Post-treatment after ophthalmic refraction correction

Description

[0001] The invention relates to a planning device for generating control data for a treatment device that creates at least one cut surface in the cornea by means of a laser device. The invention further relates to a treatment device comprising a planning device of the aforementioned type.

[0002] The invention further relates to a method for generating control data for a treatment device that creates at least one cut surface in the cornea by means of a laser device.

[0003] Finally, the invention also relates to a method for eye surgery, wherein at least one cutting surface in the cornea is created by means of a treatment device with a laser device.

[0004] Various treatment methods for refractive correction of the human eye are currently known. The aim of these surgical methods is to selectively reshape the cornea in order to influence the refraction of light within the eye. Several surgical techniques are used for this purpose. The most widespread procedure is currently laser-assisted in situ keratomileusis, also abbreviated 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 Intralase Corp., Irvine, USA. After the flap has been detached and folded back, the LASIK procedure involves the application of an excimer laser, which ablates the corneal tissue exposed beneath the flap.After the volume lying beneath the corneal surface has been evaporated in this way, the corneal flap is folded back into its original position.

[0005] The use of a laser keratome to expose the corneal flap is advantageous compared to a mechanical scalpel because it improves geometric precision and reduces the frequency of clinically relevant complications. In particular, the flap can be produced with a much more consistent thickness when laser radiation is used. Furthermore, the cut edge is precisely shaped, which reduces the risk of healing problems caused by this interface, which remains even after the operation. However, a disadvantage of this method is that two different treatment devices are required: the laser keratome for exposing the flap and the laser for vaporizing the corneal tissue.

[0006] These disadvantages have been overcome by a procedure recently implemented by Carl Zeiss Meditec AG, abbreviated as FLEX. In this lenticule extraction technique, a short-pulse laser, preferably a femtosecond laser, is used to create a cut in the cornea, separating a corneal volume (the lenticule). This lenticule is then manually removed by the surgeon after the flap covering it has been folded back. One advantage of this procedure is that the accuracy of the operation is further improved by using the femtosecond laser.

[0007] Secondly, only one treatment device is required; the excimer laser is no longer used.

[0008] A further development of the FLEX procedure is referred to in the literature as the SMILE procedure, in which no flap is created, but rather only a small incision serves as access to the lenticule located beneath the so-called cap. The separated lenticule is removed through this small incision, thus impairing the biomechanical integrity of the anterior cornea less than with LASIK, FLEX, or PRK (photorefractive keratectomy). In addition, fewer superficial nerve fibers in the cornea are severed in this way, which has been shown to have a beneficial effect on restoring the original sensitivity of the corneal surface. The symptom of dry eyes, which often requires treatment after LASIK, is thereby reduced in severity and duration. Other complications after LASIK, which are usually related to the flap (e.g., wrinkles, epithelial ingrowth in the flap bed), also occur less frequently without a flap.

[0009] When creating corneal incisions using laser radiation, the optical effect of the radiation is typically exploited by generating an optical breakthrough through individual optical pulses with durations ranging from approximately 100 fs to 100 ns. It is also known to introduce individual pulses with energies below a threshold for optical breakthrough into the tissue or material in such a superimposed manner that material or tissue separation is achieved. The concept of creating incisions in corneal tissue using a series of ultrashort laser pulses arranged over a surface allows for a wide variety of incision types.

[0010] It may become necessary to perform follow-up or repeat treatment. Reasons for this could include, for example, that the original treatment had to be discontinued or that the eye's refraction has changed in such a way that a further refractive correction is required.

[0011] For the FLEX procedure, a solution is known in the prior art (DE 10 2007 019814 A1, to which reference is hereby made in full). This solution is based on arranging the new incisions so that they do not intersect the preoperative incisions. This solution is also fundamentally applicable to the SMILE procedure. However, DE 10 2012 022 081 A1, to which reference is hereby made in full, proposed determining the position of the preoperative incisions by measurement and taking this into account in an improved correction.

[0012] However, it has been shown that measuring preoperative incisions is associated with a number of practical difficulties. Therefore, there is reason to conclude that, on the one hand, the correction methods according to the prior art have not always yielded optimal results and, on the other hand, are quite complex. A planning device according to the introductory part of claim 1 is known from US2011224658A1.

[0013] The invention is therefore based on the objective of providing a planning device for generating control data, a treatment device for refraction-corrective eye surgery, and a method for generating control data for such a treatment device, which enables improved subsequent refraction correction that is practical for users of the SMILE method even with currently available diagnostic devices.

