Cutting blade assembly for a microkeratome

A blade assembly that can be assembled into a microkeratome which is used to cut a cornea. The blade assembly is constructed in a manner that minimizes the tolerance of the cutting depth into the cornea. The blade assembly includes a blade holder that can be pressed onto a blade. The relative position of the blade holder can be calibrated to control the distance between a reference surface of the blade holder and the cutting edge of the blade. This distance defines the cutting depth of the blade. The blade holder is coupled to the blade with an interference fit that both secures the holder while providing for calibration of the assembly.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a blade assembly that can be assembled into a medical device that is used to cut a cornea.

2. Prior Art

There have been developed a number of different surgical techniques to correct hyperopic or myopic conditions of a human eye. U.S. Pat. No. 4,840,175 issued to Peyman discloses a procedure wherein a thin layer of the cornea tissue is cut and removed from the cornea. A laser beam is then directed onto the exposed corneal tissue in a predetermined pattern. The laser beam ablates corneal tissue and changes the curvature of the eye. This procedure is sometimes referred to as Laser in situ Keratomileusis (LASIK).

U.S. Pat. No. Re 35,421 issued to Ruiz et al. discloses a device for cutting a cornea in a LASIK procedure. Such a device is commonly referred to as a microkeratome. The Ruiz microkeratome includes a ring that is placed onto a cornea and a blade that is located within an opening of the ring. The device also contains a drive mechanism which moves the blade across the cornea in a first direction while the blade moves in a reciprocating transverse direction to cut the eye. The device can create a lamella flap of the cornea which is flipped back so that the stromal bed of the cornea can be ablated with a laser.

U.S. Pat. No. 6,051,009 issued to Hellenkamp et al. discloses a microkeratome that is sold under the trademark HANSATOME. The HANSATOME microkeratome moves the blade in an arcuate path about the cornea. The HANSATOME includes a disposable blade assembly that can be readily loaded and removed from the device. The blade assembly includes a blade holder that is attached to a cutting blade. The blade holder has a recess that receives the end of a drive shaft. Rotation of the output shaft both moves the blade in an arcuate path and moves the blade in a back and forth motion to create the lamella flap of the cornea.

It is critical to control the depth of the cut to prevent a deep or shallow cut of the cornea. The depth of the cut is a function of the distance between the cutting edge of the blade and a reference surface of the blade holder. The HANSATOME blade holder is attached to the cutting blade by a pair of plastic protrusions that extend from the blade holder through corresponding apertures of the blade. The plastic protrusions located on the underside of the blade holder are then ultrasonically welded to the top side of the blade. The accuracy of the distance between the cutting edge and the reference surface, and thus the depth of the cut into the cornea, is dependent upon the mechanical tolerance between the cutting edge and the aperture of the blade, and the mechanical tolerance between the protrusions and the reference surface of the blade holder. This tolerance “build up” can reduce the predictability of the cutting depth. It would be desirable to provide a blade assembly and process for assembling the blade assembly that would tightly control the tolerance between the cutting edge and the reference surface and thus the depth of the cut.

BRIEF SUMMARY OF THE INVENTION

One embodiment of the present invention is a blade assembly that can be assembled to a medical device used to cut a cornea. The blade assembly may include a blade holder that is coupled to a blade. The blade has a notch.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

In general the present invention includes a blade assembly that can be assembled into a microkeratome which is used to cut a cornea. The blade assembly is constructed in a manner that minimizes the tolerance of the cutting depth into the cornea. The blade assembly includes a blade holder that can be pressed onto a blade. The relative position of the blade holder can be calibrated to control the distance between a reference surface of the blade holder and the cutting edge of the blade. This distance defines the cutting depth of the blade. The blade holder is coupled to the blade with an interference fit that both secures the holder while providing for calibration of the assembly.

Referring to the drawings more particularly by reference numbers,FIG. 1shows an embodiment of a blade assembly10assembled into a microkeratome12. The microkeratome12is typically used to create a lamella in a cornea14as an initial step in a LASIK procedure. The microkeratome12may be the same or similar to the device disclosed in U.S. Pat. No. 6,051,009 issued to Hellenkamp et al., which is hereby incorporated by reference. The device disclosed in the '009 patent is also sold by Bausch & Lomb under the trademark HANSATOME. Although the HANSATOME is shown and described, it is to be understood that the blade assembly10of the present invention can be used in other microkeratomes.

