DE102019214020A1 - Method and device for generating control data for an ophthalmic laser therapy device - Google Patents

Abstract

Planning unit (P) for generating control data for an ophthalmic laser therapy device (1), dasa. a laser device (10) for providing a pulsed laser beam (12), b. a focusing device (20) for focusing the pulsed laser beam (12) in a focus (60), c. a scanning device (30, 32) for shifting the focus (60) of the pulsed laser beam (12) in a tissue of a patient's eye (90), in particular in a cornea (92) and / or an eye lens, for cutting through the tissue in a scan pattern ( 50) of focus spots (62) of the focus (60) of the pulsed laser beam (12) along a scan path (54) according to the control data, and d. a control unit (40) for controlling the ophthalmological laser therapy device (1) by means of the control data, the planning unit (P) having an interface (S) for transferring the control data to the control unit (40), characterized in that the planning unit (P) for this purpose is designed to generate further control data for the scan pattern (50) of focus spots (62) of the focus (60) in the tissue of the patient's eye (90), in particular in the cornea (92) and / or the eye lens, along the scan path (54) with which the ophthalmic laser therapy device (1) can be controlled so that. the laser device (10) provides a pulsed laser beam (12) with a constant laser pulse frequency fP, f. the scan path (54) rotates at a constant angular speed around a scan path center (56), a distance from the scan path center (56) evaluated at the focus spots (62) increasing or decreasing monotonically along the scan path (54), andg. the scan pattern (50) of focus spots (62) of the focus (60) of the pulsed laser beam (12) satisfies a predetermined density.

Description

The present invention relates to a planning unit for the generation of control data for an ophthalmic laser therapy device, which has a laser device for providing a pulsed laser beam, a focusing device for focusing the pulsed laser beam in a focus, a scanning device for shifting the focus of the pulsed laser beam in a tissue of a patient's eye , in particular in a cornea and / or an eye lens, for severing the tissue in a scan pattern of focus spots of the focus of the pulsed laser beam along a scan path according to the control data, and a control unit for controlling the ophthalmic laser therapy device by means of the control data, the planning unit having an interface for transferring the control data to the control unit.

The invention further relates to a corresponding planning method for the generation of control data for an ophthalmic laser therapy device, which includes a laser device for providing a pulsed laser beam, a focusing device for focusing the pulsed laser beam in a focus, a scanning device for shifting the focus of the pulsed laser beam in a tissue The patient's eye, in particular in a cornea and / or an eye lens, for cutting through the tissue in a scan pattern of focus spots of the focus of the pulsed laser beam along a scan path according to the control data, and a control unit for controlling the ophthalmic laser therapy device by means of the control data.

Laser surgical methods for severing or cutting tissue in a patient's eye are well known in eye surgery. Here, laser radiation for treating the eye is focused within the tissue - i.e. below the surface of the tissue - in such a way that optical breakthroughs are created in the tissue.

Various processes that are initiated by the laser radiation take place one after the other in the tissue. If the power density of the radiation exceeds a threshold value, an optical breakthrough occurs, which creates a plasma bubble in the material. This plasma bubble grows after the optical breakthrough has occurred due to expanding gases. If the optical breakthrough is not maintained, the gas generated in the plasma bubble is absorbed by the surrounding material and the bubble disappears again. However, this process takes much longer than the formation of the bubble itself. If a plasma is generated at a material interface, which can also lie within a material structure, material is removed from the interface. In this case, one speaks of photoablation. A plasma bubble that separates previously bonded layers of material is usually referred to as photodisruption. For the sake of simplicity, the processes mentioned are summarized here under the term optical breakthrough, i.e. this term not only includes the actual optical breakthrough but also the resulting effects in the material.

In order to ensure the high accuracy that is required for the laser surgical method, it is essential to ensure that the effect of the laser radiation is well localized and to avoid damage to adjacent tissue as far as possible. It is therefore customary in the prior art to use the laser radiation in a pulsed manner, so that the threshold value for the power density required to trigger an optical breakthrough is exceeded only in the individual pulses. In U.S. 5,984,916 it is shown that the spatial area of the optical breakthrough (in this case the interaction with tissue) strongly depends on the pulse duration. A high focusing of the laser beam in combination with very short pulses thus makes it possible to generate the optical breakthrough very locally in a material.

The use of pulsed laser radiation has established itself in ophthalmology, especially for laser-surgical correction of ametropia. An ametropia of the eye often stems from the fact that the refractive properties of the cornea and lens do not result in optimal focusing on the retina.

In the aforementioned script U.S. 5,984,916 as in U.S. 6,110,166 describes methods for creating incisions by means of suitable creation of optical breakthroughs, which allow the refractive properties of the cornea to be influenced in a targeted manner. A large number of optical breakthroughs are attached to one another in such a way that a lens-shaped partial volume is isolated within the cornea of the eye. The lens-shaped partial volume, separated from the rest of the corneal tissue, is then removed from the cornea via a laterally opening incision - a so-called access incision. The shape of the partial volume is selected in such a way that, after removal, the shape and thus the refractive properties of the cornea are changed in such a way that the desired correction of ametropia is effected. Because the cut surfaces are curved to isolate a lenticular partial volume, a three-dimensional adjustment of the focus of the laser beam is required. Therefore, a two-dimensional deflection of the laser radiation is combined with a simultaneous focus adjustment in a third spatial direction. In this way, it is possible to shift the laser beam and thus its focus in the tissue in all three spatial directions.

For the quality of a cut using a laser surgical method in the tissue of a patient's eye, it is not only the above-described optimal focusing of the focus spots that is important. In addition, it is crucial that there is a homogeneous density of focus spots within the section. In scripture DE 103 34 110 a method is therefore described for generating a cut along a scan path of focus spots of the pulsed laser radiation, in which the scan path runs along contour lines and wherein a predetermined limit value for a distance between adjacent contour lines must not be exceeded.

Further scan patterns for generating micropores in the sclera are in the document WO 2018/183987 described to achieve a rejuvenation of the eye tissue.

The aforementioned documents have in common that a cut in the tissue of a patient's eye can only be produced with the aid of a complex and expensive device in order to be able to guarantee a good cut quality.

The object of the present invention is therefore to describe the device and method which enable the generation of a cut with a homogeneous density of focus spots of the pulsed laser radiation within the cut using simple and inexpensive components.

According to the invention, the object is achieved by the features of the independent claims. Preferred developments and refinements are the subject matter of the dependent claims.

A first aspect of the invention relates to a planning unit for generating control data for an ophthalmic laser therapy device. The ophthalmic laser therapy device comprises a laser device for providing a pulsed laser beam and a focusing device for focusing the pulsed laser beam in a focus. Furthermore, the ophthalmic laser therapy device has a scanning device for shifting the focus of the pulsed laser beam in a tissue of a patient's eye, in particular in a cornea and / or an eye lens, for cutting through the tissue in a scan pattern of focus spots of the focus of the pulsed laser beam along a scan path according to the control data on. Furthermore, the ophthalmological laser therapy device comprises a control unit for controlling the ophthalmological laser therapy device by means of the control data. The planning unit has an interface for transferring the control data to the control unit.

The planning unit is characterized in that it is designed to generate the control data for the scan pattern of focus spots of the focus in the tissue of the patient's eye, in particular in the cornea and / or the eye lens, along the scan path with which the ophthalmic laser therapy device is controlled can, that the laser device provides a pulsed laser beam with a constant laser pulse _{frequency f P} , the scan path rotates at a constant angular velocity around a scan path center, a distance to the scan path center evaluated at the focus spots increases or decreases monotonically along the scan path, and the scan pattern of focus spots the focus of the pulsed laser beam of a given density is sufficient.

The tissue of the patient's eye in which cuts can be made when the ophthalmic laser therapy device is in operation is preferably the cornea (or also called the cornea) and / or the lens of the eye and the tissue that directly surrounds the cornea and the lens of the eye . The lens of the eye also includes the capsular bag surrounding the lens. In addition, the tissue can be, for example, the sclera - that is, the outer covering of the eyeball, also called the dermis - and / or the limbus - that is, the transition between the cornea and the sclera. Furthermore, the tissue can be the vitreous (vitreous body) and / or the retina (retina).

The laser device that can be used in the ophthalmic laser therapy device is preferably a device that provides laser pulses with a pulse duration of femtoseconds or picoseconds, and whose focused laser beam is able to cut through the tissue of a patient's eye by means of optical breakthroughs due to non-linear absorption. For this purpose, the laser device can comprise, for example, a femtosecond laser or a picosecond laser.

A femtosecond laser, for example, has a wavelength in a range from 750 nm to 1100 nm. The use of femtosecond lasers at other wavelengths is, however, basically also conceivable. Technically, a wavelength from the range from 375 nm to 550 nm or from the range from 250 nm to 367 nm is also relatively easy to implement, which corresponds to a doubling or tripling of the frequency of the technically currently preferred femtosecond lasers. Femtosecond lasers from the wavelength range from 1020nm to 1060nm have been established for corneal applications for many years and are used here by way of example.

The pulse duration of a femtosecond or picosecond laser, which can be used here, can advantageously be selected from a pulse duration range of 50 fs to 5 ps. In particular, a pulse duration from a range from 100fs to 1ps, and very particularly from a range from 250fs to 600fs, is preferred here.

The pulse energy of a femtosecond or picosecond laser that can be used here is advantageously in a pulse energy range of 20nJ to 2µJ. A pulse energy of approx. 130 nJ is particularly preferred.

Typically, a laser device can provide laser pulses with a laser pulse frequency f _P of up to 50 MHz. However, the laser device can be designed to reduce the laser pulse frequency. Often, however, only discrete laser pulse frequencies are available for selection. According to the invention, the planning unit is designed to _{select a laser pulse frequency f P} from a series of possible laser pulse frequencies. The selection is made depending on further calculations for which the planning unit is designed and which are described below. The laser pulse frequency is constant within the limits or tolerances given by the laser device. Deviations in the laser pulse frequency are less than ± 20%, preferably less than ± 5%, particularly preferably less than ± 1%.

The focusing device is designed to focus the pulsed laser beam in the tissue of the patient's eye so that an optical breakthrough is achieved in the focus. The focusing device is preferably designed in such a way that the optical properties of the patient's eye (such as, for example, radii of curvature of the optically effective interfaces - for example on the cornea or the lens of the eye - or the refractive indices of the irradiated tissue) are taken into account. Furthermore, the focusing device can be designed to generate a focus of the pulsed laser beam in the tissue of the patient's eye, a contact glass being arranged in front of the patient's eye in the beam path.

The scanning device of the ophthalmic laser therapy device allows the focus of the pulsed laser beam to be shifted or scanned in the tissue of the patient's eye. Scanning of the pulsed laser beam should be possible without restriction in all three spatial directions x, y, z. The scanning device should accordingly be designed to perform both lateral scans in the x and y directions and also z scans along the optical axis of the pulsed laser beam.

The scanning device can include a pair of scanning mirrors. These can be designed to deflect a laser beam in two non-parallel (preferably mutually perpendicular) directions. The first scanning mirror allows, for example, a deflection of the laser beam in the x-direction, the second scanning mirror a deflection in the y-direction. The scanning mirrors can be driven by galvanometers. The scanning mirrors can be designed as resonant scanning mirrors. The scanning device can comprise MEMS scanners (Micro-Electro-Mechanical-Systems). Furthermore, the scanning device can also be designed in such a way that the beam deflection is parameterized via radius and azimuth angle and can have a radius-azimuth scanner. Such a radius-azimuth scanner has a displacement unit which enables a radial displacement of the laser beam with respect to a scanner center, and a further displacement unit which enables an azimuthal displacement (rotation) with respect to the scanner center. The radius-azimuth scanner can, for example, comprise optics for guiding the laser beam, which optics are attached to a rotating device, and the distance between the optics and the fulcrum of the device can be changed.

The scanners described above, which enable the focus to be shifted in two spatial directions (e.g. lateral), are typically combined with a further scanner, which enables the focus to be shifted in a direction that is at an angle to the two spatial directions (preferably perpendicular). This can be an axial z-scanner that can shift the focus parallel to the optical axis. Scanning “in a tissue” also includes scanning directly on the surface of the tissue.

With the help of the focusing device and the scanning device, a focus can be generated and shifted in the tissue of the patient's eye. The focus is shifted in the tissue with the aid of the scanning device and if the laser device were to continuously emit laser radiation, the focus of the laser radiation in the tissue defines a continuous, ie spatially uninterrupted, track. This imaginary track is also referred to as a scan path. The scan path is therefore a (one-dimensional) line in a three-dimensional volume of the tissue of the patient's eye.

rotiert. Das Scanbahnzentrum kann einen Startpunkt oder einen Endpunkt der Scanbahn markieren. Das Scanbahnzentrum kann sich jedoch auch außerhalb des Scanfeldes befinden; dabei ist das Scanfeld die Gesamtheit der Scanbahn sowie deren (gedachten) Verbindungen von benachbarten Abschnitten der Scanbahn: Wenn beispielsweise ein ringförmiges Scanfeld (mit einer Aussparung in der Mitte) erzeugt werden soll, kann sich das Scanbahnzentrum in der Mitte des Ringes befinden und liegt somit außerhalb des Scanfeldes. Weiterhin kann sich das Scanbahnzentrum auf der optischen Achse der Fokussiervorrichtung befinden (x₀ = y₀ = 0 so dass $\overrightarrow{x_0}=\left(\mathrm{0,0,}z{}_0)\right).$

The control data generated by the planning unit according to the invention can be controlled by the ophthalmological laser therapy device in such a way that the scan path is at a constant angular velocity around a center of the scan path $\overrightarrow{x_0}=\left(x_0,y_0,z_0\right)$

rotates. The center of the scan path can mark a starting point or an end point of the scan path. The scan path center can, however, also be located outside the scan field; The scan field is the entirety of the scan path and its (imaginary) connections to neighboring sections of the scan path: If, for example, a ring-shaped scan field (with a recess in the middle) is to be generated, the center of the scan path can be in the middle of the ring and is therefore located outside the scan field. Furthermore, the center of the scan path can be located on the optical axis of the focusing device (x ₀ = y ₀ = 0 so that $\overrightarrow{x_0}=\left(\mathrm{0.0,}z{}_0)\right).$

The place at which the focus in the tissue of the patient's eye is currently on the scan path, at the time at which a laser pulse of the pulsed laser radiation is focused into the tissue, is called the focus spot or focus point. The ophthalmic laser therapy device thus generates a large number of focus spots during operation, which are generated along the scan path in the tissue of the patient's eye. An optical breakthrough can be achieved in the tissue of the patient's eye at each focus spot. The pulsed laser beam is not only effective in the focal point itself; rather, the laser pulse interacts with the tissue in a volume around the focal point. This volume is also called the effective focus area.