[0014] The inventors recognized that removing a lenticule from the cornea during the SMILE procedure can stimulate a change in thickness, particularly thickening of the corneal epithelium, which should be considered when planning postoperative treatment. In this way, unlike previous methods, the laborious and often less precise direct determination of the location of preoperative incisions can be completely or partially eliminated.

[0015] Therefore, this problem is solved according to the invention with a planning device of the type mentioned at the outset, which has calculation means for determining a corneal cross-section for a post-treatment, wherein the calculation means are designed in such a way that a change in thickness, in particular a thickening of the epithelium, is taken into account in the calculation, which was essentially caused by a pre-treatment (primary treatment).

[0016] The invention is further solved by a treatment device comprising a laser device which, by means of laser radiation according to control data, separates at least one cut surface in the cornea, and a planning device of the type just mentioned for generating the control data, wherein the planning device is designed in such a way that a change in thickness, in particular a thickening of the epithelium, is taken into account during the planning.

[0017] The invention is also finally solved by a method for generating control data according to the type mentioned at the outset, which comprises: determining the thickness change of the epithelium, generating a control data set for the corneal section surface for controlling the laser device, taking into account the thickness change of the epithelium.

[0018] The invention is finally also solved by a method comprising: determining the thickness change of the epithelium, generating a control data set for the corneal cut surface, transferring the control data to the treatment device and generating the cut surfaces by controlling the laser device with the control data set, wherein the thickness change of the epithelium is taken into account when generating the control data set.

[0019] A number of measuring devices are suitable for measuring changes in epithelial thickness, such as OCT (Optical Coherence Tomography), ultrasound, confocal laser scanning systems, Scheimpflug cameras, and others. It is important that the measurement accuracy is equal to or better than 2 µm. The measurement can be performed independently of the subsequent treatment, thus serving as a basis for proactive planning. Alternatively, the measurement can be performed on the treatment device itself, using a measuring device integrated into the device. Preferably, the measuring device enables the measurement of epithelial thickness in direct temporal relation to the subsequent treatment – ​​virtually in real time. This ensures that the measuring device and the treatment laser can be geometrically aligned, thus establishing a fixed coordinate reference between the diagnostic and therapeutic devices.

[0020] One method for determining the change in thickness involves comparing the epithelial thickness before primary treatment and before secondary treatment.

[0021] If the measurement is to be carried out in advance, an additional step is to assign the measured values ​​to the coordinate system of the target coordinates of the treatment laser, for which electronic data transmission and registration solutions can be used advantageously.

[0022] As an alternative to measurement, epithelial growth or thickness can also be determined using a priori knowledge, estimation, nomograms, or similar methods. This knowledge should be available, for example, as program code in the planning system. Specifically, the typical thickness change after an initial treatment should then be automatically derived from information about that treatment. This is advantageous because predicting a typical thickness change after an initial treatment depends heavily on various characteristics of the treated eye (e.g., age, size, refraction) and the initial treatment (refractive change, size of the optical zone, location of the access incision). However, it is even more important to minimize the risk of planning errors in such medical treatments, such as those that can occur due to confusion of measurements or calculation errors.

[0023] The thickness change ΔThickness is generally a function of the location on the surface of the eye being treated, i.e., ΔThickness(x,y) or ΔThickness(r, ϕ). Handling such a two-dimensional profile and ensuring correct spatial reference presents a challenge for the user, which can be significantly reduced by the planning department possessing the necessary knowledge in the form of program code.

[0024] It is understood that the features mentioned above and those to be explained below can be used not only in the combinations given, but also in other combinations or on their own, without leaving the scope of the present invention.

[0025] The invention will now be explained in more detail, for example with reference to the accompanying drawings, which also reveal essential features of the invention. They show: Fig. 1 a schematic representation of a treatment device with a planning device for treatment in ophthalmic refractive correction, Fig. 2 a schematic representation of the effect of the laser radiation in the treatment device of the Fig. 1 is used Fig. 3 another schematic representation of the treatment device of the Fig. 1 regarding the introduction of laser radiation, Fig. 4 a schematic cross-sectional view through the cornea to illustrate the removal of corneal volume in connection with ophthalmic refractive correction, Fig. 5 a schematic representation of the structure of the treatment device Fig. 1 with particular reference to the planning facility located there, Fig. 6 A schematic representation of a lenticular geometry SMILE with the cuts to be made according to the state of the art. Fig. 7 a schematic representation of the structure of the treatment device Fig. 5 with particular reference to the measuring equipment located there Fig. 8 a schematic representation of a lenticular geometry for correction according to the invention Fig. 9 a schematic representation of the relationship between epithelial thickening and refractive correction

