DE102020134039A1 - Method for providing control data of an ophthalmic surgical laser of a treatment device for individual corneal correction of a plurality of interdependent segments of the cornea; Control device and treatment device - Google Patents

Abstract

The invention relates to a method for providing control data for a corneal correction as a function of an externally determined correction value. In order to enable improved, individualized corneal correction with greater robustness, a raw image of the cornea is subdivided (S2) into several segments (22), and an actual parameter set is determined (S3), the actual parameter set each having at least one actual parameter for each of the multiple segments (22), based on the raw image of the cornea (30) and determining (S4) a target parameter set, wherein the target parameter set contains at least one target parameter for each of the multiple segments (22) after the Corneal correction included. The target parameter for a primary segment (23) is determined as a function of the actual parameter of the primary segment (23) and the correction value, and for at least one secondary segment (24, 25) the target parameter is determined as a function of the target -Parameters of the primary segment (23) determined. Depending on a difference between the actual parameter set and the desired parameter set, control data for controlling the eye surgery laser (12) are provided (S5).

Description

The invention relates to a method for providing control data of an ophthalmic surgical laser of a treatment device for a cornea correction as a function of an externally determined correction value, the method being carried out by a control device. The invention also relates to the control device, a treatment device with the control device, and a computer program and a computer-readable medium.

Treatment devices and methods for controlling eye surgery lasers for correcting an optical defect and/or areas of a patient's cornea, also called the cornea, that have been changed by a disease or are unnatural are known in the prior art. For example, a pulsed laser and a beam focusing device can be designed such that laser pulses cause photodisruption and/or photoablation in a focus located within the organic tissue in order to remove tissue, in particular a tissue lenticule, from the cornea. So that a transition from the removed tissue to the cornea is not too abrupt, for example too steep, a transition area (“transition zone”) is usually provided in the edge areas of the tissue to be removed, which provides a flattened transition for the tissue to be removed into the cornea provides.

Today's systems and procedures enable, for example, treatment methods that are generic or adapted to the patient being treated. Adapted treatment methods take into account, for example, topographical information on the patient's cornea or information on imaging errors or information on wavefronts (based on the light falling into an eye of the patient). The approaches based on measurements have in common that although they work well with regard to the correction of ametropia, they require large amounts of tissue to be removed from the cornea. In addition, the treatment methods mentioned are dependent on complex diagnostic devices, which often have a limited dynamic range and are therefore unable to measure, for example, singularities on the surface of the cornea or areas with major changes in curvature. In other words, a resolution with which the cornea is measured can be too low to find an optimal correction based on this.

It is therefore the object of the present invention to enable an improved and individualized corneal correction which is more robust in relation to the limited dynamic range and/or the singularities described.

This object is achieved according to the invention by the subject matter of the independent patent claims. Advantageous embodiments with expedient developments are the subject matter of the dependent claims.

The invention is based on the idea of dividing the cornea or a raw image of the cornea into a number of segments, with the cornea correction being planned starting from a primary segment. The correction of one or more secondary segments can then be scheduled depending on the correction of the at least one primary segment. The invention is thus based on the idea of planning the corneal correction step by step or iteratively, starting from the at least one primary segment.

• - Empfangen eines Rohabbildes einer Hornhaut von einer Sensoreinrichtung,
• - Unterteilen des Rohabbildes der Hornhaut in mehrere Segmente,
• - Bestimmen eines Ist-Parametersatzes, wobei der Ist-Parametersatz jeweils zumindest einen Ist-Parameter für jedes der mehreren Segmente beinhaltet, anhand des Rohabbildes der Hornhaut,
• - Bestimmen eines Soll-Parametersatzes, wobei der Soll-Parametersatz jeweils zumindest einen Soll-Parameter für jedes der mehreren Segmente nach der Hornhautkorrektur beinhaltet, wobei
• - für ein primäres Segment der mehreren Segmente der zumindest eine Soll-Parameter in Abhängigkeit von dem zumindest einen Ist-Parameter des primären Segments sowie dem Korrekturwert bestimmt wird und für zumindest ein sekundäres Segmnet der mehreren Segmente der zumindest eine Soll-Parameter in Abhängigkeit von dem zumindest einen Soll-Parameter des primären Segments bestimmt wird, und
• - Bereitstellen von Steuerdaten zum Steuern des augenchirurgischen Lasers in Abhängigkeit von einer Differenz zwischen dem Ist-Parametersatz und dem Soll-Parametersatz.

A first aspect of the present invention relates to a method for providing control data of an ophthalmic surgical laser of a treatment device for a cornea correction as a function of an externally determined correction value, the method having the following steps carried out by a control device:

• - receiving a raw image of a cornea from a sensor device,
• - dividing the raw image of the cornea into several segments,
• - determining an actual parameter set, the actual parameter set containing at least one actual parameter for each of the multiple segments, based on the raw image of the cornea,
• - Determining a target parameter set, the target parameter set each containing at least one target parameter for each of the plurality of segments after the corneal correction, wherein
• - the at least one target parameter is determined for a primary segment of the plurality of segments as a function of the at least one actual parameter of the primary segment and the correction value, and for at least one secondary segment of the plurality of segments the at least one target parameter meter is determined as a function of the at least one target parameter of the primary segment, and
• - Providing control data for controlling the ophthalmic surgical laser depending on a difference between the actual parameter set and the target parameter set.

