Device for the surgical correction of refractive errors in an eye and method for generating control data for this purpose

Abstract

Method for generating control data which are designed to control a laser processing device (L) for the surgical correction of refractive errors of an eye (3), wherein an anterior cutting surface (19), a posterior cutting surface (20) and a marginal cut (30) are defined for the delimitation of a volume (18) in the cornea (5), which are to be generated as cutting surfaces in the cornea (5), wherein - the posterior cut surface (20) has a non-circular, oval edge (38) which lies in a plane (40), - the marginal cut (30) connects the marginal (38) with the anterior cut surface (19) and - the boundary section (30) is formed as the lateral surface of a non-rotationally symmetric cylinder or truncated cone, whose guide curve is the boundary (38).

Description

[0001] The invention relates to a device for the surgical correction of refractive errors in an eye and a method for generating control data for controlling the device, wherein, for the removal of a volume in the cornea, an anterior surface, a posterior surface, and a marginal incision are defined, which are to be created as cutting surfaces in the cornea. The invention further relates to a method for the surgical correction of refractive errors in a patient's eye, wherein a volume in the cornea is isolated by defining an anterior surface, a posterior surface, and a marginal incision, which are created as cutting surfaces in the cornea and which delimit the volume, wherein the method is not performed on a living human or animal body.

[0002] The classic way to correct refractive errors in the human eye is with glasses. However, refractive surgery is increasingly used, which corrects refractive errors by altering the cornea. The aim of these surgical methods is to selectively modify the cornea to influence its refraction of light. Various surgical techniques are available for this purpose. The most widespread currently is laser-assisted in situ keratomileusis, also known as LASIK. In this procedure, a corneal flap is first detached from the corneal surface on one side and folded back. This flap can be detached using a mechanical microkeratome or a laser keratome, such as those distributed by Abbott Medical Optics Inc., Santa Ana, USA.After the corneal flap is detached and folded back, the LASIK procedure involves the application of an excimer laser, which ablates the exposed corneal tissue. Once the volume of tissue in the cornea has been vaporized in this way, the corneal flap is folded back into its original position.

[0003] The use of a laser keratome to expose the lamella is advantageous because it reduces the risk of infection and improves the cut quality. In particular, the lamella can be produced with a much more consistent thickness. The cut is also potentially smoother, which reduces subsequent optical disturbances caused by this interface, which remains even after the operation. To create the cut, a series of optical openings are produced at predetermined locations to form the cut surface. With the laser keratome, this cut surface forms the lamella that is folded back before the laser ablation procedure.

[0004] In the conventional LASIK method, exposed corneal tissue is vaporized, a process also known as "resurfacing" the cornea using laser radiation. The volume removal necessary for refractive error correction is adjusted for each area of ​​the exposed cornea by the number of laser pulses and their energy. Therefore, the LASIK method uses a so-called "shot file" for the ablation laser, which specifies how often the laser beam should be directed at defined points on the cornea and at what energy. The volume removal is determined heuristically, not least because it depends heavily on the ablation effect of the laser beam, i.e., on the wavelength, fluence, etc., of the radiation used. The condition of the cornea also plays a role; in particular, its moisture content.WO 96 / 11655 A1 describes a device and a method for the LASIK procedure. In particular, it specifies a formula that calculates the achievable corneal radius of curvature from the pre-operative corneal radius and the desired diopter correction. A similar calculation is described in EP 1153584 A1 – also for corneal ablation using LASIK.

[0005] US 5993438 A proposes removing a volume from the cornea by evaporation and absorption in the cornea.

[0006] WO 2005 / 092172A1 discloses how refractive power measurements obtained in one plane can be transformed into another. The document mentions that this procedure can be used for various ophthalmic treatments, in particular for laser-assisted ablation.

[0007] Another laser-based ophthalmic surgical procedure involves isolating the corneal volume to be removed not by vaporizing it, but by making a laser incision. The volume is therefore no longer ablated, but isolated within the cornea by a three-dimensional incision, thus making it removable. Experiences developed for corneal ablation using laser radiation are not applicable to such procedures. Instead, control data for operating the laser to isolate the corneal volume to be removed are required. Such an ophthalmic surgical procedure is described in US 6,110,166 A and US 7131,968 B2. US 6,110,166 A illustrates various volume shapes and states that a person skilled in the art can select the appropriate volume.

[0008] DE 102006053117 A1 and DE 102006053118 A1 describe the generation of control data for volume-isolating refractive error correction.

[0009] From DE 102006053120 A1 and DE 102006053119 A1 of Carl Zeiss Meditec AG, it is known to generate such control data based on refractive error data that specifies the refractive power of spectacles suitable for refractive error correction. It is also known from this document, which thus describes a method and a device, to use data that also effect astigmatism correction or corrections of higher aberration orders. The approach known from DE 102006053120 A1 achieves a significant simplification of preoperative eye measurements by using refractive error data intended for conventional spectacle correction, since the generation of spectacle correction data is daily practice in ophthalmology.This simplification, however, also entails a certain limitation of the possible correction results, because inevitably only corrections that would also be possible with normal glasses can be achieved. It should also be noted that corrections such as those possible with progressive lenses are not applicable to the approach according to DE 102006053120 A1, since such corrections always assume that the visual axis passes through the lens at different points depending on the direction of gaze. This makes it possible to utilize different optical properties of the glasses for different viewing directions (e.g., when reading more downwards or seeing distant objects more towards the distance). This is not applicable to refractive surgery of the cornea, because the cornea naturally moves along with the eye when the direction of gaze changes.Unlike with a spectacle lens, there is no change in the point where the visual axis passes through the cornea when the eyeball rotates. The approach known from DE 102006053120 A1 can therefore only use relatively simple spectacle refractive error correction data as input for the control data – with the consequence of correspondingly limited correction possibilities.

