Patent Publication Number: US-2012035636-A1

Title: Device for cutting the cornea of an eye

Description:
FIELD OF THE INVENTION 
     The present invention relates to a device for cutting the cornea of an eye in order to correct the refractive power thereof, with a ring body that can be suctioned onto the eye, with an applanator for deforming the cornea, and with a blade which is guided in a guide plane perpendicular to the axis of the ring body, is mounted in front of the applanator and is used to cut a pocket in the corneal tissue. 
     The applanator can be designed as a stamp for deforming the cornea within the ring body. 
     The ring body and the applanator can both be arranged in a frame. 
     The blade can be secured in a holder, which is guided on the frame in a guide plane perpendicular to the axis of the ring body, wherein the blade can pass through a peripheral recess in the frame and is mounted in front of the applanator. Moreover, in order to cut into the corneal tissue a pocket having merely a tunnel-like access, the blade is on the one hand movable radially with respect to the ring body via the holder and on the other hand pivotable about an axis perpendicular to the guide plane at each blade position within an area of a cutting plane parallel to the guide plane, wherein the blade passes through the peripheral recess with clearance, and the holder supports a vibrator for an oscillating movement of the blade in the cutting plane. 
     PRIOR ART 
     In order to be able to correct the refractive power of the cornea of an eye, it is known (US 2001/0004702 A1) to treat the interior of the corneal tissue via an access route having a width of, for example, ca. 4 mm. A pocket is created in the interior of the cornea, which pocket can be widened to form a foldable corneal flap and thus permits surgical access to the corneal stroma (deep corneal tissue) for the purpose of correcting the refractive power. 
     To be able to perform such correction of the refractive power, US 2001/0004702 A1 proposes securing a frame on the eye of a patient, on which frame a holder for a movable blade is secured. The blade passes through the frame via a peripheral recess and is guided in a guide plane via a holder. This guide plane lies parallel to the cutting plane of the blade, a pocket being produced in the cornea in said cutting plane. The blade in its cutting plane is additionally held down by a spring so as to rest on the frame, since a slipping of the blade from where it is applied to the cornea for producing the tunnel-like access must be avoided. It is in fact quite difficult to penetrate the elastic and extremely tough outer layer of the cornea. In addition, the blade must not bend during cutting, since in that case it is not possible to guarantee an exact cutting plane and to avoid perforation of the outer or inner layer of the cornea, which precludes successful correction of the refractive power. While this may be counteracted using blades of great hardness (for example made of diamond material), such blades are particularly sensitive to shear stresses, which excludes the use of such blades in the device according to US 2001/0004702 A1, given the fact that the blade rests on the frame. Moreover, in addition to the risk of their breaking, the sharpness of such blades would also be greatly impaired. 
     It is also known from the prior art (WO 2004/096106 A1) to design a somewhat narrow and pivotable blade with a vibrator and to guide it in such a way that the blade edge cannot be impaired even in the case of hard materials. A device for cutting the cornea of an eye in order to correct the refractive power thereof was thus already created with which, starting from the site where the blade was applied to the cornea, a pocket lying in the cutting plane of the blade can be cut with accurate positioning through a tunnel-like access, without any reduction in the stability of the cornea having to be considered. Moreover, the device permits a wide range of corrections of the refractive power. Compared to other methods of correcting the refractive power, where either the surface of the corneal tissue is ablated (DE 34 33 581 A1) or the cornea is broadly incised to produce a flap that may be folded back (LASIK method), treating the interior of the cornea via a tunnel-like access has the advantage that virtually no post-operative pain occurs and/or the stability of the cornea is scarcely impaired, since the top layer, which is important for the stability of the cornea and which also includes the Bowman membrane for example, remains uninjured for the most part. Therefore, treating the cornea via a tunnel-like access offers many advantages over the other methods of treatment. 
     In addition, the device permits a wide range of refractive power corrections. 
     Moreover, U.S. Pat. No. 6,599,305 B1 discloses a device in which a narrow access to a corneal pocket is possible only in very narrow corneal pockets and, consequently, a relatively wide access, with impairment of the biomechanics, is necessary in usable optical zones. Moreover, in clinical use, the principle and the design of the cutting device with blade and blade holder mean that perforations of the cornea must be expected as serious complications. 
     US 2001/0004702 A1, WO 2004/096106 A1 and U.S. Pat. No. 6,599,305 B1 do not solve the problem of how to secure the blade on the holder in such a way that, when the holder penetrates into the corneal pocket, the cutting depth and therefore the cutting precision are not impaired, and, at the same time, of how multiple sterilization can be achieved. 
     DISCLOSURE OF THE INVENTION 
     The invention solves the stated problem by virtue of the fact that the blade (in the sense of a blade that has to be secured on a receptacle) is secured on a blade receptacle of a holder or fixture in such a way that the top side of the blade receptacle does not protrude above the top side of the blade, at least within the depth of penetration of the blade receptacle into the cornea. 
     The top side of the blade receptacle or of the blade is that surface of the blade receptacle or of the blade that is directed towards the contact face of the applanator. Correspondingly, the underside of the blade receptacle or of the blade is that surface of the blade receptacle or of the blade that is directed away from the contact face of the applanator. 
     The blade receptacle ensures that the blade does not have to be mounted directly on a movable holder, such as that with reference sign  3  in  FIG. 1 , or does not have to be mounted directly on a fixture, such as that with reference sign  83  in  FIGS. 18 to 21 , and instead the blade receptacle forms an intermediate piece for indirect securing of the blade on the holder or fixture. The blade is secured at a first location on the blade receptacle and mounted on the holder or fixture at a second location different from the first location. The blade receptacle thus functions as an intermediate piece between blade and holder/fixture. 
     In one design variant, provision can be made that the blade and the blade receptacle each have a preferably flat surface on the top side, and the blade has a flat surface on the underside, in which case the cutting edge of the blade is equidistant from the two flat surfaces of the blade and, during the cutting procedure, the distance between the highest point of the flat surface on the top side of the blade receptacle and the contact face of the applanator, measured perpendicular to the cutting plane, is not less than the distance between the flat surface on the top side of the blade and the contact face of the applanator, measured perpendicular to the cutting plane. 
     In order to ensure a good connection between blade and blade receptacle, provision can be made that the blade is provided with a shaft, which shaft is adhesively bonded into the blade receptacle. Provision can additionally be made that the shaft is roughened on the surface within a partial area, on at least one side, and the roughening is adhesively bonded to the blade receptacle. 
     However, it is also possible that the blade has no shaft in the real sense, in other words the blade has a blade edge along its entire longitudinal extent (see  FIG. 22 ). In this case too, provision can be made that the blade is roughened on the surface within a partial area, on at least one side, and the roughening is adhesively bonded to the blade receptacle. 
