Device and method for a laser-assisted eye-surgery treatment system

Abstract

The invention relates to an apparatus for a laser-assisted eye-surgery treatment system, comprising a first image-acquisition unit that is designed to acquire a first image (39) of an eye to be treated. The apparatus further comprises a computer arrangement which is designed to detect at least one first feature (40) of the eye by means of image processing of the first image, and to determine a position and an orientation of the first feature in a coordinate system (S) of the treatment system. The computer arrangement is also designed to determine a position and an orientation of an incision (66) to be produced in the eye in the coordinate system (S) of the treatment system as a function of the determined position and orientation of the first feature (40) in the coordinate system and as a function of a previously determined relative position and orientation of at least one second feature (64) of the eye with respect to the first feature (40).

Claims

1. Apparatus for a laser-assisted eye-surgery treatment system, comprising: a first image-acquisition unit configured to acquire a first image of an eye to be treated; and a computer arrangement configured to: detect, by image processing of the first image, at least one first feature of the eye; determine a position and an orientation of the first feature in a coordinate system of the treatment system; and determine a position and an orientation of an incision figure defining a corneal flap with a flap hinge to be produced in the eye in the treatment coordinate system of the treatment system, a beam path of the treatment system defining a z-axis of the treatment coordinate system, a plane normal to the beam path defining an xy-plane of the treatment coordinate system, the flap hinge defining a hinge axis in the xy-plane, the position and the orientation of the incision figure determined by: defining a first feature coordinate system from coordinates of the first feature in a diagnostic image, wherein the z-axis of the first feature coordinate system is normal to the top view of the eye; expressing a position and orientation of at least one second feature in the diagnostic image in the first feature coordinate system, the at least one second feature comprising an astigmatically curved corneal region, the location of the astigmatically curved corneal region described by an astigmatism axis in the xy-plane of the first feature coordinate system; determining the position and orientation of the second feature in the first feature coordinate system according to the expression of the position and orientation of the second feature in the first feature coordinate system; determining the position and orientation of the second feature in the treatment coordinate system from the position and orientation of the second feature in the first feature coordinate system; and determining the incision based on the position and orientation of the second feature in the treatment coordinate system and the astigmatism axis, the position and orientation of the flap hinge based on the astigmatism axis and defined by a predetermined set location condition between the hinge axis and the astigmatism axis.

2. Apparatus according to claim 1, wherein the set location specifies that the hinge axis and the astigmatism axis are substantially mutually perpendicular.

3. Apparatus according to claim 1, wherein the at least one first feature has been assigned to an iris, a pupil, a limbus, a scleral blood-vessel arrangement or a corneal thickness distribution of the eye.

4. Apparatus according to claim 1, including a diagnostic instrument with a second image-acquisition unit for acquiring a second image of the eye to be treated, the diagnostic instrument being configured to detect in the second image, by image processing, the at least one first feature, and to generate feature information relating to a position and orientation of each of the two features.

5. Apparatus according to claim 4, wherein the computer arrangement is configured to determine, on the basis of the feature information, the relative position and orientation of the second feature in relation to the first feature.

6. Apparatus according to claim 4, wherein the diagnostic instrument and the first image-acquisition unit have been assigned to various workstations in a medical practice.

7. Apparatus according to claim 4, wherein a database has been assigned to the diagnostic instrument, in order to store therein the feature information or information derived therefrom, with assignment to patient-identifying information, and wherein the computer arrangement has access to the database.

8. Apparatus according to claim 1, wherein the computer arrangement is configured to bring about a pictorial representation of the incision figure that illustrates the determined position and orientation of the incision figure in relation to the first feature or to the second feature or to a corneal region to be ablated.

9. Apparatus according to claim 8, wherein the computer arrangement is configured to bring about the pictorial representation on a monitor or by insertion into an observation beam path of an operating microscope.

10. Apparatus according to claim 8, wherein the computer arrangement is configured to modify the determined position or orientation of the incision figure in accordance with a user input and to modify the pictorial representation of the incision figure in accordance with the modified position or orientation.

