Method for controlling a laser of a processing device for separating a solid body, processing device, computer program and computer-readable medium

Abstract

Method for controlling a laser (18) of a processing device (10) for separating a volume body (12) with an anterior interface (16) and with a posterior interface (14) made of a material, wherein the method is carried out by means of a control device (20) of the processing device (10) and comprises at least the following method steps: - Determining a depth relief (48) to be generated of the volume body (12) between the anterior interface (16) and the posterior interface (14) depending on at least one piece of information; - Determining a reference point (52) of an axis of symmetry of the determined depth relief (48) or of a respective interface (14, 16) by means of the control device (20), wherein the depth relief (48) is formed by a difference between the anterior interface (16) and the posterior interface (14); and - Controlling the laser (18) starting from the defined reference point (52) in at least partially circular paths such that this pulsed laser pulses emit the material in a sequence of shots in a predefined pattern, wherein the interfaces (14, 16) of the volume body (12) to be separated are defined by the predefined pattern and the interfaces are generated by means of an interaction of the individual laser pulses with the material by generating a multitude of cavitation bubbles (40) along the circular paths.

Description

[0001] The invention relates to a method for controlling a laser of a processing device for separating a solid body with an anterior interface and a posterior interface made of a material. Furthermore, the invention relates to a processing device, a computer program, and a computer-readable medium.

[0002] Clouding and scarring within the cornea caused by inflammation, injury, or congenital diseases, as well as refractive errors such as myopia or hyperopia, impair vision. Clear vision is significantly impaired, particularly when these pathological and / or abnormally altered areas of the cornea are located in the visual axis of the eye. In a conventional procedure, these altered areas are removed through a procedure called phototherapeutic keratectomy (PTA) using an ablative laser, such as an excimer laser. However, this is only possible if the pathological and / or abnormally altered areas of the cornea are located in the superficial layers of the cornea. Deeper areas, particularly within the stroma, cannot be reached using ablative laser procedures.In this case, additional measures must be taken, such as exposing the deeper areas by means of an additional corneal incision.

[0003] In particular, it is known that when using so-called femtosecond systems, corresponding xyz movements are performed in space to generate corresponding cavitation bubbles, thus creating an extractable lenticule that allows for correction. The z-direction, in other words, the depth direction, is particularly problematic, as the entire laser device must be moved. This results in problems, for example, with the speed or control of the laser device, especially with moving the laser device in the corresponding z-direction.

[0004] In order to be able to carry out a beneficial treatment on the patient, it is important that the cavitation bubbles can be generated with appropriate precision and, in order to shorten the treatment time, that the cavitation bubbles can be generated quickly.

[0005] US 2007 / 0 282 313 A1 describes the use of optical coherence tomography (OCT) to visualize corneal surface elevation and thickness. OCT maps are used to plan laser procedures to treat irregular, cloudy, or weakened corneas and to treat refractive errors. In phototherapeutic keratectomy (PTK) with an excimer laser, OCT data is used to plan the ablation depth required to restore a smooth optical surface. In photorefractive keratectomy with an excimer laser, OCT mapping of epithelial thickness is used to achieve clean laser epithelial ablation.Anterior femtosecond laser keratoplasty uses OCT data to plan the depth of femtosecond laser dissection to remove the anterior layer of the cornea, leaving a uniformly thick, smooth recipient bed to receive a disc of donated corneal tissue.

[0006] It is therefore an object of the present invention to provide a method and a processing device for controlling a laser for separating the solid body from a human or animal cornea, which overcomes the disadvantages of the prior art. In particular, the object of the invention is to be able to produce the solid body in a technically simple manner.

[0007] This object is achieved by a method, a processing device, a computer program, and a computer-readable medium according to the independent patent claims. Advantageous embodiments with expedient refinements of the invention are specified in the respective subclaims, wherein advantageous embodiments of the method are to be regarded as advantageous embodiments of the processing device, the computer program, and the computer-readable medium, and vice versa.

[0008] A first aspect of the invention relates to a method for controlling a laser of a processing device for separating a volume body with an anterior interface and with a posterior interface made of a material, in particular a cornea of ​​an eye, in particular a human or animal cornea. The method is carried out by means of a control device of the processing device. A depth relief to be generated of the volume body between the anterior interface and the posterior interface is determined as a function of at least one piece of information, in particular patient information. A reference point of an axis of symmetry of the determined depth relief or of a respective interface is determined by means of a control device of the processing device.Starting from the specific reference point, the laser is controlled in at least partially circular paths such that this pulsed laser pulse is emitted into the material in a shot sequence in a predefined pattern, wherein the interfaces of the volume body to be separated are defined by the predefined pattern and the interfaces are created by means of an interaction of the individual laser pulses with the cornea by generating a plurality of cavitation bubbles along the circular paths.

