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

Abstract

Method for providing control data for an ophthalmic surgical laser (12) of a treatment device (10) for the removal of tissue (14), the method comprising the following steps performed by a control device (18): a) Determining (S10) a preoperative corneal shape (26) of a cornea (16) of a human or animal eye from predetermined examination data; b) Determining (S12) a corneal shape (30) to be achieved from the predetermined examination data; c) Specifying (S14) exactly one or exactly two predetermined ablation depths to be achieved in a z-direction at at least one predetermined position (24) in an xy-direction between the preoperative corneal shape (26) and the corneal shape (30) to be achieved; d) Determining (S16) ablation data for the removal of the tissue (14).wherein, to determine the ablation data, the preoperative corneal shape (26) is related to the corneal shape to be achieved (30) such that the predetermined ablation depth results at the predetermined position (24) between the two corneal shapes, wherein corneal tissue (16) located between the related corneal shapes is defined in the ablation data as tissue (14) to be removed, wherein the corneal shapes (26, 30) are superimposed and subsequently the corneal shape to be achieved (30) is moved along the z-direction to the preoperative corneal shape until the predetermined ablation depth is reached at at least one predetermined position (24) between the preoperative corneal shape (26) and the corneal shape to be achieved, wherein by subtracting the corneal shape to be achieved (30), which is aligned with the predetermined ablation depth,a difference is formed from the preoperative corneal shape (26), whereby areas with a positive difference are defined as tissue to be removed (14) and areas with a negative difference as tissue not to be treated; and e) providing (S18) control data for controlling the ophthalmic surgical laser (12), which uses the ablation data to remove the tissue (14).

Description

The present invention relates to a method for providing control data for an eye surgical laser of a treatment device for the removal of tissue. The invention also relates to a treatment apparatus having at least one eye-surgery laser and a control device for carrying out the method, a computer program and a computer-readable medium.Treatment devices and methods for controlling ophthalmological lasers for correcting an optical defect and / or pathologically or unnaturally modified regions of the cornea (cornea) are known in the prior art. In this case, for example, a pulsed laser and a beam focusing device can be designed such that laser pulses cause photodisruption and / or photoablation in a focus located within the organic tissue in order to remove a tissue, in particular a tissue lenticle, from the cornea. For improved treatment, it is important to perform an individual treatment plan for each patient, in particular a topography-guided treatment plan. In known approaches, the correction to be achieved and the aberrations of higher order are known and the optical zone is fixed. From this, the depth and the volume of the tissue to be removed are then determined. However, these methods are not designed to minimize tissue to be removed, as more tissue is often ablated in individual treatments than is needed for correction.From DE 20 2019 005 517 U1 a device for correction of defective vision is known, comprising means for obtaining topographical information of a front surface and topographical information of a rear surface of a cornea of an eye, means for obtaining a desired focusing point within the eye, wherein the means for obtaining the desired focusing point is adapted to determine the desired focusing point based on the topographical information of the front surface and the rear surface of the cornea, and based on refractive aberration information for the eye.EP 3 782 591 A1 discloses a lenticular laser incision with wavefront-guided maps.From DE 10 2015 006 041 A1 a device for defining a flap geometry of a flap for the laser treatment of a human eye is known, comprising a control unit which is programmed to evaluate ablation profile data of an ablation profile for a laser ablation treatment of a human cornea and to define the flap geometry on the basis of the evaluation.The invention is based on the object of providing control data for controlling an eye surgery laser with improved ablation data for removing a tissue, in particular for minimizing the tissue to be removed.This object is achieved by the method according to the invention, the apparatuses according to the invention, the computer program according to the invention and the computer-readable medium according to the invention. Advantageous embodiments with expedient developments of the invention are specified in the respective dependent claims, wherein advantageous embodiments of the method are to be regarded as advantageous embodiments of the treatment apparatus, of the control device, of the computer program and of the computer-readable medium and vice versa.A first aspect of the invention relates to a method for providing control data for an eye surgical laser of a treatment apparatus for the removal of tissue, the method comprising the following steps carried out by a control device. A control device is understood to mean a device, a device component or a device group which is / is configured to receive and evaluate signals, and to provide, for example generate, control data. The control device can be designed, for example, as a control chip, computer program, computer program product or control device.As