FIELD OF THE INVENTION  
         [0001]    This invention relates to ophthalmic devices and procedures, and is particularly concerned with the treatment of presbyopia.  
         BACKGROUND OF THE INVENTION  
         [0002]    It is known to make radial incisions extending into the anterior ciliary area of the sclera. Such techniques were used in the early 1980s as part of radial keratotomy procedures. One disadvantage of this procedure was that it could produce a myopic shift. Any procedure which improves the working ability of the ciliary body/zonular complex will enhance accommodation of the eye. Therefore, the use alone of incisions into the sclera will increase the working circumference and enhance accommodation. However, in the healing process, new blood vessels and collagen across the width of the incisions contract as they heal. This results in shrinkage and scarring, and the effect of the original incisions is reduced.  
           [0003]    Various attempts have been made to treat presbyopia. In US 5489299 the amplitude of accommodation of the eye is increased by manipulating the ciliary muscle through intervention with external means. This can be accomplished by securing a rigid band to the portion of the sclera which radially surrounds the ciliary body.  
           [0004]    In US 5722952, the sclera is weakened by use of an enzyme which can be injected into the sclera in the region of the ciliary body.  
           [0005]    In US 5354331 the effective working distance of the ciliary muscle is increased by expanding the sclera in the region of the ciliary body. This is accomplished by suturing to the sclera in the region of the ciliary body a relatively rigid band having a diameter slightly greater than that of the sclera in that region. The scleral expansion band comprises anterior and posterior rims and a web extending between the rims.  
         SUMMARY OF THE INVENTION  
         [0006]    It is an object of the present invention to enable an effective treatment of presbyopia to be effected, by maintaining the effect of incisions made into the sclera and preventing subsequent shrinkage such as has previously taken place due to the natural healing process.  
           [0007]    This is achieved in accordance with the invention by the insertion of tissue barriers into the incisions made in the sclera. A tissue barrier inserted into the sclera will keep the incision open and healing will take place without fibrosis. The tissue barrier will prevent in-growth of tissue. The tissue barriers prevent the contracting which would otherwise occur as part of the healing process, and allow the internal pressure of the eye, i.e. the intraocular pressure, to maintain the stretching which is produced by the original incisions, and thus correcting the presbyopic condition.  
           [0008]    It is important to note that the tissue barriers of the present invention are not “implanted” in the sense of being buried in channels created by tunnelling through the sclera. The tissue barriers are placed in the incisions made in the sclera, simply as a barrier to in-growth of new tissue. It is the internal hydrodynamics of the eye, i.e. the constant intraocular pressure, which then effectively stretches the sclera, allowing for increased tension in the ciliary body/zonular complex. The use of the tissue barriers in accordance with the invention creates a passive increase in the intraocular pressure.  
           [0009]    The tissue barriers are placed in four or more incisions in the sclera. The incisions increase the effective working distance of the ciliary muscle, by increasing the radial distance between the crystalline lens and the inner diameter of the ciliary muscle. No “segments” are inserted as none are necessary. The tissue barriers are used simply to maintain the integrity of the incisions and allow continued stretching by internal ocular pressure. There is no manipulation of the ciliary muscle involved in the procedures according to the present invention. The tissue barriers serve only to maintain the integrity of the incisions.  
           [0010]    In accordance with one aspect of the present invention there is provided a tissue barrier for insertion into an incision in the sclera of the eye, comprising an elongate insert which is provided with a longitudinally extending flange at each end to prevent the barrier from being ejected from the incision.  
           [0011]    In contrast to an insert which has an inverted T cross-section and lateral flanges to prevent its ejection as healing takes place, the use of longitudinally extending flanges at each end of the insert has practical advantages in terms of making the operating procedure easier. Making a T-shaped incision is not easy. The cutting of lateral incisions after making the initial radial incision is difficult to achieve, both because of the surgical instruments needed and the fact that the sclera varies in dimensions from eye to eye. By making the radial incision in just the one plane, the procedure is simplified, while the end flanges still hold the insert in place both initially and during the healing process.  
