Abstract:
A micro-vitreoretinal (MVR) blade for incising tissue for a transvenous chorioretinotomy and similar procedures includes a shaft with a working tip having a chisel-type edge on its end or leading edge. Various embodiments of the inventive MVR blade have different chisel-type edge structures, such as a latitudinal chisel, an angled chisel, a chevron, a reverse chevron, a concave semi-lunar and a guarded or step-down working tip. The MVR blade may also include drug/chemical coatings, electrification or freezing to promote hemostasis or chorioretinal anastomosis formation.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The present invention relates generally to incising tissue and in particular to micro-vitreoretinal surgery blades. In just one example, micro-vitreoretinal (MVR) blades are used to incise tissue for a transvenous chorioretinotomy as treatment for retinal vein occlusion and other indications. Retinal vein occlusions are a common cause of visual loss. Currently, the primary treatments are macular laser (for branch retinal vein occlusion) and pharmacologic agents (for branch and central retinal vein occlusion). These treatments address the side-effects of the retinal vein occlusion, including macular edema and ocular neovascularization. Using these conventional treatments for retinal vein occlusion treatment is typically prolonged (months to years) and expensive. 
         [0002]    Recently, a new procedure for treating retinal vein occlusions was reported that involves bypassing the occlusion through surgery to create a chorioretinal anastomosis. Unlike previous attempts to perform this same procedure with laser treatments, “pars plana vitrectomy with multiple transvenous chorioretinotomies (MTC) is safer and more effective. This new method reduces or even eliminates the need for continuing medical therapy; improves or stabilizes visual acuity; and reduces the risk of visual loss. 
         [0003]    Currently, there is no ideal tool for performing the critical part of the MTC procedure, which is the transvenous chorioretinotomies themselves. Most modern vitreous surgery is performed with 23 or 25 gauge trocar systems, and the prior art MVR blades typically available for such procedures do not function well in MTCs. The drawbacks of such prior art MVR blades include: (a) the blade tips are too narrow, making it difficult to center the blade on the target vein to achieve complete transection; (b) the side edges of the blades are too dull, causing them to displace rather than transect the target vein; and (c) the blade tips are too long, resulting in increased risk of scleral perforation and globe perforation, particularly in myopic patients with thin sclera. 
         [0004]    To circumvent the shortcomings of the smaller caliber blades available with trocar-based microincisional viteoretinal surgical systems, it is generally more effective to create an additional incision in the eye (sclerotomy) to allow use of a larger 20 gauge MVR to perform the MTC part of the procedure. The 20 gauge MVR is not hampered by the drawbacks (a) and (b) above. However, the MTC incision it creates is unnecessarily large and use of the 20 gauge blade requires creation of an additional incision in the eye, which adds steps to the procedure, prolonging the surgery and increases the risk of complications. 
         [0005]    Accordingly, there is a need for a new MVR blade that addresses these drawbacks. The inventive blade described herein addresses these drawbacks and provides other related advantages. 
       SUMMARY OF THE INVENTION 
       [0006]    The present invention proposes a new MVR knife/blade for use with existing tools in MTC procedures. Overall, the tools would have the same general design as prior art tools of the same type, i.e., shaft, handle, cannula, etc. The tool could also be produced in all gauges popularly used for MVR procedures, including 20, 23, 25 and 27 gauge blades. Unique to the inventive blade is the novel configuration of the cutting tip and edges aimed at addressing the shortcomings described above. 
         [0007]    The present invention is directed to a microvitreoretinal blade that has a shaft with a working tip on a distal end thereof. The shaft defines a longitudinal axis and a latitudinal axis. A chisel-type edge is formed on the working tip and disposed in an operative plane formed by the intersection of the longitudinal axis and latitudinal axis. The working tip has two blade surfaces that are disposed on opposite sides of the operative plane and that extend from the shaft to the edge. The chisel-type edge is formed by intersecting edges of the two blade surfaces. 
         [0008]    Both the shaft and the working tip preferably have a uniform width throughout the operative plane. In addition, the thickness of the working tip is no greater than the thickness of the shaft in any plane rotated about the longitudinal axis. The chisel-type edge is preferably sharpened to a surgical grade cutting edge. 