[0009] This allows for the generation of cavitation bubbles with reduced effort. In particular, the corresponding depth relief can be evaluated depending on the determined reference point, whereby the cavitation bubbles can be generated with less effort, especially in the z-direction. In particular, a reference point of a quasi-axis of symmetry or a quasi-center of symmetry is thus described. As a reference point, for example, a center of gravity, a centroid, a barycenter, or even a center of a not "perfectly" symmetrical volume body can be determined. Furthermore, it is possible to determine appropriate reference points, for example the center of gravity as a reference point, through minimization in the case of asymmetric cernits.It can then be provided, for example, that the reference point does not coincide with a point of symmetry of the solid body, in particular viewed in the xy direction, whereby the depth relief can nevertheless be reliably generated at least in the z direction.

[0010] The paths generated by the cavitation bubbles can thus be generated as a type of iso-contour line, where height refers in particular to the z-direction. In other words, paths are determined, with the cavitation bubbles on the respective path preferably being located essentially at the same height (iso-height) relative to the z-direction of the laser device. The laser device can also be referred to as a laser.

[0011] The material can be considered to be a human or animal eye, especially a cornea. The laser can be designed as an ophthalmic surgical laser. The processing device can also be referred to as a treatment device.

[0012] In particular, the invention proposes that a reference point, for example a center of gravity, be determined from the corresponding xyz coordinates for the section of the volume body within the cornea, which in turn corresponds to a type of center of symmetry. This can be determined for both the posterior interface and the anterior interface, in particular separately from each other. In particular, the weightings of the z-positions are evenly distributed around this reference point. This point, which corresponds to the reference point, can then in turn represent a starting point or an end point for generating the cavitation bubbles, in particular along a path or trajectory.In other words, this means that the start of the generation of the cavitation bubbles does not correspond to the center of the treatment, but that the reference point is deliberately determined to be decentered in order to create simpler movements of the laser device in the z-direction. This decentering can be carried out using, for example, a scanner device of the processing device. Alternatively or additionally, the decentering can also be carried out by moving the eye or the patient. This means that the patient or the eye itself can be docked to the system and moved to the scanner device, or the system can deliberately and automatically dock the patient decentered so that the neutral position of the scanner is in this barycenter.From this point on, depending on whether the reference point was defined as the start or end, the quasi iso-contour lines can be generated. The quasi iso-contour lines, especially in the z-direction, are thus generated using the cavitation bubbles with minimal z-effort. This is advantageous because the scanner, in particular, is known to move more slowly in the z-direction than in the xy-direction.

[0013] The z-direction is understood in particular to be the direction that extends essentially parallel to the laser beam and / or to the optical axis of the laser device. The x-direction and the y-direction are then considered perpendicular to the z-direction, with the x-direction also being perpendicular to the y-direction.

[0014] As an alternative to determining the center of symmetry using the center of gravity, the opposite procedure can be used: first, the iso-contour lines can be determined and then, for example, the center of symmetry can be determined using a centroid of all iso-contour lines, which in turn determines a pseudo-center of all possible iso-contour lines. Alternatively, instead of using the iso-contour lines, the cavitation bubble paths can simply be traced in a spiral, circular, or elliptical manner, particularly with reduced z-axis effort. Due to the decentration, clipping may have to be performed at the edges, typically using some kind of optical shutter or a pulse picker, in order to ultimately achieve the desired shape in relation to the treatment center, particularly from a clinical rather than a technical perspective.

[0015] An advantageous embodiment provides for a possible tilt, or pivoting, to be determined based on the xyz coordinates or the iso-contour lines, and for this to be deliberately compensated for by further decentering, for example, depending on the curvature of a patient interface. In this case, the scanner itself is not relocated; rather, the relocation occurs either via the patient interface or via the eye, so that the curvature of the patient interface with respect to the eye counteracts this tilt.