     Roughening is to be understood as an increase of the average surface roughness, in relation to the rest of the blade surface (or, in blades with a shaft, in relation to the cutting area), by at least a factor of 1.1. Still better connections can be achieved with roughening by a factor of 2 to 100 or even higher. The roughening can have any desired macroscopic or microscopic geometry. Microscopically, it can be in the form of furrows, nipples and other elevations and depressions. The height between the lowest and next highest location (peak-to-valley heights) of the roughening should preferably be over 40 nm. Ideally, the peak-to-valley heights of the roughening are between 100 nm and 600 nm, in particular 400 nm. In particular embodiments, it can also be in the micrometre range, but preferably less than 10 μm (micrometre). Ideally, the roughening is produced by means of laser radiation. However, it can also be produced chemically by etching or mechanically or in another way. 
     Provision can additionally be made that the blade receptacle is likewise roughened in an area corresponding to the roughened area of the blade and/or of the shaft. The roughening and the way in which the latter is produced correspond to those of the blade. 
     Suitable adhesives are all those that can ensure sufficient strength and hardness even under conditions of steam sterilization. For example, epoxy adhesive or epoxy resin adhesive can be used. Such an epoxy adhesive should preferably be provided as a two-component adhesive consisting of resin and hardener, for example with 100 parts by weight of resin and 10 to 20 parts by weight, most preferably 13 parts by weight, of hardener. Aluminium oxide can be used as filler. The adhesive should be such that the hardening at room temperature does not take more than 24 hours, or at 250° C. takes ideally less than 3 hours. The viscosity before hardening can be relatively high (pasty) but can also lie in the range of 10000-30000 cps, preferably about 20000 cps, which, with 1 cps=10 −3  kg/ms, corresponds to a viscosity of ideally about 20 kg/ms or a range of 10-30 kg/ms. The thermal expansion of the finished adhesive compound should be as low as possible and should not exceed 10×10 −5 /° C. In a particular embodiment, it is 6.4×10 −5 /° C. Ideally, it is not more than 5×10 −5 /° C., approximately between 2 and 4×10 −5 /° C. The adhesive compound should be able to be sterilized more than once and should have a deformation temperature of at least 150° C. (ideally at least 200° C.) The adhesive compound should have a density of less than 2.5 g/cm 3  (between 1 and 2 g/cm 3 ), e.g. 1.9 g/cm 3 . The volume shrinkage of the adhesive in the hardening process is less than 1% (ideally 0.3% or less, e.g. 0.2%). The hardness should be between D70 and D90, ideally about D80 or D85. The weight loss over a period of 500 hours at sterilization temperatures in excess of 134° C. should be below 1% (ideally 0.5% or less), e.g. 0.5% over 1000 hours at 200° C. 
     By way of the roughened part of the blade shaft or of the blade, it is possible to connect the blade to the blade receptacle with a suitable adhesive compound in such a way that the blade receptacle, on the side directed towards the applanator or towards the contact face (applanation face) thereof, has a depression corresponding to the shaft geometry (see  FIG. 14 ) or to the blade geometry (see  FIG. 22 ). The extent of this depression should cover at least an area of 1 mm 2 . In any case, the surface area of the depression is at least as great as the surface area of the shaft of the blade. The depth of the depression in the blade receptacle should be configured such that, when an adhesive connection is made, the surface of the blade receptacle directed towards the contact face (applanation face) does not protrude further, in the direction of the contact face (applanation face), than the corresponding surface of the blade directed towards the contact face. 
     If the cutting edge is not located on the surface, a further improvement of the cutting function is possible by virtue of the fact that the top side of the blade receptacle does not protrude above the cutting edge. 
     Since the applanator prevents a migration of the tissue in front of the blade during cutting, this means that, when the blade penetrates into the cornea, the tissue has to migrate “rearwards”, that is to say in the direction of the anterior chamber of the eye, or the blade retreats relative to the surface and there is the danger of an unequal cutting depth and/or the danger of perforation of the cornea. If the top side of the blade receptacle does not protrude above the top side of the blade or the cutting edge of the latter, the blade, upon deep penetration into the cornea, does not drop away from the contact face (applanation face) and the incision depth remains constant at the front of the blade. This permits an exactly guided incision and a precisely defined corneal pocket. Unequal depths on the opposite sides of a pocket can lead to errors in the refractive power correction and to complications such as extrusion of annular implants through the corneal surface. 
     By virtue of the fact that the top side of the blade receptacle does not protrude above the top side of the blade or the cutting edge of the latter, it is also possible that, despite penetration of the blade receptacle into the cornea, an exact cut is achieved. This in turn means that shorter blades can be used, which increases the stability of the blades in terms of cutting accuracy. In fact, if the blade receptacle cannot penetrate into the cornea, only comparatively long blades can be used to produce the pocket. The longer a blade, the more “bendable” it is, and a constant cutting depth is maintained with less precision. This is of particular importance when making an incision in the cornea, since the thickness of the cornea is only ca. 500 μm (0.5 mm) and any deviation from the ideal cutting depth can have fatal consequences for the eyesight. It must also be considered that the blade is applied to an oblique and tough surface (corneal surface outside the applanation area) for penetrating into the cornea, and this in itself leads to a considerable deviation from the ideal direction of penetration, because of the resulting bending moment on the blade. For this reason, metal blades, even when diamond-coated, which is after all only a surface measure, are somewhat problematic because of their ductility. Even diamond blades, despite their great hardness, can have a certain bendability if they are long, thin and narrow. The invention thus increases the stability of the blades with the objective of increasing the cutting precision. 
     By designing the blade as a long blade (i.e. as an elongate and somewhat narrow blade) with a blade edge along at least one longitudinal side, a drawn incision can be made. Blade edge designates the areas that are bevelled in relation to the flat top side and underside of the blade and that form the cutting edge at their line of intersection. The blade width should not exceed 4 mm. Blade widths of 2 to 2.5 mm are ideal. In particular embodiments, for example for small pocket widths (less than 6 mm) and a depth of penetration of the pocket of just over the halfway point of the cornea, the blade width can also be up to 6 mm and over. 
     The thickness of the blade should be between 100 and 250 μm, ideally 150 μm to 200 μm. The length of the shaft should be 1 to 3 mm, ideally 2 mm. The shaft is ideally the same width as or narrower than the blade in the cutting area. It can have the same thickness as or be thinner than the blade in the cutting area. 