[0026] A treatment device for eye surgery is in Fig. 1 The treatment device 1 is shown and designated with the general reference numeral 1. The treatment device 1 is designed for making laser incisions in the eye 2 of a patient 3. For this purpose, the treatment device 1 has a laser unit 4 which emits a laser beam 6 from a laser source 5, which is directed as a focused beam 7 into the eye 2 or the cornea. Preferably, the laser beam 6 is a pulsed laser beam with a wavelength between 300 nanometers and 10 micrometers. Furthermore, the pulse duration of the laser beam 6 is in the range between 1 femtosecond and 100 nanoseconds, with pulse repetition rates of 200 to 20,000 kilohertz and pulse energies between 0.01 microjoules and 0.01 millijoules being possible. The treatment device 1 thus creates an incision in the cornea of ​​the eye 2 by deflecting the pulsed laser radiation. In the laser unit 4, or rather,Therefore, a scanner 8 and a radiation intensity modulator 9 are also provided for its laser source 5.

[0027] Patient 3 lies on a treatment table 10, which is adjustable in three directions to align the eye 2 with the direction of the laser beam 6. In the preferred design, the treatment table 10 is motor-adjustable. Alternatively, the treatment device can also be moved.

[0028] The control can be effected in particular by a control unit 11, which basically controls the operation of the treatment device 1 and is connected to the treatment device via suitable data connections, for example, connecting lines 12. Of course, this communication can also take place via other means, for example, fiber optics or radio. The control unit 11 makes the corresponding settings and time controls on the treatment device 1, in particular the laser unit 4, and thus accomplishes the corresponding functions of the treatment device 1.

[0029] The treatment device 1 further comprises a fixation device 15, which fixes the cornea of ​​the eye 2 in position relative to the laser device 4. This fixation device 15 can include a known contact lens 45, to which the cornea is pressed by negative pressure and which gives the cornea a desired geometric shape. Such contact lenses are known to those skilled in the art from the prior art, for example from DE 10 2005 040338 A1. The disclosure content of this publication is fully incorporated here insofar as it describes a design of the contact lens 45 that may be used for the treatment device 1.

[0030] Treatment device 1 also includes a camera (not shown) which can capture an image of the cornea 17 through the contact lens 45. The camera can be illuminated in both the visible and infrared ranges of light.

[0031] The control unit 11 of the treatment device 1 also has a planning device 16, which will be explained in more detail later.

[0032] Fig. 2 Figure 1 schematically illustrates the mode of action of the incident laser beam 6. The laser beam 6 is focused and enters the cornea 17 of the eye 2 as the focused laser beam 7. A schematically depicted optical system 18 is provided for focusing. It creates a focus in the cornea 17 where the laser radiation energy density is so high that, in combination with the pulse length of the pulsed laser radiation 6, a non-linear effect occurs in the cornea 17. For example, each pulse of the pulsed laser radiation 6 can create an optical breakthrough in the cornea 17 at the focus 19, which in turn produces a Fig. 2 A plasma bubble, only schematically indicated, is initiated. Upon formation of the plasma bubble, the tissue layer separation encompasses a larger area than focus 19, although the conditions for generating optical breakthrough are only met at focus 19. For each laser pulse to generate 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 T2. Alternatively, a tissue-separating effect can also be achieved by pulsed laser radiation by emitting several laser radiation pulses in a region, with the focus spots overlapping. In this case, several laser radiation pulses act together to achieve a tissue-separating effect.However, the type of tissue separation used by the treatment device 1 is not relevant for the following description; what is essential is only that a cutting surface is created in the cornea 17 of the eye 2.

[0033] To perform refractive surgery, a corneal volume is removed from an area within the cornea 17 using laser radiation 6. This is achieved by separating tissue layers that isolate the corneal volume, thus enabling its removal. For example, in the case of pulsed laser radiation, the position of the focus 17 of the focused laser beam 7 within the cornea 17 is adjusted to isolate the corneal volume to be removed. This is shown schematically in Fig. 3 The refractive properties of the cornea 17 are specifically altered by removing volume in order to achieve refractive correction. The volume is therefore usually lens-shaped and is called a lenticule.

