METHOD FOR CENTERING A CONTACT GLASS AND REFRACTIVE SURGICAL LASER SYSTEM

Description

[0001] The present invention relates to a method for centering a contact lens on a patient's eye, a method for preparing for refractive surgical treatment of an eye, a computing unit, and a refractive surgical laser system. The invention thus lies particularly in the field of laser systems for refractive surgery.

[0002] For refractive surgical treatments of the eye, ophthalmic femtosecond lasers are often used. The laser beam is used to perform refractive eye corrections by detaching or removing tissue from the eye, particularly the cornea. To couple the laser beam into the eye being treated, a contact lens with a contact surface is typically used. This lens is placed on the patient's eye and suctioned to it to fix the eye in place. The laser beam can then be coupled through the contact lens into the suctioned eye and applied in a controlled manner.

[0003] The center of the contact lens, typically defined by the apex of the curved contact lens surface, serves as the geometric origin of all laser-made incisions in the eye. Therefore, the positioning or centering of the contact lens relative to the eye determines the location of the incisions. Precise and controlled positioning and centering of the contact lens is thus crucial for the accuracy of refractive surgical treatment.

[0004] Positioning the contact lens typically involves the following three phases: A rough positioning, in which the contact lens is located a few centimeters to millimeters above the patient's eye and the contact lens is aligned with the eye.

[0005] Fine positioning, in which the contact lens is in contact with the eye and is brought into its desired final position relative to the eye.

[0006] A suction state in which the suction of the eye to the contact lens or vice versa is activated, so that the patient's eye is fixed to the contact lens.

[0007] Conventional laser systems for refractive surgery offer the surgeon various forms of assistance for the initial rough positioning of the contact lens relative to the patient's eye, such as a fixation light that allows the eye to align itself angularly with the contact lens. However, fine positioning is traditionally performed by the surgeon, who, at their own discretion and depending on the type of treatment, determines the exact position of the contact lens on the eye, more precisely, the desired target point on the cornea.

[0008] However, fine positioning is perceived as a challenge, as it causes a high degree of uncertainty for many physicians, leading them to perform several or even numerous positioning attempts before achieving a satisfactory result. Traditionally, fine positioning or centering of the contact lens is achieved by the physician using a printed diagnostic image of the eye to be treated, on which the desired positioning point is marked. Based on this, the physician attempts to center the contact lens on the actual eye. Furthermore, the determined fine positioning is not typically documented, making subsequent analysis impossible. A quantitative assessment and documentation of the achieved centering (or deviation from the intended target) is therefore only possible manually.

[0009] Furthermore, during fine positioning, doctors often intend to reposition the contact lens or treatment center while the eye is suctioned, which is not possible with conventional systems and may therefore require detaching the eye from the contact lens and re-fixing it.

[0010] US 2011 / 304,819 A1 describes a docking procedure for an ophthalmic lens system to an eye, which includes capturing an image of an internal structure of the eye.

[0011] The object of the invention is therefore to provide a method and a refractive surgical laser system which simplify the fine positioning of the contact lens on the eye for the user or the doctor and allow reproducibly reliable fine positioning.

[0012] This problem is solved according to the invention by a method, a computing unit, and a refractive surgical laser system with the features of the respective independent claims. Advantageous embodiments are specified in the dependent claims and in the description.

[0013] In a first aspect, the invention relates to a method for centering a contact lens (16) relative to a patient's eye (12). The method comprises a) providing a fixation light (20) through the contact lens (16) so that the patient's eye (12) is aligned relative to the contact lens (16) by fixating on the fixation light (20). Furthermore, the method comprises b) capturing an image of a light pattern (24) provided by a light source with a fixed spatial relationship relative to the contact lens, wherein the image of the light pattern (24) is formed by reflection at the surface of the eye (12).Furthermore, the method c) comprises representing the image of the light pattern (24) via the eye (12) through the contact lens (16) in superimposition with virtual markings (26), wherein a first marking of the virtual markings (26, 26a, 26b) identifies the central axis (200) of the contact lens (16) and a second marking of the virtual markings (26, 26a, 26b) identifies a reference marking which is derived from the image of the light pattern as lying on the central axis of the contact lens (16).Furthermore, the method d) includes laterally positioning the contact lens (16) relative to the eye (12) such that the distance between the first and second markings is minimized, and e) determining the position of the eye (12) where the second marking is located when the first and second markings are at the minimized distance from each other, as the position of the vertex (22) of the eye (12) and registering the position of the vertex (22) based on a feature of the eye (12) recognizable in the image of the eye (12).