           [0012]    Although the tissue barriers can be of any material, barriers of titanium or a titanium alloy are particularly preferred.  
           [0013]    Preferably, the insert has a central longitudinally extending portion with a reduced height flange at each end, the bottom surface of each flange being contiguous with the bottom surface of the central portion.  
           [0014]    In a preferred embodiment, the height of each flange is about half the height of the central portion.  
           [0015]    In some embodiments, the flanges at the respective ends of the central portion are not of equal length.  
           [0016]    The flanges desirably have a circular or rectangular cross-section.  
           [0017]    In some embodiments, the central portion has a greater width transversely to the longitudinal axis of the insert than the flanges.  
           [0018]    In some practical embodiments, the dimension of each flange transversely to the longitudinal axis of the insert is of the order of 0.20 mm, and the flanges are respectively of the order of 0.90 mm and 0.50 mm in length.  
           [0019]    The overall length of the insert is preferably between of the order of 4.25 mm and of the order of 3.75 mm.  
           [0020]    Preferably, the combined length of the two flanges is approximately equal to one third of the overall length of the tissue barrier.  
           [0021]    Also in accordance with the invention there is provided a method of treating presbyopia, which comprises making a plurality of radial incisions in the sclera of the eye, at the base of each incision making longitudinal extensions of the incision in each longitudinal direction, and inserting a tissue barrier of the type defined above into each incision so as to prevent the tissue barrier being ejected. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0022]    In order that the invention may be more fully understood, a number of embodiments of tissue barrier in accordance with the invention will now be described by way of example and with reference to the accompanying drawings. In the drawings:  
         [0023]    [0023]FIG. 1 is a top plan view of a first embodiment of tissue barrier in accordance with the invention;  
         [0024]    [0024]FIG. 2 is a side view of the tissue barrier of FIG. 1;  
         [0025]    [0025]FIG. 3 is an end view of the tissue barrier of FIGS. 1 and 2;  
         [0026]    [0026]FIG. 4 is a side view of a second embodiment of tissue barrier in accordance with the invention;  
         [0027]    [0027]FIG. 5 is an end view of the tissue barrier of FIG. 4;  
         [0028]    [0028]FIG. 6 is a top plan view of the tissue barrier of FIGS. 4 and 5;  
         [0029]    [0029]FIG. 7 is a side view of a third embodiment of tissue barrier in accordance with the invention;  
         [0030]    [0030]FIG. 8 is an end view of the tissue barrier of FIG. 7;  
         [0031]    [0031]FIG. 9 is a top plan view of the tissue barrier of FIGS. 7 and 8;  
         [0032]    [0032]FIG. 10 is a side view of a fourth embodiment of tissue barrier in accordance with the invention;  
         [0033]    [0033]FIG. 11 is an end view of the tissue barrier of FIG. 10;  
         [0034]    [0034]FIG. 12 is a top plan view of the tissue barrier of FIGS. 10 and 11;  
         [0035]    [0035]FIG. 13 is a side view of a fifth embodiment of tissue barrier in accordance with the invention;  
         [0036]    [0036]FIG. 14 is an end view of the tissue barrier of FIG. 13;  
         [0037]    [0037]FIG. 15 is a top plan view of the tissue barrier of FIGS. 13 and 14;  
         [0038]    [0038]FIG. 16 is a side view of a sixth embodiment of tissue barrier in accordance with the invention;  
         [0039]    [0039]FIG. 17 is an end view of the tissue barrier of FIG. 16; and,  
         [0040]    [0040]FIG. 18 is a top plan view of the tissue barrier of FIGS. 16 and 17. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0041]    The tissue barriers shown in the drawings are preferably made of a titanium alloy, although other materials could be used.  
         [0042]    In the drawings all the indicated dimensions are given in millimetres (mm).  
