treatment area changes due to the laser pulse positioning inaccuracy. Since the error caused by the laser pulse positioning inaccuracy is known, it can be pre-compensated to provide an improved treatment outcome. One aspect of the invention relates to a method for providing control data for an ophthalmic ablation laser of a treatment device, wherein the method comprises the following steps performed by a control unit. A control unit is understood to be a device or device component, in particular a processor or microprocessor, which can perform the following steps to generate control data. The laser pulse positioning inaccuracy is determined based on a predetermined set of eye movement statistics and a predetermined processing latency, where the processing latency includes the latency of the camera, beam deflection device, and ablation laser. Furthermore, an ablation volume for correcting a refractive error is determined based on the specified laser pulse positioning inaccuracy, and the control data for controlling the ablation laser, encompassing the determined ablation volume, is provided. In other words, laser pulse positioning inaccuracy can first be determined from predetermined eye movements and a predetermined processing latency of the treatment device. The laser pulse positioning inaccuracy can represent a deviation (error) from an ideal laser spot that would be projected onto a planned position without eye movements or processing latency. That is, the laser pulse positioning inaccuracy can take the form of a spatial distribution where the laser pulse is expected. The eye movements can be random eye movements, particularly those performed unconsciously, derived from statistics, such as saccades, vestibular movements, optokinetic movements, and / or vergence movements.Using these predetermined eye movements, a maximum or average range of movement, in particular a speed and frequency, can be determined in which the eye is expected to move, whereby the processing latency of the treatment device can be used to determine which movements are detectable and in which an error is expected. Once the laser pulse positioning inaccuracy has been determined, an ablation volume for correcting a refractive error can be calculated based on this inaccuracy. This means that the ablation volume can be planned in such a way as to compensate for the error expected due to the laser pulse positioning inaccuracy. Because of the statistical and stochastic nature of the laser pulse positioning inaccuracy, this error can be addressed, for example, by using a low-pass filter or mathematical convolution for the laser pulses, or by pre-compensating for an initially planned ablation volume through deconvolution. Finally, control data can be generated for controlling the ablation laser or treatment device, encompassing the ablation volume determined while taking into account the laser pulse positioning inaccuracy. The control data can include a separate data set for positioning and / or focusing individual laser pulses within the cornea. Additionally or alternatively, the control data can include a separate data set for adjusting at least one beam device for beam guidance, shaping, deflection, and / or focusing of a laser beam from the respective laser. The ablation laser can be, for example, an excimer laser, designed to remove corneal tissue by ablating or vaporizing it. Ablation lasers are used, for instance, in laser-assisted in situ keratomileusis (LASIK) or photorefractive keratectomy (PRK). The camera system can include one or more cameras, which can be configured to capture image data of the eye. Furthermore, the camera system can be configured to determine the eye's position from this data, particularly through image analysis. This determined eye position can then be used to position the laser pulses for creating the ablation volume. The invention offers the advantage that eye movements, especially rapid eye movements, can be better taken into account when planning the ablation volume, resulting in fewer aberrations and thus improving treatment. According to a first alternative of the invention, a probability distribution for a laser pulse position, in particular a Gaussian distribution, is provided by the laser pulse positioning inaccuracy. In other words, a probability can be calculated as to the position at which a laser pulse will strike due to eye movements and processing latency. In particular, an ideal position with an error range can be specified, for example in the form of a Gaussian distribution. Alternatively or additionally to the first alternative, a second alternative according to the invention provides that an effective laser pulse ablation volume of a laser pulse is determined by mathematically convolving the laser pulse ablation volume of the laser pulse with the laser pulse positioning uncertainty, wherein the ablation volume is determined using the effective laser pulse ablation volumes of the respective laser pulses. In other words, a laser pulse ablation volume that generates a laser pulse at an ideally assumed position can be mathematically convolved with the determined laser pulse positioning uncertainty, resulting in an effective laser pulse ablation volume. Using this effective laser pulse ablation volume, the entire ablation volume used to correct the refractive error can then be planned.This means that the ablation volume is not planned using ideal laser spots, but rather effective laser spots obtained through convolution, specifically convolution with a Gaussian profile that describes the laser pulse positioning inaccuracy. This offers the advantage that the ablation volume can be planned using "smeared" laser spots, providing a simple way to account for the effects of eye movements and processing latency. The invention also includes embodiments that offer additional advantages: One