[0034] In Fig. 3 The elements of the treatment device 1 are shown only to the extent necessary for understanding the generation of the incision surface. As already mentioned, the laser beam 6 is focused at a focus 19 in the cornea 17, and the position of the focus 19 in the cornea is adjusted so that energy from laser radiation pulses, focused at different locations, is introduced into the tissue of the cornea 17 to generate the incision surface. The laser radiation 6 is preferably provided as pulsed radiation by the laser source 5. The scanner 8 is of the design of Fig. 3 The scanner is constructed in two parts and consists of an xy-scanner 8a, which in one variant is implemented by two galvanometer mirrors deflecting the laser beam 6 from the laser source 5 in a two-dimensional manner, so that a deflected laser beam 20 is present after the scanner 9. The scanner 8a thus causes an adjustment of the position of the focus 19 essentially perpendicular to the main direction of incidence of the laser beam 6 in the cornea 17. In addition to the xy-scanner 8a, a z-scanner 8b is also provided in the scanner 8 for adjusting the depth of field. The z-scanner 8b ensures that the z-position of the focus 19, i.e., its position on the optical axis of incidence, is changed. The z-scanner 8b can be arranged upstream or downstream of the xy-scanner 8a.

[0035] For the operating principle of the treatment device 1, the assignment of the individual coordinates to the spatial directions is not essential, nor is it essential that the scanner 8a deflects about axes perpendicular to each other. Rather, any scanner capable of adjusting the focus 19 in a plane in which the axis of incidence of the optical radiation does not lie can be used. Furthermore, any non-Cartesian coordinate system can also be used for deflecting or controlling the position of the focus 19. Examples include spherical or cylindrical coordinates. The position of the focus 19 is controlled by means of the scanners 8a and 8b, controlled by the control unit 11, which makes corresponding adjustments to the laser source 5, the (in Fig. 3 The control unit 11 ensures the proper operation of the laser source 5 and the three-dimensional focus adjustment described here as an example, so that ultimately a cutting surface is formed that isolates a specific corneal volume to be removed for refractive correction.

[0036] The control unit 11 operates according to predefined control data, which, for example, in the laser device 4 described here only as an example, are specified as target points for focus adjustment. The control data is generally summarized in a control data set. This provides geometric specifications for the interface to be formed, for example, the coordinates of the target points as a template. In this embodiment, the control data set also contains specific position values ​​for the focus position adjustment mechanism, e.g., for the scanner 8.

[0037] The generation of the cut surface with the treatment device 1 is exemplified in Fig. 4 As shown, a corneal volume 21 within the cornea 17 is isolated by adjusting the focus 19, in which the focused beam 7 is concentrated. For this purpose, incision surfaces are created, which are shown here as an anterior flap incision surface 22 and a posterior lenticule incision surface 23. These terms are used here only as examples and are intended to establish a connection to the conventional LASIK or FLEX procedure, for which the treatment device 1, as already described, is also designed. The essential point here is that the incision surfaces 22 and 23, as well as the circumferential marginal incision 25, which joins the incision surfaces 22 and 23 at their edges, isolate the corneal volume 21. Through an opening incision 24, a corneal lamella anteriorly limiting the corneal volume 21 can be folded back, so that the corneal volume 21 can be removed.

[0038] Alternatively, and essential to the present invention, the SMILE method can be used, in which the corneal volume 21 is extracted through a small incision, as described in DE 10 2007 019813 A1. The full disclosure of this document is incorporated herein.

[0039] Fig. 5 Figure 1 schematically depicts the treatment device 1, and the significance of the planning device 16 will be explained in more detail using this device as an example. In this variant, the treatment device 1 has at least two devices or modules. The laser device 4, already described, emits the laser beam 6 onto the eye 2. As already described, the laser device 4 operates fully automatically via the control unit 11; that is, upon receiving a corresponding start signal, the laser device 4 initiates the generation and deflection of the laser beam 6, thereby creating cut surfaces constructed as described. The laser device 4 receives the control signals required for operation from the control unit 11, which has previously been provided with the corresponding control data. This is accomplished by means of the planning device 16, which is located in Fig. 5 The planning unit 16 is shown only as an example component of the control unit 11. Of course, the planning unit 16 can also be designed independently and communicate with the control unit 11 via wired or wireless means. The essential requirement is simply that a suitable data transmission channel is provided between the planning unit 16 and the control unit 11.

[0040] The planning device 16 generates a control data set that is provided to the control unit 11 for executing the ophthalmic refractive correction. The planning device uses measurement data of the cornea of ​​the eye. In the embodiment described here, this data originates from a measuring device 28 that has previously measured the eye 2 of the patient 3. Of course, the measuring device 28 can be configured in any way and transmit the corresponding data to the interface 29 of the planning device 16. In particular, the measuring device 28 is configured as an OCT or ultrasound measuring system or a confocal laser scanning system to provide the measurement data with the required accuracy.

