Device for changing the refractive power of the cornea

Abstract

Device for changing the refractive power of the cornea (1), in particular for correcting hyperopia or presbyopia, comprising injection means (13, 15) with at least one hollow needle (15) for injecting at least one optically transparent filling material with a predetermined refractive index into an intrastromal corneal pocket (7), characterized by: a. a controllable injection drive (17) which is at least indirectly coupled to the injection means (13, 15) and is designed to change the amount of the at least one filling material to be injected; b. an optical coherence tomography (OCT) device (19) which is designed to monitor the area of ​​the corneal pocket (7) by measuring depth profiles of the cornea (1) on a repeatedly scanned pattern; and c.a computing unit (21) which is designed and / or configured to determine, from the measurement data of the OCT device (19) during injection, at least the radii of curvature of the front (3) and back (5) of the cornea (1) in temporal sync with the repetitions of the scanning pattern, wherein the computing unit (21) is designed and / or configured to control the injection drive (17) to change the injected quantity of the at least one filling material, based on the radii of curvature of the front (3) and back (5) of the cornea (1) and / or such that a predetermined target criterion is met.

Description

[0001] The invention relates to a device for altering the refractive power of the cornea, in particular for correcting hyperopia (farsightedness) or presbyopia (age-related farsightedness), by surgically changing the curvature of the cornea. The invention specifically relates to a device comprising an injection means with at least one hollow needle for injecting an optically transparent filler material with a predetermined refractive index into an intrastromal corneal pocket.

[0002] The human eye is an optical imaging system with various components responsible for the refraction of light. Its refractive power is primarily based on the combination of light refraction at the cornea and the lens. Refractive power is measured in diopters (dpt), which is the reciprocal of the focal length in meters.

[0003] The refractive power of the cornea essentially corresponds to that of a convex-concave lens, with the convex outer surface of the cornea typically having a slightly larger radius of curvature (e.g., 7.7 mm) than the concave inner surface (e.g., 6.8 mm). Considering the typical refractive indices for the corneal stromal tissue (e.g., 1.376) and the aqueous humor behind the cornea (e.g., 1.336), as well as air (1.0), the corneal refractive power can be estimated at approximately 43 diopters (dpt). Based on these exemplary values, the convex anterior surface (converging lens) contributes approximately 49 diopters, and the concave posterior surface (diverging lens) contributes approximately -6 diopters. In comparison with the eye lens, whose refractive power varies between about 19 dpt and 34 dpt during accommodation, the cornea proves to be the more significant optical component for the overall refractive power.A calculation of corneal refractive power can be found, for example, in the work by Olsen, “On the calculation of power from curvature of the cornea”, British Journal of Ophthalmology, 1986, 70, 152–154.

[0004] Refractive errors are usually caused by an incorrect curvature of the cornea relative to the length of the eyeball. If the cornea is too curved, its refractive power is too high. Parallel light rays from a distant object are then focused in front of the retina, resulting in a blurred image on the retina; the eye is myopic (nearsighted). If the corneal curvature is too shallow, its refractive power is too weak, and the eye is hyperopic (farsighted). With age, the lens's accommodative amplitude decreases, leading to presbyopia (age-related farsightedness). This can be corrected by a localized change in the corneal curvature, which makes the eye bifocal.

[0005] Laser-assisted in situ keratomileusis (LASIK) is a now widely used eye surgery for correcting the aforementioned refractive errors. The procedure involves removing tissue using laser ablation to reshape the cornea. Tissue removal cannot be performed on the surface of the cornea because the epithelial layer there is very sensitive to pain, and the refractive error would regress as tissue regenerates. Furthermore, healing reactions can lead to opacities in the corneal stroma. Therefore, a thin corneal flap is first created and lifted. This allows for precise tissue removal within the corneal stroma using an excimer laser. After the tissue removal is complete, the flap is repositioned, and the patient regains clear vision.In particular, myopia correction, in which tissue is removed centrally along the optical axis, is very successful with the LASIK procedure for refractive errors up to high levels of more than 10 diopters.

[0006] However, correcting hyperopia or presbyopia proves considerably more difficult. Steeping the cornea, i.e., reducing its radius of curvature by removing tissue, is only possible with LASIK through a ring-shaped ablation. Even with low refractive errors of just a few diopters, the LASIK procedure exhibits problems with the stability and reproducibility of the correction.