Due to the optical breakthroughs at each focal point in the tissue of the patient's eye, the totality of the effective focus areas creates a (local) cut at which the tissue is severed. Since a focus spot is not generated at every location on the scan path, the scan field can be larger than the section. The distribution of the focus spots at which an optical breakthrough is to be generated is referred to as the scan pattern.

A cut is a partial volume in the tissue that results from the volumes of the effective focus areas and from an (imaginary) connection between adjacent effective focus areas. Typically, the named partial volume has only a small extent at each location in one spatial direction - for example of the order of magnitude of the diameter of a focus effective area - and has a larger extent in the two spatial directions perpendicular thereto. Thus, when the ophthalmological laser therapy device is in operation, there is a cut as a two-dimensional surface in the three-dimensional volume of the tissue of the patient's eye. The surface has a thickness that corresponds approximately to the diameter of an effective focus area.

Since the scan field in the tissue can be larger than the cut to be generated, it can be advantageous if not all laser pulses that would be available according to the constant laser pulse frequency are actually used for a focus spot. This is particularly advantageous when the scanning device requires more time for a shift of the focus along the scanning path than there is between two laser pulses with the constant laser pulse frequency. In such a case, for example, a laser pulse cannot be provided; At that time, only an imaginary focus spot is created at the focal point of the scan path. Alternatively, the provision of a pulsed laser beam can be suspended for the time in which the focus is scanning along the scan path outside of the cut to be generated.

Rotating the scan path around the scan path center is understood to mean that a scan angle of the straight line connecting a starting point of the scan path to the scan path center increases steadily in relation to a line connecting a point of the scan path with the scan path center along the track of the scan path. The angular velocity describes which scan angle is swept over by the scan path per time. A constant angular velocity is present if it varies within the limits or tolerances given by the scanning device. Deviations in the angular velocity are less than ± 20%, preferably less than ± 5%, particularly preferably less than ± 1%.

The inverse of the angular velocity is proportional to a rotation frequency f _R. This describes the rate at which a scan angle of 360 ° is swept over. According to the invention, the rotation frequency with which the scan path rotates around the center of the scan path is constant; the tolerance of the constancy results from the tolerance of the constant angular velocity.

Due to the constant angular velocity and the constant laser pulse frequency, an azimuth angle for an i-th focus spot can be specified via the relationship ϕ _i = 2 · π · (i − 1) · f _R / f _L + ϕ ₁ . Φ _{1 is} the azimuth angle for the first focus spot.

As a rule, the scanning device has a rotation _{frequency f R} or a range of rotation frequencies at which the positions of the scanning path can be controlled with high accuracy. For resonant scanners, this rotation frequency is close to its resonance frequency, for example. The scanning path preferably rotates at a constant angular velocity which corresponds to a rotation frequency which ensures a high degree of accuracy of the positions of the scanning path.

According to the invention, the control data are generated in such a way that a distance from the center of the scan path that is evaluated at the focus spots increases or decreases monotonically along the scan path. In other words: If the distances between the focus spots and the center of the scan path are viewed in the order in which they arise (i.e. along the scan path), the distances increase monotonically or the distances decrease monotonically. It is possible for focus spots that follow one another in time to have the same distance from the center of the scan path. It should be noted that the monotony is only required for the distance between the focus spots. The course of the scan path itself can deviate from the monotony.

Finally, with the additional control data generated by the planning unit according to the invention, the ophthalmological laser therapy device can be controlled in such a way that the scan pattern of focus spots of the focus of the pulsed laser radiation satisfies a predetermined density. Since a section is typically to be generated over a scan pattern of focus spots which corresponds to an area in the tissue of the patient's eye, the density can be defined, for example, as the number of focus spots per area. The density thus determines how many focus spots are to be generated in the scan pattern when the ophthalmic laser therapy device is in operation in order to generate the cut for severing the tissue. The density can be specified by the ophthalmic laser therapy device - for example in the planning unit. The density can be determined by the user of the ophthalmic laser therapy device. The density can be a fixed value, a limit value that must not be exceeded or fallen below, or a range of values. It is also possible that the density can be selected by the user from a selection list provided by the ophthalmic laser therapy device.

The density that the focus spots of the scan pattern satisfy, in conjunction with the size of the effective focus areas, determines whether a complete or partial severing of the tissue of the patient's eye is possible. The interaction of a laser pulse with the tissue depends on pulse parameters (such as pulse duration, wavelength or pulse energy) of the pulsed laser radiation. It is also dependent on the type of tissue in the patient's eye in which an optical breakthrough should be able to be produced. The density can be specified in such a way that the effective focus areas are on average close to one another and thus enable a complete severing of the tissue. Alternatively, the density can be specified in such a way that the effective focus areas are on average further apart, so that the effective focus areas do not overlap or butt against each other and so tissue bridges remain in the tissue within the cut surface between the effective focus areas. In this case, a partial severing of the tissue is made possible. This creates a kind of predetermined breaking point at which the tissue is prepared in such a way that it can be completely severed in a targeted and controlled manner in one step of the surgical procedure. Such a partial severing is advantageous, for example, when, during an intervention to correct ametropia, a lens-shaped partial volume of the cornea is to be removed from the cornea via a laterally opening incision - a so-called access incision.

The specified density of the focus spots is therefore typically related to a goal that is being pursued with the section to be generated.

The control data that are generated by the planning unit according to the invention and with which the ophthalmological laser therapy device can be controlled include at least the constant laser pulse frequency. The constant angular velocity, the scan path center and the specified density are variables that are included in the generation of the control data for the spatial position (x, y, z) of the focus as a function of time. These variables can also be available for discharge to the control unit.

The planning unit according to the invention allows simple and inexpensive components to be used for the ophthalmic laser therapy device due to the constant laser pulse frequency and the constant angular velocity. The constant laser pulse frequency enables a complex one To dispense with control of the laser device, which must ensure that the required pulses are available at the right time, with variable time pulse intervals and with constant pulse energy (and also pulse energy) during the generation of a scan pattern.

The constant angular speed with which the scan path rotates around the scan path center ensures that the same number of focus spots can be generated for each range of azimuth angles (with respect to the scan path center). In this way, a homogeneous density of the focus spots per azimuth angle range is ensured. Furthermore, the constant angular speed with which the scan path rotates around the scan path center and the monotony of the temporal course of the distances between the focus spots from the scan path center allow the use of a simple and inexpensive scanning device. Depending on the technology used, the scanners can be controlled with simple sine signals (x-y scanner) or a constant signal (azimuth scanner). Strong accelerations of the scanner are not necessary. No angular velocity tuning is required. The control for the scanning device can thus advantageously be simple and inexpensive and at the same time generate the focus spots with high precision at the desired locations in the tissue of the patient's eye.

The control unit, which as a rule uses the control data generated by the planning unit, can access all controllable units of the ophthalmic laser therapy device, in particular the laser device, the focusing device and the scanning device. It can be constructed in one or more parts and communicate with the controllable units of the ophthalmic laser therapy device - and possibly with other devices of the ophthalmic laser therapy device as well as with devices connected to it - via wired or wireless communication paths. Furthermore, the control unit preferably has an interface via which control data can be supplied to the control unit in a wired or wireless manner.

The considerations discussed for a cut in a plane apply to both a cut that is in a plane and a curved cut. A point or a straight line can also be assumed as the center of the scan path for a curved section. The distances between the focus spots are determined from this point (or straight line) in three-dimensional space. The density of the focus spots can be related to the cut surface or to a volume. The advantages of the planning unit according to the invention remain for curved cuts. For the sake of simplification, the projection of the scan path into a plane is considered below or it is assumed that the scan path is located in a plane that is, for example, perpendicular to the optical axis.

Typically, the incision that is to be made in the tissue of the patient's eye does not have the same extent in all three spatial dimensions; often the extent of the cut is not identical even in the lateral dimensions (x and y). Furthermore, the size (extent) of the effective focus area typically deviates in the axial direction (z) from that in the lateral direction. In addition, the dimensions of the effective focus area in the x-direction and y-direction can differ from one another; The cause of this can be the polarization of the pulsed laser beam. The asymmetry effects mentioned by way of example do not have to occur in the direction of those axes which are given via the optical axis (z-axis) and a plane perpendicular thereto (x-y plane). Rather, it is possible that the asymmetry occurs in directions that are rotated with respect to the directions x, y and z. Therefore let x ', y', z 'be a coordinate system in which the asymmetries occur in the x' direction, y 'direction and / or z' direction, and let T be a unique and reversible transformation that contains the coordinates x ' 'y', z 'transformed into x, y, z.

In order to take account of an asymmetry effect, it is advantageous to take this into account when evaluating distances in the tissue, for example to be able to generate asymmetrical cuts in a time-efficient manner or to ensure the specified density of the focus spots in the scan pattern.

In an advantageous embodiment, the distance between the focus spots and the center of the scan path therefore takes into account an asymmetry effect.

und $\overrightarrow{x{\text{'}}_2}$

in x', y', z' Koordinaten unter Berücksichtigung der Asymmetrie berechnet werden über $\Delta {\text{'}}_3\left(\overrightarrow{x{\text{'}}_1},\overrightarrow{x{\text{'}}_2}\right)=$

$\sqrt{{\left(x{\text{'}}_1-x{\text{'}}_2\right)}^2+{\alpha }_y{}^2\cdot {\left(y{\text{'}}_1-y{\text{'}}_2\right)}^2+{\alpha }_z{}^2\cdot {\left(z{\text{'}}_1-z{\text{'}}_2\right)}^2}.$

Für einen beliebigen Fokusspot $\overrightarrow{x{\text{'}}_1}$

(der sich aus $\overrightarrow{x{\text{'}}_1}$

über die eindeutig, umkehrbaren Transformation T ergibt) und ein Scanbahnzentrum $\overrightarrow{x{\text{'}}_0}$

(das sich aus $\overrightarrow{x_0}$

ebenfalls über die eindeutig, umkehrbaren Transformation T ergibt) ergibt sie der Abstand unter Berücksichtigung der Asymmetrie zu $\Delta {\text{'}}_3\left(\overrightarrow{x{\text{'}}_i},\overrightarrow{x{\text{'}}_0}\right)=$

$\sqrt{{\left(x{\text{'}}_i-x{\text{'}}_0\right)}^2+{\alpha }_y{}^2\cdot {\left(y{\text{'}}_i-y{\text{'}}_0\right)}^2+{\alpha }_z{}^2\cdot {\left(z{\text{'}}_i-z{\text{'}}_0\right)}^2}.$

Liegt die Scanbahn in einer Ebene oder wird für das Scanbahnzentrum eine Gerade angenommen, so vereinfacht sich die Berechnung des Abstands vom Scanbahnzentrum, da lediglich zwei Koordinaten berücksichtigt werden müssen.For this purpose, asymmetry factors can be introduced in the regulation for calculating the distances between two points in space. Distances are advantageously calculated with the aid of a metric in x ', y', z 'coordinates, since here an asymmetry can be represented particularly easily. If the asymmetry in the y 'direction compared to the x' direction is, for example, a factor a _y (with a _y > 0) and if the asymmetry in the z 'direction compared to the x' direction is, for example, a factor a _z (with a _z > 0), the distance between two points can be $\overrightarrow{x{\text{'}}_1}$

and $\overrightarrow{x{\text{'}}_2}$

in x ', y', z 'coordinates taking into account the asymmetry are calculated over $\Delta {\text{'}}_3\left(\overrightarrow{x{\text{'}}_1},\overrightarrow{x{\text{'}}_2}\right)=$

$\sqrt{{\left(x{\text{'}}_1-x{\text{'}}_2\right)}^2+{\alpha }_y{}^2\cdot {\left(y{\text{'}}_1-y{\text{'}}_2\right)}^2+{\alpha }_z{}^2\cdot {\left(z{\text{'}}_1-z{\text{'}}_2\right)}^2}.$

For any focus spot $\overrightarrow{x{\text{'}}_1}$

(which consists of $\overrightarrow{x{\text{'}}_1}$

via the unambiguous, reversible transformation T) and a scan path center $\overrightarrow{x{\text{'}}_0}$

(which consists of $\overrightarrow{x_0}$

also results from the unambiguous, reversible transformation T) it results in the distance taking into account the asymmetry to $\Delta {\text{'}}_3\left(\overrightarrow{x{\text{'}}_i},\overrightarrow{x{\text{'}}_0}\right)=$

$\sqrt{{\left(x{\text{'}}_i-x{\text{'}}_0\right)}^2+{\alpha }_y{}^2\cdot {\left(y{\text{'}}_i-y{\text{'}}_0\right)}^2+{\alpha }_z{}^2\cdot {\left(z{\text{'}}_i-z{\text{'}}_0\right)}^2}.$

If the scan path lies in one plane or if a straight line is assumed for the scan path center, the calculation of the distance from the scan path center is simplified, since only two coordinates have to be taken into account.

