NL8602113A - Intra-ocular lens fixing haptics - are of material returning to stable shape on heat treatment after distortion - Google Patents

Abstract

The intra-ocular lens comprises a lens or optical section and a fixing one with components holding it in position in the eye. The fixing haptics are of material with shape-producing characteristics and have a stable first functional shape to which they return after specific heat-treatment after distortion, to fix the lens section in position. The haptics can be of plastics or of metal such as a nickel-titanium alloy.

Description

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Title: Intraocular lens fixatives with shape-restoring properties

The invention relates to an intraocular lens comprising an optical and fixation part, the fixation part comprising at least one or more fixation members which can position and fix the lens in the eye.

The natural eye lens of, for example, humans, is an optically clear organ located behind the pupil opening of the human eye. The lens is one of the eye parts that ensures that a sharp image is formed on the retina. In some cases, however, the lens may become cloudy, this is called cataract or cataract, and should then be removed. After removal of the lens, due to loss of refractive power, the eye becomes optically weaker and this refractive power must be normalized again with optical aids. The optical correction of the state of lenslessness, also referred to as aphakic correction, can be performed in three ways, namely through eye goggles, an eye contact lens or an artificial lens, the intraocular lens, in the eye.

The use of the intraocular lenses mentioned in the preamble is known and generally accepted. A large number of these known lenses are described in "Intraokulairlinsen, Grundlagen und Operationslehre,

Bucherei des Augenarztes, Heft 82, Paul U. Fechner, 25 Enke Verlag Stuttgart 1980. Also intraocular lenses are known from British patent application 5376/75.

Today, the manufacture and use of the optical part is virtually no problem.

This optical part, which is usually made of polypropylene 30, can be applied before, after or in the plane of the iris. However, it will be clear 860211? -2- t f that high demands are made on the attachment of the optical part. The known mountings, however, appear to give insufficient permanent support to the optical part, so that a good fixation of the lens 5 with respect to the iris is not ensured. Moreover, the known intraocular lenses are difficult to apply. Often the small fixation members have to be inserted into the already small working area during implantation with tools. The shape of the fixation members is thereby determined not only by the desire to obtain an optimal attachment of the lens in the eye, but also to a great extent by the limitations which apply when inserting the lens. In many cases use is made of the elastic properties of the material from which the fixation members are manufactured. The fixation members are elastically deformed by a tool in such a way that the lens with the fixation members can be brought into the eye, after which the tool is removed, the fixation members return to approximately the old state and clamp themselves in the eye. However, the fixation members return to the old state with an uncontrolled movement, which could damage the delicate eye. Moreover, there is a danger that the fixation members do not take the correct position for a good fixing. The known intra-eyepiece lenses also have almost all fixation members which are shaped in such a way that it is difficult to remove the lens after implantation without undue damage.

The object of the invention is therefore to provide an intra-ocular lens, and in particular a fixation part therefor, wherein the above-described drawbacks are obviated.

According to the invention, the fixation members are made for this purpose from a material with shape-restoring properties, wherein the fixation members have a stable functional shape, in which the fixation members, after deformation, return due to a certain temperature influence. such that the fixation members can fix themselves with the lens in the eye.

The advantage of this is that the fixation members with a shape suitable for fixation in the eye can be brought into a shape suitable for placement in the eye by deformation. The lens can then be positioned with only very limited aids. By subsequently allowing the fixation members 10 to undergo a certain temperature influence, the fixation members will return to their first stable functional form and get stuck in the eye. This return to the basic form is incidentally a very gradual transition, so that there is no risk of damage to the eye. The fixation members will moreover accurately occupy the desired position. Such a lens can therefore be placed in the eye very reliably and in a safe manner for the patient.

Such a shape-restoring behavior is found with a number of plastics and a number of metals. For example, Cu-Al, Cu-Zn and Ni-Ti alloys show this behavior. Ni-Ti alloys are particularly suitable for their powerful memory effect and good mechanical properties. The Ni-Ti alloys are furthermore suitable for biomedical applications because of the proven biocompatibility and the good corrosion resistance in the human body. Incidentally, other memory material can also be used, if necessary with a coating.

