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

Abstract

Method for providing control data for a laser (18) of a treatment device (10) for the correction of a cornea (26) of a human or animal eye, the method comprising the following steps carried out by a control device (20): - determining (S10) a corneal geometry of the eye from predetermined examination data, wherein the corneal geometry comprises at least an anterior corneal curvature; - determining (S12) a correction to be achieved, wherein an anterior and a posterior boundary surface (14, 16) of a lenticule (12) of the cornea (26) are determined by the correction to be achieved; - determining (S14) a deformed cornea (26) that is expected due to the removal of the lenticule (12) from the cornea (26) by means of a corneal deformation model that is determined based on the Euler-Bernoulli beam theory, wherein in the corneal deformation model the cornea (26) with the determined corneal geometry is described by a solid body, wherein the solid body is formed from respective central corneal surfaces (34, 36) between an anterior corneal surface (30) and a posterior corneal surface (32), and to determine the deformed cornea, a closure of a region between the anterior (16) and the posterior boundary surface (14) of the lenticule (12) is modeled in the solid body, thereby changing the curvatures of the central corneal surfaces (34, 36) and the anterior corneal curvature; - determining (S16) a deformation correction value by means of the deformed cornea (26) of the corneal deformation model, which indicates which correction is achieved according to the deformed cornea; - Adjusting (S18) the correction to be achieved depending on the determined deformation correction value, - Providing (S20) the control data for controlling the laser (18) which have the adjusted correction to be achieved.

Description

The present invention relates to a method for providing control data for a laser of a treatment device for the correction of a cornea. The invention also relates to a control device for carrying out a method, a treatment device having at least one eye-surgery laser and at least one control device, a computer program and a computer-readable medium.Treatment devices and methods for controlling lasers to correct corneal optical deficiency are known in the art. In this case, for example, a pulsed laser and a beam focusing device can be designed such that laser beam pulses cause photodisruption in a focus located within the tissue of the cornea in order to separate a lentivirus from the cornea (cornea) for correction of the cornea.The determination of which geometry the lens to be removed should have is usually carried out according to known standard methods, wherein for this purpose, for example, a refractive power or diopter value to be corrected is specified, by means of which the lens to be removed can then be determined. In particular, the "collapse" or closing of the cornea after removal of the lentivirus yields the desired correction. However, in the determination of a correction of the cornea, in particular in the case of a refractive power correction which is carried out according to standard methods, slight deviations can occur from the actually planned result, since an idealised cornea and not an individual cornea is assumed.DE 10 2011 116 760 A1 discloses an ophthalmological laser system and a method for laser-surgical treatment of the cornea. In this case, an accuracy of the treatment of the cornea can be increased by recording scattered light intensities of different polarization states from the same direction before the treatment of the cornea and adapting a model of a cornea thereto in order to determine a slice geometry to be generated and adapting said slice geometry to a deformation predicted on the basis of the model. This allows the corneal surgical treatment with high accuracy because the biological state of the cornea including its internal mechanical stresses is taken into account in the incision procedure.DE 10 2020 113 820 A1 discloses a method for providing control data for an eye-surgery laser of a treatment apparatus.DE 10 2016 208 011 A1 discloses a planning device for generating control data for a treatment apparatus, which generates at least one cut surface in the cornea by means of a laser device. The planning device has calculation means for defining the corneal cut surfaces, wherein the calculation means define the corneal cut surfaces based on the data of a LIRIC structure and / or a refraction correction, and a control data set for the corneal cut surfaces for controlling the laser device, wherein the calculation means determine the corneal cut surfaces such that the LIRIC structure is enclosed by the cut surfaces.US 2019 / 0175281 A1 discloses a device for surgical correction of ametropia of an eye.US 2009 / 0187386 A1 discloses systems and methods for simulating corneal reconfiguration using a finite element model in laser-induced optical breakthroughs.The object of the present invention is to provide control data for controlling a laser in which the correction to be achieved is determined in an improved manner.