METHOD FOR PROVIDING CONTROL DATA FOR A LASER OF A TREATMENT APPARATUS

Abstract

The invention relates to a method for providing control data for a laser (18) of a treatment apparatus (10) for the correction of a cornea (26), including ascertaining (S10) an effect of a deformation of the cornea (26) on preset corneal parameters by means of a corneal deformation model, wherein the cornea (26) can be modeled in a deformed and non-deformed state by the corneal deformation model, wherein values of preset corneal parameters in the non-deformed state of the cornea (26) are varied and the effect of this variation on values of the corneal parameters in the deformed state of the cornea (26) is ascertained for determining the effect of the deformation; determining (S12) the most important corneal parameters for a treatment and/or deformation of the cornea (26) depending on a magnitude of the ascertained effect; adapting (S14) at least one preset fit function as the compensation function of the deformation to the values of the most important corneal parameters; calculating (S16) a deformation-corrected treatment value by means of the compensation function; and providing (S18) the deformation-corrected treatment value for the treatment apparatus (10).

Claims

1. A method for providing control data for a laser of a treatment apparatus for the correction of a cornea of a human or animal eye, wherein the method comprises the following steps performed by at least one control device: ascertaining an effect of a deformation of the cornea on preset corneal parameters by means of a corneal deformation model, wherein the cornea can be modeled in a deformed state and a non-deformed state by the corneal deformation model, wherein values of multiple preset corneal parameters in the non-deformed state of the cornea are varied and the effect of this variation on values of the corneal parameters in the deformed state of the cornea is ascertained for determining the effect of the deformation; determining the most important corneal parameters for a treatment and/or deformation of the cornea depending on a magnitude of the ascertained effect; adapting one or multiple respectively preset fit functions to the values of the most important corneal parameters, wherein the one adapted fit function provides a compensation function for compensating for the deformation or the multiple adapted fit functions are composed to the compensation function; calculating a deformation-corrected treatment value by means of the compensation function and preoperative values of the most important corneal parameters; and providing the deformation-corrected treatment value as control data for the treatment apparatus.

2. The method according to claim 1, wherein the corneal deformation model is based on the Euler-Bernoulli beam theory.

3. The method according to claim 1, wherein the values of the preset corneal parameters are varied within respectively preset ranges of values for determining the effect of the deformation, wherein the ranges of values comprise respective default values of the respective corneal parameter.

4. The method according to claim 1, wherein the preset fit function is a polynomial function, in particular a second order polynomial.

5. The method according to claim 1, wherein the adapted fit functions of the most important corneal parameters are multiplied by or summed with each other for the compensation function.

6. The method according to claim 1, wherein a planned refractive power correction and/or a planned lenticule diameter are adapted by the compensation function.

7. The method according to claim 1, wherein a deformation of the cornea, which is generated by a contact element, is compensated for by means of the compensation function, and/or wherein a deformation of the cornea, which is generated upon closing the cornea after removal of a lenticule from the cornea, is compensated for by means of the compensation function.

8. A control device that is formed to perform a method according to claim 1.

9. A treatment apparatus with at least one eye surgical laser for the separation of a lenticule with predefined interfaces from a human or animal eye by cavitation bubbles and with at least one control device according to claim 8.

10. The treatment apparatus according to claim 9, wherein the at least one eye surgical laser is suitable to emit laser pulses in a wavelength range between 300 nm and 1400 nm, at a respective pulse duration between 1 fs and 1 ns, and a repetition frequency of greater than 10 kHz.

11. The treatment apparatus according to claim 9, wherein the control device comprises at least one storage device for at least temporary storage of at least one control dataset, wherein the control dataset or datasets include(s) control data for positioning and/or for focusing individual laser pulses in the cornea; and includes 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.

12. A computer program including commands that cause the control device according to claim 8 to execute the method.

13. A non-transitory computer-readable medium, on which the computer program according to claim 12 is stored.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Further features of the invention are apparent from the claims, the figures and the description of figures. The features and feature combinations mentioned above in the description as well as the features and feature combinations mentioned below in the description of figures and/or shown in the figures alone are usable not only in the respectively specified combination, but also in other combinations without departing from the scope of the invention. Thus, implementations are also to be considered as encompassed and disclosed by the invention, which are not explicitly shown in the figures and explained, but arise from and can be generated by separated feature combinations from the explained implementations. Implementations and feature combinations are also to be considered as disclosed, which thus do not comprise all of the features of an originally formulated independent claim. Moreover, implementations and feature combinations are to be considered as disclosed, in particular by the implementations set out above, which extend beyond or deviate from the feature combinations set out in the relations of the claims.