[0016] Alternatively, it could be provided, for example, that the xyz coordinates of the section itself within the cornea are not used, but rather the xyz coordinates of the section from the perspective of or relative to the patient interface. This, in particular, has a zero position that does not have to coincide with the cornea coordinates. In particular, if, for example, a curved user interface / patient interface is used, the xyz coordinates based on the user interface would also take into account the sagitta of the user interface—that is, in the case of a circular arc, the distance from the center of the arc to the center of its base—which results in less overhead for the scanner.

[0017] Alternatively, it can be provided that neither the xyz coordinates of the section nor the xyz coordinates of the patient interface are used, but rather the xyz coordinates of the section from the scanner's perspective, particularly in the z-direction, which corresponds in particular to the corresponding control values. The scanner itself, in turn, has a different zero position. The xyz coordinates of the scanner device would take into account not only the sagitta of the patient interface, but also the different refractive indices and geometries of the optical components and thus also the different travel paths per scanner increment, resulting in less overhead for the scanner.

[0018] The depth relief is, in particular, the volume body itself, i.e., the difference between the anterior and posterior surfaces. In particular, the anterior and posterior interfaces are determined based on the depth relief such that the lenticule corresponds to this depth relief. Furthermore, the reference point can be determined on both the anterior and posterior interfaces. Alternatively or additionally, a common reference point can also be determined for the anterior and posterior interfaces.

[0019] In particular, it is provided that, for example, the posterior interface is generated first, followed by the anterior interface. Alternatively or additionally, the anterior interface can be generated first, followed by the posterior interface. Alternatively, it is also possible for the cavitation bubbles to be generated essentially simultaneously for both the posterior interface and the anterior interface. For example, it can be provided that a cavitation bubble is generated first within the posterior interface, and then, as the next cavitation bubble, a cavitation bubble is generated within the anterior interface.

[0020] According to an advantageous embodiment, the depth relief is determined at the posterior interface. In particular, the depth relief is thus generated only at the posterior interface. In particular, a structure, shape, or profile of the depth relief is thus determined at the posterior interface. The anterior interface can, for example, be generated essentially parallel to a surface of the eye. This makes it possible to generate the solid body in a simple manner.

[0021] It is further advantageous if the control data are generated such that the anterior interface is generated substantially parallel to a surface of the material, in particular the eye. In particular, this allows the anterior interface to be generated in a simple manner. Furthermore, it enables the volume body, and in particular the depth relief, for example, at the posterior interface to be generated reliably.

[0022] A further advantageous embodiment provides for the generation of essentially circular, spiral, or elliptical paths. This makes it possible to easily generate cavitation bubbles along the spiral paths depending on the reference point, allowing the laser device or processing device to be operated with less effort.

[0023] It is also advantageous if the reference point is determined based on the thickest point of the solid to be created or on the thinnest point of the solid. In particular, the thinnest point corresponds, for example, to a minimum depth of the solid, and the thickest point to a maximum depth of the solid. This applies particularly in the z-direction. Alternatively or additionally, the highest or deepest point of the respective interface, viewed in the z-direction relative to the solid, can also be used as the respective reference point. This allows different reference points to be used, allowing the method to be used flexibly.

[0024] Furthermore, it has proven advantageous to use a mathematical minimization method to minimize asymmetry in the depth relief when determining the reference point. For example, rotational asymmetry can be minimized using the mathematical model. Furthermore, it should be noted that the asymmetry of the respective interfaces can also be minimized.

[0025] Furthermore, it can be provided that a potential change in the position of the eye as the material relative to the laser and / or a potential change in the position of the laser relative to the eye are taken into account when controlling the laser. In particular, even minimal movements of the eye relative to the laser or of the laser relative to the eye can be taken into account, which can minimize errors in the generation of cavitation bubbles. This allows for improved solid creation.

[0026] According to a further advantageous embodiment, the reference point is defined as the beginning or end of the circular path. This makes it possible to flexibly generate reference points for the patient, allowing, for example, individual patient needs to be addressed. Furthermore, appropriate situations during treatment can be addressed, and the design of the treatment device itself can also be taken into account.

[0027] It has also proven advantageous if the reference point is determined in such a way that it does not coincide with a center of symmetry of the solid body, viewed in the direction of the cavitation bubbles to be generated. In particular, the center of symmetry of the solid body and the reference point are thus formed differently. The reference point is thus determined independently of the center of symmetry of the solid body and is preferably dependent only on the depth relief to be generated.