[0041] The planning unit now assists the operator of the treatment device 1 in defining the cutting surface for isolating the corneal volume 21. This can extend to fully automatic definition of the cutting surfaces, for example, by the planning unit 16 determining the corneal volume 21 to be removed from the measurement data, defining its boundary surfaces as cutting surfaces, and generating corresponding control data for the control unit 11. At the other end of the automation spectrum, the planning unit 16 can provide input options where a user enters the cutting surfaces in the form of geometric parameters, etc. Intermediate levels include suggestions for the cutting surfaces that the planning unit 16 automatically generates and that can then be modified by a technician.In principle, all the concepts that have already been explained in the more general description section above can be applied here in planning facility 16.

[0042] To perform a treatment, the planning unit generates 16 control data for the creation of the cutting surfaces, which are then used in the treatment device 1.

[0043] Fig. 6a Figure 1 shows a schematic representation of a corneal cross-section in the SMILE procedure to illustrate the geometric relationships. The cornea 17 has an anterior cap incision 22 with an opening incision 26. The posterior lenticule incision 23 isolates the lenticule volume 21, which can be extracted through the opening incision 26. If it is now necessary to perform a second refractive treatment, a new lenticule must be calculated. For this purpose, the position and shape of the cap incision 22 of the original treatment must be determined with the required accuracy. In a first embodiment of the invention, this can be done by a measurement with the measuring device 28. The method of such a measurement is known in principle from DE 103 23 422 A1, to which full reference is hereby made.In this document, however, the measuring device serves a different purpose: the self-calibration of the treatment laser during treatment to ensure the required accuracy (better than 5 µm). The principle of ultrasound measurement is explained in "Refractive Surface Ablation: PRK, LASEK, Epi-lasik, Custom, PTK, and Retreatment" by Paolo Vinciquerra, Fabrizio Camesasca - Chapter 36; and in "Very high frequency digital ultrasound: artemis 2 scanning in corneal refractive surgery", SLACK Inc., Thorofare, NJ, USA, 2007. The achieved measurement accuracy is 1 µm and is therefore suitable for the present task. Based on the current position of the cap incision 22 and the existing need for refractive correction, a new lenticule incision area 23 and a new marginal incision 25 are calculated in the planning device 16 and cut in the cornea 17 using the treatment device 1.

[0044] The position and shape of the reference surface in relation to the anterior corneal surface, i.e., the depth of the original cap incision 22, can change postoperatively due to epithelialization (epithelial hyperplasia), changes in the tear film, corneal swelling, corneal edema, or similar factors. In particular, a change in the thickness of the epithelial layer ΔThickness(x,y) or ΔThickness(r, ϕ) causes a corresponding change in the relative position of the original cap incision with respect to the corneal surface.

[0045] Changes such as swelling, changes in the tear film, etc., can also occur if the operation is terminated (e.g., due to loss of negative pressure on the contact lens) and must also be taken into account.

[0046] In a first variant of the invention, the changes (change in epithelial thickness as a result of the primary treatment, relative change in the position of the cuts made during the primary treatment, e.g. due to epithelial hyperplasia) are measured with the measuring device 28 and are included in the calculation of the new lenticule section area 23.

[0047] Fig. 7 shows a schematic representation of the structure of the treatment device. Fig. 5 and the coupling of the measuring device 28. The laser device 4 has a laser source 5 which generates a laser beam 6. A contact glass 45 serves for docking to the eye (not shown here). The measuring device 28 is coupled via a coupling element 30. In the case of an optical measuring device 28 (OCT, confocal laser scanning system), the coupling element 30 can be designed as an optical beam splitter. In the case of an ultrasonic measuring device 28, the coupling element is designed as an acoustic beam splitter, as described, for example, in EP 343 432 A2.

[0048] Measuring the reference surface of the previous cut (primary interface) allows for an exact alignment of the old and new cuts, even in case of decentering and tilting of the new treatment relative to the original treatment.

[0049] For example, an image or measurement of the attached cornea is taken during the initial treatment and temporarily stored in a database. If a follow-up treatment (re-treatment) is then performed, another image or measurement of the attached eye is taken and compared with the stored image or measurement.

[0050] In a basic configuration, the system could initially only compare the existing incision pattern with the planned new incision pattern and thus check whether a re-treatment is possible. A message would then inform the user whether or not they can carry out the post-treatment as planned.

[0051] In one implementation, the old incision pattern is incorporated into the calculation of the new shot pattern, taking into account effects as described above. This allows for a customized treatment tailored to the specific conditions of the patient's cornea.

[0052] Re-treatment is advantageously performed using a single incision, as this eliminates the need to maintain a distance from the previous incision, thus conserving corneal tissue and preventing the residual stromal thickness limit of 250 µm from being reached as quickly. However, even a re-treatment below the initial incision can be improved by recording the previous incisions, as the access incision for the new lenticule can be made at the same location as the original incision, eliminating the need for a new surface incision. This avoids further weakening the cornea, as would be the case with a new incision.