[0007] To achieve a higher refractive power of the anterior segment of the eye, the curvature of the cornea can be modified using rigid, permeable hydrogel lenses inserted into an intrastromal pocket previously created with a laser. However, these inlays are only suitable for minor refractive corrections; see, for example, Binder, “Intracorneal inlays for the correction of presbyopia and low hyperopia,” Ophthalmology Times EUROPE, December 1, 2015.

[0008] In publications US 5,964,748 (Peyman) and US 8,409,177 B1 (Lai), the insertion of a liquid implant into the cornea is proposed. These publications also involve first creating an intrastromal pocket in the cornea, referred to hereafter as the corneal pocket. This can be done using laser light or a surgical scalpel. Specifically for hyperopia correction, the corneal pocket is located centrally in front of the lens, perpendicular to the optical axis; see especially Peyman, Fig. 37 ff., and the accompanying figure description. A transparent, biocompatible fluid is then injected into the corneal pocket, filling it and thereby thickening the cornea overall. Depending on the chosen depth of the pocket within the stromal tissue, this can lead to bulging of the anterior cornea, resulting in a steepening of the cornea's outer surface, i.e., a reduction in the anterior radius of curvature, and thus an increase in refractive power.

[0009] The optically transparent, biocompatible fluid could be, for example, a gelable collagen, but a silicone gel or an injectable polymethyl methacrylate (PMMA) are also suitable. Furthermore, hydrogels containing hyaluronic acid and other transparent compositions approved for injection into tissue can be used.

[0010] Lai's patent builds upon Peyman's proposal, stipulating that the fluid injected into the corneal pocket should be polymerizable under the influence of light and that a photocuring step after injection solidifies the liquid implant. This fixes the implant in its current position and simultaneously stabilizes the refractive index change.

[0011] Against this background, the inventors of the present description conducted experiments on enucleated pig eyes to further investigate the feasibility of creating a corneal pocket using laser light and subsequently bulging the cornea by fluid injection. Among other findings, they discovered that the fluid volume in the corneal pocket readily assumes the shape of a lenticule. The investigation focused on the achievable results regarding the extent and predictability of the refractive power change.

[0012] In the experiments, changes in refractive power of up to 9 diopters were achieved, which strongly supports the further development of the methodology, as other methods do not currently allow such large increases in refractive power.

[0013] However, observation of the eye using a commercial optical coherence tomography (OCT) device has shown that the injection of the filler material changes not only the curvature of the anterior cornea but also that of the posterior cornea, with the latter becoming significantly flattened. While flattening the concave posterior surface reduces the diverging effect—and thus also increases refractive power—this effect is less effective relative to the injected volume of filler material than the originally planned bulging of the anterior surface, because the refractive index step at the posterior surface is much smaller than at the anterior surface.

[0014] The assumption that a previously calculated injection volume of filler material leads to a clearly predictable change in the anterior radius of curvature is therefore untenable. The deformation of the cornea with respect to changes in the radii of curvature on the anterior and posterior surfaces, as well as the lenticule shape of the injected filler material, depend strongly on the elastic-plastic properties of the cornea, the distance of the corneal pocket from the anterior corneal surface, and also the size of the pocket. Furthermore, the mechanical properties of the corneal stroma vary by up to a factor of three from person to person; see, for example, Winkler, “Nonlinear optical macroscopic assessment of 3-D corneal collagen organization and axial biomechanics”, IOVS, Vol. 52, pp. 8818–8827, 2011.

[0015] The invention therefore aims to create a device for changing the refractive power of the cornea by injecting a transparent filling material, which is capable of determining the correct injection quantity.

[0016] The problem is solved by a device for changing the refractive power of the cornea comprising injection means with at least one hollow needle for injecting at least one optically transparent filling material with a predetermined refractive index into an intrastromal corneal pocket, characterized by a controllable injection drive which is at least indirectly coupled to the injection means and is designed to change the amount of the at least one filling material to be injected; an optical coherence tomography (OCT) device designed to monitor the corneal pocket area by measuring depth profiles of the cornea on a repeatedly scanned pattern over time; a computing unit that is designed and / or configured to determine, from the measurement data of the OCT device during injection, at least the radii of curvature of the front and back of the cornea, keeping pace with the repetitions of the scanning pattern, wherein the computing unit is designed and / or configured to control the injection drive to change the injected quantity of the at least one filling material, based on the radii of curvature of the front and back of the cornea and / or in such a way as to meet a predetermined target criterion.

