DE102021130663A1 - Method for providing control data for a laser of a treatment device - Google Patents

Abstract

The invention relates to a method for providing control data for a laser (18) for correcting a cornea (26). The method includes determining (S10) a corneal geometry; determining (S12) an anterior and posterior interface (14, 16) of a lenticle (12), and determining (S14) a cornea (26) deformed by a contact element (28) by means of a cornea deformation model, the cornea ( 26) is formed from respective central corneal surfaces (34, 36) between an anterior corneal surface (30) and a posterior corneal surface (32), wherein the anterior corneal curvature is changed to a predetermined curvature of the contact element (28) to determine the deformed cornea (26). and the central corneal surfaces (34, 36) are adapted to the changed curvature of the anterior corneal surface (30) by means of a deformation. Furthermore, a deformed lenticle (12) is determined (S16) by means of the deformed cornea (26), and the deformed lenticle (12) is provided (S18) as control data for controlling the laser.

Description

The present invention relates to a method for providing control data for a laser of a treatment device for correcting a cornea. The invention also relates to a control device for carrying out the method, a treatment device with 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 an optical defect in a cornea are known in the prior art. 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 lenticle from the cornea for correction of the cornea. During treatment with a treatment device, for example for the removal of a lenticle, the eye is usually fixed by one or more contact elements of the treatment device. In this case, the contact element is a rigid element, for example a plano-concave lens, which is placed on the eye, in particular on the cornea, so that the eye is not moved during the treatment. However, a disadvantage of such a contact element is that the shape of the cornea changes due to the contact element, in particular it is compressed. As a result, the shape of the lenticle to be separated can also change, as a result of which treatment can be faulty.

From the DE 10 2008 017 293 A1 a method for generating control data for an ophthalmic surgical treatment device is known, which separates layers of tissue in the cornea by means of a laser device, wherein during operation of the laser device a contact glass having a contact surface deforms the cornea into the shape of the contact surface, for which purpose the contact surface first has a contact surface apex a corneal vertex is placed and then pressed against the cornea to deform it. The control data for the laser device are generated in such a way that they specify coordinates of target points located in the cornea for the laser device, and when generating the target point coordinates the deformation of the cornea, which is caused by the contact glass during operation of the laser device, is taken into account.

The object of the invention is to provide control data for controlling a laser, in which a deformation is compensated for by a contact element.

This object is achieved by the method according to the invention, the devices according to the invention, the computer program according to the invention and the computer-readable medium according to the invention. Advantageous configurations with expedient developments of the invention are specified in the respective dependent claims, advantageous configurations of the method being to be regarded as advantageous configurations of the treatment device, the control device, the computer program and 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 device for correcting a cornea of a human or animal eye, the method having 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 set up 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 unit. The control device determines a corneal geometry of the eye from predetermined examination data, the corneal geometry including at least an anterior corneal curvature, and determines an anterior and posterior interface of a lenticle of the cornea to provide the correction of the cornea. Furthermore, a cornea deformed by a contact element (patient interface) is determined using a corneal deformation model, which is determined based on the Euler-Bernoulli beam theory (Euler-Bernoulli beam theory), the cornea with the determined corneal geometry being provided as a volume in the corneal deformation model , wherein the volume body is formed from respective central corneal surfaces between an anterior corneal surface and a posterior corneal surface, wherein to determine the deformed cornea in the corneal deformation model, the anterior corneal curvature is changed to a predetermined curvature of the contact element and the central corneal surfaces are adapted to the changed one by means of an elastic deformation curvature of the anterior corneal surface can be adjusted. Finally, a deformed lenticule is determined using the deformed cornea, with the anterior and posterior boundary surface of the lenticle being determined as a function of the adapted central corneal surfaces of the deformed cornea, and the deformed anterior and posterior boundary surfaces being provided Chen of the lenticle as control data for controlling the ophthalmic surgical laser.

In other words, it can first be determined which corneal geometry the eye has and which geometry the lenticle requires in order to achieve a correction of the cornea. For this purpose, in particular anterior and posterior boundary surfaces, which delimit the lenticule in the direction of an optical axis to the front and to the back, can be determined. The anterior and posterior interfaces may each have predetermined curvatures to achieve correction of the cornea.