[0010] From DE 10334110 A1 of Carl Zeiss Meditec AG, it is known to generate a cross-sectional area that at least partially delimits the volume to be separated for refractive error correction by adjusting the focus of the laser beam along circular paths following contour lines or along a spiral oriented to such contour lines. The planes in which the contour lines are defined, or on the basis of which the spiral is defined, are oriented perpendicular to the main direction of incidence of the processing laser beam. This ensures that the adjustment of the focus along the optical axis, which is usually carried out by an adjustable zoom lens or similar device, has as little impact as possible on the processing speed of the path.Since this focus adjustment is usually much slower than the deflection perpendicular to the main direction of incidence of the processing laser radiation, this results in a fast overall generation of the cutting surface.

[0011] This publication describes how non-spherical cut surfaces are required for refractive error corrections that go beyond spherical correction, for example, to correct astigmatism; such as a posterior cut surface in the form of an ellipsoid. In this context, DE 10334110 A1 describes how such a cut surface, viewed along the main direction of incidence of the radiation, should be given a circular outline in top view if the processing laser radiation is deactivated in sections extending beyond this circular outline. Fig. Figure 11 illustrates the conditions present. It shows a cross-sectional view through a cornea 5 in which a volume 18 is isolated and prepared for removal. The volume 18 is defined by an anterior section 19 and a posterior section 20, both of which are essentially parallel to the anterior corneal surface 15. The posterior section 20 thus defines (together with the anterior section 19) the curvature that the anterior corneal surface 15 has after removal of the volume 18. It is therefore of particular importance for optical correction and is thus also referred to as the correction surface. In the lower part of the Fig. Figure 11 shows a top view 33 of the posterior cross-sectional surface 20. Fig. Figure 11 shows a case where astigmatic correction is to be applied, which is why the correction surface follows an ellipsoid. In the upper part of the Fig. Figure 11 shows two section lines 20.1 and 20.2 for the section surface 20, corresponding to the principal axes H1 and H2 of the correction surface. In the top view 33, the volume 18 has a circular outline. Furthermore, the ellipsoidal posterior section surface 20 is generated by a spiral path 32, along which the position of the focus of the processing laser radiation is adjusted, i.e., on which the centers of the laser beam pulses lie that produce the processing effect in the cornea 5. To ultimately achieve the circular outline of the posterior section surface 20, the processing laser radiation is dark-scanned in areas of the spiral 32 that lie outside the circular outline, i.e., modified so that no processing effect occurs there. Then, a truncated circular cone-shaped edge cut 30 establishes the connection between the posterior section surface 20 and the anterior section surface 19.In the top view 33 of the posterior section surface 20, this is illustrated by a cross-hatched lenticule rim zone 31 that extends so deep into the cornea that the volume 18 is isolated by the anterior section surface 19, the posterior section surface 20 and the frustoconical or circular cylindrical lenticule rim surface 30.

[0012] WO 2010 / 084162 A2 describes how non-rotationally symmetric correction surfaces are extended to a circular posterior cross-sectional surface by means of a transition zone. For this purpose, the outline of the correction surface, which lies in one plane, is extended by the transition zone, also lying in one plane, such that the posterior cross-sectional surface forms a rotationally symmetric circle in plan view. Here, too, a truncated circular cone or circular cylindrical boundary surface is used to connect the posterior and anterior surfaces.

[0013] Like DE 10334110 A1 or WO 2010 / 084162 A2, the invention relates to the concept of correcting optical aberrations of the human eye by using laser radiation to separate a volume of tissue in the cornea, which is then removed from the cornea. This achieves a targeted change in the refractive power of the cornea. This change occurs locally, i.e., in the area of ​​the cornea from which the tissue volume is removed. The pupil of the eye is typically used as a guide. Removing the separated volume alters the geometry, namely the curvature, of the corneal surface. Therefore, to achieve the desired refractive error correction, the separated volume to be removed must have specific properties with regard to its shape. Similar to the classic LASIK procedure, the separated volume is typically defined by three interfaces.An anterior surface is preferably created at a constant distance beneath the cornea. This is particularly easy when the cornea is flattened with a flat contact lens. Since this surface is furthest forward, it is called the anterior surface or, in analogy to the well-known LASIK procedure, the flap or cap surface. The volume is further bounded by a deeper surface, which can be called the posterior surface or, since the volume can be considered a lenticule, the lenticule surface. Care is taken to ensure that the total volume removed alters the curvature of the anterior corneal surface. One of the two surfaces, usually the posterior one, typically has a geometry that is crucial for correcting the refractive error. In principle, one could consider shaping the anterior and posterior surfaces so that they share a common cutting line.This is not possible in farsightedness correction, as the volume to be removed must be thinner in the center, i.e., in the area of ​​the visual axis, than at the periphery. Furthermore, for surgical reasons, a certain minimum thickness of the volume at the periphery is also desired in nearsightedness correction to facilitate its removal. Therefore, the anterior and posterior surfaces are connected by a so-called lenticule rim, which is also referred to as the rim incision. The separated volume can be removed through these three incision surfaces, as the volume is then completely or almost completely enclosed by them. The absolute position and relative extent of these surfaces within the cornea define the zone within which the optical effect occurs after the removal of the separated volume. As already mentioned, the pupil serves as the reference point here.This approach necessitates that the two cut surfaces—the anterior and the posterior—of which one or both may be optically effective, must be joined to form a closed volume that is appropriately positioned within the cornea. Since there are also device-related constraints, such as the possible degrees of freedom of the laser beam deflections, as well as application-related constraints, such as regression effects during the healing process, the surgical manageability of the tissue volume to be removed, the maximum tolerable time for generating the cut surfaces, etc., the resulting overall constraint problem is quite complex.

[0014] The invention is based on the objective of making the definition of the closed volume within the cornea as application-friendly as possible and, in particular, of ensuring that the boundary of the volume is safe and easy to achieve.

[0015] This task is solved by a method for generating control data for controlling a laser processing device for the surgical correction of a patient's refractive error in one eye. To remove a volume from the cornea, an anterior surface, a posterior surface, and a marginal cut are defined, which are to be created as cutting surfaces in the cornea. The posterior cutting surface has a non-circular, oval border that lies in a plane. The marginal cut connects the border to the anterior cutting surface and is designed as a non-rotationally symmetric cylinder or truncated cone whose base is the border.