[0014] In a further aspect, the invention relates to a method for preparing a refractive surgical treatment of an eye using a laser system. The method comprises a method according to the invention for centering a contact lens relative to the eye and for determining whether the pupil of the eye is covered by an optical zone of a lenticule to be removed during the refractive surgical treatment.

[0015] In another aspect, the invention relates to a computing unit which is configured to control a refractive surgical laser system for carrying out a method according to the invention.

[0016] In a further aspect, the invention relates to a refractive surgical laser system, preferably a femtosecond laser system, with a contact lens. The laser system is configured to a) provide a fixation light through the contact lens such that the patient's eye is aligned relative to the contact lens by fixating on the fixation light. Furthermore, the laser system is configured to b) capture an image of a light pattern provided by a light source with a fixed spatial relationship relative to the contact lens, wherein the image of the light pattern is formed by reflection at the surface of the eye.Furthermore, the laser system is configured to c) display an image of the light pattern via the reflection at the surface of the eye through the contact lens in superimposition with virtual markings, wherein a first marking of the virtual markings identifies the central axis of the contact lens and a second marking of the virtual markings identifies a reference marking which is derived from the image of the light pattern as lying on the central axis of the contact lens.Furthermore, the laser system is designed to d) position the contact lens laterally relative to the eye in such a way as to minimize the distance between the first mark and the second mark, and e) determine the location of the eye where the second mark is located when the first mark and the second mark are at the minimized distance, as the position of the vertex of the eye and to register the position of the vertex based on a feature of the eye recognizable in the image of the eye.

[0017] The fact that the fixation light is provided through the contact lens means that the contact lens itself provides the fixation light, for example, by means of a suitable light source integrated into the contact lens, or that the fixation light is provided by a separate light source and transmitted through the contact lens to the eye. The fixation light is a visible light signal that serves as an orientation aid for the patient's eye, enabling it to assume the desired orientation when the patient's eye is focused on the fixation light. According to an optional embodiment, the light source with its fixed position relative to the contact lens can also serve as the fixation light. According to other embodiments, one or more additional light sources can be provided as fixation lights.

[0018] "Centering the contact lens relative to the eye" means that the contact lens is placed in the desired position for the refractive surgical treatment of the eye. Centering does not necessarily require that the central axis of the contact lens coincide with the optical axis of the eye. Rather, the contact lens can also be centered on a different position of the eye desired for the surgical treatment.

[0019] Displaying the image of the eye and the virtual markers means that these are made visible to the user, for example, by means of a display unit such as a computer monitor or other display device. The fact that the virtual markers are virtual means that they are optionally only displayed in the representation, for example, on the computer monitor, but are not projected onto the eye or otherwise attached to the eye. According to other optional embodiments, however, the virtual markers can also be projected onto the eye.

[0020] The fact that the light source has a fixed spatial relationship to the contact glass means that the position of the contact glass, and optionally the position of the contact glass's central axis, can be uniquely determined from the position of the light source. Optionally, the light source is arranged directly in and / or on the contact glass. According to an optional embodiment, the light source is at least partially ring-shaped and surrounds the contact glass at least partially in the circumferential direction. The light pattern of such a light source can be in the form of a ring of light, with the center of the ring of light optionally lying on the central axis of the contact glass.

[0021] The light pattern is a geometric arrangement of light, which is visible in the illustration. The light pattern is designed in such a way that a specific point within it can be identified, such as a center point, a geometric center point, a corner point, or another clearly definable point, from which the relative position of the central axis of the contact lens can then be determined.

[0022] The fact that the light pattern is imaged via reflection at the surface of the eye means that the light path is folded at the eye's surface during optical imaging. The curved surface of the eye then optionally acts as an imaging optical element, similar to a convex mirror.

[0023] The invention offers the advantage of providing a physician with assistance in centering the contact lens, enabling reliable centering. In particular, the invention offers the advantage that reliable centering can be performed as a standard procedure and can also be carried out by users who lack extensive experience and expertise.

