Method for providing control data for an ophthalmic laser treatment device, method for controlling a treatment device, control device, treatment device computer program, and computer-readable medium

Abstract

The invention relates to a method for providing control data for a laser of a treatment device, wherein the method comprises the following steps performed by a control unit (18): determining a first interim cornea geometry of the cornea (30) based on a predetermined refractive power change ΔD0 according to a predetermined geometry determination method; determining a first effective refractive power change ΔD 1,eff = D1 - D0 between a first interim refractive power D1 of the cornea of ​​the first interim cornea geometry and the actual refractive power D0 of the cornea of ​​the actual cornea geometry; determining a first compensated refractive power change ΔD1 from the given refractive power change ΔD0 and the first effective refractive power change ΔD 1,eff; Determining a second interim cornea geometry (30) based on the first compensated refractive power change ΔD1 according to the specified geometry determination procedure; Determining a tissue ablation of tissue of the cornea (30) according to the last of the interim cornea geometries; and generating control data to control the laser (12) to perform the tissue ablation.

Description

[0001] The invention relates to a method for providing control data for an ophthalmic laser of a treatment device according to the features of the preamble of claim 1. Furthermore, the invention relates to a method for controlling a treatment device according to the features of the preamble of claim 9, a control device according to the features of the preamble of claim 10, which is configured to carry out the respective method, a treatment device with such a control device according to the features of the preamble of claim 11, a computer program according to the features of the preamble of claim 12, comprising instructions that cause the treatment device to execute the method, and a computer-readable medium according to the features of the preamble of claim 13, on which the computer program is stored.

[0002] Treatment devices and methods for controlling ophthalmic lasers to correct refractive errors and / or pathologically or abnormally altered areas of the cornea are known in the prior art. For example, pulsed lasers and a beam focusing device can be configured such that laser pulses cause photodisruption and / or ablation in a focus located within the organic tissue in order to remove tissue, in particular a tissue lenticel, from the cornea.

[0003] To correct refractive errors in an eye, ophthalmic laser treatment procedures commonly involve altering the refractive power (D) of the cornea. This is achieved by removing corneal tissue using laser pulses to change the curvature of the cornea's anterior surface. The underlying principle is to change the existing curvature of the cornea's anterior surface to a desired curvature, thereby altering the refractive power (D). A the anterior surface of the cornea changes, thus compensating for the optical refractive error of the eye.

[0004] This simple approach alone, however, is insufficient to compensate for the eye's refractive error. The reason for this is that the total refractive power of the cornea is derived from the refractive power D A the anterior surface of the cornea, the refractive power D L the thickness of the cornea as well as the refractive power D Pthe posterior surface of the cornea is composed of: D=DA+DL+DP

[0005] The tissue removal required to change the curvature of the anterior surface also leads to a change in refractive power D. A Changes in the refractive power of the cornea can occur from the anterior surface. These additional components may include changes in refractive power caused by variations in corneal thickness between the anterior and posterior surfaces. To account for these changes in refractive power, current best practices involve simple corrections to the amount of tissue removed and / or adjusting the value of the refractive power change.

[0006] These adjustments are not tailored to the individual laser treatment, but are based on statistics which offer sufficient accuracy, but have room for improvement.

[0007] The invention is based on the objective of providing a method that enables a more precise change in the refractive power of a cornea.

[0008] This problem is solved by the inventive method for providing control data according to the features of claim 1, the inventive method for controlling a treatment device according to the features of claim 9, the inventive control device according to the features of claim 10, the inventive treatment device control device according to the features of claim 11, the inventive computer program according to the features of claim 12, and the inventive computer-readable medium according to the features of claim 13. Advantageous embodiments with expedient further developments of the invention are specified in the respective dependent claims, wherein advantageous embodiments of the method are to be regarded as advantageous embodiments of the treatment device, the control device, the computer program, and the computer-readable medium, and vice versa.

[0009] A first aspect of the invention relates to a method for providing control data for an ophthalmic laser of a treatment device, wherein the method comprises the following steps, which are carried out by means of a control device. A control device is understood to be a device or device component, in particular a computer or processor, which can perform the following steps automatically or semi-automatically.

[0010] The procedure involves receiving a predetermined change in refractive power ΔD0 relating to a change in the actual refractive power D0 of a cornea, which has an actual cornea geometry, to a target refractive power D. F = D0 + ΔD0 of the cornea.

[0011] In other words, the control unit receives the specified change in refractive power ΔD0, by which the actual refractive power D0 of the cornea changes to the target refractive power D. F the cornea, which consists of D FThe result is that the refractive power D0 + ΔD0 must be changed. The cornea with the current refractive power D0 can also be called the preoperative cornea, and the cornea after the change in refractive power can also be called the postoperative cornea.

