LASER-BASED TREATMENT DEVICE FOR SURGICAL RESPIRANT VISION CORRECTION

Description

[0001] A planning device for determining control data for a treatment device for the surgical correction of refractive errors in a patient's eye is described, wherein the planning device generates the control data for a treatment device comprising a laser device which separates corneal tissue by irradiating pulsed laser radiation, wherein the laser radiation is focused on target points located in a pattern in the cornea.

[0002] The invention relates to a treatment device according to the claims for the surgical correction of a patient's eye, which device has an interface for supplying measurement data about parameters of the eye and refractive error data about the refractive error of the eye to be corrected, a laser device which separates corneal tissue by irradiating pulsed laser radiation, the laser radiation being focused on target points located in a pattern in the cornea.

[0003] Furthermore, a method for preparing control data for a treatment device for the surgical correction of a patient's eye is described, which is not part of the claimed subject matter of the invention, which has a laser device which separates corneal tissue by irradiating pulsed laser radiation, wherein the laser device, during operation, focuses the laser radiation according to the control data onto target points located in a pattern in the cornea.

[0004] Glasses have long been the traditional method for correcting refractive errors in the human eye. However, refractive surgery, which corrects refractive errors through changes to the cornea, is now increasingly being used. The goal of all surgical methods is to specifically alter the cornea in order to influence light refraction. Various surgical techniques are known for this. EP 1719483 A1 deals with the generation of data for laser-assisted refractive error correction. The most common is so-called laser in situ keratomileusis, also abbreviated to LASIK. In this procedure, a corneal flap is first detached from the corneal surface on one side and folded to the side. This flap can be detached using a mechanical microkeratome or a so-called laser keratome, such as the one sold by Intralase Corp., Irvine, USA.

[0005] The latter creates a cut surface in the cornea using laser radiation. In this process, several processes initiated by the laser radiation occur sequentially in the tissue. If the power density of the radiation exceeds a threshold, an optical breakthrough occurs, which creates a plasma bubble in the cornea. After the optical breakthrough occurs, the plasma bubble grows due to expanding gases. If the optical breakthrough is not maintained, the gas generated in the plasma bubble is absorbed by the surrounding material, and the bubble disappears again. Tissue-separating effects are also possible that occur without a plasma bubble. For simplicity, all such processes are summarized here under the term "optical breakthrough," meaning that this term is intended to include not only the optical breakthrough but also the resulting effects in the cornea.

[0006] To generate the optical breakthrough, the laser radiation is applied in pulsed form, with a pulse length of less than 1 ps. As a result, the power density required to trigger an optical breakthrough is only achieved within a narrow spatial area for each pulse. US Pat. No. 5,984,916 clearly shows that the spatial area of ​​the optical breakthrough (in this case, the generated interaction) depends strongly on the pulse duration. High focus of the laser beam in combination with the aforementioned short pulses thus allows the optical breakthrough to be applied with pinpoint precision in the cornea.

[0007] To create the thin lamella, a series of optical breakthroughs are made with the laser keratome at predetermined locations so that a cutting surface is formed which detaches the lamella from the underlying cornea.

[0008] After the flap has been released and folded aside, LASIK surgery involves the use of an excimer laser to ablate the now exposed corneal tissue. After the volume within the cornea has been vaporized in this way, the corneal flap is folded back into its original position. The LASIK method, which is already in use and is also known as fs-LASIK when a laser keratome is used, thus exposes a lid-shaped corneal flap, folds it back, and ablates the exposed tissue with an ablation laser.

[0009] The prior art also mentions that refractive error correction is achieved by isolating a lens-shaped volume in the corneal tissue using pulsed laser radiation. A corresponding description can be found, for example, in WO 2005 / 011545 A1. However, corresponding devices are not yet available on the market.

[0010] In the LASIK method, the corneal tissue exposed with a keratome is ablated using an ablation laser to remove a desired volume. The laser beam is focused at various points on the exposed cornea to ablate the material. The amount of material removed from the cornea is controlled by a so-called shot file, which determines the number of ablation laser pulses and the respective coordinates to which the pulses are delivered. The shot file is generated in the devices after prior measurement of the eye. Due to the different operating principle, it is not suitable for the surgical procedures and devices currently being scientifically investigated, which isolate a volume in the cornea.

[0011] The invention is therefore based on the object of providing a system for correcting refractive errors so that surgical refractive error correction can be carried out easily.

[0012] The problem is solved according to the independent claim.

[0013] A planning device is designed in such a way that it defines a volume from supplied measurement and refractive error data which lies within the cornea and whose removal from the cornea brings about the desired refractive error correction, defines a boundary surface which delimits the defined volume within the cornea, and generates a control data set for this boundary surface for controlling the laser device, which control data set defines a three-dimensional pattern of the target points in the cornea which lie in the boundary surface and are arranged in such a way that the boundary surface is formed as a cutting surface after irradiation of the pulsed laser radiation in accordance with the control data set, which cut surface isolates the defined volume in the cornea and thus makes it removable.

[0014] A treatment device for the surgical correction of refractive errors in a patient's eye comprises an interface for supplying measurement data on parameters of the eye and refractive error data on the refractive error of the eye to be corrected, a laser device which separates corneal tissue by irradiating pulsed laser radiation, the laser radiation being focused on target points located in a pattern in the cornea, and a planning device of the type described in the previous paragraph.

[0015] A method of the type mentioned above comprises the following steps: determining measurement data on parameters of the eye and refractive error data on the refractive error of the eye to be corrected, defining a volume from the measurement data and the refractive error data, wherein the volume lies within the cornea and wherein the removal of the volume from the cornea after operation of the treatment device results in the desired refractive error correction, defining a boundary surface that delimits the defined volume within the cornea, and defining a three-dimensional pattern of target points in the cornea, wherein the target points lie in the boundary surface and are arranged such that the boundary surface is formed as a cut surface upon irradiation of the pulsed laser radiation according to the control data, which cut surface isolates the defined volume in the cornea and thus makes it removable,Generating a control data set containing the three-dimensional pattern for controlling the laser device.,

[0016] Based on measurement and refractive error data of the eye to be corrected, a volume can first be defined that lies within the cornea and whose removal causes the desired refractive error correction. The removal can be achieved, for example, via an incision to the corneal surface that makes the volume accessible. This incision is also generated by the planning device or the control data. To ensure that the correction is as similar as possible for day and night vision, the volume should, if possible, cover the pupil of the dark-adapted eye. At least one boundary surface is then defined for this volume, preferably several, which delimit the volume. The boundary surface(s) is / are later formed into incisions using the treatment device or its laser device in order to be able to remove the volume, for example, to extract it.A control data set is determined for the interface(s). This data set specifies target points located at the interface, at each of which an optical breakthrough is to be created using the laser radiation to form the cutting surface. The target points are a three-dimensional pattern and all lie within the previously defined interface. The planning device can also be part of the laser device.

[0017] The result of the method or activity of the planning device is a control data set that enables automatic control of the laser device, so that the generation of the incision surfaces that isolate the volume in the cornea can then proceed automatically. The planning device or the treatment device equipped with it for surgical refractive error correction, as well as the method for providing control data for a treatment device, preferably generates the control data set automatically from the provided measurement data and refractive error data. In advantageous embodiments, the surgeon's involvement is not required.

[0018] The planning device can be designed as a computer that operates under the control of a program. Optionally, the planning device can be a component of the treatment device. A corresponding computer program product with program code that carries out the aforementioned method steps is thus also a solution to the aforementioned problem.

[0019] The control dataset is generated based on measured data and refractive error data from the eye. This measurement data can be acquired using a standalone measuring device. However, it is advisable to connect the treatment device directly to the measuring device. The measuring device could be, for example, an autorefractor, a refractometer, a keratometer, an aberrometer, an OCT, or a wavefront measurement device, or any combination of such devices or measuring instruments.

[0020] The refractive error can include hyperopia, myopia, presbyopia, astigmatism, mixed astigmatism (astigmatism in which there is hyperopia in one direction and myopia in a direction perpendicular to it), aspheric errors and higher-order aberrations.

[0021] A direct connection of the measuring device with the planning device or the treatment device equipped with it for data transmission, which can be used in one variant, has the advantage of eliminating the use of incorrect measurement and refractive error data with the greatest possible certainty. This is particularly true when the patient is transferred from the measuring device(s) to the laser device using a positioning device that interacts with the measuring device or laser device in such a way that the respective devices recognize whether the patient is in the appropriate position for measuring or applying the laser radiation. Transferring the patient from the measuring device to the laser device can simultaneously transmit the measurement and refractive error data to the treatment device.

[0022] It is ensured that the planning facility always generates the control data record belonging to the patient, and the erroneous use of an incorrect control data record for a patient is virtually impossible.