[0053] According to the invention, the thickness change of the epithelial layer is taken into account when planning the lenticule cut surface 23. In the first embodiment of the invention, this is achieved by considering the results of a measurement of the position of the original cap cut. In a second embodiment of the invention, the effort is reduced by predicting the typical changes due to pretreatment based on treatment parameters and taking them into account for posttreatment. This is because the thickness change is known for myopia correction using the SMILE procedure, e.g., from N. Luft, MH Ring, M. Dirisamer, AS Mursch-Edlmayr, TC Kreutzer, J. Pretzl, M. Bolz and SG Priglinger, "Corneal epithelial remodeling induced by Small Incision Lenticule Extraction (SMILE)," Invest Ophthalmol Vis Sci., Vol. 57, No. 9, pp. 176-183, 2016.

[0054] The study demonstrates that the epithelial layer thickens postoperatively. It is reasonable to assume that the extent of this change correlates with the type of change and the degree of correction, and that its dynamics are linked to the course of the healing process, beginning with treatment and continuing at least until a long-term stable refraction is achieved. According to Luft et al., the observed increase in thickness reaches a value of a few micrometers after approximately three months. It can be assumed that this value then changes very little. The data suggest that the increase in epithelial thickness during the SMILE procedure for myopia correction is almost uniform and is age-dependent. Δ Thickness = Δ Thickness Δ SE , Age . Δ Thickness = 0.707 μm + 1.268 μm / dpt Δ SE − 0.038 μm / dpt · y Δ SE · Age − 30 y .

[0055] If the increase in corneal thickness (AThickness(r, ϕ)) is uneven, as observed in a study published around the same time by S. Ganesh, "Epithelial Thickness Profile Change Following Small Incision Refractive Lenticule Extraction (SMILE) for Myopia and Myopic Astigmatism," JRS, Vol. 32, No. 7, pp. 473-478, 2016, it can cause a greater refractive change during the healing process after treatment than if it occurs uniformly, as observed by Luft et al. This refractive change could affect the sphere and cylinder as well as higher-order aberrations. Inhomogeneous thickness changes require more careful consideration when planning post-treatment.

[0056] WO 2016 / 144404 A1 also points to postoperative epithelial thickening.

[0057] The incisions of the post-treatment must be correctly positioned relative to the incisions of the initial treatment. This includes all three spatial directions. For this purpose, the device calculates a standard post-treatment based on the data from the initial treatment and suggests it to the user. By using treatment data from the initial treatment, the planning of the second treatment refers to the coordinate system of the initial treatment. However, the coordinate system of the second treatment will generally be at least shifted and / or rotated relative to that of the initial treatment. Such a shift must be taken into account according to the invention. In the following, "coordinate systems" will always be understood to mean visual coordinate systems.

[0058] Therefore, shifts can have various causes: 1. Discrepancy between device coordinate system and eye coordinate system during the initial treatment. 2. Discrepancy between device coordinate system and eye coordinate system during the second treatment. 3. Discrepancy between device coordinate systems of the initial and second treatments. 4. Discrepancy between eye coordinate systems of the initial and second treatments. One variant of the incision technique involves creating a secondary lenticule incision 23 below (posterior to) the existing interface (cap incision 22 of the initial treatment) and connecting it to the existing interface via the lenticule margin incision 25. This creates a lenticule that can subsequently be extracted manually.

[0059] This variant is in Fig. 8 shown, with the thickening of the epithelium 31 shown in a coarsened form.

[0060] A second approach involves creating a secondary lenticule section anterior to the existing interface and connecting it to the existing interface via a lenticule margin section. In this approach, the lenticule margin section is advantageously created prior to the lenticule section. This results in a manually extractable lenticule.

[0061] For both sectioning variants, it is important that the new sections have the most precise possible positional relationship to existing sections. Due to the described shifts in the coordinate systems, predicting the lateral and axial position of the existing interface during the second processing step is only possible with limited accuracy. This can lead to two significant problems: 1. The lenticule produced by the interaction of old and new sections does not have the correct shape for the intended refractive correction. In this case, the correction deviation may reduce the effectiveness of the procedure. 2. Old and new sections do not result in complete separation of a lenticule because they do not touch or intersect. In this case, lenticule extraction may fail entirely.

[0062] In one embodiment of the invention, the edge cut during the second treatment is therefore extended so that it reliably intersects the existing interface. For example, in the first variant of the cutting process, the edge cut is extended into the interior of the primary (and secondary) cap so that a cross-cut with the existing interface is created, i.e., the edge cut 25 intersects the cap cut 22 (in Fig. 8 (not shown as shown). This allows axial positional errors to be compensated for. This is particularly important because the change in the epithelium caused by the first treatment mainly results in an axial shift between the ocular coordinate systems of the first and second treatments.