However, when using a contact element or a patient interface that is pressed onto the eye, the cornea can deform, which changes the corneal geometry and also the previously determined anterior and posterior boundary surfaces of the lenticle. This means that using the originally determined anterior and posterior interfaces could lead to a different correction. In order to compensate for the effect of the contact element, a corneal deformation model can be used to calculate the geometry of the deformed cornea, it then being possible to use the deformed cornea to determine how the originally planned lenticule has been deformed. This deformed lenticle can then be used in the control data to perform the originally planned correction. For this purpose, the cornea can be described as a volume body in the cornea deformation model, which has the cornea geometry. This solid can be deformed based on the Euler-Bernoulli beam theory to obtain the deformed anterior and posterior interface.

The Euler-Bernoulli beam theory describes an elastic bending of a body, assuming that between the anterior corneal surface and a posterior corneal surface there are several central corneal surfaces that build up 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, with the other central corneal surfaces being able to be described as a function of the neutral corneal surface. In particular, the central corneal surfaces below the neutral corneal surface may be compressed and those above are stretched. This neutral corneal surface can be arranged, for example, in the middle of the cornea or also at a predetermined thickness or depth (viewed in the direction of the optical axis). Preferably, the deformation of the central corneal surfaces can be described as a function of the change in 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 calculated mathematically how the central corneal surfaces change during elastic deformation, in particular relative to the neutral corneal surface. As an elastic deformation, it is assumed in the corneal deformation model that the anterior corneal curvature changes to the specified curvature of the contact element, whereby this change can be calculated according to the Euler-Bernoulli beam theory for the respective central corneal surfaces and thus a global change in the volume body by the contact element can be determined.

Corresponding to the deformation of the volume determined in this way, the anterior and posterior boundary surfaces of the lenticle can also be calculated using the changed central corneal surfaces. In this case, for example, the anterior and posterior boundary surfaces can be assigned to respective central corneal surfaces, it being possible to determine how the corneal surfaces assigned to the boundary surfaces change as a result of the deformation. In particular, the corneal deformation model can be used to determine a deformation value, preferably a single deformation value, with which the originally planned lenticule can be scaled in order to obtain the deformed lenticule.

Finally, the control data comprising the deformed lenticle with the deformed anterior and posterior interface can be provided to the controller for controlling the laser. In other words, the laser of the treatment device for the correction of the cornea can be controlled with the control data, with the treatment device being able to separate the deformed lenticle provided in the control data from the cornea.

The method can be carried out as an analytical method, but also, for example, as a mesh method (discrete point variant). The corneal deformation model can preferably also take into account that due to an incompressibility or a minimal compressibility of the cornea, it is assumed that the cornea volume is preserved during the elastic deformation. This means that the corneal volume does not change or changes only slightly during elastic deformation.

The advantage of the invention is that deformation effects caused by the contact element can be compensated for, which leads to improved correction of the cornea.

The invention also includes configurations that result in additional advantages.

One embodiment provides that the corneal deformation model is used to determine a deformation correction value, which is used to calculate the deformed lenticule for a planned refractive power correction to compensate for the deformation caused by the contact element. In other words, the anterior and posterior boundary surfaces of the lenticle can be determined by means of a planned refractive power correction, ie a diopter value that is to be compensated. This planned refractive power correction can be scaled using a deformation correction value determined by the corneal deformation model or calculated using a difference amount through the deformation correction value in order to obtain a global transformation of the refractive power correction. A single value can preferably be determined as the deformation correction value, by means of which the planned refractive power correction is adjusted. This embodiment has the advantage that a user planning a refractive power correction can only adjust it using the deformation correction value from the corneal deformation model, in particular with scaling with the deformation correction value or a difference with the deformation correction value, in order to obtain the deformed lenticule that is provided as control data for controlling the laser.

A further embodiment provides that the corneal deformation model is used to determine a deformation correction value, which is used to calculate the deformed lenticule for a planned lenticule diameter in order to compensate for the deformation caused by the contact element. In other words, a lenticle diameter can be planned for the correction of the cornea, in particular a diameter of an optical zone or a size of the correction. Using the deformation correction value from the corneal deformation model, the planned lenticle diameter can then be adjusted using a scaling or a differential amount with the deformation correction value in order to obtain the deformed lenticle, which can be provided as control data for controlling the laser. Thus, a global transformation of the lenticle diameter can be achieved, preferably with a single deformation correction value.