         [0043]    Referring first to FIGS.  1  to  3  of the drawings, the tissue barrier  10  comprises a thin plate  12  which has a central, longitudinally extending portion  14  and a reduced height flange  16  at each end. The bottom surface of each flange is contiguous with the bottom surface of the central portion  14 . As shown in the drawing, a preferred embodiment of tissue barrier has an overall length of 3.75 mm, a length for the central portion  14  of 2.75 mm, a length of each flange  16  of 0.50 mm, a thickness of 0.10 mm, an overall height of 0.40 mm and a height of each flange of 0.20 mm. In other words, the height of each flange  16  is approximately half the overall height of the tissue barrier. This provides sufficient stability for the tissue barrier to be held in place within the incision in the sclera.  
         [0044]    Because the sclera varies from eye to eye, an overall height of the tissue barrier of 0.40 mm is considered the optimum dimension.  
         [0045]    In order to insert the tissue barrier into the sclera, the surgeon will first make a radial incision 3 mm in length in the sclera. This is just slightly longer than the length of the centre portion  14  of the tissue barrier plate. Then, using a blade having a suitably shaped head, the surgeon can insert the cutter to the base of the incision and push it forwards and backwards to cut pockets at each end of the main radial incision, into which the flanges  16  will be received. A cut of just 0.5 mm at each end of the main radial incision is sufficient. This is a simple procedure. The tissue barrier  10  can then be inserted into the incision, by retracting the sclera and springing the tissue barrier into place, first locating the flange  16  at one end in its pocket and then locating the flange  16  at the other end within its pocket.  
         [0046]    Referring now to the tissue barrier shown in FIGS.  4  to  6 , this tissue barrier  110  comprises an element of titanium or titanium alloy which has a central, longitudinally extending portion  112  and reduced height flanges  114  and  116  at each end. The flange  114  at one end of the tissue barrier is longer than the flange  116  at the other end of the tissue barrier. This is to facilitate insertion of the tissue barrier into a pocket created by an incision. The longer flange  114  is first inserted into the pocket, and when that is properly seated the shorter flange  116  can be pushed into place more easily than if it was of the same length as the longer flange. The flange lengths are still sufficient to ensure that the tissue barrier is held in place within the sclera without being ejected. As shown in the drawing, a preferred embodiment of tissue barrier has an overall length of 4.25 mm, a length for the central portion  112  of 2.85 mm, a length for the longer flange  114  of 0.90 mm and a length for the shorter flange  116  of 0.50 mm. The tissue barrier has a thickness of 0.20 mm. The overall height of the tissue barrier is 0.40 mm, with the height of each flange  114 ,  116  being approximately half the overall height of the barrier. As shown in FIG. 5, the flanges are of substantially square cross-section and the central portion  112  is of substantially rectangular cross-section, although with the corners slightly rounded to remove any sharp edges. As shown in FIG. 6, the end faces of both the central portion  112  and of the two flanges  114  and  116  are rounded, again to facilitate the insertion of the tissue barrier into the pocket.  
         [0047]    Referring now to the embodiment of tissue barrier shown in FIGS.  7  to  9 , and which is indicated generally at  210 , this has the same overall dimensions in terms of length as the tissue barrier of FIGS.  4  to  6 . However, in this embodiment, the end flanges  214  and  216  are of circular cross-section, as can be seen from FIG. 8. The central portion  212  is rounded at the top and bottom, again as shown in FIG. 8. The central section  212  therefore has parallel sides with part-circular surfaces at top and bottom. In contrast to the embodiment shown in FIGS.  4  to  6 , the end faces of the flanges and of the central portion are not radiused but are generally flat, as shown in FIG. 9.  
         [0048]    In order to insert the tissue barrier of either of these embodiments into the sclera, the surgeon will first make a radial incision in the sclera using dissecting forceps. The dissecting forceps have a cutting head which is dimensioned to match the shape of the tissue barrier, i.e. with a first cutting element extending in one direction being longer than a second cutting element which extends in the other direction. Then, holding the tissue barrier by the shorter flange using insertion forceps, the surgeon will retract the sclera and lower the tissue barrier into place, first locating the longer flange  114 ,  214  in the pocket and then locating the shorter flange  116 ,  216  within the pocket.  