[0017] The dependent claims specify advantageous embodiments of the invention.

[0018] The invention assumes the presence of a suitably placed corneal pocket in the patient's cornea following treatment by a physician. The creation, placement, and dimensioning of the pocket are not the subject of the present invention.

[0019] The basic idea of ​​the invention is to continuously measure the cornea, at least in the area of ​​the corneal pocket, using an OCT device during the injection of the filler material into the corneal pocket, and to automatically assess from this measurement data the extent to which the injection goal has been achieved. This assessment is preferably also used automatically to control the injection device to change the injected quantity of filler material if the goal has not yet been reached, and to automatically determine the optimal fill quantity for the therapeutic goal. The device is preferably designed and / or configured as an autonomous device.

[0020] The device offers the technical advantage that the correct injection volume can be automatically determined from OCT measurement data during corneal pocket filling, based on the fulfillment of a target criterion for achieving desired optical properties of the cornea. The device can be designed and / or configured accordingly.

[0021] The invention is explained in more detail below with the aid of figures. These show:

[0022] Fig. 1 a sketch of the device for changing the refractive power of the cornea;

[0023] Fig. 2 an OCT cross-sectional image of the cornea of ​​an enucleated pig eye obtained from a line grid as a scanning pattern;

[0024] Fig. 3 an OCT cross-sectional image of the eye from Fig. 2 after creating and filling a corneal pocket with a viscoelastic hydrogel containing 1% sodium hyaluronate.

[0025] The Fig. Figure 1 shows a schematic sketch of the device according to the invention. It includes an OCT device ( 19 ) which, before and especially during injection, create depth profiles of the cornea by interferometric evaluation of backscattered measurement light ( 1 ) at least in the area of ​​the corneal pocket ( 7 ) recorded and the measurement data either directly or in processed form, e.g. as cross-sectional images of the cornea ( 1 ), to the computing unit ( 21 ) transmitted. The measurement of a single depth profile is also referred to as an A-scan and is performed as a point measurement. This is used, among other things, to assess the curvature of the anterior cornea ( 3 ) and the reverse side ( 5 ) a multiple A-scans are performed at different points on the cornea ( 1 ), which, considering the location and size of the corneal pocket ( 7) are predetermined. The entirety of the measurement points forms the scan pattern. The vertical, dotted lines in Fig. Figure 1 indicates the individual OCT-A scans along the corneal extent. Once the scanning pattern is traversed, i.e., a depth profile is acquired for each point of the scanning pattern, the shape of the cornea can be determined from the combined measurement data ( 1 ) and possibly the cornea pocket ( 7 The scanning pattern can be one- or two-dimensional, meaning the measurement points can lie on a line grid or a two-dimensional grid. The grid point spacing can vary.

[0026] In the simplest case, the grid points of a one-dimensional grid are used as the scanning pattern of the OCT device ( 19 ) along a line perpendicular to the optical axis across the center of the corneal pocket – this is also known as a B-scan. The OCT device ( 19) performs a measurement of the corneal scattering intensity ( 1 ) for each grid point of the line, so that the data set of this sampling pattern is a cross-sectional image of the cornea ( 1 ) delivers, which lies in the plane spanned by the line of the scanning pattern and the optical axis (drawing plane of Fig. 1) From an OCT cross-sectional image, at least the radii of curvature of the front side can be determined ( 3 ) and the reverse side ( 5 ) of the cornea ( 1 ) determine.

[0027] For the continuous monitoring of the cornea ( 1 ) in the area of ​​the cornea pocket ( 7 ) the scanning pattern is repeated over time to detect changes during the injection of the filler material.

[0028] Determining at least the radii of curvature of the front ( 3 ) and reverse ( 5 ) of the cornea ( 1) should keep pace with the repetitions of the sampling pattern runs from the processing unit ( 21 ) can be performed. Thus, at, with, or after each or at least one pass of the scanning pattern, a re-determination of at least the radii of curvature of the front ( 3 ) and reverse ( 5 ) of the cornea ( 1). It may be intended that this does not necessarily mean that the radii of curvature must be determined for each individual pass of the scanning pattern, but rather that several successive scanning patterns, with a corresponding number of passes being predetermined, can be performed and evaluated before further determinations are carried out. A single pass of the scanning pattern usually only takes a few milliseconds, so that with slow injection of the filler material, a change in the radii of curvature may only occur after several passes of the scanning pattern.