     If the underside of the blade receptacle, that is to say the side of the blade receptacle directed away from the applanator, slopes away from the shaft and from the blade, this has the advantage that, during the movement of the blade receptacle in the pocket, the tissue displaced by the underside of the blade receptacle does not move abruptly rearwards (in the direction of the anterior chamber of the eye), and this likewise considerably improves the cutting precision and safety for the eye. It is best if no step is present on the underside of the blade at the transition between the blade receptacle and the blade, and the thickness of the blade receptacle thus constantly increases, from the zero thickness at this point, as the distance from the blade tip increases. 
     Alternatively or in addition, the blade receptacle can also slope from the lateral edges (the edges parallel to the longitudinal axis of the blade) towards the centre of the blade receptacle. In other words, the thickness of the blade receptacle can increase on the underside from the lateral edges of the blade receptacle towards the centre. This has the advantage that the tissue is not moved abruptly upon a lateral movement of the blade. Such a design is present, for example, when the shape of the blade edges and cutting edges is continued beyond the blade on the blade receptacle. 
     If, alternatively or in addition, the top side of the blade receptacle, at least as far as the blade receptacle penetrates into the cornea, is flat and preferably extends parallel to the cutting plane, this has the advantage of having no effect on the tissue in front of the blade (between blade and corneal surface). 
     It is also advantageous if the blade is made of a particularly hard material, for example diamond, ruby, semiconductor materials or ceramic. However, in addition to being made of non-metallic materials, the blade can generally also be made of metallic materials. Comparatively unfavourable cutting conditions arise with ductile or metallic blades, even if they have diamond-coated surfaces or cutting edges. However, metallic blades can be very easily connected to a blade receptacle by means of adhesives. By contrast, it is known that diamond blades can be adhesively bonded to blade receptacles only with great difficulty and also only for a limited period of use (sterilization cycles). Normally, in order to achieve a good adhesive connection, the shaft of the diamond blade is enclosed on all sides by the blade receptacle, and this enclosure is often strengthened by means of an adhesive connection. However, enclosing the blade or shaft in the blade receptacle also from the top side leads to the abovementioned considerable inaccuracy of cutting, with the risk of corneal perforation. 
     The blade receptacle can be made of any desired material, preferably of metal (steel), but also of other materials, such as ceramic (ZrO), ruby or hard plastic. In the area of the blade shaft, or also further away from the blade, the blade receptacle can be narrowed in relation to the cutting blade width. However, alternatively or in addition, the blade receptacle can be laterally shaped into a blade edge or ground. 
     The blade receptacle can be an integral part of the blade holder guided on a frame, i.e. can be designed in one piece with the holder. 
     If the preferably non-metallic blade forms a pointed tip, this facilitates the penetration of the blade from the place where it is applied to the cornea. If the blade additionally has a blade edge tapering towards the pointed tip, it is possible, by moving the blade radially with respect to the ring body, to produce a particularly narrow tunnel-like access into the cornea, which is useful for the stability of the cornea. 
     By designing the blade as a long blade with at least one blade edge, but preferably two blade edges extending along the longitudinal sides, with corresponding cutting edges which taper to a pointed tip at the end remote from the blade receptacle, provision can be made that the cutting edges are equidistant from the upper side of the blade directed towards the applanation face and the lower side of the blade directed away from the applanation face. The cutting edges can preferably extend parallel to each other along both longitudinal sides of the blade and parallel to the longitudinal axis of the blade and taper towards the pointed tip at an angle alpha of less than 90°, ideally ca. 70° (between 60 and 80°), at the end directed away from the blade receptacle. The blade edge (or more precisely the face of the blade edge) is bevelled with respect to the surface by an angle beta of in each case 10° to 25° (ideally 15° to 20°). From the shaft of the blade to the tip of the blade (the end directed away from the blade receptacle), the cutting edge, independently of the position of the cutting edge, should have a length of at least 3 mm and at most 8 mm, preferably 5-7 mm. 
     In a particular embodiment, the cutting edge can preferably be continued with an identical profile onto the blade receptacle. The continuation of the cutting edge onto the blade receptacle can be up to 7 mm, ideally 5 mm, such that a blade can effectively produce a cut of up to 12 mm (ideally between 5 mm and 12 mm). In particular, the blade receptacle can have another blade, i.e. a second blade, in which the cutting edge of the actual blade continues. This second blade can be mounted, for example, on the top side of the rest of the blade receptacle. 
     By providing a two-part receptacle for the applanator, wherein the two parts together form a peripheral groove for guiding a holder for the blade, the two parallel surfaces of the peripheral groove, between which the blade is moved precisely and practically free of clearance, can be made parallel with a very high degree of precision. 
     In a preferred embodiment, the blade and the blade receptacle pass with clearance through the peripheral recess of the frame, which ensures that the blade, when it is moved, particularly when it is inserted into its cutting position, does not rest on the frame, such that damage to the blade or to the blade edge can be ruled out. It is therefore possible to use comparatively hard materials for the blade, since the brittleness of these mostly very hard materials can in fact be ignored. In contrast to US 2001/0004702 A1, therefore, a fracture or damage to the blade edge does not have to be taken into consideration, since the blade is guided with its sensitive parts free from contact, as a result of which, according to the invention, blades with high cutting performance and small dimensions can be used. When penetrating the outer layer of the cornea in order to produce a tunnel-like access, it is thus also possible to assume that the tunnel-like access is extremely precisely contiguous to the site where the blade has previously been applied to the cornea. 
     The penetration of the blade is made easier by the fact that the holder, preferably in the area of the blade receptacle, supports a vibrator for a vibration of the blade in the cutting plane. This in particular serves to overcome the elasticity of the outer layer of the cornea without risking increased indentation of the corneal surface. The vibrator also ensures that minimal force is exerted during the cutting procedure, such that it is possible to exclude any movement of tissue that is attributable to the motion of the blade resulting from the elasticity and toughness of the tissue and that arises even when using extremely sharp blades. Thus, an especially drawn incision for high cutting precision can be ensured. 
     If the receptacle is designed as an exchangeable receptacle in which applanators with differently curved contact faces for deforming the cornea can be received in a manner limited by a stop, wherein the contact faces in successive incisions define pockets for delimiting a lens-shaped portion of tissue, it is possible, starting from a tunnel-like access, to cut out a volume of tissue without having to produce a corneal flap. The lens-shaped portion of tissue that is cut out can then be pulled out via the tunnel-like access, as a result of which it becomes possible, according to the invention, to produce a defined cavity in the cornea, without significantly impairing the stability of the cornea in comparison to the other methods. This makes it possible to create a tissue lens in the cornea through which a refractive error can be corrected. 