[0028] It is also advantageous if the shape of a patient interface of the processing device for docking the material, particularly the eye, is taken into account when determining the reference point during treatment. The patient interface, in particular, has a zero position, which does not have to coincide with the cornea coordinates. Especially if, for example, a curved user interface is used, the xyz coordinates based on the user interface would also take into account the sagitta—that is, in the case of a circular arc, the distance from the center of the arc to the center of its base—of the user interface, thus resulting in less overhead for the scanner.

[0029] In a further advantageous embodiment, a lenticule-like volume body is removed from the corneal volume by photodisruption or the volume body is removed using an ablative procedure. Thus, the correction can be performed in two different ways and, for example, using two differently designed processing devices.

[0030] According to a further advantageous embodiment, the laser is controlled such that the laser emits laser pulses in a wavelength range between 300 nanometers and 1400 nanometers, in particular between 700 nanometers and 1200 nanometers, with a respective pulse duration between 1 fs and 1 ns, in particular between 10 fs and 10 ps, ​​and a repetition frequency greater than 10 kHz, in particular between 100 kHz and 100 MHz. Such lasers are already used for photodisruptive procedures, for example in eye surgery. The produced lenticule, which corresponds to the volume body, is subsequently removed via an incision in the cornea. The use of photodisruptive lasers in the method according to the invention also has the advantage that the cornea is not irradiated in a wavelength range below 300 nm. In laser technology, this range is subsumed under the term "deep ultraviolet."This advantageously prevents these very short-wave, high-energy beams from causing inadvertent damage to the cornea. Photodisruptive 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 required for optical breakthrough to be spatially limited, ensuring high cutting precision when creating the interfaces.

[0031] It is also advantageous if the laser is controlled in such a way that topographical and / or pachymetric and / or morphological data of the cornea are taken into account. In particular, topographical and / or pachymetric measurements of the cornea to be treated, as well as the type, location, and extent of, for example, pathological and / or abnormally altered areas within the corneal stroma, as well as corresponding refractive errors of the eye, can be taken into account. In this case, these data correspond in particular to the specified parameters or patient information.In particular, control data sets are generated at least by providing topographical and / or pachymetric and / or morphological data of the untreated cornea and by providing topographical and / or pachymetric and / or morphological data of the pathological and / or unnaturally altered area within the cornea to be removed or taking into account corresponding optical corrections to correct the visual defects.

[0032] A second aspect of the invention relates to a processing device with at least one laser for separating a volume body of a human or animal eye by means of photodisruption or an ablative method, and with at least one control device for the laser(s), which is designed to carry out the steps of the method according to the preceding aspect. The processing device also comprises a rotary scanner for the predefined deflection of the laser beam of the laser in the direction of the material to be treated, in particular the eye.

[0033] The laser is suitable for emitting laser pulses in a wavelength range between 300 nm and 1400 nm, preferably between 700 nm and 1200 nm, with a respective pulse duration between 1 fs and 1 ns, preferably between 10 fs and 10 ps, ​​and a repetition frequency greater than 10 kHz, preferably between 100 kHz and 100 MHz.

[0034] The processing device can also comprise a plurality, where "plurality" means at least two, of control devices, which are then in turn designed to carry out the method according to the invention. The control device(s) comprise, in particular, electronic components such as processors, circuits, for example, integrated circuits, and other electronic components in order to be able to carry out corresponding method steps.

[0035] In an advantageous embodiment of the processing device, the processing device has a storage device for at least temporarily storing at least one control data set, wherein the control data set(s) comprise control data for positioning and / or focusing individual laser pulses in the cornea and comprise 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. Said control data sets are typically generated based on a measured topography and / or pachymetry and / or morphology of the cornea to be treated and / or the type of pathological and / or abnormally altered area within the cornea to be removed and / or the refractive error of the eye to be corrected.

[0036] Further features and their advantages can be found in the descriptions of the first aspect of the invention, wherein advantageous embodiments of each aspect of the invention are to be regarded as advantageous embodiments of the respective other aspect of the invention.

[0037] A third aspect of the invention relates to a computer program comprising instructions that cause the processing device according to the second aspect of the invention to execute the method steps according to the first aspect of the invention. A fourth aspect of the invention relates to a computer-readable medium on which the computer program according to the third aspect of the invention is stored. Further features and their advantages can be found in the descriptions of the first and second aspects of the invention, with advantageous embodiments of each aspect of the invention being regarded as advantageous embodiments of the other aspect of the invention.