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 a laser of a treatment apparatus for the correction of a cornea (cornea) of a human or animal eye, wherein the method comprises 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. The control device determines a corneal geometry of the eye from predetermined examination data, wherein the corneal geometry comprises at least one anterior corneal curvature, and determines a correction to be achieved, wherein the correction to be achieved determines an anterior and a posterior boundary surface of a lentivirus of the cornea. Furthermore, a deformed cornea, which is expected by the removal of the lentivirus from the cornea, is determined by means of a corneal deformation model, which is determined based on the Euler-Bernoulli beam theory, wherein the cornea having the determined corneal geometry is described in the corneal deformation model by a volume body, wherein the volume body is formed from respective central corneal surfaces between an anterior corneal surface and a posterior corneal surface, and, for the determination of the deformed cornea, a region between the anterior and the posterior interface of the lentivirus in the volume body is modeled, that is to say a deformation of the anterior interface of the lentivirus onto the posterior interface of the lentivirus, is modeled, thereby changing the curvatures of the central corneal surfaces and the anterior corneal curvature. Subsequently, a deformation correction value is ascertained by means of the deformed cornea of the corneal deformation model, which specifies which correction is achieved according to the deformed cornea, wherein the correction to be achieved is adapted as a function of the ascertained deformation correction value. Finally, the control data for controlling the laser are provided, which have the adapted correction to be achieved.In other words, it can first be determined which corneal geometry the eye has and which geometry the lentivirus requires in order to achieve correction of the cornea. For this purpose, the correction to be achieved can be determined by conventional methods, resulting in the anterior and posterior boundary surface of the lentivirus. Since this correction to be achieved according to standard methods can, however, deviate slightly from the planned correction value in the final result, it is furthermore provided that the closing of the cornea after removal of the lentivirus is calculated by a corneal deformation model which describes the cornea as a volume body which has the corneal geometry, in particular the individual corneal geometry of the patient. By closing the cornea modeled in this way, it can then be determined which deformation correction value is assumed by the model. A deviation between this deformation correction value and the planned correction to be achieved can then be used to adapt the previously planned correction, for example by scaling it with the difference and / or forming a difference amount.The volume body, which is modeled as a cornea in the corneal deformation model, can be deformed based on the Euler Bernoulli beam theory in order to describe the deformation of the cornea after removal of the lentivirus, in particular a deformation of the anterior interface of the lentivirus onto the posterior interface of the lentivirus. By closing the anterior interface of the lentivirus onto the posterior interface, the central corneal surfaces lying above it also change, as a result of which the entire deformation of the volume body and thus of the cornea is modeled.Euler-Bernoulli beam theory describes elastic bending of a body, it being assumed that a plurality of central corneal surfaces are arranged between the anterior corneal surface and a posterior corneal surface, said central corneal surfaces constituting the volume body. According to the Euler-Bernoulli beam theory, one of the central corneal surfaces is a neutral corneal surface or neutral membrane, the surface of which remains constant during deformation, wherein the further central corneal surfaces can be written on as a function of the neutral corneal surface. In particular, the central corneal surfaces under the neutral corneal surface can be stretched during the closing of the cornea after removal of the lentivirus and these are compressed above it. This neutral corneal surface can be arranged, for example, centrally in the cornea or else at a predetermined thickness or depth (as viewed in the direction of the optical axis). After removal of the lentivirus, the corneal neutral surface can be re-established in the remaining tissue of the cornea. Preferably, the deformation of the central corneal surfaces can be described as a function of the change in the curvature of the neutral membrane, whereby the deformation of the volume body at each surface (corneal surface) can be described.Based on the Euler-Bernoulli beam theory, it can then be mathematically calculated how the central corneal surfaces change after the distance of the lentivirus, in particular relative to the neutral corneal surface. For this deformation, it is assumed in the corneal deformation model that the anterior boundary surface of the lentivirus changes to the posterior boundary surface, in particular to the curvature of the posterior boundary surface, wherein this change can be calculated according to the Euler-Bernoulli beam theory for the respective central corneal surfaces and thus a global change of the volume body can be determined.According to the deformation of the volume body and the anterior to the posterior interface of the venticle thus determined, it is possible to calculate on the basis of the changed central corneal surfaces, which correction is obtained on the basis of the difference between the curvature of the anterior corneal surface before the engagement and the anterior corneal surface after the removal of the venticle and the closing of the hole which the venticle leaves in the cornea after the removal. This deformation correction value, which is calculated by the corneal deformation model, can then be compared with the planned correction to be achieved, wherein a possible difference can be compensated by means of adaptation of the correction to be achieved. The deformation correction value may preferably be a single value with which the originally planned lentivirus can be scaled in order to