[0023] This aspect is also taken into account by a further possible embodiment of the invention, according to which the control data record is transmitted to the treatment device and, furthermore, operation of the laser device is preferably blocked until a valid control data record is present at the laser device. A valid control data record can, in principle, be a control data record that is suitable for use with the laser device of the treatment device. In addition, however, validity can also be linked to further checks being carried out, for example whether additional information about the patient stored in the control data record, for example a patient identification number, matches other information that was separately entered, for example, at the treatment device as soon as the patient is in the correct position for operation of the laser device. The transmission can be carried out by means of memory chips (e.g. via USB or memory stick), magnetic storage devices (e.g.floppy disks), wirelessly (e.g. WLAN, UMTS, Bluetooth) or wired (e.g. USB, Firewire, RS232, CAN bus, Ethernet etc.).

[0024] To create the isolated volume, the focus of the focused pulsed laser radiation is regularly adjusted three-dimensionally. Therefore, a two-dimensional deflection of the laser radiation, e.g., using a scanning mirror, is usually combined with simultaneous focus adjustment in the third spatial direction, e.g., using a telescope. The adjustment of the focus position is, of course, crucial for the accuracy with which the cut surface isolating the volume can be created. It has proven useful to use a contact lens that is placed on the eye and fixes it. Such a contact lens is also commonly used in the laser keratomes mentioned above, which are used in the fs-LASIK method. The contact lens also regularly serves the function of giving the anterior surface of the cornea a defined shape. In the laser keratomes known to date, this shape is a plane, i.e.The eye is flattened in the corneal area to operate the laser keratome. Since this is relatively uncomfortable for the patient, a curved contact lens has already been described for approaches that isolate a volume in the cornea. Such a contact lens then gives the anterior surface of the cornea a known curvature. This curvature inevitably results in a deformation of the cornea. This deformation is all the greater the more the curvature of the contact surface of the contact lens facing the eye deviates from the actual corneal curvature of the patient's eye. In order to be able to work with a uniform contact lens curvature, it is therefore advantageous to take the corneal deformation that occurs when using a curved contact lens into account in the control data set. This way, regardless of the degree of deformation, the desired boundary surface for the defined volume is present in the free eye, i.e. the eye not deformed by the contact lens.It is therefore preferable that, when generating the control data set containing the pattern of the target points, such a deformation of the cornea of ​​the eye is taken into account, which occurs during the irradiation of the pulsed laser radiation, in particular through the mentioned contact lens.

[0025] This approach not only allows for the use of the most uniform contact lens curvature possible, but also achieves a higher quality of refractive error correction. With conventional laser keratomes, such consideration of deformation is not necessary, as the eye is flattened against the cornea by the contact lens. The lamella required for LASIK surgery is created by simply creating optical apertures in a plane parallel to the contact lens.

[0026] The generated control data set can be used directly to control the treatment device. However, it is advisable to give the treating physician the option to intervene so that they can, on the one hand, review the control data set and, on the other hand, take special cases or special requests into account. One possible special request is, for example, the position of the incision through which the isolated volume is to be removed from the cornea. Ophthalmologists often have different opinions on this. However, it may also be desirable for the physician to have the option to intervene for liability reasons. It is therefore advisable for the device to have a display device for the visual representation of control data from the control data set and an input device for subsequently changing or influencing the control data set.

[0027] Optical systems are generally imperfect. This also applies to the focusing of the laser beam into the cornea. Here, for example, a curvature of the image field can occur, resulting in focal positions that appear to be positioned in one plane not actually lying in one plane, but in a curved surface. With conventional laser keratomes, this aspect is not important, since the creation of the incision that exposes the lamella has no effect on the optical quality of the correction. The actual correction is determined exclusively by the volume of the exposed cornea vaporized by the ablation laser. Error correction, for example with regard to a curvature of the image field, is therefore not of interest in the state of the art, especially with regard to laser keratomes.

[0028] Since the volume to be sampled is defined entirely by the focusing of the pulsed laser radiation, it is expedient for the planning device to generate the control data set to account for and thus compensate for optical focus position errors, which lead to a deviation between the specified and actual position of the target points when focusing the pulsed laser radiation, by means of a lead dependent on the position of the respective target point. This lead can be determined, for example, by the planning device accessing a correction table or function that specifies the focus position error depending on the position of the respective target point. The correction table or function can be specified uniformly for the respective device type or, which is preferred for reasons of precision, can be determined individually for each device.

[0029] The same applies to the procedure in which, for the determination of the interface or the three-dimensional pattern of the target points, optical focus position errors, which lead to a deviation between the specified and actual position of the target points when focusing the pulsed laser radiation, are taken into account and thus compensated for by a lead that depends on the position of the respective target point.

[0030] The interface isolates the volume when it is formed as a cut surface after the application of pulsed laser radiation. The interface thus automatically has anterior and posterior sections, whereby the terms "anterior" and "posterior" correspond to standard medical nomenclature. In principle, it is possible to design the interface as a free surface. However, the generation of the control data set is simplified if the interface is composed of an anterior partial surface and a posterior partial surface. One of the partial surfaces can then be formed at a constant distance from the corneal surface. The other then necessarily has a different distance from the anterior surface. The partial surface at a constant distance from the anterior surface of the cornea, usually the anterior partial surface, is therefore usually spherical. This is certainly true when the cornea is pressed against a spherical contact lens.The optical correction is then performed based on the shape of the other partial surface, usually the posterior partial surface. This significantly simplifies the computational effort.

[0031] One way to specify the refractive power data is to determine the refractive power B BR of a pair of spectacles suitable for correcting refractive errors, which must be positioned at a distance d HS in front of the corneal vertex to achieve the desired refractive error. Determining these parameters is a common standard in ophthalmic optics and allows the use of widespread and long-established measuring devices. To generate the control data set, only the refractive power data for a standard spectacle correction is used. Of course, such data can also include astigmatism corrections. A common formula for the refractive power B BR of spectacles is, for example, equation (1) given in the following figure description. It specifies the spherical refractive error Sph and the cylindrical refractive error Cyl and, for the latter, naturally requires knowledge of the cylinder axis θ.

[0032] To correct refractive errors, a volume of cornea is removed using the treatment device or the control data sets generated in the described procedure. The ultimate goal is to change the curvature of the cornea so that refractive error is corrected. A particularly direct, precise, and simple calculation of the curvature of the anterior corneal surface required for the correction is obtained using the following equation: R CV * = 1 / 1 / R CV + B BR / n c − 1 1 − d HS · B BR + F .

[0033] In this equation, Rcv* denotes the radius of curvature of the anterior corneal surface after removal of the volume, Rcv denotes the radius of curvature of the cornea before removal of the volume (it is included in the measurement data), nc denotes the refractive power of the corneal material (usually about 1.376), d HS denotes the distance at which a pair of glasses with the specified refractive power must be positioned in front of the corneal vertex, and F denotes a factor that measures the optical effect of the reduction in corneal thickness on the visual axis due to the removal of the volume. For a simplified calculation, the factor F can be set to zero. For a more precise calculation, F can be calculated as follows: F = 1 − 1 / n c · d C * − d C , where dc and dc* denote the thickness of the cornea before and after removal of the volume, respectively. The radius Rcv* is then calculated iteratively by inferring the value (dc* - dc) from the difference (Rcv* - Rcv) at each iteration step. The resulting result is applied to the change in thickness when calculating Rcv* in the next iteration step. The iterative calculation can be aborted, for example, if the difference for F between two iterations is less than a certain threshold.

[0034] The treatment device according to the invention with the planning device operates particularly simply if, as mentioned, the optical correction to be achieved by removing the volume is primarily formed by the curvature of a partial surface that is not at a constant distance from the anterior corneal surface and that delimits the volume. The posterior partial surface is expediently selected for this purpose, since this partial surface then has the aforementioned radius of curvature, at least in the case of myopia correction, reduced by the constant distance between the anterior partial surface and the anterior corneal surface.

[0035] The control data set provides a file that enables a fully automated surgical procedure with regard to the control of the treatment device or a corresponding operation of the treatment device. The control data set specifies the target points to which the focused laser beam must be directed in order to emit laser pulses. The focus of the focused laser radiation is then adjusted so that it runs in a trajectory over the specified target points. From a calculation point of view and with regard to the adjustment speed, it is particularly advantageous if the trajectory is a spiral. In the case of the anterior or posterior partial area mentioned, a spiral is then specified for each partial area. The course of the focus along a spiral enables operation of the corresponding deflection device of the treatment device close to the cutoff frequency, since, for example,When writing a spiral, two galvanometer scanners can each be operated close to or at their cutoff frequency.

[0036] Fundamentally, when defining the trajectory, it must be ensured that the laser pulses are emitted along this trajectory. The target points then define support points in the trajectory. The density with which the target points specify the trajectory can, but does not necessarily have to, correspond to the density with which the points on the trajectory are arranged to each of which a pulse of laser radiation is emitted. On the contrary, it is even preferable for the target points to represent only a subset of the points to which laser pulses are emitted. On the one hand, the control data set is then drastically reduced in terms of data volume, and on the other hand, the computational effort is simplified in all steps in which a functional description of the trajectory curve in the interface cannot or should not be used, but in which the target points must be processed individually. One example of this is the aforementioned correction for image field curvature.