[0029] Since the injection of the filling material simultaneously causes a bulging of the anterior cornea ( 3 ) and a flattening of the back of the cornea ( 5 ) causes the radii of curvature of the front side ( 3 ) and the reverse side ( 5 ) of the cornea ( 1) together provide information about the increased refractive power. Therefore, the determined radii of curvature can serve as a basis for the injection drive ( 17 ) to control via the computing unit.

[0030] Since the device according to the invention is preferably designed for autonomous control of the injection, in particular the injection speed, the computing unit ( 21 ) advantageously also be trained and / or configured to autonomously decide and / or determine how many passes of the sampling pattern it analyzes before performing the next check of the target criterion and deciding on the further course of the injection.

[0031] In a preferred case, the predetermined target criterion for therapeutic success is the achievement of a predetermined target value for the refractive power of the cornea ( 1 ). Since the injection of the filling material simultaneously causes a bulging of the anterior cornea ( 3) and a flattening of the back of the cornea ( 5 ) causes both of which increase the refractive power; the refractive power is a strictly monotonically increasing function of the injected amount of filler material. Provided the corneal pocket ( 7 If the refractive index was created at a suitable depth and size, then the target criterion can be met by the exact agreement between the measured and calculated refractive power and the predetermined target value.

[0032] If the transparent filling material has at least essentially the same refractive index as the stromal tissue of the eye, then the refractive power of the cornea ( 1 ) with the filled cornea pocket ( 7 ) than that of a convex-concave lens, calculated solely from the radii of curvature determined in the OCT image. Otherwise, the stroke of the corneal pocket ( 7 ) along the optical axis and the radii of curvature of the front ( 9) and the rear boundary surface ( 11 ) the cornea pocket ( 7 ) to determine. The stroke is the largest measurable distance between the front ( 9 ) and the reverse side ( 11 ) the filled cornea pocket ( 7 ). These additional measurements allow the refractive power of the cornea to be determined ( 1 ) taking into account the refractive indices of the filling material and stromal tissue, the refractive power of a concentric arrangement of a plurality of lenses can be calculated.

[0033] The concentric arrangement of several lenses can be understood as a convex-concave lens with an embedded lens that passes through the filled corneal pocket ( 7 ). The shape of the embedded lens is typically that of a convex-concave lenticule; however, with large amounts of filling material or small pockets – especially in presbyopia correction – it can also assume a biconvex shape.

[0034] The device according to the invention comprises a computing unit ( 21 ), which can be, for example, a conventional personal computer (PC) and which – for example, through appropriate software – is trained and / or configured to perform the aforementioned calculations from the electronic measurement data sets of the OCT device ( 19 ) to execute. At least the hardware of a corresponding OCT system ( 19 ) is commercially available. OCT device ( 19 ) and computing unit ( 21 ) can form a structural unit.

[0035] The device according to the invention comprises injection means ( 13 , 15 ,) with at least one hollow needle (cannula) ( 15 ). At least one hollow needle ( 15 ) is either directly or via a hose with a reservoir ( 13 ) connected to at least one transparent filling material. The filling quantity of the reservoir ( 13) is usually predetermined. The reservoir ( 13 ) can be formed by a flexible container or by a rigid container with a reservoir ( 13 ) insertable piston (not shown). In a preferred embodiment, controlled pressure is exerted on the filling material in order to convey it – possibly through a tube – and expel it from the end of the hollow needle ( 15 ) to allow it to escape. The pressure can be exerted either on the flexible walls of the reservoir ( 13 ) or applied to the piston in the manner of a conventional syringe.

[0036] The injectables ( 13 , 15 ) can also be a plurality of hollow needles ( 15 ) include the simultaneous injection of the filling material at different access sites for the corneal pocket ( 7 ) in the patient's eye. The injection agents ( 13 , 15 ) can still have a majority of reservoirs (13 ) include, where each reservoir ( 13 ) at least one predetermined hollow needle ( 15 ) can be assigned. The individual reservoirs ( 13 ) can contain various substances as transparent filling materials, which differ, among other things, in their refractive index. The allocation of the reservoirs ( 13 ) onto the hollow needles ( 15 ) can be changed – for example by closing and opening taps.