     If the peripheral edges of the contact faces of the applanators inserted in succession into the receptacle have different perpendicular distances from the cutting plane of the blade, the cutting out of a lens-shaped portion of tissue is thus made easier. Although this difference in the perpendicular distances requires two tunnel-like accesses to be produced in the corneal tissue, this nevertheless has the advantage that the two pockets are prominent in their common sectional line, which excludes the possibility of only partial cutting out of the volume of tissue. 
     If the applanator is made of transparent material, this allows the surgeon to easily observe the contact face and/or the cutting process. If the applanator is additionally designed as a magnifying lens, the focal point of which lies in the area of the contact face for deforming the cornea, preferably on the axis of symmetry of the applanator, this observation is made even easier. 
     In order to be able to optimally adjust the size of the contact face of the applanator placed on the eye and/or in order to obtain as exact a cutting area of the pocket as possible, it is recommended that the transparent applanator has markings on its side directed towards the eye, for determining the size of the contact face of the applanator as well as the cutting face on the eye. 
     If the option of exchanging the applanators for cutting out a lens-shaped portion of tissue is to be dispensed with, this can be achieved if at least the contact face of the applanator is made of a deformable material, which can then be curved by means of an actuator to obtain different shapes that are maintained. The actuator can thus be used to give the applanator inserted in the receptacle differently curved contact faces, so as to ensure that a lens-shaped portion of tissue is cut out. 
     If the blade holder has an actuator operating perpendicularly with respect to the cutting plane of the blade, it is easily possible for a surgeon to adjust the depth of the pocket cut in the corneal surface, since this actuator can be used to adjust the distance of the blade from the applanator and/or from the contact face of the applanator on the eye. 
     The blade holder consists, for example, of a lever system comprising at least two lever arms with pivot axes perpendicular to the cutting plane of the blade. If one arm receives the blade and the other arm is articulated on the frame, this provides a simple construction ensuring that the blade can be moved radially with respect to the ring body and also pivoted about an axis perpendicular to its guide plane. 
     A further option is for the blade holder to comprise a fork-like blade guide, which is guided, as far as possible without clearance, between parallel surfaces of a peripheral groove provided on the frame, in particular on the receptacle. Not only is this embodiment particularly simple in its construction, it also predefines the space within which the surgeon can move the blade. 
     In order to permit particularly simple insertion and/or exchange of the applanators with differently curved contact faces, it is proposed that the applanator be held in the receptacle in a manner limited by a stop and by using a partial vacuum. The only requirement for this is to provide the receptacle with a pressure line which sucks out air present between the recess and the applanator. 
     According to another embodiment, a vibrator can be designed and arranged in such a way that the blade executes an oscillating movement with an amplitude of less than 0.2 mm, preferably of less than 0.1 mm, in particular of less than 0.05 mm. 
     In addition, a vibrator can be designed and arranged in such a way that the blade executes an oscillating movement with a frequency greater than 400 Hertz, preferably greater than 700 Hertz. 
     The oscillating movement of the blade by a vibrator (vibration) does not represent any relevant direct cutting movement for producing the corneal pocket. The influence of the vibration on the cutting procedure is instead indirect, because of the comparatively small movement amplitude, and is such that the actual blade movement for forming the corneal pocket is made easier by the vibration of the blade and is improved in terms of its precision. 
     When using a device according to the invention, provision is made that, when the pocket is being cut, part of the blade receptacle penetrates into the cornea. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       Illustrative embodiments of the invention are depicted schematically in the drawings, in which: 
         FIG. 1  shows a partially sectioned side view of a device according to the prior art, 
         FIG. 2  shows a partially sectioned side view of a second illustrative embodiment of a device according to the prior art, 
         FIGS. 3   a  to  3   c  show plan views of the cuts made by the blade of the devices according to  FIG. 1  or  FIG. 2 , 
         FIG. 3   d  shows a plan view of the pocket produced by the cuts made in  FIGS. 3   a  to  3   c,    
         FIG. 4   a  shows a cross section through a cornea deformed by an applanator, with a blade applied for producing a pocket, 
         FIG. 4   b  shows a cross section illustrating the pocket produced according to  FIG. 4   a , with the cornea undeformed, 
         FIG. 5  shows the blade secured on the holder, which comprises a fork-like blade guide according to the prior art, 
         FIGS. 6   a  to  6   c  are cross sections showing the cuts made to cut out a lens-shaped portion of tissue using applanators with differently curved contact faces, 
         FIG. 7  shows a design variant of an applanator with a curvable contact face on an enlarged scale, 
         FIGS. 8   a  to  8   g  show side views of different applanators for the device according to the invention, 
         FIG. 9  shows a plan view and a side view of a blade according to the invention, and 
         FIG. 10  shows a plan view of the device into which a transparent applanator has been inserted, 
         FIG. 11  shows a bottom view (plan view from below) of a blade according to the invention with shaft and cutting area, and also with a roughened area, 
         FIG. 12  shows a side view of the blade according to the invention adhesively bonded in a blade receptacle, with the cutting edge at the top and the blade receptacle sectioned, 
         FIG. 13  shows a side view of the blade according to the invention adhesively bonded in a blade receptacle, with the cutting edge in the middle, the blade receptacle sectioned, and with the contact face of the applanator, 
         FIG. 14  shows a top view of the blade from  FIG. 13  adhesively bonded in a blade receptacle, with the cutting edge additionally continued onto the blade receptacle, 
         FIG. 15  shows the blade from  FIG. 13  and  FIG. 14  as seen from the pointed tip, 
         FIG. 16  shows a section through a two-part receptacle, 
         FIG. 17  shows an illustrative embodiment for limiting the blade movement to what is substantially only a linear forward drive, 
         FIG. 18  shows an alternative device from the prior art, 
         FIG. 19  shows an exploded view of the device from  FIG. 18 , 
         FIG. 20  shows a plan view of an illustrative embodiment of a blade receptacle according to the invention for a device from  FIG. 19 , 
         FIG. 21  shows a partially sectioned side view of an illustrative embodiment of a blade receptacle according to the invention for a device from  FIG. 19 , 
         FIG. 22  shows a plan view and side view of an embodiment in which the cutting edge of the blade is continued onto a second blade, which is mounted behind the first blade on the blade receptacle. 