[0037] It is therefore preferred for the device that the laser device adjusts the focused laser radiation along a path over the pattern of target points, wherein pulses of the pulsed laser radiation are emitted into the cornea at points that lie on the path between the target points.

[0038] The same applies to the described method, namely that the control data set is provided for a laser device that adjusts the focused laser radiation along a path across the pattern of target points. The control data set is generated such that the target points in the pattern represent a subset of the points to which the laser device emits the pulsed laser radiation. The control data set is thus adapted to the possible adjustment speed of the laser device.

[0039] As a result, a different frequency of the support points is specified or applied in the laser device for adjusting the focus position than that which occurs when generating the laser pulses. Of course, the control data set does not contain any information about the frequency per se, even if this is possible. Due to the maximum adjustment speed or the highest signal frequencies used when adjusting the focus of the laser radiation, the specification of the target points naturally corresponds to a path speed or an adjustment speed in the respective coordinates used for the description. The spatial distance of the target points in combination with the path speed and the laser pulse frequency that can be realized by the laser device now leads, in the preferred embodiment, to laser pulses being automatically emitted at times at which the focus is adjusted from one target point to the next.This approach has the advantage that during operation of the treatment device, the target points are specified with a frequency that is lower than the frequency with which the pulses of the pulsed laser radiation are emitted by the laser device into the cornea.

[0040] Of course, the specification of target points in the control data set does not mean that the adjustment speed at these target points must be zero when the laser pulse is emitted at the target point. In order to quickly create the cutting surface at the specified boundary surface of the defined volume, it is advantageous if the adjustment of the focus position and emission of the laser pulses are synchronized in such a way that a laser pulse is emitted with continuous deflection of the focus and yet still hits the cornea at the target point. The pulsed laser radiation is therefore applied with continuous adjustment of the focus position, e.g. with moving scanning mirrors. This design results in a systematic difference compared to known shot files for ablation lasers, in which a shot from the ablation laser is only fired when the deflection of the laser beam is stationary and aimed at a specific point.The scope of the claimed subject matter of the invention is defined by the claims. Described methods and method steps are expressly not part of the claimed invention.

[0041] The invention will be explained in more detail below by way of example with reference to the drawings. In the drawings: Fig. 1a schematic representation of a treatment device or a treatment device for correcting vision defects, Fig. 1aa schematic representation regarding the structure of the treatment device of the Fig. 1 , Fig. 2 a schematic diagram of the introduction of pulsed laser radiation into the eye for the correction of refractive errors with the treatment device of Fig. 1 , Fig. 3 another schematic representation of the treatment device of the Fig. 1, Fig. 4in sub-figures (a), (b) and (c) schematic sectional views to illustrate the need for correction of the human eye in the case of ametropia, Fig. 5a schematic sectional view through the cornea with representation of a volume to be removed for ametropia correction, Fig. 6a section through the cornea after removal of the volume of Fig. 5 , Fig. 7 a sectional view similar to the Fig. 5 , Fig. 8 a schematic sectional view through the cornea to illustrate the volume removal, Fig. 9 a top view of a spiral trajectory curve used to isolate the volume of the Fig. 5 , 7 and 8 is used, Fig. 10 an enlarged view of the trajectory of the Fig. 9 , Fig. 11an alternative trajectory for the correction of cylindrical refractive errors, Fig. 12a schematic representation to explain the function of a contact lens in the treatment device of the Fig. 1, Fig. 13 to 15 schematic representations regarding the effects of the contact lens by deformation of the cornea, Fig. 16 and 17 schematic representation regarding the approximation of the area limiting the volume posteriorly in the case of cylindrical corrections of defective sealing, Fig. 18 a schematic representation of a method used in the determination of control data for the treatment device of the Fig. 1 used field curvature correction and Fig. 19 a schematic representation of the process for preparing and carrying out a refractive error correction.

[0042] Figure 1shows a treatment device 1 for an ophthalmic surgical procedure similar to that described in EP 1159986 A1 or US 5549632. The treatment device 1 uses a treatment laser radiation 2 to correct a refractive error in an eye 3 of a patient 4. The refractive error can include hyperopia, myopia, presbyopia, astigmatism, mixed astigmatism (astigmatism in which hyperopia is present in one direction and myopia in a direction perpendicular to it), aspheric errors, and higher-order aberrations. In the described embodiment, the treatment laser radiation 2 is applied as a pulsed laser beam focused into the eye 3. The pulse duration is, for example, in the femtosecond range, and the laser radiation 2 acts in the cornea by means of non-linear optical effects. The laser beam has, for example, 50 to 800 fs short laser pulses (preferably 100 - 400 fs) with a pulse repetition frequency between 10 and 500 kHz.In the described embodiment, the components of the device 1 are controlled by an integrated control unit, which can of course also be designed independently.

[0043] Before using the treatment device, the refractive error of eye 3 is measured using one or more measuring devices.

[0044] Figure 1ashows a schematic of the treatment device 1. In this variant, it has at least two devices or modules. A laser device L emits the laser beam 2 onto the eye 3. The operation of the laser device L is fully automatic, i.e. the laser device L starts the deflection of the laser beam 2 upon a corresponding start signal and in doing so creates cutting surfaces which are constructed in a manner to be described and which isolate a volume in the cornea. The laser device L receives the control data required for operation in advance from a planning device P as a control data set via control lines not designated in more detail. The transmission takes place before the laser device L is operated. Of course, communication can also be wireless. As an alternative to direct communication, it is also possible to arrange the planning unit P spatially separate from the laser unit L and to provide a corresponding data transmission channel.

[0045] Preferably, the control data record is transmitted to the treatment device 1, and further preferably, operation of the laser device L is blocked until a valid control data record is present at the laser device L. A valid control data record can be a control data record that is fundamentally suitable for use with the laser device L of the treatment device 1. In addition, however, validity can also be linked to the passing of further checks, for example whether additional information stored in the control data record about the treatment device 1, e.g., a device serial number, or the patient, e.g., a patient identification number, matches other information that was, for example, read out at the treatment device or entered separately as soon as the patient is in the correct position for operation of the laser device L.

[0046] The planning unit P generates the control data set, which is made available to the laser unit L for performing the operation, from measurement data and refractive error data determined for the eye to be treated. These data are fed to the planning unit P via an interface S and, in the illustrated embodiment, originate from a measuring device M that previously measured the eye of the patient 4. Of course, the measuring device M can transmit the corresponding measurement and refractive error data to the planning unit P in any desired manner.

[0047] The transfer can be carried out via memory chips (e.g., USB or memory stick), magnetic storage (e.g., floppy disks), wirelessly (e.g., Wi-Fi, UMTS, Bluetooth), or wired (e.g., USB, Firewire, RS232, CAN bus, Ethernet, etc.). The same applies, of course, to data transfer between planning device P and laser device L.

[0048] A direct radio or wired connection between the measuring device M and the treatment device 1 for data transmission, which can be used in one variant, has the advantage that the use of incorrect measurement and refractive error data is excluded with the greatest possible certainty. This applies in particular when the patient is transferred from the measuring device M or the measuring devices to the laser device L using a positioning device (not shown in the figure) that interacts with the measuring device M or the laser device L in such a way that the respective devices recognize whether the patient 4 is in the respective position for measuring or introducing the laser radiation 2. By transferring the patient 4 from the measuring device M to the laser device L, the measurement and refractive error data can also be transferred to the treatment device 1 at the same time.

[0049] It is preferably ensured by suitable means that the planning device P always generates the control data record belonging to patient 4, and an erroneous use of an incorrect control data record for a patient 4 is virtually excluded.

[0050] The mode of action of laser beam 2 is Figure 2 schematically indicated. The treatment laser beam 2 is focused into the cornea 5 of the eye 6 by means of an unspecified optic. This creates a focus in the cornea 5 that covers a spot 6 and in which the laser radiation energy density is so high that, in combination with the pulse length, a non-linear effect occurs in the eye. For example, each pulse of the pulsed laser radiation 2 at the respective spot 6 can create an optical breakthrough in the cornea 5, which in turn Figure 2A plasma bubble is initiated, indicated schematically. This laser pulse separates tissue in the cornea 5. When a plasma bubble forms, the tissue layer separation encompasses a larger area than the spot 6 covered by the focus of the laser radiation 2, even though the conditions for generating the breakthrough are only met at the focus. In order for each laser pulse to generate an optical breakthrough, the energy density, i.e., the fluence of the laser radiation, must be above a certain, pulse-length-dependent threshold. This relationship is known to the person skilled in the art, for example, from DE 69500997 T2.

[0051] Alternatively, a tissue-severing effect can also be achieved by pulsed laser radiation by emitting multiple laser radiation pulses in one area, with spots 6 overlapping for multiple laser radiation pulses. Multiple laser radiation pulses then work together to achieve a tissue-severing effect.