[0063] In another embodiment of the invention, the displacement caused by the epithelial alteration is estimated and compensated for accordingly. This estimate is based on information from the initial treatment, in particular the intended and / or achieved refractive change, the patient's age, and keratometry. For the displacement caused by the epithelial alteration, an approximation formula known from Luft et al., for example, can be used, or another approximation formula that may also take into account inhomogeneous thickening. The displacement of the interface relative to its position planned in the initial treatment can thus be calculated. For example, homogeneous epithelial thickening ultimately leads to a homogeneous displacement of the existing interface with respect to the device coordinate system for the subsequent treatment.This fact is taken into account during post-treatment by shifting, tilting or bending the lenticule cut surface accordingly.

[0064] In a further embodiment of the invention, the change in the epithelium (epithelial hyperplasia) is measured, and this information is combined with the also known information about the position of the sections from the initial treatment, thus adjusting the position of the new sections accordingly. The measurement of the change in the epithelium (epithelial hyperplasia) can be performed, for example, with a high-resolution OCT or ultrasound device. The subsequent treatment is adapted accordingly by curving and positioning the lenticule section surface 23.In particular, the secondary lenticule surface, just as with a primary treatment, can be executed with the desired refractive effect by spatially aligning the virtual cap surface of the second treatment, which already exists as the primary interface and therefore does not need to be cut again, with the existing interface of the first treatment in terms of shape and position for calculating the correct lenticule cut surface. Alternatively, a quantified deviation can be counteracted by a corresponding adjustment during the second treatment.

[0065] In a further embodiment of the invention, the displacement caused by the change in the epithelium (epithelial hyperplasia) is measured, and the position of the new sections is corrected accordingly. The measurement of the position and shape of the existing interface can be performed, for example, with a high-resolution OCT or ultrasound measuring device, as shown in Fig. 7The post-treatment is adapted accordingly by curving and positioning the lenticule cut surface 23. In particular, the lenticule surface, as with a primary treatment, can be designed with the desired refractive effect by spatially aligning the virtual cap surface of the second treatment, which already exists as an interface and therefore does not need to be cut again, with the existing interface of the first treatment for the calculation of the correct lenticule cut surface in terms of shape and position.

[0066] The described embodiments can be implemented individually or in combination. Combining them also offers the possibility of calculating deviations between the different planning methods. This information can be used not only for plausibility checks but also to derive cross-cuts whose extent is adapted to the inaccuracies of the various calculation methods.

[0067] In a further development of the invention, the position and shape of the interface resulting from the primary treatment are calculated with respect to the coordinate system of the treatment device. For example, in the case of a vacuum-fixed contact lens, it suffices to determine the depth of the interface as a function of its position relative to the surface of the eye. This can be done efficiently using high-resolution OCT. The resulting data T(r, ϕ) generally exhibit rotational symmetry and can be well approximated by a rotationally symmetric polynomial P(r). The lenticule section L(r, ϕ) is first calculated, for example, in the first variant of the sectioning procedure, assuming a homogeneous cap of thickness D, and subsequently applied the function P(r) - D.The resulting lenticule section L'(r, ϕ)=L(r, ϕ)+P(r)-D is corrected for the displacement of the primary interface relative to the surface of the eye caused by epithelial remodeling. This correction method, based on the principle of perturbation analysis, can be refined step by step by a person skilled in the art.

[0068] In another embodiment, the user can view the new sections in a simulated cross-sectional image of the cornea, along with the sections remaining from the initial treatment. Furthermore, existing information on anatomical changes is used to calculate a correction for the display. Epithelial thickening, for example, can be derived from the difference between the preoperative pachymetry, the lenticule thickness (or lenticule profile) during the initial treatment, and the current pachymetry. This simple estimate can be supplemented with further information, such as measured epithelial thickness, an epithelial thickness profile, subepithelial topography, or a high-resolution cross-sectional image (OCT image (B-scan), Scheimpflug, etc.) and the interface profile identified therein with respect to the anterior surface of the cornea. The geometric uncertainty of the displayed sections is appropriately represented (e.g.,Error bars or semi-transparent widening of an affected element in the display). Incorrect or critical geometries are visually highlighted (e.g., warning signs).