The correction value can characterize the correction desired for the patient or his cornea. For example, the correction value can be derived from a previously measured surface of the cornea and/or from a previously determined ametropia. The ametropia can, for example, have been determined as part of a so-called refractometry, for example by an ophthalmologist. The correction value can thus be derived from a result of the refractometry or from refractometry data relating to the refractometry. For example, as the correction value or as part of the correction value, a desired change in a refractive power of the cornea, a desired change in a curvature of the cornea, a desired size (e.g. diameter or radius) of an optical zone and/or a desired position of the optical zone in relation to the cornea definitely. The desired curvature can be given in the form of an absolute value or in the form of a relative value. An absolute value can directly indicate which curvature the cornea should have in the area of the optical zone after the treatment has been completed, i.e. after the corneal correction. An absolute value of the curvature can, for example, be specified directly by a radius of curvature or indirectly by a focal length or a refractive power. A relative value of the curvature can, for example, be indicated analogously by a difference in the radius of curvature or by a difference in the focal length or refractive power. In this case, the difference is preferably related to the state of the cornea before the first cornea correction or after the first cornea correction. Of course, the curvature can also be described by any other suitable physical variable, whether absolute or relative to the current curvature.

The raw image of the cornea can be retrieved or received, for example, from a corresponding sensor device of the treatment device. In particular, the raw image of the cornea can characterize or depict a surface of the cornea. In other words, the raw image can be a digital image of the surface of the cornea. The sensor device can be part of the treatment device, set up at the location of the treatment device or spatially separated from the treatment device.

The raw image of the cornea is divided into the multiple segments. At least one of the multiple segments is determined as the primary segment. At least one of the multiple segments is designated as a secondary segment. Each of the plurality of segments can be either a primary or a secondary segment. In other words, the primary segment or the primary segments and the secondary segment or the secondary segments are each different from the plurality of segments. The subdivision of the cornea or the raw image of the cornea into the plurality of segments can take place by determining segment boundaries in the raw image. In other words, segment boundaries can be generated in the raw image, by which the multiple segments are separated from one another. In this case, the subdivision into the plurality of segments can take place in accordance with a predetermined rule. A geometry on which the resulting subdivision is based can be predetermined by the predetermined rule.

The actual parameter set can describe a shape or surface of the cornea in an actual state, ie in particular specify or parameterize it. For this purpose, the actual parameter set is composed of several actual parameters. In this case, each of the actual parameters relates in particular to exactly one segment. The at least one respective actual parameter can be determined for each of the plurality of segments. In other words, one or more actual parameters can be determined for each of the multiple segments. The respective actual parameters of the multiple segments can together form the actual parameter set. In other words, the actual parameter set is determined by determining the respective actual parameters. The actual parameter set characterizes or describes in particular the surface or a shape of the cornea. In this case, the actual parameter set relates to a condition of the cornea at a point in time before the start of the cornea correction, as an actual condition during the planning of the cornea correction.

The target parameter set can describe the shape or the surface of the cornea in a desired target state, that is to say in particular specify or parameterize it. For this purpose, the setpoint parameter set is composed of several setpoint parameters. In this case, each of the target parameters relates in particular to precisely one segment. In this case, for the at least one primary segment, the respective target parameter is determined as a function of the at least one actual parameter of the primary segment and the correction worth determined. For the at least one secondary segment, the at least one target parameter is determined as a function of the at least one target parameter of the primary segment. In other words, the target parameter is determined only for the at least one primary segment as a function of the correction value. The correction value is used, for example, to derive the at least one target parameter of the primary segment from the at least one actual parameter of the primary segment.

For the remaining segments, namely in particular the at least one secondary segment, the respective at least one target parameter is then determined as a function of the target parameter of the at least one primary segment. The at least one target parameter of the at least one secondary element can be determined, for example, as a function of the at least one target parameter of the primary segment and a predetermined parameter that represents a difference between the respective target parameters of the at least one primary segment and the at least one secondary segment. In other words, based on the target parameter of the at least one primary segment, the at least one target parameter of the at least one secondary segment can be determined in such a way that it deviates from the target parameter of the at least one primary segment by the predetermined parameter. The predetermined parameter can be a smoothing parameter, for example, which is explained in more detail below.

Depending on the difference between the actual parameter set and the target parameter set, the eye surgery laser can then be controlled. In general, corresponding control data for controlling the eye surgery laser are provided, with the control data being dependent on the difference between the actual parameter set and the target parameter set. The actual parameter set can relate to the actual state of the cornea and the target parameter set can relate to the target state of the cornea. In particular, the difference mentioned results in a necessary ablation of tissue of the cornea or of tissue of the eye. A corresponding ablation of tissue can provide that the cornea is given a shape, at least in regions, as is parameterized or specified by the set of parameters.

According to a development, it is provided that a curvature, preferably in the radial direction, is determined for the corresponding segment as the actual parameter and as the target parameter. In other words, a respective value for the curvature of the segments is specified as the actual parameter and/or as the target parameter. For example, a respective value for an actual curvature and/or a respective value for a target curvature can be determined as an actual parameter or target parameter for the multiple segments, in particular the at least one primary segment and/or the at least one secondary segment will. The respective actual parameter or the respective actual curvature of a respective segment can specify at least one value for a measured curvature of the cornea in the corresponding segment. The target parameter or the target curvature can specify at least one value for a desired curvature of the cornea after the cornea correction. The target curvature for the at least one primary segment can then be determined as a function of the correction value and the actual curvature of the at least one primary segment. The curvature of the target parameter for the at least one secondary segment can be determined as a function of the target curvature of the at least one primary segment. In general, the eye or a surface of the cornea can be characterized particularly well by determining the respective parameters for the curvature.

In particular, it is provided that exactly two respective values for the curvature of the cornea are determined as actual parameters of the actual parameter data set for each of the segments. In other words, the actual parameter for each of the multiple segments can contain exactly two values for the curvature of the cornea in the corresponding segment. For this purpose, exactly two respective values for the curvature of the cornea can be determined for each segment. Thus, the actual curvature of each of the segments can be characterized by two values for the curvature. Thus, the curvature of each of the segments is characterized by exactly two values by the actual parameters or the actual parameter set, that is to say they are described or indicated.