adapt the correction.The control data which have the adjusted correction to be achieved can finally be provided to the control device for controlling the laser. In other words, the laser of the treatment device can be controlled with the control data for the correction of the cornea, wherein the treatment device can separate the correction value provided in the control data and thus the adapted lentivirus from the cornea.The method can be carried out as an analytical method, but also, for example, as a mesh method (discrete point variant). Preferably, it can be additionally taken into account in the corneal deformation model that, on account of incompressibility or minimal compressibility of the cornea, retention of the corneal volume minus the lentivirus during the deformation is assumed. This means that the corneal volume does not change, or only slightly changes, during the deformation, apart from the volume of the lentivirus.The invention has the advantage that deformation effects which arise as a result of the removal of the lentivirus can be compensated or taken into account, which leads to an improved correction of the cornea.The invention also encompasses embodiments which result in additional advantages.One embodiment provides that a planned refractive power correction is adapted by the deformation correction value. In other words, the correction to be achieved or planned can be a refractive power correction, i.e. a diopter value, which is to be compensated. In this case, the anterior and posterior boundary surfaces of the lentivirus can be determined by known methods for the planned refractive power correction, wherein the refractive power correction and thus the lentivirus to be removed can be adapted to the individual cornea of the patient by means of the method and the deformation correction value determined therefrom. That is, the planned refractive power correction can be scaled by the deformation correction value determined by the corneal deformation model or can be calculated by a difference amount by the deformation correction value to obtain a global transformation of the refractive power correction. Preferably, an individual value can be determined as deformation correction value, by means of which the planned refractive power correction is adapted. This embodiment provides the advantage that a user planning a refractive power correction can adapt it from the corneal deformation model only by means of the deformation correction value, in particular with a scaling with the deformation correction value or a difference amount with the deformation correction value, in order to obtain the individually deformed cornea.A further embodiment provides that a planned grating diameter is adapted by the deformation correction value. In other words, a lenticular diameter can be planned for the correction of the cornea, in particular a diameter of an optical zone or a size of the correction. By means of the deformation correction value from the corneal deformation model, the planned lenticular diameter can then be adapted with the deformation correction value via a scaling or a difference amount in order to take into account the individual cornea. Thus, a global transformation of the lenticular diameter, preferably with a single deformation correction value, can be achieved.A further embodiment provides that in the corneal deformation model a lateral boundary surface of the lentivirus in a radial direction is freely deformed by the deformation of the volume body. In other words, it can be assumed in the corneal deformation model that the volume body representing the cornea is deformed without boundary conditions. In a real situation in the eye, the edges of the lentivirus, i.e. the lateral interface, cannot shift freely in the corneal volume, since these are bounded by corneal tissue. In this embodiment, a simplified consideration of the cornea and the lentivirus is assumed by assuming the lentivirus as a free body in space, the lateral boundary surface of which can move within the cornea during deformation due to the closing of the cornea. Thus, the lateral boundary surface can expand or deform unimpeded by deformation, in particular laterally in the radial direction. The lateral boundary surface is understood to mean points or the surfaces that laterally delimit the grating in the radial direction. In particular, the lateral boundary surface can be arranged at the edge of the anterior and / or posterior boundary surface, preferably at the larger of the two in the radial direction, wherein the lateral boundary surface can be vertical or perpendicular to a surface of the cornea. This embodiment has the advantage that a simplification of the corneal deformation model is made possible.In a further embodiment, it is provided that in the corneal deformation model a lateral boundary surface of the lentivirus is deformed in a radial direction during the deformation of the volume body into an intermediate position, wherein the intermediate position is located between an initial position of the lateral boundary surface and a position of the boundary surface during a free deformation of the boundary surface. In other words, in this embodiment it is taken into account that the cornea, in particular in the region of the lentivirus, is not freely deformable in space and is at least partially bounded at least at the lateral boundary surface of the lentivirus. In this embodiment, it is assumed that the cornea can yield by a predetermined deformation value at the edge (lateral boundary surface) of the lentivirus when the lentivirus is closed, so that the volume body is deformed into an intermediate position, wherein the intermediate position assumes between the position that the lateral boundary surface would assume