embodiment provides that the eye movements comprise saccades, vestibular movements, optokinetic movements, vergence movements, and / or miniature movements, the parameters of which are provided from statistics of investigated eye movements. Saccades can be spontaneous eye movements that occur rapidly and move from one fixation point to another. Vestibular eye movements are reflexive eye movements that can be triggered by the vestibular system of the inner ear. Optokinetic eye movements are reflexive eye movements that can be triggered by visual perception from a peripheral visual field, with optokinetic movements also being referred to as optokinetic nystagmus. Vergence movements are disconjugate eye movements, for example, to fixate on objects.Miniature movements, also known as microsaccades, are very small, unconscious eye movements that can occur at regular intervals, even when the eye is fixed on a single point. Another embodiment provides that the parameters of the eye movements include speeds and frequencies. In other words, the speed at which the eye movement is performed and its frequency can be known from the statistics of the aforementioned eye movements. Another embodiment provides that saccade movements include a maximum speed of 170 mm / s and a maximum frequency of 35 Hz, vestibular movements include a maximum speed of 21 mm / s and a maximum frequency of 50 Hz, optokinetic movements include a maximum speed of 8 mm / s and a maximum frequency of 60 Hz, vergence movements include a maximum speed of 2 mm / s and a maximum frequency of 80 Hz, and / or miniature movements include a maximum speed of 1 mm / s and a maximum frequency of 100 Hz. In other words, one or more parameters of these eye movements can be used to determine the laser pulse positioning inaccuracy, with values ​​between 0 and a previously specified maximum value being selectable to describe a patient to be treated.In this case, either a previously mentioned statistical value, for example a mean value, can be assumed, or the patient can be examined individually, and the corresponding parameters of the eye movements can be used to determine the laser pulse positioning inaccuracy. Another embodiment provides that the processing latency of the camera device includes a camera frame rate, a camera latency, and / or an image processing time. For example, the camera frame rate can range from 40 to 4000 Hz, the camera latency can range from 1 to 25 ms, and the image processing time can be up to 1 ms. However, the values ​​mentioned above are only examples, and these values ​​may change as camera technology advances. Another embodiment provides that the processing latency of the beam deflection device and / or the ablation laser includes a positioning time for the beam deflection device, a repetition rate of the ablation laser, and / or a laser trigger delay. The positioning time of the beam deflection device to set a new position can range from 0.5 to 15 ms, the repetition rate of the ablation laser can range from 10 to 2000 Hz, and the laser trigger delay, which describes the time between triggering and the arrival of a laser pulse at a planned position, can range up to 150 µs. These values ​​are also only examples and may change with ongoing technical development. Another embodiment involves determining an initial ablation volume with an ideally assumed laser pulse positioning accuracy. This initial ablation volume is then mathematically expanded using the determined laser pulse positioning inaccuracy to calculate the ablation volume used in the control data. In other words, an initial ablation volume can be determined that assumes ideal laser pulses with no inaccuracy. To account for the effects of eye movements and processing latency, the initial ablation volume can then be mathematically expanded using the determined laser pulse positioning inaccuracy. This yields the (precompensated) ablation volume that can be used in the control data.This embodiment offers the advantage of providing an additional way to take laser pulse positioning inaccuracies into account when planning the ablation volume. Another embodiment involves determining an initial ablation volume with an assumed ideal laser pulse positioning accuracy. This initially determined ablation volume is then calculated by scaling it to the ablation volume used in the control data, with a scaling factor determined based on the laser pulse positioning inaccuracy. This means that, again, an initial ablation volume can be planned where the laser pulses are ideally positioned and no inaccuracy is assumed. This initial ablation volume can then be scaled by a scaling factor derived from the determined laser pulse positioning inaccuracy. For example, the scaling factor can be calculated as the ratio of an ideal laser spot to an effective laser spot.This offers the advantage of providing a further design option to take eye movements and processing latency into account. The procedure may include at least one additional step that is executed precisely when a use case or application situation occurs that is not explicitly described here. This step may, for example, include the output of an error message and / or a prompt for user feedback. Additionally or alternatively, it may include setting a default value and / or a predetermined initial state. Another aspect of the invention relates to a control device configured to perform the steps of at least one embodiment of the previously described method. For this purpose, the control device may include a computing unit for electronic data processing, such as a processor. The computing unit may comprise at least one microcontroller and / or at least one microprocessor. The computing unit may be implemented as an integrated circuit and / or a microchip. Furthermore, the control device may include an (electronic) data storage device