[0024] Furthermore, the invention offers the advantage that the contact lens can be centered semi-automatically or fully automatically by the laser system. This reduces, minimizes, or even completely eliminates the manual tasks that the user must perform during centering. This, in turn, lowers the required knowledge and / or motor skills of the user. It also simplifies the user's work, particularly the operation of the laser system. Finally, the invention reduces the risk of user-induced errors.

[0025] The invention also offers the advantage that the centering of the contact lens can be reliably recorded, and in particular, this recording can be automated. This increases the reliability and verifiability of refractive surgical treatments.

[0026] Typically, the fixation light is aligned perpendicular to the optical axis of the treatment optics. Optionally, the fixation light can be positioned at other angles to the optical axis, making it appear movable to the patient. Optionally, the fixation light can be switched off. Both of these features allow the physician or user to verify that the patient is actually fixating on the light by switching it on and off and / or moving it and observing the eye's reaction.

[0027] Optionally, the center of the pupil is used as the recognizable feature of the eye in the image. This offers the advantage that it can be reliably determined in the image, and this determination can also be automated using image analysis. Optionally, the virtual markers also include a virtual marker of the pupil's center. This offers the advantage that the position of the pupil's center is easily recognizable for the user, who can use the virtual marker for orientation purposes. Optionally, infrared illumination of the eye can be used to facilitate reliable detection of the pupil, and especially its center, even in dark eyes or eyes with a dark-colored iris.

[0028] Optionally, the light pattern is a ring light provided by a light source designed as a ring illuminator and directed through the contact lens onto the eye. Alternatively, the ring illuminator can also be located outside the contact lens. Preferably, the ring is arranged concentrically around the central axis of the contact lens. The reflection of the ring illuminator on the eye is visible in the image of the eye. The use of the projection ring offers the advantage that, when reflected off the curved surface of the eye, the shape of the projection ring's reflection changes if the projection ring is not perpendicular to and concentric with the vertex of the eye facing the contact lens. Based on the shape deviations of the projection ring's reflection, conclusions can then optionally be drawn about the positioning of the contact lens relative to the eye.

[0029] Optionally, the center point of the projection ring forms the center point of the light pattern. If the light pattern includes other elements, these are preferably arranged concentrically around the center point. This facilitates the determination of the contact lens's relative position to the eye based on the deformation of the projected marking's reflection. Optionally, the light pattern can include multiple projection rings, which can optionally be arranged concentrically to the central axis of the contact lens. Alternatively or additionally, the light pattern can include a predetermined dot pattern.

[0030] According to an optional embodiment, the light pattern comprises a polygon and / or a grid and / or a cross. The polygon can optionally be configured as a triangle, quadrilateral, hexagon, or octagon, with any other number of vertices also being possible. The light pattern is optionally configured such that a reference mark can be derived from a center point and / or a centroid of the light pattern and / or from another distinguished point, which is derived from the image of the light pattern as lying on the central axis of the contact lens. According to an optional embodiment, the light pattern is configured such that, based on distortions in the image of the light pattern across the surface of the eye relative to an image of an ideal surface of the eye, the shape of the eye's surface can be at least partially determined.

[0031] Optionally, the image of the light pattern is captured via reflection from the surface of the eye in such a way that both the light pattern and the eye feature are recognizable in the image. This can be achieved, for example, by using an image with a sufficiently large depth of field, so that both the light source and the surface of the eye, and optionally the underlying iris and pupil, are sharply focused in the captured image. This offers the advantage that the eye feature used to register the position of the vertex is recognizable in the same image that also depicts the light source or the light pattern. Optionally, the image is captured with a depth of field of at least 10 mm, optionally at least 15 mm, optionally at least 20 mm, and optionally at least 30 mm. This offers the advantage that both the plane of the light source and the plane of the eye feature can be captured within the depth of field.

[0032] Optionally, when performing steps a) to e), the contact lens is positioned at a distance from the eye, with this distance optionally ranging from 1 mm to 10 cm. This offers the advantage that the contact lens can be centered before it makes contact with the eye. Furthermore, it allows the area of ​​the eye that can be imaged by the contact lens to be adjusted to the specific requirements. Additionally, it allows the reflection of the projected marking to be at least partially transmitted, detected, and displayed by the contact lens.