The invention will now be explained in more detail with reference to a number of embodiments and a drawing. In the drawing: Figure 1 .: Temperature-induced transformation diagram; Figure 2 .: voltage-induced transformation diagram; figure 3 .: with one road effect, voltage induced 35 transformation and temperature induced 8602113 -4-

Hr Λ, back transformation; figure 4: diagram with two-way effect; figure 5: a cross section of an eye; figure 6.: tension-elongation diagram, with pseudoelastic effect; Figure 7.a, b, c: an embodiment of the lens according to the invention in the undeformed (a, b) and deformed state (c); figures 8.a, b: another embodiment of the lens according to the invention, in undeformed and deformed form; figure 9.: a lens with a spiral wire; Figure 10.: an embodiment of the lens according to the invention and of the lobster claw type; figure 11.: an iris-clip lens according to the invention.

In order to provide more clarity about the effect of the shape-restoring behavior, this behavior will be briefly and very generally described for metals and in particular for a Ni-Ti alloy. More deeply and extensively, this phenomenon is described in "Shape

Memory effects in Alloys, J. Perkins Plenum Press, New York "75".

For almost all materials, when they are deformed beyond their yield point, a permanent plastic deformation occurs, which can only be eliminated by a subsequent plastic deformation. However, with shape memory materials, the phenomenon occurs that after an apparently plastic deformation at a certain temperature, this deformation is completely or almost completely eliminated by heating to a higher temperature and that the material returns to its original shape.

This phenomenon is due to the fact that a martensitic transform takes place in the material during deformation. When this material is brought to a higher temperature, a transition from the martensite to a higher temperature phase takes place and the material thereby returns to the original shape and phase as it was before deformation. This last phase is also called austenjet.

In principle, there are two types of transformations, namely the thermal and the voltage-induced martensic transformation. The thermally induced transformation 10 is shown in Figure 1. The vertical axis shows the volume fraction of martensite and the horizontal axis shows the temperature. Below a certain temperature (Mf), the material is completely martensitic and stable. When heating is now carried out at a certain temperature (As), the transformation of the material will start to become completely austenitic at temperature Af and above. When the material is cooled down again, it will transform back to martensite with a certain hysteresis at a certain temperature Ms.

Figure 2 shows a voltage-induced transformation, namely for a deformation temperature above Af. When the tension, shown a-m on the horizontal axis, increases, the martensitic transformation will start at a certain tension ςτ and after some tension increase the material becomes completely martensitic. However, because the martensite above Af is not stable, when the tension is removed, the material with some hysteresis will become completely austenitic again. This is called pseudoelasticity. However, if deformed at a temperature below Af, the martensite formed is stable.

Figure 3 shows a combination of both transformations.

8602113 -6-

In the top half of the diagram, the material (along the vertical axis) is loaded at a temperature between Ms and Af. The material will first elastically deform (A-B) and then apparently plastic (B-C). The material will spring back to D after removal of the load, so with a permanent elongation A-D. If the material is now heated according to the bottom half of the diagram, at temperature As, and thus from E, the martensite will transform back to austenite and return completely to the initial state. With TiNi 10, 100% shape recovery can be achieved from a plastic stretch to 8%. This is called the one-way effect.

However, a number of shape memory materials may also have another phenomenon, namely the two-way effect. This means that the material not only returns to the undeformed form after deformation by heating, but also that the deformed form is resumed by subsequently cooling. This is illustrated in figure 4. The material is initially strongly deformed, such that martensite is formed. The martensite is then loaded so that it locally deforms plastically. This creates a reoriented stress-induced inhomogeneous martensitic structure, with high internal stresses and a pronounced texture.

25 During heating, the less deformed parts return to the old shape, but are somewhat restrained by the more deformed parts, so that residual stresses arise and therefore no complete shape recovery occurs (A-C). On cooling, the material will remember the deformed state due to the residual stresses and return, albeit partially.

The main parameters such as the transformation temperature Af, As, Ms and Mf can be influenced by varying the composition and in particular the mixing ratio of the alloying elements. The production process followed for the manufacture of the material, such as annealing treatments, cooling rates and conditions and deformations, can also influence these parameters. This is in particular also important in the present field of application, namely implantation in a human body, because the material, if necessary after transformation when heated or cooled by the body, must be in a stable and suitable form suitable for internal use.