[0012] The specified change in refractive power ΔD0 can, for example, be intended to correct a refractive error. The actual refractive power D0 of the cornea is known and results from the actual refractive power D A0 the anterior surface of the cornea, the actual refractive power D L0 the thickness of the cornea and the actual refractive power D 0P the posterior surface of the cornea: D0=DA0+DL0+DP0

[0013] The actual corner geometry can be determined by an actual radius of curvature R. A0 the anterior surface of the cornea, a central actual thickness d0 of the cornea, and an actual radius of curvature R P0the posterior surface of the cornea. The parameters in question can be determined and are therefore known. The corneal geometry can also be described by a first actual curvature of the anterior surface of the cornea K. 1A0 , a second actual curvature of the anterior surface of the cornea oriented perpendicular to the first actual curvature of the anterior surface of the cornea K 2A0 , an actual apex A A0 the anterior surface of the cornea, the central actual thickness d0 of the cornea, a first actual curvature of the posterior surface of the cornea K 1P0, a second actual curvature of the posterior surface of the cornea K, oriented perpendicular to the first actual curvature of the posterior surface of the cornea 2P0 , and an actual apex A P0 The posterior surface of the cornea must be known. The actual refractive power D0 of the cornea can be derived from the actual corneal geometry using known methods according to the state of the art.

[0014] The procedure involves determining a first interim cornea geometry based on the specified refractive power change ΔD0 according to a predefined geometry determination method. This first interim cornea geometry is a virtual, preliminary geometry. The first interim cornea geometry can be defined by a first interim radius of curvature R. A1 the anterior surface of the cornea, a first interim thickness d1 of the cornea, and a first interim curvature R P1 the posterior surface of the cornea. The first interim corneal geometry can also be described by a first interim X-curve of the anterior surface of the cornea K. 1A1 , a first interim Y-curve of the anterior surface of the cornea oriented perpendicular to the first interim X-curve of the anterior surface of the cornea K 2A1 , a first interim apex A A1of the anterior surface of the cornea, a central first interim thickness d1 of the cornea, a first interim X-curve of the posterior surface of the cornea K 1P1 , a first interim Y curvature of the posterior surface of the cornea oriented perpendicular to the first interim X-curvature of the cornea K 2P1 , and a first interim apex A P1 the posterior surface of the cornea.

[0015] The specified geometry determination method can be based on simplified assumptions. As a result, the cornea of ​​the first interim cornea geometry can have a first interim refractive force D1, which differs from the target refractive force D. Fthe cornea can be distinguished. This can facilitate a simpler geometry determination. The idea of ​​this approach is to compensate for this difference by providing an initial compensated refractive power change ΔD1, which may differ from the given refractive power change ΔD0. The first interim cornea geometry thus serves only to derive the first compensated refractive power change ΔD1.

[0016] The first interim refractive force D1 is determined for the cornea described by the first interim cornea geometry.

[0017] In a further step, an effective change in refractive power ΔD is determined. 1,eff = D1 - D0 between the first interim refractive power D1 of the cornea and the actual refractive power D0 of the cornea. The first effective change in refractive power ΔD 1,effThis can also be described as a virtual change in refractive power. It describes how the refractive power of the cornea would change when the actual corneal geometry is changed to the first interim corneal geometry. The first effective change in refractive power ΔD 1,eff is compared with the given refractive power change ΔD0 in order to determine the first compensated refractive power change ΔD1 according to a given formula.

[0018] The first interim cornea geometry can be determined using a simple method, which should at least approximately produce the specified change in refractive power ΔD0. Advantageously, the method can be based on simple geometric and optical assumptions, such that by changing the actual cornea geometry to the interim cornea geometry, instead of the target change in refractive power ΔD, the first effective change in refractive power ΔD is achieved. 1,effThe change in refractive power ΔD0 is caused by the change in refractive power D1 - D0, which may deviate from the target change ΔD0. To account for this deviation, it is planned to determine the first compensated change in refractive power ΔD1 based on the first effective change in refractive power D1 - D0.

[0019] The first compensated refractive power change ΔD1 is an adapted value of the given refractive power change ΔD0, wherein the first compensated refractive power change ΔD1 is parameterized such that when the first compensated refractive power change ΔD0 is used in the given geometry determination procedure, a second interim corneal geometry results, which yields a second effective refractive power change ΔD 2,eff exhibits this second effective refractive power change ΔD 2,eff exhibits a smaller deviation from the specified refractive power change ΔD0 than the first effective refractive power change ΔD 1,effIn other words, the specified geometry determination procedure is applied again, but instead of the specified refractive power change ΔD0, the first compensated refractive power change ΔD1 is used as input.

[0020] Based on the last of the interim corneal geometries, a final corneal geometry is determined. The final corneal geometry may be identical to the last interim corneal geometry. Alternatively, the final corneal geometry may be based on the last interim corneal geometry and differ only by adjustments due to the laser procedure. In a subsequent step, the amount of tissue to be removed is determined, which is necessary to change the current corneal geometry to the final corneal geometry.

[0021] A further step involves generating control data to control the laser to perform tissue ablation of the cornea.

[0022] The control data can include a data set for positioning and / or focusing individual laser pulses in the cornea. Additionally or alternatively, the control data can include a data set for adjusting at least one beam device for beam guidance and / or beam shaping and / or beam deflection and / or beam focusing of a laser beam from the respective laser.