11. Apparatus according to claim 1, wherein the computer arrangement is configured to receive a confirmation, entered by the user, for the position and orientation of the incision figure and to generate, in a manner depending on the reception of this confirmation, control data for a laser device and to control the laser device in accordance with these control data for the purpose of producing the incision figure in the eye.

12. Apparatus according to one of claims 2 to 11, wherein the incision figure further defines an auxiliary channel that extends from an incision surface of the flap in the direction away from the flap, the computer arrangement being configured to produce, in a manner depending on the determined position and orientation of at least those parts of the incision figure which define the flap, control data for the production of the auxiliary channel in such a manner that the auxiliary channel extends at least into the region of the limbus of the eye.

13. Apparatus according to claim 12, wherein the computer arrangement is configured to generate the control data for the production of the auxiliary channel in such a manner that the auxiliary channel extends beyond the limbus of the eye.

Description

(1) The invention will be elucidated further in the following on the basis of the accompanying drawings, in which:

(2) FIG. 1 shows an overall representation of an apparatus for an eye-surgery treatment system according to an embodiment,

(3) FIG. 2a shows a schematic representation of an image generated by an image-acquisition unit of the apparatus represented in FIG. 1, into which several projected images generated by a computer arrangement of the apparatus have been inserted,

(4) FIG. 2b shows a schematic representation of a diagnostic image generated by a diagnostic instrument of the apparatus represented in FIG. 1,

(5) FIG. 3 shows an overall representation of a method for an eye-surgery treatment according to an embodiment,

(6) FIG. 4 shows a further representation of a diagnostic image generated by a diagnostic instrument of the apparatus represented in FIG. 1,

(7) FIG. 5 shows a further representation of an image generated by an image-acquisition unit of the apparatus represented in FIG. 1, into which several projected images generated by a computer arrangement of the apparatus have been inserted,

(8) FIG. 6 shows a representation of an incision profile, generated by a diagnostic instrument of the apparatus represented in FIG. 1 for generating a diagnostic image,

(9) FIG. 7 shows a representation of an incision profile, generated by an image-acquisition unit of the apparatus represented in FIG. 1 for generating an image, and

(10) FIG. 8 shows a further representation of a diagnostic image generated by a diagnostic instrument of the apparatus represented in FIG. 1.

(11) In FIG. 1, components of a laser-assisted eye-surgery treatment system 10 have been represented schematically. This treatment system 10 includes a laser 12 which provides a laser beam 14 consisting of short-pulse laser radiation, for example with pulse durations within the attosecond, femtosecond or picosecond range. The laser beam 14 is directed, via means described in more detail below for beam control and beam shaping, onto a human eye 16 to be treated. The eye 16 is fixed with the aid an applicator 18 in an x,y,z coordinate system S of the treatment system 10. The applicator 18 includes a contact element 20, represented here in exemplary manner as a plane-parallel applanation plate that is transparent to the laser radiation and that, for example, is pressed against the eye 16 so that the eye 16 conforms to the contact element 20 with its anterior surface. The applicator 18 further includes a support body 21 for the contact element 20, the support body 21 having been represented here in exemplary manner as a conically widening sleeve body which in the region of its wider sleeve end is capable of being releasably coupled to a focusing objective which is not represented in any detail.

(12) The laser beam 14 is directed via several mirrors 22, 24, 26 into the aforementioned focusing objective (for example, an f-theta objective). In the exemplary case shown, mirrors 22, 24 are capable of swivelling about mutually perpendicular tilting axes, so that by appropriate drive of mirrors 22, 24 the site of the focus of the laser beam 14 in the x,y plane (i.e. transverse to the direction of beam propagation at the eye 16) can be adjusted. For the purpose of longitudinal local control of the site of the focus (i.e. in the z-direction), for example a lens that is adjustable along the beam path of the laser beam 14, a lens with variable refractive power, or an adaptive optical mirror (ao mirror) may have been provided (not represented in any detail), with which the divergence of the laser beam 14 and hence the z-position of the beam focus can be influenced. In the exemplary case shown, mirror 26 takes the form of an immovable dichroic deflecting mirror.