In figure 5 an eye is schematically shown in cross section. The front of the eye is covered by the cornea 1. Behind the cornea is a chamber 2 with fluid. The chamber is covered at the rear by the iris 3 and normally a natural lens behind the. pupil opening 3a. However, when this lens 15 no longer functions, for reasons previously described, it is removed and replaced with an intraocular lens placed in front of, behind or in the plane of the iris. Many constructions 2o have already been used for attaching the artificial lens, but all with unsatisfactory results. Most of the constructions use constraints by elastic elements on the iris or, for example, at a or b. To effect such a numbing, the elements must initially be elastically deformed and held in that deformed state by a tool. Then the lens should be positioned in the eye. This is very complicated because the tool which retains the elastic elements in the deformed condition must also be handled in the already very limited area of the opening in the iris. It often goes wrong and the lens is not properly positioned. In addition, the elastic elements return to their original position with an uncontrolled movement when the tool is removed 8602113 »* -8- * *, which can not only damage the eye but also cause the elements to move out of position.

The intraocular lenses according to the invention, on the other hand, are equipped with fixation members with shape-restoring properties. The fixation members have a first functional shape that is stable at body temperature, in which the fixation members can fix the lens firmly in the eye.

The advantage of this is that the fixation members can be deformed in an appropriate form before implantation. This can be done, for example, with a material that is stable in deformed form at body temperature, so a material with an Ms of about 20 ° C and an AS greater than about 37 ° C. This uses the temperature hysteresis during deformation. The lens and the fixation members can then be positioned without too many complicated tools. Finally, the fixation means can for instance be heated thermally or inductively so that the material can return to the stable austenite phase in a quiet manner and thus the fixation members can return to the functional form under fixation in the eye.

The shape memory material can also be selected with other parameters. For example, the material could be stably deformable below body temperature to return to its original shape at body temperature. The lens would then have to be implanted chilled and then heated to body temperature by the body and transformed into the blank under entrapment in the eye.

30 Them is another advantage of the memory material

that due to the so-called pseudoelastic effect, the material always exerts approximately the same tension with different deformations, i.e. with different shapes, as opposed to elastic clamping. This is shown in figure 6. In the elastic region AB

8602113 * -9- the material exerts different stresses at different degrees of deformation. However, in the region B-C, i.e. with different shapes of the fixation members and the associated different deformation degrees, approximately the same tension is always exerted. This is very advantageous for implantation into the eye because it allows the fixation members, regardless of their shape, to be set at a constant optimum pressure acceptable to the eye tissue, thus preventing tissue damage. As stated, the molding memory material can be a plastic or a metal, and in particular a titanium-nickel alloy. It is very advantageous to use a material with a two-way effect, the second shape of which, i.e. the deformed stable shape, has a shape suitable for implantation. The advantage of this is that an implanted lens can be removed without damage to the eye. This has not been possible up to now. Now it is sufficient to cool the fixation members, which thereby return to the deformed shape and no longer clamp in the eye so that the lens can be removed.

The memory material can often be produced in a wire form in a relatively simple manner. It is therefore advantageous to manufacture the fixation members of the lens from wires to be attached to the lens. An embodiment is shown in figure 7. Two wires 5, 6 are attached to the lens 4, by always securing one end of each wire to the lens. The secured ends, of the wires, respectively bent in the same sense, are situated diametrically relative to each other.

For implantation, for example, these wires can be bent in front of the face of the lens (Fig. 7c) so that only the 8602113-10 space of the lens surface is required during implantation. The implantation proceeds as described previously.

Another embodiment, according to Fig. 8a, also has two wires 7, 8, which, however, are now fixed to the lens 4 with both ends, mirrored in the axis of the lens. In this way the threads describe eai loop in their stable form. By deforming the filaments inwardly by pressing inward in the center to the shape of Figure 8b, the lens can be easily implanted and fixed by clamping by heating.

A lens that also fixes in the eye by clamping is a lens with a wire attached spirally around the lens (figure 9). The advantage of this construction is that the spiral wire 9 clings to the eye wall on all sides around the lens 15 after heating.

Another embodiment according to the invention does not clamp against the eye wall, but rather clamp a part of the eye wall between the fixation members (figure 10). This lobster claw type lens consists of two fixation members 20, 10, 11 both formed by two parts 12, 13 and 121, 131 bent to each other on the lens 4, thus forming a slit 14 between the two parts. Before implantation, this gap can be enlarged by bending the parts apart. After positioning and during the heating of the threads they will move together again, thereby clamping a piece of eye tissue between them.

Another type of lens is attached to the iris.