[0023] The invention offers the advantage of enabling more precise compensation for changes in refractive power caused by tissue abrasion than is possible with statistically based approaches. At the same time, this approach requires less computational effort than wavefront-based methods.

[0024] The invention also includes further developments that result in additional advantages.

[0025] A further development of the invention provides that the first compensated refractive power change ΔD1 is determined from the refractive power change ΔD0 to be set and the first effective refractive power change ΔD1 according to the formula: ΔD1=ΔD02 / ΔD1,eff This is done. In other words, the plan is to square the given change in refractive power ΔD0 and divide it by the first effective refractive power ΔD. 1,eff to divide in order to determine the first compensated refractive power change ΔD1, which is used instead of the given refractive power change ΔD0.

[0026] A further development of the invention provides that the compensated first refractive power change ΔD1 is determined from the predetermined refractive power change ΔD0 and the first effective refractive power change ΔD 1,eff according to the formula: ΔD1=2ΔD0−ΔD1,eff This is done. In other words, the plan is to multiply the given refractive power change ΔD0 by a factor of two and obtain the first effective refractive power ΔD. 1,eff to subtract in order to determine the first compensated refractive power change ΔD1, which is used instead of the given refractive power change ΔD0.

[0027] A further development of the invention provides that the method includes determining a second effective change in refractive power ΔD. 2,eff = D2 - D0 between a second interim refractive power D2 of the cornea of ​​the second interim cornea geometry and the actual refractive power D0 of the cornea of ​​the actual cornea geometry. In other words, a further step takes place in which the second interim refractive power D2 of the second interim cornea geometry, as well as the second effective change in refractive power ΔD 2,eff= D2 - D0 is determined. In a subsequent step, a second compensated refractive power change ΔD2 is calculated from the given refractive power change ΔD0, the first compensated refractive power change ΔD1, and the second effective refractive power change ΔD 2,eff The third interim corneal geometry is determined. In a further step, a third interim corneal geometry is determined based on the second compensated refractive power change ΔD2 according to the specified geometry determination procedure. In other words, the third interim corneal geometry is determined. This third interim corneal geometry represents the last of the interim corneal geometries and serves as the basis for the final corneal geometry. This refinement has the advantage that the refractive power of the final corneal geometry is even closer to the target refractive power.

[0028] A further development of the invention provides that the determination of the second compensated refractive power change ΔD2 from the refractive power change to be set ΔD0, the first compensated refractive power change ΔD1 and the second effective refractive power change (D2 - D0) according to the formula: ΔD2=ΔD0∗ΔD1 / (D2−D0) This is done. In other words, the plan is to multiply the given refractive power change ΔD0 by the first compensated refractive power change ΔD1 and divide by the second effective refractive power ΔD 2,eff to divide in order to determine the second compensated refractive power change ΔD2, which is used instead of the given refractive power change ΔD0.

[0029] A further development of the invention provides that the determination of the second compensated refractive power change ΔD2 from the refractive power change to be set ΔD0, the first compensated refractive power change ΔD1 and the second effective refractive power change (D2 - D0) according to the formula: ΔD2=ΔD0+ΔD1−(D2−D0) This is done. In other words, it is intended to add the first compensated refractive power change ΔD1 to the given refractive power change ΔD0 and the second effective refractive power ΔD 2,eff to subtract in order to determine the second compensated refractive power change ΔD2, which is used instead of the given refractive power change ΔD0.

[0030] A further development of the invention provides that determining the first interim cornea geometry according to the specified geometry determination method involves determining a first interim radius of curvature R. A1 the anterior surface of the cornea as a function of an actual radius of curvature R A0 the anterior surface of the cornea and the predetermined refractive power change ΔD0 to achieve a first refractive power change ΔD 1A, the anterior surface to effect the specified refractive power change ΔD0. In other words, it is intended to effect the specified refractive power change ΔD0 according to the specified geometry determination method by changing the refractive power of the anterior surface of the cornea. It is thus intended to effect the specified refractive power change ΔD0 by first changing the refractive power ΔD 1A The refractive power change ΔD0 is set to the anterior surface of the cornea. Other contributions to the corneal refractive power are therefore disregarded. These may include, in particular, the refractive power components influenced by the posterior surface and corneal thickness. The influence of these components is accounted for by determining the compensated first refractive power change ΔD1.

[0031] In a further step, it is planned that determining the second interim cornea geometry according to the specified geometry determination procedure will involve determining a second interim radius of curvature R. A2 the anterior surface of the cornea as a function of the actual radius of curvature R A0 the anterior surface of the cornea and the first compensated refractive power change ΔD1 includes the second refractive power change ΔD 2A , to cause the first compensated refractive power change ΔD1 on the anterior surface. The advantage of this approach is that the change in refractive power is focused solely on the dominant component.