In particular, the precisely two respective values for the curvature, which are determined for each of the segments as actual parameters or as part of the actual parameter set, can specify a maximum curvature and a minimum curvature within the corresponding segment. In other words, a first of the exactly two respective values for the curvature can indicate the maximum curvature of the cornea within the respective segment. A second of the exactly two respective ones Values for the curvature can indicate or characterize the minimum curvature of the cornea in the respective segment. The respective value for the maximum curvature or the minimum curvature is measured or determined in particular along a diameter of the cornea. Thus, the minimum and maximum curvature of each of the segments is characterized by the actual parameters or the actual parameter set, that is to say they are described or specified.

According to a development, it is provided that the curvature and/or the values for the curvature are assigned an angle, in particular an azimuthal angle, as a further actual parameter. The angle or the respective angle can be used to define an axis or a diameter to which the curvature or the respective value for the curvature relates. It can thus be specified at which angles the cornea has which curvature in the respective segment. In a further embodiment, it can be specified or defined by the further actual parameter, ie the angle, at which angle or at which diameter the cornea in the respective segment has the maximum and/or the minimum curvature. A respective axis or a respective angle is thus assigned to the maximum curvature and/or the minimum curvature in the respective segment. The advantage here is that a particularly simple but particularly meaningful parameterization of the surface of the cornea is made possible by a corresponding pair of actual parameters, namely the curvature and the associated angle. As a result, a particularly advantageous, individualized corneal correction can also be determined in a particularly simple manner and with reduced demands on the accuracy of the measurement of the surface of the cornea.

A further development provides that a shape of the cornea in the actual parameter set and/or the target parameter set is parameterized exclusively by the curvature and/or the values for the curvature of the respective segments and optionally the respectively assigned angles. In other words, it can be the case, for example, that the shape of the cornea in the actual parameter set and/or the target parameter set is parameterized exclusively by the curvature or the values for the curvature in the respective segments. Alternatively, it can be provided that the shape of the cornea in the actual parameter set and/or the target parameter set is parameterized exclusively by the curvature or the values for the curvature and the respectively assigned angle.

A sufficiently precise and stable parameterization of the surface of the cornea can be carried out by such a focus on the mentioned actual parameters and/or desired parameters. On the other hand, small-scale features, non-resolvable singularities and the like are avoided, which on the one hand leads to a lower ablation depth and on the other hand to reduced inaccuracies.

According to a development, it is provided that one of the several segments, in particular the primary segment, has the shape of a circle and the other segments each have the shape of a circular ring. In particular, exactly one primary segment is provided, which is of circular design. The remaining segments can each have the shape of a circular ring, with the individual segments not overlapping in particular. In this way, the plurality of segments can each have an increasing radius, with the individual segments being separated from one another by the segment boundaries. The segment boundaries can each be arranged equidistantly from one another in terms of their radius. Such a shape of the segments has proven to be particularly advantageous. In this way, the target parameters can be determined continuously from the inside out with respect to the cornea of the eye. In particular, it is provided that the inner segments are each arranged radially symmetrically around an optical center of the eye or the cornea.

According to one development, the at least one target parameter of the at least one secondary segment is also determined as a function of the smoothing parameter, with the smoothing parameter specifying a value for the difference in curvature of the primary segment and the at least one secondary segment. In particular, the smoothing parameter is the predetermined parameter described above. In a further refinement, it can be provided that the at least one target parameter of the at least one secondary segment is determined exclusively as a function of the smoothing value and the at least one target parameter of the primary segment. In other words, the target parameter for the secondary segment is set to represent a curvature that is increased by a predetermined difference, namely, as through given the smoothing parameter, deviates from the curvature of the primary segment. In this way, there is a continuous change in curvature across the segments.

According to one development, it is provided that the at least one target parameter of at least one tertiary of the plurality of segments is determined as a function of the at least one target parameter of the secondary segment and optionally the smoothing parameter. In other words, the target parameter of the at least one tertiary segment can be determined exclusively as a function of the at least one target parameter of the at least one secondary segment or exclusively as a function of the at least one target parameter of the at least one secondary segment together with the smoothing parameter . Of course, this can be continued further for quaternary, fifth, sixth, and so on segments. In this way, the idea of the invention is further developed, the shape of the cornea is continuously adapted by the respective target parameters of the segments, starting from the primary segment, so that starting from the primary segment, a balanced surface results. In particular, this takes place along a number of rings or circular rings from the inside to the outside.

The actual parameter set or the actual parameter(s) can relate to the condition and/or the surface of the cornea. For example, a measured curvature of the cornea is determined as part of the actual parameter set. The measured curvature can be given in the form of an absolute value, for example. An absolute value can directly indicate the curvature of the cornea in the area of the optical zone before the treatment has started or has been completed, for example before the first cornea correction or after the first but before the second cornea correction. An absolute value of the curvature can, for example, be specified directly by a radius of curvature or indirectly by a focal length or a refractive power. A relative value of the curvature can, for example, be indicated analogously by a difference in the radius of curvature or by a difference in the focal length or refractive power. In this case, the difference is preferably related to the state of the cornea before the first cornea correction or after the first cornea correction. Of course, the curvature can also be described by any other suitable physical variable, whether absolute or relative to the current curvature.

A second aspect of the present invention relates to a control device that is set up to carry out one of the methods described above. The advantages listed above result. The control device can be designed, for example, as a control chip, control device or user program (“app”). The control device can preferably have a processor device and/or a data memory. A processor device is understood to mean a device or a device component for electronic data processing. The processor device can have at least one microcontroller and/or at least one microprocessor, for example. A program code for carrying out the method according to the invention can preferably be stored on the optional data memory. The program code can then be designed to cause the control device, when executed by the processor device, to carry out one of the above-described embodiments of one or both methods according to the invention.

A third aspect of the present invention relates to a treatment device with at least one ophthalmic surgical laser for the separation of a tissue predefined by the control data, in particular a corneal volume with predefined boundary surfaces of a human or animal eye by means of photodisruption and/or photoablation, and at least one control device for the or the Laser adapted to carry out the steps of the method according to the first aspect of the invention. The treatment device according to the invention makes it possible for the disadvantages that occur when using conventional ablative treatment devices to be reliably reduced or even avoided.