[0037] For the sake of simplicity, the following description assumes that the injection agents ( 13 , 15 ) exactly one reservoir ( 13 ) with exactly one filling material and exactly one hollow needle ( 15 ) include.

[0038] The device according to the invention further comprises an injection drive ( 17) which is preferably designed to apply a controlled pressure to the liquid in the reservoir based on electrical control signals from a control unit ( 13 ) to exert. Preferably, the injection drive comprises ( 17 ) an electric motor. The control unit can be located in the injection drive ( 17 ) be structurally integrated and digital commands of the computing unit ( 21 ) receive and translate into electrical control signals, e.g., analog voltage values. Alternatively, the processing unit ( 21 ) itself via a converter interface electrical control signals for controlling the injection drive ( 17 ) spend.

[0039] The injection drive ( 17) can, for example, consist of two parallel plates whose distance from each other can be adjusted by a controllable electric motor. A flexible bag containing liquid filling material can be placed between the plates so that the liquid is pressurized when the plates approach each other and – if necessary through a tube – is forced out of the hollow needle ( 15 ) exits. Thus, a distinction can be made between the injection drive ( 17 ) and the injectables ( 13 , 15 ) a preferably mechanical coupling is designed which allows a change in the amount of filling material to be injected by controlling the injection drive ( 17 ) is permitted. In principle, a coupling between the injection drive ( 17 ) and the injectables ( 13 , 15) may also be designed in another way to create at least an indirect coupling that ensures controlled changes to the amount of filler material to be injected. It is considered advantageous to design the reservoir ( 13 ) to be designed in the style of a syringe and to provide the injection drive ( 17 ) to provide an electric motor that controls the position of the piston. In this way, the injection drive can be controlled ( 17 ) both overpressure and underpressure in the reservoir ( 13 ) relative to the end of the hollow needle ( 15 ) can be generated. This allows the injection drive ( 17 ) are targeted to remove any excess injected filler material from the corneal pocket ( 7 ) to extract.

[0040] The total amount of filling material to be injected into the patient's eye is on the order of microliters or cubic millimeters. The injection drive ( 17) should have sufficient positioning accuracy to change the injected volume in small steps, preferably by about 0.1 microliters per step.

[0041] The device described so far comprising injection means ( 13 , 15 ), injection drive ( 17 ), OCT facility ( 19 ) and computing unit ( 21 ) is able to provide the intended increase in refractive power of a farsighted eye in which a radially symmetrical, central corneal pocket previously existed ( 7 ) has been created, the automatic filling of the bag ( 7The procedure involves injecting a transparent filler material. The precise amount of filler material injected is precisely what produces the predetermined target refractive power. While the a priori unknown mechanical properties of the patient's corneal stroma are not explicitly determined, they are usefully incorporated because they are implicitly considered in the effect measurement.

[0042] Out of Fig. 2 shows how an OCT device ( 19 ) determined cross-sectional image of the cornea ( 1 ) for a line grating as a scanning pattern. In the upper part of the image is a cross-section through the entire cornea ( 1 ) of an enucleated pig's eye with anterior ( 3 ) and reverse ( 5 ) to see. The measuring range of the OCT device ( 19) is generally limited, typically to a depth interval with a width of approximately 2 millimeters. However, it can be shifted by changing the reference arm length. The lower part of the image of Fig. Figure 2 shows a measurement area shifted along the direction of the eye's optical axis, from which the radius of curvature of the back of the cornea can be determined ( 5 ) can be determined better than from the measurement area of ​​the upper image section, which in turn determines the curvature of the front ( 3 ) shows it better. The lower part of the image also contains a mirror image of the front ( 3 ), which is an artifact of the OCT recording. In principle, both radii of curvature could be determined solely from the lower image section, but the weak ones in the shifted measurement area from the anterior corneal surface ( 3 The contrasts originating from the source material make automatic image analysis difficult. However, it is quite possible to use the OCT setup ( 19) designed to operate simultaneously with different reference arm lengths and to simultaneously capture measurement ranges that are shifted relative to each other or even widely separated, cf. DE 10 2007 023 293 B3.