A further embodiment provides that in the corneal deformation model a lateral boundary surface of the volume body in a radial direction is deformed freely, in particular obliquely, by the deformation of the volume body. In other words, in the corneal deformation model it can be assumed that the solid representing the cornea is deformed without boundary conditions. In a real situation in the eye, the cornea can be limited in its extent, particularly in a lateral direction, due to morphological conditions in the eye. For example, a body would expand sideways under pressure from above, but this lateral expansion in the cornea is limited by the tissue of the eye. In this embodiment, a simplified view of the cornea is assumed, in that it is assumed to be a free volume body in space. This means that it can expand or deform unhindered by deformation, in particular laterally in the radial direction. The lateral boundary surface means the surfaces that laterally delimit the volume body in the radial direction. This embodiment has the advantage that the corneal deformation model can be simplified.

In a further embodiment it is provided that in the corneal deformation model a lateral boundary surface of the volume body in a radial direction is deformed into an intermediate position during the deformation of the volume body, the intermediate position moving between an initial position of the lateral boundary surface and a position of the boundary surface during free deformation the interface is located. In other words, this embodiment takes into account that the cornea cannot be deformed freely in space and is at least partially delimited at least to the sides, in particular at the lateral boundary surface of the volume body. In particular, a cornea in the eye can be delimited laterally by the sclera or sclera of the eye, with the lateral interface of the volume body being able to be located at a transition zone between the cornea and sclera, the so-called limbus. In this embodiment, it is assumed that the corium can yield by a predetermined amount of deformation, such that the solid is deformed to an intermediate position, the intermediate position being between the position that the lateral interface would assume under free deformation and an initial position that having the lateral interface before deformation. For example, starting from the center of the cornea and viewed radially, the sclera can begin at 6.5 millimeters and an outer edge point of the lateral boundary surface could be expanded up to a value of 7.3 millimeters with a deformation. The intermediate position can thus preferably be a position between 6.5 milli meters and 7.3 millimeters, preferably between 6.5 millimeters and 6.9 millimeters. 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 free deformation and then the points of the lateral interface are scaled using a deformation value, which preferably takes into account a resistance of the sclera during deformation, so that the Edge points of the interface can be moved to the intermediate position. However, not only do the edge points of the lateral boundary surface change to the intermediate position due to the deformation value, but the shape of all central corneal surfaces can also change, whereby this at least partial limitation by the sclera can be taken into account in the corneal deformation model. This embodiment results in the advantage that a real situation in the eye can be better taken into account, which can further improve the determination of the deformed lenticle.

A further advantageous embodiment provides that in the corneal deformation model a lateral boundary surface of the volume body in a radial direction 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 volume body in the radial direction, can be fixed in at least one position. It can thus be assumed in the corneal deformation model that the sclera cannot be compressed at this position and therefore the volume body at this position cannot deviate to the sides when it is deformed by the contact element. In this context, the initial position means the position of the boundary surface that it has before the deformation of the volume body. This means that the position of the boundary surface before the deformation is the same in this embodiment as the lateral boundary surface after the deformation. This embodiment results in the advantage that the corneal deformation model better describes a situation in a real eye, as a result of which the determination of the deformed lenticle can be further improved.

It is preferably provided that in the corneal deformation model a lateral boundary surface of the volume body 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 interface is not only fixed in an initial position, that is to say at at least one point of the interface, but at all points that the lateral interface initially had before the deformation. This means that the solid is considered laterally rigid and incompressible in the eye.

It is preferably provided that, in order to fix the volume body at the at least one position of the interface, a transformation point is specified on the respective corneal surface, which, viewed in the radial direction, is outside the initial position of the interface, with the transformation point after the elastic deformation being scaled to a initial position of the transformation point before the elastic deformation is reset, and after the transformation point has been reset to the initial position, only the area of the corneal surface that is radially inside the interface is considered. In other words, a transformation point or support point can be defined which, viewed in the radial direction, is outside the lateral boundary surface and which, after the elastic deformation of the volume body, is reset to an initial position that the transformation point had before the elastic deformation by means of a scaling factor. Subsequently, only the area of the solid, in particular only the central corneal surfaces of the solid, which are located within the fixed lateral boundary surface, is considered. The transformation point can be specified for a respective corneal surface of the volume body. After the elastic deformation, the scaling factor can be used to bring the transformation point or points displaced by the deformation back to the initial position, with the respective central corneal surfaces being able to be adjusted accordingly at the same time. The effect of fixing the volume body can thus be described by mathematical methods, with the transformation point outside the lateral boundary surface being able to better avoid edge effects, in particular wrinkling, which could otherwise occur during scaling by the scaling factor at the lateral boundary surface.