In a further advantageous embodiment of the treatment device according to the invention, the laser can be suitable for laser pulses in a wavelength range between 300 nm and 1400 nm, preferably between 700 nm and 1200 nm, with a respective pulse duration between 1 fs and 1 ns, preferably between 10 fs and 10 ps, and a repetition frequency greater than 10 kilohertz (KHz), preferably between 100 KHz and 100 megahertz (MHz). Such a femtosecond laser is particularly well suited for removing tissue within the cornea. The use of photodisruptive and/or photoablative lasers in the method according to the invention also has the advantage that the cornea does not have to be irradiated in a wavelength range below 300 nm. In laser technology, this range is subsumed under the term "deep ultraviolet". This is advantageous avoids unintentional damage to the cornea caused by these very short-wave and high-energy rays. Photodisruptive lasers of the type used here usually introduce pulsed laser radiation with a pulse duration between 1 fs and 1 ns into the corneal tissue. As a result, the power density of the respective laser pulse, which is necessary for the optical breakthrough, can be narrowly limited spatially, so that a high level of cutting accuracy is made possible when producing the interfaces. In particular, the range between 700 nm and 780 nm can also be selected as the wavelength range.

In further advantageous configurations of the treatment device according to the invention, the control device can have at least one storage device for at least temporarily storing at least one control data set, the control data set or sets comprising control data for positioning and/or for focusing individual laser pulses in the cornea or cornea; and can have at least one beam device for beam guidance and/or beam shaping and/or beam deflection and/or beam focusing of a laser beam of the laser. Said control data set includes the control data determined in the method for removing the tissue.

Further features and their advantages can be found in the descriptions of the first aspect of the invention, with advantageous configurations of each aspect of the invention being to be regarded as advantageous configurations of the respective other aspect of the invention.

A fourth aspect of the invention relates to a computer program comprising instructions which cause the treatment device according to the fourth aspect of the invention to carry out the method steps according to the first aspect of the invention and/or the method steps according to the second aspect of the invention.

A fifth aspect of the invention relates to a computer-readable medium on which the computer program according to the fourth aspect of the invention is stored. Further features and their advantages can be found in the descriptions of the first to fourth aspects of the invention, advantageous refinements of each aspect of the invention being to be regarded as advantageous refinements of the other aspect of the invention in each case.

• 1 eine schematische Darstellung einer erfindungsgemäßen Behandlungsvorrichtung gemäß einer beispielhaften Ausführungsform;
• 2 ein Ablaufdiagramm eines erfindungsgemäßen Verfahren gemäß einer beispielhaften Ausführungsform;
• 3 ein beispielhaftes schematisches Abbild einer krankhaften und zu korrigierenden Hornhaut; und
• 4 ein beispielhaftes schematisches Abbild einer gesunden Hornhaut mit einer durch eine Korrektur anzustrebenden Form.

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

• 1 a schematic representation of a treatment device according to the invention according to an exemplary embodiment;
• 2 a flow chart of a method according to the invention according to an exemplary embodiment;
• 3 an exemplary schematic image of a diseased cornea to be corrected; and
• 4 an exemplary schematic image of a healthy cornea with a shape to be aimed for by a correction.

the 1 shows a schematic representation of a treatment device 10 with an ophthalmic surgical laser 12 for the removal of tissue 14 of a human or animal eye 16 by means of photodisruption and/or photoablation. The tissue 14 can represent, for example, a lenticle or also a volume body, which can be separated from a cornea of the eye 16 with the ophthalmic surgical laser 12 in order to correct ametropia. A geometry of the tissue 14 to be removed, i.e. a tissue removal geometry 14, can be provided by a control device 18, in particular in the form of control data, so that the laser 12 emits pulsed laser pulses in a pattern predefined by the control data into the cornea of the eye 16 to ent the tissue 14 distant. Alternatively, the control device 18 can be a control device 18 that is external to the treatment device 10 .

Furthermore, the 1 that the laser beam 19 generated by the laser 12 can be deflected in the direction of the eye 16 by means of a beam deflection device 22, namely a beam deflection device such as a rotary scanner, in order to remove the tissue 14. The beam deflector 22 can also be controlled by the controller 18 to remove the tissue 14 .

The laser 12 shown can preferably be a photodisruptive and/or photoablative laser that is designed to emit laser pulses in a wavelength range between 300 nanometers and 1400 nanometers, preferably between 700 nanometers and 1200 nanometers, with a respective pulse duration of between 1 femtosecond and 1 nanosecond, preferably between 10 femtoseconds and 10 picoseconds, and a repetition frequency greater than 10 kilohertz, preferably between 100 kilohertz and 100 megahertz. The control device 18 optionally also has a storage device (not shown) for at least temporarily storing at least one control data record, the control data record(s) including control data for positioning and/or focusing individual laser pulses in the cornea. The position data and/or focusing data of the individual laser pulses, ie the tissue removal geometry 14, is determined using the method described below.

2 shows a flow chart of an exemplary embodiment of a method for providing control data of the ophthalmic surgical laser 12 of the treatment device 10. The control data of the ophthalmic surgical laser 12 of the treatment device 10 for a corneal correction are determined depending on an externally determined correction value. The cornea correction can thus be carried out on the basis of the control data. In other words, the ophthalmic surgical laser 12 or the treatment device 10 carries out the corresponding corneal correction determined as a function of the correction value when controlled according to the control data generated by means of the method.