[0043] The Fig. 3 now shows the same cornea ( 1 ) after applying and filling the cornea pocket ( 7 ). Both the bulge of the front ( 3 ) as well as the flattening of the back ( 5 ) are compared to Fig. 2 is clearly visible. Likewise, the bag ( 7 ) is very easy to discern, as the liquid filling material scatters light very weakly compared to the stromal tissue. The morphology of the pocket ( 7 ) corresponds to that of a lenticule, such as those removed during conventional LASIK myopia correction. Therefore, a synthetic lenticule is indeed inserted into the natural tissue. However, it is in Fig. 3. It is also evident that the lenticule also changes when a radially symmetrical pocket is created ( 7 ) does not necessarily have to develop in a completely radially symmetrical manner. The reason for this can lie in varying mechanical properties of the cornea ( 1 ) in the area of ​​the bag ( 7 ) are suspected.

[0044] If there are discrepancies between the actual and the originally planned shape of the filled cornea pocket ( 7 If this occurs, it can introduce irregular or regular astigmatism. Irregular astigmatism can arise, for example, if a viscous filler material does not settle evenly in the corneal pocket immediately after injection ( 7 ) distributed and stably filled all pocket edges. The doctor can then press on or stroke the front of the cornea ( 3 ) intervene to provide support, so that a state of even distribution is achieved as soon as possible.

[0045] Regular astigmatism can generally be addressed by the doctor removing the corneal pocket ( 7 ) opens further at some edges, so that the shape of the bag ( 7 ) by redistributing the filling material. Such post-processing can preferably be carried out by laser cutting in the vicinity of the pocket edge, even if the pocket has already been filled previously ( 7 ) are executed.

[0046] The device according to the invention can be designed to assist the physician by detecting and quantifying the presence of regular astigmatism and even indicating at which peripheral points the pocket ( 7 ) should be opened further to correct the astigmatism.

[0047] For this, it is first necessary that the OCT facility ( 19 ) in the area of ​​the cornea pocket ( 7) repeatedly scans the grid points of a two-dimensional grid in the plane perpendicular to the optical axis as a scanning pattern over time. For example, a two-dimensional scanning pattern can include the intersection points of intersecting sets of lines or the nodes of a honeycomb grid. It is advantageous if one measurement point of the scanning pattern lies on the optical axis where the corneal pocket has its greatest thickness ( 7 ) is to be expected.

[0048] The computing unit ( 21 ) the device is further trained and / or configured to extract measurement data from the OCT device ( 19 ) keeping pace with the repetitions of the two-dimensional scanning pattern, a three-dimensional (3D) model of the cornea's shape is generated ( 1 ) and the cornea pocket filled with filling material ( 7) to calculate. Due to the relatively simple structure of the target shapes, this is easily possible by interpolating the relative distances determined by OCT onto the discrete grid points of the scan pattern.

[0049] The resulting 3D model represents a composite optical system with known refractive indices. The light-guiding properties of such a system can now be effectively simulated, particularly through the application of modern ray-tracing software. Furthermore, the graphics cards of modern PCs are specifically designed for such computational operations. The processing unit ( 21 ) the device according to the invention can therefore be configured to keep pace with the model calculation by calculating the regular astigmatism of the cornea ( 1 ) and filled cornea pocket ( 7 ) formed optical system to determine and represent as a tuple of parameters.

[0050] For example, the computing unit ( 21 For a plurality of directions perpendicular to the optical axis, the focusing of a simulated, collimated light beam as it passes through the optical system according to the 3D model is calculated, thus determining the two directions exhibiting the greatest and smallest refractive power. These can be referred to as the principal astigmatic axes. The principal axis directions—described as plane direction vectors—and the calculated refractive powers associated with these principal axes then form a tuple of parameters that describes the astigmatism.

[0051] The computing unit ( 21 The system continuously recalculates the 3D model and assesses astigmatism during injection, generating a time-varying tuple of actual values. This can be compared to a target value tuple.

[0052] The target value tuple can, for example, be predefined such that it specifies only one predetermined refractive power and no astigmatism. In the case of the example above, where two principal axis directions and two refractive powers are defined as actual value tuples, both refractive powers in the target value tuple would then be equal to the predetermined value, and the principal axis directions would be arbitrary, random, or zero.

[0053] The target value tuple can also be specifically tailored to a predetermined astigmatism of the cornea ( 1 ) to, for example, correct astigmatism present in the lens.