By taking asymmetry effects into account according to the invention, a severing of tissue with a given density of focus spots in the scan pattern using simple and inexpensive components of the ophthalmic laser therapy device is also ensured for asymmetrical effective focus areas or asymmetrical cuts.

According to an advantageous embodiment of the planning unit, the control data are generated in such a way that for each rotation of the scan path around the scan path center the absolute amount of a difference between the distances from the scan path center evaluated at the focus spots at the beginning of the rotation and at the end of the rotation with an increasing mean distance from Scan path center decreases.

A rotation of the scan path around the scan path center is to be understood as a section of the scan path in which an azimuth angle with respect to the scan path center of 360 ° is swept over. The scan path can thus be composed of several rotations.

If the scan path is viewed at the beginning of the rotation (at an azimuth angle ϕ), a distance from the center of the scan path can be assigned to it via the distance of a focus spot from the center of the scan path immediately before or after the start of the rotation. The scan path at the end of a rotation (at an azimuth angle ϕ + 360 °) can also be assigned a distance via the distance of a (different) focus spot from the center of the scan path immediately before or after the end of the rotation. The amount of the difference in the distances from the center of the scan path at the beginning and at the end of a rotation corresponds to a radial width of a rotation. The mean distance of a rotation from the center of the scan path is the mean value of the distances to the start and end of the rotation. The end of a rotation corresponds to the beginning of a subsequent rotation. If one considers the mean intervals of a temporal series of rotations of the scan path around the scan path center, then these increase or decrease monotonically.

An azimuthal length can be assigned to a rotation via the mean distance (by multiplying by a factor of 2π). If the azimuthal length is multiplied by the radial width, this corresponds to an area that can be assigned to the rotation.

Since (on average) each rotation has the same number of focus spots, it is advantageous if the radial width of a rotation (and thus the distance between two rotations) becomes smaller, the larger the mean distance of the rotation from the center of the scan path, since the larger it is mean distance of a rotation is associated with a greater azimuthal length. This compensates for the fact that the area that can be assigned to a rotation increases with the azimuthal length.

The inventive decrease in the radial widths of each rotation with increasing mean distance of the rotation leads to the density of the focus spots in the scan pattern being adapted over radial distances from the center of the scan path.

According to a particularly advantageous embodiment of the planning unit, the control data are generated in such a way that for each rotation of the scan path around the scan path center, the absolute amount of the difference between the distances from the scan path center evaluated at the focus spots at the start of the rotation and at the end of the rotation is proportional to the inverse mean distance of the rotation from the scan path center.

Let r _{a be} the distance at the beginning of a rotation (evaluated on a focus spot that is located immediately before or after the start of the rotation on the scan path) and let r _{e be} the distance to the end of a rotation (evaluated on another focus spot that is immediately before or after the end of the rotation on the scan path). The mean distance of the rotation thus corresponds to r _m = (r _a + r _e ) / 2. The absolute amount of the difference in the distances is Δr = | r _a - r _e |, where "|. |" Means the formation of an absolute amount.

Typically, all of the focus spots of the rotation lie in one plane (for example the xy plane or the x'-y 'plane) or they have an offset in the z direction that is small compared to the z extension of the effective focus areas. Then the center of the scan path is also in this plane and the area that can be assigned to the rotation is A _Rot = π · | r _a ² - r _e ² |. This corresponds to A _Rot = π · r _m · Δr. In other words, the area of a rotation is proportional to the product of the azimuthal length and the radial width of a rotation. The surface has the shape of a ring in the plane. If the absolute amount of the difference between the distances from the center of the scan path evaluated at the focus spots at the beginning of the rotation and at the end of the rotation decreases proportionally to the inverse mean distance of the rotation from the center of the scan path (Δr∼1 / r _m ), then it is achieved according to the invention that the areas which can be assigned to each rotation, just remain constant. This ensures that a specified density of focus spots in the scan pattern is achieved for all distances from the center of the scan path. This enables a particularly precise severing of tissue over the entire incision.

The considerations retain their validity (and derive their particular advantageous benefit as a result) when asymmetry effects are taken into account.

According to a particularly advantageous embodiment of the planning unit, the control data are generated in such a way that the focus spots lie on a spiral around the center of the scan path.

A spiral is characterized by the fact that it rotates around a center and that the distance to the center along the track of the spiral increases or decreases strictly monotonically. A spiral in three-dimensional space takes the form of a helix, the distance from the center of which changes in a strictly monotonous manner.

The scan path may deviate from a spiral between two successive focus spots as long as the scan path again corresponds to points of a spiral at the locations of the focus spots.

By means of the embodiment presented here, it is possible to further simplify the control of the scanning device, since accelerations of the scanner are further reduced due to the strict monotony of the distances from the center of the scan path. In this way, focus spots can be realized with high precision but with comparatively low demands on the scanning device.

According to a further particularly advantageous embodiment of the planning unit, the control data are generated in such a way that the focus spots lie on a spiral around the center of the scan path and that the absolute value of the difference between the distances from the center of the scan path of two successive focus spots is proportional to an inverse mean distance between the successive focus spots and the center of the scan path.

Two successive focus spots that lie on a spiral around the center of the scan path are focus spots that are generated one after the other in time. The focus spot following a focus spot can also be an imaginary focus spot if, for example, the imaginary focus spot lies outside the section to be generated.

Let r _{s, i be} the distance from the center of the scan path for an i-th focus spot and let r _{s, i + 1 be} the distance for the i + 1-th focus spot that follows in time; The index "s" indicates that there are distances on a spiral path. The mean distance between the successive focus spots corresponds to r _{s, im} = (r _{s, i} + r _{s, i + 1} ) / 2. The absolute amount of the difference in the distances is Δr _{s, i} = | r _{s, i} - r _{s, i + 1} |, where "|. |" Means the formation of an absolute amount.

Dabei sind t_i bzw. t_i+1 die Zeitpunkte, zu denen der i-te bzw. i+1-ten Fokusspot erzeugt werden. Die dem i-ten Fokusspot zugeordnete Fläche entspricht $A_i=\pi \cdot r_{s,im}\cdot \Delta r_{s,i}\cdot \frac{t_{i+1}-t_i}{1/f_R}.$

Die Fläche hat die Form eines Ringsegments in der Ebene. Nimmt der Absolutbetrag der Differenz der Abstände vom Scanbahnzentrum zweier aufeinanderfolgender Fokusspots proportional zum inversen mittleren Abstand der Fokusspots ab (Δr_s,i∼1/r_s,im), so wird erfindungsgemäß erreicht, dass die Flächen, die einem jeden Fokusspot zugeordnet werden können, gerade konstant bleiben. Auf diese Weise wird sichergestellt, dass eine vorgegebene Dichte von Fokusspots im Scanmuster für alle Abstände vom Scanbahnzentrum erzielt wird. Dies ermöglicht ein besonders präzises Durchtrennen von Gewebe über den gesamten Schnitt.If the successive focus spots lie in one plane (for example the xy plane or the x'-y 'plane) or if they only have a slight offset in the z direction, the center of the scan path is also in this plane and the area that can be assigned to the i-th focus spot is ${\mathrm{A.}}_i=\pi \cdot \left|r_{s,i}{}^2-r_{s,i+1}{}^2\right|\cdot \frac{t_{i+1}-t_i}{1/f_{\mathrm{R.}}}.$

Here, t _i and t _{i + 1 are} the times at which the i-th and i + 1-th focus spots are generated. The area assigned to the i-th focus spot corresponds to ${\mathrm{A.}}_i=\pi \cdot r_{s,im}\cdot \Delta r_{s,i}\cdot \frac{t_{i+1}-t_i}{1/f_{\mathrm{R.}}}.$

The surface has the shape of a ring segment in the plane. If the absolute amount of the difference between the distances from the center of the scan path of two successive focus spots decreases proportionally to the inverse mean distance between the focus spots (Δr _{s, i} ∼1 / r _{s, im} ), the invention achieves that the areas that can be assigned to each focus spot , just stay constant. This ensures that a predetermined density of focus spots in the scan pattern for all distances from the center of the scan path is achieved. This enables a particularly precise severing of tissue over the entire incision.

The considerations retain their validity (and derive their particular advantageous benefit as a result) when asymmetry effects are taken into account.

The planning method according to the invention thus enables the generation of control data for a scan pattern of focus spots that lie on a spiral around the center of the scan path, the specified density being achieved for all distances from the center of the scan path.

According to an advantageous embodiment of the planning unit, the control data are generated in such a way that the scan pattern of the focus spots of the focus of the pulsed laser beam satisfies a limit value for a distribution measure for evaluating the distribution of the focus spots.

A distribution measure assigns a value to the scan pattern which evaluates the distribution of the focus spots in the section generated by the scan pattern. The distances between the focus spots are advantageously incorporated into this value. Even if a predetermined density of focus spots is implemented in a sub-area of the scan pattern (for example in an azimuth angle area or for radial ring segments), focus spots can nevertheless accumulate locally. This can lead to the fact that the tissue can be completely severed in regions with many focus spots, while tissue bridges remain in regions between clusters of focus spots, so that the tissue can only be partially severed there.

The distribution measure can be implemented, for example, in such a way that some of the focus spots (for example those that are at a large distance from the center of the scan path) or all of the focus spots are assigned a mean distance from adjacent focus spots. To determine the mean distance from a focus spot to its neighbors, the following procedure can be used, for example: A circle is placed in the cut surface around the focus spot. This circle is broken down into circle segments; Advantageously, all segments are of the same size and there are at least three segments. The radius of the circle must be large enough so that there is at least one focus spot in each segment of the circle (except for the focus spot in the center of the circle). The minimum distance between the focus spots in the circle segment and the focus spot in the center of the circle is determined for each segment. A mean value of the minimum distances over the circle segments can then be calculated. Alternatively, the maximum of the minimum distances can be formed over the circle segments or the difference between the maximum and the minimum of the minimum distances. In this way, a focus spot can be assigned a measure of the distance to neighboring focus spots. The division of the circle into circle segments ensures that it is recognized when neighboring focus spots are piling up in one direction, while there is a large distance to the next focus spot in other directions. The determined dimensions can then be averaged so that a single value is assigned to a scan pattern as a distribution measure of the focus spots. Alternatively, for example, the mean value and standard deviation can be determined as a pair of values of the distribution measure. Alternatively or additionally, the maximum and the minimum can also be determined as a distribution measure.

Alternatively, the distribution measure can be designed in such a way that the size (and shape) of the effective focus areas of the focus spots are taken into account. For this purpose, for example, the size of the corresponding effective focus area can be marked in the cutting plane for each focus spot of the scan pattern. An area can be assigned to the totality of the effective focus areas of all focus spots of the scan pattern. Overlapping areas of two or more effective focus areas of different focus spots are only taken into account once (and not more than once) when assigning the area. This area of the totality of the effective focus areas of the focus spots of the scan pattern in the cutting plane can be set in relation to the area of the cut. If, for example, a value of 1 is achieved for the relation, a complete severing of the tissue is made possible without leaving any tissue bridges. If, for example, a value of 0.5 is achieved for the relation, the proportion of remaining tissue bridges is 50% of the cut area. This exemplary value as a distribution measure thus provides information about the type of severing that can be achieved with a given scan pattern. In addition (or alternatively), the ratio of the area of the totality of the focus effective areas of the focus spot of the scan pattern in the cutting plane to the sum of all sizes of the focus effective areas of the focus spot of the scan pattern in the cutting plane can also be formed as a distribution measure. Such a distribution measure describes how much the effective focus areas overlap: Is the ratio 1 , there is no overlap; if the ratio is 0.5, for example, there is a high proportion of overlaps; in such a case, the focus spots are very likely to be set too narrowly and a comparatively long time is required for the generation of the scan pattern.

A value (or values) for evaluating the distribution of the focus spots in the scan pattern can be determined by means of the exemplary distribution measures and the described variants thereof. It is particularly advantageous to take into account any asymmetry effects that may be present, for example when calculating distances between focus spots with a metric that includes the asymmetry, or when determining the size of the effective focus areas.

The limit value that the distribution measure should satisfy for evaluating the distribution of the focus spots can be a limit for each value that the distribution measure provides. For the sake of simplicity, only a single limit value is spoken of in the following; However, this is to be understood as meaning that the limit value can also be limits for various values that are provided by the distribution measure.

The limit value can act as a number (possibly including the associated units) or a range of values. It can be a one-sided limit value or a two-sided limit value. The limit value can be stored in the planning unit or specified by a user of the ophthalmic laser therapy device.

If the distribution of the focus spots in the scan pattern satisfies the limit value for the degree of distribution, then according to the invention it is ensured that, in addition to a predetermined density of focus spots, there is also a distribution with homogeneous distances between focus spots. In this way, local accumulations of focus spots can be avoided and a severing of the tissue with a high cut quality over the entire cut surface is further improved.

In a further advantageous embodiment of the planning unit, the laser device of the ophthalmological laser therapy device comprises a laser source for generating laser pulses with a laser repetition frequency f _L and a pulse selection device which is set up to select the generated laser pulses according to the further control data according to a division ratio D and for the pulsed Provide laser beam. The planning unit is designed to determine the division ratio D such that the constant laser pulse frequency f _P results. The result is f _p = f _L / D.