A lens of this type is the iris-clip lens (Figure 11) in which the fixation members 16 and 16 are made of memory material. When the lens is mounted, these members can for instance be brought in a straight form perpendicular to the plane of the lens, so that the members can be inserted through the pupil without touching the iris 3.

When warmed, they will bend and settle behind the iris 35 and pinch the lens in cooperation with the members 15, 8602113 -11-115.

All these fixation members, in particular the threads, can, according to another feature of the invention, be hollow or capillary-shaped for the passage of a thermal medium in order to heat or cool the fixation members.

For example, the wires can be plugged into the lens, cast, glued. In order to obtain an optimal fastening in the lens and to prevent twisting, the fastening ends of the wires can be converted or flattened. According to a special feature of the invention, the shape-restoring properties of the material can also be used in the attachment of the threads in the lens. For this purpose, the thread in the first stable functional form can have, for example, a hook-shaped end. This hook-shaped end can then be deformed into a straight shape for fastening the wire in the lens.

By placing this threaded end in a bore, which ends in an undercut cavity, and treating it thermally, the end will return in the hook shape and thereby settle in the undercut cavity. The wire is thus attached to the lens.

The fixation members can further be provided with a biocompatible and corrosion resistant coating without thereby impairing the operation of the fixation members.

It will be clear that many lens embodiments are still possible within the scope of the invention, using the shape-restoring ability of the material from which the fixation members are made and that the invention is not limited to embodiments described here.

8602113

Claims (19)

An intraocular lens, comprising a lens or optical portion and a fixation portion, the fixation portion comprising at least one or more fixation members that can position and fix the lens in the eye, characterized in that the fixation members are wholly or partially are made of a material with shape-restoring properties, and that the fixation members have a stable first functional shape, in which the fixation members return after deformation due to a certain temperature influence, such that they can fix themselves with the lens part in the eye. Lens according to claim 1, characterized in that the material from which the fixation members are made is a plastic. Lens according to claim 1, characterized in that the material from which the fixation members are made is a metal. Lens according to claim 3, characterized in that the metal is a nickel-titanium alloy. Lens according to claims 1-4, characterized in that the fixation members are made of a material with a two-way effect, and that the fixation members have a stable deformed second shape in which the fixation members have a and disposal have suitable shape. Lens according to claims 1-5, characterized in that the fixation members in the functional first form have pseudoelastic properties. 7. Lens according to claims 1-6, characterized in that the fixation members consist of at least one wires connected to the lens. 8602113 -13- 8. A lens according to claim 7, characterized in that two wires are mounted on or in the lens, each wire being fixed with one end on the lens and the two mounting locations being diametrically opposite each other, and that both wires are hooked in the same sense are bent into their first stable functional form. 9. Lens according to claim 7, characterized in that, on or in the lens, two wires are mounted, that of each wire both ends are fixed on the lens, such that each wire encloses almost a semicircular arc of the lens, and that the two threads are mirrored relative to each other with respect to the axis of the lens, each thread having a first stable loop shape. 10. Lens as claimed in claim 7, characterized in that a spiral wire arranged around the lens is mounted on the lens. 11. Lens according to claim 7, characterized in that two wires are mounted on the lens with a first functional shape, the wires extending hook-shaped perpendicularly from the lens plane. 12. Lens according to claims 1-6, characterized in that two fixation members, mirrored with respect to a centerline of the lens, are arranged on or in the lens, and that each fixation member consists of two mounted on the lens elements bent towards each other, which in their first stable form define a narrow gap. 13. Lens according to any one of the preceding claims, characterized in that the fixation members can be treated by means of an external thermal medium. Lens according to any one of claims 1-12, characterized in that the fixation members can be treated inductively. 15. Lens as claimed in any of the claims 1-12, characterized in that the fixation members are hollow or have a capillary-shaped shape with an inlet or outlet opening for guiding a thermal medium through the fixation member. 16. Lens as claimed in any of the claims 4-15, characterized in that the threads are pinched in the lens. Lens according to any one of claims 7-14 or 15, characterized in that the attachment ends of the wires are flattened or bent. Lens according to any one of claims 7-15, characterized in that - the wires are mounted on or in the lens by applying the shape-restoring properties of the material. 19. A lens according to any one of the preceding claims, characterized in that the fixation members are provided with a biocompatible coating. 8602113