[0054] In any case, it can be assumed that it will not be easy to reconcile the actual value tuple with the target value tuple, because the only control parameter available is the fill level of the corneal pocket ( 7) available. In particular, it may be impossible to precisely adjust two different breaking forces along different principal axis directions simultaneously solely by the fill quantity.

[0055] The target criterion should therefore consist of assuming an optimum that can be described by a minimum "difference" between the actual value tuple and the target value tuple, which the processing unit ( 21) should be found. Here, "distance" can be understood quite generally as a positive value assignment, in the sense of a norm, to the pair of actual value tuple and target value tuple. The distance is zero if both match and greater than zero otherwise. A precise definition of the distance can only be made in consideration of the specific application and with the parameters appearing in the tuples specified. Ultimately, the distance is nothing more than a suitably chosen mathematical function of the actual value tuple and the target value tuple. As such, it can easily be coded in software, and the processing unit ( 21 ) is then trained and / or configured to check the approximation of the actual value tuple to a predetermined target value tuple to a minimum distance as a target criterion.

[0056] It is preferably intended that the computing unit ( 21 ) the injection drive ( 17) controls the system so that a minimal difference between the actual value tuple and the target value tuple is created, preferably to meet the target criterion. While the processing unit ( 21 ) the injection drive ( 17 When the system is driven to determine the minimum difference between the actual value tuple and the target value tuple, and thus to fulfill the target criterion, a brief deviation from the desired optimum is to be expected. It is therefore particularly advantageous if the injection drive ( 17 ) both to increase and to decrease the amount of fluid in the corneal pocket ( 7 ) is trained and / or able to do so.

[0057] If the found actual value tuple ultimately fulfills the target criterion and has the minimum distance to the target value tuple, this distance is usually not zero. The unit of calculation ( 21) can now also be trained and / or configured to calculate and / or output, from the actual value tuple when the target criterion is met and from the predetermined target value tuple, at which boundary points the corneal pocket ( 7 ) to increase in order to further reduce the remaining distance between the actual value tuple and the target value tuple.

[0058] To achieve this, a modeling of the mechanical properties of the stroma tissue can be performed, at least in the peripheral regions of the pocket ( 7 ) can be done. For this purpose, the computing unit ( 21 ) be formed and / or configured. The modeling assumes that variations in the shape of the corneal pocket ( 7) can be attributed solely to the mechanical properties of the stromal tissue and are not determined by the course of the injection procedure. This requirement should be approximately met if the treating physician waits for the even distribution of the filler material in the pocket after the injection or achieves this by applying supportive pressure.

[0059] The actual shape of the filled cornea pocket ( 7 ) is the computing unit ( 21 ) known, and this form is shown, for example, in Fig. 3.00 different thicknesses along the lenticule edge. It can be concluded that some areas of the tissue are more easily forced apart by the filling material than others, and it can be assumed that this mechanical behavior changes only slowly in the local environment. Therefore, if a rather thick edge area of ​​the pocket is separated ( 7) further, then one can expect that the tissue of the widened edge can also be easily pushed apart by the filling material.

[0060] With this mechanical information indirectly encoded in the pocket shape, one can now proceed to numerical modeling, e.g. with a finite element method, to model the expected change in the shape of the pocket volume when one considers the edge regions of the pocket ( 7 ) further separates the pocket shapes with the laser. These pocket shapes, modified in the numerical modeling – i.e., simulated – are then subjected to a ray tracing analysis, as described above. This analysis allows us to predict those pocket shapes that are likely to produce a better optical result, i.e., a smaller distance between the actual value tuple and the target value tuple. From the prediction of a more favorable pocket shape, we can then identify the edge regions of the pocket actually created in the patient's eye ( 7) are determined which should be opened first to achieve the more favorable pocket shape. The unit of calculation ( 21 Based on the model calculations described above, the system is therefore able to issue a recommendation to the doctor, e.g. by outputting vector coordinates related to the optical axis, indicating where he could place the post-processing with the greatest probability of success. QUOTES INCLUDED IN THE DESCRIPTION

[0061] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0062] US 5964748

[0008] US 8409177 B1

[0008] DE 102007023293 B3

[0042] Zitierte Nicht-Patentliteratur

[0063] Olsen, „On the calculation of power from curvature of the cornea“, British Journal of Ophthalmology, 1986, 70, 152–154