[0032] A further development of the invention provides that determining the first effective change in the refractive power of the cornea involves determining an effective actual refractive power D. A0,eff the anterior surface of the cornea for an ocular interior from the actual refractive power D A0the anterior surface of the cornea. In other words, the actual refractive power D is used to calculate the refractive power. A0 the effective actual refractive power D of the anterior surface of the cornea A0,eff The refractive power of the anterior surface of the cornea is calculated, which describes the refractive power in a medium within the eye's interior. The medium within the eye can primarily be water, so the refractive index of water can be used. DA0,eff=nWaterfA0,eff

[0033] An effective actual focal length f A0,eff the anterior surface of the cornea results from an actual focal length f A0 the anterior surface of the preoperative cornea: fA0,eff=fA0=nWaterDA0

[0034] A further step involves determining a relative shift F of the cornea's principal optical planes between the current cornea geometry and the first interim cornea geometry. Changing the cornea geometry alters the position of the cornea's principal optical planes, thereby changing the effective focal length of the anterior cornea surface in the first interim cornea geometry compared to the effective focal length of the anterior cornea surface in the current cornea geometry. This change in the cornea's principal optical planes is accounted for by the factor F.

[0035] In one step, an effective first interim refractive power D is determined. A1,eff the anterior surface of the cornea for the ocular interior from the first interim refractive power D A1the anterior surface of the cornea and the relative displacement F of the cornea's principal optical planes. In other words, the effective first interim refractive power D is determined. A1,eff the anterior surface of the cornea. This is determined according to the formula given below. DA1,eff=nWasserfA1,eff

[0036] The effective first interim focal length of the anterior surface of the cornea is determined by the following formula, which takes into account the relative displacement F of the optical principal planes of the cornea as well as the central thickness of the cornea d. fA1,eff=fA1+dF

[0037] In a subsequent step, the first effective change in refractive power ΔD is determined. 1,eff The cornea is determined, which describes how the effective refractive power of the cornea changes. In this advanced training, it is assumed that the first effective refractive power change ΔD 1,effthe cornea through the first effective change in refractive power ΔD A1,eff is described for the anterior surface of the cornea. In other words, the first effective refractive power change ΔD is described. 1,eff the cornea through the first effective change in refractive power ΔD A1,eff equated to the anterior surface of the cornea. This approximation is possible because the first effective refractive power D A1,eff the anterior surface a dominant proportion of the first effective refractive power D1, eff which makes up the cornea.

[0038] A further development of the invention provides that determining the effective change in refractive power of the cornea comprises the following steps.

[0039] One of the steps involves determining the effective actual refractive power D. 0,eff The cornea's refractive power for the inner eye is derived from the cornea's actual refractive power D0. In other words, the effective refractive power D is calculated from the cornea's actual refractive power D0. 0,effThe refractive index of the cornea is calculated, which describes the actual refractive power of the cornea in a medium within the eye's interior. The medium within the eye can primarily be water, so the refractive index of water can be used. D0,eff=nWasserf0,eff

[0040] The effective actual focal length f 0,eff The preoperative cornea is determined from the actual focal length f0 of the preoperative cornea: f0,eff=f0=nWaterD0

[0041] A further step involves determining a relative shift F of the corneal principal optical planes between the preoperative and postoperative cornea. Due to the change in geometry, the position of the corneal principal optical planes changes, thereby altering the effective focal length of the postoperative cornea compared to the effective focal length of the preoperative cornea. This change in the corneal principal optical planes is accounted for by the factor F.

[0042] In one step, an initial effective interim refractive power D is determined. 1,eff The cornea's refractive power for the eye's interior is determined from the cornea's first interim refractive power D1 and the relative displacement F of the cornea's principal optical planes. In other words, the effective first interim refractive power D is determined. 1,eff the cornea exhibits. This is calculated according to the formula given below. D1,eff=nWasserf1,eff

[0043] The effective first interim focal length of the postoperative cornea is determined by the following formula, which takes into account the relative displacement F of the optical principal planes of the cornea as well as the central width of the cornea d. f1,eff=f1+dF

[0044] In a subsequent step, the first effective change in refractive power ΔD is determined. 1,effThe cornea is determined, which describes how the first effective refractive power changes due to the change in corneal geometry from the current corneal geometry to the first interim corneal geometry. In this further development, it is assumed that the first effective refractive power change ΔD 1,eff the cornea through the first effective change in refractive power ΔD 1,eff of the entire cornea. In other words, the first effective change in refractive power ΔD is described. 1,eff the cornea through the first effective change in refractive power ΔD 1,,eff The entire cornea is described. This training does not include an approximation of the first effective change in refractive power ΔD. 1,eff the cornea through the first effective change in refractive power ΔD A1,eff The anterior surface is not the only system considered; rather, the entire cornea system is taken into account.

[0045] A second aspect of the invention relates to a method for controlling a treatment device. This method comprises the steps of at least one embodiment of a method as previously described. Furthermore, the method for controlling the treatment device includes the step of transmitting the provided control data to at least one ophthalmic laser of the treatment device.

[0046] The respective procedure may include at least one additional step that is executed precisely when a use case or application situation occurs that is not explicitly described here. This step may, for example, include the output of an error message and / or a prompt for user feedback. Additionally or alternatively, it may be provided that a default setting and / or a predetermined initial state is set.