[0035] FIG. 1 depicts a schematic representation of a treatment apparatus according to an exemplary embodiment.

[0036] FIG. 2 depicts a schematic method diagram for providing control data according to an exemplary embodiment.

[0037] FIG. 3a depicts a schematically illustrated cornea of the corneal deformation model in the non-deformed state.

[0038] FIG. 3b depicts the cornea of the corneal deformation model deformed by a contact element.

[0039] FIG. 4a depicts a schematically illustrated cornea of the corneal deformation model in the non-deformed state before removal of a lenticule.

[0040] FIG. 4b depicts the deformed cornea of the corneal deformation model after closing the lenticule.

[0041] FIG. 5a depicts an exemplary representation of a first varied corneal parameter.

[0042] FIG. 5b depicts an exemplary representation of a second varied corneal parameter.

[0043] In the figures, identical or functionally identical elements are provided with the same reference characters.

DETAILED DESCRIPTION

[0044] FIG. 1 shows a schematic representation of a treatment apparatus 10 with an eye surgical laser 18 for the separation of a lenticule 12 defined by control data from a cornea 26 by means of photodisruption and/or ablation, wherein the cornea 26 is bounded by an anterior corneal surface 30 and a posterior corneal surface 32 in the direction of an optical axis. For separating the lenticule 12, a posterior interface 14 and an anterior interface 16 of the lenticule 12 are preset in the control data, on which a cavitation bubble path for separating the lenticule 12 from the cornea 26 can be generated. One recognizes that a control device 20 for the laser 18 can be formed besides the laser 18 such that it can emit pulsed laser pulses for example in a predefined pattern for generating the interfaces 14, 16. Alternatively, the control device 20 can be a control device 20 external with respect to the treatment apparatus 10.

[0045] Furthermore, FIG. 1 shows that the laser beam 24 generated by the laser 18 is deflected towards the cornea 26 by means of a beam device 22, namely a beam deflecting device such as for example a rotation scanner. The beam deflecting device 22 is also controlled by the control device 20 to generate the interfaces 14, 16, preferably also incisions or cuts, along preset incision courses.

[0046] The illustrated laser 18 can preferably be a photodisruptive and/or ablative laser, which is formed to emit laser pulses in a wavelength range between 300 nm and 1400 nm, preferably between 700 nm and 1200 nm, at a respective pulse duration between 1 fs and 1 ns, preferably between 10 fs and 10 ps, and a repetition frequency of greater than 10 kHz, preferably between 100 kHz and 100 MHz. Optionally, the control device 20 additionally comprises a storage device (not illustrated) for at least temporary storage of at least one control dataset, wherein the control dataset or datasets include(s) control data for positioning and/or for focusing individual laser pulses in the cornea. The position data and/or focusing data of the individual laser pulses, that is the lenticule geometry of the lenticule 12 to be separated, are generated based on predetermined control data, in particular from a previously measured topography and/or pachymetry and/or the morphology of the cornea or of the optical visual disorder correction to be generated.

[0047] For determining the visual disorder data, which can for example indicate a value in diopters, suitable examination data for describing the visual disorder can be received by the control device 20 from a data server or the examination data can be directly input into the control device 20.

[0048] Further, a contact element 28 can be provided, which can belong to the treatment apparatus 10. Alternatively, the contact element 28 can also be provided separately from the treatment apparatus 10. The contact element 28, which can also be referred to as patient interface or fixing system, serves to fix the eye or the cornea 26 for the treatment. Hereto, the contact element 28 can comprise a plano-concave lens, which is adapted to the cornea 26 for fixing. By fixing by means of the contact element 28, however, it can occur that the cornea 26 deforms and thus the geometry of the lenticule 12 does no longer have the originally planned dimensions. Therefore, it can occur that a planned refractive power value or refractive power value to be corrected for example deviates from an achieved refractive power value after the treatment with the treatment apparatus 10.