[0033] Optionally, the method further comprises (f) reducing the distance between the contact lens and the eye and making contact between the eye and the contact lens, and (g) fine-positioning the contact lens laterally relative to the eye such that the central axis of the contact lens is positioned at a predetermined position on the eye, wherein steps (f) and (g) can optionally be performed in any order and / or multiple times. This offers the advantage that further fine-positioning can be carried out when the contact lens is already in contact with the eye. This can be particularly advantageous in that it allows for the compensation of changes resulting from making contact between the contact lens and the eye, such as deformations of the eye and, in particular, the cornea.Fine positioning can also involve several passes in contact with the eye and at a distance from the eye, thus enabling a gradual approach to the desired position and / or testing of different positions.

[0034] Optionally, the procedure also includes determining a kappa angle based on the position of the vertex and the center of the pupil. This offers the advantage of detecting particularly large kappa angles, which typically lead to undesirable rotation of the eye when suctioned to the contact lens. If a large kappa angle is detected, a notification or warning can optionally be issued to the user, indicating the presence of a large kappa angle and the associated risks. Optionally, a laser system can also be configured to prevent suction of the eye if a kappa angle is detected that deviates from a predetermined value by a specific amount.

[0035] Optionally, the virtual markers can also include a virtual marker for a predetermined point on the eye, where this predetermined point is user-defined. For example, the user can specify one or more points on the eye, which are also marked with a virtual marker in the image of the eye. For instance, the user can mark the point where they intend to center the contact lens. In other words, the user can specify one or more (alternative) user-defined positioning targets, which might be defined by the physician during treatment planning, and optionally display each of these user-defined positioning targets with a virtual marker in the image of the eye. Optionally, the user can show or hide the virtual markers.For example, the user can provide the coordinates of the point to be marked. These coordinates can be provided directly (using Cartesian and / or radial coordinates) with respect to the pupil center (especially for a specific pupil size, to account for pupil center shift), or on a topography, wavefront image, or OCT-generated image (e.g., pachymap, epithelial map) of the eye.

[0036] Optionally, step (c) of the procedure described above further includes, at least partially, the display of a topography and / or wavefront image and / or an OCT-generated image of the eye, such as a pachymap and / or an epithelial map. Optionally, the user can choose to show or hide one or more of the aforementioned elements. Optionally, the user can select to display one or more of these image elements as a semi-transparent overlay and / or switch between the different displays of the image information.

[0037] Optionally, the invention further comprises detecting a reflection of the projected optical marking generated at the eye and characterizing the shape of the eye based on the detected reflection of the light pattern. This offers the possibility of determining the position of the contact lens relative to the eye, at least partially automatically, by means of image analysis.

[0038] Optionally, steps d), f), and / or g) are performed by the user, i.e., manually or predominantly manually, as desired and under the user's guidance. Alternatively or additionally, the procedure can be carried out semi-automatically or fully automatically. This offers the advantage of reducing the user's required knowledge and simplifying the workload. In both semi- and fully automated procedures, the user can always intervene manually to interrupt, resume, or abort the automated movements and continue manually. This allows the user to intervene, for example, in the event of a malfunction.

[0039] Optionally, the procedure includes checking whether the pupil is covered by the optical zone of the lenticule, optionally including a safety margin. The mesopic pupil is preferably used for this purpose, but the scotopic pupil can also be used if necessary. This offers the advantage of reducing the risk of an incorrect refractive surgical treatment by detecting insufficient coverage in advance and alerting the user.

[0040] Optionally, the procedure also includes performing a plausibility check of the determined distance between the position of the vertex and the center of the pupil. Such a plausibility check can, for example, be based on a comparison of the relative position, and thus also the distance, of the vertex to the center of the pupil determined according to the procedure steps described above with information obtained separately using other diagnostic devices, such as (Scheimpflug) topographers and / or OCTs.

[0041] The image of the eye through the contact lens can optionally be captured using a digital video camera. This camera can, for example, be positioned on the side of the contact lens facing away from the eye and capture and detect at least some of the light transmitted through the contact lens. According to other embodiments, an analog video camera can also be used.

[0042] Optionally, the refractive surgical laser system, and in particular the digital video camera, features telecentric optics, which eliminate or at least reduce the scale dependence on the distance between the contact lens and the eye. This enables reliable image capture of the eye with the video camera at varying distances between the contact lens and the eye.