[0047] A third aspect of the invention relates to a control device configured to perform the steps of at least one embodiment of one or both of the methods described above. For this purpose, the control device may include a computing unit for electronic data processing, such as a processor. The computing unit may comprise at least one microcontroller and / or at least one microprocessor. The computing unit may be implemented as an integrated circuit and / or microchip. Furthermore, the control device may include an (electronic) data storage device or a storage unit. Program code, which encodes the steps of the respective embodiment of the respective method, may be stored on the data storage device. The program code may include the control data for the respective laser.The program code can be executed by the processing unit, which then causes the control unit to execute the respective configuration. The control unit can be designed as a control chip or control device. The control unit can, for example, be part of a computer or computer network.

[0048] A fourth aspect of the invention relates to a treatment device comprising at least one ophthalmic or surgical laser and a control unit configured to perform the steps of at least one embodiment of one or both of the methods described above. The respective laser may be configured to at least partially separate a predefined corneal volume with predefined interfaces of a human or animal eye by means of optical breakthrough, in particular to at least partially separate it by means of photodisruption, and / or to ablate corneal layers by means of (photo)ablation, and / or to cause a laser-induced change in the refractive index of the cornea and / or the lens of the eye.

[0049] A fifth aspect of the invention relates to a computer program. The computer program comprises instructions that, for example, constitute program code. The program code can include at least one control data set with the respective control data for the respective laser. When the program code is executed by a computer or a computer network, it is caused to execute the method described above, or at least one embodiment thereof.

[0050] A sixth aspect of the invention relates to a computer-readable medium (storage medium) on which the aforementioned computer program or its instructions are stored. To execute the computer program, a computer or a computer network can access the computer-readable medium and read its contents. The storage medium is, for example, configured as a data storage device, in particular at least partially as a volatile or non-volatile data storage device. A non-volatile data storage device can be flash memory and / or an SSD (solid-state drive) and / or a hard drive. A volatile data storage device can be RAM (random access memory). The instructions can be, for example, in the form of source code of a programming language and / or as assembly language and / or as binary code.

[0051] Further features and advantages of one of the described aspects of the invention may arise from further developments of another aspect of the invention. The features of the embodiments of the invention can therefore exist in any combination with one another, unless they have been explicitly described as mutually exclusive.

[0052] Additional features and advantages of the invention are described below with reference to the figures in the form of advantageous embodiments. The features or combinations of features of the embodiments described below can be present in any combination with one another and / or with the features of the embodiments. That is, the features of the embodiments can complement and / or replace the features of the embodiments, and vice versa. Thus, embodiments that are not explicitly shown or explained in the figures, but which can be derived and generated from separate combinations of features in the embodiments and / or embodiments, are also to be considered as encompassed and disclosed by the invention.Thus, embodiments that do not exhibit all the features of an originally formulated claim, or that go beyond or deviate from the combinations of features set forth in the cross-references of the claims, are also to be considered disclosed. For exemplary embodiments, see: Fig. 1 a schematic representation of a treatment device with an ophthalmic surgical laser for the treatment of the cornea of ​​an eye by means of photodisruption and / or, for example, ablation; Fig. 2 a schematic representation of a preoperative cornea; Fig. 3a a schematic representation of a preoperative cornea and a postoperative cornea according to an interim curvature; Fig. 3b a further schematic representation of a preoperative cornea and a postoperative cornea according to a target curvature; and Fig. 4 A schematic representation of a method for controlling a treatment device.

[0053] In the figures, identical or functionally equivalent elements are provided with the same reference symbols.

[0054] Fig. Figure 1 shows a schematic representation of a treatment device 10 with an ophthalmic surgical laser 12 for treating the cornea of ​​an eye 16 by photodisruption and / or, for example, ablation. For corneal treatment, treatment positions within the treatment area 14 are specified in the control data, where, for example, tissue to be cauterized or ablated is present. In addition to the laser 12, a control unit 18 for the laser 12 can be provided, enabling it to emit pulsed laser pulses, for example, in a predefined pattern. Alternatively, the control unit 18 can be an external control unit 18 with respect to the treatment device 10.

[0055] Furthermore, the Fig. 1. The laser beam 20 generated by the laser 12 is deflected towards the eye 16 by means of a beam deflection device 22, such as a rotary scanner. The beam deflection device 22 is also controlled by the control unit 18 to treat the eye 16.

[0056] The laser 12 shown is preferably a photodisruptive and / or ablative laser configured to emit laser pulses in a wavelength range between 300 nm and 1400 nm, preferably between 700 nm and 1200 nm, with a pulse duration between 1 fs and 1 ns, preferably between 10 fs and 10 ps, ​​and a repetition frequency greater than 10 kHz, preferably between 100 kHz and 100 MHz. The control unit 18 also includes a storage device for storing at least one control data set, wherein the control data set(s) comprise control data for positioning and / or focusing individual laser pulses in the area 14 to be treated. The storage device can be part of the control unit 18, or the storage device can be provided as external storage, in particular in the form of a computer network (cloud).The position data and / or focusing data of the individual laser pulses, especially for laser treatment, can be generated based on predetermined measurements, for example from a previously measured topography and / or pachymetry and / or the morphology of the cornea or the optical refractive error correction to be produced.