[0052] The type of tissue separation used by the treatment device 1 is not relevant for the following description; the only important thing is that pulsed treatment laser radiation 2 is used for this purpose. For example, a treatment device 1 as described in WO 2004 / 032810 A2 can be used. It is also important that a plurality of laser pulse foci in the tissue form a cutting surface, the shape of which depends on the pattern with which the laser pulse foci are arranged in the tissue. The pattern specifies target points for the focus position, at which one or more laser pulses are emitted, and defines the shape and position of the cutting surface. The pattern of the target points is important for the methods and devices explained below and will be described in more detail.

[0053] In order to correct a refractive error, material is removed from an area within the cornea 5 using pulsed laser radiation. This is done by separating tissue layers that isolate the material and then allow the material to be removed. The removal of the material causes a volume change in the cornea, which results in a change in the optical imaging effect of the cornea 5, which is precisely dimensioned so that the previously determined refractive error is / will be corrected as far as possible. To isolate the volume to be removed, the focus of the laser radiation 2 is directed at target points in the cornea 5, usually in an area located below the epithelium and Bowman's membrane, as well as above Decemet's membrane and the endothelium. The treatment device 1 has a mechanism for adjusting the position of the focus of the laser radiation 2 in the cornea 5. This is shown schematically in Figure 3 shown.

[0054] In Figure 3Elements of the treatment device 1 are shown only to the extent that they are necessary for understanding the focus adjustment. The laser radiation 2 is, as already mentioned, bundled into a focus 7 in the cornea 5, and the position of the focus 7 in the cornea is adjusted so that, to create the incision, energy from laser radiation pulses is introduced into the tissue of the cornea 3 at various points. The laser radiation 2 is provided by a laser 8 as pulsed radiation. An xy scanner 9, which in one variant is realized by two essentially orthogonally deflecting galvanometer mirrors, deflects the laser beam coming from the laser 8 two-dimensionally, so that a deflected laser beam 10 is present after the xy scanner 9. The xy scanner 9 thus effects an adjustment of the position of the focus 7 essentially perpendicular to the main direction of incidence of the laser radiation 2 into the cornea 5.To adjust the depth of field, a z-scanner 11, designed, for example, as an adjustable telescope, is provided alongside the xy-scanner 9. The z-scanner 11 ensures that the z-position of the focus 7, i.e., its position on the optical axis of incidence, is changed. The z-scanner 11 can be arranged upstream or downstream of the xy-scanner 9. The coordinates designated x, y, and z below therefore refer to the deflection of the focus 7.

[0055] For the functional principle of the treatment device 1, the assignment of the individual coordinates to the spatial directions is not essential; however, for the sake of simplicity of description, z always denotes the coordinate along the optical axis of incidence of the laser radiation 2, and x and y denote two mutually orthogonal coordinates in a plane perpendicular to the direction of incidence of the laser beam. Those skilled in the art will of course be aware that a three-dimensional description of the position of the focus 7 in the cornea 5 can also be achieved using other coordinate systems; in particular, it does not have to be a rectangular coordinate system. It is therefore not mandatory for the xy scanner 9 to deflect around mutually perpendicular axes; rather, any scanner capable of adjusting the focus 7 in a plane in which the axis of incidence of the optical radiation does not lie can be used. Thus, oblique coordinate systems are also possible.

[0056] Furthermore, non-Cartesian coordinate systems can also be used to describe or control the position of focus 7, as will be explained below. Examples of such coordinate systems are spherical coordinates (also called spherical coordinates) and cylindrical coordinates.

[0057] To control the position of focus 7, the xy scanner 9 and the z scanner 11, which together implement a concrete example of a three-dimensional focus adjustment device, are controlled by a control unit 12 via unspecified lines. The same applies to the laser 8. The control unit 3 ensures suitably synchronous operation of the laser 8 and the three-dimensional focus adjustment device, exemplarily implemented by the xy scanner 9 and the z scanner 11, so that the position of focus 7 in the cornea 5 is adjusted such that a material of a specific volume is ultimately isolated, with the subsequent volume removal effecting a desired refractive error correction.

[0058] The control unit 12 operates according to predetermined control data which specify the target points for the focus adjustment. The control data is generally summarized in a control data set. In one embodiment, this specifies the coordinates of the target points as a pattern, whereby the sequence of the target points in the control data set determines the sequence of the focus positions and thus ultimately a trajectory curve (also referred to here as path for short). In one embodiment, the control data set contains the target points as concrete control values ​​for the focus position adjustment mechanism, e.g. for the xy scanner 9 and the z scanner 11. In preparation for the ophthalmic surgical procedure, i.e. before the actual surgical procedure can be carried out, the target points and preferably also their sequence in the pattern are determined.The surgical procedure must be planned in advance to determine the control data for the treatment device 1, the application of which will then achieve optimal refractive error correction for the patient 4.

[0059] First, the volume to be isolated from the cornea 5 and later removed must be determined. As already shown in the Fig. 1a As described, this requires an assessment of the need for correction. Figure 4shows in sub-figures a), b) and c) the optical conditions in eye 3 of patient 4. Without refractive error correction, the situation shown in sub-figure a) exists. The cornea 5, together with the eye lens 13, focuses an object lying at infinity into a focus F, which lies on the z-axis behind the retina 14. The imaging effect comes on the one hand from the eye lens 13, which is relaxed when the eye is not accommodated, and on the other hand from the eye cornea 5, which is essentially defined by an anterior corneal surface 15 and a posterior corneal surface 16 and, due to its curvature, also has an imaging effect. The optical effect of the cornea 5 is determined by the radius of curvature Rcv of the anterior corneal surface. Sub-figure a) only represents the refractive error as an example; the more complex refractive errors mentioned above can actually occur.However, the following description also applies to them, although the given equations may then sometimes contain an additional angular dependence, even if this is not explicitly stated.

[0060] For the correction of vision defects, as shown in part b) the Figure 4 shown, an auxiliary lens 17 in the form of spectacles is placed in front of the eye 3 at a distance d HS from the vertex of the cornea 5. The lens 17 of the spectacles is adjusted in its refractive power B BR so that it shifts the far point of the entire system, ie of spectacles and eye, from the focal point F to the corrected focal point F*, which lies on the retina 14.

[0061] Regarding the nomenclature used in this description, it should be noted that the addition of an asterisk to quantities indicates that these are quantities obtained after a correction. The focus F* is therefore the focus obtained after the optical correction, which is shown in sub-figure b) of the Figure 4 through the lens 17 of the glasses.

[0062] Under the justified assumption that a change in the thickness of the cornea 5 essentially modifies the radius of curvature of the anterior corneal surface 15 facing the air, but not the radius of curvature of the posterior corneal surface 16 facing the interior of the eye, the volume removal modifies the radius of curvature Rcv of the anterior corneal surface 15. The cornea 5, reduced by the volume, has a modified imaging effect such that the then corrected focus F* lies on the retina 14. After the correction, a modified anterior corneal surface 15* exists, and a refractive error correction is achieved even without glasses.

[0063] To determine the target point pattern, the desired curvature of the modified anterior corneal surface 15* is determined. The starting point is the refractive power of the lens 17 of the spectacles, as determining the corresponding parameters is a standard procedure in ophthalmic optics. The following formula applies to the refractive power B BR (ϕ) of the lens 17 of the spectacles: B BR φ = Sph + Cyl · sin 2 φ − θ .

[0064] In this equation, Sph and Cyl denote the correction values ​​to be achieved for spherical and astigmatic refractive errors, respectively, and θ denotes the position of the cylinder axis of the cylindrical (astigmatic) refractive error, as known to those skilled in optometry. Finally, the parameter ϕ refers to a cylindrical coordinate system of the eye and is counted counterclockwise, looking at the eye, as is common in ophthalmology. Using the value B BR, the curvature of the modified anterior corneal surface 15* is now set as follows: R CV * = 1 / 1 / R CV + B BR / n c − 1 1 − d HS · B BR + F

[0065] In equation (2), nc denotes the refractive power of the corneal material. The corresponding value is typically 1.376; d HS denotes the distance at which a pair of spectacles with a refractive power of B BR must be positioned from the corneal vertex to produce the desired refractive error correction; B BR denotes the aforementioned refractive power of the spectacles according to equation (1). The value for the refractive power of B BR can also capture refractive errors that go beyond a normal spherical or cylindrical correction. B BR (and thus automatically also Rcv*) then have additional coordinate dependencies.

[0066] The factor F expresses the optical effect of the change in corneal thickness and can be considered a constant factor in a first approximation. For a highly accurate correction, the factor can be calculated using the following equation: F = 1 − 1 / n c · d C * − d C . dc and dc* are the corneal thickness before and after the optical correction, respectively. For a precise determination, Rcv* is calculated iteratively. In the i-th calculation, the difference (Rcv* - Rcv) is used to determine the value (dc* - dc) and the resulting thickness change is applied to the (i+1)-th calculation. This can be repeated until a termination criterion is met, for example, if the difference in the thickness change result for two consecutive iteration steps is below a specified limit. This limit can be set, for example, using a constant difference that corresponds to an appropriate refractive correction accuracy for the treatment.