[0016] This task is further solved by a device for generating control data, which is designed to control a laser processing device for the surgical correction of refractive errors in a patient's eye. To remove a volume from the cornea, an anterior surface, a posterior surface, and a marginal cut are defined, which are to be created as cutting surfaces in the cornea. The posterior cutting surface has a non-circular, oval border that lies in a plane. The marginal cut connects the border to the anterior cutting surface and is designed as a non-rotationally symmetric cylinder or truncated cone whose base is the border.

[0017] The problem is ultimately solved by a procedure for the surgical correction of refractive errors in an eye, in which an anterior cut, a posterior cut, and a marginal cut are defined to remove a volume. These cuts are created in the cornea, but the procedure is not performed on a living human or animal body. The posterior cut has a non-circular, oval rim that lies in a plane. The marginal cut connects the rim to the anterior cut. The marginal cut is formed as a non-rotationally symmetric cylinder or truncated cone, the base of which is the rim.

[0018] Understanding the invention requires distinguishing between different surfaces or cut surfaces that define the boundary of the volume to be harvested for refractive error correction. The volume is bounded by an anterior cut surface, which, in accordance with the known LASIK procedure, is referred to as the anterior cut surface, anterior surface, flap surface, or flap cut (or cap surface or cap cut). Posteriorly, the volume is bounded by a posterior cut surface, posterior surface, lenticule surface, or lenticule cut. At least one of these surfaces affects the postoperative curvature of the anterior cornea, i.e., the curvature of the anterior cornea after the volume has been harvested. For the sake of simplicity, this description assumes that the corrective surface is exclusively the posterior cut surface.However, this should not be interpreted as a limitation.

[0019] The corrective area of ​​the relevant cut surface(s) is referred to in the prior art as the correction zone. For example, the correction zone as described in WO 2010 / 084162 A2 or DE 10334110 A1 forms part of the posterior cut surface. Optionally, in the present invention, the entire posterior surface forms the correction zone. This is the case, for example, when astigmatism is taken into account in a refractive error correction. Due to the different refractive power along the principal axes of the eye in astigmatism, the posterior surface of the correction zone is non-circular. For this purpose, the posterior surface has an oval edge. In a further development, unlike in the prior art, no transition zones are necessary to create a connection between the edge of the correction zone lying in a plane and the edge of the posterior surface.In another advanced training course, a non-rotationally symmetric correction zone is extended to a posterior cut surface with an oval border using transition zones. The methods for generating the transition zones described in WO 2010 / 084162 A2 can be used for this purpose with appropriate modifications.

[0020] In the present invention, "oval" is understood in the usual mathematical sense, namely as a closed, twice continuously differentiable, convex curve lying in a plane. The oval edge of the posterior surface thus has no corners, lies in a plane, and is always curved in one direction. An example of a surface with an oval edge is an egg-shaped surface. Normally, oval also includes circular shapes, but this is excluded for the purposes of this invention.

[0021] The anterior and posterior cross-sectional surfaces do not yet circumscribe a closed volume. A boundary section, which connects the boundary of the posterior cross-sectional surface to the anterior cross-sectional surface, is still needed. Since the boundary of the posterior surface is oval and directly adjoins the boundary section, the boundary section has a base boundary formed by the boundary of the posterior surface. To connect the posterior cross-sectional surface to the anterior cross-sectional surface, the lateral surface of a non-rotationally symmetric body, namely a non-rotationally symmetric cylinder or a non-rotationally symmetric frustum, is used as the boundary section. The circumferential surface has the base boundary as its directrix. The term "directrix" is used here in the usual mathematical sense, as known, for example, from Bronstein I., Taschenbuch der Mathematik (Pocketbook of Mathematics), Teubner Verlag, 22nd edition, 1985, section 2.6.2.4.

[0022] The cylinder or truncated cone is preferably straight, i.e., the height of the cylinder / truncated cone is perpendicular to the plane in which the oval rim lies.

[0023] The distance between the base edge and the anterior cutting surface, i.e., the height of the cylinder or truncated cone, optionally has a minimum extent. This is provided to ensure that the volume to be removed has a minimum thickness and a certain degree of stability. This prevents damage to the lenticule being removed, which could lead to corneal residue and thus affect the refractive error correction.

[0024] In the case of a cylindrical surface, the upper edge, which lies in the anterior cross-section, is identical in shape to the base edge. The anterior cross-section can be more extensive than the cylinder's upper edge. Due to the generating lines that always pass through a vertex there, the upper edge of a truncated cone's surface is either larger or smaller than the base edge, so that the upper edge represents an identical enlargement or reduction of the base edge.

[0025] The marginal incision thus has a non-circular base and top edge and coincides with the oval edge of the posterior incision surface at its base. Consequently, with an oval correction zone, there is no transition zone in the posterior incision surface to transform the oval edge into a circular one; instead, the marginal incision abuts the edge of the correction zone without any gap. Therefore, less volume is removed from the cornea, as the volume beneath the transition zones used in prior art techniques does not need to be removed. Furthermore, the incision procedure is simplified because no transition zones are required. The posterior incision surface is created using established methods, and the marginal incision is then made in the cornea. By omitting the transition zone, the procedure can also be performed more quickly.

[0026] Furthermore, the transition zone prevents the actual refractive power change from deviating from the calculated refractive power change. Additionally, the computational effort required to generate the posterior cross-sectional area can be reduced, as methods for generating the transition zones are no longer necessary. Moreover, the technically complex dark-scanning of laser radiation is no longer required.

[0027] As mentioned, it makes no difference whether one or two corrective surfaces are used. If only one corrective surface is used, this is usually the posterior cut surface, as it is generally created first. However, this is not mandatory. If only one corrective surface is used (e.g., the posterior cut surface), the other surface (e.g., the anterior cut surface) must be at a constant distance from the anterior corneal surface. In the case of two corrective surfaces, the information regarding the design of the corrective surface applies equally to both.

[0028] For refractive error correction that, as a higher aberration correction, only affects astigmatism, it is preferred that the posterior surface has an elliptical border. Due to the elliptical border, the border section exhibits an elliptical guiding curve for the cylinder or truncated cone. However, it is also possible to extend a non-rotationally symmetric or non-elliptical correction surface to a posterior section with an elliptical border. The methods for generating the transition zones described in WO 2010 / 084162 A2 can be used for this purpose with appropriate modifications.