step a), the control device determines a preoperative corneal shape, in particular an anterior cornea or anterior stroma, a cornea of a human or animal eye from predetermined examination data, as step b) determines a corneal shape to be achieved from the predetermined examination data, and as step c) determines at least one predetermined ablation depth, which is to be achieved in a z-direction at at least one predetermined position in an x-y direction between the preoperative corneal shape and the corneal shape to be achieved. In this case, exactly one predetermined ablation depth or exactly two predetermined ablation depths is defined or predefined, which ablation is intended to achieve in the z-direction, i.e. a depth direction or in the direction of an optical axis of the eye, between the preoperative corneal shape and the corneal shape to be achieved at a position in the x-y direction, i.e. perpendicular to the optical axis. This means that it is predetermined at at least one position how much corneal tissue is to be ablated in the depth direction. This predetermined ablation depth may be, in particular, between the surfaces of the corneal shapes, for example, a stromal depth or total depth to the epithelium.Furthermore, the method comprises as step d) determining ablation data for removing the tissue, wherein for determining the ablation data the preoperative corneal shape is related to the corneal shape to be achieved in such a way that the predetermined ablation depth results at the predetermined position between the two corneal shapes, wherein tissue of the cornea, which is localized between the related corneal shapes, is defined in the ablation data as tissue to be removed, and as step e) providing control data for controlling the eye surgery laser, which control data use the ablation data for removing the tissue.In other words, the preoperative corneal shape, i.e. the shape of the cornea as it is present before the treatment, and the corneal shape to be achieved, which is to be achieved after the treatment, are first determined. These can be determined from predetermined examination data according to known methods. In this case, the corneal shape can be defined, for example, by a corneal curvature, a corneal volume and / or a corneal asphericity. Corneal asphericity means a deviation from a spherical curvature of the cornea. Thus, the cornea can be arched, for example, in the central part than at an edge.After it has been determined how the cornea is to look before and after the treatment, at least one ablation depth in the z-direction is predetermined, which is to be ablated at a predetermined position between the preoperative corneal shape and the corneal shape to be achieved. The ablation depth at the predetermined position can also be determined, for example, from the examination data. This can then be used to determine the ablation data by means of which the tissue to be removed is localized in the cornea. For this purpose, the preoperative corneal shape is aligned with the corneal shape to be achieved in such a way that the predetermined ablation depth is obtained at the predetermined position. Thus, the corneal shapes are placed one above the other and subsequently the corneal shape to be achieved (target corneal shape) is displaced along the z-direction to the preoperative corneal shape until the predetermined ablation depth is reached at the at least one predetermined position between the preoperative corneal shape and the corneal shape to be achieved. The tissue now located between the preoperative corneal shape and the aligned corneal shape to be achieved in the cornea is then marked as tissue to be removed. In other words, a difference is formed by subtracting the corneal shape to be achieved, which is aligned with the predetermined ablation depth, from the preoperative corneal shape, wherein regions with a positive difference are defined as tissue to be removed and remaining regions, in particular the regions with a negative difference, are defined as tissue not to be treated.Preferably, a position and thickness of an epithelial layer of the cornea can be known, wherein these can be taken into account in determining the corneal shape to be achieved, since in particular only stroma tissue is permanently removed and epithelial tissue grows. For example, at positions where tissue is present for removal, but this tissue is only in the corneal epithelial layer, it may be determined not to be treated.The tissue to be removed determined in this way can finally be stored in the ablation data, wherein the ablation data are provided as control data for controlling the eye surgery laser.The invention provides the advantage that the tissue to be removed can be optimized, in particular minimized, since it can be determined more accurately which tissue is to be removed. Thus, the target corneal shape to be achieved can be corrected, in particular for cases with measurable topographies but unreliable refraction data, in particular in corneal pathologies, keratoconus, postkeratoplasty, or decentrated optical zones. The method allows true regularization of the corneal shape to a selectable target optim. In addition, it allows limiting excessive ablation.The invention also encompasses embodiments which result in additional advantages.According to an advantageous embodiment, it is provided that at least one corneal curvature is predetermined for the corneal shape to be achieved. Preferably, in this case exactly one corneal curvature is predetermined which the cornea is intended to reach after the treatment. Thus, it can be accurately adjusted how the corneal curvature and