(13) A program-controlled computer arrangement 28 with a data memory 30, with a scan-software module 32 for time-dependent local control of the radiation focus of the laser beam 14 in the coordinate system S of the treatment system 10, and with an image-processing software module 34 serves as control unit of the treatment system 10.

(14) A first image-acquisition unit 36 has been arranged behind the dichroic mirror 26. The image-acquisition unit 36 is, for example, a digital CCD camera, an OCT image-acquisition unit and/or a Scheimpflug image-acquisition unit with, in each instance, suitable imaging optics. A green-light source 38 which casts green light onto the eye 16 has been assigned to the image-acquisition unit 36. The image-acquisition unit 36 acquires a two-dimensional (x-y plane in coordinate system S), digital and true-to-scale image 39 (cf. FIG. 2a and FIG. 5) of the eye 16. The image 39 shown in FIG. 2a and FIG. 5 is a top view of the eye 16. The image 39 includes at least one projected image of at least one first feature of the eye 16. In the image 39 in FIG. 2a, scleral blood vessels 40, 40a of the sclera 41, the iris 42 with structural features 44a, 44b, the limbus 46 with a structural feature 48, and the pupillary margin 50 with a structural feature 52 have been shown by way of exemplary features. In the image 39 in FIG. 5, the iris 42 with a structural feature 44a, the limbus 46 and the pupillary margin 50 with the pupillary centre 51 have been shown by way of exemplary features. In the following it will be assumed in exemplary manner that scleral blood vessel 40 is being used as first feature.

(15) The image-acquisition unit 36 supplies image data, which represent the image 39, to the computer arrangement 28. The image-processing software module 34 processes these image data and evaluates them in a manner yet to be elucidated.

(16) Diagnostically determined reference data may be stored in advance in the memory 30. For the purpose of determining the reference data, in the exemplary case of FIG. 1 which is shown a diagnostic instrument 54 has been provided which includes a second image-acquisition unit 56, by means of which, in a preliminary examination of the eye 16 taking place temporally ahead of the laser treatment, a two-dimensional, digital and true-to-scale diagnostic image 55 (cf. FIG. 2b, FIG. 4 and FIG. 8) of the eye 16 to be treated can be acquired in an x,y,z coordinate system S of the diagnostic instrument. As can be discerned, for example, in FIG. 4 and FIG. 6, the eye 16 is not loaded or deformed by external action during the preliminary examination, so the internal pressure of the eye 16 has its natural value. The image-acquisition unit 56 includes, for example, a digital camera and also a topographer (ophthalmometer, keratometer or videokeratographer) configured to acquire a topography of the cornea of the eye 16 and therefrom to assign to each pixel of the diagnostic image 55 a curvature value that is representative of a surface curvature of the cornea at a lateral position of the cornea corresponding to the pixel. The data acquired by the camera and by the topographer enter jointly into the diagnostic image 55.

(17) The diagnostic image 55 according to FIG. 2b, FIG. 4 and FIG. 8 is a z-top view of the eye 16. The diagnostic image 55 (FIG. 2b) also contains projected images of the same structures which are also to be seen in the image 39 (FIG. 2a). These structures are denoted in FIG. 2b by the same reference symbols as in FIG. 2a, but without added dash. Therefore the diagnostic image 55 according to FIG. 2b contains a projected image of the sclera 41, projected images of scleral blood vessels 40, 40a, a projected image of the iris 42 with structural features 44a, 44b, a projected image of the limbus 46 with a structural feature 48, and also a projected image of the pupillary margin 50 with a structural feature 52. For the purpose of better detection of the eye-internal features, the diagnostic instrument 54 exhibits a green-light source 58. Furthermore, the diagnostic instrument 54 includes an image-processing unit 60 which is able to detect two defined selected features of the eye 16 on the basis of the data supplied by the image-acquisition unit 56. In the present example, scleral blood vessel 40 serves as first feature. An astigmatically curved corneal region 64, which is characterised by two astigmatism axes 64a, 64b intersecting in FIG. 2b in the centre of the pupil, serves as second feature.