In a further advantageous embodiment, it is provided that, in order to fix the volume body in the initial position of the entire lateral boundary surface, the corneal surfaces are adjusted by a scaling factor, with the scaling factor being used to adjust edge points of the respective corneal surfaces that are on the initial position of the lateral boundary surface before the deformation are located, are transformed back to the initial position of the lateral interface after the deformation. In other words, a free deformation of the cornea is carried out for the fixation of the volume body at the initial position of the entire lateral interface, in which the edge points of the lateral boundary surface deform, with a subsequent transformation to the initial position of the edge points being achieved by the scaling factor and at the same time an associated adaptation of the respective corneal surfaces, in particular the anterior, posterior and/or central corneal surfaces. This embodiment results in the advantage that a deformation can be carried out taking into account a fixation of the volume body on the entire lateral interface, which can better simulate the situation in the real eye.

Provision is preferably made for the lateral interface to be predetermined at a beginning (limbus) of a dermis (sclera) of the eye. For example, the sclera can be about 6.5 millimeters away from a center of the cornea in the radial direction. Preferably, the beginning of the sclera defines the lateral interface, the lateral interface preferably being fixed at this position in the corneal deformation model.

A further embodiment provides that in the corneal deformation model the volume body is described on the anterior corneal surface by an anterior corneal ellipsoid and on the posterior corneal surface by a posterior corneal ellipsoid, with a specified contact element ellipsoid being provided for the specified curvature of the contact element, to which the anterior corneal ellipsoid for the elastic deformation is changed. In other words, it is assumed for the volume body that it is bounded at the top or front by an anterior corneal surface that is designed as an anterior corneal ellipsoid and at the bottom or back by a posterior corneal surface that is designed as a posterior corneal ellipsoid. Correspondingly, the central corneal surfaces can be described as respective corneal surface ellipsoids. The ellipsoids can be rotationally symmetrical to define a three-dimensional body. However, the ellipsoids can also be rotationally asymmetrical, for example to describe a keratoconus. Provision is preferably made for the respective ellipsoids to be in the form of a paraboloid or spheroid. By describing the respective corneal surfaces as an ellipsoid, a preferred embodiment of the corneal deformation model, in particular the change in the volume body, can be described by the Euler-Bernoulli beam theory.

A second aspect of the present invention relates to a control device that is set up to carry out the method described above. The advantages listed above result. 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 a device or a device component for electronic data processing. The processor device can have at least one microcontroller and/or at least one microprocessor, for example. A program code for carrying out the method according to the invention can preferably be stored on the optional data memory. 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 device with at least one ophthalmic surgical laser for the detachment of a lenticle with predefined boundary surfaces 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 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 laser pulses in a wavelength range between 300 nm and 1400 nm, preferably between 900 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 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 cornea does not have to be irradiated in a wavelength range below 300 nm. In laser technology, this range is subsumed under the term "deep ultraviolet". This advantageously prevents the cornea from being unintentionally damaged by these very short-wavelength and high-energy rays. 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 cornea tissue. As a result, the power density of the respective laser pulse, which is necessary for the optical breakthrough, can be narrowly limited spatially, so that a high level of cutting accuracy is made possible when producing the interfaces. In particular, the range between 700 nm and 780 nm can also be selected as the wavelength range.

In further advantageous configurations of the treatment device 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, the control data set or sets comprising 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 found in the descriptions of the first aspect of the invention, with advantageous configurations of each aspect of the invention being 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 carry out 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 found in the descriptions of the first to fourth aspects of the invention, with advantageous configurations of each aspect of the invention being to be regarded as advantageous configurations of the respective other aspect of the invention.