[0043] The processing unit can optionally be integrated into the laser system or be a separate unit. The processing unit can, for example, include a microcontroller and / or a CPU and / or a personal computer, or be configured as such. The processing unit is optionally configured to at least partially control the laser system and, optionally, to control a digital video camera of the laser system in order to display the captured image of the eye on a display device and, optionally, to overlay virtual markers. The processing unit can optionally perform other functions as well.

[0044] The features and embodiments mentioned above and explained below are not only to be regarded as disclosed in the combinations explicitly mentioned, but are also covered by the disclosure content in other technically meaningful combinations and embodiments.

[0045] Further details and advantages of the invention will now be explained in more detail with reference to the following examples and preferred embodiments and the figures.

[0046] They show: Fig. 1 a refractive surgical laser system according to an optional embodiment in a schematic representation; Fig. 2 a schematic explanation of the characteristic parameters of the eye and the contact lens; Figs. 3-5 pictorial explanations of a method for centering a contact lens according to an optional embodiment.

[0047] For the sake of simplicity, identical or similar elements in the various embodiments are designated with the same reference numerals in the following figures.

[0048] Fig. 1Figure 1 shows a schematic representation of a refractive surgical laser system 10 for performing refractive surgical treatments of an eye 12 of a patient 14 according to an optional embodiment.

[0049] The laser system 10 has a contact lens 16 by means of which the laser system 10 couples to the eye 12 of the patient 14. For this purpose, the patient 14 is positioned lying on a couch 15 so that his gaze is directed upwards and the laser system 10 can contact and fix the eye vertically from above by means of the contact lens 16.

[0050] Furthermore, the laser system 10 features a femtosecond laser 17, which is integrated into the laser system 10. The laser beam provided by the femtosecond laser 17 is used for refractive surgical treatment of the eye 12 of the patient 14 and can be applied to the eye 12 through the contact lens 16.

[0051] Furthermore, the laser system 10 has a display unit 18 by means of which an image of the patient's eye 12 to be treated, as well as an image of a light source 23 arranged on the contact lens 16, can be displayed to the user of the laser system 10 or the physician via a reflection on the surface of the eye 12. The image of the eye 12 to be displayed is taken through the contact lens 16, for example by means of a digital video camera (not shown) which is integrated into the laser system 10. The image of the eye captured by the digital video camera can then be displayed by the display unit 18 together with superimposed virtual markings, so that the physician or user of the laser system 10 can check the eye 12 to be treated and in particular its position relative to the contact lens 16.

[0052] The laser system 10 is designed such that relative movement of the patient 14 to the contact lens and / or the laser system 10 can be achieved. For example, the contact lens can be moved laterally, i.e., perpendicular to the optical axis of the contact lens 16, to achieve a suitable position for the refractive surgical treatment of the eye 12, and also longitudinally, i.e., along the optical axis of the contact lens, to change the distance between the contact lens 16 and the eye 12, and in particular to fix the contact lens 16 to and detach it from the eye 12. Alternatively or additionally, the patient can be moved vertically using the table 15.

[0053] Furthermore, the laser system 10 includes a computing unit 19, which is set up to control the laser system 10 and to display the image of the eye 12 on the display unit 18.

[0054] Figure 2This section explains the geometric parameters of the contact lens 16 and the eye 12 using a schematic diagram. In the diagram, the contact lens 16 is positioned above and at a distance from the eye 12. On the side facing the eye 12, the contact lens 16 has a curved contact surface 16a, the radius of curvature of which corresponds approximately to the radius of curvature of the cornea 12a of the eye 12. The contact lens 16 is transparent to the wavelength of the laser beam and optionally also to the visible spectral range, in order to allow observation of the eye through the contact lens 16. On the side of the contact lens 16 facing away from the eye 12 is the point light source for a fixation light 20, which propagates along a central axis or visual axis 200 of the contact lens 16 through the contact lens towards the eye 12.The terms central axis 200 of the contact lens 16 and visual axis 200 of the contact lens 16 are used synonymously.

[0055] In the illustration shown, eye 12 is positioned and oriented such that the optical axis 100 of eye 12 runs obliquely upwards and to the right. The optical axis 100 passes through the center point C of the eye and centrally through the pupil 12c, which is bounded by the iris 12b.