     
    
    
     WAY OF IMPLEMENTING THE INVENTION 
     According to the illustrative embodiment in  FIG. 1  and the illustrative embodiment in  FIG. 2 , the devices according to the prior art for cutting a cornea  1  of an eye in order to correct the refractive power thereof generally comprise a frame  2  and a holder  3  for a blade  4 . The frame  2  has a ring body  5 , which can be suctioned onto the eye, and an applanator  7 , which is adjustable coaxially with respect to the ring body  5 , and/or a receptacle  6 , which is adjustable coaxially with respect to the ring body  5  and serves to receive an applanator  7  for deforming the cornea within the ring body  5 . The cornea  1  thus extends through the ring body  5  within which, in particular offset vertically in relation to the ring body  5 , the applanator  7  for deforming the cornea is located. For the coaxial adjustment of the receptacle  6 , the ring body  5  is provided with a thread  8 , in which a nut  9  engages that is mounted rotatably on the receptacle  6 . By rotating the nut  9 , the receptacle  6  and/or the applanator  7  can thus be adjusted relative to the ring body  5  and/or the cornea  1 . If the adjustability of the receptacle  6  is omitted, the same variability can be produced equally through the use of different frame dimensions and/or also applanator dimensions. In each embodiment, the applanator  7  can be moved coaxially with respect to the receptacle  6  and/or pivoted in equally from the side. The holder  3  for the blade  4  is guided on the frame  2  in a plane perpendicular to the axis of the ring body  5 , and the blade  4  passes with clearance through a peripheral recess  10  in the frame  2  and is mounted in front of the applanator  7 . In particular, the blade  4  is guided by the holder  3  in such a way that, in order to cut into the corneal tissue a pocket  12  having merely a tunnel-like access  11 , the blade  4  is on the one hand radially movable with respect to the ring body  5  via the holder  3  and on the other hand pivotable about an axis perpendicular to the guide plane, as can be seen in particular from  FIGS. 3   a  to  3   c . It is conceivable that the cutting plane E of the blade  4  also lies in the guide plane of the blade  4 . 
     According to the invention, the blade  4  in  FIGS. 1 and 2  is replaced by a blade  4  secured on a blade receptacle  50 , wherein the blade receptacle  50  is connected to the holder  3 . This can be achieved, for example, by means of a fork-like blade guide  28 , which is shown in  FIG. 5 . The blade receptacle  50  in  FIG. 5 , however, protrudes with its top side above the top side of the blade  4 , as can be seen from the fact that, in the blade receptacle  50 , the shaft of the blade  4  can be discerned only on account of the cross-sectional view, which shaft, according to  FIG. 9 , has the same thickness as the blade  4 . According to the invention, therefore, the blade receptacle in  FIG. 5  is to be reduced in thickness such that its top side does not protrude above the top side of the blade  4 . 
     Accordingly, it is now no longer the blade  4  that passes with clearance through the peripheral recess  10 , but at least part of the blade receptacle  50 . 
     If a pocket  12  is now to be cut into the cornea  1  ( FIG. 4   a ), an applanator  7  is first pressed onto the corneal surface in such a way that the cornea  1  is deformed in a defined manner corresponding to the contact face  13  of the applanator  7 , with the shape of the applanator  7  being stamped on the cornea  1 . With such pressing of the cornea  1 , a suitably large pocket  12  can then be cut into the cornea  1 . Once the applanator  7  has accordingly deformed the cornea  1 , the blade  4  is applied to the cornea  1  and cuts through the outer tissue layers of the cornea  1  in order to produce a tunnel-like access  11 . It is of crucial importance in this respect that the blade  4  does not slip from where it is applied to the corneal surface. The invention therefore comprises on the one hand a blade  4  that passes with clearance through the recess  10  in the frame, and on the other hand the holder  3  supports a vibrator  14  for setting the blade  4  in vibration in the cutting plane E, as can be seen from  FIG. 5 . By passing through the peripheral recess  10  of the frame free of clearance, the blade  4  does not lie as in the prior art, such that damage to the blade  4 , particularly to the edge of the blade  4 , can be ruled out. Therefore, particularly hard and brittle materials can also be used for the blade  4 , and the resulting sharpness of the blade  4  means that slipping of the latter as it penetrates into the cornea  1  is virtually ruled out. However, it has been found that, despite such blades  4 , great force is required to penetrate the outer layer of the cornea  1 , and this is made easier, according to the invention, by vibration of the blade  4 . For this purpose, the holder  3  preferably has a vibrator  14 , which is designed as a piezo element, vibrates in the cutting plane E of the blade  4  and thus acts on the blade  4 , which is attached to the holder  3  by springs  15 , with the aid of a web  16  bearing on the piezo element. Instead of the piezo element, however, it is conceivable to use an unbalance motor or another suitable source of vibration. Once the tunnel-like access  11  has been cut through the outer tissue layers of the cornea  1 , the blade is then guided for the purpose of cutting a pocket  12  in such a way that no further contact with the corneal surface is made. Therefore, a pocket  12  is cut in the cornea  1  only via the tunnel-like access  11 , and this cutting is of course also made easier by the vibrator  14  and can also be done with great precision. The pocket  12  and the tunnel-like access  11  can be widened by spreading them using a suitable instrument, by which means the insertion of implants can be made easier. With the aid of another device, a preferably foldable or deformable implant can be introduced into the implant bed in the cornea  1  through the tunnel-like opening  11  that has been formed. The implant then unfolds into the desired shape in the pocket  12 . 
     Since the invention allows a very exact pocket  12  to be created inside a cornea  1 , it is possible, among other things, to implant lenses with a standardized radius of curvature into the area of the optical centre. This is significant because the natural curvature of the cornea varies between about 7 mm and 9 mm and, with a flat, uncurved impingement of the cornea  1 , a defined radius of curvature of the pocket  12  may not be achieved. By using an applanator  7  with a defined curvature of the contact face  13  and by fixing a defined cutting depth, the radius of curvature of the pocket  12  to be produced can be exactly defined, and this means that lenses that are standardized in terms of the curvature of their surface can be implanted in all patients, thus providing considerable cost savings in lens production. 
     The receptacle  6  for the applanator  7  is designed as an exchangeable receptacle, in which applanators  7  with differently curved contact faces  13  for deforming the cornea can be received in a manner limited by a stop. This stop  17  can be seen in particular in  FIGS. 1 and 2 . In this way, pockets  12  for delimiting a lens-shaped portion of tissue  18  can be easily produced by performing successive incisions. In particular however, since the frame  2  does not need to be removed from the eye when changing applanators, an exchangeable receptacle ensures that a lens-shaped portion of tissue  18  with a predefined size is always cut out, which is not the case in the known devices. The lens-shaped portion of tissue  18  can be produced according to  FIGS. 6   a  to  6   c . After a first pocket  12  has been cut into the corneal tissue, as has also been described above, the blade  4  is removed from the corneal tissue ( FIG. 6   a ) and a second pocket  12 , stamped by another applanator  7  with a differently curved contact face  13 , is cut ( FIGS. 6   b  and  6   c ). For this purpose, the applanator  7  either has to be changed or have its contact face  13  altered, as is possible, for example, using an applanator  7  according to  FIG. 7 . A further incision through the tunnel-like access  11  not only produces a new pocket  12  but also cuts out a lens-shaped portion of tissue  18  ( FIG. 6   c ) which, for example, can be removed through the tunnel-like access  11  using tweezers. The lens-shaped portion of tissue corresponds in form to the difference of the differently curved contact faces  13  of the two applanators  7  and/or the desired dioptric change through corresponding alteration of the anterior corneal curvature. The applanator  7  also has, in its upper area, a grip  36  with an engraved surface ( FIG. 8   e ), which makes the applanator  7  easy to change. It is useful in this case if the applanator  7  protrudes from the receptacle  6  so as to be easily grasped. 