The microkeratome12includes a ring16that is placed onto the cornea14and typically held in place by a vacuum pressure. The microkeratome12also includes a cutting head assembly18that is coupled to the ring16. The cutting head assembly18includes a motor20that is coupled to an output shaft22by a gear assembly24. The output shaft22has an external thread26that is coupled to a corresponding thread28of a drive shaft30. The drive shaft30is coupled to a track (not shown) of the ring16. Rotation of the output shaft22, turns the drive shaft30and causes the entire cutting head assembly18to move about the cornea14along an arcuate path.

The output shaft22also has a pin32that extends into a corresponding slot34of a blade holder36. The blade holder36is attached to a blade38which has a cutting edge40that cuts the cornea14. Rotation of the output shaft22causes a reciprocating transverse movement of the blade38. The reciprocating movement of the blade38cuts corneal tissue while the drive shaft30moves the entire assembly18across the cornea14. The blade assembly10can be replaced by removing the assembly10from a blade cavity42of the cutting head assembly18.

FIG. 2shows an embodiment of a blade assembly10that includes the blade holder36and a blade38. The blade38is typically constructed from a hard stainless steel material that is stamped or machined into the configuration shown. The blade38is disposed in a blade plane and may include the cutting edge40, a rear edge44and a pair of side edges46. The front cutting edge40is disposed at a distance from the rear edge44along a first direction generally indicated by an arrow122. The side edges46are disposed at a distance from each other along a second direction generally indicated by an arrow124. The first direction122from the rear edge44to the front cutting edge40is thus a back-to-front direction and the second direction124is a side-to-side direction. The first direction122and the second direction124lie in the plane of the blade38. The side edges46may each have a notch48. The rear edge44may also have a notch50. As illustrated inFIG. 2, the notch50may includes a first inside edge126, a second inside edge128facing the first inside edge126, and a third inside edge136interposed between the first inside edge126and the second inside edge128.

The notches48may provide a feature that allows an operator to grab the blade assembly10and load the assembly10into the microkeratome12. Additionally, a plurality of blades38may be loaded and transported on a rack (not shown) with pins that extend through the notches48. The notches48may also provide reference surfaces for fixture alignment pins (not shown) used to align and calibrate the blade holder36with the blade38.

As shown inFIG. 3, the blade holder36may have an outer groove52. The blade holder36may also have a tapered top surface53to provide clearance for the pin32when the blade assembly10is loaded into the microkeratome12. The blade holder36may be constructed from a plastic material, wherein the groove52and slot34are either molded or machined into the blade holder36. Referring toFIG. 2, the blade holder36can be assembled onto the blade38by pushing the blade holder36into the notch50as indicated by an arrow132, so that the edge of the notch50extends into the groove52(FIG. 3) of the side of the blade holder36. The front side of the blade holder36generally facing the front cutting edge40includes a reference surface84(see alsoFIG. 13) that may generally adjoin the top surface53(FIG. 3). When the blade assembly10is installed in the blade cavity42of a cutting head assembly18such as illustrated by example inFIG. 1, the reference surface84of the blade holder36abuts against a corresponding reference surface86of the cutting head assembly18(such as may be located in or provided as an inside surface of the blade assembly cavity42shown inFIG. 1). As noted previously, the distance between the reference surface84of the blade holder36and the front cutting edge40of the blade38dictates the cutting depth of the blade38. InFIG. 2, this distance is indicated by an arrow134. It can be seen that this distance134may be adjusted, and the cutting depth thereby controlled or selected, during the assembly of the blade assembly10. That is, in the present example the distance134may be adjusted by how far the blade holder36is pushed into the notch50of the blade38along the direction132(or, similarly, along the above-referenced first direction122, or in the back-to-front direction).

As shown inFIG. 4, the blade holder36engages the inner edges54of the blade notch50. The blade holder36is held in place by frictional forces between the blade holder36and the edges54to create a frictional fit. The blade holder36may be further secured to the blade38by an adhesive or other means.

