Microsurgical Instrument

The present invention relates to a microsurgical cutting instrument to be used in surgical treatment of glaucoma by means of a novel operational procedure, which significantly may be called "selective trabeculectomy".

Glaucoma is an ailment resulting in increased inner pressure in the eyeball. Within the eye, aqueous humor is produced at a fairly constant rate. This liquid is drained out through filterlike tissue (trabecular meshwork) in the area between iris and cornea into a collector canal running circularly along the transition between cornea and sclera (Canal of Schlemm), and from this canal through 20-30 drainage outlets in the eye wall into blood vessels (water veins).

The cause of glaucoma is believed to be a type of "clogging" of the trabecular meshwork, so that the outflow resistance increases. Then, also the pressure increases to allow the same volume of liquid to be drained out per time unit. All treatment aims at reducing the eye pressure. Such treatment is primarily medical, but when this is intolerable and/or insufficient, surgical treatment is used.

The surgical treatment may be subdivided according to three principles, namely:

1. Operations aiming at reduced production of aqueous humour.

2. Fistulizing procedures, i.e., surgical provision of artificial slits in the eye walls through which the liquid may seep out of the eye.

3. Operations on the trabecular meshwork. Existing procedures of this kind are of two types, i.e.:

(a) Approach through the anterior chamber of the eye by means of goniotomy or cautery of the trabecular meshwork with laser beams.

(b) Approach through the Canal of Schlemm. Such approach consists in opening this canal through a radial incision in the eye wall above the canal and insertion of a blunt probe or probe means with a cutting edge (trabeculotome). This instrument is then manipulated in such a way that it tears open or cuts through the trabecular meshwork into the anterior chamber of the eye. With such procedure a narrow slitlike opening is formed through the trabecular meshwork. Such slits exhibit, however, a considerable tendency to close.

In order to inhibit such closure it is an object of the present invention to provide a microsurgical instrument which through appropriate use may form a permanent opening from the anterior chamber of the eye to the Canal of Schlemm by selective removal of the inner wall of this canal along a certain sector. In this manner the aqueous humour gains direct access to the outer wall of the Canal of Schlemm, which has outlets or drainage canals, so that normal drainage of aqueous humour may be reestablished.

Thus, the invention concerns a microsurgical instrument for performing selective traveculectomy in surgical treatment of glaucoma, the instrument including flexible probe means and a cutting member fixed to the same. With this background the general inventive feature of the instrument is that the cutting member comprises two knife blades protruding in different directions from the probe and each providing at least one sharp cutting edge turned towards a free end of the probe means.

This instrument may be called a trabeculectome, as it is designed to be pulled through the Canal of Schlemm along a certain peripheral sector of the eye. By this the inner wall of the canal and the corresponding portion of the 0.1 mm thick trabecular meshwork are cut away.

As indicated, the trabeculectome consists of probe means and a cutting member. The probe means is preferably knob-shaped at the extreme end and made of flexible material, but this still sufficiently rigid to be inserted into and directed through the Canal of Schlemm. The cutting member has a double-cutting knife, the two cutting edges of which are angularly separated to such extent that the issuing V-form fits into the scleral groove in the eye wall, in which the trabecular meshwork is embedded. Advantageously, the cutting member is assymetrical in such a manner that the knife blade that projects perpendicularly into the anterior chamber towards the iris is short, whereas the blade that projects obliquely into the anterior chamber and forms a small angle with the back side of the cornea is longer. This feature stabilizes the correct position of the knife.

The probe means of the trabeculectome is directed through an incision in the eye wall into and along the Canal of Schlemm, and is pulled out through another incision at a certain distance from the first one. The cutting member of the trabeculectome is pulled after the probe means through the Canal of Schlemm with the two knife edges projecting into the anterior chamber of the eye and thereby cutting away a strip of the trabecular tissue and the inner wall of the Canal of Schlemm which are located between the cutting edges. This tissue strip is preferably removed together with the trabeculectome when it is pulled out through the second incision in the eye wall. Such removal of the tissue strip may be secured by mounting one or more hooks in the angle between the two knife edges in order to catch the cut away strip and carry it out of the eye.