[0067] If the change in corneal thickness is neglected, which is perfectly acceptable for a simplified procedure, F in equation (2) can be set to zero for a simplified calculation, i.e., neglected and omitted. Surprisingly, the following simple equation for the refractive power of the modified cornea 5* is obtained: B CV * = B CV + B BR / 1 − B BR · d HS

[0068] From this equation, the expert can easily calculate the radius Rcv* of the anterior corneal surface 15* using the equation Bcv* = (n-1) / Rcv*, which must be present after the modification in order to obtain the desired refractive error correction, as follows: Rcv* = 1 / ( (1 / Rcv) + B BR / ( (nc -1) (1 - d HS • B BR )))

[0069] The volume-isolating boundary surface is now defined for the volume whose removal results in the above-mentioned change in the curvature of the anterior corneal surface 15. It is preferable to consider that the diameter of the area to be corrected, and thus the diameter of the volume to be removed, should, if possible, extend beyond the pupil size of a dark-adapted eye.

[0070] In a first variant, a free surface is defined using numerical methods known to those skilled in the art. This free surface defines a volume whose removal causes the change in curvature. For this purpose, the change in thickness required for the desired curvature modification is determined along the z-axis. This yields the volume as a function of r, ϕ (in cylindrical coordinates), and from this, its boundary surface.

[0071] A simple analytical calculation is provided by the following second variant, in which the boundary surface of the volume is constructed by two partial surfaces, an anterior partial surface located towards the corneal surface 15 and an opposite posterior partial surface. The corresponding ratios are shown Figure 5 The volume 18 is delimited towards the anterior corneal surface 15 by an anterior cut surface 19, which lies at a constant distance d F below the anterior corneal surface 15. This anterior cut surface 19 is also referred to as a flap surface 19 in analogy to laser keratomes, since it serves there, in combination with an opening incision towards the edge, to lift the cornea 5 from the underlying cornea 5 in the form of a "flap." This type of removal of the previously isolated volume 18 is, of course, also possible here.

[0072] The anterior cut surface 19 has a curvature that lies by dF below the anterior corneal surface 15. If this is spherical, a radius of curvature can be specified for the flap surface 19 that is dF smaller than the radius of curvature Rcv. As will be described later for preferred variants, when creating the cut surface 19 using a contact lens, it can be ensured that the anterior corneal surface 15 is spherical at the time the cut surface is created, so that the pattern of the target points results in a spherical cut surface. Relaxation of the eye 3 after removal of the contact lens may then lead to a non-spherical cut surface 19, but it still maintains a constant distance from the anterior corneal surface 15 or 15*. This will be explained later.

[0073] Posteriorly, the volume 18 to be removed from the cornea 5 is limited by a posterior cutting surface 20, which fundamentally cannot be at a constant distance from the anterior corneal surface 15. The posterior cutting surface 20 is therefore designed such that the volume 18 is in the form of a lenticule, which is why the posterior cutting surface 20 is also referred to as the lenticule surface 20. In Figure 5 it is shown as an example as a spherical surface with a radius of curvature RL, whereby of course the center of this curvature does not coincide with the center of curvature of the Figure 5 also spherical anterior corneal surface 15.

[0074] Figure 6shows the conditions after removal of volume 18. The radius of the modified corneal anterior surface 15* is now Rcv* and can be calculated, for example, according to the equations described above. The thickness d L of the removed volume 18 is decisive for the radius change, as Figure 7 This figure also shows the height h F of the spherical cap defined by the anterior cut surface 19, the height h L of the spherical cap defined by the posterior cut surface 20, and the thickness d L of the volume 18 to be removed.

[0075] Due to the constant distance between the anterior corneal surface 15 and the anterior corneal surface 19, the posterior cut surface 20 determines the curvature of the anterior corneal surface 15* after removal of the volume 18. Thus, the posterior cut surface 20 will have an angle-dependent radius of curvature, for example, in the case of a refractive error correction that takes cylindrical parameters into account. Figure 7 The lenticule area 20 shown generally applies: R L φ = R CV * φ − d F , or in cylindrical coordinates (z, r, ϕ) z L r , φ = R L φ − R L 2 φ − r 2 1 / 2 + d L + d F .

[0076] Without considering astigmatism, the dependence on ϕ is eliminated, and the lenticule surface 20 is spherical. However, assuming the need for a cylindrical refractive error correction, the lenticule surface 20 usually has different radii of curvature on different axes, although these usually have the same vertex.

[0077] This automatically makes it clear that in the case of a cylindrical correction, the theoretical intersection line between flap surface 19 and lenticule surface 20 is not in one plane, ie, at constant z-coordinates. The smallest radius of curvature of the lenticule surface 20 is at ϕ = θ + π / 2, the largest, of course, on the axis θ of the cylindrical refractive error, ie, at ϕ =θ. In the case of a hyperopia correction, the representation of the Figure 7 the apex of flap surface 19 and lenticule surface 20 together and the lenticule surface 20 is more curved than the flap surface 19. The thickness d L of the lenticule results as the edge thickness.

[0078] The volume 18, which can be considered as a lenticule, has the smallest edge thickness at ϕ = θ = π / 2, since this is where the lenticule surface 20 and the flap surface 19 intersect. For all other values ​​of ϕ, a finite edge thickness is given if a given z-coordinate is taken as the lower limit of the lenticule surface 20.

[0079] Alternatively, in addition to the flap surface 20 and the lenticule surface 19, an additional edge surface can be provided, which borders the volume 18 in the intersection area of ​​the flap surface 20 and the lenticule surface 19 or connects these surfaces where they do not converge at a given z-coordinate. The intersection of this edge surface is also performed with the pulsed laser beam. The edge surface can, for example, have a cylindrical shape, but can also have an elliptical shape (in plan view) or a conical shape (in side view).

[0080] The configuration of the volume 18 shown in the figures as being delimited by an anterior cutting surface 19 with a constant distance to the anterior corneal surface 15 and a posterior cutting surface 20 is only one variant for delimiting the volume 18. However, it has the advantage that the optical correction is essentially determined by only one surface (the lenticule surface 20), so that the analytical description of the other partial surface of the interface is simple.

[0081] Furthermore, optimal safety margins are provided with regard to the distance of the volume to the anterior corneal surface 15 and the posterior corneal surface 16. The residual thickness d F between the anterior cut surface 19 and the anterior corneal surface 15 can be set to a constant value of, for example, 50 to 200 µm. In particular, it can be selected such that the pain-sensitive epithelium remains in the lamella formed by the flap surface 19 beneath the anterior corneal surface 15. Furthermore, the formation of the spherical flap surface 19 is consistent with previous keratometer cuts, which is advantageous for the acceptance of the method.

[0082] After creating the cut surfaces 19 and 20, the volume 18 isolated in this way is then removed from the cornea 5. This is shown schematically in Figure 8which also illustrates that the cutting surfaces 19 and 20 are produced by the action of the treatment laser beam incident in a focus cone 21, for example by arranging plasma bubbles in a row, so that in a preferred embodiment the flap cutting surface 19 and the lenticule cutting surface 20 are produced by suitable three-dimensional adjustment of the focus position of the pulsed laser radiation 2.

[0083] If both the lenticule surface 20 and the flap surface 19 are created by means of pulsed laser radiation, it is expedient to form the lenticule surface 20 before the flap surface 19, since the optical result for the lenticule surface 20 is better (if not achievable at all) if no change in the cornea 5 has yet occurred above the lenticule surface 20.

[0084] The removal of the volume 18 isolated by the pulsed laser radiation can, as in Figure 8indicated, can be achieved by an edge cut 22, which allows the volume 18 to be cut in the direction of a Figure 8drawn arrow 23. Alternatively, the marginal incision 22 can be designed such that it connects the anterior incision surface 19, i.e. the flap surface 19, in the form of a ring with the anterior surface 15 of the cornea, whereby the marginal incision does not, however, completely encircle an angle of 360°. The lamella isolated in this way remains in contact with the remaining tissue of the cornea 5 in a narrow area. This connecting bridge then serves as a joint to fold the otherwise isolated lamella away from the cornea 5 and to be able to remove the already isolated volume 18, which is thereby accessible, from the rest of the cornea 5. The position of the connecting bridge can be specified when generating the control data or the target points. The described procedure orFrom this perspective, the device isolates volume 19 within the cornea 5 and creates a flap that acts as a lid over the volume, connected to the remaining cornea via a tissue bridge. The lid can be folded back, and volume 18 can be removed.