in the case of free deformation and an initial position that the lateral boundary surface has before deformation. In order to take this deformation into account in the corneal deformation model, it can be provided, for example, that the volume body is deformed by a free deformation and subsequently the points of the lateral boundary surface are scaled by means of a deformation value, which preferably takes account of a resistance of the corneal tissue during the deformation, so that the edge points of the boundary surface are displaced into the intermediate position. However, not only do the edge points of the lateral boundary surface change into the intermediate position by the deformation value, but the shape of all central corneal surfaces can also change, whereby this at least partial limitation of the cornea can be taken into account in the corneal deformation model. This embodiment provides the advantage that a real situation in the eye can be better taken into account, which can further improve the determination of the deformation correction value.A further advantageous embodiment provides that in the corneal deformation model a lateral boundary surface of the lentivirus is fixed at at least one initial position of the boundary surface during the deformation of the volume body. In other words, the lateral boundary surface, which laterally delimits the lentivirus in the radial direction, can be fixed at at least one position. Thus, it can be assumed in the corneal deformation model that the cornea cannot be compressed at this position and thus the region of the removed lentivirus in the volume body cannot escape to the sides at this position when it closes. The initial position here means the position of the boundary surface which it has before the removal of the lentivirus. That is, the position of the boundary surface before deformation is equal to the lateral boundary surface after deformation in this embodiment. This embodiment provides the advantage that the corneal deformation model better describes a situation in a real eye, whereby the determination of the deformed cornea can be further improved.It is preferably provided that in the corneal deformation model a lateral boundary surface of the lentivirus in a radial direction is fixed at an initial position of the entire lateral boundary surface during the deformation of the volume body. This means that the lateral boundary surface is fixed not only in an initial position, i.e. at at least one point of the boundary surface, but at all points that the lateral boundary surface initially exhibited before the deformation. This means that the volume body is viewed as laterally fixed and incompressible in the eye at these positions.Preferably, it is provided that, for fixing the lentivirus at the at least one position of the boundary surface, a transformation point is specified on the respective corneal surface or anterior and / or posterior boundary surface of the lentivirus, which transformation point, as viewed in the radial direction, is located outside the initial position of the boundary surface, wherein the transformation point, after the elastic deformation, is reset by a scaling factor to an initial position of the transformation point before the elastic deformation, wherein, after the transformation point is reset to the initial position, only the region of the corneal surface that is located inside the boundary surface in the radial direction is taken into account. In other words, a transformation point or support point can be defined which, viewed in the radial direction, is located outside the lateral boundary surface and which, after the deformation of the solid body, is reset by means of a scaling factor to an initial position which the transformation point had before the deformation. Subsequently, only the region of the volume body, in particular only the central corneal surfaces of the volume body, which is located within the fixed lateral boundary surface is taken into account. The transformation point can be predetermined for a respective corneal surface of the volume body, preferably on an extension of the anterior and / or posterior boundary surface. By means of the scaling factor, after the deformation of the transformation point or points displaced by the deformation can thus be brought back to the initial position, wherein at the same time the respective central corneal surfaces can be adapted accordingly. The effect of fixing the solid body to the edge of the lentivirus can thus be described by mathematical methods, wherein edge effects can be prevented in an improved manner by means of the transformation point outside the lateral boundary surface, in particular wrinkling, which could otherwise occur at the lateral boundary surface during the scaling by the scaling factor.In a further advantageous embodiment, it is provided that, for fixing the lentivirus at the initial position of the entire lateral boundary surface, the corneal surfaces are adapted by a scaling factor, wherein edge points of the respective corneal surfaces that are located on the initial position of the lateral boundary surface before the deformation are transformed back to the initial position of the lateral boundary surface after the deformation by the scaling factor. In other words, for the fixation of the volume body at the edge of the lentivirus at the initial position of the entire lateral boundary surface, a free deformation of the cornea is carried out, in which the edge points of the lateral boundary surface deform, wherein subsequently a reverse transformation to the initial position of the edge points is achieved by the scaling factor and simultaneously an associated adaptation of the respective cornea surfaces. This embodiment has the