Further features of the invention result 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 combination specified in each case, but also in other combinations, without going beyond the scope of the invention leave. The invention is therefore also to be considered to include and disclose embodiments that are not explicitly shown and explained in the figures, but that result from the explained embodiments and can be generated by separate combinations of features. Versions and combinations of features are also to be regarded as disclosed which therefore do not have all the features of an originally formulated independent claim. Furthermore, embodiments and combinations of features, in particular through the embodiments presented above, are to be regarded as disclosed which go beyond or deviate from the combinations of features presented in the back references of the claims. It shows:

• 1 eine schematische Darstellung einer Behandlungsvorrichtung gemäß einer beispielhaften Ausführungsform;
• 2 ein schematisches Verfahrensdiagramm zum Bereitstellen von Steuerdaten gemäß einer beispielhaften Ausführungsform;
• 3a ein schematisch dargestellter Volumenkörper in einem nichtdeformierten Zustand;
• 3b der Volumenkörper in einem frei-deformierten Zustand;
• 3c der Volumenkörper in dem deformierten Zustand mit Fixierung an den seitlichen Grenzflächen.

It shows:

• 1 a schematic representation of a treatment device according to an exemplary embodiment;
• 2 a schematic process diagram for providing control data according to an exemplary embodiment;
• 3a a schematically represented solid in an undeformed state;
• 3b the solid in a free-deformed state;
• 3c the solid in the deformed state with fixation at the lateral interfaces.

Elements that are the same or have the same function are provided with the same reference symbols in the figures.

The 1 shows a schematic representation of a treatment device 10 with an ophthalmic surgical laser 18 for the separation of a lenticle 12 defined by control data from a cornea 26 by means of photodisruption and/or ablation, the cornea 26 being in the direction of an optical axis through an anterior corneal surface 30 and a posterior corneal surface 32 is defined. To separate the lenticle 12, a posterior boundary surface 14 and an anterior boundary surface 16 of the lenticle 12 are specified in the control data, on which a cavitation bubble path for separating the lenticle 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 it can emit pulsed laser pulses, for example in a predefined pattern, to generate the boundary surfaces 14, 16. Alternatively, the control device 20 can be a control device 20 that is external to the treatment device 10 .

Furthermore, the 1 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 rotary scanner. The beam deflection device 22 is also controlled by the control device 20 in order to produce the boundary surfaces 14, 16, preferably also incisions or cuts, along predetermined incision courses.

The laser 18 shown can preferably be a photodisruptive and/or ablative laser that is designed as a laser pulse 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 100MHz. The control device 20 optionally also has a storage device (not shown) for at least temporarily storing at least one control data record, the control data record(s) comprising control data for positioning and/or focusing individual laser pulses in the cornea. The position data and/or focusing data of the individual laser pulses, i.e. the lenticle geometry of the lenticle 12 to be separated, is generated using predetermined control data, in particular from a previously measured topography and/or pachymetry and/or the morphology of the cornea or the optical ametropia correction to be generated.

In order to determine the ametropia data, which can indicate a value in dioptres, for example, suitable examination data for describing the ametropia can be received by the control device 20 from a data server or the examination data can be entered directly into the control device 20 .

Furthermore, a contact element 28 can be provided, which can belong to the treatment device 10 . Alternatively, the contact element 28 can also be provided separately from the treatment device 10 . The contact element 28, which can also be referred to as a patient interface or fixation system, is used to fix the eye or the cornea 26 for the treatment. For this purpose, the contact element 28 can have a plano-concave lens, which is adapted to the cornea 26 for fixation. However, the fixation by means of the contact element 28 can result in the cornea 26 being deformed and thus the geometry of the lenticle 12 no longer having the originally planned dimensions. It can therefore happen that, for example, a planned refractive power value or one to be corrected deviates from a refractive power value achieved after treatment with the treatment device 10 .

In 2 1 is a schematic process diagram for providing control data for the laser 18 of the treatment device 10 for correcting the cornea 26, with the deformation of the cornea 26 by the contact element 28 being able to be taken into account by the process. The method steps can preferably be carried out by the control device 20 which is separate from the treatment device 10 and/or which can be integrated into the treatment device 10 . In a step S10, a corneal geometry of the eye can be determined from predetermined examination data, the corneal geometry comprising at least an anterior corneal curvature of the anterior corneal surface 30 . In a step S12, an anterior boundary surface 16 and a posterior boundary surface 14 of a lenticle 12 of the cornea 26 that is to be removed for correction of the cornea can be determined. The anterior and posterior interfaces 14, 16 can preferably be determined based on the previously determined corneal geometry.