         [0009]    In various embodiments, the chisel-type edge possesses different configurations. In one preferred embodiment, the chisel-type edge is disposed at an angle of 0 to 45 degrees relative to the latitudinal axis. In another preferred embodiment, the chisel-type edge has a chevron or V-shape with a central point and lateral edges swept back at an angle of 0 to 45 degrees relative to the latitudinal axis. The chisel-type edge may also have a reverse chevron or inverted V-shape with an internal peak and lateral edges swept forward at an angle of 0 to 45 degrees relative to the latitudinal axis. The chisel-type edge may also have a concave, semi-lunar shape with an arc spanning no more than 30 degrees of a circle. Finally, the blade may have a guarded working tip having a step-down from the shaft to the working tip, the step-down forming a stop ledge at the junction of the working tip and the shaft. 
         [0010]    The working tip may include a coating to enhance hemostasis or chorioretinal anastomosis. The working tip may also be electrified or brought to freezing temperatures as by liquid nitrogen or similarly known mechanisms to enhance hemostasis or chorioretinal anastomosis. 
         [0011]    Other features and advantages of the present invention will become apparent from the following more detailed description, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    The accompanying drawings illustrate the invention. In such drawings: 
           [0013]      FIG. 1  illustrates a perspective view of a prior art blade typically used for MVR procedures; 
           [0014]      FIG. 1   a  illustrates a top view of a prior art blade typically used for MVR procedures; 
           [0015]      FIG. 2  is a perspective view of a first preferred embodiment of an MVR blade of the present invention; 
           [0016]      FIG. 3  is a perspective view of a second preferred embodiment of and MVR blade of the present invention; 
           [0017]      FIG. 3   a  is a side view of the second preferred embodiment of an MVR blade of the present invention; 
           [0018]      FIG. 3   b  is a top view of the second preferred embodiment of an MVR blade of the present invention; 
           [0019]      FIG. 4  is a perspective view of a third preferred embodiment of and MVR blade of the present invention; 
           [0020]      FIG. 4   a  is a side view of the third preferred embodiment of an MVR blade of the present invention; 
           [0021]      FIG. 4   b  is a top view of the third preferred embodiment of an MVR blade of the present invention; 
           [0022]      FIG. 5  is a perspective view of a fourth preferred embodiment of and MVR blade of the present invention; 
           [0023]      FIG. 5   a  is a side view of the fourth preferred embodiment of an MVR blade of the present invention; 
           [0024]      FIG. 5   b  is a top view of the fourth preferred embodiment of an MVR blade of the present invention; 
           [0025]      FIG. 6  is a perspective view of a fifth preferred embodiment of and MVR blade of the present invention; 
           [0026]      FIG. 6   a  is a side view of the fifth preferred embodiment of an MVR blade of the present invention; 
           [0027]      FIG. 6   b  is a top view of the fifth preferred embodiment of an MVR blade of the present invention; 
           [0028]      FIG. 7  is a perspective view of a sixth preferred embodiment of and MVR blade of the present invention; 
           [0029]      FIG. 7   a  is a side view of the sixth preferred embodiment of an MVR blade of the present invention; 
           [0030]      FIG. 7   b  is a top view of the sixth preferred embodiment of an MVR blade of the present invention; 
           [0031]      FIG. 8  is a perspective view of a seventh preferred embodiment of and MVR blade of the present invention; 
           [0032]      FIG. 8   a  is a side view of the seventh preferred embodiment of an MVR blade of the present invention; 
           [0033]      FIG. 8   b  is a top view of the seventh preferred embodiment of an MVR blade of the present invention; 
           [0034]      FIG. 9  is an environmental view illustrating insertion of an MVR blade into an eye; 
           [0035]      FIG. 10  is an environmental view illustrating an MVR blade approaching an occluded retinal vein preparing to perform a transvenous chorioretinotomy; 
           [0036]      FIG. 11  is a cross-sectional view taken along line  11 - 11  of  FIG. 10 ; 
           [0037]      FIG. 12  is an environmental view illustrating an MVR blade contacting an occluded retinal vein preparing to perform a transvenous chorioretinotomy; 
           [0038]      FIG. 13  is a cross-sectional view taken along line  13 - 13  of  FIG. 12 ; 
           [0039]      FIG. 14  is an environmental view illustrating an MVR blade transecting an occluded retinal vein after performing a transvenous chorioretinotomy; 
           [0040]      FIG. 15  is a cross-sectional view taken along line  15 - 15  of  FIG. 14 ; 
           [0041]      FIG. 16  is an environmental view illustrating a transvenous chorioretinotomy incision after the MVR blade has been removed; and 
           [0042]      FIG. 17  is a cross-sectional view taken along line  17 - 17  of  FIG. 16 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0043]    The present invention is directed to novel MVR blades for use in MTC procedures and other similar surgical procedures. In  FIGS. 2 through 8 , various embodiments of the inventive MVR blades are depicted and referred to by reference numerals  30 ,  40 ,  50 ,  60 ,  70 ,  80 , and  90 . In each embodiment, the differences lie in the shape and configuration of the blade tip—the shaft of each embodiment is generally uniform and configured as the shaft on existing MVR blades. 