[0056] The center of curvature of the cornea, designated C c, also lies on the optical axis 100 of the eye. The connecting line between the position of the point light source of the fixation light 20 and the center of curvature of the cornea C c represents the keratometric axis 300, at whose intersection with the outer surface of the cornea 12a the corneal vertex 22 is located.

[0057] Furthermore, for clarification, the line of sight 400 of the eye 12 and the kappa angle 500, i.e. the angle between the optical axis of the eye and the visual axis 200 of the contact lens 16, are shown.

[0058] The following will be based on the Figures 3 to 5 A method for centering a contact lens 16 relative to an eye 12 according to an optional embodiment is described. Figures 3 to 5 The figures show in the lower left area a schematic representation of the relative arrangement of the contact lens to eye 12 and in the upper right area an exemplary representation 1000 of an image of eye 12 with superimposed markings.

[0059] As a first step (i), prior to the refractive surgical treatment of eye 12, the physician ascertains whether eye 12 exhibits any problematic irregularities on its surface that could impede the treatment. If this is not the case, the preparation for the treatment and the centration of the contact lens 12 are continued.

[0060] In a second step (ii), the contact lens 16 is attached to the laser system 10 and positioned above the patient's eye 12 at a z-distance of several centimeters. The patient is instructed to fixate on the fixation light 20 with eye 12.

[0061] In a further step (iii), the laser system 10 projects a light pattern 24 onto the eye 12 by means of a light source 23. According to the optional embodiment, this light pattern is designed as a ring of light concentric around the center of the contact lens or around the central axis 200. According to an optional embodiment, the light source 23 is arranged in and / or on the contact lens 16 such that the light emitted by the light source 23 exits along the edge of the contact lens 16 in the direction of the eye 12 and provides the ring-shaped light pattern 24 concentric to the central axis of the contact lens 16. The light pattern 24 is at least partially reflected by the cornea 12a and is therefore visible in the illustration of the light source 23 and the eye 12 and is shown in Figure 1000 of the illustration of the eye 12. According to the illustrated embodiment, the origins of the light rays of the light pattern 24 are concentric around the central axis 200 of the contact lens.In contrast, the light rays reflected at the surface of the eye are arranged concentrically around the keratometric axis.

[0062] In illustration 1000 of the image of eye 12, which is taken through the contact lens 16, eye 12 and in particular the pupil 12c are visible, as well as the reflection of the light pattern. In addition, several virtual markings 26 are shown superimposed on the image of eye 12, whereby virtual marking 26a identifies the central axis 200 of the contact lens 16 and the edge of the contact lens 16, virtual marking 26b identifies the reference marking, which is derived from the image of the light pattern 24 as lying on the central axis of the contact lens, and virtual marking 26c identifies the center point of the pupil 12c determined from the image by means of image evaluation.

[0063] Using display 1000, the doctor can thus identify the contact lens rim, the pupil and the projection ring in one step (iv).

[0064] The system optionally determines continuously and automatically the center of the pupil, the central axis of the contact lens 16 and the center of the projection ring and displays the corresponding virtual markers 26a, 26b, 26c in a constantly updated position so that the doctor can follow them (step (v)).

[0065] In a further step (vi), as described in Figure 4 As shown, the doctor then reduces the z-distance between contact lens 16 and eye 12. This increases the diameter of the projection ring on the eye (see Figure 1000 in [reference]). Figure 4 The doctor reduces the z-distance until the projection ring 24 is larger than the diameter of the pupil 12c but smaller than the diameter of the contact lens 16.

[0066] In a further step (vii), the physician pauses the approach of the contact lens 16 to the eye 12 and again asks the patient 14 to fixate on the fixation light 20 with eye 12. Then, by laterally shifting the patient's eye 12 relative to the contact lens 16 (or vice versa), the physician aligns the center point of the contact lens 16, or the central axis 200 of the contact lens 16, with the center point of the light pattern 24. In this case, the center of the light pattern 24 effectively marks the vertex 22 of the eye.

[0067] In a further step (viii), the physician instructs the system to save the position of the vertex 22 determined using the center of the positioning ring 24. The system defines the determined position as the position of the vertex 22 and automatically registers this position based on a feature of the eye 12 recognizable in the depicted image of the eye 12. According to this embodiment, the laser system 10 uses the center of the pupil 12c as such a feature, since this can be reliably identified and determined by means of image analysis. According to other embodiments, however, other features of the eye 12 can be used alternatively or additionally.

