The present invention relates in general to the field of refractive treatment of the eye, in particular the human eye, in order to treat defective vision.
In order to treat low-order types of defective vision such as myopia, hyperopia, astigmatism, myopic astigmatism and hyperopic astigmatism, inter alia the so-called LASIK (LASer In situ Keratomileusis) and so-called LASEK (LASer Epithelial Keratomileusis) methods have been established. In both methods a flap with a diameter of for example about 8 to 10 mm is stripped from the surface of the cornea as far as a small remaining part serving as hinge. This flap is folded to one side, the corneal material lying thereunder thereby being made accessible for refractive laser treatment. After the treatment the flap is folded back again. Within the scope of the laser treatment, which is normally carried out with an excimer laser at a wavelength of for example 193 nm, material is ablated (removed) from the corneal stroma according to an ablation profile that was determined beforehand and possibly adapted during the treatment. The reshaping of the cornea achieved in this way alters the refractive properties of the cornea and thus of the optical system of the eye as a whole. On account of the fact that the flap is folded back, no externally open wound remains and the healing process is as a rule relatively quick.
In the LASIK method the flap is produced by means of a so-called microkeratome, which shaves off the flap from the surface of the cornea. The microkeratome has a cutting head, which is normally moved linearly over the cornea. The cutting head is loaded with a planar cutting blade, which is adjusted to a specific setting angle (angle of attack) relative to an applanation surface of the cutting head and projects by an amount, determined by the desired flap thickness, over the applanation surface. If the cutting head is moved over the cornea, the cutting blade cuts into the cornea and thereby forms the flap. In addition to the feed movement of the cutting head the cutting blade is normally caused to execute lateral oscillations.
In the LASIK method it was for a long time normal practice to produce the flap with a thickness of about 100 μm to 200 μm. In this case the cut goes through the approximately 40 μm to 60 μm thick corneal epithelium and the approximately 8 μm to 15 μm thick Bowman membrane lying underneath, directly into the stroma, the thickness of which is for example about 400 μm to 500 μm.
In DE 103 17 972 B3 it is proposed to adjust the cutting angle and the cutting radius of the cutting blade so that the blade is on the one hand sharp enough to fully penetrate the corneal epithelium, but on the other hand is not so sharp as to penetrate also the Bowman membrane. With such a blade the epithelium should be able to be cleanly separated from the Bowman membrane, without any epithelial cells remaining and without the Bowman membrane being damaged. The flap that is formed is thus a pure epithelial flap, which is only about 50 μm thick.
In the LASIK method the problem arises that the cornea can, on account of its elasticity, evade the cutting blade when the latter is inserted from the side. This can result in an irregular flap edge and a not uniquely reproducible flap size. With a relatively blunt cutting edge, as is proposed in DE 103 17 972 B3, this process can be particularly serious.
In the LASEK method similarly only the epithelium is separated from the cornea. The flap size is defined by means of a so-called microtrepan, which is a cutting element with a circular cutting edge running along a circular arc, wherein the cutting edge does not extend over a full circle but only over part of the circumference of a circle, for example about 250° to 300°. A gap is provided in the remaining circumferential region. The trepan is placed on the eye and, when rotated clockwise and anticlockwise by a limited small angle of rotation of for example about 10°, its circular cutting edge penetrates into the cornea. A circular cut is made in the epithelium, the length of which is equal to that of the circular cutting edge plus the angle of rotation of the trepan. The region that has not been cut forms the hinge of the flap. For the cut the trepan is guided in a guide body with a cylindrical receptacle opening, into which the trepan is inserted.
After the cutting with the trepan the epithelial tissue is softened by means of an alcoholic solution that is dripped into a cylinder placed on the eye, until the flap can be lifted with a ductor or spatula from the Bowman membrane and moved to one side. The use of the alcohol solution has disadvantages however, since it can kill the cells of the basal membrane lying between the epithelium and Bowman membrane. This delays the closure of the wound, since new epithelial cells can grow only slowly.
Cutting instruments for the LASIK and LASEK methods generally include an instrument base body unit that is placed on the eye and can be fixed relative to the eye. In order to fix the instrument base body unit on the eye it is known to provide the unit with a suction ring, which is placed on the limbus and held on the latter under suction produced by a vacuum. For this purpose the instrument base body unit includes an evacuation connection, which can be connected via a hose line system to an external vacuum pump and is joined, via an evacuation path system formed in the instrument base body unit, to an annular evacuation groove provided on the lower side of the suction ring facing towards the eye.
Previous cutting instruments were designed either specifically for the LASIK method or specifically for the LASEK method.
The object of the present invention is to provide a microsurgical cutting instrument with which improved treatment results can be achieved compared to the previously employed LASEK and LASIK methods.
To achieve this object a microsurgical cutting instrument for refractive opthalmological treatments is proposed according to the invention, with an instrument base body unit to be placed on the eye and which can be fixed relative to the latter, wherein guide holding means are associated with the instrument base body unit, which means are intended and designed for the movably guided holding, relative to the instrument base body unit, of at least two cutting units with different cutting geometries. In particular the guide holding means can include at least a first guide formation for guiding a first cutting unit and at least a second guide formation, different from the first guide formation, for guiding a second cutting unit.