[0085] To generate the cutting surfaces 19 and 20, the target points can be arranged in a variety of ways. For example, WO 2005 / 011546, for generating cutting surfaces in the cornea, describes the use of special spirals that run, for example, around a main axis substantially perpendicular to the optical axis (z-axis) in the manner of a helix. The use of a scan pattern that arranges the target points line by line is also known (cf. WO 2005 / 011545). These options can, of course, be used to generate the cutting surfaces defined above and with the transformations explained below.

[0086] The adjustment of the position of the focus in the cornea is carried out by means of the Figure 3schematically illustrated three-dimensional deflection device, which uses the displacement of lenses or other optically active elements to adjust the focus in the z-direction. Now, the adjustment of lenses or similar is generally not as fast as the pivoting of mirrors, as are generally used in an xy scanner. Therefore, the adjustment speed of the z-scanner usually limits the speed with which the cutting surfaces in the cornea can be created. In order to create the cutting surfaces 18 and 19 as quickly as possible, in a preferred embodiment the focus is guided along a spiral path, with one spiral in each case lying in the spatially curved cutting surface. While the spiral is being written, the z-scanner is adjusted so that the arms of the spiral follow the spatially curved cutting surface.

[0087] Figure 9shows an exemplary trajectory curve 24 as a spiral, which in the illustration shown is designed as a circular spiral. The radius of the illustrated planar spiral increases in circular coordinates with increasing angle of rotation ϕ, so that: r φ = φ · d T / 2 π

[0088] In this equation, d T denotes the distance between the spiral arms; it is Figure 10 which shows an enlarged section of the Figure 9 The distance between the individual spots 6, onto which the pulsed laser radiation is focused and at which, for example, a plasma bubble is generated by a laser pulse, is constant in the spiral equal to ds, so that the angular distance Δϕ between the individual spots 6, at which a laser pulse is introduced into the tissue, is: Δφ = d S / r

[0089] Since, as already mentioned, the lenticule surface 20 is generally non-spherical, the trajectory curve 24 along which the laser focus is adjusted is an elliptical spiral, for which, of course, a constant distance between the spiral arms is no longer given. However, a respective trajectory distance d Tb and d Ta can be defined along the principal axes a and b, as Figure 11 shows.

[0090] In Figure 10 Spots 6 are shown to indicate the position of the focus for the individual laser pulses. In fact, the plasma bubbles naturally expand so much after the introduction of the respective laser pulse that the cutting surface is created, and the trajectory curve 24 is then no longer visible in the cutting surface.

[0091] In preparation for the surgical procedure, after defining the cutting surfaces 19 and 20, the trajectories 24 with which the cutting surfaces are created must now be defined.

[0092] When determining the trajectories 24, it must of course be taken into account that the volume 18 in the eye should ultimately be defined in the normal state. The cut surfaces 19 and 20, as explained so far, refer to the natural eye. However, it must now be taken into account that the treatment device 1, for reasons of fixation of the eye, works with a contact lens 25, which, as shown in Figure 12shown, is placed on the anterior corneal surface 15 of the cornea 5. The contact glass 25, which has already been the subject of several patent publications (as an example, reference is made to WO 2005 / 048895 A), is only of interest for the present description of the treatment device 1 or the associated methods for preparing and / or carrying out the surgical intervention insofar as it imparts a defined curvature to the anterior corneal surface 15 and, on the other hand, holds the cornea 5 spatially in a predefined position relative to the treatment device 1. With regard to the spherical curvature of the contact surface of the contact glass 25, the approach described here differs significantly from the approach described, for example, in WO 2003 / 002008 A, which uses a flat contact glass that flattens the cornea.

[0093] If the eye is pressed against the contact lens 25 with a spherical contact surface, a spatial deformation of the eye occurs. Since the cornea is usually only tangentially compressible, i.e., its thickness does not change when pressed in this way, the pressing corresponds to a transformation of the eye's coordinate system, as shown in Figure 13 shown, into the coordinate system of the contact glass, which is shown in Figure 14 This connection is known to the person skilled in the art from WO 2005 / 011547 A1, the disclosure of which is hereby incorporated in its entirety. Figures 13 and 14 Coordinates marked with an apostrophe denote the coordinates of the quantities related to the contact lens 25 or its underside 26 facing the eye.

[0094] The contact lens has another advantage. By pressing against the spherical contact lens base 26, the anterior corneal surface 15 is automatically spherical as well. The anterior cut surface 19, located at a constant distance below the anterior corneal surface 15, is thus also spherical when the contact lens is pressed against it, which leads to considerably simplified control. Therefore, completely independent of other features, it is preferable to use a contact lens 25 with a spherical contact lens base 26 and to delimit the volume by an anterior cut surface 19 and a posterior cut surface. Target points are / are specified for the anterior cut surface, which form this cut surface as a spherical surface at a constant distance d F below the anterior corneal surface 15.For the posterior incision surface, target points are / will be specified that define a curvature that, with the eye relaxed—i.e., after removing the contact lens—corresponds to the desired curvature for refractive error correction, except for the distance d F to the anterior corneal surface. The same applies to the procedure for defining the target points and the surgical procedure.

[0095] The representations in the Figures 13 and 14 show the coordinate transformation that occurs in the eye when the contact lens is put on or removed. They contain both spherical coordinates (R, α, ϕ) relative to the origin of the curved surface (corneal anterior surface 15 or contact lens underside 26) and cylindrical coordinates (r, z, ϕ) relative to the vertex of the corneal anterior surface 15 or contact lens underside 26, defined by the point of intersection of the optical axis OA.

[0096] In the coordinate transformation from the eye-related coordinate system, as in Figure 13 shown, in the system related to the contact glass according to Figure 14 the arc length, ie α•R, the radial depth (Rcv - R) and the angle ϕ are retained. The transformation of the angles that are for the natural eye, ie in the coordinate system of the Figure 13, underlying shapes of the cutting surfaces 19 and 20 is thus an important step in calculating the control variables for the three-dimensional focus adjustment device. It proceeds fundamentally differently than with a flat contact lens, in which, for example, the flap surface 19 degenerates into a plane. Essentially, only the shape for the cutting surface 20 needs to be transformed, since the cutting surface 19 is only to be formed at a constant distance d F from the anterior corneal surface 15. The cutting surface 19 is therefore a sphere in the transformed system with a radius of curvature RF that is reduced by d F compared to the underside of the contact lens.

[0097] The pressing of the cornea 5 of the eye 3 against the spherically curved contact lens underside 26 is in Figure 15The right-hand illustration shows schematically the state when the contact lens underside 26 is only in contact with the anterior corneal surface 15 at the apex. To clarify the geometric relationships, the anterior corneal surface 15 is schematically shown in Figure 15 drawn as a circle, although the spherical curvature is only present in a smaller circular section. Pressing the contact lens 25 onto the cornea 5 causes the transition to the state of the left side of the cornea, symbolized by arrow 27. Figure 15 . Removing the contact lens 25 causes a relaxation of the eye 3 opposite to the direction of the arrow 27

[0098] Due to the described conditions, the coordinates for each point in the cornea 5 are transformed from the Figure 13 system shown in the system of Figure 14This is now taken into account when selecting the control values ​​for the focus adjustment, in that the cut surfaces 19 and 20 must be described in the transformed contact lens system, since they only have the desired shapes after removing the contact lens 26, i.e., after retransformation into the eye's natural coordinate system. Since the anterior corneal surface 15 is generally applied by suction using negative pressure, the described transformation is also referred to below as the suction transformation.

[0099] To cut the flap surface 19, which is spherical as mentioned, the following speed of adjustment of the z-scanner, ie the following feed rate in the z-direction, is set: v Z t = d S · f L · d T / 2 π · R F 2 − t · d S · f L · d T / π 1 2 , where f L is the frequency of the laser pulses of the laser radiation 2. Equation (5) assumes that the z-velocity vz can be freely adjusted and continuously changed.

[0100] If one wants to write a sphere with a velocity vz chosen from a group of discrete velocities, which is usually the case when the z-scanner is driven by a stepper motor, one obtains the time dependence of the radial function r(t): r t = d S · f L · d T · t / π − d S · f L · d T · t 2 / 2 π · R F 2 1 / 2 as well as for the angle function φ t = 4 π · d S · f L · t / d T − d S · f L · t 2 / R 2 1 / 2 .

[0101] The t 2< terms under the root of the radial and angular functions show that an ideal Archimedean spiral is no longer written, so the orbit and spot bubble distances vary in favor of the z-velocity, which only changes in steps.

[0102] If a constant z-feed is desired during the focus adjustment, the result is not a sphere, as with the speed according to equation (4), but a paraboloid, and the following applies: z r = v Z / d s · d r r 2 · π / f L

[0103] As mentioned above, in some treatment devices 1, the speed at which the z-scanner shifts the focus in the z-direction can only be adjusted within a set of discrete speeds. If one then wishes to describe a specific parabola with a given speed vz, the product dS •dT must be selected accordingly so that the first square bracket of equation (8) assumes the desired value. The distance between the paths, defined by dT, as well as the spot spacing along the path described by dS, can thus be varied to write a specific parabola with a given vz.