     To make it easier to cut out a lens-shaped portion of tissue  18 , the blade  4  for the second incision can be inserted somewhat deeper into the cornea  1  ( FIGS. 8   a  and  8   b ). This can be achieved by ensuring that the perpendicular distances h 1  and h 2  of the peripheral edges of the contact faces  13  of the applanators  7 , successively inserted into the receptacle  6 , are different with respect to the cutting plane E of the blade  4 . Illustrative embodiments of different contact faces  13  of applanators  7  are shown in  FIGS. 8   a  to  8   g . The dimensions of the lens-shaped portion of tissue  18  that is cut out using the applanators according to  FIGS. 8   a  and  8   b  and  FIGS. 8   c  and  8   d  are indicated by hatching. 
     According to  FIG. 9 , the preferably non-metallic blade forms a pointed tip  19  with two blade edges  20  originating from this tip. This specific type of pointed tip  19  has proven useful in particular for penetrating the outer layer of the cornea  1  and/or for producing a tunnel-like access  11 . The shape of the blade  4  resembles that of a double-edged knife. 
     The applanators  7  are preferably made of transparent material, such as plastic or glass, and are designed, as in  FIGS. 1 and 2 , as magnifying lenses  21 , with their focal point lying in the area of the contact face  13 , preferably on the axis of symmetry  22  of the applanator. With an applanator  7  of such a design, it is quite easy for a surgeon to monitor the progress of treatment of the cornea  1 . 
     The transparent applanator  7  has markings  23  on the side directed towards the eye. These markings  23  allow a surgeon to optimally orientate himself, for example in terms of where to apply the blade  4  for cutting a tunnel-like access. Markings  23  can also be applied for the optical treatment zone in order to indicate to the surgeon the boundaries of the pocket  12  that is to be cut. The transparent applanator  7  also has markings  23  on its side directed away from the eye, which are related to markings  23  on the receptacle  6  for the applanator  7  ( FIG. 10 ). This allows the surgeon, by rotating the applanator  7  in relation to the receptacle  6 , to perform refractive power corrections, especially in cases of astigmatism. 
     The contact face  13  of the applanator shown in  FIG. 7  is made of a deformable material  24 , which can be curved via an actuator  25  in order to assume different shapes that are maintained. Through a supply line to the actuator  25 , compressed gas and compressed liquid or the like can be fed into the cavity of the actuator  25 , by which means the contact face  13  of the applanator  7  can be curved so as to obtain different shapes that are maintained. 
     According to the illustrative embodiment in  FIG. 2 , the holder  3  consists of a lever system comprising at least two lever arms  26  having pivot axes  27  that are perpendicular to the cutting plane E of the blade  4 , wherein one lever arm  26  receives the blade  4 , and the other lever arm  26  is articulated on the frame  2 , preferably on the receptacle  6 . 
     According to the illustrative embodiment in  FIG. 1 , the holder  3  can also comprise a fork-like blade guide  28 , which receives the blade  4  and which is guided, as far as possible free of clearance, between parallel surfaces  29  of a peripheral groove  30  provided on the frame  2 , in particular on the receptacle  6 . The blade  4  is offset in relation to the fork-like blade guide  28 , and the distance between the cutting plane E of the blade  4  and the contact face  13  of the applanator  7  is adjustable by means of an actuator  31  in the form of a screw drive. A knob  35  is provided on the receptacle  6  in order to ensure that the fork-like blade guide  28  can be easily pushed in. 
     The applanator  7  can be fixed in the receptacle  6  by means of a partial vacuum. For this purpose, air can be sucked out of a chamber located between receptacle and applanator by way of a line  32 . For this purpose, the applanator has the shape of a truncated cone, which allows easy insertion of the applanator. It is also conceivable, instead of the pressure line, to use other mechanical holders, for example a bayonet closure, or magnetic, electromagnetic, hydraulic or equivalent mechanisms. The ring body  5  is suctioned onto the eye in a similar way via a pressure line  34 . 
     It will be seen from  FIG. 11  that the blade  4  has a shaft  41 , for securing the blade  4  in the blade receptacle  50 , and a cutting area  42 , and also a roughened area  43  on at least one side of the shaft  41 , which can be a partial area of the surface of the underside of the shaft  41 . The cutting area  42  is the longitudinal area of the blade which has a blade edge and with which cuts can therefore be made. The longitudinal area of the blade that does not have a blade edge, for example the shaft  41  of the blade, does not belong to the cutting area. The shaft can be narrowed in relation to the cutting area  42  ( FIG. 11 ) or of the same width ( FIG. 22 ) or, in special cases, it can even be wider, for example if the cutting edge is continued onto the blade receptacle or onto a second blade. 
     According to  FIG. 12 , the blade  4  is now adhesively bonded into the blade receptacle  50  in such a way that the flat top side  51  of the blade receptacle  50  (the side directed towards the applanator or contact face  13 ) does not protrude above the flat top side  44  of the blade. In this example, the flat top side  51  of the blade receptacle  50  and the flat top side  44  of the blade form a common flat surface. The cutting edge is indicated here on the flat top side  44  of the blade, but it can also extend centrally between the top side  44  and underside  46  of the cutting area  42  of the blade  4 . Ideally, not only is the underside of the shaft  41  roughened, or a partial surface  43  thereof, but also a corresponding surface of the blade receptacle  50 , which is designed here as a depression  52  in the area where the shaft  41  is received in the blade receptacle  50 . The adjoining surfaces  43  of the blade and  52  of the blade receptacle are connected by means of a suitable adhesive  60 . 
     In another embodiment, according to  FIG. 13 , the top side  51  of the blade receptacle is not intended to protrude above the cutting edge  45  of the blade  4 , for which reason a corresponding depression  52  is provided. Here, in contrast to  FIG. 12 , the cutting edge  45  is arranged in the centre between the top side  44  and underside  46  of the blade. The roughened area  43  and the roughened depression  52  are again connected to each other by means of adhesive  60 . A poorer design variant is one in which, with a symmetrical cutting edge (in the centre between the top side and underside of the blade), the top side  51  of the blade receptacle  50  protrudes above the cutting edge  45  of the blade  4  but does not protrude above the top side  44  of the blade  4 . 