advantage that a deformation can be carried out taking into account a fixing of the solid body at the entire lateral boundary surface of the lentivirus, which can better reproduce the situation in the real eye.It is preferably provided that a side surface of the solid body is additionally fixed at a beginning of a leather hide (sclera) of the eye. In particular, when closing the region of the lentivirus, the solid body as a whole can be deformed, as a result of which the side surface of the solid body which delimits the cornea laterally with respect to the sclera of the eye in the radial direction would also be deformed. In other words, in the corneal deformation model, the deformation resulting from the closing of the lentivirus would propagate to the lateral surface of the corpuscle. In the real eye, however, the side surface of the cornea is bounded by the leather hide, which cannot expand or can only expand very slightly. Therefore, in this embodiment, it is provided that the volume body is additionally fixed on its side surface. This can be taken into account, for example, by an additional scaling factor which scales the edge points of the side surface back to the initial positions after deformation. This embodiment provides the advantage that a real situation in the eye can be better taken into account, which further improves a determination of the deformation correction value.A further embodiment provides that the corneal surfaces of the cornea and the boundary surfaces of the lentivirus are described as ellipsoids by the volume body of the corneal deformation model, wherein the anterior ellipsoid is deformed to a curvature of the ellipsoid of the posterior lentivirus for closing the region between the anterior and the posterior boundary surfaces of the lentivirus. As a result, the ellipsoids of the corneal surfaces, in particular the anterior corneal surface, also adapt accordingly, whereby the deformed volume body or the deformed cornea is produced. In other words, it is assumed for the volume body that it is delimited upward or forward by an anterior corneal surface which is formed as an anterior corneal ellipsoid and downward or rearward by a posterior corneal surface which is formed as a posterior corneal ellipsoid. Similarly, the interfaces of the lentivirus and the central corneal surfaces are described as respective ellipsoids. The ellipsoids may be rotationally symmetric to define a three-dimensional body. The ellipsoids can, however, also be rotationally asymmetrical, in order to describe, for example, a keratoconus. It is preferably provided that the respective ellipsoids are designed as paraboloid or spheroid. By describing the respective corneal surfaces as ellipsoids, a preferred configuration of the corneal deformation model, in particular the change of the volume body by the Euler-Bernoulli beam theory, can be described.A second aspect of the present invention relates to a control device which is configured to carry out the method 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 the separation of a lentivirus with predefined interfaces from a human or animal eye by means of photodisruption and / or ablation, and 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.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, at a respective pulse duration 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 region is subsumed in laser technology under the term "deep ultraviolet". This advantageously prevents unintentional damage to the cornea from occurring due to these very short-wave and high-energy beams. Photodisruptive and / or ablative lasers of the type used here usually introduce pulsed laser radiation with a pulse duration between 1 fs and 1 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.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 control device according to the second aspect of the invention to execute the method steps according to the first 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 an exemplary embodiment; FIG. 2 shows a schematic method diagram for providing control data according to an exemplary embodiment; FIG. 3 ashows a schematically illustrated volume body in a non-deformed state; FIG. 3 b shows the volume body with the lentivirus to be removed; FIG. 3 cshows the deformed volume body after closing the lentivirus.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-surgery laser 18 for separating a lentivirus 12 defined by control data from a cornea (cornea) 26 by means of photodisruption and / or ablation, wherein the cornea 26 is bounded in the direction of an optical axis by an anterior corneal surface 30 and a posterior corneal surface 32. For separating the lentivirus 12, a posterior interface 14 and an anterior interface 16 of the lentivirus 12 are specified in the control data, on which a cavitation bubble path for separating the lentivirus 12 from the cornea 26 can be generated. It can be seen that, in addition to the laser 18, a control device 20 for the laser 18 can be formed, so that this can emit pulsed laser pulses, for example, in a predefined pattern for generating the boundary surfaces 14, 16. Alternatively, the control device 20 can be a control device 20 external with respect to the treatment apparatus 10.Furthermore, FIG. 1 shows that the laser beam 24 generated by the laser 18 is deflected in the direction of the cornea 26 by means of a beam device 22, namely a beam deflection device, such as a rotation scanner. The beam deflection device 22 is likewise controlled by the control device 20 in order to generate the boundary surfaces 14, 16, preferably also incisions or cuts, along predetermined incision profiles.The laser 18 illustrated can preferably be a photodisruptive and / or ablative laser which is designed to