or a storage unit. Program code, which encodes the steps of the respective embodiment of the respective method, may be stored on the data storage device. The program code may include the control data for the respective laser.The program code can be executed by the processing unit, which then causes the control unit to execute the respective configuration. The control unit can be designed as a control chip or control device. The control unit can, for example, be part of a computer or computer network. Another aspect of the invention relates to a treatment device comprising at least one ophthalmic ablation laser and a control unit configured to perform the steps of at least one embodiment of the previously described method. The ablation laser can be configured to remove a predefined ablation volume of a human or animal eye by means of optical breakthrough, in particular to remove corneal layers by means of (photo)ablation. In an advantageous further development of the treatment device, the ablation laser can be configured to emit laser pulses in a wavelength range between 150 nm and 250 nm, preferably between 175 nm and 215 nm, with a pulse duration between 1 fs and 100 ns, preferably between 10 ps and 10 ns, and a repetition frequency greater than 100 hertz (Hz), preferably between 400 Hz and 10 kilohertz (MHz). Such an ablation laser, which can be configured in particular as an excimer laser, is especially well suited for the ablation of corneal tissue. The use of lasers in a wavelength range below 300 nm, also known as "deep ultraviolet," can ablate corneal tissue particularly efficiently due to these very short-wavelength and high-energy beams. Photoablative lasers of the type used here typically introduce pulsed laser radiation with a pulse duration between 1 fs and 100 ns into the corneal tissue.The wavelength range can also be selected, in particular, between 175 nm and 215 nm. In a further advantageous embodiment of the treatment device, the control unit can have at least one storage device for at least temporary storage of at least one control data set, wherein the control data set(s) comprise control data for positioning and / or focusing individual laser pulses in the cornea; and can have at least one beam deflection device for beam guidance and / or beam shaping and / or beam deflection and / or beam focusing of a laser beam of the laser. Another aspect of the invention relates to a computer program. The computer program comprises instructions that, for example, constitute program code. The program code can include at least one control data set with the respective control data for the respective laser. When the program code is executed by a computer or a computer network, it is caused to execute the method described above, or at least one embodiment thereof. Another aspect of the invention relates to a computer-readable medium (storage medium) on which the aforementioned computer program or its instructions are stored. To execute the computer program, a computer or a computer network can access the computer-readable medium and read its contents. The storage medium is, for example, designed as a data storage device, in particular at least partially as a volatile or non-volatile data storage device. A non-volatile data storage device can be flash memory and / or an SSD (solid-state drive) and / or a hard drive. A volatile data storage device can be RAM (random access memory). The instructions can be, for example, in the form of source code of a programming language and / or as assembly language and / or as binary code. Further features and advantages of one of the described aspects of the invention may arise from further developments of another aspect of the invention. The features of the embodiments of the invention can therefore exist in any combination with one another, unless they have been explicitly described as mutually exclusive. Additional features and advantages of the invention are described below with reference to the figure(s) in the form of advantageous embodiments. The features or combinations of features of the embodiments described below can be combined with each other and / or with the features of the embodiments. That is, the features of the embodiments can complement and / or replace the features of the embodiments, and vice versa. Therefore, embodiments that are not explicitly shown or explained in the figures, but which can be derived and generated from separate combinations of features in the embodiments and / or embodiments, are also to be considered as encompassed and disclosed by the invention.Thus, embodiments that do not exhibit all the features of an originally formulated claim, or that go beyond or deviate from the combinations of features set out in the cross-references of the claims, are also to be considered disclosed. Regarding exemplary embodiments: Fig. 1 shows a treatment device according to an exemplary embodiment; Fig. 2 shows a schematic process diagram for a process according to an exemplary embodiment. In the figures, identical or functionally equivalent elements are provided with the same reference symbols. Figure 1 shows a schematic representation of a treatment device 10 with an ophthalmic ablation laser 12 for the removal of an ablation volume 14 or tissue from a human or animal cornea 16 by ablation. The ablation volume 14 can be created, for example, by removing corneal layers from the cornea 16 using the ablation laser 12, for instance, to correct refractive errors. A geometry of the ablation volume 14 to be removed can be provided by a control device 18, in particular in the form of control data, so that the ablation laser 12 emits pulsed laser pulses into the cornea 16 of the eye in a pattern predefined by the control data and in a predefined temporal pulse sequence to create the ablation volume 14. Alternatively, the control device 18 