[0057] Fig. Figure 2 shows a schematic representation of a preoperative cornea.

[0058] Fig. Figure 2 shows a schematic representation of a preoperative cornea 30 to be treated. The preoperative cornea 30 may have an existing corneal geometry. The cornea 30 may have an anterior surface 32, by which the preoperative cornea 30 may be bounded to an extraocular space 34. The anterior surface 32 of the preoperative cornea 30 may have an existing curvature K A0 exhibiting which are defined by an actual radius of curvature R A0This can be described. On one side of the preoperative cornea 30 opposite the anterior surface 32, the cornea 32 may have a posterior surface 36, by which the preoperative cornea 30 may be bounded to an ocular interior 38. The posterior surface 36 of the preoperative cornea 30 may have an actual curvature K P0 exhibiting which are defined by an actual radius of curvature R P0 The posterior surface 36 of the preoperative cornea 30 can be described. The anterior surface 32 and the posterior surface 36 can have a distance from each other which can describe a central thickness d of a corneal volume 40 of the preoperative cornea 30. The preoperative cornea 30 can be optically described as a thick lens. Incident light rays 42 can be refracted by the preoperative cornea 30. An actual refractive power D0 of the preoperative cornea 30 can be derived from an actual refractive power D A0the anterior surface 32 of the preoperative cornea 30, a thickness-dependent actual refractive power D L0 the preoperative cornea 30 and an actual refractive power D P0 to the posterior surface of the preoperative cornea 30. D0=DA0+DL0+DP

[0059] The actual refractive power D A0 the anterior surface 32 of the preoperative cornea 30 can determine the actual refractive power D A0 describe which form the boundary between the outer eye space 34 of the refractive index of the air n Air and the corneal volume 40 of the refractive index of the cornea n Cornea has an effective anterior surface 32. DA0=nCornea−nAirRA0

[0060] The thickness-dependent actual refractive power D L0 can the actual refractive power D L0 describe which is caused by guiding the light rays 42 within the corneal volume 40 over the thickness d. DL0=dRA0RP0(nCornea−nAir)(nCornea−nAqua)nCornea

[0061] The actual refractive power D P0 the posterior surface 36 of the preoperative cornea 30 can increase the refractive power D P0 describe which form the interface between the corneal volume 40 and the refractive index of the cornea n Cornea and the interior of the eye 38 of the refractive index of water n Aqua has an effective posterior surface 36. DP0=nAqua−nCorneaRP0

[0062] The actual refractive power D A0 The anterior surface 32 can account for a major part of the refractive power D0 of the preoperative cornea 30. The optical properties of the preoperative cornea 30 can be determined by two principal optical planes H A0 , H P0 be described.

[0063] Fig. Figure 3a shows a schematic representation of a preoperative cornea and a postoperative cornea according to an interim curvature.

[0064] Fig. Figure 3a shows an intermediate step in determining the final postoperative cornea, as seen in Fig. Figure 3b shows that, to treat refractive error, it may be possible to change the actual refractive power D0 of the cornea 30 by a predetermined refractive power change ΔD0. To change the actual refractive power D0 of the cornea, it may be possible to adjust the curvature of the anterior surface 32 of the cornea 30 from the actual curvature of the actual radius of curvature R. A0 into a final radius of curvature R to be determined A2 to alter by removing tissue from the cornea 30. According to the state of the art, it is common to achieve the specified change in refractive power ΔD0 by changing the actual refractive power D. A0 to effect the anterior surface 32 of the cornea 30. The intended purpose is to determine the target radius of curvature R. A2 to determine at which the anterior surface 32 of the cornea 30 provides a refractive power D A2exhibits. The change in the radius of curvature R A1 The anterior surface 32 of the cornea 30 can be modified by removing tissue from the anterior surface 32 of the cornea 30. A predetermined tissue volume 44 is removed from the cornea 30. This changes the thickness d of the cornea by a thickness change value Δd from a central actual thickness d0 of the preoperative cornea 30 to a central target thickness d1 of a postoperative cornea 46.

[0065] However, due to the change in the thickness d of the cornea 30, the actual refractive power D can also change. L0 The corneal volume changes by 40. This is achieved by changing the actual refractive power D. L0 The corneal volume 40 thus undergoes an additional change in refractive power ΔD. A refractive power change ΔD acting on the anterior surface 32 L of the cornea 30. Due to this additional change in refractive power ΔD LA deviation from the refractive power change ΔD0 of the cornea 30 to be set may occur. According to the current state of the art, only simple modifications to the described procedure are made to compensate for this deviation. However, these compensations are relatively inaccurate and / or complex. One objective of this disclosure is to provide a method for determining the target radius of curvature R. A2 to provide the anterior surface 32. The described procedure follows an iterative approach.

