Abstract:
A method is provided for performing an anterior capsulotomy as part of a cataract extraction. The instrument used comprises a cutting blade attached to a handle in such a way as to allow said blade to rotate 360 degrees. The shape and method of attachment of said cutting blade to said handle provides that the blade orients itself with the cutting edge forward in the direction of movement of the blade.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to a method for performing an anterior capsulotomy during a cataract extraction and particularly to a method using an instrument designed to make the task simpler and more adequate. 
     In the past decade cataract extraction by the extracapsular technique has returned as a common method of cataract extraction, replacing in part intracapsular cataract extraction method. During extracapsular cataract extraction the anterior capsule of the lens is incised to allow its removal and to allow access to the underlying cortex and nucleus of the lens for their eventual removal. The most common method used today for an anterior capsulotomy is to use a small sharp hook called a cystotome. Through a small incision in the peripheral cornea, small connecting tears are made in the anterior lens capsule in a circular pattern around the periphery of the lens capsule. When a complete circle has been made by connecting the tears, the anterior capsule of the lens is free to be removed. 
     The cystotome method is combersome, time consuming and leaves tags of anterior capsule which often interfere with later removal of the cortex of the lens. In addition, traction on one of these tags can lead to a tear extending posteriorly into the posterior capsule of the lens; this is a significant complication. Furthermore, during the anterior capsulotomy by this method the cystotome often inadvertently and unknowingly slips below the level of the capsule. The operator is then given the false impression that he is cutting anterior capsule when in fact he is making an incision in the subjacent lens cortex. As a result, an inadequate opening is made in the anterior capsule. Finally, when the pupil is small, the procedure by the cystotome method becomes very difficult. 
     If the central cornea is removed as during a cornea transplant a very large opening is made into the eye. Through this large opening a scissors or conventional knife can be used to make a smooth circular incision into the anterior capsule. This could circumvent many of the above mentioned problems. Such a large incision, however, is impractical for routine cataract extractions. 
     The method and instrument herein described are designed for a simple anterior capsulotomy which is both performed through a small incision and leaves behind a smooth circular anterior capsule edge. 
     SUMMARY OF THE INVENTION 
     A method and instrument for performing a simple anterior capsulotomy as part of a cataract extraction operation is provided. The instrument comprises a cutting blade which is attached to a handle in such a way as to allow said cutting blade to rotate around said handle 360 degress. The shape and method of attachment of said cutting blade to said handle provides that the blade orients itself parallel to the vector of said blade&#39;s motion. The blade handle assembly may be equipped with irrigation for maintaining the anterior chamber during the procedure. 
     This method comprises the steps of placing the instrument in the eye through a small 2-3 mm incision at the corneo-scleral junction. The blade engages the anterior capsule near its periphery and with a circular motion the instrument with the knife trailing is moved around the edge of the anterior capsule incising the capsule as the blade is moved. The instrument may be moved beneath the iris to allow a large capsulotomy in an eye with a small pupil. When a complete circular incision has been made the instrument is removed. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     This invention may better be understood when taken in conjunction with the following detailed description,wherein: 
     FIG. 1. is a cross-sectional view along the length of the pin-handle assembly of this invention; 
     FIG. 2. is a cross-sectional view of the distal end of the assembled instrument; 
     FIG. 3. is a cross sectional view of the distal end of a modification of this invention; 
     FIG. 4 is an elevational view of the rotating portion of a modification of this invention; 
     FIG. 5. is an elevational view illustrating the use of this instrument in the anterior chamber of an eye; 
     FIG. 6. is an elevational view of the rotating portion of this invention. 
    
    
     DESCRIPTION 
     This anterior capsulotomy instrument has as its essential feature a cutting blade which rotates and thereby orients itself for most effective cutting of the anterior capsule of the lens. It allows for a simple method of performing an anterior capsulotomy even in an eye with a small pupil and leaves behind a smooth circular edge of lens capsule. In this embodiment, the instrument portion of this invention comprises a handle portion and a rotating portion. 