can be an external control device 18 with respect to the treatment device 10. Furthermore, Fig. 1 shows that the laser beam 20 generated by the ablation laser 12 can be deflected towards the cornea 16 by means of a beam deflection device 22, such as a rotary scanner or controllable mirror, in order to create the ablation volume 14. The beam deflection device 22 can also be controlled by the control unit 18. The laser 12 shown is preferably a photoablative laser, in particular an excimer laser, configured to emit laser pulses in a wavelength range between 150 nanometers and 250 nanometers with a pulse duration between 1 femtosecond and 100 nanoseconds and a repetition frequency between 100 hertz and 10 kilohertz. The control device 18 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 into the cornea. Furthermore, the control data may include a pulse sequence in which a temporal order of the respective laser pulses is defined. To detect eye movements during treatment, the treatment device 10 can further include a camera device 24, which is configured to capture images of the eye and to determine the position and / or orientation of the eye from a characteristic of the eye, for example, the center of the pupil. Based on the determined position and / or orientation of the eye, the treatment device 10 can then adjust the laser beam 20 by means of the beam deflection device 22 such that the planned ablation volume 14 is still removed. However, rapid eye movements, such as saccades, vestibular movements, optokinetic movements, vergence movements, and / or miniature eye movements, can be problematic. These eye movements can be so fast that they cannot be detected with sufficient precision by the camera 24 and / or the laser beam 20 cannot be adjusted to a new position quickly enough by the beam deflection device 22. This means that eye movements faster than the processing latency of the camera 24 and the beam deflection device 22 cannot be accurately detected and compensated for. To take these rapid eye movements into account during treatment planning, the procedure shown in Fig. 2 can be performed. Figure 2 shows a schematic process diagram for providing control data for the ophthalmic ablation laser 12 of the treatment device 10, wherein the process can be carried out by the control unit 18. In step S10, a laser pulse positioning inaccuracy can be calculated based on a predetermined statistic of eye movements, which includes in particular the speeds and frequencies of the eye movements, and a processing latency. The processing latency can include a latency of the camera device 24, which can be determined, for example, from a camera acquisition rate and / or an image processing time, as well as a latency of the beam deflection device 22 and the ablation laser 12, such as a positioning time for the beam deflection device 22 to set a new position, a repetition rate of the ablation laser 12, and / or a laser trigger delay. Eye movements can include the following parameters as maximum speed and maximum frequency, which can be derived from statistical studies of eye movements. For example, saccade movements may have a maximum speed of 170 mm / s and a maximum frequency of 35 Hz, vestibular movements a maximum speed of 21 mm / s and a maximum frequency of 50 Hz, optokinetic movements a maximum speed of 8 mm / s and a maximum frequency of 60 Hz, vergence movements a maximum speed of 2 mm / s and a maximum frequency of 80 Hz, and / or miniature movements a maximum speed of 1 mm / s and a maximum frequency of 100 Hz. For each of these movements, a maximum positional error can then be calculated from the quotient of the speed and the frequency; for example, for vestibular movement, 21 mm / s / 50 Hz = 0.42 mm. A maximum laser pulse positioning inaccuracy can then be determined, for example, using where F is the maximum laser pulse positioning inaccuracy, vmax is a maximum speed of the respective eye movement, fmax is a maximum frequency of the respective eye movement, AR is a recording rate of the camera device 24, LZ is a latency of the camera device 24, and TV is a laser trigger delay. Thus, the laser pulse positioning inaccuracy can be provided as a probability distribution for a laser pulse position, for example by a Gaussian distribution. In step S12, the ablation volume 14 for correcting a refractive error can then be determined as a function of the specified laser pulse positioning inaccuracy. For this purpose, an intermediate step can be inserted, in which an initial ablation volume is determined with an ideally assumed laser pulse positioning accuracy, i.e., without any inaccuracy. This initial ablation volume is then mathematically deconvolutiond with the specified laser pulse positioning accuracy to pre-compensate for the effect of eye movement. Instead of deconvolution, the initially determined ablation volume can also be scaled, with the scaling factor being derived from the specified laser pulse positioning inaccuracy. In an alternative embodiment, it is also possible to mathematically convolution the laser pulse ablation volume generated by a single laser pulse using the determined laser pulse positioning uncertainty in order to obtain effective laser pulse ablation volumes for the respective laser pulses. In other words, the laser pulse positioning uncertainty can be used as a filter function to determine an assumed effective ablation volume for each laser pulse. The ablation profile 14 can then be planned using this effective laser pulse ablation volume. Finally, in step S14, the control data for controlling the treatment device 10, which includes the ablation profile 14, can be generated, and the treatment device 10 can be controlled using this data to correct the refractive error. By precompensating for eye movements and processing latency, a better treatment outcome can thus be achieved.