(18) The image processing unit 60 is configured to detect the first feature 40 in the diagnostic image 55 by virtue of three characteristic points R.sub.1, R.sub.2, R.sub.3 of the first feature 40 which do not lie on a common straight line. The three points R.sub.1, R.sub.2, R.sub.3 represent in the present example the ends of three arteries of scleral blood vessel 40 extending from a central point. The positions of points R.sub.1, R.sub.2, R.sub.3 are determined in the coordinate system S of the diagnostic instrument 54 and are uniquely defined by three corresponding vectors R.sub.1, R.sub.2, R.sub.3 (vectors have been represented here in bold type).

(19) The position of the first feature 40 has been uniquely defined in coordinate system S by the vectors R.sub.1, R.sub.2, R.sub.3. Similarly, the orientation of the first feature 40 in coordinate system S has been uniquely defined by vectors R.sub.1, R.sub.2, R.sub.3 or by two of the three relative vectors R.sub.2-R.sub.1, R.sub.3-R.sub.1, R.sub.3-R.sub.2. For example, these are the two vectors r.sub.12 and r.sub.13, where
r.sub.12=R.sub.2R.sub.1
r.sub.13=R.sub.3R.sub.1.

(20) The size and the shape of the first feature are also uniquely characterised by points R.sub.1, R.sub.2, R.sub.3. Since points R.sub.1, R.sub.2, R.sub.3 do not lie on a straight line, vectors r.sub.12 and r.sub.13 are linearly independent and span in the diagnostic image 55 an eye-internal coordinate system which is individual to the eye 16.

(21) The image-processing unit 60 is furthermore configured to detect the second feature 64 in the diagnostic image 55 by virtue of three characteristic points P.sub.1, P.sub.2, P.sub.3 equally not lying on a straight line, and to represent these three points P.sub.1, P.sub.2, P.sub.3 by three corresponding vectors P.sub.1, P.sub.2, P.sub.3 in the eye-internal coordinate system that is spanned by vectors r.sub.12 and r.sub.13. As can be discerned in FIG. 2b, points P.sub.1 and P.sub.2 lie in exemplary manner on one of the two astigmatism axes 64a, 64b. The diagnostic instrument can in this way determine the position, the orientation, the size and the shape of the second feature 64 on the basis of the determination of the coefficients a.sub.1, a.sub.2, a.sub.3, b.sub.1, b.sub.2, b.sub.3 in
P.sub.1=a.sub.1r.sub.12+b.sub.1r.sub.13
P.sub.2=a.sub.2r.sub.12+b.sub.2r.sub.13
P.sub.3=a.sub.3r.sub.12+b.sub.3r.sub.13.

(22) The points P.sub.1, P.sub.2, P.sub.3 of the second feature 64 are consequently referenced with respect to the coordinate system defined by the first feature 40, the origin of which is formed by point R.sub.1. The coefficients a.sub.1, a.sub.2, a.sub.3, b.sub.1, b.sub.2, b.sub.3 are individual to the eye 16 and independent of the choice of the coordinate system S. The coefficients a.sub.1, a.sub.2, a.sub.3, b.sub.1, b.sub.2, b.sub.3 can be stored in a database 62 as reference data jointly with digital image data of the diagnostic image 55 and with information from which it is evident which is the first feature 40 with respect to which the second feature 64 has been referenced. In FIG. 1 the database 62 has been integrated into the diagnostic instrument 54. But the database may also have been formed independently of any instrument or external to any instrument, that is to say, for instance as an online database, as a mobile data carrier (diskette, CD, DVD, USB stick, memory card, . . . ), etc.