• S1: Empfangen eines Rohabbildes der Hornhaut 30 von einer Sensoreinrichtung,
• S2: Unterteilen des Rohabbildes der Hornhaut 30 in mehrere Segmente 22,
• S3: Bestimmen eines Ist-Parametersatzes, wobei der Ist-Parametersatz jeweils zumindest einen Ist-Parameter für jedes der mehreren Segmente 22 beinhaltet, anhand des Rohabbildes der Hornhaut 30,
• S4: Bestimmen eines Soll-Parametersatzes, wobei der Soll-Parametersatz jeweils zumindest einen Soll-Parameter für jedes der mehreren Segmente 22 nach der Hornhautkorrektur beinhaltet, wobei für ein primäres Segment 23 der mehreren Segmente 22 der zumindest eine Soll-Parameter in Abhängigkeit von dem zumindest einen Ist-Parameter des primären Segments 23 sowie dem Korrekturwert bestimmt wird und für zumindest ein sekundäres Segment 24, 25 der mehreren Segmente 22 der zumindest eine Soll-Parameter in Abhängigkeit von dem zumindest einen Soll-Parameter des primären Segments 23 bestimmt wird, und
• S5: Bereitstellen von Steuerdaten zum Steuern des augenchirurgischen Lasers 12 in Abhängigkeit von einer Differenz zwischen dem Ist-Parametersatz und dem Soll-Parametersatz.

The method has the following steps, for example, which are carried out by the control device 18:

• S1: receiving a raw image of the cornea 30 from a sensor device,
• S2: subdividing the raw image of the cornea 30 into several segments 22,
• S3: determining an actual parameter set, the actual parameter set containing at least one actual parameter for each of the plurality of segments 22, based on the raw image of the cornea 30,
• S4: Determining a target parameter set, with the target parameter set containing at least one target parameter for each of the multiple segments 22 after the corneal correction, with the at least one target parameter for a primary segment 23 of the multiple segments 22 depending on the at least one actual parameter of primary segment 23 and the correction value is determined and for at least one secondary segment 24, 25 of the plurality of segments 22 the at least one target parameter is determined as a function of the at least one target parameter of primary segment 23, and
• S5: Provision of control data for controlling the ophthalmic surgical laser 12 depending on a difference between the actual parameter set and the target parameter set.

The individual steps and the underlying process are explained in more detail below.

Wavefront-guided (also referred to as “wavefront-guided”) treatments individually adapted to a patient or their cornea are often used for treatment, in particular for correcting a refractive error of a cornea, for example as part of a follow-up treatment of a cornea correction that has already taken place. Such treatments have been found to be effective in reducing lower and higher order aberrations and/or expanding the optical zone and/or subjective reports of undesirable aberration consequences such as reflections (so-called "glares") and the perception of halos (so-called "halos") to improve. Due to the limitations of corresponding sensors for the wavefront-guided measurement of the eye 16 or the cornea (also referred to as wavefront sensors or in English as "wavefront sensors") in the precise measurement of large curvatures, large aberrations and singularities, in a treatment using such a wavefront-guided treatment other errors occur. is present therefore, a simple and inexpensive (non-wavefront-guided) algorithm is shown to correct the optical zone ("OZ") and correct the refractive error with minimal tissue removal. Due to its tissue-friendly properties, this method can be used to advantage, especially in patients with a critical residual corneal thickness. A respective target curvature for the different segments or zones is determined on the basis of a zonal reconstruction of the topography for a plurality of segments. A net ablation map for corneal correction can be calculated from a current and the target curvature and is suitable for correcting low-order refractive components and high-order aberration components alike in one procedure. The results of simulations evaluating the procedure show minimal tissue removal. Accordingly, this method enables an improvement in the visual results in the treatment of extreme cases and therefore represents an uncomplicated and cost-effective alternative to wavefront-guided treatments.

Aberrometry techniques, in which the wavefront of the eye 16 can be individually determined, opened up new possibilities for customized wavefront-guided treatments by extending refractive treatment to higher-order aberrations (HOA) such as coma and trefoil. Such individualized treatment aims to improve not only vision (based on Snellen tests) but also the quality of vision (i.e. visual acuity measured as contrast sensitivity and fine vision).

The present method is based, among other things, on determining the correction for the curvature of the cornea zonally, ie individually for each segment. The aim is to improve the most important components of vision with minimal tissue ablation and to normalize the higher-order aberrations. For this purpose, the present approach provides for determining the net ablation map on the basis of the current zonal curvatures (actual parameter set) of the topography and the target curvatures (target parameter set). The net ablation map is determined on the basis of the respective parameters, ie the actual parameters and the target parameters, of each segment.

This is exemplified in the 2 shown. In 2 a cornea 30 of a human eye 16 is shown as an example. In this case, the cornea 30 is divided into several segments 22 . The segments 22 are radially symmetrical in the present example. A first segment 23 is arranged, for example, in a circle around a center point 28 of the cornea 30 . A second segment 24 and a third segment 25 are arranged, for example, in the shape of a circular ring around a center point of the cornea 30 . The first segment 23 has a radius of 3 mm purely by way of example. The second segment 24 has, purely by way of example, an inner radius of 3 mm and an outer radius of 5 mm. The third segment 25 has, purely by way of example, an inner radius of 5 mm and an outer radius of 7 mm.

The actual parameter set can be understood as a description, in particular as a characterization or reconstruction, of the topography of the cornea 30 . In other words, the actual parameter set can describe or reproduce the surface of the cornea 30 in an actual state. A simplification can result from the restriction to the actual parameters of the actual parameter set. The surface of the cornea 30 is thus characterized or described in a simplified manner by the actual parameter set or the actual parameters. The cornea 30 in the actual parameter set is characterized, for example, exclusively on the basis of the respective (zonal) curvatures of the segments 22 . The actual parameters indicate a respective value for the curvature of the cornea 30 in a respective one of the segments 22 .