With a cutting instrument according to the invention the advantages of the conventional LASEK and LASIK techniques can be combined in a single instrument. Thus, the instrument base body unit is loaded or can be loaded with a first cutting unit, which enables a cut to be made which defines only the flap edge, without penetrating underneath the epithelium and lifting the latter. The instrument base body unit is furthermore loaded or can be loaded with a second cutting unit, which enables the instrument to engage with the cut made by the first cutting unit and remove the flap from the corneal material lying underneath. The use of an alcohol solution can thus be dispensed with, and at the same time it is possible to make flaps of reproducible size with a clean, uniform edge. Conveniently the first cutting unit has a circular cutting edge, wherein the at least one first guide formation is designed for the rotatory guidance of the first cutting unit, while the second cutting unit has a rectilinear cutting edge and the at least one second guide formation is designed for the at least approximately linear guidance of the second cutting unit.
Since the flap edge is uniquely defined by the first cut, the cutting edge of the second cutting unit can be comparatively blunt. In particular it can be sufficiently blunt that essentially there is no danger that it will cut into the Bowman membrane and thereby reach the corneal stroma. The cutting edge of the second cutting unit must simply be sufficiently sharp that it can remove the epithelium from the Bowman membrane. In contrast to the method discussed in DE 103 17 972 B3, the cutting edge of the second cutting unit does not itself have to cut into the epithelium from outside. It can instead utilise the circular cut made beforehand by the first cutting unit as an “entry”, and is then as it were guided in the circular cut.
In a preferred embodiment the guide holding means are designed so that they allow the simultaneous arrangement of both cutting units on the instrument base body unit.
The guide holding means can include a guide body separate from the instrument base body unit but positionable on the latter, on which guide body is formed the at least one first guide formation, while the at least one second guide formation is formed on the instrument base body unit. For the cutting operation of the second cutting unit the guide body can in this case be removed from the instrument base body unit.
The guide body preferably comprises an approximately cylindrical guide receptacle opening, in which the first cutting unit can be accommodated and can rotate about the cylindrical axis. For this purpose the guide body and the instrument base body unit advantageously comprise co-operating rotation prevention means, which prevent the guide body rotating relative to the instrument base body unit about the cylindrical axis.
The cutting edge of the second cutting unit can be formed by a planar cutting blade, a setting angle of the cutting blade of between 18° and 32°, preferably between 21° and 28° and most particularly preferably of about 25° with respect to the guidance direction of the second cutting unit being preferred.
The invention furthermore relates to a method for forming a corneal flap on the eye, this method including the following steps:
In particular this method can be implemented with a cutting instrument of the type described hereinbefore, in which the first and the second cutting unit can be used in succession without temporarily removing the instrument base body unit from the eye.
The circular cut preferably extends only so deep in the cornea that a ca. 50 μm thick epithelial flap can be removed from the surface of the cornea without damaging the Bowman membrane. As previously mentioned, in this connection the sharpness of the rectilinear cutting edge is preferably such that there is essentially no danger of damaging the Bowman membrane when the rectilinear cutting edge cuts into the cornea.
The scope of the invention also covers a purposefully blunt cutting element with a rectilinear cutting edge of circular cross-section, which is intended for use in a cutting instrument of the type described beforehand and/or for use within the scope of the method described beforehand. According to the invention the cutting edge of such a cutting element has a radius of curvature of between 1 and 10 μm, preferably between 3 and 8 μm and most particularly preferably between 4 and 6 μm. Also, the cutting element in a first cutting region immediately adjoining the cutting edge has a cutting angle of between 15° and 22°, preferably between 16° and 20° and most preferably of about 18°.
In a second cutting region adjoining the first cutting region the cutting element can have a cutting angle between 10° and 18°, preferably between 11° and 16° and most preferably of about 13°, in which the cutting angle of the second cutting region is smaller than the cutting angle of the first cutting region. If desired the cutting element can furthermore have, in a third cutting region adjoining the second cutting region, a cutting angle between 7° and 15°, preferably between 8° and 12° and most preferably of about 9°, wherein the cutting angle of the third cutting region is smaller than the cutting angle of the second cutting region.
