Method for providing control data for an ophthalmic laser of a treatment device

Abstract

The invention relates to a method for providing control data for an ophthalmic laser of a treatment device. The method comprises, as steps: determining a wavefront map from a wavefront measurement acquired in a defined measurement area of ​​an eye; calculating an approximate wavefront map profile for an area outside the measurement area using an approximation method; determining correction data for correcting a refractive error based on the wavefront map and the approximate profile; and providing the control data for the ophthalmic laser, which includes the correction data.

Description

The invention relates to a method for providing control data for an ophthalmic 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 focusing device can be configured such that laser pulses cause photodisruption and / or ablation in a focus located within the organic tissue in order to remove tissue, in particular a tissue lenticel, from the cornea. The amount of tissue to be removed, or rather the geometry of the tissue to be removed to correct the refractive error, can be determined through measurements. One known method for determining the correction data that defines the tissue to be removed is wavefront measurement of the eye. Here, wavefront errors that occur as the signal passes through the eye can be determined using an aberrometer, such as a Hartmann-Schack sensor. These wavefront errors, or imaging errors, can then be subdivided into individual components or orders by fitting them to polynomials, particularly Zernike polynomials, which provide a wavefront map of the eye. The correction data can then be planned based on this wavefront map.For example, lower-order Zernike polynomials may include optical aberrations of sphere and cylinder, which could also be corrected by means of glasses or contact lenses, and higher-order Zernike polynomials may include coma, asymmetry errors and spherical aberration, which can be corrected by means of the laser methods mentioned above. However, it can happen that the wavefront measurement and thus the wavefront map does not capture imaging errors in a desired area, or only captures them insufficiently, which can lead to an impairment of the correction data. From US patent 8,444,632 B2, a method for performing refractive laser eye surgery is known that is centered along a visual axis of a human eye. From DE 10 2023 103 190 A1, a method for providing control data for an ophthalmic laser of a treatment device is known, comprising determining refractive error correction data for correcting a cornea of ​​an eye, determining Zernike polynomials from the determined refractive error correction data, determining an offset vector from a pupil center to another predetermined reference center of the eye, calculating corrected Zernike polynomials in which higher-order aberrations are calculated by adjusting the corresponding Zernike polynomials by the offset vector, and providing the control data for the treatment device, wherein the control data are generated using the corrected Zernike polynomials. Therefore, the object of the invention is to provide improved correction data for correcting refractive errors for an ophthalmic laser. This problem is solved by the independent patent claims. Advantageous embodiments of the invention are disclosed in the dependent patent claims, the following description, and the figures. One aspect of the invention relates to a method for providing control data for an ophthalmic 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 that can perform the following steps. The process involves determining a wavefront map from a wavefront measurement taken in a defined measurement area of ​​an eye, calculating an approximate wavefront map profile for an area outside the measurement area using an approximation method, determining correction data to correct a refractive error based on the wavefront map and the approximate profile, and providing the control data for the ophthalmic laser, which includes the correction data. In other words, measurement data from a wavefront measurement can be provided, from which a wavefront map can be derived. The wavefront measurement may have been performed within a defined measurement area of ​​the eye, in particular a measurement area corresponding to the diameter of the eye's pupil. However, for determining correction data, it may be necessary, for example, to plan a wavefront map with a larger diameter than the pupil diameter. To obtain a wavefront map for areas of the eye that lie outside the measurement range, an approximate wavefront map can be determined using an approximation method. This means the wavefront map can be extended to areas that were not directly measured. Interpolation or extrapolation methods, based on fit functions or piecewise polynomials (splines), can be used for this approximation. Using the extended wavefront map, which displays the approximate wavefront, correction data for refractive errors can then be determined and incorporated into the control data for the ophthalmic laser. For example, this allows for improved planning of transition zones adjacent to optical zones.These wavefront map extensions can also be performed starting from a desired centering reference, for example from the center of a pupil or a visual axis. The control data can include a data set for positioning and / or focusing individual laser pulses in the cornea. Additionally or alternatively, the control data can include a data set for adjusting at least one beam device for beam guidance and / or beam shaping and / or beam deflection and / or beam focusing of a laser beam from the respective laser. The invention offers the advantage that enlarged wavefront maps can be provided, which improves the determination of correction data and, in particular, produces fewer aberrations through correction. Furthermore, according to the invention, the wavefront measurement acquired within the defined measurement range of the eye is fitted for the extrapolation of the wavefront map to the diameter of the area outside the measurement range. In other words, the measurement points from the wavefront measurement cannot be fitted, as is usual, to the diameter of the measurement range in which measurement data is present, but rather the fitting area is extended to a larger diameter, in particular to the diameter of the area in which no measurement data is present and which lies outside the measurement range. That is, the fit to obtain the wavefront map to the polynomials, in particular the Zernike polynomials, is performed directly on an enlarged diameter that is larger than the diameter of the measurement range.The wavefront map is provided by Zernike polynomials. The wavefront measurements are fitted to Zernike polynomials within an enlarged diameter range that