         [0044]      FIGS. 1 and 1   a  depict a prior art version of an MVR blade  20  having a stiletto-style geometry, i.e., coming to a sharp point  22  with steep edges  24 . The blade  20  has ears  26  with an associated width that is greater than the width of the shaft  28 . Such a prior art design is constrained because of how the blade  20  must be ground, such that there is a portion of the blade  20  between the ears  26  and shaft  28  that does not cut tissue. The exaggerated width of the ears  26  also prevents the blade  20  from being fully inserted into or through a 23 or 25 gauge trocar cannula. Prior art MVR blades of smaller gauges, such as 23, 25 and 27, are generally too steep and the edges too blunt for easy and effective transvenous chorioretinotomy. 
         [0045]    Rather than having the profile of prior art MVR blades, i.e., very steep, acutely angled edges such as in  FIGS. 1 and 1   a , the inventive blades are designed with a far less acute blade angle. In addition, some embodiments present a concave cutting edge. These modifications address the above shortcomings by permitting increased ease of centration and “purchase” of the target vein. This provides for more effective and efficient transection by increasing anterior-posterior compression of the target vein coincident with transection and minimizes “escape” of the target vein by lateral displacement. 
         [0046]    By increasing the effectiveness and efficiency of the blades, smaller gauge MVR blades can be used in place of the larger gauge blades currently required for microincisional trocar systems, making the additional incisions required for larger blades unnecessary. At the same time, the smaller gauge blades reduce the required size of incisions resulting in reduced recovery time and potential complications from the incision. Finally, the less pointed/less acute angle of the inventive MVR blade minimizes the risk of unnecessarily deep penetration into or through the sclera, while still ensuring complete retinal venous transection and associated chorioretinotomy. Such is required to properly promote the formation of the chorioretinal anastomosis, which will bypass the retinal vein occlusion. 
         [0047]      FIG. 2  depicts a first preferred embodiment of the inventive MVR blade  30 . In this embodiment, a working tip  31  of the MVR blade  30  has a shape similar to a chisel, i.e., a flat or horizontal chisel-type edge  32  that is generally perpendicular to a longitudinal axis  34  on the shaft  36 . As used herein, a “chisel-type edge” means a characteristically flat or planar shaped cutting edge (with some exceptions as described below) on the end or a leading edge of a blade and not on the sides of the blade. A latitudinal axis  35  is disposed perpendicular to the longitudinal axis  34  and is oriented laterally, i.e., side-to-side, with respect to the shaft  36 . The intersection of the longitudinal axis  34  and latitudinal axis  35  form an operative plane  37  in which the blade  30  lies. The chisel-type edge  32  is formed by two blade surfaces  38  that extend from the shaft  36  to the chisel-type edge  32 . The chisel-type edge  32  is formed where edges of the two blade surfaces  38  intersect. 
         [0048]    Both the shaft  36  and the working tip  31  have a uniform width throughout the operative plane  37 . In addition, the thickness of the working tip  31  is no greater than the thickness of the shaft in any plane rotated about the longitudinal axis  34 . The chisel-type edge  32  is sharpened so as to provide a surgical grade cutting edge. All further embodiments of the inventive MVR blade discussed herein have the same general characteristics, including but not limited to a longitudinal axis  34 , a latitudinal axis  35 , an operative plane  37 , a chisel-type edge, a surgical grade cutting edge, and the width and thickness of the working tip with respect to the shaft. 