[0049] In FIG. 2, a schematic method diagram for providing control data for the laser 18 of the treatment apparatus 10 is illustrated, which can for example be performed by the control device 20. In a step S10, an effect of a deformation of the cornea on preset corneal parameters can first be determined by means of a corneal deformation model, wherein the corneal deformation model can describe the cornea 26 as a volume body, and which is preferably based on the Euler-Bernoulli beam theory. Thus, the cornea 26 can be modeled in a deformed and non-deformed state, wherein a value of at least one corneal parameter in the non-deformed state of the cornea is varied and an effect of this variation on values of the further corneal parameters in the deformed state is ascertained for determining the effect of the deformation.

[0050] For illustrating the corneal deformation model, the deformation of the volume body of the cornea 26 is shown for the deformation by the contact element 28 in FIGS. 3a and 3b and is shown for the deformation, which occurs in closing the cornea 26 after removing the lenticule 12 in FIGS. 4a and 4b.

[0051] Herein, FIG. 3a for example shows the volume body of the cornea 26 in a free state before the deformation by the contact element 28, which is not illustrated in this figure. Therein, the volume body can be bounded by the anterior corneal surface 30 and the posterior corneal surface 32 in the direction of the optical axis and by lateral interfaces 38 in radial direction (lateral). Herein, the anterior corneal surface 30 and the posterior corneal surface 32 can be provided as ellipsoids, wherein a two-dimensional cross-section through the volume body is shown in this figure for illustration and the volume body can be present in a three-dimensional shape, in particular rotationally symmetrical. Besides the anterior and posterior corneal surfaces 30, 32, central corneal surfaces 34, 36 of the volume body are also illustrated, wherein a central corneal surface can be provided within the volume body for each position in z-direction (direction of the optical axis), which is not shown here for reasons of clarity. One of the central corneal surfaces, for example the central corneal surface 36, can be a neutral corneal surface or neutral membrane, which has the same surface before and after the deformation according to the Euler-Bernoulli beam theory, which is taken into account in modeling the cornea 26 based on the corneal deformation model. Preferably, a respectively central corneal surface 34 can be described in relation to this neutral corneal surface in the corneal deformation model.

[0052] Thus, a radius of curvature of a respectively central corneal surface 34 can preferably be described by means of the corneal deformation model according to the formula

[00001]$\frac{1}{r_{\mathrm{cent},\mathrm{pre}}}=\left(\frac{q}{r_{\mathrm{ca}}}+\frac{1-q}{r_{\mathrm{cp}}}\right)$

[0053] wherein it provides the radius of curvature of the central corneal surface 34 before the deformation (r.sub.cent,pre). Therein, r.sub.ca describes the radius of curvature of the anterior corneal surface 30 and rip describes the radius of curvature of the posterior corneal surface 32. The variable q describes a relative position of the central corneal surface 34 to the neutral corneal surface 36, wherein q can take a value between 0 and 1.

[0054] In similar manner, a position in z-direction, which is dependent on the radial position, can also be described to the radius of curvature, wherein the z-direction extends in the direction of the optical axis. It can be described for the respective central corneal surface 34 with the formula

[00002]${𝓏}_{\mathrm{cent},\mathrm{pre}}\left(r_x\right)=\left(q-1\right)d_{\mathrm{cc}}-\frac{r_x^2}{2}\left(\frac{q}{r_{\mathrm{ca}}}+\frac{1-q}{r_{\mathrm{cp}}}\right)$

[0055] wherein r.sub.X describes a radial position starting from the center of the cornea 26 and dcc describes a central thickness of the cornea 26 at the highest point or inflection point of the cornea 26.

[0056] Upon the deformation of the cornea 26 by the contact element 28, it can be provided in the corneal deformation model that the radius of curvature of the anterior corneal surface 30 is adapted to a radius of curvature of the contact element 28. This situation is for example illustrated in FIG. 3b, wherein the contact element 28 is not shown here for reasons of clarity. It is seen that the anterior corneal surface 30 is impressed and thus also the central corneal surfaces 34 and 36. However, according to the Euler-Bernoulli beam theory, it further remains considered that the neutral corneal surface 36 has the same surface as before the deformation. In this deformation, it is assumed that the volume body can freely deform and is not bounded towards the sides.