The microsurgical instrument according to the invention allows a surgical procedure which secures a permanent, broad opening between the anterior chamber of the eye and the outlets from the Canal of Schlemm by removing the trabecular meshwork and the inner wall of the canal. Tissue removal together with maintained cell casing on the outer wall of the Canal of Schlemm make a closure of this opening improbable, even after a long period of time.

Experiences with this method up to now suggest a low rate of complications, so that the operational indications probably may be extended. This means that the patients may be operated at an earlier stage and thus expensive and troublesome medical treatment is avoided.

The invention will now be explained in more detail with reference to exemplified embodiments as shown in the accompanying drawings.

FIG. 1 shows a first embodiment of the instrument in a cross-section through the cutting member at a right angle to the longitudinal axis of the probe means.

FIG. 2 is a side elevation of the instrument shown in FIG. 1.

FIG. 3 shows the instrument in FIGS. 1 and 2 in perspective view.

FIG. 4 is a side elevation of another embodiment of the instrument.

FIG. 5 shows a cross-section through the cutting member at a right angle to the longitudinal axis of the probe means in the embodiment of FIG. 4, and

FIG. 6 shows a perspective view of a further embodiment of the inventive instrument.

The probe means A is in the embodiment shown in FIGS. 1-3 a monofilament of nylon, which is fused at one end to form a rounded knob. The other end of the probe is inserted into a hole in steel member B and rigidly clamped to this member. The knife member C is formed from a 1/100-5/100 mm thick stainless steel foil, which is finely sharpened at the front side E1 and bent into an approximate V-form adapted to the local anatomical features of the eye at the Canal of Schlemm and the trabecular meshwork. The member C is fixed to the member B and thereby also the probe A by means of a two-component epoxy glue. A point welding technique may also be used if the probe means is mounted on the member B after the welding step. An arrow above the probe in FIG. 2 shows the pulling direction in use. Between the knife blades a barbed hook D is fixed to the steel member B in order to catch the tissue strip which is cut free between the knives. This hook is also fastened by means of epoxy resin. Finally, a layer of epoxy resin is applied to the joints and transitions between the steel member B and the probe A to provide a completely smooth surface. Teflon and similar polymers may also be used as covering layer and silicone is considered particularly advantageous for this purpose.

Another embodiment is illustrated in the FIGS. 4 and 5.

In this case the probe is made of flexible metal and welded to the knife member. The extreme rear end of the probe is bent forward between the knife blades to form a small sharp hook D. All joints are provided with a cover of epoxy resin and the probe is furnished with a layer of resin at the end to form a finely rounded knob.

The knife blades C1, C2 need not necessarily have a free end. Thus, the extreme ends of the knife blades may well be interconnected to form a closed knife blade ring, e.g., of approximate triangular shape. The cut-away tissue strip may then be captured by closing the rear opening of the knife ring, thereby catching the strip in the "container" thus formed. This embodiment of the inventive instrument is depicted in FIG. 6.

The instrument must necessarily be quite small to allow the intended surgical treatment of the eye. Thus, in the illustrated embodiments the probe has a diameter of approximately 0.25 mm and a length of the order of magnitude 4-8 cm and rather freely adaptable to the requirements of the eye surgeon. The shorter knife of the cutting member may suitably have a length of about 0.7-1.0 mm, while the longer, preferably curved knife may have a length of 1.5-1.8 mm. The width of the knives may be of the order of magnitude 0.3.varies.0.5 mm.

In the embodiments shown in the drawings and described above the cutting member is fixed at one end of the probe means. However, the cutting member may well be fixed to the probe at another location, e.g., on the central part of the same. The portion of the probe projecting from the rear side of the cutting member may then be used for improved steering of the instrument, when it is guided between the two incisions in the eye wall. If the cutting member is located approximately centrally on the probe, the protruding knife blades may further be provided with a cutting edge on both sides, so that the instrument may be effectively pulled in both directions through the Canal of Schlemm.

Although the cutting edges are shown in the drawing to form essentially right angles with the longitudinal axes of the probe means, the edges may also according to the invention advantageously be inclined at an angle of .theta. axis (see FIG. 4). This angle .theta. can vary from 45.degree. to 90.degree.. An inwards directed radial force is then exercised against the tissue strip during the movement of the cutting member through the Canal of Schlemm.