         [0049]      FIGS. 3 ,  3   a  and  3   b  depict a second preferred embodiment of the inventive MVR blade  40 . In this embodiment, the MVR blade  40  again has a shape similar to a chisel, i.e., a chisel-type edge  42 , that is generally angled at approximately thirty degrees with respect to the latitudinal axis  35 . The chisel-type edge  42  is again formed by the intersecting edge of two blade surfaces  48 . One end of the chisel-type edge  42  is then angled back from the latitudinal axis  35  such that it forms a thirty degree angle therewith. The chisel-type edge  42  is sharpened so as to provide a surgical grade cutting tool. 
         [0050]      FIGS. 4 ,  4   a  and  4   b  depict a third preferred embodiment of the inventive MVR blade  50 . In this embodiment, the MVR blade  50  again has a shape similar to a chisel, i.e., a chisel-type edge  52 , that is generally angled at approximately forty-five degrees with respect to the latitudinal axis  35 . The chisel-type edge  52  is again formed by the intersecting edges of two blade surfaces  58 . One end of the chisel-type edge  52  is then angled back from the latitudinal axis  35  such that it forms a forty-five degree angle therewith. The chisel-type edge  52  is sharpened so as to provide a surgical grade cutting tool. 
         [0051]    Between the first, second and third embodiments depicted in  FIGS. 2-4 , the angle of the chisel-type edge  32 ,  42 ,  52  may vary from between zero degrees and forty-five degrees from the latitudinal axis  25 . The exact angle that is used can depend upon the specific needs of the surgery being performed. 
         [0052]      FIGS. 5 ,  5   a  and  5   b  depict a fourth preferred embodiment of the inventive MVR blade  60 . In this embodiment, the MVR blade  60  again has a shape similar to a chisel, except, rather than a horizontal, flat or angled edge, a chevron, i.e., a V-shape, chisel-type edge  62  is presented. The chevron edge  62  comes to a slight point  64  with lateral edges  66  angled or swept back at a slight angle with respect to the latitudinal axis  35 . The angle may vary from zero degrees to no more than forty-five degrees from the latitudinal axis  35 , but preferably is between zero and thirty degrees. The chevron edge  62  is sharpened so as to provide a surgical grade cutting tool. 
         [0053]      FIGS. 6 ,  6   a  and  6   b  depict a fifth preferred embodiment of the inventive MVR blade  70 . In this embodiment, the MVR blade  70  again has a shape similar to a chisel, except, rather than a horizontal, flat or angled edge, a reverse chevron, i.e., an inverted V-shape, chisel-type edge  72  is presented. The reverse chevron edge  72  comes to a slight peak  74  with lateral edges  76  angled or swept forward at a slight angle with respect to the latitudinal axis  35 . The angle may vary from zero degrees to no more than forty-five degrees from the latitudinal axis  35 , but preferably is between zero and thirty degrees. The reverse chevron edge  72  is sharpened so as to provide a surgical grade cutting tool. 
         [0054]      FIGS. 7 ,  7   a  and  7   b  depict a sixth preferred embodiment of the inventive MVR blade  80 . In this embodiment, the MVR blade  80  again has a shape similar to a chisel, except, rather than a horizontal, flat or angled edge, a concave semi-lunar, i.e., crescent-shape, chisel-type edge  82  is presented. The concave semi-lunar edge  82  has a gradual concave arc  84  that extends smoothly from a first point  86  to a second point  88  of the blade  80  to form the concave semi-lunar edge  82 . The arc  84  preferably represents no more than thirty degrees of a complete revolution on a circle. The concave semi-lunar edge  82  is sharpened so as to provide a surgical grade cutting tool. 
