Field of the Invention

This invention relates to scalpels which include means to control the depth of cut. More particularly, this invention relates to scalpels for use in radial keratotoirty.

Background of the Invention

In certain surgical procedures, it is necessary for the surgeon to determine and accurately control the depth to which he or she cuts with a scalpel. A specific example is the surgical procedure known as radial keratotomy. This procedure corrects myopia (nearsightedness) by altering the curvature of the cornea of the eye. The curvature is altered by making a series of radial incisions in, but not through, the cornea itself.

To have predictable and favorable results, the depth of cut into the cornea must be accurately determined and controlled. The incisions must have sufficient depth, usually just greater than three- quarters of the depth of the cornea, but should not

1 penetrate the cornea itself. Penetration of the cornea would release fluid from the anterior chamber of the eye, increase the likelihood of infection, and detract from the predictability of the results of '5 the procedure.

In controlling the depth of cut, it is to be noted that the thickness of the cornea varies from patient to patient and accordingly, must be accurately determined by known means prior to surgery. Once the

10 thickness of the cornea has been accurately determined, the appropriate depth of cut can be selected.

To accommodate the varying thicknesses of corneas, and accordingly, the desired depth of cut, it has been known to provide for adjustable scalpels. However,

15 adjustable scalpels have several drawbacks. One drawback relates to the predictability of the depth of the cut. To set the depth of cut, the surgeon must, by hand and using a scale or a gauge, adjust depth of' cut of the scalpel. One type of adjustable scalpel

20 includes a blade coupled with an adjustable micrometer¬ like knob on the handle. Another type uses a depth gauge separate from the scalpel and provides for adjustment of the depth of cut by movement of a guard relative to the scalpel blade cutting edge, the

25 guard being positionally fixed to the scalpel handle by a thumbscrew after determination of the desired cut depth.

As can be appreciated, the setting of depth of cut either by using the adjustment knob or by com-

30 parison with the depth gauge does not always produce accurate, predictable results, particulary results having an accuracy to within 10 microns, i.e., +_ 0.010 mm. In many cases, the gauges are not accurate.

35

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1 Another problem of scalpels having an adjustable depth of cut occurs in setting the depth of cut after - ^* - ^* --- _r p- ^ς -.djustment has been ascertained by use of a gauge. The fixing of the adjustable member may '5 alter the setting, thereby again detracting from the accuracy of the depth of cut setting. Still another drawback is that adjustable scapels tend to be expen¬ sive. Yet another drawback is that reusable scalpels must be sterilized and their blades tend to dull with

10 repeated use. Also, the adjustment can be disturbed inadvertently in the course of the surgical procedure.

Summary of the Invention

15 There is, therefore, provided in the practice of this invention a disposable scalpel particularly adapted for radial keratotomy. The scalpel includes a handle which mounts a blade at one end, the blade having a suitable cutting edge. A sleeve is fixed to

20 the handle near its one end and includes an outwardly projecting mount. The mount, in cooperation with the handle and the sleeve, enables the surgeon to securely and comfortably grip the scalpel between the index finger, middle finger, and thumb, and with the cutting 5 edge consistently oriented in a proper position. To control the depth of cut, a foot is provided. The foot is preferably metallic to resist bending and twisting which would effect the depth of cut and has one end attached to the sleeve. Additionally, the 0 metallic foot can be made relatively narrow so as not to interfere with the surgeons view while still resis¬ ting deflection. From the sleeve, the foot projects toward the blade to define, remote from the sleeve, a bifurcated guard defined by a pair of arms which run 5 parallel to and straddle the blade cutting edge.

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1 During the surgical procedure, the arms are adapted to bear against the cornea, the extension of the cutting edge past the guard determining the depth of cut. By accurately fixing the position of the sleeve •5 on the handle during manufacture of the scalpel, the position of the guard relative to the cutting edge is accurately preset, thereby accurately determining the depth of cut to within 10 microns.

Also disclosed is a kit including a plurality of

10 sets of scalpels, all scalpels in a set having a particular depth of cut and the depth of cut varying from set to set within the range between 0.435mm to 0.755mm. The number of scalpels in any particular set is determined by the normal population distribution

X5 of the likelihood that any particular depth of cut will be required. Accordingly, the sets corresponding to rarely used depths of cuts will contain relatively few scalpels whereas the sets corresponding to often used sets of cut will contain more scalpels.