thus the refractive properties of the cornea after treatment should look.It is particularly preferred that two corneal curvatures are specified for the corneal shape to be achieved. For example, one corneal curvature may lie in an x-direction of the eye and the second corneal curvature may lie in a y-direction of the cornea. This has the advantage that aberrations of the cornea, in particular astigmatism, can be better treated.Furthermore, it is preferably provided that at least one corneal asphericity is additionally predefined for the corneal shape to be achieved. In this case, preferably exactly one corneal asphericity can be predetermined. This means that, in addition to the one or the two corneal curvatures, the corneal asphericity to be achieved can also be predefined, as a result of which further aberrations, in particular coma or distortions, can be compensated.According to a further advantageous embodiment, it is provided that in step c) two predetermined ablation depths are predetermined at respectively predetermined positions between the preoperative corneal shape and the corneal shape to be achieved. In other words, the ablation depth in the z direction is specified not only at a specified position in the x-y direction, but also at a second specified position which has different x-y coordinates than the first position. Thus, the corneal shape to be achieved and thus the tissue to be removed can be adapted even more accurately, which improves a treatment with the treatment device.Preferably, it is provided that when two predetermined ablation depths are specified for the corneal shape to be achieved, either a corneal curvature or a corneal asphericity is specified, the respective other one being mathematically calculated. In other words, when specifying two predetermined ablation depths, the corneal shape to be achieved can either be adapted on the basis of the corneal curvature such that the surface of the corneal shape to be achieved runs through both ablation depths, or the corneal asphericity can be aligned such that the corneal shape to be achieved runs through both ablation depths, it being possible for the respective other to be mathematically calculated depending on whether the corneal curvature or the corneal asphericity is specified. The mathematical calculation can be carried out by means of known mathematical methods, in particular by means of the two predetermined ablation depths as intersection points of the corneal shape. This results in the advantage that an even more precise adaptation of the tissue to be removed can be achieved.According to a further advantageous embodiment, it is provided that the at least one predetermined position in the x-y direction is in the middle of the cornea. In particular, if two ablation depths are predetermined at two positions, at least one of the two ablation depths may be predetermined in the middle of the cornea. The center of the cornea means, for example, the center of the optical axis in the cornea. The specification of the ablation depth in the middle of the cornea has the advantage that an effect of the correction is greatest here and this can be set most accurately by the specified ablation depth.In a further advantageous embodiment, it is provided that the at least one predetermined ablation depth for the at least one predetermined position is zero or has a thickness of an epithelial layer. In other words, it can be established that no ablation is to take place at the one predetermined position or at most a thickness of the epithelial layer which can grow after the treatment is ablated. This enables regions which are not to be treated to be determined in an improved manner.According to a further advantageous embodiment, it is provided that a minimum ablation depth for the tissue to be removed in the cornea at each position in the x-y direction satisfies the following conditions:at the respective position tissue is present between the associated corneal shapes;the minimum ablation depth is greater than or equal to a predetermined minimum value;the minimum ablation depth is greater than or equal to a thickness of an epithelial layer of the cornea;wherein the minimum ablation depth is set to 0 or a thickness of the epithelial layer for positions not satisfying these conditions. In other words, in this embodiment, it is additionally possible to check for the determined tissue to be removed whether a minimum ablation depth is provided at each position in the x-y direction. It can be checked whether tissue to be removed at all between the surfaces of the fabric to be removed.This means that reference corneal shapes are present, i.e. greater than or equal to 0. Furthermore, a minimum value can be specified, wherein the minimum ablation depth at each position must be greater than or equal to this minimum value. As another condition, it may be checked whether the minimum ablation depth is equal to or beyond a thickness of an epithelial layer. If one or more of these conditions are not fulfilled, then for each position for which these conditions are not fulfilled, ablation can be set to 0, that is to say not to be removed or to a thickness of the epithelial layer which can subsequently grow after the treatment. The minimum value can be predefined in such a way that stroma is also achieved in the case of real perturbation operations. For example, positions that would not reach 5 micrometers by time cannot be irradiated. The predefined minimum value can be, for example, between 1 and 12 micrometers, in particular 5 micrometers. This embodiment has the advantage that ablation can be limited and is not unnecessarily irradiated