A laser source is typically built in such a way that it can provide laser pulses with reproducible parameters (such as pulse energy, wavelength, spectral width, pulse duration, polarization) with a fixed laser repetition frequency f _L. A change in the laser repetition frequency is possible, but requires a great deal of technical effort. There is the risk that the parameters of the laser pulses are not stable, which has a negative effect on the quality of a cut to be produced in a tissue of a patient's eye. The laser repetition frequency of the laser source, ie the repetition rate of the laser pulses, is therefore advantageously permanently set with a value from a range from 10 kHz to 50 MHz; a laser pulse repetition frequency from a range from 200 kHz to 20 MHz is advantageous.

A pulse selection device is arranged downstream of the laser source in the beam path. Such a pulse selection device can be implemented, for example, via an acousto-optical modulator (AOM) which, depending on an activation, can bring about a beam deflection of the laser radiation in order to direct laser pulses out of the beam path in the direction of the tissue of the patient's eye so that it cannot generate a focus spot.

The pulse selection device can be part of the laser source, or it can be arranged directly downstream of the laser source in the beam path. However, further optical elements and / or the scanning device and / or the focusing device can also be located in the beam path between the laser source and the pulse selection device. However, an order close to the laser source is preferred.

The division ratio D indicates which proportion of the laser pulses generated by the laser source is to be passed on in the direction of the patient's eye. In other words, the division ratio corresponds to the number of transmitted laser pulses to the number of generated pulses. The division ratio can be an integer; every D-th laser pulse is passed on, while all D - 1 laser pulses in between are not passed on. Alternatively, the division ratio can be a rational number; in this case, the desired division ratio is obtained on average after a series of transmitted laser pulses. If an irrational number is chosen for k, this is only approximated after many laser pulses.

With the advantageous embodiment presented here, it is possible to further reduce the complexity and the costs for the ophthalmic laser therapy device, which can avoid the considerable technical effort for a laser source that can provide variable laser pulse frequencies.

According to a further advantageous embodiment, the planning unit is designed to generate control data for at least two scan patterns with which the ophthalmic laser therapy device can be controlled. The first laser pulse frequency can differ from the at least one further laser pulse frequency, the first scan path center from the at least one further scan path center and / or the first angular velocity from the at least one further angular velocity.

The cut to be produced in the tissue of the patient's eye can have a shape that is, for example, significantly larger in one direction than in another. In this case it may be that the cut can be generated more quickly via two (or more) scan patterns in which the scan patterns have scan path centers that deviate from one another.

If the cut to be generated is a surface that is at a large distance from the center of the scan path, it can be advantageous to generate the cut using two scan patterns as well. In this case, for example, the first scan pattern can be a pattern in which focus spots are generated close to the center of the scan path. Another pattern only generates focus spots at a greater distance from a scan path center (which can be identical to the first scan path center), a higher constant laser pulse frequency and / or a higher constant angular velocity being used for the further scan pattern. This, too, can lead to the cut to be generated being generated more quickly overall.

A quick creation of a cut is advantageous in order to reduce the treatment time. On the one hand, this reduces the burden on the patient. On the other hand, it also reduces the risk that the patient's eye will move in relation to the ophthalmic laser device, and thus a faulty scan pattern and thus a faulty cut will be generated.

In a particularly advantageous further development of the embodiment, the planning unit is designed in such a way that the at least two scan patterns do not spatially at least partially overlap.

Two scan patterns overlap when focus effective areas of one scan pattern overlap with focus effective areas of another scan pattern.

Overlapping two scan patterns ensures that a continuous cut can be created in the tissue via the two scan patterns.

In order to further reduce the time for generating the section, the scan patterns should only overlap to the extent necessary for reliable generation of the section (taking into account the specified density of focus spots and advantageously taking into account the limit value for a distribution measure). An overlapping of two scan patterns is as little as possible less than 50%, preferably less than 10%, particularly preferably less than 2%.

An ophthalmic laser therapy device according to the invention for generating a scan pattern comprises a laser device for providing a pulsed laser beam and a focusing device for focusing the pulsed laser beam in a focus. Furthermore, the ophthalmic laser therapy device has a scanning device for shifting the focus of the pulsed laser beam in a tissue of a patient's eye, in particular in a cornea and / or an eye lens, for cutting through the tissue in the scan pattern from focus spots of the focus of the pulsed laser beam along a scan path, which is determined by control data is determined on. In addition, the ophthalmological laser therapy device comprises a control unit for controlling the ophthalmological laser therapy device by means of the control data. In addition, the ophthalmological laser therapy device has a planning unit for generating the control data. The planning unit is designed in such a way that it generates the control data in such a way that it is described in one of the embodiments described above.

According to an advantageous embodiment, the ophthalmological laser therapy device further comprises a measuring device for generating data for a characterization of the patient's eye. In particular, it is a measuring device from the following group: auto refractor, Refractometer, keratometer, aberrometer, wavefront measuring device, optical coherence tomograph (OCT), Scheimpflug camera, ultrasound imaging system, microscope.

The ophthalmic laser therapy device can of course also contain several measuring devices that can be used one after the other or at the same time to characterize the patient's eye.

The data generated by the measuring device can be used to determine the geometry and the position of the cut to be generated in the tissue of the patient's eye. It should be noted, however, that the planning unit described in the various embodiments can generate the control data regardless of whether the patient's eye is connected to the ophthalmic laser therapy device.

Furthermore, the data generated by the measuring device can be used to monitor the generation of the incision in the tissue when the ophthalmic laser therapy device is in operation.

• - Vorgabe eine Dichte von Fokusspots des Fokus des gepulsten Laserstrahls im Scanmuster,
• - Auswahl einer konstanten Laserpulsfrequenz f_Pdes gepulsten Laserstrahls,
• - Zuweisung eines Scanbahnzentrums,
• - Berechnung einer konstanten Winkelgeschwindigkeit mit der die Scanbahn um das Scanbahnzentrum rotiert, wobei aus der Laserpulsfrequenz, dem Scanbahnzentrum und der Winkelgeschwindigkeit weitere Steuerdaten derart ermittelt werden, dass das ophthalmologische Lasertherapiegerät so steuerbar ist, dass das Scanmuster im Gewebe des Patientenauges mit der vorgegebenen Dichte der Fokusspots erzeugt werden kann, und dass ein an den Fokusspots ausgewerteter Abstand zum Scanbahnzentrum entlang der Scanbahn monoton steigt oder monoton fällt, und
• - Zuführung dieser Steuerdaten zu der Steuereinheit des ophthalmologischen Lasertherapiegerätes.

A second aspect of the invention relates to a planning method for the generation of control data for an ophthalmological laser therapy device. The ophthalmic laser therapy device comprises a laser device for providing a pulsed laser beam and a focusing device for focusing the pulsed laser beam in a focus. Furthermore, the ophthalmic laser therapy device has a scanning device for shifting the focus of the pulsed laser beam in a tissue of a patient's eye, in particular in a cornea and / or an eye lens, for cutting through the tissue in a scan pattern of focus spots of the focus of the pulsed laser beam along a scan path according to the control data , and a control unit for controlling the ophthalmic laser therapy device by means of the control data. The planning method according to the invention has the following steps:

• - Specification of a density of focus spots of the focus of the pulsed laser beam in the scan pattern,
• - Selection of a constant laser pulse frequency f _{P of} the pulsed laser beam,
• - Allocation of a scan path center,
• - Calculation of a constant angular speed with which the scan path rotates around the scan path center, further control data being determined from the laser pulse frequency, the scan path center and the angular velocity in such a way that the ophthalmic laser therapy device can be controlled so that the scan pattern in the tissue of the patient's eye with the specified density of Focus spots can be generated, and that a distance from the center of the scan path that is evaluated at the focus spots increases or decreases monotonically along the scan path, and
• - Feeding of these control data to the control unit of the ophthalmic laser therapy device.

The following describes the case in which the distance from the center of the scan path, evaluated at the focus spots, increases monotonically along the scan path. The scan pattern follows a scan path that sweeps over the section to be generated from the inside out and has focus spots within the section to be generated.

On the basis of the specified density of the focus spots, a mean area in the section to be generated can be assigned to each focus spot. Assuming a circular surface, the diameter corresponds to an average distance between two focus spots that is to be achieved. Alternatively, a square area can be assumed.

A minimum distance to the center of the scan path can be assigned to the cut to be generated; this distance can be zero if the center of the scan path lies in the section to be generated. If the distance is zero, a point can be selected as the starting point of the scan path which corresponds, for example, to a third or half of the desired mean distance; or the center of the scan path can be selected as the starting point of the scan path. A first focus spot can be generated at this starting point (with a distance r _{0 from} the center of the scan path). In order to generate a scan pattern as quickly as possible, it is advantageous to choose the constant angular speed so that it is close to the maximum possible angular speed of the scanning device (for example 95% of the maximum speed), at which a scan path with high accuracy of the positions is still along the scan path is guaranteed. The choice of the angular velocity results in a rotation _{frequency f R} with which the scan path rotates around the center of the scan path. This in turn results in the time with which the scan path rotates once around the center of the scan path in a first (innermost) scan path section (first rotation). If you take a constant distance of this Rotation from the center of the scan path, it can be calculated how many focus spots have to be generated along this first rotation so that they have a distance that corresponds, for example, to a desired mean distance that is to be achieved on the basis of the specified density of the focus spots. If the starting point of the scan path is a point whose distance from the center of the scan path corresponds, for example, to a third or half of the desired mean distance, then k focus spots can be selected within the time for a first rotation of the scan path, where k is between two and five is. K does not have to be an integer; rather, it can also be a rational or irrational number. If the starting point of the scan path is a point which is at a greater distance from the center of the scan path than the desired mean distance between two focus spots, more focus spots can be selected within the time for a first rotation of the scan path. The number can be chosen so that these focus spots ultimately have a distance that deviates, for example, by less than ± 50%, preferably less than ± 10%, particularly preferably less than ± 2%, from the desired mean distance between the focus spots.

The angular velocity and the number of desired focus spots on the first rotation determine which laser pulse frequency f _P can be selected: f _P = f _R · k. Since the laser pulse frequencies can typically not be selected from continuous values, but rather from discrete values, it may be that the desired number k of focus spots for the first scan path section cannot be hit exactly, but is slightly adapted. Alternatively, the value of the constant angular velocity can be adjusted again so that the desired number k of focus spots results.

The control data for the scan path are then determined in such a way that, on the one hand, the monotony is maintained and, on the other hand, the specified density is satisfied: The specified density shows how many focus spots K in total are to be generated in the section in the tissue. This in turn shows how often the scan path rotates around the scan path center (N), since the number k of focus spots per revolution is fixed (K = N. K). In accordance with the monotony of the distances from the center of the scan path evaluated at the focus spots, the scan path is selected in such a way that it covers the entire section to be generated.

Alternatively, a scan path can be selected in such a way that the distance from the center of the scan path that is evaluated at the focus spots falls monotonically along the scan path. The scan pattern follows a scan path that sweeps over the section to be generated from the outside inwards and has focus spots within the section to be generated.

Here, too, a mean area in section can be assigned to each focus spot on the basis of the specified density of the focus spots. There is again a mean distance between two focus spots that is to be achieved.

A maximum distance to the center of the scan path can be assigned to the cut to be generated. A location with the maximum distance can be selected as the starting point of the scan path. A first focus spot can be generated at this starting point (with a distance r _{max from} the center of the scan path). In order to generate a scan pattern as quickly as possible, it is again advantageous to choose the constant angular speed so that it is close to the maximum possible angular speed of the scanning device (for example at 95% of the maximum speed) at which there is still a scan path with high accuracy of the positions is guaranteed along the scan path. The choice of the angular velocity results in a rotation _{frequency f R} with which the scan path rotates around the center of the scan path. This results in the time with which the scan path rotates once around the center of the scan path in a first (outermost) scan path section. Assuming a constant distance of this rotation from the center of the scan path, a number can be calculated how many focus spots would have to be generated along this outermost rotation so that they have a distance that corresponds, for example, to a desired mean distance based on the specified density of the focus spots should be achieved. The number k of focus spots for the first scan path section is advantageously selected to be smaller than this number which is required for the focus spots to already have the desired mean spacing on the first scan path section. The reason for this is that for sections of the scan path which are at a smaller distance from the center of the scan path, the distances between successive focus spots are smaller than the desired mean distance. The generation of the scan pattern would then take longer than it would be necessary. The number k can be selected to be a factor of 2, 10 or 50, 100, 200 (or more) smaller than the number that would be necessary for the focus spots on the first scan path section to already have the desired mean distance. The factor can be selected as a function of the size of the difference between a maximum and a minimum distance between the required focus spots in the section to be generated.

The angular velocity and the number k of the desired focus spots on the first scan path section again determine which laser pulse frequency f _P can be selected: f _P = f _R · k. Here, too, k and / or f _R can be adapted again in order to satisfy the equation.

The control data for the scan path are then determined as described for a scan path that is generated from the inside out.

With the aid of the method steps described, control data are available for generating a scan pattern of focus spots, the scan pattern being able to be generated with the aid of an ophthalmic laser therapy device which can have simple and inexpensive components and which enables tissue to be severed according to a predetermined density of focus spots becomes. A homogeneous density of the focus spots per azimuth angle area is ensured.

It should be noted that the planning method described can be carried out without the patient's eye having to be connected to the ophthalmic laser therapy device. Rather, all steps of the planning process can take place long (e.g. hours or days) before a surgical intervention, so that the control data are already available before the patient's eye is optically coupled to the ophthalmic laser therapy device.

In an advantageous planning method, an asymmetry effect is taken into account when calculating the distance between the focus spots and the center of the scan path.