(23) For the laser treatment of the eye 16, in the course of which an incision figure is to be produced in the eye 16 by laser technology by stringing photodisruptions together, the reference data are read out from the database 62 and communicated to the computer arrangement 28. The dividing line 65 drawn in dashed manner in FIG. 1 is intended to make it clear that the treatment station at which the laser 12, the computer arrangement 28 and the image-acquisition unit 36 are located may be spatially separated from the diagnostic station with the diagnostic instrument 54, and that the determination of the reference data takes place temporally ahead of the laser treatment of the eye 16.

(24) The image-processing software module 34 of the computer arrangement 28 has access to the database 62, reads the reference data, stored therein, of the patient in question, and determines, on the basis of the reference data, what the first feature 40 is to be detected by. Subsequently the image-processing software module 34 determines, from the image 39 according to FIG. 2a acquired by the image-acquisition unit 36, the positions of the corresponding characteristic points R.sub.1, R.sub.2, R.sub.3 of the first feature 40 in coordinate system S on the basis of coefficients c.sub.1, c.sub.2, c.sub.3, d.sub.1, d.sub.2, d.sub.3, whereby the following holds:
R.sub.1=c.sub.1x+d.sub.1y
R.sub.2=c.sub.2x+d.sub.2y
R.sub.3=c.sub.3x+d.sub.3y.

(25) Coordinate system S is spanned by three vectors x, y, z, where z runs parallel to the direction of the laser beam 14 and consequently is not acquired in the two-dimensional image 39. From the coefficients c.sub.1, c.sub.2, c.sub.3, d.sub.1, d.sub.2, d.sub.3 the image-processing unit 34 now determines the representation of relative vectors r.sub.12, r.sub.13 according to
r.sub.12=R.sub.2R.sub.1
r.sub.13=R.sub.3R.sub.1.

(26) From this, the computer arrangement 28 can calculate the relative positions of points P.sub.1, P.sub.2, P.sub.3 in relation to points R.sub.1, R.sub.2, R.sub.3 by means of
P.sub.1=a.sub.1r.sub.12+b.sub.1r.sub.13+R.sub.1
P.sub.2=a.sub.2r.sub.12+b.sub.2r.sub.13+R.sub.1
P.sub.3=a.sub.3r.sub.12+b.sub.3r.sub.13+R.sub.1,
this being effected as a function of the coefficients a.sub.1, a.sub.2, a.sub.3, b.sub.1, b.sub.2, b.sub.3 previously determined by the diagnostic instrument 54 and included in the reference data.

(27) The computer arrangement 28 can consequently determine the positions of the points P.sub.1, P.sub.2, P.sub.3 characterising the second feature 64, and hence the position and the orientation of the second feature 64 in the coordinate system S of the treatment system 10, without thereby having to detect the second feature 64 itself directly in the image data acquired by the image-acquisition unit 36. Also, the size and the shape of the second feature 64 in coordinate system S can be determined automatically, since the image 39 and the diagnostic image 55 are true-to-scale projected images of the eye 16, and on the basis of the size of the first feature 40, 40 in the image 39 or in the diagnostic image 55 a scaling (zooming) can be performed by the computer arrangement 28.

(28) The computer arrangement 28 can also determine from the relative location of vectors r.sub.12, r.sub.13 in relation to r.sub.12, r.sub.13 an angle of rotation by which coordinate system S has been rotated in relation to coordinate system S with respect to the z-axis or z-axis. Any orientations of the eye 16 in the x-y plane (for instance, by virtue of rotations of the eye 16 about the z-axis) can in this way be detected by the computer arrangement 28 and incorporated by the treatment system 10 into the determination of the position, orientation, size and shape of the incision figure, without this having to be performed manually by a physician or surgeon.