emit laser pulses in a wavelength range between 300 nm and 1400 nm, preferably between 700 nm and 1200 nm, at 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. The control device 20 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, that is to say the lenticular geometry of the lenticular 12 to be separated, is generated on the basis of predetermined control data, in particular from a previously measured topography and / or pachymetry and / or the morphology of the cornea or the optical refractive error correction to be generated.For detecting the vision deficiency data, which may indicate a value in diopters, for example, appropriate examination data for describing the vision deficiency may be received by the controller 20 from a data server, or the examination data may be directly input to the controller 20.The planning of the correction to be achieved and thus the geometry of the lentivirus 12 to be removed is usually carried out according to standard methods, wherein a refractive power correction and / or a lentivirus diameter is planned, and the anterior and posterior boundary surfaces 14, 16 of the lentivirus 12 then result therefrom. The disadvantage of this is that a standard cornea is assumed and, in particular, the closing of the region at which the lentivirus 12 was located is not modeled individually. In order to take this closing into account, the method steps shown in FIG. 2 are therefore preferably carried out.In FIG. 2, a schematic method diagram for providing control data for the laser 18 of the treatment device 10 for correction of the cornea 26 is shown, wherein the deformation of the cornea 26 can be taken into account by closing the region at which the lentivirus 12 to be removed was located. The method steps can preferably be carried out by the control device 20, which is separate from the treatment apparatus 10 and / or which can be integrated into the treatment apparatus 10. In a step S 10, a corneal geometry of the eye can be determined from predetermined examination data, wherein the corneal geometry comprises at least one anterior corneal curvature of the anterior corneal surface 30. In a step S 12, a correction to be achieved can be determined, for example by means of standard methods, wherein the correction to be achieved determines an anterior boundary surface 16 and a posterior boundary surface 14 of a lentivirus 12 of the cornea 26, which is to be removed for correction of the cornea. The anterior and posterior interfaces 14, 16 may preferably be determined based on the previously determined corneal geometry.In a step S 14, it can then be determined how the cornea 26 changes as a result of the removal of the lentivirus 12. For this purpose, the cornea can be modeled by means of a corneal deformation model, wherein the corneal deformation model is based on the Euler-Bernoulli beam theory and it is determined in this case how corneal surfaces within the cornea 26 change by deformation. In this case, the cornea 26 can be modeled as a volume body which is formed from respective central corneal surfaces 34, 36, wherein, in order to determine the deformed cornea in the corneal deformation model, the anterior boundary surface 16 of the lentivirus is pressed onto the posterior boundary surface 14 of the lentivirus 12, as a result of which they change the curvatures of the corneal surfaces 30, 34 situated above it.To illustrate the corneal deformation model, the corpuscle of the cornea 26 is shown in Figures 3a through 3c. In this case, FIG. 3 ashows, for example, the volume body of the cornea 26 in a state before the deformation. The volume body can be bounded in the direction of the optical axis by the anterior corneal surface 30 and the posterior corneal surface 32 and in the radial direction (laterally) by the side surface 38. In this case, the anterior corneal surface 30 and the posterior corneal surface 32 can be provided as a corneal ellipsoid, wherein in this figure a two-dimensional cross section through the volume body is shown for the purpose of illustration and the volume body can be present in a three-dimensional form, in particular rotationally symmetrical. Alternatively, the solid body can also deviate from the rotational symmetry and have an irregular shape.In addition to the anterior and posterior corneal surfaces 30, 32, central corneal surfaces 34, 36 of the volume body are also shown, wherein a central corneal surface can be provided for each position in the z direction (direction of the optical axis) within the volume body, which is not shown here for reasons of clarity. One of the central corneal surfaces, for example the central corneal surface 34, can be a neutral corneal surface or neutral membrane which, according to the Euler-Bernoulli beam theory, has the same surface before and after the deformation, which is taken into account in the modelling of the cornea 26 on the basis of the corneal deformation model. Preferably, a respective central corneal surface can be described in relation to this neutral corneal surface 34 in the corneal deformation model.Preferably, a radius of curvature of a respective central corneal surface 36 can thus be described by means of the corneal deformation model according to the formula, wherein said model provides the radius of curvature of the central corneal surface 36 before the deformation (r cent,pre). Here, r ca describes the radius of curvature of the anterior corneal surface 30 and r cp describes the radius of curvature of the posterior corneal surface 32. the variable q describes a relative position of the central corneal surface 36 to the neutral corneal surface 34, wherein q can assume a value between 0 and 1. Preferably, after removal of the lentivirus 12 from the cornea 26 in the corneal deformation