An asymmetry effect can be taken into account, for example, using asymmetrical metrics, as introduced above. Such a metric is advantageously used, for example, to determine the number of focus spots on the first scan path section.

According to an advantageous planning method, the further control data are determined in such a way that for a rotation of the scan path around the scan path center, a difference between the distances from the scan path center evaluated at the focus spots at the beginning of the rotation and at the end of the rotation decreases with an increasing mean distance from the scan path center. The further control data are determined in particular in such a way that the difference in the distances is proportional to the inverse mean distance of the rotation from the center of the scan path.

Since each rotation has the same number k of focus spots, it is advantageous if the radial width of a rotation (and thus the distance between two rotations) becomes smaller, the greater the mean distance of the rotation from the center of the scan path, since a larger mean distance is Rotation is associated with a greater azimuthal length. This compensates for the fact that the area that can be assigned to a rotation increases with the azimuthal length.

The area that can be assigned to a rotation is kept constant for each rotation if the difference between the distances evaluated at the focus spots at the beginning of the rotation and at the end of the rotation is proportional to the inverse mean distance of the rotation from the center of the scan path. This property of the scan path describes its slope as a function of the rotation. _{This results in r j} = c · √j + r ₀ at the focus spots for the scan path. Here, r _{j is} the distance of the j-th rotation from the center of the scan path with j = 0.1, ..., N. In addition, c is a constant of proportionality and r ₀ is the distance of the first (innermost) focus spot from the center of the scan path. Since the entire section is covered after N rotations, r _N corresponds to the distance of the last rotation or the most distant focus spot from the center of the scan path. This results in c = (r _N - r ₀ ) √N. This in turn results in the distances for the rotation of the scan path $r_j=\left(r_N-r_0\right)\cdot \sqrt{j/N}+r_0.$

The method specified here results in control data for the scan path which ensure that a specified density of focus spots in the scan pattern is achieved for all distances from the center of the scan path.

In a particularly advantageous planning method, the further control data are determined in such a way that the focus spots lie on a spiral around the center of the scan path. In particular, the further control data are determined in such a way that for a difference in the distances from the center of the scan path of two successive focus spots is proportional to an inverse mean distance of the successive focus spots from the center of the scan path.

Due to the spiral path, focus spots can be realized with high precision but comparatively low demands on the scanning device, since accelerations of the scanners can be further reduced.

Dabei sind r_s,i der Abstand der i-ten Fokusspots vom Scanbahnzentrum, c_s ein Proportionalitätskonstante undr_s,1 ist der Abstand des ersten Fokusspots vom Scanbahnzentrum. Der Index „s“ zeigt an, dass die Fokusspots spiralförmig um das Scanbahnzentrum erzeugt werden können. Da nach K Fokusspots der gesamte Schnitt überdeckt ist, entspricht r_s,K dem Abstand des letzten Fokusspots bzw. dem am weitesten entfernten Fokusspot vom Scanbahnzentrum. Daraus ergibt sich $c_s=\left(r_{s,K}-r_{s\mathrm{,1}}\right)/\sqrt{K-1}.$

Damit ergeben sich für die Fokusspots entlang der Scanbahn die Abstände r_s,i = $\left(r_{s,K}-r_{s\mathrm{,1}}\right)\cdot \sqrt{\left(i-1\right)/\left(K-1\right)}+r_{s\mathrm{,1}}.$

In order to keep the area that can be assigned to a focus spot on a spiral arrangement of the focus spots constant for all focus spots, the difference between the distances from the center of the scan path of two successive focus spots is to be chosen proportional to an inverse mean distance of the successive focus spots from the center of the scan path. This property of the scan path describes its slope for each focus spot i, with i = 1, 2, ..., K. This results in the focus spots for the scan path r _{s, i} = $c_s\cdot \sqrt{i-1}+r_{s\mathrm{,1}}.$

Here r _{s, i is} the distance of the i-th focus spot from the center of the scan path, c _{s is} a constant of proportionality and r _{s, 1} is the distance of the first focus spot from the center of the scan path. The index "s" indicates that the focus spots can be created in a spiral around the center of the scan path. Since the entire section is covered after K focus spots, r _{s, K} corresponds to the distance of the last focus spot or the most distant focus spot from the center of the scan path. This results in $c_s=\left(r_{s,K}-r_{s\mathrm{,1}}\right)/\sqrt{K-1}.$

_{This results in the distances r s, i} = for the focus spots along the scan path $\left(r_{s,K}-r_{s\mathrm{,1}}\right)\cdot \sqrt{\left(i-1\right)/\left(K-1\right)}+r_{s\mathrm{,1}}.$

According to a particularly advantageous method, the planning method also has the step that a limit value for a distribution measure for evaluating the distribution of the focus spots of the focus of the pulsed laser beam in the scan pattern is specified, and that the further control data are determined in such a way that the scan pattern of the focus spots a The limit value for the distribution measure is sufficient.

According to a further particularly advantageous planning method, at least the method steps of selecting the laser pulse frequency and calculating the angular velocity are iterated until the scan pattern of the focus spots satisfies the limit value for the distribution measure.

If a scan pattern does not meet the limit value for the distribution measure, the occurrence of local clusters of focus spots can typically be the cause. Such accumulations can occur if the number k of focus spots per revolution of the scan path around the scan path center can be approximated via a fraction k ≈p / q and if q ≪ N. Here p and q are natural numbers greater than zero. As a result, the pattern of the focus spots is repeated after just a few rotations (compared to the total number of rotations N). The scan pattern forms so-called spokes of focus spots. Such a formation of spokes is recognized by evaluating the distribution of the focus spots by means of a distribution measure.

Since the formation of spokes in the scan pattern preferably occurs at greater distances between the focus spots and the center of the scan path, it can be advantageous to determine the degree of distribution for focus spots at large distances from the center of the scan path.

gilt. Dabei sind z_l positiv ganzzahlige Koeffizienten. Diese sind vorteilhaft alle kleiner oder gleich 5; vorzugsweise sind alle Koeffizienten kleiner oder gleich 3. In an iteration of the determination of the laser pulse frequency and angular velocity, the following procedure can be used: The laser pulse frequency f _P and the angular velocity (proportional to f _R ) are chosen so that the number of pulses k per revolution k = f _{P /} f _{R is} an approximation the sum of a natural number M greater than zero and an irrational number IR results in: k ≈M + IR. The approximation can take place via a continued fraction, where $$\mathrm{I.}\mathrm{R.}=\frac{1}{z_1+\frac{1}{z_2+\frac{1}{z_3+\cdots }}}$$

applies. Here, z _{l are} positive integer coefficients. These are advantageously all less than or equal to 5; all coefficients are preferably less than or equal to 3.

If there are still spokes for an approximation of IR of level /, the next approximation of IR with level 1 + 1 (or greater) is used. Values for the laser pulse frequency and the speed of rotation are determined in such a way that the number k of focus spots per revolution results in accordance with the next approximation level. A number k of focus spots per revolution calculated in this way has the property that, as the approximation level increases, the continued fraction only changes with one With a higher number of revolutions, repetitions of patterns in the focus spots are formed, and the formation of spokes only occurs later.

Alternatively, the number k of focus spots per revolution can be formed from a sum of a natural number M greater than zero and a rational number R _F : k ≈M + R _F. R _{F is} the ratio of two consecutive numbers in the Fibonacci sequence (1, 2, 5, 6, 13, 21, 34, 55, 89, ...); R _F converges to an irrational number. If a scan pattern results for a value R _F that does not meet the limit value for the distribution measure, new values are determined for the laser pulse frequency and / or the angular velocity that _{correspond to a ratio R F of} two consecutive, higher numbers of the Fibonacci sequence. Due to the properties of the Fibonacci sequence, it follows that for increasing, consecutive numbers of the Fibonacci sequence, repetitions of patterns of the focus spots only develop with a much higher number of revolutions and thus spokes only appear later.

Ideally, the value for k is already selected in the first iteration in such a way that no further iterations are required. For this purpose, for example, a high approximation level of a continued fraction or a quotient of two consecutive, large Fibonacci numbers can be used.

With the aid of the iteration described, it is thus possible to generate control data for a scan pattern of focus spots, the distribution of the focus spots in the entire scan pattern satisfying a predetermined limit value for a distribution measure.

In a further advantageous planning method, the laser device comprises a laser source for generating laser pulses with a laser repetition frequency f _L and a pulse selection device which is set up to select the laser pulses generated according to the control data according to a division ratio D and to provide them for the pulsed laser beam. In one process step, the division ratio D is determined in such a way that the constant laser pulse frequency f _P results. The division ratio D is fed to the control unit of the ophthalmic laser therapy device.

Advantageously, the division ratio is selected in particular so that it assumes an integer value and / or that for the number k of focus spots with k = f _{p /} f _R = f _L / (D · f _R ) a value results that is a Avoids spokes.

According to a further advantageous planning method, control data are generated for at least two scan patterns, wherein the first laser pulse frequency can deviate from the at least one further laser pulse frequency, the first scan path center from at least one further scan path center and / or the first angular speed can differ from the at least one further angular speed. In this case, the control data for the at least two scan patterns are generated, in particular, in such a way that the at least two scan patterns do not at least partially overlap spatially.

A computer program product comprises a program code which, when executed on a computer, executes the planning method described above for generating control data for generating a scan pattern for an ophthalmic laser therapy device and / or which can be read on a planning unit described above for generating control data. The program code can be read in particular by a processor of such a planning device, and preferably such a planning device for consecutive control of an ophthalmic laser therapy device with the generated control data. Furthermore, the program code, when it is executed by the planning device, generates control data in order to operate the ophthalmological laser therapy device for severing the tissue of the patient's eye.

The computer program product described above is stored on a computer-readable medium according to the invention.

In a method according to the invention for cutting a tissue in a patient's eye, control data for the generation of a scan pattern along the scan path of focus spots in the tissue of the patient's eye, in particular in a cornea and / or an eye lens, are generated for an ophthalmic laser therapy device using a planning method described above transferred to this. In the method, the ophthalmic laser therapy device is operated with the aid of these control data in order to cut through tissue in a patient's eye.

It goes without saying that the features mentioned above and those yet to be explained below can be used not only in the specified combinations, but also in other combinations or on their own, without departing from the scope of the present invention.

• - 1 ein Schema einer Ausführungsform eines erfindungsgemäßen ophthalmologischen Lasertherapiegerätes;
• - 2 eine dreidimensionale Darstellung einer Scanbahn und Fokusspots;
• - 3 eine Scanbahn, Fokusspots und Schnitt gemäß einem ersten Beispiel;
• - 4 ein resultierendes Scanmuster gemäß dem ersten Beispiel aus 3;
• - 5 eine Scanbahn, Fokusspots und Schnitt gemäß einem zweiten Beispiel;
• - 6 eine Darstellung der Abstände der Fokusspots zum Scanbahnzentrum gemäß ihrer zeitlichen Entstehung für das zweite Beispiel nach 5;
• - 7 einen symmetrischer (a) und asymmetrischer (b) Fokuswirkbereich um einen Fokusspot
• - 8 eine Scanbahn, Fokusspots und Schnitt gemäß einem dritten Beispiel mit asymmetrischen Fokuswirkbereichen;
• - 9 eine Darstellung der Abstände der Fokusspots zum Scanbahnzentrum gemäß ihrer zeitlichen Entstehung für das erste Beispiel nach 2;
• - 10 eine Darstellung zur Bewertung eines Scanmusters mit einem Verteilungsmaß;
• - 11 eine Darstellung zur Bewertung eines Scanmusters mit einem alternativen Verteilungsmaß;
• - 12 ein Scanmuster für ein viertes Beispiel mit lokaler Häufung von Fokusspots;
• - 13 ein Scanmuster für ein fünftes Beispiel ohne lokale Häufung von Fokusspots;
• - 14 ein Scanmuster für ein sechstes Beispiel mit lokaler Häufung von Fokusspots;
• - 15 ein Scanmuster für ein siebtes Beispiel ohne lokale Häufung von Fokusspots;
• - 16 ein erstes und einen Ausschnitt eines zweiten Scanmusters gemäß einem achten Ausführungsbeispiel;
• - 17 Ausschnitte eines zweiten und eines dritten Scanmusters gemäß einem achten Ausführungsbeispiel.

The invention is explained in more detail below, for example with reference to the accompanying drawings, which also disclose features essential to the invention. Show it:

• - 1 a scheme of an embodiment of an ophthalmic laser therapy device according to the invention;
• - 2 a three-dimensional representation of a scan path and focus spots;
• - 3 a scan path, focus spots and section according to a first example;
• - 4th a resulting scan pattern according to the first example 3 ;
• - 5 a scan path, focus spots and section according to a second example;
• - 6th an illustration of the distances between the focus spots and the center of the scan path according to their temporal origin for the second example 5 ;
• - 7th a symmetrical (a) and asymmetrical (b) effective focus area around a focus spot
• - 8th a scan path, focus spots and section according to a third example with asymmetrical focus effective areas;
• - 9 a representation of the distances of the focus spots to the scan path center according to their temporal origin for the first example 2 ;
• - 10 a representation for evaluating a scan pattern with a distribution measure;
• - 11 a representation for evaluating a scan pattern with an alternative distribution measure;
• - 12th a scan pattern for a fourth example with local accumulation of focus spots;
• - 13th a scan pattern for a fifth example without local accumulation of focus spots;
• - 14th a scan pattern for a sixth example with a local accumulation of focus spots;
• - 15th a scan pattern for a seventh example without a local accumulation of focus spots;
• - 16 a first and a section of a second scan pattern according to an eighth embodiment;
• - 17th Excerpts from a second and a third scan pattern according to an eighth exemplary embodiment.