[0066] A first step in the process involves determining an initial interim radius of curvature R. A1 the anterior surface 32. The first interim radius of curvature R A1 is determined from the given change in refractive power ΔD0: RA1=(nCornea−nAir)(nCornea−nAir)RA0+ΔD0

[0067] The relevant factor is the first effective change in refractive power ΔD. 1,effof the cornea 30. The first effective change in refractive power ΔD 1,eff The cornea can, for example, be affected by a first effective change in refractive power ΔD. A1,eff which is approximated to the anterior surface 32 of the cornea 30, or by the change in refractive power ΔD 1,eff the effective refractive power D 1,eff of an entire system of the cornea 32.

[0068] Fig. Figure 3b shows a further schematic representation of a preoperative cornea and a postoperative cornea according to a target curvature.

[0069] For the anterior surface 32 of the cornea 33, the first interim radius of curvature R can be A1 of the anterior surface 32 have been determined. In Fig. Figure 3a shows the cornea 30, which is responsible for the first interim radius of curvature R. A1 which would result in anterior surface 32. A subsequent step involves determining a final radius of curvature R. A2of the anterior surface 32, to avoid a deviation ΔD error of the effective refractive power change ΔD 1,eff to reduce the specified change in refractive power ΔD0.

[0070] The final radius of curvature R A2 can be like the interim radius of curvature R A1 to be determined. To determine the deviation ΔD error To reduce this, however, it may be possible to reduce the interim radius of curvature R. A1 to determine, based on a compensated change in refractive power ΔD1, which is the value for the interim radius of curvature R A1 determined deviation ΔD error taken into account. RA2=(nCornea−nAir)(nCornea−nAir)RA0+ΔD1

[0071] In the procedure, it may therefore be possible to use the first compensated refractive change ΔD1 instead of the refractive change ΔD0 to be provided, which is derived from the specified refractive change ΔD0 and the determined first effective refractive change ΔD 1,effThis can result in... ΔD1=ΔD2 / ΔD1,eff

[0072] Will the first effective change in refractive power ΔD 1,eff through the first effective change in refractive power ΔD A1,eff the anterior surface 32 of the cornea 30 approximates the following: ΔD1,eff=ΔDA,eff=DA1,eff−DA0,eff

[0073] The effective actual refractive power D A0,eff the anterior surface 32 of the preoperative cornea 30 results from: DA0,eff=nAquafA0,eff

[0074] The effective actual focal length f A0,eff the anterior surface 32 of the preoperative cornea 30 results from the actual focal length f A0 anterior surface 32 of the preoperative cornea 30: fA0,eff=fA0=nAquaDA0

[0075] An appreciation of a shift in the optical principal planes H A , H P the cornea 30 through the material removal of H A0 , H P0 to H A1, H P1 This is done by a factor F.

[0076] This results in the following for the first effective interim refractive power D A1,eff anterior surface 32 of the postoperative cornea 30: DA1,eff=nAquafA1,eff

[0077] The first effective interim focal length f A1,eff the anterior surface 32 of the postoperative cornea 30 results from the displacement of the main planes H A , H P according to: fA1,eff=fA1+dF where fA1=nAquaDA1

[0078] When considering the first effective change in refractive power of the cornea, the following applies: ΔD1,eff=D1,eff−D0,eff

[0079] The effective actual refractive power D 0,eff The preoperative cornea 30 results from: D0,eff=nAquaf0,eff

[0080] The effective actual focal length f 0,effThe preoperative cornea 30 results from the actual focal length f0 of the preoperative cornea: f0,eff=f0=nAquaD0

[0081] The appreciation of the displacement of the principal planes H A , H P The initial material removal is caused by the factor F already described.

[0082] This results in the following for the first effective interim refractive power D 1,eff postoperative cornea 30: D1,eff=nAquaf1,eff

[0083] The first effective interim focal length f 1,eff The postoperative cornea 30 results from the displacement of the main planes H A , H P according to: f1,eff=f1+dF where f1=nAquaD1

[0084] The final radius of curvature R determined using the compensated refractive index ΔD1 A2 leads to a second effective change in refractive power ΔD 2,eff, which exhibits a smaller deviation from the refractive index ΔD0 to be provided than the radius of curvature R determined using the refractive index ΔD0 to be provided A1 For the final radius of curvature R A2 the final principal optical planes H result A2 , H P2 .