The invention is described in more detail hereinafter with the aid of the accompanying drawings, in which:
Reference will first of all be made to
The cutting instrument 10 comprises an instrument base body 12 made for example of stainless steel, on which a trepan 14 forming a first cutting unit and a cutting head 16 (
The instrument base body 12 furthermore comprises a guide and holding frame 30, connected in particular in one piece to the suction ring 18, which consists of two rectilinear longitudinal struts 32 extending spaced apart and parallel to one another, and two arcuately curved connection pieces 34 joining the longitudinal struts 32 to one another at their ends. On their upper side facing away from the eye the longitudinal struts 32 are formed having a toothed section 36 on a part of their longitudinal extension, which serves for toothed engagement with drive pinions 38 (
The guide sleeve 44 is a structural part separate from the instrument base body 12 and serves for the rotationally movable guidance of the trepan 14. The sleeve is inserted between the two longitudinal struts 32 in a region above the suction ring 18 and is supported on the one hand downwardly (referred to the direction of view in
In the illustration shown in
The trepan 14 is rotatable about a restricted angle of rotation relative to the guide sleeve 44. An axially projecting pin 52 provided on the guide sleeve 44 in the example shown in
The cutting head 16 and the guide sleeve 44 with the trepan 14 inserted therein can be arranged simultaneously on the instrument base body 12. This state of the cutting instrument is shown in
The cutting head 16 is mounted on the instrument base body 12 by inserting it in the rear region of the guide and holding frame 30 between the longitudinal struts 32. As shown in
The cutting blade unit 62 can readily be seen in
The cutting blade unit 62 also comprises an attachment 72 on one of the flat blade sides, which for example is made of plastics material and is firmly connected to the cutting blade 64. The attachment 72 is formed with an elongated depression 74 on its upper side remote from the cutting blade 64, in which an eccentric pin (not shown in more detail) of a drive shaft of the aforementioned electric motor drive means engages during operation of the cutting head 16. The cutting blade unit 62 is thereby caused to execute lateral oscillations, which are superimposed on the feed movement of the cutting head 16 effected by the engagement of the drive pinions 38 with the teeth 36.
On at least one of its lateral sides the attachment 72 also comprises an undercut T-shaped groove 76, which serves for the coupling of a slide (not shown in more detail), with which the cutting blade unit 62 is inserted into the receiving pocket 60 of the cutting head 16 and can be removed therefrom after use. The groove 76 thus allows a simple manipulation of the cutting blade unit 62.
The attachment 72 finally also carries spring elements 78, which are arranged on the side of the attachment 72 facing away from the rear blade edge. When the cutting blade unit 62 is inserted into the receiving pocket 60 of the cutting head 16, the spring elements 78 co-operate in such a way with a boundary surface of the receiving pocket 60 as to produce a pretensioning, by means of which the cutting blade unit 62 is pressed against the rear abutment surface of the cutting head 16. In this way a precise positioning and alignment of the cutting blade unit 62 in the receiving pocket 60 is achieved.
As can readily be seen in
The cutting head 16 has an applanation surface 82 arranged in the feed direction in front of the cutting edge 66 of the cutting blade 64, the said applanation surface pressing against the surface of the cornea when the cutting head 16 is in use. The cutting edge 66, which forms a rectilinear cutting edge and thus a further cutting geometry within the meaning of the invention, projects somewhat above the applanation surface 82, in order to be able to penetrate the cornea when the cutting head 16 is being driven.
The parameters influencing the cutting action of the cutting blade 64 are therefore adjusted so that the cutting blade 64 does not damage the Bowman membrane and thus the corneal stroma. This is achieved in particular by a certain bluntness of the cutting edge 66, which is chosen so that although the cutting blade 64 can remove the corneal epithelium from the Bowman membrane, it cannot however penetrate this membrane. Moreover, the setting angle of the cutting blade 64 with respect to the applanation surface 82 and with respect to the feed direction of the cutting head 16 can influence the cutting action. Good results have been achieved with a value of the setting angle of about 25°. Also, the projection of the cutting edge 66 over the applanation surface 82 is conveniently adjusted to be sufficiently small so that it basically corresponds to the desired flap thickness, i.e. roughly to the thickness of the corneal epithelium (typically about 50 to 55 μm).
For reasons of clarity the part of the cutting head 16 lying underneath the cutting blade 64 in
The circular cut thus made with the trepan 14 is identified by the reference numeral 84 in
In the example of implementation described hereinbefore the frame 30 and the guide sleeve 44 form guide holding means in the context of the invention. It is understood that the guide holding means are in no way restricted to such a configuration as is shown in
Reference will now be made to
In an adjoining second cutting region the cutting angle—here identified by α2—is smaller than in the first cutting region and is about 13°, in which connection an upward deviation of about 4° is allowable, though preferably no downward deviation is allowable. Finally, a third cutting region is also provided, in which the cutting angle—here identified as α3—is again smaller than in the previous cutting regions and is about 9°, with a possible upward deviation of about 3°. Downwards the cutting angle α3 should not be smaller than this value. Overall the blade section from the cutting edge 66 up to the point at which the oppositely facing blade sides become parallel (indicated by the line 86 in
It is understood that the numerical values mentioned above are given only by way of example and are in no way intended to restrict the invention. However, these numerical values have provided particularly good results.
In
Number | Date | Country | Kind |
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05018391.2 | Aug 2005 | EP | regional |
This application was originally filed as Patent Cooperation Treaty Application Number PCT/EP2006/007929 filed Aug. 10, 2006, which claims priority of European Application Number 05018391.2, filed Aug. 24, 2005. This application is a United States national phase application of co-pending international patent application number PCT/EP2006/007929, filed Aug. 10, 2006, the disclosure of which is incorporated herein by reference.
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/EP2006/007929 | 8/10/2006 | WO | 00 | 11/3/2008 |