model, the corneal neutral surface 34 can be displaced and only the upper portion of the volume body can be viewed, i.e., the portion between the anterior corneal surface 30 and the anterior interface 16.Similarly, a position in the z direction, which is dependent on the radial position, can also be described with respect to the radius of curvature, wherein the z direction runs in the direction of the optical axis. This can be described for the respective central corneal surface 36 with the formula wherein r X describes a radial position starting from the center of the cornea 26 and dcc describes a central thickness of the cornea 26 at the highest point or inflection point of the cornea 26.In the deformation of the cornea 26 by closing the region of the lentivirus in the corneal deformation model, it may be provided that the radius of curvature of the anterior interface 16 is matched to a radius of curvature of the anterior interface 14, which is illustrated, for example, in FIG. 3 b. In this case, the anterior interface 16 can move downward onto the posterior interface 14, wherein the corneal surfaces located above the anterior interface are thus also adapted, in particular the neutral corneal surface 34 and the anterior corneal surface 30. However, according to the Euler-Bernoulli beam theory, it is still taken into account that the neutral corneal surface 34 has the same surface as before the deformation.In a simplified case, it can be assumed that the lateral boundary surface 28 of the lentivirus 12 is free to deform and expand within the volume body. However, since the lateral interface 28 of the lentivirus 12 cannot move freely in the cornea in a real situation, it can preferably be provided that this is taken into account in the corneal deformation model and the lentivirus 12 is fixed at the lateral interface 28 at at least one position, preferably at the entire lateral interface 28.In order to model this, it can preferably be provided that the deformation of the volume body of the cornea 26 and of the lentivirus 12 is carried out in the free state, wherein respective edge points of the lentivirus 12 are transformed back to the initial position of the lateral interface 28 by means of a scaling factor after the deformation or the closing of the region of the lentivirus 12 and thus the edge points of the lateral interface 28 of the lentivirus 12 are transformed back to the original position. This has the advantage that it is also possible to take account of morphological boundary conditions in the cornea 26, which improves the corneal deformation model.Alternatively or additionally, a transformation point can also be provided for fixing the lateral boundary surface 28, which transformation point is located outside the initial position of the boundary surface 28, for example on the left and right of the boundary surface 28 in FIG. 3 b, wherein the transformation point is also deformed and, after the deformation, is transformed back to the initial position of the respective transformation point by means of the scaling factor, wherein subsequently only the region which is located within the lateral boundary surface 28 is taken into account. In other words, the scaling can be performed at a transformation point or interpolation point that is located outside the lateral interface 28, as a result of which artifacts at the lateral interface 28 can be reduced.Partial deformations of the lateral boundary surface 28 can preferably also be taken into account, wherein here the edge points are not transformed back to the initial position, but to an intermediate position, i.e. a point which is located between the initial position of the lateral boundary surface 28 and a position in the case of a freely assumed deformation of the lateral boundary surface 28, by the scaling factor. This takes into account, for example, that the tissue of the cornea 26 can be at least partially compressed, which describes the cornea 26 even better in the corneal deformation model.In a step S 16, a deformation correction value can then be determined on the basis of the determined deformed volume body which is obtained after the region between the anterior and posterior boundary surfaces 14, 16 has been closed, that is to say the volume body which is illustrated in FIG. 3 c, which deformation correction value specifies which correction according to the corneal deformation model is to be expected by the removal of the lentivirus 12. In particular, the deformation correction value can deviate from the initially planned correction.In a step S 18, therefore, the correction to be achieved can be adjusted with the determined deviation of the deformation correction value in order to adjust the correction of the cornea 26 to the originally planned treatment result, for example by scaling a planned refractive power correction with a difference factor. In other words, for example, a correction that is too low by 10% compared to the originally planned refractive power correction can be determined by the deformation correction value, wherein the originally planned refractive power correction can then be increased by this 10% in order to compensate for the effect. In particular, instead of a point-by-point scaling, a global adaptation of the refractive power correction can thus be carried out, which describes the closing of the cornea 26 and thus contributes to an improvement in the correction of the cornea 26.Finally, in a step S 20, the control data for controlling the laser 18 can be provided, which control data comprise the adapted correction to be achieved.Overall, the examples show how a deformation model can be provided by the invention, by means of which it is possible to describe closing of the cornea 26 after removal of the lentivirus 12.