         [0055]      FIGS. 8 ,  8   a  and  8   b  depict a seventh preferred embodiment of the inventive MVR blade  90 , sometimes referred to as a guarded blade. In this embodiment, the MVR blade  90  may have an edge similar to any of the earlier embodiments.  FIG. 8  illustrates a thin chisel shape, i.e., a flat or horizontal, chisel-type edge  92 , configured similarly to the first embodiment MVR blade  30 . The distinguishing feature of this embodiment is the step-down  94 , i.e., sudden reduction in cross-sectional width, from the shaft  96  to the blade body  98 . The step-down  94  operates to limit the depth of penetration to reduce the risk of scleral perforation or other negative effects of over-insertion. The step-down  94  provides a lip or stop ledge  94   a  on the end of the shaft  96  that contacts but does not cut or penetrate tissue. It is this contact that stops the cutting motion and prevents over-insertion. Although the blade body  98  may be longer, it is preferably approximately 1 mm-2 mm in length. As in the other embodiments, the chisel-type edge  92  is sharpened so as to provide a surgical grade cutting tool. 
         [0056]      FIG. 9  illustrates an environmental view of an MVR blade  80  of the present invention, in this instance the sixth embodiment, penetrating an eye  100  through an incision  102 . This and any other similar procedure may be performed with a blade of any other embodiment described herein. In accessing the retina of an eye for performing a transvenous chorioretinotomy or other similar procedures, an MVR blade must pass through the eye  100  in this way and access the retina at the back of the eye  100 . 
         [0057]      FIGS. 10 through 17  illustrate various views of an MVR blade  80  performing such a transvenous chorioretinotomy procedure. In these illustrations, the interior  100   a  of the eye is on top and the exterior  100   b  of the eye is on bottom. 
         [0058]    In  FIGS. 10 and 11 , the blade  80  is approaching the back of the eye  100 , which is comprised of various layers, including the retina  104 , the choroid  106  and the sclera  108 . The retina  104  contains a vast number of veins  110 , of which only one is shown in this illustration for clarity. In performing a transvenous chorioretinotomy, a vein  110  in the retina  104  is occluded or blocked. The healing response to transvenous chorioretinotomy leads to formation of a chorioretinal anastomosis which effectively bypasses the occlusion of the retinal vein. 
         [0059]    In  FIGS. 12 and 13 , the MVR blade  80  has contacted the occluded retinal vein  110 . Placement of the blade  80  over the occluded retinal vein  110  is simplified by the concave semi-lunar edge  82 , which fixes the blade over the vein  110  preventing displacement of the vein  110  when making the incision. In  FIGS. 14 and 15 , the MVR blade  80  has incised the tissue and transected the occluded retinal vein  110  only and not the underlying choroid  106  and sclera  108 . Insertion of the blade  80  completely transects the occluded retinal vein  110  creating the chorioretinotomy. As illustrated in  FIG. 15 , the edge  82  of the blade  80  stops upon reaching the choroid  106 . In  FIGS. 16 and 17 , the blade  80  has been withdrawn, leaving an incision  112  that transects the occluded retinal vein  110 , as well as the choroid  106  layer underneath. The body&#39;s natural healing response results in formation of a chorioretinal anatomosis, which bypasses the blocked retinal vein  110 . 
         [0060]    Any of the above described blades may be manufactured from any available surgical grade material known in the art. In another embodiment, the blade may be coated with a chemical or drug intended to enhance either (a) hemostasis; or (b) chorioretinal anastomosis formation. Such chemical or drug may comprise a topical thrombogenic and/or anti-thromolytic agent, including, but not limited to, a pharmacologic or mineral blade coating or surface treatment. Such chemicals and/or drugs and methods of coating or treating are known to those skilled in the art. In addition, the blade may be electrified, such as in retinal diathermy, or including a freezing mechanism, such as in retinal cryopexy, to enhance either (a) hemostasis; or (b) chorioretinal anastomosis formation. Methods such as diathermy or cryopexy are standard and long-used methods in such surgical procedures. Cryopexy may be achieved by the use of a probe cooled by liquid nitrogen or other similar agent. Alternatively, one may use a non-cutting probe that is either electrified or features a freezing mechanism to promote chorioretinal anastomosis formation without need for actual tissue incision. Furthermore, any of the above described embodiments may be used to create partial rather than complete transvenous chorioretinotomies for creation of chorioretinal anastomoses. 
         [0061]    Certain detailed embodiments of the present invention are disclosed herein. However, it should be understood, that the disclosed embodiments are merely exemplary of the invention, which may be embodied in various forms. Various modifications may be made without departing from the scope and spirit of the invention.