FIGS. 5,6and7show another embodiment of a blade assembly10′. In this embodiment, the blade38′ has a plurality of fingers56within the notch50′. The fingers56may extend in a direction opposite and away from the cutting edge40of the blade38′, in a generally coplanar relation with the blade38′. The fingers56can extend into corresponding slots58of the blade holder36′. The fingers56increase the surface area and corresponding frictional forces that couple the blade38′ to the blade holder36. As illustrated, each finger56includes an area142(FIG. 5), a thickness144(FIG. 7) perpendicular to the area142, and a finger edge146(FIGS. 5 and 7) bounding the area142and extending along the direction of the thickness144. One or more portions of the finger edge146may frictionally engage the corresponding slot58of the blade holder36′. As in the case of the implementation described above and illustrated inFIGS. 2-4, the distance between the reference surface84of the blade holder36′ and the front cutting edge40of the blade38′ is adjustable by the amount by which the blade holder36′ is pushed into the notch50′ of the blade38′, and in the present example by how far the fingers56extend into the slots58.

FIGS. 8,9and10show yet another embodiment of a blade assembly10″. The blade holder36″ of the assembly10″ has a pair of clips60that secure the holder36″ to the blade38″ within blade notches48″. The clips60secure the holder36″ to the blade38″ with frictional forces. With this embodiment the blade holder36″ can move relative to the blade38″ during installation into the microkeratome12. The relative movement provides a mechanical float feature that compensates for tolerances in the cutting head assembly18, particularly the cavity42of the microkeratome.

FIG. 11shows another embodiment of a blade holder assembly70wherein a blade72can pivot relative to the blade holder74as indicated by the arrow. This embodiment provides a mechanical float that will compensate for tolerances in the assembly20and the microkeratome12. The float is created by a gap75between the blade holder74and the blade72. The blade holder74may be held in place by frictional forces between an inner edge of the holder74and an outer edge of the blade72.

FIGS. 12 and 13show a method for assembling and calibrating the blade holder36′ to the blade38′. The blade38′ may be held in place by a pair of stabilizer posts76. The posts76extend through the notches48(FIG. 2) of the blade38′. Each stabilizer post76includes a stop78that is connected to a pin80. Each pin80is attached to a fixture plate82.

The blade holder36′ is pushed onto the blade38′ until a reference surface84of the blade holder36′ abuts against the stop78. The reference surface84rests against a corresponding reference surface86of the cutting head assembly18shown inFIG. 1. The stop78provides a datum point that closely controls the distance between the reference surface84and the cutting edge40of the blade38. The distance between the reference surface84and the cutting edge40defines the cutting depth of the blade38′. The blade holder36′ may have a pair of outer notches88that provide a clearance for the pins80when the holder36′ is pushed onto the blade ′38.

FIG. 14shows another means for assembling and calibrating the blade holder36′ to the blade38′. The blade38′ can be secured to a fixture plate82by a couple of pins90that extend into the blade notches. A clamp92is then coupled to the blade38. The blade holder36′ is pushed onto the blade38′ until the reference surface84abuts against the clamp92. The distance between the clamp92and the cutting edge40can be accurately controlled to minimize the tolerance between the reference surface84and the cutting edge40.

FIG. 15shows another embodiment of a blade assembly100that includes a blade holder102which has one or more cavities104. The blade holder102is coupled to a blade106by any of the embodiments shown inFIGS. 2-11. The cavities104reduce the stiffness of the blade holder104so that the blade holder102can be more readily installed into an undersized blade cavity42. Additionally, a tool (not shown) can be inserted in a cavity104and used to push the blade holder102onto the blade106. The blade holder102may also have a contoured top surface108that reduces the surface area in contact with the cutting head assembly18. The contoured surface108reduces the tolerance requirements of the holder102and the cavity42.

FIGS. 16 and 17show another embodiment of a blade assembly110that includes a blade holder112coupled to a blade114. The blade holder112can be attached to the blade114by an interference fit as described inFIGS. 2-11. The blade holder112includes a plurality of fingers116. The fingers116provide a means to grasp the assembly110. The individual fingers116also minimize the friction and lack of fit with the blade cavity42. The most distal finger116provides a reference surface that abuts against the corresponding reference surface of the cavity42.

For example, although the blade assembly10shown inFIG. 2shows a notch50in the blade38, the assembly10could be constructed to eliminate the notch50and form a deep groove within the blade holder36′, essentially a mirror image of the embodiment shown.