[0085] Possible values ​​that result for a method based on determining the first effective change in refractive power ΔD 1,eff from the first effective change in refractive power ΔD A1,eff The values ​​for the anterior surface 32 are shown in Table 1. Possible values ​​resulting from a method based on the determination of the effective refractive power change ΔD 1,eff from the effective change in refractive power ΔD 1,eff The total number of corneas 30 can be found in Table 2. Table 1 Einheit PreoperativeCornea PostoperativeCornea (Interim) PostoperativeCornea (final) n Air 1,0001 1,0001 1,0001 n Cornea 1,3763 1,3763 1,3763 n Aqua 1,3371 1,3371 1,3371 R A m 7,81E-03 8,68E-03 8,66E-03 R P m 6,40E-03 0,0064 6,40E-03 d m 5,43E-04 4,48E-04 4,50E-04 ΔD m -1 -4,820 -4,715 D A m -1 48,153 43,333 43,438 D P m -1 -6,117 -6,117 -6,117 D L m -1 0,116 0,086 0,087 D T m -1 42,152 37,302 37,408 f Cornea m 0,0317 0,0358 0,0357 F 0,78 0,78 f eff m 0,0317 0,0359 0,0358 D eff m -1 42,152 37,225 37,332 ΔD eff m -1 -4,927 -4,821 ΔD ind m -1 -0,107 -0,105 ΔD rail ind 2,2% 2,2% ΔD error m -1 0,107 0,000 Table 2 Einheit PreoperativeCornea PostoperativeCornea (Initial) PostoperativeCornea (Final) n Air 1,0001 1,0001 1,0001 n Cornea 1,3763 1,3763 1,3763 n Aqua 1,3371 1,3371 1,3371 R A m 7,81E-03 8,68E-03 8,66E-03 R P m 6,40E-03 0,0064 6,40E-03 d m 5,43E-04 4,48E-04 4,50E-04 ΔD m -1 -4,820 -4,715 D A m -1 48,153 43,333 43,438 D P m -1 -6,117 -6,117 -6,117 D L m -1 0,116 0,086 0,087 D T m -1 42,152 37,302 37,408 f A m 0,0278 0,0309 F 0,78 0,78 f A,eff m 0,0278 0,0308 D A,eff m -1 42,152 37,225 ΔD A,eff m -1 48,153 43,438 ΔD A,ind m -1 -0,107 -0,105 ΔD rail A,ind 2,2% 2,2% ΔD A,error m -1 0,107 0,001

[0086] Fig.Figure 4 shows a schematic representation of a method for controlling a treatment device.

[0087] The procedure for controlling the treatment device 10 may include the following steps to be carried out by a control unit 18.

[0088] The procedure can include process steps S1 to S10 for providing control data for a laser 12 of the treatment device 10.

[0089] A first step S1 can include receiving a given refractive power change ΔD, relating to a change in the actual refractive power D0 of a preoperative cornea 30.

[0090] A second step S2 can be used to determine a first interim radius of curvature R. A1 an anterior surface 32 of the postoperative cornea in 30 dependence on an actual radius of curvature R A0the anterior surface 32 of the preoperative cornea 30 and the predetermined refractive power change ΔD to achieve a refractive power change ΔD A the anterior surface 32 to effect the specified change in refractive power ΔD.

[0091] A third step S3 can be used to determine a parameter for changing the actual radius of curvature R. A0 the anterior surface 32 of the cornea 30 into the preliminary target radius of curvature R A1 the required initial tissue removal of tissue from the preoperative cornea 30 on the anterior surface 32 of the cornea 30.

[0092] A fourth step, S4, can be used to determine the first effective change in refractive power ΔD caused by the initial tissue removal. 1,eff the cornea comprise 30.

[0093] A fifth step S5 can be used to determine a first compensated refractive power change ΔD1 from the refractive power change to be set ΔD and the first effective refractive power change ΔD caused by the initial tissue removal. 1,eff include.

[0094] A sixth step S6 can be used to determine a second preliminary target radius of curvature R. A2 or a final target radius of curvature R A2 the anterior surface 32 of the postoperative cornea 30 depending on the current curvature R A0 the anterior surface 32 of the preoperative cornea 30 and the first compensated refractive power change ΔD1 to effect the predetermined refractive power change ΔD.

[0095] A seventh step, S7, can involve determining a final tissue removal from the preoperative cornea 30 to change the actual radius of curvature R. A0the anterior surface 32 of the preoperative cornea 30 into the second provisional target radius of curvature R A2 the anterior surface 32 of the postoperative cornea 30.

[0096] An eighth step S8 can determine a second effective refractive power change ΔD caused by tissue removal. 2,eff the cornea comprise 30.

[0097] A ninth step, S9, can include a check to see if a predefined termination criterion has been met. For example, it can be checked whether a difference ΔD exists. error between the resulting second effective change in refractive power ΔD 2,eff and the specified change in refractive power ΔD falls below a specified difference value.

[0098] If the specified termination criterion is met, the procedure can be continued with step S10.

[0099] In the event that the specified termination criterion is not met, the procedure can be continued with step S5, whereby a second compensated refractive power change ΔD2 is derived from the refractive power change ΔD to be set and the second effective refractive power change ΔD caused by tissue removal. 2,eff can be determined.

[0100] Step S10 may include generating the control data to control the laser 12 to perform the final tissue ablation of the tissue of the preoperative cornea 30.

[0101] A step S11 can include transferring the provided control data to a respective ophthalmic surgical laser 12 of the treatment device 10.

[0102] Overall, the examples show how a method for determining a target curvature can be provided. Reference sign 10 Treatment device 12 lasers 14 area 16 Eye 18 Control unit 20 laser beam 22 Beam deflection device 30 Cornea 32 anterior surface 34 Outer eye space 36 posterior surface 38 Eye interior 40 corneal volume 42 light rays 44 Tissue volume 46 Cornea

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