Since the anterior and posterior boundary surfaces 14, 16 also change when the cornea 26 is deformed by the contact element 28, a deformed cornea can be modeled by means of a cornea deformation model in a step S14 to compensate for this deformation, the cornea deformation model being based on the Euler-Bernoulli Beam theory based and it is determined how corneal surfaces change within the cornea 26 by deformation. The cornea 26 can be modeled as a volume body, which is formed from respective central corneal surfaces 34, 36, with the anterior corneal curvature being changed to a predetermined curvature of the contact element 28 in order to determine the deformed cornea in the corneal deformation model, and the central corneal surfaces 34, 36 being be adapted to the changed curvature of the anterior corneal surface 30 by an elastic deformation.

To illustrate the corneal deformation model, the deformation of the volume body of the cornea 26 is shown in FIGS 3a until 3c shown. Here shows the 3a For example, the volume body of the cornea 26 in a free state before deformation by the contact element 28. The volume body can be limited 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 lateral boundary surfaces 38. Here, the anterior corneal surface 30 and the posterior corneal surface 32 can be provided as a corneal ellipsoid, a two-dimensional cross section through the solid being shown in this figure for illustration and the solid being present in a three-dimensional form, in particular rotationally symmetrical. Alternatively, the solid can also deviate from 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 solid 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 36, can be a neutral corneal surface or neutral membrane, which according to the Euler-Bernoulli beam theory has the same area before and after the deformation, which is taken into account when modeling the cornea 26 based on the corneal deformation model becomes. A respective central corneal surface 34 can preferably be described in relation to this neutral corneal surface 36 in the corneal deformation model.

beschrieben werden, wobei diese den Krümmungsradius der zentralen Hornhautfläche 34 vor der Deformation (r_cent,pre) bereitstellt. Dabei beschreibt r_ca den Krümmungsradius der anterioren Hornhautfläche 30 und r_cp den Krümmungsradius der posterioren Hornhautfläche 32. Die Variable q beschreibt eine relative Position der zentralen Hornhautfläche 34 zu der neutralen Hornhautfläche 36, wobei q ein Wert zwischen 0 und 1 annehmen kann.A radius of curvature of a respective central corneal surface 34 can thus preferably be calculated using the corneal deformation model according to the formula $$\frac{1}{{\mathrm{right}}_{cent,p\mathrm{right}e}}=\left(\frac{q}{{\mathrm{right}}_{ca}}+\frac{1-q}{{\mathrm{right}}_{cp}}\right)$$

, providing the radius of curvature of the central corneal surface 34 before deformation (r _cent,pre ). r _ca describes the radius of curvature of the anterior corneal surface 30 and r _cp the radius of curvature of the posterior corneal surface 32. The variable q describes a relative position of the central corneal surface 34 to the neutral corneal surface 36, where q can have a value between 0 and 1.

beschrieben werden, wobei rx eine Radialposition ausgehend von der Mitte der Hornhaut 26 beschreibt und dcc eine zentrale Dicke der Hornhaut 26 an dem höchsten Punkt beziehungsweise Wendepunkt der Hornhaut 26.In a similar way, a position in the z-direction, which is dependent on the radial position, can also be described for the radius of curvature, the z-direction running in the direction of the optical axis. This can be done for the respective central corneal surface 34 with the formula $${\mathrm{e.g}}_{cent,p\mathrm{right}e}\left({\mathrm{right}}_x\right)=\left(q-1\right){\mathrm{i.e}}_{cc}-\frac{{\mathrm{right}}_x^2}{2}\left(\frac{q}{{\mathrm{right}}_{ca}}+\frac{1-q}{{\mathrm{right}}_{cp}}\right)$$

described, where rx 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.

When the cornea 26 is deformed by the contact element 28 , it can be provided in the cornea deformation model that the radius of curvature of the anterior corneal surface 30 is adapted to a radius of curvature of the contact element 28 . This situation is, for example, in 3b shown, the contact element 28 is not shown here for reasons of clarity. It can be seen that the anterior corneal surface 30 is depressed and thus also the central corneal surfaces 34 and 36. However, according to the Euler-Bernoulli beam theory, this still takes into account that the neutral corneal surface 36 has the same area as before the deformation.