[0104] Each of equations (5), (6) / (7), and (8) can be used to determine the target points and thus control the focus adjustment, whereby the corresponding spiral shape / surface shape must of course be used as a basis. When it is stated below that the equations are used for control, this is to be understood in particular that the target points are determined using the equations; this can be done, for example, by evaluating the functional equations at equidistant points in time. The speed equations are used in one variant to ensure that the determined target points do not require adjustment speeds that are not even feasible for the focus adjustment device.

[0105] For the shapes of surfaces 19 and 20 mentioned above and determined as described, a spiral is now placed in the respective surface. This spiral is written using a control system as described above. The calculation of the z-velocity as well as the r- and ϕ-velocities takes into account the surface shape of surface 19 and 20, respectively.

[0106] The lenticule surface 20 is spherical if no cylinder correction is to be performed. Therefore, the control according to equations (4) / (5) or (6) / (7) is used to generate this sphere. However, as is well known, a sphere can also be approximated by a paraboloid. Therefore, one variant provides for approximating a sphere by a paraboloid, as is well known to those skilled in the art, and for the control according to equation (8).

[0107] Through the intake transformation according to Figure 15The geometry of the lenticule surface 20 changes. The lenticule surface 20 must exhibit the curvature of the corrected anterior corneal surface 15* in the coordinate system of the contact lens 25. It cannot be referenced to a center of curvature that coincides with the center of curvature of the contact lens. The curvature defined according to equation (2) is therefore converted with respect to the suction transformation.

[0108] The radius of curvature defined in equation (2) is, of course, a function of ϕ. As already mentioned and common in ophthalmology, two radii of curvature, ra and rb, can be specified: one along the axis θ of the cylindrical refractive error and one for an axis perpendicular to it. From a computational point of view, it is particularly advantageous to approximate the resulting toroidal curvature by a parabola, so that the lenticule surface 20 is approximated by a paraboloid. This is preferably done before the contact pressure transformation, but can also be performed afterward.

[0109] The approximation is achieved by finding a parabola for each of the two radii of curvature that passes through both the vertex of the lenticule surface 20 and a point located as close to the edge as possible. The corresponding relationships in the coordinate system of the eye are shown in Figure 16This figure shows the spherical lenticule surface 20 before the contact pressure transformation. In the figure, the sections through the toroidal lenticule surface 20 in the generalized case are superimposed along the two semi-axes a and b. The corresponding curves are labeled A and B respectively and are circular with a radius of curvature ra and rb respectively. On each curve, an edge point T is described in cylindrical coordinates by the corresponding radius r and the height h, whereby these parameters are related to the vertex S, which is identical for the two semi-axis sections. The point T a is therefore characterized by the radius ra and the height ha. The same applies to T b .

[0110] A parabola is now sought for which h = k - r 2< applies. The resulting parabolic parameters ha for the parabola along the major semi-axis a and kb for the parabola along the minor semi-axis b define the paraboloid, which is then written by adjusting the focus point in the z-direction, for example, by means of a constant z-feed (cf. equation (7)) or by selecting the z-speed from a set of discrete speeds (modification of equation (7)). The Figure 16 The sections of the toriodal lenticule surface 20 shown along the small main axis b and the large main axis a refer to the representation in the coordinate system of the eye.

[0111] If the approximation was performed using parabolic equations after the contact pressure transformation, the transformed values ​​naturally appear there. The explicit calculation of transformed values ​​can be avoided at this point if the approximation is performed first and the parabolic parameters found are subjected to the contact pressure transformation into the coordinate system of the contact lens, after which the Figure 17 the conditions described exist.

[0112] The specification of the parabola parameters in the coordinate system of the eye is Figure 16 as follows: k a = z T a − z S / r T a 2 , k b = z T b − z S / r T b 2 .

[0113] In equations (9) and (10), z(S) denotes the z-coordinate of point S. If the origin of the coordinate system is placed at the vertex, as in the previous figures, the z-coordinate is zero. The coordinates z(T a ) and z(T b ) as well as r(T a ) and r(T b ) are the z- and r-coordinates of the corresponding points T a and T b in the cylindrical coordinate system, respectively.

[0114] If the parabolic parameters ka and kb are not calculated in the coordinate system of the eye according to Figure 16 , but in the coordinate system of the contact lens according to Figure 17 required, the points S, T a and T a are replaced by the points Figure 17 drawn transformed points S', T a ', T b '.

[0115] To represent the lenticule surface 20 in the pressed-on eye 3 by a (then usually elliptical) spiral with the main axes ra ' and rb ', the spiral is constructed from a circular spiral with radius r 0 ' by stretching in the direction ϕ = θ and compressing in the direction ϕ = θ + π / 2. The simultaneous compression and stretching maintains the mean track or spot spacing. If compression or stretching were performed in only one direction, the mean spacing would change.

[0116] The actual radii can be calculated from the radius r 0 of the circular spiral, which is Figure 17 is shown in dashed lines, is calculated using ellipticity as follows: e ′ = r a ′ / r b ′ = k B ′ / k A ′ 1 / 2 .

[0117] The ellipticity e' is the ellipticity of the transformed toriodal lenticule surface 20. The parameters kb ' and ka ' are given by equations (11) and (12), respectively, for the transformed points S', T a ', and T b '. The parabola parameters result from the fact that the circular spiral with radius r 0 , from which the lenticule surface 20 is constructed, is supposed to be an arithmetic or geometric mean of the curvatures of the major and minor semi-axes of the paraboloid. Because r 0 ' = (ra ' • rb ') 1 / 2< we get for the parabola parameter k = (ka • kb ) 1 / 2< as well as the semiaxes of the ellipse: ra ' = r 0 ' • (e') 1 / 2< and rb ' = r 0 ' • (e') -1 / 2< .

[0118] At this point in the determination of the target points, two trajectories 24 are now available, which are described by functional equations. The pattern of the target points is determined by evaluating the functional equations.

[0119] However, it must still be considered that the focusing of the laser beam into focus 7 is subject to a focus position error. This focus position error is a property of the optical system, i.e., it is based on the optical implementation used. It is essentially determined by the optical design. Due to finite manufacturing accuracies within the permissible tolerance, the focus position error is also device-specific. It is therefore expediently determined independently for each device.

[0120] The focus position error is taken into account using a generally non-linear transformation (hereinafter also referred to as NL transformation). It is therefore not possible to perform the NL transformation by modifying the trajectory parameters. In a preferred embodiment, the focus position error is expressed using a correction table or a correction function. This is derived from a measurement of the optics of the treatment device 1. The measurement can be device-type-specific or device-specific. The correction function can be obtained from an interpolation of the measurement results, e.g., using polynomials or splines. The focus position error is usually rotationally symmetrical with respect to the optical axis. In cylindrical coordinates, it then depends only on r and z.

[0121] The points previously calculated using the trajectories are pre-distorted in the NL transformation so that, after the laser spots are introduced, they are positioned exactly at the desired location using the optical system that exhibits the focal position error. Applying the pre-distorted coordinates thus compensates for the focal position error occurring in the optical system.

[0122] The NL transformation is based on the idea that for every point with the coordinates (z, r), there is a contact glass sphere shifted by z 0 on which this point lies. The vertex of this sphere is then precisely at z 0 (z, r) = z - z KGL (r). The effect of the predistortion to compensate for the focus position error is Figure 18It shows the contact glass underside 26, which is spherical in the present example, but can also have a different shape. Due to the predistortion, it becomes a transformed contact glass sphere 26^. The parameters that take the predistortion of the focus position error into account are shown in Figure 18 symbolized by an appended "^". For a transformed axis point in the cornea, z 0 ^ = z 0 . This takes into account the fact that the focal position error, although usually rotationally symmetric, also results in a shift in the z-direction.

[0123] For pre-distortion, the calculated trajectories are converted into individual target point coordinates for the spots, which are then Figure 18The correction transformation symbolized by K(r, z), i.e., the NL transformation, can be shifted. If the focus position error is specified as a function K, the coordinate of each target point only needs to be evaluated with the function to obtain the shift or the transformed coordinate.

[0124] The result is a set of target point coordinates for surfaces 19 and 20, along which the focus is guided. Through the NL transformation and the contact pressure transformation, the coordinates, relative to the natural, i.e., naked eye, lie exactly in the desired anterior and posterior intersection surfaces 19 and 20.

[0125] The coordinates for the target points thus obtained must then be converted into control signals for the three-dimensional deflection unit, e.g., the xy scanner and the z scanner. For this purpose, a corresponding functional relationship or characteristic map is used that is known for the scanners and may have been determined in advance.

[0126] In particular, the response function was previously determined for the xy scanners, which in the example are implemented as galvanometer mirrors. Applying a frequency sweep to the galvanometer mirrors and measuring the actual galvanometer movement yields an amplitude and phase response function. These are taken into account when determining the control signals.