is larger than the diameter of the region outside the measurement range. Subsequently, the fitted Zernike polynomials are scaled back to the diameter of the region outside the measurement range, and at least two orders of magnitude of the largest scaled-back Zernike polynomials are removed. This means that, specifically for Zernike polynomials, an initially enlarged diameter is assumed as the fitting range. This enlarged diameter also extends beyond the diameter of the ultimately desired region for the wavefront map.In simplified terms, there is a diameter d1 corresponding to the measurement range, a diameter d2 corresponding to the final desired diameter of the range for which the wavefront map is to be extended and which is larger than diameter d1, and a diameter d3 (enlarged diameter) that serves as an intermediate step for the calculation and which is larger than diameters d1 and d2. Here, the wavefront measurement data acquired in diameter d1 are first fitted to the enlarged diameter d3. These Zernike polynomials fitted to the enlarged diameter d3 can then be scaled back to the diameter d2 of the desired range, removing at least the two largest Zernike orders of this expansion.In particular, it may be possible to initially fit more orders for Zernike polynomials than originally desired, in order to ultimately remove them again, which can be done due to numerical effects and avoids edge effects. Alternatively or additionally, the invention provides that two wavefront maps with different diameters are provided, wherein the wavefront profile in the area between the wavefront maps is approximated by interpolation. It is possible to provide two different wavefront measurements with different diameters or only one wavefront measurement that can be divided into two different diameters. Interpolation can determine a transition between the two wavefront maps with different diameters, resulting in an enlarged, continuous wavefront map. The same methods used for extrapolation can also be applied for interpolation, with the additional possibility of using interpolation methods such as K-Nearest Neighbors (k-NN) interpolation. Alternatively or additionally, according to the invention, the wavefront measurement is interpolated to a larger aspherical wavefront using an interpolation corridor between the wavefront map derived from the wavefront measurement and the aspherical wavefront. In particular, the wavefront measurement can be extended to an aspherical spherocylindrical wavefront with a larger diameter, wherein a transition between the measured wavefront map and the extended larger aspherical wavefront is formed by means of an interpolation corridor. The interpolation corridor can typically have a size between 20 percent and 41 percent. The interpolation corridor can, for example, provide a transition from the measured wavefront map as a boundary condition, so that the wavefront profile is preserved at the edge.Furthermore, the interpolation corridor can be approximated from the edge of the measured wavefront map to an edge of the target region, i.e., the larger aspheric wavefront, using splines or a biquadratic profile. For example, a wavefront map of a spectacle correction might be known, containing lower-order Zernike polynomials and possibly an aspheric component. In this case, a boundary condition can be set that a profile is preserved at the edge of the measured wavefront map and transitions to an edge of the larger aspheric wavefront using splines or a biquadratic profile. Instead of a spectacle correction, a regular subset of previously measured Zernike polynomials can also be used as a starting point, in particular C[2,0], C[2,+2], or C[4,0]. The invention also includes embodiments that offer additional advantages. One embodiment provides for the diameter of the wavefront map to be increased by extrapolation. This means that the wavefront map can be extended outwards into areas where no wavefront measurement data is available. This can be achieved using extrapolation methods, such as linear or polynomial extrapolation, splines, statistical extrapolation (where the approximate waveform can be inferred from the distribution of the measured data), or artificial intelligence (where the approximate waveform can be inferred from the measured patterns and trained waveforms). It is also possible for the wavefront measurement to include central areas of high intensity, for example, in small disks with a diameter of approximately 3 mm, which can then be extrapolated outwards. Another embodiment provides for the wavefront map to be provided by Zernike polynomials, where the Zernike polynomials are extrapolated for values ​​of p > 1. The parameter p in Zernike polynomials is defined as the radial spacing, with Zernike polynomials specified in a range of p between 0 and 1. Through extrapolation, the radial spacing of the Zernike polynomials can thus be extended beyond the defined range to provide enlarged wavefront maps. Another embodiment provides that the wavefront map is supplied by Zernike polynomials, wherein the Zernike polynomials are extrapolated such that a back-scaling of the extrapolated Zernike polynomials to a diameter of the defined measurement range yields the original Zernike polynomials. In other words, a set of Zernike coefficients of a predetermined order equal to or higher than the original Zernike polynomials can be computed for a diameter larger than the measurement range, but with the restriction that a scaling transformation of these modified Zernike polynomials back to the original definition range yields the original Zernike polynomials. Thus, the Zernike polynomials can be enlarged by scaling without altering an original form that exists in the range between p from 0 to 1. Another embodiment provides that the approximate wavefront map is generated using splines. Splines allow for a continuous, continuously differentiable approximate wavefront map expansion at controlled points, particularly endpoints. 