     The applanator  7  with the contact face  13  is also indicated in  FIG. 13 . It will be noted that, during the cutting procedure, the distance x between the highest point of the flat surface on the top side  51  of the blade receptacle  50  and the contact face  13  of the applanator  7 , measured perpendicular to the cutting plane, is not less than the distance y between the flat surface on the top side  44  of the blade  4  and the contact face  13  of the applanator  7 , measured perpendicular to the cutting plane E. 
       FIG. 14  shows a plan view of the blade from  FIG. 13 . The blade  4  is designed as a longitudinal blade with two cutting edges  45 , which extend along the longitudinal sides and which taper towards a pointed tip  19  at the end directed away from the blade receptacle. The cutting edges  45  extend in parallel along both longitudinal sides of the blade and taper towards the pointed tip  19  at an angle alpha of ca. 70° at the end directed away from the blade receptacle. 
     The blade edge  20 , i.e. the areas bevelled in relation to the flat top side and underside of the blade and forming the cutting edge  45  at their line of intersection, is bevelled with respect to the surface by an angle beta of about 15° (see  FIG. 15 ). 
     From the shaft to the blade tip (=pointed tip, the end directed away from the blade receptacle), the cutting edge has a length of at least 3 mm and preferably 5 mm. The cutting edge  45  or blade edge  20  is continued with an identical profile into the blade receptacle  50  (see reference sign  53 ). The continuation  53  of the cutting edge onto the blade receptacle can be up to 7 mm long, ideally 5 mm, such that the blade can effectively produce a cut of up to 12 mm (ideally of between 5 mm and 12 mm). 
     The blade is preferably designed with a thickness of below 300 micrometres, ideally between 100 micrometres and 200 micrometres, such that the cutting edge is preferably constantly 50 to 100 micrometres equidistant from the blade surfaces  44 ,  46 . The blade is ca. 2 mm wide and, at the end directed towards the blade receptacle  50 , has a shaft  41 , which is ca. 2 mm long and at least 1 mm wide. The geometry of the shaft can in principle be of any kind. The thickness of the shaft in this illustrative embodiment is identical to the thickness of the blade. On the side directed away from the applanation face  13 , the shaft  41  is roughened (reference sign  43 ) compared to the rest of the blade surface. The rest of the blade surface is preferably lapped and very smooth. The roughened surface should measure at least 1 mm 2 , but ideally 2 mm 2  or more. The three side surfaces of the shaft can also be roughened. 
     The shaft can of course also be thicker or thinner than the cutting blade part. 
     The freedom of movement of the blade  4  in the cutting plane (cutting surface) E is at least in the radial direction in each position within the cutting surface. The blade is radially movable in different directions and pivotable about an axis perpendicular to the cutting plane. The blade in each position within the cutting surface can be oriented and moved freely in all directions of the cutting plane. Moreover, a limiting mechanism can be provided, for example for limiting the amplitude of a reciprocating movement to defined levels of the amplitude along the forward movement of the blade. In the preferred design variant, such a limitation of the amplitude of a lateral movement is not provided. In each case, an additional vibration, which does not cause any actual cutting when the blade is at rest (no radial and/or pivoting movement), can be included as third movement component. Thus, a maximum of three different blade movements can be superposed in each point of the physical cutting plane (radial movement, pivoting movement, vibration). The vibration is preferably of such small excursion and of sufficiently high frequency that it cannot be seen by the naked eye. The amplitude is preferably less than 0.2 mm (ideally less than 0.1 mm or even less than 0.05 mm) and the frequency preferably greater than 400 Hertz (ideally greater than 700 Hertz). 
     The applanator  7  should have a height (along the centre axis) of more than 1 cm. The peripheral recess  10  of the frame  2 , for the passage of the blade  4  through the frame  2 , should be not more than 5 mm away from the lower edge of the ring body  5  (ideally between 2 and 5 mm) (see reference sign a in  FIG. 1  and  FIG. 2 ). The stop provided for the applanator  7  in the receptacle  6  should be not more than 4 mm (ideally between 0.5 mm and 2 mm) from the applanation face (=contact face)  13  of the applanator  7  fixed in the receptacle  6  (see reference sign b in  FIG. 1 ,  FIG. 2  and  FIG. 8 . 
     The applanator  7  can also be fixed in the frame  2  with a lever device for example. 
     The blade receptacle  50  can be an integral part of the holder  3  for the blade  4  guided on the frame  2 , i.e. can be formed in one piece with the holder  3 . In the illustrative embodiment according to  FIG. 5 , the blade receptacle  50  would accordingly be part of the fork-like blade guide  28 . 
     The receptacle  6  from  FIGS. 1 and 2  can also be designed in two parts in accordance with  FIG. 16 , such that an upper receptacle part  70  with a flange-like continuation forms an upper surface  29 - 1  of the peripheral groove  30 , while a lower receptacle part  71  with a flange-like continuation forms a lower surface  29 - 2  of the peripheral groove  30 . The two receptacle parts  70 ,  71  are connected to each other by a connection  72 , preferably an adhesive, or by other means, such as a form fit or a thread. The upper receptacle part  70  lies in a recess on the lower receptacle part  71 . 
     By virtue of the fact that one surface  29 - 1  belongs to one part  70  of the receptacle and the other surface  29 - 2  belongs to the other part of the receptacle and the two are then suitably connected to each other, it is possible, for example by means of a turning machine, to produce both surfaces exactly perpendicular to the axis  22 . If this is not the case, in other words if the peripheral groove  30  is made in a one-part receptacle, there is a danger, particularly in the case of very hard material, of the two surfaces  29 - 1 ,  29 - 2  not extending exactly in parallel. If the receptacle is designed in two parts, the surfaces  29 - 1  and  29 - 2  can be turned flat from “in front”, whereas in a one-part design the peripheral groove  30  has to be turned using a “grooving chisel”. It has been found that the latter method gives much poorer parallelism of the surfaces  29 - 1 ,  29 - 2  than the first method. In particular, in the latter method, the peripheral groove  30  will be somewhat thicker in the outer area away from the axis  22 , in other words the surfaces  29 - 1 ,  29 - 2  lie further apart there than they do centrally (near the axis). This can lead to considerable imprecision of cutting, with a risk to the patient&#39;s eyesight. 