[0069] Since the refractive effect of the secondary lenticule is directly related to its shape, a positioning error of the second treatment compared to the existing incisions affects the refractive effect of the secondary lenticule. Therefore, in a further development of the invention, the expected refractive power of the lenticule, including the positioning errors and variance in the refractive effect resulting from changes in epithelial thickness, can be displayed. The user then has the opportunity to make corresponding optimizations to optimally plan a target refraction, even taking potential errors into account. For example, considering the existing accommodative ability of the eye (in young patients), the target refraction can be shifted into the range of very low hyperopia.

[0070] The planning tool visualizes the section geometry in a virtual representation of the existing geometric situation at eye level and the superimposed representation of the planned sections. Sections from the initial treatment are also displayed. In a further development, the inaccuracy of the position of these sections will be appropriately visualized (e.g., error bars, semi-transparency, cross-sectional view).

[0071] The planning tool can include a prognostic model for typical postoperative anatomical changes after SMILE, which serves as a starting point for treatment planning of a SMILE revision ("first-order approximation"). Diagnostic data acquired immediately before the second procedure (topography, wavefront, pachymetry, OCT, Scheimpflug) can be used to refine the planning ("second-order approximation"). Intraoperative diagnostic data (OCT after docking) can also be included. The various input data may also serve only to confirm the existing planning or for error estimation and prognosis.

[0072] The prediction of the refractive effect can extend beyond the target refraction (mean value) and thus also include shifts and expected variance. The various causes of deviations can be taken into account for this purpose.

[0073] It should also be noted that the treatment device 1 or the planning device 16 naturally also implements the previously explained procedure in general terms.

[0074] Another embodiment of the planning device consists in the form of a computer program or a corresponding data carrier with a computer program that implements the planning device on a corresponding computer, so that the input of the measurement data is made to the computer via suitable data transmission means and the control data is transmitted from this computer to the control unit 11, for which data transmission means known to the skilled person are again suitable.

Claims

1. Planning device (16) for creating control data for a treatment apparatus (1) for eye surgery, which creates at least one cut surface (22, 23, 24, 25, 26) in the cornea (17) by means of a laser device (4), wherein the planning device comprises calculation means for defining corneal cut surfaces, such as the cap incision (22), lenticule incision (23), (lenticule) edge incision (25), access or opening incision (26, 24), wherein the calculation means define the corneal cut surfaces on the basis of the data of a refraction correction, with the data of the refraction correction also including data of a pretreatment, and create for the corneal cut surfaces a control data record for controlling the laser device, characterized in that the planning device (16) is designed in such a way that a change in thickness of the epithelium (31) is taken into account in the planning, and wherein the change in thickness is essentially a thickness growth caused by a pretreatment.

2. Treatment apparatus (1) for eye surgery, which comprises - a laser device (4) which in accordance with control data creates at least one cut surface in the cornea (17) by means of laser radiation (6), and - a planning device (16) for creating the control data according to Claim 1.

3. Method for creating control data for a treatment apparatus (1) for eye surgery, which by means of a laser device (4) creates at least one cut surface (22, 23, 24, 25, 26) in the cornea, wherein the method is characterized by following steps: measuring the position of preoperative incisions, providing corneal data on the basis of data of a refraction correction, defining corneal cut surfaces, and creating a control data record for controlling the laser device for cutting the corneal cut surfaces, wherein a change in thickness of the epithelium (31) is taken into account when creating the control data record, and the data of the refraction correction also include data of a pretreatment, and wherein the change in thickness is essentially a thickness growth caused by a pretreatment.

4. Method according to Claim 3, wherein the change in thickness of the epithelium (31) is determined using a measuring apparatus which is preferably from the group of optical coherence tomography (OCT) device, Scheimpflug camera, ultrasonic measuring system and confocal laser scanning system and whose measurement accuracy is equal to or better than 2 µm.

5. Method according to Claim 3, wherein the change in thickness is determined by means of program codes available as nomogram, a-priori knowledge or estimation.

6. Device according to either of Claims 1 and 2, characterized in that a measuring device (28) is provided for measuring the epithelial thickness and is connected to the planning device and preferably is from the group of optical coherence tomography (OCT) device, Scheimpflug camera, ultrasonic measuring system and confocal laser scanning system.

7. Device according to Claim 6, characterized in that the measuring device is essentially connected online to the planning device.

8. Device according to Claim 6 or 7, wherein the change in thickness of the epithelium is determined using a measuring apparatus whose measurement accuracy is equal to or better than 2 µm.

9. Device according to either of Claims 1 and 2, wherein the change in thickness by means of nomogram, a-priori knowledge or estimation is present as program code.

10. Computer program product with program code which, upon execution on a computer, carries out the method according to Claim 4 or 5.

11. Data medium having a computer program product according to Claim 10.