at positions where the irradiation has no effect.In a further advantageous embodiment, it is provided that it is determined whether a maximum ablation depth for the tissue to be removed in the cornea at each position in the x-y direction is less than or equal to a predefined maximum value, wherein the maximum ablation depth is set to zero or to a thickness of the epithelial layer or to the predefined maximum value for positions which are greater than the predefined maximum value. In other words, a maximum ablation depth is also limited by checking beforehand whether a predefined maximum value is exceeded. Thus, too much stroma tissue can be prevented from being removed. For example, the predefined maximum value in the z direction can apply to positions that would reach over 100 micrometers, wherein the value can be between 50 and 160 micrometers, preferably between 90 and 120 micrometers. If this value is exceeded, the ablation depth for these positions can be set to 0, that is to say not to be treated, or to a thickness of the epithelial layer or to the predefined maximum value.In a further advantageous embodiment, it is provided that a region is specified in the ablation data, which region bounds the tissue to be removed in the x-y direction, wherein the region is specified in a circular or elliptical manner or by specified value pairs which define a circumference. In other words, not only the ablation depth, but also the region in the x-y direction in which the irradiation is to take place can be limited. In this case, it is preferably provided that the region is predetermined in a circular manner, that is to say with a center and a radius, or in an ellipsoidal manner, that is to say with a center point and two predetermined radii, or by predetermined x-y value pairs which define a circumference, it also being possible for the circumference to be defined by a plurality of associated radii and angles (theta angles). This embodiment has the advantage that the tissue to be removed can be bounded in the x-y direction, as a result of which less tissue has to be removed.A second aspect of the present invention relates to a control device which is configured to carry out one of the methods described above. The advantages listed above are obtained. The control device can be designed, for example, as a control chip, control device or user program ("app"). The control device can preferably have a processor device and / or a data memory. A processor device is understood to mean an apparatus or an apparatus component for electronic data processing. The processor device can have, for example, at least one microcontroller and / or at least one microprocessor. The optional data memory can preferably store a program code for carrying out the method according to the invention. The program code can then be designed to cause the control device, when executed by the processor device, to carry out one of the above-described embodiments of one or both methods according to the invention.A third aspect of the present invention relates to a treatment apparatus having at least one eye-surgery laser for separating tissue predefined by the control data, in particular a corneal volume having predefined boundary surfaces of a human or animal eye by means of photodisruption and / or photoablation, and having at least one control device for the laser or lasers which is designed to carry out the steps of the method according to the first aspect of the invention. The treatment device according to the invention makes it possible that the disadvantages occurring when using conventional ablative treatment devices are reliably reduced or even avoided.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 100 nm and 1400 nm, preferably between 700 nm and 1200 nm, at a respective pulse duration between 1 fs and 20 ns, preferably between 1 fs and 10 ps, and a repetition frequency greater than 1 kilohertz (KHz), preferably between 100 KHz and 100 megahertz (MHz). Such a femtosecond laser is particularly well suited for removing tissue within the cornea. The use of photodisruptive and / or photoablative lasers in the method according to the invention additionally has the advantage that the irradiation of the cornea can take place in a wavelength range from 100 nm, which is particularly advantageous for excimer or ablation systems. This region is subsumed in laser technology under the term "deep ultraviolet". A lower limit of 100 nm advantageously prevents unintentional damage to the cornea from occurring due to these very short-wave and high-energy beams. Photodisruptive lasers of the type used here usually introduce pulsed laser radiation with a pulse duration between 1 fs and 20 ns into the corneal tissue. As a result, the power density of the respective laser pulse required for the optical breakdown can be spatially narrowly limited, so that a high cutting accuracy is made possible during the generation of the boundary surfaces. The wavelength range selected can also be, in particular, the range between 700 nm and 780 nm.In further advantageous embodiments of the treatment apparatus according to the invention, the control device can have at least one storage device for at least temporarily storing at least one control data set, wherein the control data set or sets comprise control data for positioning and / or for focusing individual laser pulses in the cornea / 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. The control data set mentioned here comprises the control data for removing the tissue determined in the method.Further features and their advantages can be gathered from the descriptions of the first aspect