[0029] To minimize the volume of corneal tissue removed, it is preferred in advanced training that the marginal incision connects the posterior surface to a circumferential line of the anterior surface. If the marginal incision is cylindrical, the edge of the posterior incision surface should be identical to the circumferential line of the anterior incision surface. If a truncated cone is used for the marginal incision, the area in the plane bounded by the edge is larger or smaller, but has the same shape as the anterior surface.

[0030] The design of the edge of the posterior cut surface is particularly simple if the plane of the edge is perpendicular to a principal direction of incidence of the laser radiation used to generate the cut surfaces. In particular, the plane in which the circumferential line of the anterior cut surface runs is also perpendicular to the principal direction of incidence of the laser radiation. If the edge cut is a cylinder, the circumferential surface of the edge cut is parallel to the principal direction of incidence.

[0031] All variants of the process for generating the control data can be executed without human intervention. In particular, they can be carried out by a computer, which, under the control of a program according to the invention, executes the process and determines the control data for the laser device from corresponding specifications. The process merely prepares a therapy device. Specifically, the involvement of a physician is in no way required for determining the control data, since no therapeutic intervention is involved in determining the control data. This only occurs at the earliest when the previously determined control data is applied.

[0032] Insofar as this description describes methods or individual steps of a method for determining control data for optical refractive error correction, the method or individual steps of the method can be carried out by a suitably designed device. The same applies to the explanation of the operating mode of a device that performs method steps. In this respect, the device and method features of this description are equivalent. In particular, it is possible to implement the method with a computer on which a corresponding program according to the invention is executed.

[0033] The features described here can also be combined in any way, as long as they do not contradict each other technically.

[0034] With regard to the surgical procedure that is not performed on a living human or animal body, the considerations, developments and advantages set out in connection with the procedure for generating control data and the device for generating control data apply analogously.

[0035] The invention is explained in more detail below with reference to the drawings by way of example. The drawings show: Fig. 1 a schematic representation of a treatment device or appliance for correcting refractive errors, Fig. 2. A schematic representation of the structure of the treatment device. Fig. 1, Fig. 3. A schematic diagram of the introduction of pulsed laser radiation into the eye during refractive error correction with the treatment device of the Fig. 1, Fig. 4 another schematic representation of the treatment device of the Fig. 1, Fig. 5 a schematic cross-sectional view through the cornea showing a volume to be removed to correct refractive error, Fig. 6. A cut through the cornea after removal of the volume of the Fig. 5, Fig. 7 a sectional view similar to the Fig. 5, Fig. 8 a schematic cross-sectional view through the cornea to illustrate volume removal, Fig. 9 a diagram showing possible progressions of a refractive power distribution, which is used to determine the volume to be removed, Fig. 10 a flowchart for determining the volume to be removed, Fig. 11 a cross-sectional view through the cornea to illustrate an anterior and a posterior cross-sectional surface in combination with a top view of the posterior cross-sectional surface, wherein the cross-sectional surface designs correspond to the state of the art, Fig. 12 a cross-sectional view through the cornea to illustrate an anterior and a posterior cross-sectional surface in combination with a top view of the posterior cross-sectional surface, wherein a truncated cone shell is provided as the cross-sectional surface, Fig. 13 a cross-sectional view through the cornea to illustrate an anterior and a posterior cross-sectional surface in combination with a top view of the posterior cross-sectional surface, wherein a cylindrical shell is provided as the cross-sectional surface, Fig. 14 a cross-sectional view of the volume to be removed of Fig. 12 along a main axis H2, and Fig. 15 a cross-sectional view of the volume to be removed of Fig. 13 along the main axis H2.

[0036] Fig. Figure 1 shows a treatment device 1 for an ophthalmic surgical procedure similar to that described in EP 1159986 A1 and US 5549632. The treatment device 1 uses a treatment laser beam 2 to correct refractive errors in the eye 3 of a patient 4. The refractive error can include hyperopia, myopia, presbyopia, astigmatism, mixed astigmatism (astigmatism with hyperopia in one direction and myopia in a perpendicular direction), aspheric aberrations, and higher-order aberrations. In the described embodiment, the treatment laser beam 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 beam 2 acts on the cornea by means of non-linear optical effects. The laser beam has, for example, short laser pulses of 50 to 800 fs (preferably 100 - 400 fs) with a pulse repetition frequency between 10 and 500 kHz.In the described embodiment, the components of device 1 are controlled by an integrated control unit, which can of course also be designed independently.

[0037] Before the treatment device is used, the refractive error of eye 3 is measured with one or more measuring devices.

[0038] Fig. Figure 2 schematically depicts the treatment device 1. In this variant, it comprises at least two units or modules. A laser unit L emits the laser beam 2 onto the eye 3. The operation of the laser unit L is fully automatic; that is, upon receiving a corresponding start signal, the laser unit L initiates the deflection of the laser beam 2, thereby creating cut surfaces that are constructed in a manner to be described later and isolate a volume within the cornea. The control data required for operation is received by the laser unit L beforehand from a planning unit P as a control data set via control lines not specified. This transmission takes place before the laser unit L begins operation. Wireless communication is also possible. As an alternative to direct communication, it is also possible to arrange the planning unit P spatially separate from the laser unit L and provide a corresponding data transmission channel.

[0039] 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, in principle, suitable for use with the laser device L of the treatment device 1. In addition, validity can also be contingent upon passing further checks, for example, whether additional information about the treatment device 1, e.g., a device serial number, or the patient, e.g., a patient identification number, stored in the control data record matches other information that was read from the treatment device or entered separately once the patient is in the correct position for operation of the laser device L.

[0040] The planning unit P generates the control data set, which is provided to the laser unit L for executing the operation, from measurement data and refractive error data determined for the eye to be treated. This data is supplied to the planning unit P via an interface S and, in the illustrated embodiment, originates from a measuring device M that previously measured the eye of 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.