In 1 is an embodiment of the ophthalmic laser therapy device 1 shown schematically. A laser device 10 which in this embodiment is a laser source 14th and a pulse selection device 16 includes, emits the pulsed laser beam 12th from. The laser beam 12th is from the scanning device 30th lateral and from that of the scanning device 32 axially deflected. The focusing device 20th bundles the pulsed laser beam 12th in one focus 60 in the cornea 92 of the patient's eye 90 (or in the lens of the eye or in the limbus or the sclera). In 1 is the focus 60 for two positions in the cornea 92 for different settings of the lateral scanning device 30th and he axial scanning device 32 drawn in as an example. A possibly advantageous fixation of the patient's eye 90 by means of a patient interface to the ophthalmic laser therapy device 1 is not shown.

The laser device is controlled during operation 10 , the scanning devices 30th , 32 and the focusing device 20th fully automatically via signal data from the control unit 40 to the respective device 10 , 20th , 30th , 32 be transmitted. This is indicated by arrows, each from the control unit to the devices 10 , 20th , 30th and 32 point. The control unit 40 ensures suitable synchronous operation of the laser source 10 , the three-dimensional scanning device 30th , 32 as well as the focusing device. The signal data can be transmitted via signal data lines or wirelessly. The signal data required during operation are stored in the control unit 40 determined on the basis of the tax data. The control unit receives the control data 40 previously from the planning unit P as a control data record via unspecified communication paths, such as control lines. The control data can also be transmitted using memory chips (e.g. USB or memory stick), magnetic storage media (e.g. floppy disks), wirelessly by radio (e.g. WLAN, UMTS, Bluetooth) or wired (e.g. USB, Firewire, RS232, CAN bus, Ethernet, etc.) .) respectively. As an alternative to direct communication, the planning device P can also be spatially separated from the control unit 40 to be arranged and to provide a corresponding data transmission channel. The transmission preferably takes place before the ophthalmic laser therapy device is operated 1 instead of, ie before control signals to the laser device 10 who have favourited scanning devices 30th , 32 and to the focusing device 20th be transmitted.

The control data set preferably becomes the control unit 40 of the ophthalmic laser therapy device 1 Transmitted via an interface S of the planning device P and operation of the ophthalmic laser therapy device is further preferred 1 locked until at the control unit 40 a valid tax data record is available. A valid control data record can be a control data record that is principally intended for use with the control unit 40 of the ophthalmic laser therapy device 1 suitable is. In addition, the validity can also be linked to the fact that further tests are passed. To this end, it can be checked, for example, whether information about the ophthalmic laser therapy device is also recorded in the control data record 1 , for example a device serial number, or about the patient, for example a patient identification number, match other information, for example on the ophthalmic laser therapy device 1 read out or entered separately as soon as the patient is in the correct position for the operation of the ophthalmic laser therapy device 1 is.

The planning device P generates the control data or the control data record of the control unit 40 of the ophthalmic laser therapy device 1 is made available to perform the operation. The measuring device M included in this embodiment generates measurement data from the eye to be treated 90 of the patient (indicated by a double arrow with a line of dots and lines), which are transmitted to the planning device P via a measurement data line. The data or measurement data generated by the measuring device M can be used to determine the geometry and the position of the in the tissue of the patient's eye 90 to determine the cut to be generated. However, it should be pointed out once again that the planning unit P can generate the control data regardless of whether the patient's eye is 90 with the ophthalmic laser therapy device 1 connected is. The presence of the measuring device is optional.

Furthermore, the data generated by the measuring device M can be used during the operation of the ophthalmological laser therapy device 1 monitor the creation of the cut in the tissue. The advantageous data connection between the measuring device M and, for example, the control unit 40 is in 1 not shown.

In the embodiment according to 1 are the elements of the ophthalmic laser therapy device 1 although specified more precisely, but only entered here insofar as they are necessary to understand the focus adjustment.

The coordinates designated below with x, y, z relate to the deflection of the position of the focus 60 . For the functional principle of the ophthalmic laser therapy device 1 the assignment of the individual coordinates to the spatial directions is not essential, but for the sake of simpler description, the coordinate along the optical axis of the focusing device is always indicated below with z 20th designated.

In 2 shows a three-dimensional representation of a scan path 54 and of focus spots 62 on this scan path 54 . The scan path shown here rotates around a scan path center 56 that occupies a point in space. The time course with which the scan path 54 from the scanning device 30th , 32 is followed by an arrow at the end of the scan path 54 shown. In the example shown, the distance between the focus spots increases 62 along the scan path 54 strictly monotonous too. The scan path 54 thus takes the form of a spiral.

The scan path 54 has coordinates that take on different values along the drawn z-axis. That through the focus spots 62 Patterns generated along the scan path, the scan pattern 50 , thus creates a cut 70 that occupies a two-dimensional, curved surface in space. In such a case it can be advantageous to use the scan path 54 not to be described in Cartesian coordinates (in x, y and z), but in cylindrical coordinates with a radius r, an angle of rotation ϕ and a height h. The angle of rotation ϕ with respect to the x-axis is measured in the cylinder coordinate system shown.

In 3 is are a scan path 54 , Focus spots 62 , Scan pattern 50 and a cut 70 shown according to a first example. What is shown here is a view along the optical axis (z-axis). In this example there are all focus spots 62 in one plane. The scan path 54 rotates around the scan path center 56 . For every focus spot 62 is a focus effective area here 64 drawn. This marks the volume (or the two-dimensional projection onto the xy plane) in which the focus spot 62 creates an interaction with the tissue. The totality of the focus effective areas 64 generated due to the optical breakthroughs at each focus spot 62 in the tissue of the patient's eye 90 a cut 70 . The edge of the cut 70 is shown as a dotted line.

In the example shown here, the section 70 has an irregular edge. As a rule, a cut is made during operation 70 generated, which compared to the size of a focus effective area 64 is much bigger. So there are typically several thousand focus spots 62 generated in the tissue. This results in a more regular edge of the cut 70 .

Furthermore shows 3 a cut 70 that is smaller than that of the scan path 54 covered area. Thus the scan field is sufficient 80 , the edge of which is drawn in as a line of dots and lines, in some places over the edge of the cut 70 out. The illustration shows imaginary focus spots 66 . These are locations on the scan path 54 at which a focus spot could be generated (according to the constant laser pulse frequency). However, these lie outside the cut 70 to be generated, so that in this case no laser pulse is provided for generating a focus spot.

This first example is a scan path 54 in the form of a spiral. The number of focus spots 62 per rotation is k≈3,304.

In 4th is the edge of the resulting scan pattern 50 according to the first example 3 shown as a dashed line. The extent of the scan pattern 50 is smaller than the cut 70 (dotted line), which with the help of the scan pattern 50 can be generated. The reason for this is that due to the size of the effective focus areas 64 that are at the edge of the scan pattern 50 reach beyond this and also for severing tissue and thus for cutting 70 contribute. Furthermore, the size of the scan pattern 50 be smaller than the scan field 80 (Line made of dots and lines), because - as shown in this example - a focus spot does not have to be generated at every possible location, but a scan field 80 also imaginary focus spots 66 may have.

In 5 are a scan path 54 , Focus spots 62 and a cut 70 shown according to a second example. It is a scan path 54 in the form of (almost complete) circles with transition pieces between the circles. In the example shown, the transition pieces each have the same angle with respect to the center of the scan path 56 on; alternatively, the transition pieces can also cover different angles or have the same lengths. Every almost complete circle together with a transition piece corresponds to a rotation in this example. The scan path distance from the center of the scan path 56 changes monotonically, but not strictly monotonously. The distances between the focus spots remain within an (almost complete circle) 62 on the scan path 54 constant. The distances only change between two circles. Becomes a focus spot 56 generated on a transition piece (not shown in the example), there is also a change in distance from the center of the scan path 56 two consecutive focus spots 54 . In the example shown, the distances increase monotonically (shown by the direction of the arrow at the end of the scan path 54 ). Due to the constant angular velocity and the constant laser pulse _{frequency f P} , the number of focus spots is 62 per revolution also constant, so that in this way a homogeneous density of the focus spots 62 is ensured per azimuth angle range.

In 6th are the distances between the focus spots and the center of the scan path 56 according to their temporal origin for the second example 5 shown. The time t is on the horizontal axis and the distance Δ between the focus spots is on the vertical axis 62 to the scan path center 56 shown. On the first (innermost) almost complete circle of the scan path 54 will be four focus spots 62 generated; these are shown as filled dots around the diagram. Then there are three or four focus spots on the second or third (almost complete) circle 62 generated. There is only one focus spot on each of the fourth and fifth circles 62 generated. In addition, there are two imaginary focus spots in the diagram 66 (as unfilled points). The mean distances of a rotation are also marked with an x on the vertical axis. According to this advantageous example, the absolute amount of the difference decreases at the focus spots 62 at the beginning of the rotation and at an end of the rotation evaluated distances from the center of the scan path 56 with increasing mean distance from the center of the scan path 56 from. This ensures that the density of the focus spots 62 in the scan pattern 50 via radial distances from the center of the scan path 56 is adapted.

In 7a is a three-dimensional representation of a symmetrical focus effective area 64 around a focus spot 62 shown. The expansion of the effective focus area 64 is the same in all three spatial dimensions (x, y, and z).

In 7b however, is a three-dimensional representation of an asymmetrical focus effective area 64 around a focus spot 62 shown. The expansion of the effective focus area 64 has the shape of a triaxial or triaxial ellipsoid. The semi-axes of the ellipsoid are aligned in the direction of the coordinate axes x ', y' and z '. In the example shown, the z'-axis coincides with the z-axis (optical axis of the focusing device). The x 'and y' axes emerge from the x and y axes via a rotation about the z axis. In the example shown, all three semi-axes of the ellipsoid have different lengths. A focus effective area 64 can have such a shape if the focus along the optical axis has a different extent than in the directions perpendicular thereto (xy plane); typically the focus is longer in the z-direction. In addition, an effective focus area can have such a shape if the focus in the focal plane (xy plane, perpendicular to the optical axis) is not rotationally symmetrical; this can occur, for example, when the light is polarized in the focus. In the case of a rotationally symmetrical focus in the focal plane, the effective focus area can have the shape of an ellipsoid of revolution.

In 8th are a scan path 54 , Focus spots 62 and a cut 70 shown according to a third example. An asymmetry effect is taken into account. What is shown here is a view along the optical axis (z-axis). In this example there are all focus spots 62 in one plane. The scan path 54 rotates around a scan path center 56 . For every focus spot 62 is a focus effective area here 64 drawn. The effective focus areas applied here 64 have an asymmetrical size in the xy plane. The size (diameter) along the x-axis is 35% larger than along the y-axis. The totality of the focus effective areas 64 generated due to the optical breakthroughs at each focus spot 62 in the tissue of the patient's eye 90 a cut 70 . The edge of the cut is shown as a dotted line.

die z-Koordinaten sind identisch und können daher vernachlässigt werden. Die x'- und y'-Achsen fallen mit den x- und y-Achsen zusammen. Das Scanbahnzentrum liegt im Koordinaten-Ursprung bei $\overrightarrow{x_0}=\left(\mathrm{0,0}\right).$

Der Abstand des i-ten Fokusspots 62 zum Scanbahnzentrum 56 ergibt sich somit zu $\Delta {\text{'}}_2\left(\overrightarrow{x{\text{'}}_1},\overrightarrow{x{\text{'}}_2}\right)=\sqrt{{\left(x_i\right)}^2+{\alpha }_y{}^2\cdot {\left(y_i\right)}^2}$

mit a_y = 1.35. Entsprechend dieser Metrik weisen die Fokusspots 62 entlang der Scanbahn 54 einen streng monotonen der Abstände zum Scanbahnzentrum 56 auf. In diesem dritten Beispiel weist jede Rotation k≈3.618 Fokusspots auf. Auf diese Weise wird eine homogene Dichte der Fokusspots 62 pro Azimut-Winkel-Bereich sichergestellt.This third example is a scan path 54 in the form of an elliptical spiral. The asymmetry effect is taken into account here, in which the metric for determining the distances has an asymmetry factor a _y ≠ 1: $\Delta {\text{'}}_2\left(\overrightarrow{x{\text{'}}_1},\overrightarrow{x{\text{'}}_2}\right)=\sqrt{{\left(x{\text{'}}_1-x{\text{'}}_2\right)}^2+{\alpha }_y{}^2\cdot {\left(y{\text{'}}_1-y{\text{'}}_2\right)}^2};$

the z-coordinates are identical and can therefore be neglected. The x 'and y' axes coincide with the x and y axes. The scan path center is included in the coordinate origin $\overrightarrow{x_0}=\left(0.0\right).$

The distance of the i-th focus spot 62 to the scan path center 56 thus results in $\Delta {\text{'}}_2\left(\overrightarrow{x{\text{'}}_1},\overrightarrow{x{\text{'}}_2}\right)=\sqrt{{\left(x_i\right)}^2+{\alpha }_y{}^2\cdot {\left(y_i\right)}^2}$

with a _y = 1.35. The focus spots show according to this metric 62 along the scan path 54 a strictly monotonous distance to the center of the scan path 56 on. In this third example, each rotation has k≈3,618 focus spots. In this way there is a homogeneous density of the focus spots 62 ensured per azimuth angle range.

It should also be noted for this example that 8th also the projection of a three-dimensional scan path 54 who have made a cut 70 generated, which has the shape of a curved surface in three-dimensional space, corresponds along the z-axis.