[0038] Further features emerge from the claims, the figures and the description of the figures. The features and combinations of features mentioned above in the description, as well as 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 respective combination specified, but also in other combinations without departing from the scope of the invention. Thus, embodiments are to be regarded as encompassed and disclosed by the invention that are not explicitly shown and explained in the figures, but which emerge and can be produced by separate combinations of features from the explained embodiments. Embodiments and combinations of features are also to be regarded as disclosed that therefore do not have all the features of an originally formulated independent claim.Furthermore, embodiments and combinations of features are to be regarded as disclosed, in particular by the embodiments set out above, which go beyond or deviate from the combinations of features set out in the reliances of the claims.

[0039] Showing: Fig. 1 is a schematic side view of an embodiment of a processing device; Fig. 2 shows a further schematic side view of an embodiment of a processing device; and Fig. 3 a schematic sectional view of a material, in particular of an eye; and Fig. 4 a schematic top view of an exemplary solid body.

[0040] In the figures, identical or functionally identical elements are provided with the same reference numerals.

[0041] Fig. 1 shows a schematic representation of a processing device 10 with a laser 18 for the separation of a predefined corneal volume / cornea volume or volume body 12. A cornea 44 ( Fig. 3) has predefined interfaces 14, 16 ( Fig. 2), wherein the cornea 44 is in particular that of a human or animal eye 42. The volume body 12 can be created by means of photodisruption. Alternatively, the volume body 12 can also be removed by means of an ablative process. In particular, a posterior actual boundary surface 14 and an anterior actual boundary surface 16 of the cornea 44 are shown. It can be seen that, in addition to the laser 18, a control device 20 is formed for the laser 18, so that it emits pulsed laser pulses, for example, in a predefined pattern into the cornea 44, wherein boundary surfaces 14, 16 of the volume body 12 to be separated are created by the predefined pattern, for example by means of photodisruption. The processing device 10 can also have further control devices.In the illustrated embodiment, the boundary surfaces 14, 16 of the volume body 12 form a lenticule-like volume body 12, wherein the position of the volume body 12 in this embodiment is selected such that a pathological and / or unnaturally altered region 32 (see . Fig. 2), for example, a visual impairment, is enclosed within a stroma 36 of the cornea 44. Furthermore, Fig. 1 shows that the so-called Bowman membrane 38 is formed between the stroma 36 and an epithelium 28.

[0042] Furthermore, it can be seen that the laser beam 24 generated by the laser 18 is deflected toward a surface 26 of the cornea by means of a beam device 22, namely a beam deflection device, such as a rotary scanner (scanner, scanner device). The beam deflection device is also controlled by the control device 20 to generate the aforementioned predefined pattern in the cornea.

[0043] The laser 18 shown is a photodisruptive laser or a laser 18 configured to emit laser pulses in a wavelength range between 300 nm and 1400 nm, preferably between 700 nm and 1200 nm, with a respective pulse duration between 1 fs and 1 ns, preferably between 10 fs and 10 ps, ​​and a repetition frequency greater than 10 kHz, preferably between 100 kHz and 100 MHz. Alternatively, the laser 18 can also be configured to remove the solid body 12 using an ablative method.

[0044] The control device 20 also has a memory 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 44. The position data and / or focusing data of the individual laser pulses are generated based on a previously measured topography and / or pachymetry and / or the morphology of the cornea and, for example, the pathological and / or abnormally altered region 32 to be removed or the optical refractive error correction to be produced within the stroma 36 of the eye 42. Furthermore, data such as the shape and position of the posterior actual boundary surface 14 of the cornea 44 and the anterior actual boundary surface 16 of the cornea 44 are also determined. These data are also referred to below as predefined parameters.

[0045] Fig. 2 shows a schematic diagram of the generation of the volume body 12 to be separated according to an embodiment of the present method. It can be seen that the interfaces 14, 16 of the volume body 12 are generated by means of the pulsed laser beam 24, which is directed via the beam deflection device 22 in the direction of the cornea 44 or in the direction of the surface 26 of the cornea 44. The interfaces 14, 16 of the volume body 12 form a lenticule-like volume body 12, which, for example, encloses the pathological and / or unnaturally altered region 32 within the stroma 36. Furthermore, in the illustrated embodiment, the laser 18 generates a further cut 34, which intersects the volume body 12 at a predefined angle and with a predefined geometry and extends up to the surface 26 of the cornea 44.The volume body 12 defined by the interfaces 14, 16 can then be removed from the cornea 44 via the incision 34. In the illustrated embodiment, the pathological and / or abnormally altered region 32 is formed within the stroma 36 and outside an optical axis 30 of the eye 42.