of the invention, wherein advantageous configurations of each aspect of the invention are to be regarded as advantageous configurations of the respective other aspect of the invention.A fourth aspect of the invention relates to a computer program comprising instructions which cause the treatment apparatus according to the third aspect of the invention to execute the method steps according to the first aspect of the invention and / or the method steps according to the second aspect of the invention.A fifth aspect of the invention relates to a computer-readable medium on which the computer program according to the fourth aspect of the invention is stored. Further features and their advantages can be gathered from the descriptions of the first to fourth aspects of the invention, advantageous configurations of each aspect of the invention being regarded as advantageous configurations of the respective other aspect 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, and the features and combinations of features mentioned below in the description of the figures and / or shown alone in the figures, can be used not only in the respectively specified combination but also in other combinations without departing from the scope of the invention. Therefore, embodiments of the invention are also to be considered as included and disclosed which are not explicitly shown and explained in the figures, but which emerge from the explained embodiments and can be generated by separate combinations of features. Embodiments and combinations of features are also to be considered as disclosed, which therefore do not have all features of an originally formulated independent claim. Furthermore, embodiments and combinations of features, in particular by the embodiments set forth above, are to be considered as disclosed which go beyond or deviate from the combinations of features set forth in the references of the claims. The following shows:The following shows: FIG. 1 shows a schematic illustration of a treatment apparatus according to the invention according to an exemplary embodiment; FIG. 2 shows a schematic method diagram for providing control data for an eye-surgery laser of a treatment device for the removal of tissue; FIGS. 3a / 3b show an exemplary application with reference to a cornea's myopie.In the figures, identical or functionally identical elements are provided with the same reference numerals.FIG. 1 shows a schematic representation of a treatment device 10 with an eye-surgical laser 12 for removing a tissue 14 from a cornea (cornea) 16 of a human or animal eye by means of photodisruption and / or photoablation. The tissue 14 can be, for example, a lentivirus or else a volume body which can be separated from the cornea 16 of the eye by means of the eye surgical laser 12 in order to correct a refractive error. A geometry of the tissue 14 to be removed can be provided by a control device 18, in particular in the form of control data, so that the laser 12 emits pulsed laser pulses in a pattern predefined by the control data into the cornea 16 in order to remove the tissue 14. Alternatively, the control device 18 can be a control device 18 external with respect to the treatment apparatus 10.Furthermore, FIG. 1 shows that the laser beam 20 generated by the laser 12 can be deflected in the direction of the cornea 16 by means of a beam device 22, namely a beam deflection device such as a rotational scanner, for example, in order to remove the tissue 14. The beam deflector 22 may also be controlled by the controller 18 to remove the tissue 14.The laser 12 illustrated can preferably be a photodisruptive and / or photoablative laser which is designed to emit laser pulses in a wavelength range between 100 nanometers and 1400 nanometers, preferably between 700 nanometers and 1200 nanometers, at a respective pulse duration between 1 femtosecond and 20 nanoseconds, preferably between 10 femtoseconds and 10 picoseconds, and a repetition frequency greater than 1 kilohertz, preferably between 100 kilohertz and 100 megahertz. The control device 18 optionally also has a storage device (not shown) for at least temporarily storing at least one control data set, wherein the control data set or sets comprise control data for positioning and / or focusing individual laser pulses in the cornea. The position data and / or focusing data of the individual laser pulses, i.e. the geometry of the tissue 14, is determined on the basis of the method described below.In FIG. 2, a schematic method diagram for providing control data for the eye surgical laser 12 of the treatment apparatus 10 for the removal of the tissue 14 is shown, wherein the following steps are carried out by the control device 18.In a step S 10, a preoperative corneal shape of the cornea 16 is determined from predetermined examination data. The preoperative corneal shape can have, for example, a corneal curvature and asphericity, wherein, in addition to the corneal shape, a position and shape of a stroma tissue of the cornea 16 and an epithelial layer of the cornea 16, in particular an anterior and posterior epithelial surface (AES, PES), can also be determined. The predetermined examination data can originate, for example, from topography-guided examination data of the eye or from wavefront-guided examination data.In a step S 12, the corneal shape to be achieved is additionally determined from the predetermined examination data. The corneal shape to be obtained is the shape to be obtained after treatment with the treatment device 10 for the eye. For this purpose, the corneal shape to be achieved can be determined by means of known methods, in order to