[0041] Data transfer can be carried out using memory chips (e.g., USB or memory stick), magnetic storage devices (e.g., floppy disks), wirelessly (e.g., WLAN, UMTS, Bluetooth), or via wired connections (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.

[0042] A direct wireless 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 of virtually eliminating the use of incorrect measurement and refractive error data. This is particularly true when the patient is transferred from the measuring device M(s) 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 detect whether the patient 4 is in the correct position for measurement or the application of the laser radiation 2. The transfer of the measurement and refractive error data to the treatment device 1 can also occur simultaneously with the transfer of the patient 4 from the measuring device M to the laser device L.

[0043] It is preferably ensured by suitable means that the planning device P always generates the control data record belonging to patient 4, and the erroneous use of an incorrect control data record for patient 4 is virtually impossible.

[0044] The mode of operation of laser beam 2 is described in Fig. Figure 3 schematically indicates the process. The treatment laser beam 2 is focused into the cornea 5 of the eye 6 by means of an unspecified optical system. This creates a focus in the cornea 5 that covers a spot 6, and in this focus 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 can create an optical breakthrough in the cornea 5 at the respective spot 6, which in turn produces a Fig. A plasma bubble, shown schematically in Figure 3, is initiated. This laser pulse separates tissue in the cornea. When a plasma bubble forms, the tissue layer separation covers a larger area than the spot 6, which is covered by the focus of the laser radiation 2, even though the conditions for generating the breakthrough are only met at the focus. 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 those skilled in the art, for example, from DE 69500997 Part 2.

[0045] Alternatively, a tissue-separating effect can also be generated by pulsed laser radiation by emitting multiple laser pulses in one area, whereby spots 6 overlap for several laser pulses. In this case, several laser pulses work together to achieve a tissue-separating effect.

[0046] The type of tissue separation used by treatment device 1 is not relevant for the following description, even though pulsed treatment laser radiation 2 is described in this description. For example, a treatment device 1 as described in WO 2004 / 032810 A2 can be used. A multitude of laser pulse foci form a cut surface in the tissue, the shape of which depends on the pattern in 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 delivered and defines the shape and position of the cut surface.

[0047] To correct a refractive error, pulsed laser radiation is used to remove material from a specific area within the cornea 5. This is achieved by separating tissue layers that isolate the material and allow for its removal. The material removal causes a change in the cornea's volume, which in turn alters the cornea's optical imaging power. This change is precisely calibrated to correct the previously determined refractive error as effectively as possible. To isolate the volume to be removed, the laser beam 2 is focused on target points within the cornea 5, typically in an area located below the epithelium and Bowman's membrane, and above Deceme's membrane and the endothelium. The treatment device 1 incorporates a mechanism for adjusting the position of the laser beam 2's focus within the cornea 5. This is shown schematically in Fig. 3 shown.

[0048] In Fig. The elements of the treatment device 1 are shown in Figure 4 only to the extent necessary for understanding the focus adjustment. As already mentioned, the laser radiation 2 is focused at a focus 7 in the cornea 5, and the position of the focus 7 in the cornea is adjusted so that energy from laser radiation pulses is focused at various points to create the incision surface and introduced into the tissue of the cornea 3. The laser radiation 2 is provided by a laser 8 as pulsed radiation. An xy-scanner 9, which in one variant is implemented 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 causes 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 is provided in addition to the xy-scanner 9; this z-scanner is designed, for example, as an adjustable telescope. 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 positioned upstream or downstream of the xy-scanner 9. The coordinates subsequently designated x, y, and z therefore refer to the deflection of the focus 7.

[0049] For the operating 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, z will always denote the coordinate along the optical axis of incidence of the laser radiation 2, and x and y will denote two mutually orthogonal coordinates in a plane perpendicular to the direction of incidence of the laser beam. It is of course known to those skilled in the art 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 need not be a rectangular coordinate system. Therefore, it is not mandatory that the xy-scanner 9 deflects about axes perpendicular to each other; 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.

[0050] 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 and cylindrical coordinates.

[0051] To control the position of focus 7, the xy-scanner 9 and the z-scanner 11, which together constitute 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, exemplified by the xy-scanner 9 and the z-scanner 11, so that the position of focus 7 in the cornea 5 is adjusted in such a way that ultimately a material of a certain volume is isolated, the subsequent removal of which achieves the desired refractive error correction.

[0052] The control unit 12 operates according to predefined control data, which specifies the target points for focus adjustment. The control data is generally summarized in a control data set. In one embodiment, this data set 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 focus positions and thus ultimately a trajectory (here also referred to simply as a path). In one embodiment, the control data set contains the target points as concrete setpoints for the focus position adjustment mechanism, e.g., for the xy-scanner 9 and the z-scanner 11. To prepare for the ophthalmic surgical procedure, i.e., before the actual surgical procedure can be performed, the target points and preferably also their sequence in the pattern are determined.Pre-planning of the surgical procedure is necessary to determine the control data for the treatment device 1, the application of which then achieves an optimal refractive error correction for the patient 4.

[0053] First, the volume to be isolated from corneal tissue 5 and later removed must be determined. As already discussed in the following... Fig. As described in point 2, this requires a determination of the need for correction.

[0054] Regarding the nomenclature used in this description, it should be noted that the addition of an asterisk to quantities clarifies that these are quantities obtained after a correction. Under the justified assumption that a change in corneal thickness 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 radius of curvature R is determined by the volume removal. CV The anterior surface of the cornea 15 is modified. The cornea 5, with its reduced volume and altered corneal surface 15*, has a correspondingly altered imaging effect due to the modified anterior curvature, resulting in a corrected focus on the retina 14.

[0055] To determine the pattern of target points, the curvature R* to be achieved is therefore used. CV the modified corneal anterior surface 15* determined.

[0056] With the value B COR The curvature of the modified anterior corneal surface 15* is now set as follows: RCV*(r,φ)=1 / ((1 / RCV(r,φ))+BCOR(r,φ)−(nC−1))+F,

[0057] In equation (1) n denotes c The refractive power of the corneal material. The corresponding value is usually 1.376; B COR This refers to a change in refractive power that is necessary for correcting refractive errors. B COR is radially dependent. Radial dependence means that there are two values ​​r1 and r2 for the radius r, for which the change in refractive power has different values ​​at all angles φ.