[0046] In the illustrated embodiment, the deeper interface, i.e., the interface of the volume body 12 located deeper in the eye 42 or the stroma 36, ​​can first be created using the laser beam 24. This can be achieved by guiding the laser beam 24 at least partially in a circular and / or spiral manner according to the predefined pattern. Subsequently, the higher interface of the volume body 12 is created in a comparable manner, so that the interfaces 14, 16 form the lenticular volume body 12. Subsequently, the cut 34 is also created using the laser 18. However, the order in which the interfaces 14, 16 of the volume body 12 and the cut 34 are created can also be changed.

[0047] Fig. 3 shows a schematic sectional view of the eye 44 with the solid body 12. In particular, it is shown that the solid body 12 has the anterior interface 16 and the posterior interface 14. In the present case, the eye 44 corresponds in particular to a material. In the present exemplary embodiment, the anterior interface 16 is formed in particular substantially parallel to a surface 46 of the eye 44. The posterior interface 14, in turn, has a deep relief 48. The solid body 12 has a center of symmetry 50. Furthermore, a reference point 52 is shown.

[0048] In the method for controlling the laser 18 of the processing device 10, the separation of the solid body 12 occurs in such a way that the depth relief 48 of the solid body 12 to be generated between the anterior interface 16 and the posterior interface 14 is determined as a function of the at least one piece of information, in particular patient information. The reference point 52 of an axis of symmetry of the determined depth relief 48 or of a respective interface 14, 16 is determined by means of the control device 20.The laser 18 is then controlled again, starting from the specific reference point 52, in at least partially circular paths such that this pulsed laser pulse is emitted into the cornea 44 in a firing sequence in a predefined pattern. The interfaces 14, 16 of the volume body 12 are defined by the predefined pattern, and the interfaces 14, 16 are created by means of an interaction of the individual laser pulses 40 with the cornea 44 by generating a plurality of cavitation bubbles 40 along the circular paths. In particular, the circular paths can be spiral or elliptical.

[0049] The symmetry point 50 is, in particular, a symmetry point, particularly viewed in the xy direction. The reference point 52 is, in particular, a center of symmetry with respect to the z coordinate. In particular, as shown in the Fig. 3, the reference point 52 is determined in such a way that it does not coincide with the center of symmetry 50 of the solid body 12 when viewed in the direction of the cavitation bubbles 40 to be generated.

[0050] The z-direction is understood in particular to mean the direction that extends substantially parallel to the laser beam 24 and / or to an optical axis of the beam device 22 or laser device. The x-direction and the y-direction are then again to be considered perpendicular to the z-direction, with the x-direction also being perpendicular to the y-direction.

[0051] It can be provided, for example, that the reference point 52 is determined as a function of the thickest point of the solid body 12 to be generated or a thinnest point of the solid body 12. Furthermore, it is particularly provided that a mathematical minimization method for minimizing an asymmetry of the depth relief 48 is used to determine the reference point 52.

[0052] Furthermore, it can be provided that a potential change in position of the eye 42 relative to the laser 18 and / or a potential change in position of the laser 18 relative to the eye 42 are taken into account when controlling the laser 18.

[0053] As already mentioned, the reference point 52 can be regarded as the beginning of the circular path or as the end of the circular path.

[0054] Furthermore, the Fig. 3 shows that the shape of a patient interface 54 of the processing device 10 for docking the eye 42 during treatment is also taken into account when determining the reference point 52. In particular, a deformation of the eye 42 during docking to the patient interface 54 can be taken into account when determining the reference point 52.

[0055] Fig. 4 shows a plan view of a volume body 12. In particular, a depth relief 48 is shown. For example, a first region 56 is not located as deep in the cornea 44 as a second region 58. Furthermore, it can be provided that a third region 60 is again at the same depth as the first region 56. A fourth region 62 can again be deeper than the first region 56 and the second region 60, wherein the fourth region 62 is again higher than the third region 58. Furthermore, a fifth region 64 is shown, which again is essentially on the same depth level and, for example, is higher than the regions 56, 58, 60, 62. In particular, in the Fig. 4 shows a so-called Zernik polynomial.