         [0049]    Referring next to the tissue barrier shown in FIGS.  10  to  12 , this tissue barrier  310  comprises an element of titanium or titanium alloy which has a central, longitudinally extending portion  312  and reduced height flanges  314  and  316  at each end. The flange  314  at one end of the tissue barrier is longer than the flange  316  at the other end of the tissue barrier. This is to facilitate insertion of the tissue barrier into a pocket created by an incision, as explained above. As shown in the drawing, a preferred embodiment of tissue barrier has an overall length of 4.25 mm, a length for the central portion  312  of 2.85 mm, a length for the longer flange  314  of 0.90 mm and a length for the shorter flange  316  of 0.50 mm. The overall height of the tissue barrier is 0.40 mm, with the depth of each flange  314 ,  316  being approximately half the overall height of the barrier.  
         [0050]    As shown in FIG. 12, the thickness of the tissue barrier, transversely to the longitudinal axis, is 0.30 mm, with the thickness of the flanges  314  and  316  being 0.20 mm.  
         [0051]    As shown in FIG. 11, the flanges  314  and  316  are of circular cross-section and the central portion  312  is rounded at the top and the bottom, so as to have parallel sides with part-circular surfaces at top and bottom.  
         [0052]    Referring now to the embodiment of tissue barrier shown in FIGS.  13  to  15 , and which is indicated generally at  410 , this has the same overall dimensions in terms of length as the tissue barrier of FIGS.  10  to  12 . The end flanges  414  and  416  are also the same length as in the preceding embodiment. The flanges  414  and  416  are also circular in cross-section in this embodiment but are chamfered at each end as indicated at  418  in order to facilitate the insertion of the tissue barrier into the incision in the sclera. The taper angle is shown as 50°. It is to be noted that the provision of a chamfer at the outer ends of the flanges is a feature which could be used in any of the embodiments described above.  
         [0053]    In the embodiment shown in FIGS.  13  to  15  the thickness of the tissue barrier is substantially greater, namely 0.60 mm. The thickness of each flange  414  and  416  is one-third of the thickness of the central portion  412  of the tissue barrier, i.e. 0.20 mm. As shown in FIG. 14, the central portion  412  has a substantially rectangular cross-section, although with the corners slightly rounded to remove any sharp edges.  
         [0054]    FIGS.  16  to  18  show a further embodiment of tissue barrier in accordance with the invention. In this embodiment the two flanges  514  and  516  are of equal length, namely 0.70 mm. The outer end of each flange is chamfered as indicated at  518 . However, in this embodiment, the central portion  510  is not of constant thickness in the vertical direction but, as shown most clearly in FIG. 17, is sector-shaped. The lower part of the central portion  512  conforms to the shape of the end flanges, but the central portion broadens out in an upward direction and has an arcuate upper surface  520 . In contrast to the embodiments described above, where the height of the flanges is approximately one half the height of the central portion, in this embodiment the ratio of the height of the flanges to the height of the central portion is approximately 2 to 5. The sector angle of the central portion  512  is 42°, although other angles of that order of magnitude could alternatively be used.  
         [0055]    In this embodiment, as in the earlier embodiments, although the flanges  514  and  516  are of equal length, the combined length of the two flanges is approximately equal to one-third of the overall length of the tissue barrier.
A tissue barrier ( 410), for example of titanium alloy, for insertion into an incision in the sclera of the eye for the treatment of conditions such as presbyopia, comprises an elongate insert which is provided with a longitudinally extending flange ( 414, 416) at each end to prevent the barrier from being ejected from the incision. Each flange ( 414, 416) is preferably about half the height of the central portion ( 412) of the insert. Preferably, the flanges are of unequal length. The flanges may be circular or rectangular in cross-section. The central portion ( 412) may be thicker than the flanges transversely to the longitudinal axis of the insert. The outer ends of the flanges may be chamfered ( 418).