This deformation assumes that the solid is free to deform and is not constrained to the sides. Therefore, during the deformation, the lateral boundary surfaces 38 are also deformed obliquely outwards compared to the non-deformed cornea 26 in 3a . Since the central corneal surfaces 34 change in their radius of curvature and their position in the z-direction according to the formulas given above from the corneal deformation model, it follows that the lenticle 12 defined in step S12, which is not shown in these figures, also changes. since the radii of curvature of the anterior interface 16 and the posterior interface 14 of the lenticle also deform. This deformation can preferably be determined in a step S16 of the method by determining it from the adapted corneal surfaces 34, 36 of the deformed cornea.

Subsequently, the deformed anterior and posterior boundary surfaces 14, 16 of the lenticle 12 can be provided in a step S18 as control data for controlling the laser in order to compensate for the deformation of the cornea by the contact element 28.

However, the in 3b The situation shown is only a theoretical assumption and in particular the lateral boundary surfaces 38 cannot deform freely in a real eye, but are fixed by the morphological properties of the eye. This boundary condition can preferably also be taken into account in the corneal deformation model, which is shown, for example, in 3c is shown.

Here, the volume body of the cornea 26 is shown after the deformation by the contact element 28, with the lateral boundary surfaces 38 not being able to deviate laterally as in the case of the free cornea, but rather being at least partially fixed to the lateral boundary surface 38. It can be assumed here that the lateral boundary surface 38 represents the beginning (limbus) of a dermis (sclera) which is not or only very slightly compressible. Here, for example, the limbus can be assumed to have a radial position (rx) of 6.5 millimeters.

In order to take this fixation at the lateral boundary surface 38 into account, it can be provided that a deformation of the cornea 26 is carried out in the free state, i.e. a deformation as described in 3b is shown, with respective Edge points of the respective corneal surfaces 34, 36 are transformed back to the initial position of the lateral boundary surface 38 after the deformation by means of a scaling factor and the oblique lateral boundary surface (as in 3b ) back to the laterally fixed (vertical interface as in 3a and 3c ) can be transformed back. This has the advantage that morphologically existing boundary conditions in the cornea 26 can also be taken into account, which improves the corneal deformation model and the anterior and posterior boundary surfaces 14, 16 of the lenticle 12 determined therefrom.

Alternatively or additionally, to fix the lateral boundary surfaces 38, a transformation point can also be provided on the respective corneal surfaces 34, 36, which is outside the initial position of the boundary surfaces 38, for example to the left and right of the boundary surfaces 38 in 3a , is located, wherein this 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, with only the area that is located within the lateral boundary surfaces 38 then being taken into account. In other words, the scaling can be performed at a transformation point that is outside of the lateral boundary surfaces 38, as a result of which artifacts at the lateral boundary surfaces 38 can be reduced.

Partial deformations of the lateral boundary surfaces 38 can preferably also be taken into account, in which case the edge points are not transformed back to the initial position by the scaling factor, but rather to an intermediate position, i.e. a point on the lateral boundary surface 38 that lies between the in 3a and the 3b shown lateral boundary surface 38 is located. For example, the initial position of the lateral boundary surface 38 can be 6.5 millimeters and a maximum extension of the freely deformed lateral boundary surface 38 can be 7.3 millimeters, with the respective edge points being able to be transformed back to an intermediate position between these values. Here, for example, it is taken into account that the sclera can be at least partially compressed, which describes the cornea 26 even better in the corneal deformation model.

In the practical application for considering the deformation by the contact element 28, a deformation correction value can thus be determined, for example, by which a planned refractive power correction can be scaled in order to calculate a compensation for the deformation by the contact element. Thus, instead of a point-by-point scaling, a global transformation can be carried out, which provides compensation for the deformation caused by the contact element 28 and thus contributes to an improvement in the correction of the cornea 26.

Overall, the examples show how a deformation model can be provided by the invention, with which a deformation of the cornea 26 by the contact element 28 can be taken into account.