obtain, for example, a refractive correction of the eye. For this purpose, at least one corneal curvature can be specified for the corneal shape to be achieved, in particular exactly one corneal curvature or two corneal curvatures. Furthermore, a corneal asphericity may additionally be predefined, which the cornea 16 is intended to have after the treatment.Subsequently, in a step S 14, at least one predetermined ablation depth can be predefined, which is to be achieved in a z-direction or depth direction of the eye at least at one predefined position in an x-y direction between the preoperative corneal shape and the corneal shape to be achieved. This ablation depth may be, for example, a stromal depth or an overall depth to a posterior epithelial surface. Preferably, two predetermined ablation depths can also be predetermined at respectively different predetermined positions between the preoperative corneal shape and the corneal shape to be achieved, wherein in this case either a corneal curvature or a corneal asphericity can be predetermined for the corneal shape to be achieved and the respectively other non-predetermined parameter of the corneal shape can then be mathematically calculated by means of the two predetermined ablation depths and the predetermined parameter.The at least one predetermined ablation depth can also be determined, for example, from the predetermined examination data, wherein it can be established, for example, that a predetermined position in the x-y direction of the cornea 16 must necessarily be ablated by the amount predetermined with the ablation depth in order to achieve the desired treatment result or that no tissue is to be applied at a position, i.e., the ablation depth is set to zero. For example, at least one of the predetermined positions in the x-y direction can lie in the center of the cornea 16, i.e. centrally in the optical axis, so that the desired amount of tissue 14 can be removed securely here. Alternatively, in certain treatments, it can also be provided that the predetermined ablation depth for the predetermined position is at 0, i.e. that no tissue is ablated or that the predetermined ablation depth has a thickness of an epithelial layer of the cornea 16.With these data, the ablation data for removing the tissue 14 can then be determined in a step S 16, wherein for this purpose the preoperative corneal shape is used as starting point and the corneal shape to be achieved is related to the latter in such a way that the predetermined ablation depth is present at the predetermined position in the x-y direction between the two corneal shapes. The tissue 14, which is then between the related corneal shapes, may then be marked as tissue to be removed.In other words, in step S 16, the preoperative corneal shape and the corneal shape to be achieved can be superimposed in a coordinate system. Subsequently, the corneal shape to be achieved can be displaced along the z-direction of the coordinate system in such a way as to the preoperative corneal shape until the predetermined ablation depth is reached at the predetermined position in the x-y direction between the two corneal shapes. The corneal shape to be achieved in this way can then be subtracted from the preoperative corneal shape. Thus, regions in which the difference has a positive coefficient and regions having a negative coefficient can be represented in the coordinate system. The regions with positive coefficients mean that tissue is present between the preoperative corneal shape and the corneal shape to be achieved, which tissue can be defined as tissue to be removed in the ablation data. Regions with negative coefficients of subtraction can indicate, for example, that no corneal tissue is present here and, speaking pictorially, tissue should rather be "added", which is not possible by the treatment, however. These areas are defined as tissue not to be treated, which means that no ablation takes place in these areas.It is preferable to set, as another condition for the tissue to be removed, a minimum ablation depth for the tissue to be removed in the cornea 16 at each position in an x-y plane to be in accordance with the following predetermined conditions, the minimum ablation depth being set to be 0 or a thickness of the epithelial layer of the cornea 16 for positions not in accordance with the following conditions. As a first condition, tissue must be present at the respective position between the related corneal shapes. As a second condition, a minimum value can be predefined in order to ensure that stroma of the cornea 16 is also reached in the case of real perturbations, wherein positions at which the predefined minimum value of the ablation depth is not reached are then not subjected to load at all, that is to say are treated by ablation. The predefined minimum value can be, for example, between 1 and 12 micrometers, preferably 5 micrometers. The predetermined minimum value can be derived from experience values, in particular from previously carried out treatments with the treatment device 10. As a third condition, it can be provided that the minimum ablation depth at each position is greater than or equal to a thickness of the epithelial layer of the cornea 16, since if the ablation depth does not exceed the thickness of the epithelial layer of the cornea 16, no treatment success can be achieved since the epithelial layer regenerates.Additionally or alternatively, a maximum ablation depth at each position in the x-y direction for the tissue 14 to be removed can also be predefined for the minimum ablation depth by checking whether the respective positions in the x-y plane of the eye