In particular, it is provided that exactly two respective values for the curvature of the cornea 30 are specified or determined as actual parameters of the actual parameter data set for each of the segments 22 . In other words, the actual parameters for each of the segments 22 can in each case specify exactly two values which relate to the curvature of the cornea 30 in the corresponding segment, that is to say in particular specify or describe it. For this purpose, exactly two respective values for the curvature of the cornea 30 can be determined for each segment 22 . Thus, the actual curvature of each of the segments 22 can be characterized by two values for the curvature. In particular, the precisely two respective values for the curvature, which are determined for each of the segments 22 as actual parameters or as part of the actual parameter set, can indicate a maximum curvature and a minimum curvature within the corresponding segment 22 . In other words, a first of the exactly two respective values for the curvature can indicate the maximum curvature of the cornea 30 within the respective segment 22. A second of the exactly two respective values for the curvature can indicate the minimum curvature of the cornea 30 in the respective segment 22, respectively characterize. The minimum and maximum curvature of each of the segments 22 is thus characterized by the actual parameters or the actual parameter set.

In the present case, an angle, in particular an azimuthal angle, or an angle specification, in particular an azimuthal angle, is additionally assigned to the curvature or the values for the curvature as a further actual parameter. The angle or the respective angular specification can be used to define an axis or a diameter to which the curvature or the respective value for the curvature relates. It can thus be specified at which angles the cornea 30 has which curvature in the respective segment. In particular, it can be specified or defined by the further actual parameter, ie the angle, at which angle or at which diameter the cornea 30 has the maximum and/or the minimum curvature in the respective segment. A respective axis or a respective angle is thus assigned to the maximum curvature and/or the minimum curvature in the respective segment. The advantage here is that a particularly simple but particularly meaningful parameterization of the surface of the cornea 30 is made possible by a corresponding pair of actual parameters, namely the curvature and the associated angle. As a result of this, a particularly advantageous, individualized cornea correction can also be determined in a particularly simple manner and with reduced demands on the accuracy of the measurement of the surface of the cornea 30 . The respective actual parameters of a respective segment 22 can thus contain at least one actual curvature and optionally at least one actual angle.

3 and 4 show two different examples with differently shaped corneas. while showing 4 a normally shaped, healthy cornea 30. The cornea 30 off 4 (normal cornea 30) has a subtle flattening from the first segment 23 (3mm disk) to the third segment 25 (7mm circular disk) (this generally stays below 1D of flattening). 4 (normal cornea 30) also shows a subtle increase in astigmatism from the first segment 23 (3mm disc) to the third segment 25 (7mm disc) (this generally remains below 1D increased toricity). At the cornea 30 off 4 (normal cornea 30), the axis for maximum curvature tends to be near vertical for all zones (90 degree and 270 degree axis, respectively). In addition, the cornea is 30 off 4 (normal cornea 30) the axis of minimum curvature tends to be near horizontal for all zones (180 degree and 0 degree axis respectively). At the cornea 30 off 4 (normal cornea 30), for example, the angle between the axes of maximum curvature and minimum curvature for all segments 22 is around 90 degrees.

Related to 3 , which shows a cornea 30 to be corrected, the target curvature as a target parameter for the first segment 23 (3mm disc) is either determined by the average actual curvature (as part of the actual parameters of the first segment 23) of the first segment 23 ( left 45.86D) and the defocus component of the refraction determined (e.g. -1D; which in this case would give 44.97D (ie around 45D) since the difference is non-linear and takes into account the vertex distance and the refractive indices of the cornea 30 and the topographer target). In the present case, the defocusing component of the refraction is the externally determined correction value. Starting from the correction value, the following target parameters for curvature and angle of the first segment 23 would result from the two curvatures: 45.35D (curvature) at 106 degrees and 44.59D (curvature) at 16 degrees.

From the normal corneal progression (which yes from 3B known) would then follow for the second segment 24, starting from the first segment 23, a somewhat flatter curvature, for example -0.25D difference in curvature, i.e. for example 44.75D curvature and for the third segment 25 a further -0.5D difference in the curvature i.e. 44.25D curvature as an example. In general, the target curvature or the target parameter for the second segment 24 is determined as a function of the target curvature or the target parameter of the first segment 23 and a smoothing parameter. The smoothing parameter describes, i.e. defines or indicates, the difference in the curvature relative to the first segment 23. The target curvature can thus be determined as the target parameter of the second segment 24, for example using a first value of the smoothing parameter, for example by subtraction or addition be derived from the target curvature as a target parameter of the first segment 23. In the above example, the smoothing parameter specifies a difference of -0.25D in the respective target curvature of the first segment 23 and the second segment 24, for example. Thus, the target curvature as a target parameter of the third segment 25 can be calculated, for example, using a second value of the smoothing parameter, for example by subtraction or addition, from the target curvature as a target parameter of the first segment 23 and/or from that of the target curvature be derived as target parameters of the second segment 24. In the example above, the smoothing parameter gives a difference in the respective desired curvature of the second segment 24 and the third segment 25 of -0.5D. As an alternative or in addition, the smoothing parameter in the above example can assign a difference of −0.75D between the respective setpoint curvature of the first segment 23 and the third segment 25 .

Generalized again, the target parameter of a secondary segment, here the second segment 24, can be derived (exclusively) from the smoothing parameter and from the target parameter of a primary segment, here the first segment 23. Analogously, the target parameter of a tertiary segment, here the third segment 25, can be derived (exclusively) from the smoothing parameter and from the target parameter of a primary segment, here the first segment 23. Alternatively or additionally, the target parameter of the tertiary segment, here the third segment 25, can be derived (exclusively) from the smoothing parameter and from the target parameter of the secondary segment, here the second segment 24.

Assuming normal corneal progression, we would then see a slight increase in corneal toricity for the second segment 24 of approximately 0.25D; 1D cyl and the third segment 25 about another 0.5D; 1.5D cyl. The target curvatures are 45.22D at 106 degrees (minimum curvature) and 44.22D (maximum curvature) at 16 degrees for the second segment 24 and 44.97D at 106 degrees (minimum curvature) and 43.47D (maximum curvature) at 16 degrees for the third segment 25.