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. A further aspect of the invention relates to a treatment device comprising at least one ophthalmic or surgical laser and a control unit configured to perform the steps of at least one embodiment of the method described above. The respective laser can be configured to at least partially separate a predefined corneal volume with predefined interfaces of a human or animal eye by means of optical breakthrough, in particular by means of photodisruption, and / or to ablate corneal layers by means of (photo)ablation, and / or to cause a laser-induced change in the refractive index of the cornea and / or the lens of the eye, and / or to increase corneal crosslinking. In a further advantageous embodiment of the treatment device according to the invention, the laser can be suitable for emitting laser pulses in a wavelength range between 300 nm and 1400 nm, preferably between 900 nm and 1200 nm, with a pulse duration of between 1 fs and 1 ns, preferably between 10 fs and 10 ps, ​​and a repetition frequency greater than 10 kilohertz (kHz), preferably between 100 kHz and 100 megahertz (MHz). The use of such lasers in the method according to the invention also has the advantage that the irradiation of the cornea does not have to take place in a wavelength range below 300 nm. This range is subsumed under the term "deep ultraviolet" in laser technology. This advantageously avoids unintentional damage to the cornea caused by these very short-wavelength and high-energy beams.Photodisruptive and / or ablative lasers of the type used here typically deliver pulsed laser radiation with a pulse duration between 1 fs and 1 ns into the corneal tissue. This allows the power density of the respective laser pulse, necessary for optical breakthrough, to be spatially tightly limited, thus enabling high cutting accuracy in the generation of interfaces. The wavelength range between 700 nm and 780 nm can also be selected. In a further advantageous embodiment of the treatment device according to the invention, the control device 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 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 schematic representation of a treatment device according to an exemplary embodiment; Fig. 2 shows a schematic representation of a wavefront measurement; Fig. 3 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 or surgical laser 12 for removing tissue 14 from the cornea of ​​a human or animal eye 16 by means of photodisruption and / or ablation. The tissue 14 can, for example, be a lenticule or a volumetric body that can be removed from the cornea of ​​the eye 16 with the surgical laser 12 to correct a refractive error. A correction profile or a geometry of the tissue 14 to be removed can be provided by a control unit 18, in particular in the form of correction data. Furthermore, the control unit 18 can be configured to generate control data that includes the correction data, so that the laser 12 emits pulsed laser pulses into the cornea of ​​the eye 16 in a pattern predefined by the control data in order to remove the tissue 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 laser 12 can be deflected towards the eye 16 by means of a beam deflection device 22, such as a rotary scanner, in order to remove the tissue 14. The beam deflection device 22 can also be controlled by the control device 18 to remove the tissue 14. The laser 12 shown is preferably a photodisruptive and / or photoablative laser configured to emit laser pulses in a wavelength range between 300 nanometers and 1400 nanometers, preferably between 700 nanometers and 1200 nanometers, with a pulse duration between 1 femtosecond and 1 nanosecond, preferably between 10 femtoseconds and 10 picoseconds, and a repetition frequency greater than 10 kilohertz, preferably between 100 kilohertz and 100 megahertz. 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 in the cornea. The determination of the correction data of the tissue to be removed 14 can be carried out, for example, using wavefront measurement. A wavefront determined in this way can be divided into different components of refractive errors or aberrations by fitting it to polynomials, in particular Zernike polynomials, in order to determine a geometry of the tissue to be removed 14 for correcting the respective aberration. Figure 2 shows a schematic representation of a wavefront measurement. Here, a predefined wavefront, for example a plane wavefront, can be projected into the eye 16 by a wavefront sensor (not shown), in particular a Hartmann-Shack sensor. The wavefront passes through a cornea 24, an iris 26, and a lens 28, and on its return path, it can be measured outside the eye 16 by sensors that provide the eye's wavefront 30. Due to the different aberrations of the aforementioned components of the eye 16, the original wavefront can be distorted according to these aberrations into wavefront 30. This wavefront 30 can then be fitted to polynomials, in particular Zernike polynomials, for partitioning into the different aberrations, thereby providing a wavefront map of the eye 16 for the different aberrations. Since the wavefront is measured through a pupil of the eye 16, the diameter of which is determined by the iris 26, the measurement range for the wavefront measurement has a diameter d defined by the pupil. However, it may be necessary to determine the correction data using a larger diameter d', for which no wavefront 30 measurement data is available. For example, diameter d' values ​​between 7 mm and 13 mm may be used. To nevertheless provide correction data based on a wavefront map in a region with a diameter d' that lies outside the measurement range, the method shown in Fig. 3 can be carried out. In step S10, a wavefront map can be determined from a wavefront measurement that was recorded in a defined measurement area with a diameter of d. In step S12, an approximate wavefront map can be measured for a region with a diameter d', where at least parts of the diameter d' lie outside the original measurement range and contain no measurement data. The approximate wavefront map can be determined, for example, using approximation methods, in particular interpolation or extrapolation methods, which extend or supplement the wavefront map. Extrapolation allows the range of Zernike polynomials to be extrapolated for values ​​of p > 1, where Zernike polynomials are defined in a range of p between 0 and 1. To ensure that the boundary conditions of the Zernike polynomials remain valid, the extrapolation can be performed such that a scale-back of the extrapolated Zernike polynomials to the range of p between 0 and 1 yields the original Zernike polynomials. Extrapolation here refers to an extension of the existing polynomials, particularly Zernike polynomials, outwards, for example, by using splines provided at the endpoints on the boundary of the polynomials. Alternatively, the fit to determine the wavefront map can also be performed directly in the area with the increased diameter d' in order to obtain the approximate profile. Interpolations between wavefront maps with different diameters are also possible in this way, whereby a region between the wavefront maps can be approximated by interpolation. In step S14, correction data can then be determined based on the wavefront map, which shows the approximate course, providing a geometry of the tissue to be removed 14. Finally, in one step S16, control data can be generated that control the ophthalmic laser 12 and / or the beam deflection device 22 in such a way that the tissue 14 specified by the correction data can be removed from the cornea 24 of the eye 16. Overall, the examples show how wavefront extrapolation models can be provided to determine correction data.