[0057] In FIG. 4a, the cornea 26 is illustrated in a non-deformed state before the removal of the lenticule 12. Here too, the cornea 26 can be modeled as a volume body, which is formed of respective central corneal surfaces 34, 36, wherein the anterior interface 16 of the lenticule is pressed onto the posterior interface 14 of the lenticule 12 for determination of the deformed cornea in the corneal deformation model, whereby they change the curvatures of the corneal surfaces 30, 34 situated above. Therein, the corneal deformation model is based on the same principles and formulas as already described to the FIGS. 3a and 3b.

[0058] In the deformation of the cornea 26 by closing the area of the lenticule 12, it can be provided in the corneal deformation model that the radius of curvature of the anterior interface 16 is adapted to a radius of curvature of the anterior interface 14 such that the cornea 26 according to FIG. 4b results. Herein, the anterior interface 16 can move downwards to the posterior interface 14, wherein the corneal surfaces situated above the anterior interface are thus also adapted, in particular the neutral corneal surface 34 and the anterior corneal surface 30.

[0059] In FIGS. 5a and 5b, exemplary variations of corneal parameters and the effect of them on further corneal parameters in the deformed state of the cornea are illustrated as they can be performed in the method step S10. Therein, effects on the corneal parameters, which can be induced by a deformation of the cornea 26 by the contact element 28, are shown in both figures FIGS. 5a and 5b.

[0060] On the x-axis of FIG. 5a, the corneal parameter r.sub.ca is represented, which represents a radius of curvature of the anterior corneal surface 30. This corneal parameter r.sub.ca is varied within a preset range of values, which preferably comprises default values of the corneal parameter from a patient collective, and the effect of this variation on further corneal parameters, which are represented on the y-axis of FIG. 5a, is ascertained. In this example, the further corneal parameters are a refractive power, in particular a ratio of a planned refractive power correction D.sub.plan and the refractive power correction D.sub.post ascertained by the corneal deformation model, a ratio of the planned radius of the anterior interface 16 ascertained by the corneal deformation model (R.sub.cap) and a ratio of the planned lenticule diameter ascertained by the corneal deformation model (including the transition zone TZ). Besides these exemplarily shown corneal parameters, effects on further corneal parameters can also be ascertained in the corneal deformation model, such as for example an optical distance between the anterior corneal surface and a posterior corneal surface, a thickness of the cornea, a radial distance from a limbus to a center of the cornea, an optical distance between the anterior corneal surface and an anterior interface of a lenticule to be separated, a thickness of the lenticule, a radius of curvature of the contact element, a relative thickness of the cornea and/or an incision angle of an incision cut.

[0061] For determining the graphic shown in FIG. 5a, it can for example be proceeded as follows by means of the corneal deformation model: As a first preset corneal parameter, the radius of curvature of the anterior corneal surface r.sub.ca can be selected, wherein it has to have a radius of curvature of 7 mm in the non-deformed state as a first value. By the corneal deformation model, the cornea, which has a radius of curvature of 7 mm, is deformed, wherein the effect, which the deformation of the cornea, which has a radius of curvature of 7 mm, has on the further corneal parameters, which are plotted on the y-axis, is ascertained. Subsequently, the corneal parameter r.sub.ca can be varied, which means that a radius of curvature of 7.5 mm in the non-deformed state is next assumed and the cornea is deformed by means of the corneal deformation model in the same manner as previously described, and the effect on the further corneal parameters is ascertained. This variation can then be repeated until a sufficient number of values is ascertained. When the entire range of values of the radius of curvature of the anterior corneal surface r.sub.ca has been determined, thus, it can be comprehended with known radius of curvature of a real cornea how a planned refractive power correction D.sub.plan for example changes to D.sub.post by the deformation of the cornea.