(29) On the basis of the positions P.sub.1, P.sub.2, P.sub.3 and the orientations P.sub.1-P.sub.2, P.sub.3-P.sub.2, P.sub.2-P.sub.1 established therefrom, the size and shape of the second feature 64 in the coordinate system S the scan software module 32 automatically calculates an incision FIG. 66 to be produced in the eye 16. In the exemplary case shown, the incision FIG. 66 defines a corneal flap with a hinge 68 (in the specialist terminology often designated, even in German, by the English term hinge) represented by a hinge axis Q.sub.1-Q.sub.2. In addition, the incision FIG. 66 further includes an auxiliary incision 71.

(30) The auxiliary incision offers a degassing channel, through which surgical gases that arise in the course of the photodisruptive machining of the eye tissue can be vented. A penetration of such gases into critical tissue regions of the eye can be avoided in this way. It is preferred firstly to produce the auxiliary incision; only then is the flap cut.

(31) After the flap has been cut, it is folded aside, connected to the hinge 68, in order to expose corneal tissue (stroma) which is then machined in an ablation zone 70, in accordance with a previously determined ablation profile, with an excimer laser, not represented in any detail, of the treatment system 10, in order to correct the weakness of vision of the eye 16 (that is to say, the astigmatism of the eye 16) caused by the second feature 64 (that is to say, the astigmatically curved corneal region). The incision FIG. 66 is adapted in its position, orientation, size and shape by the scan software module 32 to the position, orientation, size and shape of the second feature 64. The positions of points Q.sub.1, Q.sub.2 are calculated by
Q.sub.1=u.sub.1P.sub.1+v.sub.1P.sub.2
Q.sub.2=u.sub.2P.sub.1+v.sub.2P.sub.2
Q.sub.3=u.sub.3P.sub.1+v.sub.3P.sub.2

(32) The coordinates u.sub.1, u.sub.2, u.sub.3, v.sub.1, v.sub.2, v.sub.3 are treatment-specific and have been adapted to the weakness of vision characterised by the second feature 64. The coordinates u.sub.1, u.sub.2, u.sub.3, v.sub.1, v.sub.2, v.sub.3 are, for example, adapted in such a way that the hinge axis Q.sub.1-Q.sub.2 of the hinge has been oriented perpendicular to the astigmatism axis P.sub.1-P.sub.2, points Q.sub.1 and Q.sub.2 have the same spacing from the astigmatism axis P.sub.1-P.sub.2, and with respect to their lateral positions (that is to say, along x and y in coordinate system S) have been arranged in a region of the iris 42 approaching the limbus 46, see FIG. 2a.

(33) The position, orientation, shape and/or size of the auxiliary incision 71 are treatment-specific and have been adapted to the position and orientation of the hinge 68, in particular to the position and orientation of the hinge axis Q.sub.1-Q.sub.2. The auxiliary incision 71 extends from the cornea of the eye 16 to the sclera 41 of the eye 16 and passes through the limbus 46. The auxiliary incision 71 which is formed in planar manner, substantially as a flat channel, is connected to the remaining incision FIG. 66 and terminates on the surface of the eye 16. The auxiliary incision 71 therefore makes it possible that gases arising in the course of the cutting of the flap and of the remaining incision FIG. 66 are able to escape from the eye 16.

(34) The computer arrangement 28 is configured to generate a pictorial representation of the incision FIG. 66 and of the second feature 64 and also, where appropriate, of the ablation zone 70 in accordance with the position and orientation and also size and shape in coordinate system S that have been determined for these elements. The treatment system 10 may include a device 72 configured to superimpose this pictorial representation on the image 39 acquired by the image-acquisition unit 36 and to display the overall image that has arisen therefromas represented in FIG. 2aon an output instrument 74 (e.g. a monitor) in a manner that is true to scale. An overall image of such a type has been represented in FIG. 5. Alternatively or additionally, the device 72 can insert the pictorial representation into the observation image of an operating microscope of the treatment system 10 (not shown in any detail).

(35) The position, orientation and dimensioning of the incision image 66 determined by the computer arrangement 28 can in this way be observed and monitored by the treating physician or surgeon in relation to the first feature 40 of the eye 16.