[0056] In particular, it is now provided that the reference point 52 is determined depending on the “altitudes” of these regions 56, 58, 60, 62 and is used as the starting point or end point of the cavitation bubbles 40 to be generated, and not the center of symmetry 50 of the volume body 12 to be generated.

Claims

[1] Method for controlling a laser (18) of a processing device (10) for separating a volume body (12) with an anterior boundary surface (16) and with a posterior boundary surface (14) made of a material, wherein the method is carried out by means of a control device (20) of the processing device (10) and comprises at least the following method steps: - determining a depth relief (48) of the volume body (12) to be generated between the anterior boundary surface (16) and the posterior boundary surface (14) as a function of at least one piece of information; - determining a reference point (52) of an axis of symmetry of the determined depth relief (48) or of a respective boundary surface (14, 16) by means of the control device (20), wherein the depth relief (48) is formed by a difference between the anterior boundary surface (16) and the posterior boundary surface (14); and - Controlling the laser (18) starting from the specific reference point (52) in at least partially circular paths such that said pulsed laser pulses emit the material in a shot sequence in a predefined pattern, wherein the boundary surfaces (14, 16) of the volume body (12) to be separated are defined by the predefined pattern and the boundary surfaces are generated by means of an interaction of the individual laser pulses with the material by generating a plurality of cavitation bubbles (40) along the circular paths. [2] Method according to claim 1, characterized by that the depth relief (48) is determined at the posterior interface (14). [3] Method according to claim 1 or 2, characterized by that the control data are generated such that the anterior interface (16) is generated substantially parallel to a surface (46) of the material. [4] Method according to one of the preceding claims, characterized bythat spiral or elliptical orbits are generated as essentially circular orbits. [5] Method according to one of the preceding claims, characterized by that the reference point (52) is determined as a function of a thickest point of the solid body (12) to be generated or a thinnest point of the solid body (12) to be generated. [6] Method according to claim 5, characterized by that a mathematical minimization method for minimizing an asymmetry of the depth relief (48) is used to determine the reference point (52). [7] Method according to one of the preceding claims, characterized by that the control data for removing the volume body (12) are generated in an eye (42) and / or in a cornea (44) of a human or an animal. [8] Method according to claim 7, characterized bythat a potential change in position of the eye (42) relative to the laser (18) and / or a potential change in position of the laser (18) relative to the eye (42) are taken into account when controlling the laser (18). [9] Method according to one of the preceding claims, characterized by that the reference point (52) is determined as the beginning of the circular path or as the end of the circular path. [10] Method according to one of the preceding claims, characterized by that the reference point (52) is determined in such a way that it does not coincide with a center of symmetry (50) of the volume body (12) viewed in the direction of the cavitation bubbles (40) to be generated. [11] Method according to one of the preceding claims, characterized by that a shape of a patient interface (54) of the processing device (10) for docking the material during a processing operation is taken into account when determining the reference point (52). [12] Method according to one of the preceding claims, characterized by that the control of the laser (18) is carried out in such a way that a lenticular solid body (12) is separated. [13] Method according to one of the preceding claims, characterized by that the control of the laser (18) is carried out in such a way that topographical and / or pachymetric and / or morphological data of the material are taken into account. [14] Method according to one of the preceding claims, characterized by that the control of the laser (18) is carried out in such a way that the laser (18) emits laser pulses in a wavelength range between 300 nm and 1400 nm, in particular between 700 nm and 1200 nm, with a respective pulse duration between 1 fs and 1 ns, in particular between 10 fs and 10 ps, ​​and a repetition frequency greater than 10 kHz, in particular between 100 kHz and 10 MHz. [15] Processing device (10) with at least one laser (18) for the separation of a volume body (12) with predefined interfaces (14, 16) from a material by means of photodisruption or ablation and with at least one control device (20) for the laser(s) (18), which is designed to carry out the steps of the method according to one of claims 1 to 13. [16] Processing device (10) according to claim 15, characterized by that the control device (20) - at least one storage device for at least temporarily storing at least one control data set, wherein the control data set(s) comprise control data for positioning and / or focusing individual laser pulses in the cornea; and - 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 (24) of the laser (18). [17] Computer program comprising instructions which cause the processing device (10) according to claim 15 or 16 to carry out the method steps according to one of claims 1 to 14. [18] A computer-readable medium on which the computer program according to claim 17 is stored.

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