[0068] Subsequently, in step (ix), the physician continues to reduce the z-distance between the contact lens 16 and the eye 12. The position of the vertex, stored by the laser system 10 and registered based on the recognizable feature, is now continued as a virtual marker 26b in Figure 1000 by the laser system 10, even though the projection ring 24 is no longer visible in the image due to the reduced z-distance, as shown in Figure 1000. Figure 5 This allows the position of the vertex 22 to remain identifiable for the physician and to be used for orientation. The physician then centers the central axis 200 of the contact lens 16 on the position of the vertex 22 or another point of the eye 12 designated by him.

[0069] When the contact lens 16 comes into contact with the eye 12, a water meniscus 28 (tear film) forms between the eye 12 and the contact lens 16, as shown in Figure 5The water meniscus prevents the refractive effect of air between the contact lens 16 and the eye 12. The cornea 12a is deformed or flattened by contact with the contact lens 16, whereby the radius of curvature of the cornea 12a adapts to the radius of curvature of the contact surface 16a of the contact lens 16. The laser system 10 takes into account the deformation of the cornea 12a caused by the contact and the change in the image scale due to the water meniscus and displays the corrected vertex position 22 to the physician.

[0070] In a further step (x), the physician can then fine-tune the positioning of the contact lens 16 relative to the eye, using the virtual markings shown in the illustration as a guide. Once the fine-tuning is complete, the physician can confirm the procedure and induce suction and fixation of the eye 12 to the contact lens 16.

[0071] The laser system 10 then calculates and records the position of the contact lens 16 relative to the eye 12 and relative to the recognizable feature of the eye, such as relative to the center of the pupil, and optionally the diameter of the pupil, and saves this information to record the process, so that this information is available for a subsequent evaluation of the refractive surgical treatment. Reference symbol list

[0072] 10 Refractive surgical laser system 12 Eye 12a Cornea 12b Iris 12c Pupil 14 Patient 15 Table 16 Contact lens 17 Femtosecond laser 18 Display unit for showing an image of the eye 19 Computing unit 20 Fixation light 22 Vertex or position of the vertex 23 Light source 24 Light pattern 26 Virtual marking 26 Virtual marking of the central axis and edge of the contact lens 26b Virtual marking of the center of the projection ring or the projected optical marking 26c Virtual marking of the center of the pupil 28 Water meniscus or tear film 100 Optical axis of the eye 200 Central axis or visual axis of the contact lens 300 Keratometric axis 400 Line of sight of the eye 500 Kappa angle 1000 Representation of the image of the eye

Claims

1. Method for centring a contact glass (16) relative to an eye (12) of a patient, the method comprising the steps of: a) providing a fixation light (20) by the contact glass (16) such that the patient's eye (12) is aligned relative to the contact glass (16) by fixation on the fixation light (20); characterized in that the method further comprises: b) capturing an image representation of a light pattern (24) provided by a light source (23) with a fixed spatial relationship relative to the contact glass (16), with the imaging of the light pattern (24) being implemented via a reflection off the surface of the eye (12); c) displaying the image representation of the light pattern (24) via the eye (12) through the contact glass (16) with overlaid virtual markings (26), with a first marking (26a) of the virtual markings (26, 26a, 26b) identifying the central axis (200) of the contact glass (16) and a second marking (26b) of the virtual markings (26, 26a, 26b) identifying a reference marking which, from the image representation of the light pattern, is derived as being located on the central axis (200) of the contact glass (16); d) laterally positioning the contact glass (16) relative to the eye (12) in such a way that a distance between the first marking (26a) and the second marking (26b) is minimized; e) defining the location of the eye (12) at which the first marking (26a) is situated when the first marking and the second marking are at the minimized distance from one another as the position of the vertex (22) of the eye (12), and registering the position of the vertex (22) on the basis of a feature of the eye (12) that is recognizable in the image representation of the eye (12).

2. Method according to Claim 1, further comprising: - illuminating the eye with infrared illumination; and - recognizing the pupil and optionally the centre of the pupil of the eye illuminated with the infrared illumination.