QUOTES INCLUDED IN DESCRIPTION

This list of documents cited by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent Literature Cited

• DE 102008017293 A1 [0003]

Claims (17)

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 having the following steps carried out by a control device (20): - determining (S10) a corneal geometry of the eye from predetermined examination data, the corneal geometry comprising at least an anterior corneal curvature; - determining (S12) an anterior and posterior interface (14, 16) of a lenticle (12) of the cornea (26) for providing the correction of the cornea (26); - Determining (S14) a cornea (26) deformed by a contact element (28) using a cornea deformation model that is determined based on the Euler-Bernoulli beam theory, the cornea deformation model providing the cornea (26) with the determined corneal geometry as 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), wherein to determine the deformed cornea (26) in the corneal deformation model, the anterior corneal curvature is converted to a predetermined curvature of the contact element (28) is changed and the central corneal surfaces (34, 36) are adapted to the changed curvature of the anterior corneal surface (30) by means of an elastic deformation; - determining (S16) a deformed lenticule (12) by means of the deformed cornea (26), the anterior and posterior interface (14, 16) of the lenticule (12) depending on the adapted central corneal surfaces (34, 36) of the deformed cornea (26) to be determined; - Providing (S18) the deformed anterior and posterior boundary surfaces (14, 16) of the lenticle (12) as control data for controlling the laser. procedure after claim 1 , a deformation correction value being determined by the corneal deformation model, by means of which the deformed lenticule (12) is calculated for a planned refractive power correction to compensate for the deformation by the contact element (28). procedure after claim 1 , wherein a deformation correction value is determined by the corneal deformation model, by means of which the deformed lenticule (12) is calculated for a planned lenticle diameter to compensate for the deformation by the contact element (28). Method according to one of the preceding claims, wherein in the corneal deformation model a lateral boundary surface (38) of the volume body 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 (38) of the volume body in a radial direction is deformed into an intermediate position during the deformation of the volume body, the intermediate position moving between an initial position of the lateral boundary surface (38) and a position of the lateral boundary surface (38) in a free deformation of the lateral boundary surface (38). Method according to one of the preceding claims, wherein in the corneal deformation model a lateral boundary surface (38) of the volume body in a radial direction is fixed at at least one initial position of the lateral boundary surface (38) 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 (38) of the volume body in a radial direction is fixed at an initial position of the entire lateral boundary surface (38) during the deformation of the volume body. Procedure according to one of Claims 6 or 7 , wherein a transformation point on the respective corneal surface (30, 32, 34, 36) is specified for fixing the volume body at the at least one position of the lateral boundary surface (38), which, viewed in the radial direction, is outside the initial position of the lateral boundary surface (38) located, 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 reset of the transformation point to the initial position only the area of the respective corneal surface (30, 32, 34, 36) is taken into account, which is located in the radial direction inside the initial lateral boundary surface (38). Procedure according to one of Claims 6 or 7 , wherein the corneal surfaces (30, 32, 34, 36) are adjusted by a scaling factor to fix the volume body at the initial position of the entire lateral boundary surface (38), whereby edge points of the respective corneal surfaces (30, 32, 34, 36 ), which are on the initial position of the lateral interface (38) before the deformation, are transformed back to the initial position of the lateral interface (38) after the deformation. Procedure according to one of Claims 4 until 9 , wherein the lateral interface (38) is predetermined at a beginning of a sclera of the eye. Method according to one of the preceding claims, wherein in the corneal deformation model the volume body is described on the anterior corneal surface (30) by an anterior corneal ellipsoid and on the posterior corneal surface (32) by a posterior corneal ellipsoid, wherein for the predetermined curvature of the contact element (28). predetermined contact element ellipsoid is provided, to which the anterior corneal ellipsoid is changed for the elastic deformation. Control device (20), which is designed to use a method according to one of Claims 1 until 11 to perform. Treatment device (10) with at least one eye surgery laser (18) for the separation of a lenticle (12) with predefined interfaces (14, 16) from a human or animal eye by cavitation bubbles and at least one control device (20). claim 12 . Treatment device (10) after Claim 13 , characterized in that the laser (18) is suitable for laser pulses in a wavelength range between 300 nm and 1400 nm, preferably between 900 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. Treatment device (10) after Claim 13 or 14 , characterized in that the control device (20) - has at least one storage device for the at least temporary storage of at least one control data set, the control data set or sets comprising control data for positioning and/or for 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). Computer program comprising instructions that cause the control device (20) according to claim 12 the method steps according to one of Claims 1 until 11 executes Computer-readable medium on which the computer program Claim 16 is saved.

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