(36) The incision FIG. 66 serves as a suggestion determined by the computer arrangement 28, which can be modified. If the physician/surgeon is dissatisfied with the suggestion, he/she can modify the position, orientation and dimensioning of the incision FIG. 66, in order to make the treatment even more ideal. For this purpose the physician/surgeon can make use of an input device 76 of the treatment system 10, which permits him/her to communicate desired modifications of the position, orientation, size or/and shape of the incision FIG. 66 to the computer arrangement 28 by manual input. The computer arrangement 28 takes these modifications into account and re-determines the position, orientation, size or/and shape of the incision FIG. 66 appropriately. Since the displayed/inserted visualisation of the incision FIG. 66 always reflects the current position, orientation, size and shape of the incision FIG. 66 relative to the second feature 64 in the image 39, this optimisation can be effected by the physician/surgeon online, as it were.

(37) As soon as the physician/surgeon is satisfied with the position, orientation, size and shape of the incision FIG. 66 or, to be more precise, with the visualised representation of the same, he can confirm the current incision FIG. 66 manually by input via the input device 76. Subsequently the treatment system 10 then produces the incision FIG. 66 confirmed by the physician/surgeon in the eye 16 of the patient by means of the laser 12.

(38) In FIG. 3 the treatment procedure just described has been represented once again in the form of a flow chart. Firstly, in a preliminary examination S102 of the eye 16 taking place temporally ahead of the laser treatment S100, a recording of the iris representing the diagnostic image 55 (cf. FIG. 2b and FIG. 4) of the eye 16 to be treated is acquired, see step S104. From the recording of the iris, image data are generated which represent individual features 40-52 of the eye 16, see step S106. Within the scope of a feature extraction S108, position, orientation and size of the first feature 40 in the x,y,z coordinate system S of the diagnostic instrument 54 are determined. In addition, diagnostic data are determined in parallel, see step S110. The diagnostic data include, in particular, keratometer values, a corneal thickness distribution (as represented in FIG. 8) and also position, orientation and size (length) of the astigmatism axes 64a, 64b (as represented in FIG. 2b) in coordinate system S. The data determined during the preliminary examination S102 are stored in a database or on a data carrier, see step S112.

(39) After the preliminary examination S102 has been concluded, the actual laser treatment S100 takes place. For this purpose, in step S114 the eye 16 to be treated is docked onto the applanation lens 20 of the treatment system 10, and in step 116 an image 39 of the eye 16 is recorded. Within the scope of a feature extraction S118, position, orientation and size of the first feature 40 in the x,y,z coordinate system S of the treatment system 10 are determined. By matching of the position, orientation and size, determined in this way, of the first feature 40 in coordinate system S with the position, orientation and size, read out from the data memory or database, of the first feature 40 in coordinate system S, the position, orientation, and size (length) of the astigmatism axes 64a, 64b in coordinate system S are determined by computation.

(40) In step S122, on the basis of the previously determined diagnostic data, in particular the keratometer values, parameters for an ablation profile are calculated which have been adapted to the position, orientation and size (length) of the astigmatism axes 64a, 64b in coordinate system S. In order also actually to be able to expose this ablation profile in the eye 16 for the purpose of machining, in step S124 the position, the orientation, the shape and the size of the incision FIG. 66, including the corresponding positions, orientations, shapes and sizes of the flap, of the hinge and of the auxiliary incision 71 are calculated. In step S126 the incision FIG. 66 calculated in this way is, together with the recording acquired in step S116, displayed on a graphical user interface (GUI) or/and inserted by a suitable insertion device (in the manner of a head-up display, HUD) into the observation beam path of the operating microscope (see also FIG. 2b and FIG. 5).