In 9 are the distances between the focus spots and the center of the scan path 56 according to their temporal origin for the first example 3 shown. The time t is on the horizontal axis and the distance Δ between the focus spots is on the vertical axis 62 to the scan path center 56 shown. The scan path 54 was done from the inside (small distances from the center of the scan path 56 ) to the outside (larger distances from the center of the scan path 56 ) departed. The distance between the focus spots 62 from the scan path center 56 increases strictly monotonously with time t. The scan path 54 know the shape of a spiral. The strict monotony also applies to three imaginary focus spots 66 that are entered in the diagram as unfilled points. The mean distances between two consecutive focus spots are also shown on the vertical axis with a crossing x 62 marked. According to this advantageous example, the absolute value takes the difference in the distances from the center of the scan path 56 two consecutive focus spots 62 proportional to an inverse mean distance between the successive focus spots 62 from the scan path center 56 from. The example shows a scan pattern 50 of focus spots 62 on a spiral around the center of the scan path 56 lie at which the density of the focus spots 62 in the scan pattern 50 over all radial distances from the center of the scan path 56 is equal to. This thus enables a particularly homogeneous cut to be produced 70 in a patient's eye 90 .

In 10 a scheme is shown for evaluating a scan pattern 50 with a distribution measure. The evaluation serves to identify local accumulations of focus spots 62 to recognize. These are from the first Example according to 3 the innermost focus spot 62 and ten other focus spots are shown. In addition, there is a circle (dotted line) around the innermost focus spot 62 - the focus spot in the center of the circle - is drawn. The circle is divided into four equal segments I, II, III and IV. The circle has a radius that is so large that at least one further focus spot 62 is present in every segment of the circle. For each segment of a circle, the smallest distance between all the focus spots present in the segment of a circle is now 62 determined to be the focus spot in the center of the circle. These distances are shown as arrows with a line of dots and lines. The difference between the maximum and the minimum of the four minimum distances from the four circle segments is now assigned as a measure to the focus spot in the center of the circle. This measure describes the extent to which the distances to neighboring focus spots deviate 62 are. The measure for the distance of a focus spot 62 becomes its neighbors for all focus spots 62 in the scan pattern 50 educated. A mean value and a standard deviation are then assigned to the distribution of these measures. This is the measure of distribution. If the mean value and / or the standard deviation exceed a limit value, local accumulations of focus spots occur 62 on. In such a case, new control data are advantageously generated until the distribution measure satisfies the limit value.

If asymmetry effects are to be taken into account, this effect is advantageously taken into account when calculating the distances. For this purpose, a corresponding asymmetry factor is used in the metric, for example.

In 11 a scheme is shown for the evaluation of a scan pattern 50 with an alternative distribution measure. Here is everyone's focus spot 62 of the scan pattern 50 according to the first example 3 an area corresponding to the size of the effective focus area 64 assigned. The totality of the focus effective areas 64 of all focus spots 62 of the scan pattern 50 an area will be assigned. Thereby, overlapping areas of two or more effective focus areas become 64 different focus spots 62 only taken into account once (and not more than once) when assigning the area. This area of the totality of the focus effective areas 64 the focus spots 62 of the scan pattern 50 in the cutting plane is set in relation to the area of the section 70 . In the example shown, the alternative distribution measure has a value of 0.8, which means that 80% of the cut surface is covered by effective focus areas.

befindet. Dort wird auch der erste Fokusspot 62 gesetzt. Der Abstand zwischen zwei aufeinanderfolgende Fokusspots 62 nimmt mit dem inversen mittleren Abstand vom Scanbahnzentrum 62 ab. Der Abstand zwischen zwei Fokusspots 62 entspricht dem Durchmesser eines Fokuswirkbereiches 64 von 2µm. Um im zentralen Bereich des Scanmusters 50 nicht zu viele Fokusspots 62 zu setzen, wurde ein Wert von k≈3.7209 Fokusspots pro Umdrehung gewählt. Dieser Wert entspricht einer Summe aus einer ganzen Zahl M=3 und der Approximation einer irrationalen Zahl IR, die über einen Kettenbruch beschrieben wird. Dabei werden für die sieben Koeffizienten z₁ bis z₇ die Zahlen 1, 1, 2, 1, 1, 2 und 1 verwendet.In 12th is a scan pattern 50 shown for a fourth example. There is a local accumulation of focus spots 62 on. The figure shows a central section of 140 µm by 140 µm around the origin in the xy plane. The size of the points shown corresponds to a diameter of about 2 µm and corresponds to the diameter of an effective focus area 64 . The basis of the scan pattern is a laser source 14th , which generates laser pulses with a laser repetition frequency f _L = 1MHz. The scan path 54 runs in a spiral around the center of the scan path 54 , which is located in the coordinate origin at $\overrightarrow{x_0}=\left(0.0\right)$

is located. The first focus spot will also be there 62 set. The distance between two consecutive focus spots 62 decreases with the inverse mean distance from the center of the scan path 62 from. The distance between two focus spots 62 corresponds to the diameter of a focus effective area 64 of 2 µm. To in the central area of the scan pattern 50 not too many focus spots 62 To set a value of k≈3.7209 focus spots per revolution was chosen. This value corresponds to a sum of an integer M = 3 and the approximation of an irrational number IR, which is described by a continued fraction. The numbers 1, 1, 2, 1, 1, 2 and 1 are used for the seven coefficients z ₁ to z _7.

A pulse selection device is controlled in such a way that it only detects every 768th laser pulse for the pulsed laser beam 12th provides. The division ratio is D = 768. This results in a laser pulse _{frequency of f P} = f _L / D ≈1.3 kHz. A constant rotation _{frequency of f R} = 349.936Hz results from f _P = f _{R · k.}

Mit r_s,1 = 0µm und r_s,K = 100µmvereinfacht sich dies zu $r_{s,i}=100\mathrm{\mu }m\cdot \sqrt{\left(i-1\right)/\left(K-1\right)}.$

A focus spot 62 can be a focus effective area 64 of π µm ^{2 can be} assigned if the radius is assumed to be 1 µm. To make a cut 70 in the form of a circular area with a radius of 100 µm with focus spots 62 to generate, the number K focus spots is chosen so that the sum of all areas of the focus effective areas 64 just results from the cut surface, then K = 1000 focus spots are required. This results in the distance of the i-th focus spot 62 (i = 1, 2, ... K) $r_{s,i}=\left(r_{s,K}-r_{s\mathrm{,1}}\right)\cdot \sqrt{\left(i-1\right)/\left(K-1\right)}+r_{s\mathrm{,1}}.$

With r _{s, 1} = 0 µm and r _{s, K} = 100 µm, this is simplified to $r_{s,i}=100\mathrm{\mu }m\cdot \sqrt{\left(i-1\right)/\left(K-1\right)}.$

Mit ϕ₁ = 0 ergibt sich diesem vierten Beispiel ${\varphi }_i=2\cdot \pi \cdot \left(i-1\right)/k.$

Mit den genannten Ausdrücken für r_s,i und ϕ_i sind die Positionen der Fokusspots 62 in 12 beschrieben. Die angegebenen Formeln für Abstand und Azimut-Winkel gegenüber dem Scanbahnzentrum 56 gilt für eine Scanbahn 54, bei der die erzeugten Fokusspots 62 einen streng monoton wachsenden Abstand vom Scanbahnzentrum 56 aufweisen. Soll eine Scanbahn 54 von außen nach innen erzeugt werden, so muss i durch K-i+1 ersetzt werden.A scan pattern is used 50 aimed at where the focus spots 62 on a spiral around the center of the scan path 56 and for the difference in the distances from the center of the scan path 56 two consecutive focus spots 62 proportional to an inverse mean distance between the successive focus spots 62 from the scan path center 54 is. For the azimuth angle of the i-th focus spot 62 applies ${\varphi }_i=2\cdot \pi \cdot \left(i-1\right)\cdot f_{\mathrm{R.}}/f_{\mathrm{L.}}+{\varphi }_1.$

This fourth example results with ϕ _{1 = 0} ${\varphi }_i=2\cdot \pi \cdot \left(i-1\right)/k.$

With the mentioned expressions for r _{s, i} and ϕ _i are the positions of the focus spots 62 in 12th described. The specified formulas for distance and azimuth angle with respect to the center of the scan path 56 applies to one scan path 54 , in which the generated focus spots 62 a strictly monotonically growing distance from the center of the scan path 56 exhibit. Should a scan path 54 are generated from the outside in, then i must be replaced by K-i + 1.

12th shows local clusters of focus spots 62 at greater distances from the center of the scan path 56 . Spoke formation takes place. The value of the alternative measure of distribution in the in 12th The section shown is about 0.65, ie about 65% of the cut area 70 become of focus effective areas 64 covered. The value varies between about 0.8 for the inner area of the cut shown 70 and 0.53 for the edge area. Spoke formation is therefore advantageous through an assessment of the scan pattern 50 by applying the distribution measure for focus spots 62 for large distances from the center of the scan path 56 recognized.

If the described alternative distribution measure is assumed as the distribution measure, that in an edge area of the scan pattern 50 is evaluated, and if a limit value of 0.8 is assumed, the scan pattern shown is sufficient 50 not the limit. Therefore, according to the invention, further approximation stages of the continued fraction are used: In 13th is a scan pattern 50 shown for a fifth example. The section shown and the parameters for the laser pulse frequency correspond to the values from the fourth example. For the continued fraction to approximate the irrational number IR, however, nine coefficients z ₁ to z _9, the numbers 1, 1, 2, 1, 1, 2, 1, 1 and 2, are used. The result is a constant rotation _{frequency of f R} = 350.188Hz. The resulting scan pattern 50 does not show any local clusters of focus spots 62 . The value of the alternative distribution measure is about 0.84. At the edge of the section shown, the value of the alternative distribution measure is around 0.87. 12th and 13th show that the formation of spokes is recognized with the aid of the distribution measure and is eliminated by increasing the approximation levels according to the invention. This can be used to ensure that a scan pattern 50 for cutting through tissue with a high cutting quality is made possible.

At this point it should be pointed out again that the irrational number IR approximated via a continued fraction should have the smallest possible coefficients. If larger coefficients are used (for example greater than 5), the irrational number can often be approximated by a rational number that corresponds to a fraction of numbers smaller than 500. Even then, spokes can easily form in the scan pattern 50 .

In 14th is a spiral scan pattern 50 shown for a sixth example. Here again there is a local accumulation of focus spots 62 on. The section shown as well as the size of the effective focus areas and the parameters for the laser repetition frequency correspond to the values from the fourth example (after 12th ). A value of k ≈M + R _F ≈3.6182 focus spots per revolution was chosen. This value corresponds to a sum of an integer M = 3 and the approximation of an irrational number R _F , which is the ratio of the two consecutive numbers of the Fibonacci sequence 34 and 55 is.

A pulse selection device is activated again in such a way that it only sends every 768th laser pulse for the pulsed laser beam 12th provides. The result is a constant rotation _{frequency of f R} = 349.851Hz.

The further calculation of the distances and azimuth angles of the focus spots 62 opposite the scan path center 56 takes place as in the fourth example 12th is described.

14th shows local clusters of focus spots 62 at greater distances from the center of the scan path 56 (Spoke formation). The value of the alternative measure of distribution in the in 14th The section shown is about 0.74. The value varies between about 0.85 for the inner area of the cut shown 70 and 0.64 for the edge area.

If the described alternative distribution measure is assumed as the distribution measure, that in an edge area of the scan pattern 50 is evaluated, and if a limit value of 0.8 is assumed, the scan pattern shown is sufficient 50 not the limit. Therefore, according to the invention, larger, consecutive numbers of the Fibonacci sequence are used: In 15th is a scan pattern 50 shown for a seventh example. For the quotient R _{F of} two, 55 and 89 are used here. This results in k ≈M + R _F ≈3.6180 focus spots per revolution, a constant rotation _{frequency of f R} = 349.870Hz. The resulting scan pattern 50 does not show any local clusters of focus spots 62 . The value of the alternative measure of distribution is around 0.86. At the edge of the section shown, the value of the alternative distribution measure is approximately 0.88. 14th and 15th show that the formation of spokes is recognized with the aid of the distribution measure and is eliminated by increasing the approximation levels according to the invention.

Typically it is required in the eye 90 a patient an incision 70 with a diameter of about 6mm. Such a cut 70 can for example be generated over several scan patterns. This is done in 16 and 17th shown for an eighth example. It shows 16 a central section of 70 μm × 70 μm in the xy plane for a laser device with a laser repetition frequency f _L = 1 MHz and a desired spot spacing of 2 μm. A first scan pattern 50 (Zone 1) becomes spiral up to a distance from the center of the scan field 56 generated by about 31 µm; the focus spots 62 are marked as black dots (the radius in this example does not correspond to the effective focus area 64 ). A second scan pattern closes radially 51 (Zone 2) whose focus spots 62 are shown as black squares. Zone 2 extends up to a distance of about 227 µm from the center of the scan path 56 that coincides with the scan path center of zone 1. Zone 2 is followed by zone 3 with a third scan pattern 52 at. A transition area between zones 2 and 3 of 70µm × 70µm is in 17th shown. The focus spots 62 of the third scan pattern 52 are shown as black diamonds.

Table 1 shows the parameters of a total of 4 scan patterns that can generate a total of a section with a diameter of 6mm. The IR was the consecutive Fibonacci numbers 21 and 34 selected for which there is no formation of spokes in the zones shown. The scan path centers are identical for all four scan patterns. Table 1. Parameters for an eighth embodiment which has four scan patterns. Zone 1 2 3 4th Division ratio D 790 29 4th 1 Distances from the center of the scan path 0mm - 0.031 mm 0.031mm-0.227mm 0.277mm - 0.910mm 0.910mm-3mm Focus spots per rotation 3 + IR 98 + IR 714 + IR 2857 + IR time 0.76s 1.47s 3.11s 8.17s Rotation frequency 349.902Hz 349,661 Hz 349.837Hz 349.942Hz

The cut 70 in the eighth example will be generated in a time of about 13.5 seconds.