Claims

Method for providing control data for a laser (18) of a treatment apparatus (10) for the correction of a cornea (26) of a human or animal eye, wherein the method has the following steps, carried out by a control device (20): - determination (S10) of a corneal geometry of the eye from predetermined examination data, wherein the corneal geometry comprises at least one anterior corneal curvature; - determination (S12) of a correction to be achieved, wherein an anterior and a posterior interface (14, 16) of a lentivirus (12) of the cornea (26) are determined by the correction to be achieved; determining (S14) a deformed cornea (26), which is expected by the removal of the lentivirus (12) from the cornea (26), by means of a corneal deformation model, which is determined based on the Euler-Bernoulli beam theory, wherein in the corneal deformation model the cornea (26) with the determined corneal geometry is described by a volume body, wherein the volume body is formed from respective central corneal surfaces (34, 36) between an anterior corneal surface (30) and a posterior corneal surface (32), and for determining the deformed cornea a closing of a region between the anterior (16) and the posterior interface (14) of the lentivirus (12) in the volume body is modeled, whereby the curvatures of the central corneal surfaces (34, 36) and the anterior corneal curvature are changed; determining (S16) a deformation correction value by means of the deformed cornea (26) of the cornea deformation model, which specifies which correction is achieved according to the deformed cornea; adapting (S18) the correction to be achieved as a function of the determined deformation correction value, providing (S20) the control data for controlling the laser (18), which control data have the adapted correction to be achieved.Method according to claim 1, wherein a planned refractive power correction is adapted by the deformation correction value.Method according to claim 1, wherein a planned grating diameter is adjusted by the deformation correction value.Method according to one of the preceding claims, wherein in the corneal deformation model a lateral boundary surface (28) of the lentivirus (12) in a radial direction is freely deformed by the deformation of the volume body.Method according to one of the preceding claims, wherein in the corneal deformation model a lateral boundary surface (28) of the lentivirus (12) in a radial direction is deformed into an intermediate position during the deformation of the volume body, wherein the intermediate position is located between an initial position of the lateral boundary surface (28) and a position of the boundary surface (28) during a free deformation of the boundary surface (28).Method according to one of the preceding claims, wherein in the corneal deformation model a lateral boundary surface (28) of the lentivirus (12) in a radial direction is fixed at at least one initial position of the boundary surface (28) during the deformation of the volume body.Method according to one of the preceding claims, wherein in the corneal deformation model a lateral boundary surface (28) of the lentivirus (12) in a radial direction is fixed at an initial position of the entire lateral boundary surface (28) during the deformation of the volume body.Method according to one of claims 6 or 7, wherein for fixing the lentivirus (12) at the at least one position of the boundary surface (28), a transformation point is specified on the respective corneal surface, which transformation point, viewed in the radial direction, is located outside the initial position of the boundary surface (28), wherein the transformation point is reset after the deformation by a scaling factor to an initial position of the transformation point before the deformation, wherein after the transformation point is reset to the initial position, only the region of the corneal surface which is located in the radial direction within the boundary surface (28) is taken into account.Method according to one of claims 6 or 7, wherein, in order to fix the lentivirus (12) at the initial position of the entire lateral boundary surface (28), the cornea surfaces are adapted by a scaling factor, wherein edge points of the respective cornea surfaces which are located on the initial position of the lateral boundary surface before the deformation are transformed back to the initial position of the lateral boundary surface (28) after the deformation by the scaling factor.Method according to one of Claims 4 to 9, wherein a side face (38) of the solid body is additionally fixed at a start of a leather hide of the eye.Method according to one of the preceding claims, wherein the corneal surfaces (30, 32, 34, 36) of the cornea (26) and the boundary surfaces (14, 16) of the lentivirus (12) are described as ellipsoids by the volume body of the corneal deformation model, wherein the anterior ellipsoid is deformed to a curvature of the ellipsoid of the posterior lentivirus for the closing of the region between the anterior (16) and the posterior boundary surface (14) of the lentivirus (12).Control device (20) which is designed to carry out a method according to one of Claims 1 to 11.Treatment device (10) having at least one eye-surgery laser (18) for the separation of a lentivirus (12) having predefined boundary surfaces (14, 16) from a human or animal eye by cavitation bubbles and at least one control device (20) according to Claim 12.Treatment device (10) according to claim 13, characterised in that the laser (18) is suitable for emitting laser pulses in a wavelength range between 300 nm and 1400 nm, preferably between 900 nm and 1200 nm, at 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.Treatment apparatus (10) according to Claim 13 or 14, characterized in that the control device (20) - 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 for 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 (24) of the laser.A computer program comprising instructions for causing the controller (20) of claim 12 to perform the method steps of any one of claims 1 to 11.A computer readable medium having stored thereon the computer program of claim 16.

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