[0058] Examples of possible patterns of refractive power change are in Fig. 9 are shown as examples, which the function B COR in various example curves Ka to Ke as a function of the radius r.

[0059] Ka is the conventional refractive index of a spectacle of the prior art according to DE 102006053120 A1, in the representation of the Fig. 9, however, already refers to the level of the corneal apex. There is no justification for this reference in the prior art. It was included here only for better comparability with the exemplary profiles Kb to Ke according to the invention. Profile Kb extends to a radius that is beyond a radius r s The radius r is constant at its base and then decreases. s is the scotopic pupil radius, i.e., the pupil radius that occurs when seeing in the dark. The change in refractive power according to curve Kc is up to the value r. s piecewise constant, below a radius r pThe refractive power correction, which corresponds to the photopic pupil radius, jumps from a higher to a lower value. Such a variation in refractive power correction across the pupil cross-section is particularly advantageous in presbyopia. Near vision in this condition typically occurs in good lighting, for example, when reading. Due to the good lighting, the pupil is then usually constricted to the photopic pupil radius. The refractive power correction value required then provides optimal adaptation for near vision, e.g., an optimal viewing distance of approximately 25 to 70 cm. In the other extreme case, namely night vision, which is usually associated with distance vision (e.g., when driving at night), the pupil is maximally dilated. In this case, areas of the pupil with a different (e.g., lower) refractive power correction value also contribute to the optical image formation.The human brain is capable of correcting such an optically flawed image (different focus points for the center of the pupil and the peripheral areas of the pupil) during visual perception. The refractive power correction curves shown in Kc or Kd therefore allow for an increase in depth of field by consciously accepting an optical aberration, as the brain compensates for the aberration.

[0060] From the pupil radius r s The refractive power correction then decreases further. The non-step-like decrease in refractive power correction to zero is anatomically advantageous. It allows the corrected anterior corneal radius, which results from the correction, to adapt to the original corneal radius of curvature, i.e., the pre-operative radius, at the edge of the corrected area, i.e., at the edge of the volume to be removed. Regarding the representation of the Fig. 5 means that in the boundary region of the volume to be removed, where in the representation of the Fig. 5 the radii R F and R L As the radii converge, they become more aligned. This results in a smooth transition at the anterior corneal surface after correction, from the new anterior corneal radius R*. CV , which is located in the area from which volume 18 was removed, to the original corneal radius of curvature R CV comparatively. This results in a better overall optical correction, which is only achievable through radially varying refractive power correction.

[0061] The reduction of the refractive power correction to zero preferably occurs in an area outside the dark-adapted pupil radius, i.e., in an area of ​​the cornea that is no longer relevant for vision.

[0062] The curve Kd shows a similar pattern, however, here there is a gradual transition from the first value of the refractive power change below r. p , to the second value, which is at r s Instead, the first value is lower than the second value. This can, of course, also be used for curve Kc, depending on the desired correction. Curve Ke shows a moving average that decreases continuously.

[0063] The based Fig. The 9 described locally dependent changes in refractive power with radial dependence are examples of a change in refractive power that is used in determining the volume to be removed in the operation.

[0064] The factor F expresses the optical effect of the change in corneal thickness caused by the surgical procedure and can, to a first approximation, be considered a constant factor that can be determined experimentally beforehand. For highly accurate correction, the factor can be calculated according to the following equation: F=(1−1 / nc)⋅Δz(r=0,φ) Δz(r = 0, φ) is the central thickness of the volume to be removed.

[0065] For an exact determination, a calculation of R is performed. CV * iteratively, by substituting the difference 1 / R for the i-th calculation CV *(r=0,φ) - 1 / R CV (r=0,φ) is used to determine the quantity Δz(r=0,φ) and the corresponding result obtained from this for the thickness change in the (i+1)th calculation of R* CVThis process can be applied until a termination criterion is met, for example, if the difference in the result for the thickness change between two successive iteration steps falls below a predefined limit. This limit can be defined, for example, by a constant difference that corresponds to an accuracy of refractive correction appropriate for the treatment.

[0066] In general, this can be done in Fig. The procedures described in section 10 are performed. In step S1, the corneal topography is calculated from diagnostic data, as already mentioned in the general section of the description. From this topography, the radial curvature of the anterior cornea is determined. This determination can also be performed directly from diagnostic data instead of the topography data from step S1, so that step S2 is either subordinate to step S1 or directly uses diagnostic data, as described above. Fig. 10. This is clarified by the addition of “(optional)”. Step S1 is therefore optional.

[0067] In step S3, the local refractive power of the cornea is then determined.

[0068] From data of the desired refractive correction, the required local change in refractive power B is calculated in step S4. COR and using this to determine the desired local refractive power after correction from the local refractive power.

[0069] From this, the new local radius of curvature R* is obtained in section S5. CV (r, φ). Instead of calculating the local refractive power B CV In step S3, the local curvature R can also be used directly. CV from step S2, if the above equation (1) is used. It is fundamentally important to note that refractive power and radius of curvature can be converted into each other using a simple equation. The following holds true: B = (n C -1) / R, where B is the refractive power and R is the radius associated with this refractive power. Therefore, within the scope of the invention, it is possible at any time to switch between considering the radius and considering or representing the refractive power. The equation used to determine the control data in refractive power representations is: B*CV(r,φ)=11BCV(r,φ)+BCOR(r,φ)+F(nC−1)

[0070] Insofar as the radius of the anterior corneal surface is mentioned here, the refractive power can be used in a completely analogous way, so that all explanations given here in connection with the radius of the anterior corneal surface naturally also apply analogously to the representation or view of refractive power if R is replaced by B according to the aforementioned relationship.

[0071] For the volume whose removal causes the above change in curvature of the anterior corneal surface 15, the boundary surface is now defined in step S6, isolating the volume. The desired basic shape of the volume must be taken into account.