Claims

A method for providing control data for an ophthalmic laser of a treatment device, wherein the method comprises the following steps performed by a control device: - determining a wavefront map from a wavefront measurement acquired in a defined measurement area of ​​an eye; - calculating an approximate wavefront map profile for an area outside the measurement area using an approximation method; - determining correction data for correcting a refractive error based on the wavefront map and the approximate profile; and - providing the control data for the ophthalmic laser, which includes the correction data; - wherein the wavefront measurement acquired in the defined measurement area of ​​the eye is fitted to extrapolate the wavefront map for the diameter of the area outside the measurement area.wherein the wavefront map is provided by Zernike polynomials, wherein the wavefront measurement is fitted to Zernike polynomials in an enlarged diameter range larger than the diameter of the region outside the measurement range, wherein the fitted Zernike polynomials are subsequently scaled back to the diameter of the region outside the measurement range, and at least two orders of the largest scaled-back Zernike polynomials are removed, and / or wherein two wavefront maps with different diameters are provided, wherein the waveform in the region between the wavefront maps is approximated by interpolation, and / or wherein the wavefront measurement is interpolated to an aspherical larger wavefront with an interpolation corridor between the wavefront map from the wavefront measurement and the aspherical larger wavefront. Method according to claim 1, wherein a diameter of the wavefront map is increased by extrapolation. The method of claim 2, wherein the wavefront map is provided by Zernike polynomials, wherein the Zernike polynomials are extrapolated for values ​​of p > 1. Method according to claim 2, wherein the wavefront map is provided by Zernike polynomials, wherein the Zernike polynomials are extrapolated such that a backscaling of the extrapolated Zernike polynomials to a diameter of the defined measurement range yields the original Zernike polynomials. Method according to one of the preceding claims, wherein the approximate wavefront map is generated by splines. Control device configured to perform a procedure according to any of the preceding claims. Treatment device comprising at least one ophthalmic laser for treating a human or animal eye and at least one control device according to claim 6. Computer program comprising commands that cause the treatment device according to claim 7 to execute a method according to any one of claims 1 to 5. Computer-readable medium on which a computer program according to claim 8 is stored.

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