[0127] Furthermore, to simplify control, the scanner is not given a signal for the target to be approached for each point. Instead, the control unit 12 specifies support points that characterize the scanner's trajectory. This significantly reduces the number of points. This can be advantageously exploited in the NL transformation by subjecting only those target points for the trajectory curves to the transformation that are intended to be support points for control. In one embodiment, the evaluation of the functional equations is thus carried out using a time interval that is shorter than the time interval between the laser pulses.

[0128] Thus, before the NL transformation, the trajectory points are filtered, which provides the aforementioned support points—i.e., points at a frequency of the scanner control—for the transformation. Equivalent to such filtering is an evaluation of the functionally described trajectories at support points spaced according to the scanner control. This reveals a further advantage of the function-based approach described here: The decision as to which points are target points for controlling the focus adjustment device only needs to be made before the NL transformation. Only the trajectory parameters need to be appropriately converted beforehand. Furthermore, only then are data sets with a large number of points available.

[0129] The support points thus define target points that form only a subset of the set of points to which a laser pulse is delivered. This is Figure 10illustrated, in which those spots 6 which are a target point 28 in the control data set are marked as black filled circles.

[0130] This approach also has the advantage that the maximum frequency fs that occurs when controlling the scanner is much lower than the laser pulse frequency fp . For example, a control frequency of 20 kHz and a laser pulse frequency of 200 kHz can be used. As a result, one or more spots 6 are located between the target points 28 that are specified when controlling the scanner, to which pulsed laser radiation is also emitted.

[0131] Thus, not only is pulsed laser radiation emitted while the scanners are in an adjustment process, for example, while the galvanometer mirrors are moving, but laser pulses are deflected by the scanners as they move from one predetermined target point to the next. To achieve the highest possible deflection speed, this movement represents an oscillation, which in the case of perfect circular spirals (as occurs in the anterior cutting surface 19) is even a purely sinusoidal oscillation. Since the actual spiral shape of the lenticule surface 20 also deviates only slightly from ideal circular or elliptical spirals, the scanners can be operated close to their cutoff frequency, so that the described paths along which the spots are arranged allow for very fast cutting surface generation.

[0132] After determining the control data sets containing the target points from the described point sets obtained for the trajectories, the preliminary procedure performed to provide the corresponding control values ​​or parameters is completed. Human intervention, and in particular the involvement of a physician or surgeon, is not required for this preliminary procedure. The procedure is carried out by the control unit 12 without the intervention of a physician. Their presence is only required for the subsequent surgical procedure.

[0133] The procedure for preparing the device 1 for use in an ophthalmic refractive error operation is shown schematically in Figure 19summarized. In a step S1, the eye 3 is measured. In this process, correction parameters are obtained for the visual impairment present in patient 4, such as those commonly found for conventional glasses. The parameters established in step S2 are then used in a step S3 to determine the new curvature of the cornea 5 required for the correction. Once this calculation is completed in step S3, the volume that must be removed from the cornea is determined in S4. This is usually done by determining the lenticule area 20 and the flap area 19 in a step S5. Once the corresponding functional descriptions of these areas have been obtained, the suction transformation that occurs when the eye is sucked onto the contact lens is taken into account in step S6.

[0134] Next, the coordinates of the trajectories from which the cutting surfaces are constructed are determined. This is schematically indicated in step S7 by the parameters r, ϕ, z. At the end of step S7, a point pattern is created with the coordinates of the spots to be impacted by a laser radiation pulse. The density of the target points can be reduced to simplify the computational effort by not specifying a reference point for each spot exposed to laser radiation when controlling the scanners.

[0135] Subsequently, the coordinate set thus obtained is transformed again in step S8 to account for the focus position error. In step S11, the actual control parameters are determined, incorporating a response function obtained in step S10 from a previous measurement (step S9) of the scanner's amplitude and frequency response.

[0136] With the control parameters determined in this way, the actual operation is then carried out in step S12, in which additional spots are now preferably exposed to laser radiation pulses between the individual support points on which the control of the scanner is based.

Claims

1. A treatment apparatus for the surgical correction of defective vision in an eye (3) of a patient (4), which has a laser device (L) that separates corneal tissue by irradiating pulsed, focused laser radiation (2) , a contact glass (25) for placing on and fixing the eye (3), which gives the corneal front surface (15) a known spherical shape, and a planning device (P), wherein the planning device (P) - comprises an interface (S) for receiving measurement data about parameters of the eye (3) and defective vision data about the defective vision of the eye (3) to be corrected, - defines a volume (18) from the received measurement and defective vision data, which volume is situated within the cornea (5) and the removal of which from the cornea (5) effects the desired defective vision correction, - defines a boundary surface (19, 20) which confines the defined volume (18) within the cornea (5), and - for this boundary surface (19, 20) generates a control data set for controlling the laser device (L), which defines in the cornea (5) a three-dimensional pattern of target points (28) which lie in the boundary surface (19, 20) and are arranged in such a way that, after irradiating the pulsed laser radiation (2) in accordance with the control data set, the boundary surface (19, 20) is formed as a cut surface which isolates the defined volume (18) in the cornea (5) and thus makes it removable, characterized in that - the planning device (P) composes the boundary surface from an anterior surface part (19) and a posterior surface part (20), the anterior surface part (19) being a paraboloid that approximates a sphere that lies at a constant distance from the corneal front surface (15), and the posterior partial surface (20) does not have a constant distance from the corneal front surface (15).

2. The treatment apparatus according to claim 1, characterized in that the defective vision data includes the refractive power BBR of a pair of glasses (17) suitable for correcting defective vision, and the distance dHS, at which the spectacles (17) with the refractive power BBR must lie in front of the apex of the cornea in order to achieve the desired correction of defective vision by means of the spectacles (17).

3. The treatment apparatus according to claim 2, characterized in that the planning device (P) defines the volume (18) such that the corneal front surface (15*) of the eye (3) assumes a radius of curvature RCV* after removal of the volume (18), and uses the following equation for this purpose RCV * = 1 / 1 / RCV + BBR / nc − 1 1 − dHS · BBR + F , where RCV is the radius of curvature of the cornea (5) before removal of the volume (18), nc is the refractive power of the material of the cornea (5) and F is a factor, in particular F = 1 − 1 / nc • dC* − dC , where dC and dC* denote the thickness of the cornea (5, 5*) and after removal of the volume (18), respectively, and the planning module (P) iteratively calculates the radius RCV* by iteration step, the difference (RCV* - RCV) is used to infer the size (dC* - dC) and the corresponding result obtained therefrom for the change in thickness is used in the calculation of RCV* in the next iteration step.

4. The treatment apparatus according to one of the above claims, characterized in that the laser device (L) comprises a three-dimensional focus adjustment device (28) which adjusts the focused laser radiation (2) along a path (24) over the pattern of target points (28) and also emitting pulses of the pulsed laser radiation (2) into the cornea (5) at points (6) which lie on the path (24) between the target points (28).

5. The treatment apparatus according to one of the above claims, characterized in that it comprises a three-dimensional focus adjustment device and the control unit (12) is configured to control the three-dimensional focus adjustment device (9, 11) so as to that it adjusts the three-dimensional focus adjustment device (9, 11) in such a way that the latter adjusts the focus (7) of the focused laser radiation (2) along a path, the treatment apparatus applying the pulsed laser radiation during continuous adjustment of the focus position, and cylindrical or spherical coordinates being used to control the position of the focus (7).

6. The treatment apparatus according to one of the above claims, characterized in that the boundary surface (19, 20) bounds a volume (18) within the cornea (5), isolates it in the cornea (5) and thus makes it removable, and the volume (18) covers the pupil of the dark-adapted eye (3).

7. The treatment apparatus according to one of the above claims, characterized in that a data link or a data carrier is provided for transmitting the control data from the planning device (P) to the laser device (L).

8. The treatment apparatus according to one of the above claims, characterized in that a measuring device (M) for determining measurement data relating to parameters of the eye (3) and defective vision data relating to the defective vision of the eye (3) to be corrected is connected directly to the treatment apparatus (1).

9. The treatment apparatus according to one of the above claims, characterized in that it comprises a display device for visually displaying the control data and an input device for subsequently modifying the control data.

10. The treatment apparatus according to one of the above claims, characterized in that it comprises a three-dimensional focus adjustment device and the control unit (12) is configured to control the three-dimensional focus adjustment device (9, 11) so that it adjusts the focus (7) of the focused laser radiation (2) along a path which comprises a curve in the form of a spiral.

11. The treatment apparatus according to one of the above claims, characterized in that the corneal deformation that occurs when the curved contact glass (25) is used is taken into account in the control data set, so that a desired interface (19, 20) is present in the eye (3) not deformed by the contact glass (25) independently of the degree of deformation.

12. The treatment apparatus according to one of the above claims, characterized in that the laser device (L) focuses the laser radiation (2) by means of an optical system into a focus (7) which covers a spot (6), and emits pulses of the laser radiation (2) into an area of the cornea (5), the spots (6) overlapping for a plurality of the pulses.