[0072] In a first approach, a free surface is defined using numerical methods known to those skilled in the art. This free surface circumscribes the volume whose removal causes the change in curvature. For this purpose, the volume thickness required for the desired curvature modification is determined along the z-axis. From this, the volume is obtained as a function of r and φ (in cylindrical coordinates), and from this, in turn, its boundary area is calculated.

[0073] An analytical calculation, however, yields the following variant, already mentioned in DE 102006053120 A1, in which the boundary surface of the volume is essentially composed of two sub-surfaces: an anterior sub-surface facing the corneal surface 15 and an opposing posterior sub-surface. The corresponding relationships are shown Fig. 5. The volume 18 is bounded towards the anterior corneal surface 15 by an anterior cut surface 19, which is at a constant distance d FThis anterior incision surface 19 lies beneath the anterior corneal surface 15. Analogous to laser keratomes, this anterior incision surface 19 is also referred to as the anterior incision surface 19, as it serves there, in combination with an opening incision towards the periphery, to lift a flap of the cornea 5 from the underlying cornea 5. This method of removing the previously isolated volume 18 is, of course, also possible here.

[0074] The anterior cut surface 19 is preferably spherical, since then a radius of curvature can be specified for it which is proportional to the lamella thickness d. F is smaller than the radius of curvature Rcv.

[0075] Posteriorly, the volume 18, which is to be removed from the cornea 5, is bounded by a posterior cutting surface 20, which cannot, by its very nature, be at a constant distance from the anterior corneal surface 15. The posterior cutting surface 20 will therefore be shaped such that the volume 18 is present in the form of a lenticule, which is why the posterior cutting surface 20 is also referred to as the posterior cutting surface. Fig. Figure 5 is an example of a spherical surface with a radius of curvature R. L drawn, whereby of course the center of this curvature does not coincide with the center of curvature of the in Fig. 5 also coincides with the spherical anterior corneal surface 15. At the edge, the two surfaces 19, 20 are preferably connected by a lenticule edge surface, which is hereinafter referred to as the edge cut 30, in order to completely delimit the volume to be removed and at the same time ensure a minimum thickness at the edge.

[0076] Fig. Figure 6 shows the conditions after removal of volume 18. The radius of the modified anterior corneal surface 15* is now R CV * and can be calculated, for example, according to the equations described above. The thickness d L The Δz(r=0,φ) of the extracted volume 18 is decisive for the change in radius, as Fig. Figure 7 illustrates this. In this simplified figure, the posterior cross-sectional surface is spherical. Consequently, the height h is also a factor. F the spherical cap defined by the anterior cut surface 19, the height h L the spherical cap defined by the posterior cross-sectional surface 20 and the thickness d L The volume to be removed is shown in 18.

[0077] The posterior cut surface 20 determines the curvature of the corneal anterior surface 15* after removal of volume 18 due to the constant distance between the corneal anterior surface 15 and the anterior cut surface 19.

[0078] If the factor F is to be considered in the calculation, the change in corneal topography is taken into account in step S7, i.e., the current mid-thickness is calculated. The resulting value for factor F can then be used to repeat steps S4 to S6 or S5 to S6, or to iterate several times.

[0079] The configuration of volume 18 shown in the figures, as bounded by an anterior cross-sectional surface 19 at a constant distance to the corneal anterior surface 15 and a posterior cross-sectional surface 20, is only one variant for limiting volume 18. However, it has the advantage that the optical correction is essentially determined by only one surface (the posterior cross-sectional surface 20), so that the analytical description of the other part of the interface is simple.

[0080] Furthermore, optimal safety margins are given 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 The distance between the anterior cut surface 19 and the anterior corneal surface 15 can be constantly set to a value of, for example, 50 to 200 µm. In particular, it can be chosen such that the pain-sensitive epithelium remains within the lamella formed by the anterior cut surface 19 beneath the anterior corneal surface 15. Furthermore, the formation of the spherical anterior cut surface 19 is consistent with previous keratometer sections, which is advantageous for the acceptance of the method.

[0081] After creating the cut surfaces 19 and 20, the isolated volume 18 is then removed from the cornea 5. This is shown schematically in Fig. Figure 8 illustrates that the cut surfaces 19 and 20 are generated by the action of the treatment laser beam incident in a focus cone 21, for example by arranging plasma bubbles in succession, so that in a preferred embodiment the anterior cut surface 19 and the posterior cut surface 20 are generated by suitable three-dimensional adjustment of the focus position of the pulsed laser radiation 2.

[0082] The features described above and below are also possible in such variants, especially with regard to the determination of the boundary surface, its geometric definition and the determination of control parameters.

[0083] If both the posterior cut surface 20 and the anterior cut surface 19 are created using pulsed laser radiation, it is advantageous to form the posterior cut surface 20 before the anterior cut surface 19, since the optical result for the posterior cut surface 20 is better (if not only achievable) if no change in the cornea 5 has yet occurred above the posterior cut surface 20.

[0084] Fig. Figure 12 shows a representation whose upper part differs from the type of view of the Fig. 5 corresponds. In the lower part, a top view 33 of the posterior section surface 20 and the edge section 30 is shown, which is illustrated in the section view above only by a section line 20.1.

[0085] To isolate volume 18, both the anterior and posterior cut surfaces 19 are created in the cornea 5 as described. This creates a correction surface that is non-circular and oval—here elliptical to correct astigmatism. As shown in the top view 33 of the posterior cut surface 20, this correction surface is created by a spiral 32 extending from the interior of the correction surface outwards. The spiral 32 defines a trajectory for adjusting the position of the laser beam focus. The center of the spiral 32 is preferably (but not necessarily) located at the highest point of the correction surface. The spiral 32 is based on contour lines, which continuously adjusts the z-position (position along the principal direction of incidence A of the laser radiation) of the focus position. Instead of a group of closed scan lines that never intersect, a single continuous scan line is present.Local location-dependent bending force corrections B(r, φ) can be easily represented and generated by modulating the angle-dependent radial function r(φ) by such a radially “deformed” spiral 32.