are less than or equal to a predefined maximum value. The predetermined maximum value may serve to prevent too much stroma from being removed from the cornea 16, which value may be determined from empirical values and / or the predetermined examination data. For example, positions which penetrate over 100 micrometers into the cornea 16, i.e. in the depth direction, cannot be stressed or only deepithelized or "saturated" up to the predetermined maximum value. The predefined maximum value can be between 50 and 150 micrometers in the depth direction, in particular 100 micrometers.Furthermore, a region of the tissue to be removed in the ablation data can be laterally delimited in the x-y plane of the cornea 16, so that tissue of the eye which does not contribute to the correction of the refractive error is not irradiated. For this purpose, the region can be predetermined, for example, in the shape of a circle, ellipse or by a defined circumference.Finally, in a step S 18, the control data for controlling the eye surgical laser 12 can be provided, which data comprise the previously determined ablation data for removing the tissue 14.FIGS. 3 aand 3 b show an exemplary application with reference to a myopie (temporary vision) of a cornea, in which a position 24 with a predetermined ablation depth is predetermined. Here, FIG. 3 ashows a preoperative corneal shape 26 (solid line), which can be an anterior epithelial layer (AES). The abscissa in this figure may represent an x direction of the cornea 16, and the ordinate may represent a z direction, i.e., the depth direction. Thus, a cross-section of the cornea 16 is shown in two dimensions, it being understood by those skilled in the art that the cornea 16, particularly the corneal shape 26, is three-dimensional.In this example, the preoperative corneal shape 26 may have, for example, a corneal curvature of 6.1 millimeters (radius of curvature) with a corneal asphericity of -2.0 (outward curvature). Furthermore, a posterior epithelial layer 28 (PES) is illustrated (dotted line), wherein, viewed from the posterior epithelial layer 28 in the depth direction (z-axis), a stroma of the cornea 16 can run. In addition, FIG. 3 ashows the corneal shape 30 to be achieved (dashed line), which has been related to the preoperative corneal shape 26 in such a way that the predefined ablation depth results at the predefined position 24, wherein this ablation depth can be selected in this example such that a difference between the posterior epithelial layer 28 and the corneal shape 30 to be achieved at the predefined position 24 is 0 micrometers. Furthermore, it can be specified from predetermined examination data that a corneal curvature of the corneal shape 30 to be achieved is 7.8 millimeters and a corneal asphericity is -0.2.Using the method of the present invention, the tissue to be removed is the tissue that is located between the preoperative corneal shape 26 and the corneal shape 30 to be obtained.The tissue to be removed or the ablation depth for the example shown in FIG. 3 ais illustrated in FIG. 3 b. The x-axis is here the same as in FIG. 3 a, and the ablation depth is indicated in micrometers on the z-axis. On the right-hand side of FIG. 3 b, at the predefined position 24, which is approximately 1.5 millimeters in the x-direction, it can be seen that the predetermined ablation depth of 0 micrometers between the posterior epithelial layer 28 and the corneal shape 30 to be achieved limits the ablation and, moreover, no tissue to be removed is present, that is >1.5 millimeters in the x-direction, since the subtraction of the corneal shape 30 to be achieved from the preoperative corneal shape 26 is "negative" in this region or lies in an epithelial layer of the cornea 16 (dashed line 30 lies further outwards than solid line 26 or dotted line 28, compare FIG. 3 a ). A boundary is shown on the left side at position 32 at approximately 120 micrometers in the z direction and 2.5 millimeters in the x direction, wherein the position 32, in particular the ablation depth of approximately 120 micrometers, can be defined by a predefined maximum value, which limits a maximum ablation depth for the tissue to be removed. Thus, an optical zone of only about 4 millimeters is obtained overall, which is required for the correction of the myopie.The preceding example of FIGS. 3 aand 3 bhas been described with reference to a autopilot with a predefined ablation depth. In a further embodiment, it is also possible to specify two ablation depths at different positions, wherein preferably a further ablation depth can be specified in the middle (vertex) of the preoperative corneal shape 26, wherein in this case either the corneal curvature or the corneal asphericity can be specified for the corneal shape 30 to be achieved and the respectively non-specified parameter can be calculated.Both methods, i.e. with exactly one predetermined ablation depth and with two predetermined ablation depths, allow the correction of corneal shapes, in particular for cases with measurable topography. Furthermore, both models make it possible to adapt the corneal shape to a selectable optimum, in particular to change a corneal curvature, to correct the refractive power and higher optical aberrations, to center a corneal shape and / or to reduce a corneal curvature gradient. Both methods can avoid excessive ablation and the resulting ablation volumes provide an optical zone size and centering that is not directly controllable in other methods used heretofore.Overall, the examples show how a topography-guided treatment calculation with a limited ablation volume can be achieved by the invention.