       FIG. 17  shows an illustrative embodiment for limiting the blade movement to what is substantially only a linear forward drive. This is obtained if the device according to the invention has no vibrator and/or if the fork-like blade guide  28  from  FIG. 5  and the peripheral groove  30  on the receptacle  6  of the frame  2  for the applanator  7  are designed such that only a linear or radial movement (forward drive) of the blade is possible in the cornea, that is to say without substantial pivotability or reciprocating movement. A restriction to a merely radial or linear movement can be achieved, for example, if the outer sides of the peripheral groove  30  and the inner sides of the fork-like blade guide  28  extend exactly parallel to each other and without clearance or in practice with only minimal clearance. 
     In another design variant, but one which is preferably suitable for producing comparatively small corneal pockets and has no frame  2  through which the blade can be passed with clearance, for example according to U.S. Pat. No. 6,599,305 B1, the safety of the patient can be greatly improved by a blade receptacle and blade according to the invention and by securing of the blade (adhesion and, if appropriate, roughening). 
       FIG. 18  and  FIG. 19  show a corresponding design from the prior art according to U.S. Pat. No. 6,599,305 B1. They show a device that also has a ring body.  5 . A fixture  83 , which has both a blade and also an applanator, the latter at a fixed distance from the blade, can be pushed forward by the device. The blade oscillates, under the action of the fixture  83 , about the forward direction with an amplitude that determines the width of the pocket. The blade is clamped on both sides (laterally) into the fixture  83 . Therefore, the only material suitable in practice for such a blade is a ductile material (metal), since solid materials such as diamond, ceramic, etc., would break during lateral clamping in the fixture  83 . Moreover, such a large diamond, for example, would be difficult to produce and extremely expensive, among other reasons because of only limited availability on the market. Blades made of metal, however, can in practice be used only as disposable blades and are extremely unstable (bendable) in this size, which increases the tolerance of the fit of each blade and thus also increases the imprecision when cutting. However, if the fixture  83  and the blade were designed in one piece, then hard materials such as ceramic could also be used. 
     If, according to the invention, a blade receptacle is used which is secured on the fixture  83 , then materials can also be combined. For example, a blade receptacle made of metal, semiconductor, plastic or ceramic with a blade made of any desired material, but preferably of any desired hard material such as diamond, ruby, ceramic, etc. Such a design variant is seen in  FIG. 20  and  FIG. 21  for example. There, a blade receptacle  50 , which supports the blade  4 , is clamped in the fixture  83 . According to the invention, the top side of the blade receptacle  50  does not protrude above the top side of the blade  4  or the cutting edge thereof. The blade  4  is shown in section in  FIG. 21 . In terms of its function of securing the blade receptacle, the guide  83  is equivalent to the holder  3 . 
     In a particularly advantageous embodiment of the invention, the cutting edge of the blade is continued onto the blade receptacle by up to 7 mm, ideally by 5 mm, such that a blade can effectively produce a cut of up to 12 mm (ideally between 5 mm and 12 mm) (see  FIG. 14 ). The cutting edge  45  of the blade  4  is continued in a plane extending on the blade receptacle  50  merging into each other. In a particular design variant according to  FIG. 22 , this cutting edge  45  can also be formed on the blade receptacle  50  by a second blade  55  arranged there. The cutting edge  45  of the blade  4  then continues into the cutting edge  56  of the blade  55 . Typically, the length of the cutting edge  45  is between 4 and 6 mm (ideally 5 mm) and that of the cutting edge  56  is between 2 and 6 mm (ideally 4 mm). The boundary line  57  between both blades  4 ,  55 , which then abut each other, can be of any desired form and is straight in  FIG. 22 . The blade  4  in  FIG. 22  has no shaft  41  in the real sense and consists merely of a cutting area  42 . In principle, the second blade  55  could also be omitted, in which case the blade  4  would then be maintained in its form without an actual shaft. If appropriate, however, that part of the blade  4  that lies directly over the blade receptacle  50  or overlaps the latter can be designated as shaft  41 . 
     The shaft geometry can in principle be of any kind. 
     Generally, an oscillation or a vibration can be provided to support the cutting movement. It is of course also possible to work without oscillation and vibration. 
     An oscillating cutting movement is to be understood here as meaning that, when the blade  4  is periodically moved perpendicular to the forward drive axis, this excursion about the forward drive axis represents a relevant cutting movement, and the incision into the tissue along the excursion thus determines and/or at least directly contributes to the pocket dimension and pocket size in the cornea. By contrast, the movement of the blade by a vibrator (vibration) does not represent any relevant direct cutting movement for producing the corneal pocket. The pocket dimension or pocket size is not determined or not essentially determined by the direct blade movement resulting from the vibration. The influence of the vibration on the cutting procedure is instead indirect, because of the comparatively small movement amplitude, and is such that the actual blade movement for forming the corneal pocket is made easier by the vibration of the blade and is improved in terms of its precision. 
     In principle, the various elements of the embodiments can be combined to form new embodiments. 
     LIST OF REFERENCE SIGNS 
     
         
           1  cornea 
           2  frame 
           3  holder 
           4  blade 
           5  ring body 
           6  receptacle for an applanator  7   
           7  applanator 
           10  peripheral recess of the frame  2   
           11  tunnel-like access of the pocket  12   
           12  pocket in the corneal tissue 
           13  contact face (applanation surface or applanator) 
           14  vibrator 
           17  stop in the receptacle  6  for the applanator  7   
           18  lens-shaped portion of tissue 
           19  pointed tip of the blade  4   
           20  blade edge 
           21  magnifying lens of the applanator  7   
           22  axis of symmetry of the applanator 
           23  markings on the applanator  7   
           24  deformable material of the contact face  13  of the applanator  7   
           25  actuator for deformable material  24   
           26  lever arm of the holder  3   
           27  pivot axes of the lever arms  26   
           28  fork-like blade guide 
           29 - 1  surface of the peripheral groove  30  on the upper holder part  70   
           29 - 2  surface of the peripheral groove  30  on the lower holder part  71   
           30  peripheral groove on the frame  2   
           31  actuator 
           32  line 
           35  knob on the receptacle  6   
           41  shaft of the blade  4   
           42  cutting area 
           43  roughened area of the shaft  41  of the blade  4   
           44  top side of the blade  4   
           45  cutting edge of the blade  4   
           46  underside of the blade 
           50  blade receptacle 
           51  top side of the blade receptacle  50   
           52  roughened depression of the blade receptacle  50   
           53  cutting edge on the blade receptacle  50   
           54  underside of the blade receptacle 
           55  second blade on the blade receptacle  50   
           56  cutting edge of the second blade  55   
           57  boundary line between blade  4  and blade  55   
           60  adhesive 
           70  upper receptacle part 
           71  lower receptacle part 
           72  connection between receptacle parts  70 ,  71   
           83  fixture for receiving the blade