[0086] In contrast to the state of the art according to Fig. 11 forms a perimeter of the correction surface simultaneously a boundary 38 of the posterior cut surface 20. For the boundary 38 r MAX' (f P , φ) of the posterior cut surface 20, z = const.; it therefore lies in an x / y plane 40. The correction surface, which is required for the optical correction, thus extends over the entire posterior cut surface 20. Here, the trajectory 32 is shown as a solid line. The edge 38 of the posterior cut surface 20, like the edge of the correction surface, is therefore non-circular and oval, in particular elliptical. Therefore, no lenticule edge zone 31 is required as in the prior art according to Fig. 11 are planned.

[0087] The sectional view shows in Fig. 12, that the edge 38 of the posterior cut surface 20 lies in the plane 40, which is perpendicular to the principal direction of incidence A. It is done with a Fig. The cone-shaped marginal section 30 shown in Figure 12 establishes the connection between the posterior cut surface 20 and the anterior cut surface 19. The base of the truncated cone, whose lateral surface forms the marginal section 30, is the edge 38 of the posterior cut surface 20. The guiding curve, and thus the base edge of the truncated cone for the marginal section 30, is therefore non-circular and oval, specifically elliptical. A cover edge 42 of the truncated cone's lateral surface follows the non-circular oval profile of the base surface of the posterior cut surface 20. The marginal section 30 is in Fig. 12 are shown hatched.

[0088] The volume 18, composed of the posterior cross-sectional surface 20, the anterior cross-sectional surface 19, and the marginal cross-section 30, is in cross-section in Fig. Figure 13 shows that the oval edge 38, and thus the guide curve of the truncated cone's surface, lies in the plane 40. In particular, it is also evident that the edge section 30 intersects a circumferential line of the anterior section surface 19, so that the top edge 42 and the outline of the anterior section surface coincide. In this case, the anterior section surface 19 has the shape of the edge 38 of the posterior section surface 20. However, this is optional; the anterior section surface 19 can also be larger than the base of the truncated cone in the anterior section surface 19 or rotationally symmetric. In the first variant, the volume 18 has an oval, and in particular elliptical, outline in plan view.

[0089] The posterior section surface 20 is optionally an ellipse that can be described by principal axes H1 and H2. If the anterior section surface 19 has a circumferential line that coincides with the top edge of the marginal section 30, the anterior section surface 19 can be described by the same principal axes H1 and H2.

[0090] The in Fig. 13 and Fig. The embodiment of the volume 18 to be removed shown in Figure 15 differs from the one shown in Figure 15. Fig. 12 and Fig. In the embodiment shown in Figure 14, the edge section 30 is designed as a cylindrical shell rather than a truncated conical shell. In both embodiments, the plane 42 is perpendicular to the main direction of incidence of the laser radiation. The edge section 30 is shown in top view 33. Fig. 13 not recognizable, since the edge cut 30 is a cylinder.

[0091] The use of pulsed laser radiation is not the only way in which surgical refractive correction can be performed. Rather, the determination of control data for the operation of the device described here can be used for virtually any surgical procedure in which a volume is removed from or added to the cornea 5 by means of a device controlled by control data, as already explained in the general part of the description.

Claims

[1] Method for generating control data which are designed to control a laser processing device (L) for the surgical correction of refractive errors of an eye (3), wherein an anterior cutting surface (19), a posterior cutting surface (20) and a marginal cut (30) are defined for the delimitation of a volume (18) in the cornea (5), which are to be generated as cutting surfaces in the cornea (5), wherein - the posterior cut surface (20) has a non-circular, oval edge (38) which lies in a plane (40), - the marginal cut (30) connects the marginal (38) with the anterior cut surface (19) and - the boundary section (30) is formed as the lateral surface of a non-rotationally symmetric cylinder or truncated cone, whose guide curve is the boundary (38). [2] Method for the surgical correction of refractive error of an eye (3) wherein a volume (18) in the cornea (5) is delimited by an anterior cut surface (19), a posterior cut surface (20) and a marginal cut (30) which are produced as cut surfaces in the cornea (5) wherein - the posterior cut surface (20) has a non-circular, oval edge (38) which lies in a plane (40), - the marginal cut (30) connects the marginal (38) with the anterior cut surface (19) and - the boundary section (30) is formed as the lateral surface of a non-rotationally symmetric cylinder or truncated cone, whose guide curve is the boundary (38), - whereby the procedure is not performed on a living, human or animal body. [3] Method according to claim 1 or 2, characterized by , that the posterior cut surface (20) has an elliptical border (38). [4] Method according to claim 1, 2 or 3, characterized by , that the marginal cut (30) connects the posterior cut surface (20) with a perimeter of the anterior cut surface (19) which is similar in shape to the marginal (38). [5] Method according to claim 4, characterized by , that the anterior cut surface (19) has an elliptical perimeter. [6] Method according to any one of the above claims, characterized by , that the plane (40) of the edge (38) is perpendicular to a principal direction of incidence of a laser radiation to generate the cut surfaces (19, 20). [7] Device for generating control data which is designed to control a laser processing device (L) for the surgical correction of refractive errors of an eye (3), and for defining an anterior cut surface (19), a posterior cut surface (20) and a marginal cut surface (30) which are to be generated as cut surfaces in the cornea (5) for the delimitation of a volume (18) in the cornea (5), wherein - the posterior cut surface (20) has a non-circular, oval edge (38) which lies in a plane (40), - the marginal cut (30) connects the marginal (38) with the anterior cut surface (19) and - the boundary section (30) is formed as the lateral surface of a non-rotationally symmetric cylinder or truncated cone, whose guide curve is the boundary (38). [8] Device according to claim 7, characterized by , that the posterior cut surface (20) has an elliptical border (38). [9] Device according to claim 8 or 7, characterized by , that the marginal cut (30) connects the posterior cut surface (20) with a perimeter of the anterior cut surface (19) which is similar in shape to the marginal (38). [10] Device according to claim 9, characterized by , that the anterior cut surface (19) has an elliptical perimeter. [11] Device according to any one of claims 7 to 10, characterized by , that the plane (40) of the edge (38) is perpendicular to a principal direction of incidence of a laser radiation to generate the cut surfaces (19, 20).

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