In a further embodiment, starting from the normal cornea 30, the axes cannot be specified at an unchanged angle, ie here 106//16 degrees, but at 90//0 degrees. An axis or an angle of 90 degrees (minimum curvature) or 0 degrees (maximum curvature) can thus be assigned to the curvatures described above as additional target parameters.

In summary, an accurate sphere and cylinder of refraction can be determined to determine the desired curvatures of the first segment 23 . Starting from the target curvatures of the first segment 23, the target curvatures of the second segment 24 and the third segment 25 can be clearly determined by approximating a normal curve (specified by the smoothing parameter).

A quantity of tissue to be removed can be determined on the basis of a difference between a surface parameterized by the actual parameter set and a surface parameterized by the target parameter set. For example, a net ablation map can be generated by subtraction between the surface parameterized by the actual parameter set and a surface parameterized by the target parameter set. In particular, the surface parameterized by the setpoint parameter set and a surface parameterized by the actual parameter set are subtracted.

• Wie bereits beschrieben werden ausgehend von dem extern bestimmten Korrekturwert sowie den Ist-Parametern des ersten Segments 23 die Soll-Parameter des ersten Segments 23 bestimmt. Ausgehend von den Soll-Parameter des ersten Segments 23 sowie dem Glättungsparameter, welcher anhand eines natürlichen Verlauf des Krümmung und Torizität vorgegeben sein kann, werden die Soll-Parameter des zweiten Segments 24 sowie es dritten Segments 25 bestimmt.

These are sphere and cylinder values, so that the continuity between the segments 22 is not necessarily given. Natural movements and uncertainties in the technical system can lead to gaps or overlaps between the segments 22. To avoid this, the present method also offers an alternative solution, which looks like this:

• As already described, the target parameters of the first segment 23 are determined on the basis of the externally determined correction value and the actual parameters of the first segment 23 . The target parameters of the second segment 24 and the third segment 25 are determined on the basis of the target parameters of the first segment 23 and the smoothing parameter, which can be specified using a natural course of the curvature and toricity.

The idea on which the further embodiment is based is to determine these respective parameters (actual parameters and/or target parameters) for a plurality of, for example three, circular segments of different radii. The circular segments can then overlap and, in particular, stacked one on top of the other (added together) to produce the required zonal changes in curvature. The respective parameters, in particular target parameters, for a non-overlapping circular first segment 23 and two non-overlapping annular segments 24 and 25 can be derived from this. The target parameter set or the target parameters for non-overlapping segments 23, 24, 25 can accordingly be derived from analogous parameters of overlapping segments.

For non-overlapping segments 23, 24, 25: $$\text{kr}\ddot{\text{and}}\text{mming}\ddot{\text{a}}\text{changes}\left(\text{n}\right)=\text{is}-\text{parameter}\left(\text{n}\right)-\text{Should}-\text{parameter}\left(\text{n}\right)$$

For overlapping segments: $$\begin{array}{l}\text{total kr}\ddot{\text{and}}\text{mming}\ddot{\text{a}}\text{change}=\text{sum of kr}\ddot{\text{and}}\text{mming}\ddot{\text{a}}\text{changes of}\\ \ddot{\text{and}}\text{overlapping segments}\end{array}$$

In this case, the target parameters of the first circular segment, the second circular segment (example with 5mm diameter) and the third circular segment (example with 7mm diameter) add up within the first circular segment (example with 3mm diameter), since here all circular segments overlap. The parameter Tx stands for, for example, that part of the desired change in curvature which is based on the target parameter of the corresponding segment: $$\begin{array}{l}\text{total kr}\ddot{\text{and}}\text{mming}\ddot{\text{a}}\text{change}\left(\text{first segment}\right)=\text{tx}\left(\text{first segment}\right)+\text{tx}\\ \left(\text{second segment}\right)+\text{tx}\left(\text{third segment}\right)\end{array}$$

The actual parameter of the circular third segment (example 7mm diameter) subtracted by the target parameters of the circular third segment results in the change in curvature of the circular third segment and the parameter Tx (third segment): $$\begin{array}{l}\text{tx}\left(\text{third segment}\right)=\text{kr}\ddot{\text{and}}\text{mming}\ddot{\text{a}}\text{changes}\left(\text{third segment}\right)=\text{is}-\text{parameter}\\ \left(\text{third segment}\right)-\text{Should}-\text{parameter}\left(\text{third segment}\right)\end{array}$$

The actual parameter of the circular second segment (example with 5mm diameter) subtracted by the target parameter of the circular second segment and the parameter Tx (third segment) results in a change in curvature of the circular second segment: $$\begin{array}{l}\text{tx}\left(\text{second segment}\right)=\text{kr}\ddot{\text{and}}\text{mming}\ddot{\text{a}}\text{changes}\left(\text{second segment}\right)-\text{tx}(\text{third}\\ \text{segment})=\text{is}-\text{parameter}\left(\text{second segment}\right)-\text{Should}-\text{parameter}\left(\text{second segment}\right)-\text{tx}\\ \left(\text{third segment}\right)\end{array}$$

The same applies to the first segment: $$\begin{array}{l}\text{tx}\left(\text{first segment}\right)=\text{is}-\text{parameter}\left(\text{first segment}\right)-\text{Should}-\text{parameter}(\text{first}\\ \text{segment})-\text{tx}\left(\text{second segment}\right)-\text{tx}\left(\text{third segment}\right)=\text{entire}\\ \text{kr}\ddot{\text{and}}\text{mming}\ddot{\text{a}}\text{change}\left(\text{first segment}\right)-\text{tx}\left(\text{second segment}\right)-\text{tx}(\text{third}\\ \text{segment})\end{array}$$

Of course, the use of three segments 22 is to be understood purely as an example in all application examples. The method can be used with more or less than three segments 22 as well. The respective size of the segments 22 is also to be understood purely as an example in all application examples. The segments 22 can each have any desired and/or different size. Likewise, it is not necessary (although advantageous) that the segments 22 be concentric. However, it is particularly advantageous if the larger segments 22 completely enclose the inner segments 22 .