[0003] Binder, „Intracorneal inlays for the correction of presbyopia and low hyperopia“, Ophthalmology Times EUROPE, December 01, 2015

[0007] Winkler, „Nonlinear optical macroscopic assessment of 3-D corneal collagen organization and axial biomechanics“, IOVS, Vol. 52 8818–8827, 2011

[0014]

Claims

[1] Device for changing the refractive power of the cornea ( 1 ), in particular for the correction of hyperopia or presbyopia, having injection means ( 13 , 15 ) with at least one hollow needle ( 15 ) for injecting at least one optically transparent filling material with a predetermined refractive index into an intrastromal cornea pocket ( 7 ), marked by a. a controllable injection drive ( 17 ), who with the injectables ( 13 , 15 ) is coupled at least indirectly and is designed to change an amount of the at least one filling material to be injected; b. a facility for optical coherence tomography (OCT) ( 19 ) used to monitor the area of ​​the corneal pocket ( 7 ) by measuring depth profiles of the cornea ( 1 ) is formed on a time-repeated scanning pattern; and c. a unit of account ( 21 ), which is designed and / or configured from the measurement data of the OCT device ( 19 ) during injection at least the radii of curvature of the front ( 3 ) and the back ( 5 ) of the cornea ( 1 ) in time step with the repetitions of the run of the scanning pattern, where i.e. the unit of account ( 21 ) is formed and / or configured, the injection drive ( 17 ) to change the injected amount of the at least one filling material based on the radii of curvature of the front face ( 3 ) and the back ( 5 ) of the cornea ( 1 ) and / or until a predetermined target criterion is met. [2] Device according to claim 1, characterized, that the predetermined refractive index of the filling material at least essentially corresponds to that of the stromal tissue of the cornea ( 1 ) and that the arithmetic unit ( 21 ) is designed and / or configured to increase the refractive power of the cornea ( 1 ) than that of a convex-concave lens, based on the calculated radii of curvature of the front side ( 3 ) and the back ( 5 ) of the cornea ( 1 ). [3] Device according to claim 1, characterized, that the unit of account ( 21 ) is designed and / or configured from the measurement data of the OCT device ( 19 ) a stroke of the corneal pocket ( 7 ) along the optical axis of the cornea ( 1 ) and the radii of curvature of the front ( 9 ) and the rear boundary surface ( 11 ) of the corneal pocket ( 7 ) in time step with the repetitions of the run of the scanning pattern. [4] Device according to claim 3, characterized, that the unit of account ( 21 ) is designed and / or configured to increase the refractive power of the cornea ( 1 ), taking into account the refractive indices of the at least one filling material and the stromal tissue, to calculate the refractive power of a concentric array of a plurality of lenses. [5] Device according to one of claims 2 or 4, characterized, that the unit of account ( 21 ) is designed and / or configured to match the calculated refractive power of the cornea ( 1 ) with a predetermined target value as target criterion. [6] Device according to one of the preceding claims, characterized, that the lattice points of a two-dimensional lattice in the plane perpendicular to the optical axis as the scanning pattern of the OCT device ( 19 ) are predetermined. [7] Device according to claim 6, characterized, that the unit of account ( 21 ) is designed and / or configured to, from the measurement data of the OCT device ( 19 ) keeping pace with the iterations of the scan pattern run, a three-dimensional model of the shape of the cornea ( 1 ) and the cornea pocket filled with filling material ( 7 ) to calculate. [8] Device according to claim 7, characterized, that the unit of account ( 21 ) is designed and / or configured to calculate the regular astigmatism of the through cornea ( 1 ) and filled cornea pocket ( 7) formed optical system and represent it as a tuple of parameters. [9] Device according to claim 8, characterized, that the unit of account ( 21 ) is designed and / or configured to check the approach of an actual value tuple to a predetermined target value tuple to a minimum distance as a target criterion. [10] Device according to claim 9, characterized, that the unit of account ( 21 ) is designed and / or configured to calculate from the actual value tuple when the target criterion is met and from the predetermined target value tuple at which edge points the cornea pocket ( 7 ) is to be separated further in order to reduce the remaining distance between the actual value tuple and the setpoint tuple. [11] Device according to claim 10, characterized, that the unit of account ( 21 ) is designed and / or configured to output the edge locations at which the cornea pocket ( 7 ) is to be separated further in order to reduce the remaining distance between the actual value tuple and the setpoint tuple.

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