[0062] In corresponding manner, further corneal parameters can also be varied except for the radius of curvature of the anterior corneal surface r.sub.ca 30, as for example illustrated in FIG. 5b. FIG. 5b is substantially identically configured as FIG. 5a, wherein an optical distance between the anterior corneal surface 30 and the anterior interface of the lenticule 12 to be separated, which is here denoted by k.sub.cap, is illustrated as the corneal parameter, which is varied, in FIG. 5b. This means that the corneal parameter k.sub.cap is varied in FIG. 5b and the effect of the deformation of the cornea on the further corneal parameters, which are the same as in FIG. 5a in this case, is stored for the respective value of k.sub.cap in the non-deformed state.

[0063] Returning to the method diagram of FIG. 2, after determining the effect of the deformation in step S10 (which are illustrated in FIGS. 5a and 5b), it can be determined in a step S12, which are the most important corneal parameters for a treatment and/or deformation of the cornea 26 in that those corneal parameters are determined, which have the greatest effect by the deformation. In this example, the deformation of the cornea can be a deformation by the contact element 28, and the treatment can be a refractive power correction of the cornea 26. From the effects of the deformation ascertained in step S10, for example from multiple tables or graphs, which can be similarly constructed as FIGS. 5a, 5b, wherein further corneal parameters not shown here are additionally varied, it can then be determined, which initially assumed corneal parameters cause the greatest effect on the refractive power correction by the deformation of the cornea 26. In this example, the corneal parameters r.sub.ca and k.sub.cap shown in FIGS. 5a and 5b can have the greatest effect of all of the corneal parameters on the refractive power correction D.sub.post/D.sub.plan, wherein more than two corneal parameters can also be determined. For reasons of clarity, the example is subsequently continued with two corneal parameters (r.sub.ca, k.sub.cap).

[0064] After determining the most important corneal parameters for the treatment and/or deformation, one or multiple respectively preset fit functions can be adapted to the values of the ascertained most important corneal parameters in a step S14, to determine a compensation function, which can be provided for compensating for the deformation, in particular the refractive power correction. As illustrated in FIGS. 5a and 5b, only a finite number of values is preferably ascertained, in this example five values or supporting points. The respective fit functions can then be adapted to these values, wherein a polynomial function, in particular a second order polynomial, can preferably be used as the fit function, to obtain the values of the entire parameter range of the respective corneal parameter. In other words, the first polynomial function can be fitted to the values of D.sub.post/D.sub.plan of FIG. 5a and a second polynomial function can be fitted to the corresponding values of FIG. 5b, wherein the respective polynomial function can be identical or different, or a single fit function can be adapted to both functions, in particular a mixed polynomial with two variables.

[0065] In this example, a first polynomial function can have been adapted to FIG. 5a and a second polynomial function can have been adapted to FIG. 5b for the refractive power correction D.sub.post/D.sub.plan, wherein the two polynomial functions can be composed to a compensation function. In particular, the respective polynomial functions/fit functions can be combined as a product or sum in the compensation function, wherein the type of the operation can depend on the respective corneal parameter.

[0066] This compensation function can then be provided to the treatment apparatus 10, in particular to the control device 20, for compensating for the deformation to perform a deformation-corrected refractive power correction.

[0067] Thus, a deformation-corrected treatment value can be calculated by means of the compensation function in a step S16, in that preoperative values of the most important corneal parameters are substituted into the compensation function and thus the deformation-corrected treatment value is generated. In this example, the deformation-corrected treatment value is the refractive power correction, which is to be ascertained by the compensation function. In order to correct the originally planned refractive power correction for the deformation to be expected, the preoperative values of the most important corneal parameters, which are r.sub.ca and k.sub.cap in this example, can be ascertained from predetermined examination data, wherein they can be substituted into the ascertained compensation function. Thus, both the influence of the corneal parameter r.sub.ca and k.sub.cap upon deformation of the cornea 26 on the refractive power correction can be compensated for by the compensation function, in particular at the same time, which provides an improved deformation correction since the most important corneal parameters are taken into account in the compensation function. In corresponding manner, a compensation function with the most important corneal parameters can also be ascertained for the further corneal parameters R.sub.cap, TZ and further corneal parameters, wherein the deformation can then be compensated for also for these corneal parameters in corresponding manner.

[0068] Finally, the thus obtained deformation-corrected treatment values can be provided as control data for the treatment apparatus 10, in particular the control device 12, in a step S18.

[0069] Overall, the examples show how a simple and fast compensation for deformation effects can be achieved by means of the compensation function.