If the entire section were to be generated with the parameters of zone 4, this would take place in less time, but the distance between successive focus spots would be 62 for distances from the center of the scan path 56 of less than 0.91mm is too small, which would lead to unnecessary strain on the eyes. With the parameters of zone 1, one would do the entire cut 70 generate, it would take a time of just under two hours. The division of the cut 70 in several zones with different scan patterns makes it possible to minimize the treatment time, while at the same time a predetermined density of focus spots can be maintained.

In an alternative embodiment of the invention, the above dependency of the radius of the scan path can be used for all radial zones 54 also describe the index i of the focus spots by a time dependency of the scan path radius:

wobei $\frac{1}{\Delta t}=f_P$

der je nach radialen Zone heruntergeteilten Frequenz des Laser f_IL/D entspricht und to den Zeitpunkt bezeichnet, zu dem der Scan-Bahn-Radius ro beträgt. Damit hängt der Scan-Bahn-Radius r(t) (abgesehen von dem Radius r₀) nicht linear von der Zeit t sondern von einer Wurzelfunktion der Zeit t ab.For the case of scanning the zone with increasing scanning radius r (t), the following results: $$r\left(t\right)=\sqrt{\frac{\Delta s^2}{\pi }*\frac{\left(t-t_0\right)}{\Delta t}+r_0^2}$$

in which $\frac{1}{\Delta t}=f_P$

_{corresponds to the frequency of the laser f IL} / D divided down according to the radial zone and to denotes the point in time at which the scan path radius is ro. Thus, the scan path radius r (t) (apart from the radius r ₀ ) does not depend linearly on the time t but on a root function of the time t.

wobei spätestens zu dem Zeitpunkt, bei dem der Radikand null wird, der Scan beendet wird. Der Scan-Bahn-Radius r(t) hängt damit auch hier, abgesehen von einer Konstanten, von einer Wurzelfunktion der Zeit ab.For the case of scanning the zone with a decreasing scan radius r (t) the following results: $$r\left(t\right)=\sqrt{r_0^2-\frac{\Delta s^2}{\pi }*\frac{\left(t-t_0\right)}{\Delta t}}$$

the scan being terminated at the latest at the point in time at which the radicand becomes zero. The scan path radius r (t) therefore also depends here, apart from a constant, on a root function of time.

In order to realize this scan path, the focus of the laser beam can be moved by means of a scan mirror or a rotary scanner (an objective is rotated around an axis of rotation) according to the above formulas as a function of time.

1. 1. Verfahren zur Generierung eines Schnittmusters für eine Laserbehandlung am Auge, bei der die Scan-Bahn der Fokuspunkte eines optischen Systems mit konstanter Winkelgeschwindigkeit und einem Radius, der von einer Wurzelfunktion der Zeit abhängt, durchlaufen wird.
2. 2. Verfahren nach Punkt 1, bei dem während des Durchlaufens der Scan-Bahn zeitlich-äquidistante Laserpulse gesetzt werden.

This solution according to the invention is characterized as follows:

1. 1. Method for generating a cutting pattern for a laser treatment on the eye, in which the scan path of the focal points of an optical system is traversed at a constant angular velocity and a radius that depends on a root function of time.
2. 2. Method according to point 1, in which time-equidistant laser pulses are set while the scan path is being passed through.

The features of the invention mentioned above and described in various exemplary embodiments can be used not only in the specified exemplary combinations, but also in other combinations or alone, without departing from the scope of the present invention.

A description of a device based on method features applies analogously to the corresponding method with regard to these features, while method features correspondingly represent functional features of the device described.

QUOTES INCLUDED IN THE DESCRIPTION

This list of the documents listed 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

• US 5984916 [0005, 0007]
• US 6110166 [0007]
• DE 10334110 [0008]
• WO 2018/183987 [0009]

Claims (23)

Planning unit (P) for the generation of control data for an ophthalmic laser therapy device (1), which a. a laser device (10) for providing a pulsed laser beam (12), b. a focusing device (20) for focusing the pulsed laser beam (12) in a focus (60), c. a scanning device (30, 32) for shifting the focus (60) of the pulsed laser beam (12) in a tissue of a patient's eye (90), in particular in a cornea (92) and / or an eye lens, for cutting through the tissue in a scan pattern ( 50) of focus spots (62) of the focus (60) of the pulsed laser beam (12) along a scan path (54) according to the control data, and d. a control unit (40) for controlling the ophthalmological laser therapy device (1) by means of the control data, the planning unit (P) having an interface (S) for transferring the control data to the control unit (40), characterized in that the planning unit (P) is designed to add further control data for the scan pattern (50) of focus spots (62) of the focus (60) in the tissue of the patient's eye (90), in particular in the cornea (92) and / or the eye lens, along the scan path (54) generate, with which the ophthalmic laser therapy device (1) can be controlled so that e. the laser device (10) provides a pulsed laser beam (12) with a constant laser pulse _{frequency f P} , f. the scan path (54) rotates at a constant angular velocity around a scan path center (56), a distance from the scan path center evaluated at the focus spots (62) (56) increases or decreases monotonically along the scan path (54), and g. the scan pattern (50) of focus spots (62) of the focus (60) of the pulsed laser beam (12) satisfies a predetermined density. Planning unit (P) according to Claim 1 , characterized in that the distance between the focus spots (62) and the center of the scan path (56) takes into account an asymmetry effect. Planning unit (P) according to Claim 1 or 2 , characterized in that for each rotation of the scan path (54) around the scan path center (56) the absolute amount of a difference between the distances from the scan path center (56) evaluated at the focus spots (62) at the beginning of the rotation and at an end of the rotation with a increasing mean distance from the center of the scan path (56) decreases. Planning unit (P) according to Claim 3 , characterized in that for each rotation of the scan path (54) around the scan path center (56) the absolute amount of the difference between the distances from the scan path center (56) evaluated at the focus spots (62) at the start of the rotation and at the end of the rotation is proportional to the inverse mean The distance of the rotation from the center of the scan path (56) is. Planning unit (P) according to one of the preceding claims, characterized in that the focus spots (62) lie on a spiral around the center of the scan path (56). Planning unit (P) according to Claim 5 , characterized in that the absolute amount of the difference between the distances from the center of the scan path (56) of two successive focus spots (62) is proportional to an inverse mean distance of the successive focus spots (62) from the center of the scan path (56). Planning unit (P) according to one of the preceding claims, characterized in that the scan pattern (50) of the focus spots (62) of the focus (60) of the pulsed laser beam (12) satisfies a limit value for a distribution measure for evaluating the distribution of the focus spots (62) . Planning unit (P) according to one of the preceding claims, characterized in that the laser device (10) a. a laser source (14) for generating laser pulses with a laser repetition frequency f _L and b. a pulse selection device (16) which is set up to select the generated laser pulses according to a division ratio D according to the further control data and to provide them for the pulsed laser beam (12), the planning unit (P) being designed to set the division ratio D so to determine that the constant laser pulse frequency f _P results. Planning unit (P) according to one of the preceding claims, characterized in that the planning unit (P) is designed to generate control data for at least two scan patterns (50, 51) with which the ophthalmic laser therapy device (1) can be controlled, wherein the The first laser pulse frequency can deviate from the at least one further laser pulse frequency, the first scan path center (56) from the at least one further scan path center and / or the first angular velocity can deviate from the at least one further angular velocity. Planning unit (P) according to Claim 9 , characterized in that the at least two scan patterns (50, 51) spatially at least partially do not overlap. Ophthalmic laser therapy device (1) for generating a scan pattern (50), comprising: - a laser device (10) for providing a pulsed laser beam (12), a focusing device (20) for focusing the pulsed laser beam (12) in a focus (60), and a scanning device (30, 32) for shifting the focus (60) of the pulsed laser beam (12) in a tissue of a patient's eye (90), in particular in a cornea (92) and / or an eye lens, for cutting through the tissue in the scan pattern ( 50) of focus spots (62) of the focus (60) of the pulsed laser beam (12) along a scan path (54) which is determined by control data, - a control unit (40) for controlling the ophthalmic laser therapy device (1) by means of the control data, and - A planning unit (P) for generating the control data according to one of the Claims 1 to 10 . Ophthalmological laser therapy device (1) according to Claim 12 , which further comprises a measuring device (M) for generating data of a characterization of the patient's eye (90), in particular a measuring device (M) from the following group: auto refractor, refractometer, keratometer, aberrometer, wavefront measuring device, optical coherence tomograph (OCT), Scheimpflug camera , Ultrasound imaging system, microscope. Planning method for the generation of control data for an ophthalmic laser therapy device (1), which a. a laser device (10) for providing a pulsed laser beam (12), b. a focusing device (20) for focusing the pulsed laser beam (12) in a focus (60), c. a scanning device (30, 32) for shifting the focus (60) of the pulsed laser beam (12) in a tissue of a patient's eye (90), in particular in a cornea (92) and / or an eye lens, for cutting through the tissue in a scan pattern ( 50) of focus spots (62) of the focus (60) of the pulsed laser beam (12) along a scan path according to the control data, and d. comprises a control unit (40) for controlling the ophthalmological laser therapy device (1) by means of the control data, characterized in that the planning method has the following steps: e. Specification of a density of focus spots (62) of the focus (60) of the pulsed laser beam (12) in the scan pattern (50), f. Selection of a constant laser pulse frequency f _{P of} the pulsed laser beam (12), g. Allocation of a scan path center (56), h. Calculation of a constant angular speed with which the scan path (54) rotates around the scan path center (56), further control data being determined from the laser pulse frequency, the scan path center (56) and the angular velocity in such a way that the ophthalmic laser therapy device (1) can be controlled in such a way that the scan pattern (50) can be generated in the tissue of the patient's eye (90) with the predetermined density of the focus spots (62), and that a distance from the scan path center (56) evaluated at the focus spots (62) increases or monotonically along the scan path (54) falls monotonically, and i. These control data are supplied to the control unit (40) of the ophthalmological laser therapy device (1). Planning process according to Claim 13 , characterized in that an asymmetry effect is taken into account when calculating the distance between the focus spots (62) and the center of the scan path (56). Planning process according to Claim 13 or 14th , characterized in that the further control data are determined in such a way that, for a rotation of the scan path (54) around the scan path center (56), a difference between the distances evaluated at the focus spots (62) at the beginning of the rotation and at an end of the rotation from Scan path center (56) decreases with an increasing mean distance from the scan path center (56), in particular that the difference in the distances is proportional to the inverse mean distance of the rotation from the scan path center (56). Planning process according to one of the Claims 13 to 15th , characterized in that the further control data are determined in such a way that the focus spots (62) lie on a spiral around the scan path center (56) and that in particular for a difference in the distances from the scan path center (56) of two successive focus spots (62) proportional to an inverse mean distance of the successive focus spots (62) from the center of the scan path (56). Planning process according to one of the Claims 13 to 16 , characterized in that a. the planning method comprises the step that a limit value for a distribution measure for evaluating the distribution of the focus spots (62) of the focus (60) of the pulsed laser beam (12) in the scan pattern (50) is specified, and that b. the further control data are determined in such a way that the scan pattern (50) of the focus spots (62) satisfies the limit value for the distribution measure. Planning process according to Claim 17 , characterized in that at least the method steps of selecting the laser pulse frequency and calculating the angular velocity are iterated until the scan pattern (50) of the focus spots (62) satisfies the limit value for the distribution measure. Planning process according to one of the Claims 13 to 18th , characterized in that the laser device (10) a. a laser source (14) for generating laser pulses with a laser repetition frequency f _L and b. a pulse selection device (16) which is set up to select the generated laser pulses according to a division ratio D according to the control data and to provide them for the pulsed laser beam (12), the division ratio D being determined such that the constant laser pulse frequency f _p results, and the division ratio D of the control unit (40) of the ophthalmic laser therapy device (1) is fed. Planning process according to one of the Claims 13 to 19th , characterized in that control data are generated for at least two scan patterns (50, 51), the first laser pulse frequency from the at least one further laser pulse frequency, the first scan path center (56) from at least one further scan path center and / or the first angular velocity from the at least one can deviate further angular velocity and wherein in particular the at least two scan patterns (50, 51) do not spatially at least partially overlap. Computer program product with program code which, when executed on a computer, executes the planning method for the generation of control data for generating a scan pattern (50) for an ophthalmic laser therapy device (1) according to one of the Claims 13 to 20th executes and / or on a planning unit (P) for generating control data according to one of the Claims 1 to 10 , in particular by a processor of such a planning device, and preferably such a planning device for the consecutive control of an ophthalmic laser therapy device (1) with the generated control data, and which, when executed by the planning device, generates control data in order to control the ophthalmic laser therapy device ( 1) operate to sever the tissue of the patient's eye (90). Computer-readable medium on which the computer program product is based Claim 21 is stored. Method for cutting a tissue in a patient's eye, in which with a planning method according to one of the Claims 13 to 20th Control data for generating a scan pattern (50) along the scan path (54) of focus spots (62) in the tissue of the patient's eye (90), in particular in a cornea (92) and / or an eye lens, for an ophthalmic laser therapy device (1) are generated and be transferred to this, and in which the ophthalmic laser therapy device (1) is operated with the aid of this control data in order to cut through tissue of a patient's eye (90).

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