Claims

Method for providing control data for an eye-surgical laser (12) of a treatment apparatus (10) for the removal of a tissue (14), wherein the method has the following steps, carried out by a control device (18): a) determining (S10) a preoperative corneal shape (26) of a cornea (16) of a human or animal eye from predetermined examination data; b) determining (S12) a corneal shape (30) to be achieved from the predetermined examination data; c) defining (S14) exactly one or exactly two predetermined ablation depths which are to be achieved in a z-direction at at least one predetermined position (24) in an x-y direction between the preoperative corneal shape (26) and the corneal shape (30) to be achieved; d) determining (S16) ablation data for the removal of the tissue (14), wherein, for determining the ablation data, the preoperative corneal shape (26) is related to the corneal shape (30) to be achieved in such a way that the predetermined ablation depth results at the predetermined position (24) between the two corneal shapes, wherein tissue of the cornea (16), which is localized between the related corneal shapes, is defined in the ablation data as tissue (14) to be removed, wherein the corneal shapes (26, 30) are placed one above the other and subsequently the corneal shape (30) to be achieved is displaced along the z-direction to the preoperative corneal shape until the predetermined ablation depth is achieved at the at least one predetermined position (24) between the preoperative corneal shape (26) and the corneal shape to be achieved, wherein the predetermined ablation depth is achieved by subtracting the corneal shape (30) to be achieved which is aligned with the predetermined ablation depth, In the present invention, a difference is formed from the preoperative corneal shape (26), wherein regions having a positive difference are set as tissue (14) to be removed and regions having a negative difference are set as tissue not to be treated; and e) providing (S18) control data for controlling the eye surgery laser (12), which control data use the ablation data for removing the tissue (14).Method according to claim 1, characterised in that at least one corneal curvature is predetermined for the corneal shape (30) to be achieved.Method according to claim 2, characterised in that two corneal curvatures are predetermined for the corneal shape (30) to be achieved.Method according to one of Claims 2 or 3, characterized in that at least one corneal asphericity is additionally predefined for the corneal shape (30) to be achieved.Method according to one of the preceding claims, characterized in that in step c) two predetermined ablation depths are predetermined at respectively predetermined positions between the preoperative corneal shape (26) and the corneal shape (30) to be achieved.Method according to claim 5, characterised in that either a corneal curvature or a corneal asphericity is predetermined for the corneal shape (30) to be achieved, the respective other being mathematically calculated.Method according to one of the preceding claims, characterized in that the at least one predetermined position in the x-y direction is in the middle of the cornea.Method according to any of the preceding claims, characterized in that the at least one predetermined ablation depth for the at least one predetermined position is zero or has a thickness of an epithelial layer.Method according to one of the preceding claims, characterized in that a minimum ablation depth for the tissue (14) to be removed in the cornea (16) at each position in the x-y direction satisfies the following conditions: - tissue is present between the related corneal shapes at the respective position; - the minimum ablation depth is greater than or equal to a predetermined minimum value; - the minimum ablation depth is greater than or equal to a thickness of an epithelial layer of the cornea; wherein the minimum ablation depth is set to zero or to a thickness of the epithelial layer for positions which do not satisfy these conditions.Method according to one of the preceding claims, characterized in that it is determined whether a maximum ablation depth for the tissue to be removed in the cornea (16) at each position in the x-y direction is less than or equal to a predetermined maximum value, wherein the maximum ablation depth is set to zero or to a thickness of the epithelial layer or to the predetermined maximum value for positions which are greater than the predetermined maximum value.Method according to one of the preceding claims, characterized in that a region which delimits the tissue to be removed in the x-y direction is specified in the ablation data, wherein the region is specified in the form of a circle or ellipse or by specified value pairs which define a circumference.Control device (18) which is designed to carry out a method according to one of the preceding claims.Treatment device (10) having at least one eye-surgery laser (12) for removing a tissue (14) of a human or animal eye, in particular a tissue lenticle, by means of photodisruption and / or photoablation and at least one control device (18) according to Claim 12.Treatment device (10) according to claim 13, characterised in that the laser (12) is designed to emit laser pulses in a wavelength range between 100 nm and 1400 nm, preferably between 700 nm and 1200 nm, at a respective pulse duration between 1 fs and 20 ns, preferably between 10 fs and 10 ps, and a repetition frequency greater than 1 KHz, preferably between 100 KHz and 100 MHz.Treatment apparatus (10) according to one of Claims 13 or 14, characterized in that the control device (18) - has at least one storage device for at least temporarily storing at least one control data record, wherein the control data record or records comprise control data for positioning and / or focusing individual laser pulses in the cornea; and - comprises at least one beam device (22) for beam guidance and / or beam shaping and / or beam deflection and / or beam focusing of a laser beam (20) of the laser (12).A computer program comprising instructions for causing the treatment device (10) according to any one of claims 13 to 15 to execute a method according to any one of claims 1 to 11.A computer readable medium on which the computer program of claim 16 is stored.

Images