Here, simple parabolic profiles are used for the parameterization of the surfaces (paraxial approximation of the Munnerlynn profiles), but the present method can also be used with other profiles for the parameterization of the surfaces (aspheric or wavefront-optimized).

A transition zone for overall treatment could (and should) be included. However, if a transition zone is also included for the smaller parts of the ablation, its refractive effect must also be taken into account when calculating the larger zones. For this reason we prefer not to provide a transition zone for the inner components and to use only a transition zone from the outermost segment 22, here the third segment 25, to the untreated cornea 30.

Under- or over-correction are common problems with refractive procedures. Also, decentration due to human or mechanical error cannot be avoided at the sub-clinical level. Eyes with decentered ablations show a significantly higher degree of induced aberrations and poorer distance vision than eyes with well-centered ablations. Smaller optical zones, which are reached during refractive procedures, lead to postoperative problems such as impaired night vision, reduced contrast sensitivity and ghosting. In such cases, wavefront-guided post-treatment is often performed. However, critical residual corneal thickness and inaccurate wavefront measurement represent a limitation in extreme cases. Improving wavefront sensor technology is the ideal solution for such extreme cases. This problem is addressed by the present method, with a completely new, simple and easy to implement alternative approach that is tissue-sparing and focuses on increasing the optical zone while removing lower and higher order residual aberrations.

This method may be particularly useful for overcorrections, as topographers and aberrometers may not correctly reconstruct the optical systems for such cases due to the strong gradient between myopic and hyperopic areas. The only requirement for using this method is that only a single good postoperative topography, taken with any topographer, can be a sufficient starting point.

The presented method can serve as a ready-to-use alternative to wavefront-guided treatments with their inherent advantages and limitations.

Reference List

10

treatment device

12

laser

14

tissue

16

Eye

17

beam deflection device

18

control device

19

laser beam

22

segments

23

first segment

24

second segment

25

third segment

28

Focus

30

cornea

Claims (15)

Method for providing control data of an ophthalmic surgical laser (12) of a treatment device (10) for a cornea correction depending on an externally determined correction value, the method having the following steps carried out by a control device (18): - Receiving (S1) a raw image a cornea (30) from a sensor device, - subdividing (S2) the raw image of the cornea into a plurality of segments (22), - determining (S3) an actual parameter set, the actual parameter set having at least one actual parameter for each of the plurality segments (22), based on the raw image of the cornea (30), - determining (S4) a target parameter set, the target parameter set containing at least one target parameter for each of the multiple segments (22) after the cornea correction, wherein - For a primary (23) of the plurality of segments (22), the at least one target parameter depending on the at least one actual parameter of the primary segment (23) and the correction value is determined and for at least one secondary (24, 25) of the plurality of segments (22) the at least one target parameter is determined as a function of the at least one target parameter of the primary segment (23), and - Providing (S5) control data for controlling the ophthalmic surgical laser (12) depending on a difference between the actual parameter set and the target parameter set. procedure after claim 1 , characterized in that a curvature, preferably in the radial direction, is determined for the corresponding segment (22) as the actual parameter and as the target parameter. procedure after claim 1 or 2 , characterized in that exactly two respective values for a curvature of the cornea are determined as actual parameters of the actual parameter data set for each of the segments (22). procedure after claim 3 , characterized in that the exactly two respective values for the curvature, which are determined as actual parameters for a respective one of the segments (22), indicate a maximum curvature and a minimum curvature within the corresponding segment (22). Procedure according to one of claims 2 until 4 , characterized in that the curvature and/or the values for the curvature are each assigned an angle, in particular an azimuthal angle, as a further actual parameter. Procedure according to one of claims 2 until 5 , characterized in that a shape of the cornea (30) in the actual parameter set and/or the target parameter set is parameterized exclusively based on the curvature and/or the values for the curvature of the respective segments (22) and optionally based on the respectively assigned angles becomes. Method according to one of the preceding claims, characterized in that one of the several segments (22), in particular the primary segment (23), has the shape of a circle and the remaining segments (24, 25) each have the shape of a circular ring. Method according to one of the preceding claims, characterized in that the at least one target parameter of the at least one secondary segment (24, 25) is also determined as a function of a smoothing parameter, the smoothing parameter being a value for the difference in curvature of the primary segment (23) and the at least one secondary segment (24, 25). Method according to one of the preceding claims, characterized in that the at least one target parameter of at least one tertiary of the plurality of segments (25) is determined as a function of the at least one target parameter of the secondary segment (24) and optionally the smoothing parameter. Control device (18) which is designed to carry out a method according to one of the preceding claims. Treatment device (10) with at least one eye surgery laser (12) for performing a corneal correction on a cornea (30) with a control device (18). claim 10 . treatment device claim 11 , characterized in that the laser (12) is designed to emit laser pulses in a wavelength range between 300 nm and 1400 nm, preferably between 700 nm and 1200 nm, with a respective pulse duration between 1 fs and 1 ns, preferably between 10 fs and 10 ps, and a repetition frequency greater than 10 KHz, preferably between 100 KHz and 100 MHz. Treatment device (10) after claim 11 or 12 , characterized in that the control device - has at least one storage device for the at least temporary storage of at least one control data record, the control data record(s) comprising control data for positioning and/or focusing individual laser pulses in the cornea (30); and - at least one beam device (22) for beam guidance and/or beam shaping and/or beam deflection and/or beam focusing of a laser beam (24) of the laser. Computer program comprising instructions that cause the treatment device (10) according to any one of Claims 11 until 13 a method according to one of Claims 1 until 9 executes Computer-readable medium on which the computer program Claim 14 is saved.

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