3. Method according to Claim 1 or 2, wherein the centre of the pupil (12c) of the eye (12) is used as the feature of the eye (12) that is recognizable in the image representation of the eye and wherein optionally the virtual markings (26) further comprise a third marking (26c) which identifies the centre of the pupil (12c).

4. Method according to any of the preceding claims, wherein step c) further at least partially comprises a display of a topography and / or wavefront image and / or OCT-generated image of the eye (12).

5. Method according to Claim 4, further comprising optionally showing and / or hiding the topography and / or the wavefront image and / or the OCT-generated image of the eye (12) and / or representing the topography and / or a wavefront image and / or an OCT-generated image of the eye (12) as a partially transparent overlay.

6. Method according to any of the preceding claims, further comprising checking an overlap of the pupil with an optical zone of a lenticule to be extracted from the eye, wherein the overlap is optionally checked taking account of a safety margin.

7. Method according to Claim 3 or any of Claims 4 to 6, if referred back to Claim 3, further comprising determining a kappa angle (500), i.e. the angle between the optical axis of the eye and the visual axis (200) of the contact glass (16), on the basis of the position of the vertex (22) and the centre of the pupil (26c).

8. Method according to Claim 7, further comprising outputting a warning and / or a message to a user if the determined kappa angle (500) deviates from a specification by at least a predetermined amount.

9. Method according to any of the preceding claims, wherein the image representation of the light pattern (24) with overlaid virtual markings (26) is displayed by means of a display unit, and wherein the virtual markings are optionally displayed exclusively by means of the display unit without being projected onto the eye (12).

10. Method according to Claim 9, wherein displaying the image representation of the light pattern (24) with overlaid virtual markings (26) by means of a display unit further comprises displaying an image representation of the eye (12) to be treated.

11. Method according to any of Claims 8 to 10, wherein the display unit comprises a computer display.

12. Method according to any of the preceding claims, wherein the capturing of the image representation of the light pattern (24) via the reflection off the surface of the eye (12) is implemented in such a way that the light pattern (24) and the feature of the eye (12) are recognizable in the image representation, wherein the imaging is effected with a depth of field of at least 10 mm, optionally at least 15 mm, optionally at least 20 mm and optionally at least 30 mm.

13. Method according to any of the preceding claims, wherein the contact glass (16) is spaced apart from the eye (12) when steps a) to e) are implemented and the distance of the contact glass (16) from the eye (12) is in the range from 1 mm to 10 cm.

14. Method for preparing a refractive surgical treatment of an eye (12) by means of a laser system (10), the method comprising a method for centring a contact glass (16) relative to the eye (12) according to any of the preceding claims and an ascertainment of an overlap of the pupil (12c) of the eye (12) with an optical zone of a lenticule to be extracted during refractive surgery.

15. Computing unit (19) configured to control a refractive surgical laser system (10) for implementing a method according to any of the preceding claims.

16. Refractive surgical laser system (10), preferably a femtosecond laser system with a contact glass (16), the laser system (10) being configured to a) provide a fixation light (20) by the contact glass (16) in such a way that the patient's eye (12) is aligned relative to the contact glass (16) by fixation on the fixation light (20); characterized in that the laser system is furthermore configured to: b) capture an image representation of a light pattern (24) provided by a light source (23) with a fixed spatial relationship relative to the contact glass (16), with the imaging of the light pattern (24) being implemented via a reflection off the surface of the eye (12); c) display an image representation of the light pattern (24) via the reflection off the surface of the eye (12) through the contact glass (16) with overlaid virtual markings (26, 26a, 26b), with a first marking (26a) of the virtual markings (26, 26a, 26b) identifying the central axis (200) of the contact glass (16) and a second marking (26b) of the virtual markings (26, 26a, 26b) identifying a reference marking which, from the image representation of the light pattern (24), is derived as being located on the central axis (200) of the contact glass (16); d) laterally position the contact glass (16) relative to the eye (12) in such a way that a distance between the first marking (26a) and the second marking (26b) is minimized; e) define the location of the eye (12) at which the first marking (26a) is situated when the first marking (26a) and the second marking (26b) are at the minimized distance as the position of the vertex (22) of the eye (12), and register the position of the vertex (22) on the basis of a feature of the eye (12) that is recognizable in the image representation of the eye (12).