     The handle portion is a pin-handle assembly shown in FIG. 1. In this embodiment, it is a metal tube which tapers from the proximal hand held end (2) to the distal end (3). An optional bend (4) in the handle can be placed 5-15 mm from the distal end to aid its ease of use for some operators. From the inferior aspect of this tapered end extends a rigidly and perpendicularly attached pin (6) with shaft (7). At its unattached end the pin has a semi-circular enlargement (8) whose diameter is greater than the diameter of the shaft (7). In this embodiment the pin is metallic. 
     Because of the tubular construction of the handle and distal end, intervenous line tubing can be easily attached to the proximal end (2). Fluid can then flow through the handle and exit at the distal end outlet (5). This constant flow maintains the volume of the anterior chamber during the anterior capsulotomy. 
     The rotating portion of this instrument is a plate-blade assembly as shown in FIGS. 2 and 6. In this embodiment both are metal. The plate (10) is ellipsoid in shape approximately 4-5 mm along its longer axis (11) and approximately 2 mm along the shorter axis (12). The cutting blade (13) is thin flat and triangular in shape with a cutting edge (14) and a non-cutting edge (15) converging to a point at a first blade end (16) and diverging to a flat second blade end (17). The cutting blade is attached to the plate along its second blade end (17). The attachment is perpendicular and rigid and is along a line through the long axis of the elliptical plate. The attachment is toward one end of the plate so that the non-cutting edge (15) is nearly adjacent to an edge of the plate. The areas of the plate between the blade and either of the longer sides (18) act like flanges and will be herein referred to as the flanges (19). There is a hole (20) through the plate through the line along the longer axis of the plate. This hole is positioned between the cutting edge of the blade and the edge of the plate. The hole is large enough to easily accomodate the shaft (7) of the pin (6) of the handle. A corridor (21) is cut from a side of the hole (2)which is smaller in width than the diameter of the hole. The corridor (21) connects a longer side of the plate (18) with the hole. 
     To assemble the instrument, the shaft (7) of the pin-handle assembly is placed over the external corridor area (22) of the blade-plate assembly. With forcefull pressure on the shaft, said shaft is snapped through the corridor into the hole. In the assembled position (FIG. 2.) the shaft is in the hole and yet free rotation of the blade-plate assembly around the pin is possible. 
     The method of this invention allows that the above assembled instrument be placed into the anterior chamber of the eye through a 3 mm incision at the corneo-scleral junction (23). Once in the eye, downward pressure is exerted at the distal end of the handle which causes the blade to cut through the anterior capsule into the underlying cortex of the lens. The flanges on either side of the blade allow penetration into the cortex only as deep as the length of the blade. The flanges also prevent the blade from inadvertently falling below the level of the anterior capsule into the substance of the cortex when downward pressure is transferred to the blade-plate assembly from the handle. 
     Linear movement of the distal end of the handle in the plane of and toward the periphery of the anterior capsule will cause rotation of the plate-blade assembly as shown in FIG. 5, so that the cutting edge is in the direction of movement. This forward orientation feature is an important part of this invention. This rotation is due to the displacement of the axis of rotation of the blade-plate assembly (25) away from the theoretical center of rotation of the blade-plate assembly (26). This displacement causes the assembly to rotate preferentially and align the blade-plate assembly with the cutting edge (14) forward in the direction of movement. This will insure a cutting action rather than a tearing action upon the anterior capsule. An obvious modification of this feature would be to construct the cutting edge (27) very thin and the non-cutting edge (28) substantially thicker as in FIG. 4. This construction would also orient the cutting edge properly. 
     When assembled the assembly is small enough that it can be inserted under the iris to accomplish an anterior capsulotomy in an eye with a small pupil. 
     An obvious modification of this instrument is to rigidly attach the pin to the blade or the blade-plate assembly rather than the handle. This is shown in FIG. 3. Thus a hole could be fashioned in the distal end of the handle and allow for attachment, orientation and rotation of the blade.