(41) Position, orientation, shape and size of the incision FIG. 66 can be modified by an operating surgeon conducting the treatment, see step S130. In the course of a modification S132 the operating surgeon changes the parameters proposed by the treatment system by manual setting via the GUI. After this, the incision FIG. 66 is re-determined in accordance with the modification and re-displayed on the GUI or in the HUD. As soon as the operating surgeon is satisfied with the position, orientation, shape and size of the incision FIG. 66, he/she confirms the set parameters in step S134. After this, the treatment of the eye 16 is undertaken by the treatment system 10 in accordance with the set parameters, see step S136. Alternatively it is also conceivable that the second feature represents a pathological tissue region of the eye 16 of a patient, which is clouding the sight of the patient, such as, for example, a cataract region, that is to say, a region that has become diseased with so-called grey cataract. The incision FIG. 66 then has to be determined in its position, orientation, size and shape with respect to the cataract region, and has to be brought about in the human lens of the eye 16.

(42) The diagnostic instrument 54 includes, for example, a digital camera and also a topographer (ophthalmometer, keratometer or videokeratographer) and is configured to acquire a topography of the cornea of the eye 16 and/or a corneal thickness distribution of the eye 16 and from this to assign to each pixel of the diagnostic image 55 a curvature value that is representative of a surface curvature of the cornea at a lateral position of the cornea corresponding to the pixel.

(43) The diagnostic instrument 54 may furthermore be configured, within the scope of a pachymetric recording of the eye 16, to acquire a corneal thickness distribution of the eye 16, see FIG. 8. In this case, to each pixel of the diagnostic image 55 a thickness value is assigned that is representative of the thickness of the cornea at a lateral position of the cornea corresponding to the pixel. In this representation the pupillary margin 50, the pupillary centre 51 and the corneal apex 53 can be detected. The various thickness values, or, to be more precise, the corneal thickness distribution resulting from the thickness values, permit an individual characterisation of the eye. The corneal thickness distribution can therefore serve as the first feature. The corneal thickness distribution then defines an eye-internal coordinate system, with respect to which the position, orientation and size of the second feature, for instance an astigmatically deformed corneal region or astigmatism axes, are referenced. For this purpose, for example, the corneal apex 53 can be chosen as origin of coordinates (x [mm]=0, y=[mm]).

(44) The corneal thickness distribution is determined, for example, on the basis of an OCT measurement or a Scheimpflug measurement. In the case of an OCT measurement a plurality of two-dimensional incision profiles of the eye 16 are acquired, on the basis of which two-dimensional and/or three-dimensional projected images of the eye 16 are possible. For example, for this purpose the incision profiles run parallel to one another or intersect one another along an axis of the eye (visual axis, optical axis of the eye, . . . ). An incision profile of such a type can be seen in FIG. 6. The diagnostic instrument 54 determines from the incision profiles in each instance the thickness values of the cornea along the cross section corresponding to the respective incision profile. In exemplary manner, three thickness values D.sub.1, D.sub.2, D.sub.3 of the cornea have been labelled in FIG. 6. The totality of the thickness values yield in their spatial assignment the corneal thickness distribution as represented in FIG. 8. Regions of constant thickness appear as contour lines. For the purpose of better differentiation of the various contour lines, the same have been colour-coded. From an OCT image, characteristic layer distributions can also be extracted.

(45) Just like the diagnostic instrument 54, the treatment system 10 may be configured, within the scope of a pachymetric recording of the eye 16, to acquire the corneal thickness distribution of the eye 16. In FIG. 7 an OCT recording has been represented which shows an incision profile of the cornea in the course of the treatment and from which thickness values for the corneal thickness distribution are obtained. The cornea in this case is in a flattened state which is brought about with the aid of the applanation lens 20. In exemplary manner, in FIG. 7 three thickness values D.sub.1, D.sub.2, D.sub.3 of the cornea corresponding to the thickness values D.sub.1, D.sub.2, D.sub.3 shown in FIG. 6 have been labelled.

(46) Since the corneal thickness distribution remains unchanged both in the applanated state and in the relaxed state, the referencing, determined during the preliminary examination with the aid of the diagnostic instrument 54, of the astigmatically deformed corneal region or of the astigmatism axes retains its validity during the actual treatment.