Claims

Method for providing control data for an ophthalmic ablation laser (12) of a treatment device (10), wherein the method comprises the following steps performed by a control device (18): - Determining a laser pulse positioning inaccuracy based on a predetermined statistic of eye movements and a predetermined processing latency, wherein the processing latency includes a latency of a camera device (24), a beam deflection device (22), and the ablation laser (12); - Determining an ablation volume (14) for correcting a refractive error depending on the determined laser pulse positioning inaccuracy; - Providing the control data for controlling the ablation laser (12), which includes the determined ablation volume (14); - wherein the laser pulse positioning inaccuracy provides a probability distribution for a laser pulse position. Method for providing control data for an ophthalmic ablation laser (12) of a treatment device (10), wherein the method comprises the following steps performed by a control device (18): - Determining a laser pulse positioning inaccuracy based on a predetermined statistic of eye movements and a predetermined processing latency, wherein the processing latency includes a latency of a camera device (24), a beam deflection device (22), and the ablation laser (12); - Determining an ablation volume (14) for correcting a refractive error depending on the determined laser pulse positioning inaccuracy; - Providing the control data for controlling the ablation laser (12), which includes the determined ablation volume (14);- wherein an effective laser pulse ablation volume of a laser pulse is determined by a mathematical convolution of a laser pulse ablation volume of the laser pulse with the laser pulse positioning uncertainty, wherein the ablation volume (14) is determined by means of the effective laser pulse ablation volumes of the respective laser pulses.; Method according to claim 1 or 2, wherein the eye movements comprise saccade movements, vestibular movements, optokinetic movements, vergence movements, and / or miniature movements, the parameters of which are provided from a statistic of investigated eye movements. Method according to claim 3, wherein the parameters of the eye movements include velocities and frequencies. The method of claim 4, wherein: - saccade movements comprise a maximum speed of 170 mm / s and a maximum frequency of 35 Hz; - vestibular movements comprise a maximum speed of 21 mm / s and a maximum frequency of 50 Hz; - optokinetic movements comprise a maximum speed of 8 mm / s and a maximum frequency of 60 Hz; - vergence movements comprise a maximum speed of 2 mm / s and a maximum frequency of 80 Hz; and / or - miniature movements comprise a maximum speed of 1 mm / s and a maximum frequency of 100 Hz. Method according to one of the preceding claims, wherein the processing latency of the camera device (24) comprises a camera acquisition rate, a camera latency time and / or an image processing time. Method according to one of the preceding claims, wherein the processing latency of the beam deflection device (22) and / or the ablation laser (12) comprises a positioning time for the beam deflection device (22), a repetition rate of the ablation laser (12) and / or a laser trigger delay. Method according to claim 1 or one of claims 3 to 7, wherein the probability distribution is a Gaussian distribution. Method according to claim 1 or one of claims 3 to 8, wherein an initial ablation volume is determined with an ideally assumed laser pulse positioning accuracy, wherein the initially determined ablation volume is calculated by a mathematical unfolding with the determined laser pulse positioning inaccuracy to the ablation volume (14) used in the control data. Method according to claim 1 or one of claims 3 to 8, wherein an initial ablation volume is determined with an ideally assumed laser pulse positioning accuracy, wherein the initially determined ablation volume is calculated by scaling to the ablation volume (14) used in the control data, wherein a scaling factor of the scaling is determined as a function of the laser pulse positioning inaccuracy. Control device (18) which is configured to carry out a respective procedure according to one of the preceding claims. Treatment device (10) comprising at least one ophthalmic ablation laser (12) for the removal of a corneal volume of a human or animal eye by means of optical breakthrough and at least one control device (18) according to claim 11. Computer program comprising commands that cause the treatment device (10) according to claim 12 to execute a method according to any one of claims 1 to 10. Computer-readable medium on which a computer program according to claim 13 is stored.

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