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25

30

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Brief Descripton of the Drawings

These and other features and advantages of the present invention will be appreciated as the same becomes better understood by reference to the following details description of the presently preferred embodiments when considered in connection with the accompanying drawings in which like reference numerals refer to like features and wherein:

FIG. 1 is a perspective side view of an adjustable scalpel according to the prior art;

FIG. 2 is a side elevation view of a scalpel according to the present invention;

FIG. 3 is an enlarged side elevation view of the tip of the scalpel shown in FIG. 2; FIG. 4 is a front end view of the scalpel shown in

FIG. 2;

FIG. 5 is a partial top view of the scalpel shown in FIG. 2;

FIG. 6 is a partial side view of the scalpel as held in the hand;

FIG. 7 is a front end view of the scalpel as held in the hand; and

FIG. 8 is a graphical depiction of the distri¬ bution of the required depth of cut based upon emperical data with the ordinate representing depth of cut and the abscissa representing number of occurrences in which a particuliar depth of cut was required in a radial keratotomy procedure.

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Detailed Description

Turning to FIG. 1, a scalpel 10 according to the prior art is shown. The scalpel 10 has a handle 12 which may be fashioned from plastic or the like. At one end of the handle is fixed a blade 14 having a suitable cutting edge 16. The cutting edge 16 is adapted to make incisions into the cornea of the patient during the surgical procedure known as radial keratotomy. To control the depth of cut of the scalpel 10, a sleeve 18 is adjustably mounted to the handle 12. As can be appreciated from FIG. 1, the sleeve 18 passes over the handle 12 and can be fixed relative thereto by a set screw 20. The sleeve 18 includes a foot 22 which projects toward the blade 14 to define a guard shown generally as 24. The guard 24 is bifurcated to define a pair of parallel arms 26 spaced apart by a gap 28, the arms 26 straddling and extending parallel to the blade and normal to the length of the scalpel handle at the anterior end of the scalpel. As can be seen, the blade cutting edge 16 extends through the gap 28 and past the arms 26. During radial keratotomy, the anterior surfaces of the arms 26 bear against the cornea to prevent the cutting edge 16 from cutting too deep into or penetrating the cornea.

By adjusting the position of sleeve 18 along the handle 12, the extent to which the cutting edge 16 protrudes through the gap 28 outwardly (anteriorly) of the guard 24 can be determined. The amount to which the cutting 16 protrudes past the guard 24 defines the depth of cut of the scalpel 10.

OMP

One drawback of the prior art, adjustable scalpel 10, involves the setting of the depth of cut. To set the depth of cut, a separate depth gauge is used to determine the position of the guard 29 relative to the tip of the blade cutting edge 16. A surgeon or technician is required to compare the depth of cut as set on the scalpel 10 with the gauge and adjust the position of the sleeve 18 accordingly. As can be appreciated, the setting of the depth of cut is not exact. Misperception, inaccuracy of the gauge, or other factors noted above, either acting in combination or acting independently, can detract from the overall accuracy of the depth of cut setting. As discussed above, an inaccurate setting of the depth of cut can result in complete penetration of the cornea or an improper depth of cut, thus causing the result of the surgical procedure to be other than as desired. As can be appreciated, it has been found that setting the depth of cut to an accuracy within 10 microns cannot be consistently accomplished.

To further detract from the accuracy of the scalpel, the tightening of the set screw 20 may in and of itself tend to alter the position of the sleeve 18 along the handle 12 and thereby the location of the arms 26 relative to the cutting edge 16. This in turn, causes a deviation in the depth of the cut setting. Furthermore, since the scalpel 10 is adapted to be used repeatedly, the tightening of the set screw 20 may produce dimples in the handle 12. In setting the depth of cut, the set screw 20 may tend to seek an adjacent dimple thereby altering the position of the sleeve 18 along the handle 12 and the setting of the depth of cut.

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1 Turning to the FIGS. 2 through 5, a presently preferred scalpel 30 according to the present invention is shown. The scalpel 30 includes a handle 32 preferably molded from plastic or the like. The

'5 handle 32 is cylindrical having a longitudinal axis and having one end tapered to define a forward tip 34. Mounted to the tip 34 is a blade 36 having a surgical cutting edge 38. To mount the blade 36, the tip 34 is provided with an axial aperture 40 which

10 may mount the blade 36 by an interference fit.

Alternatively, the blade may be secured to the handle by insert molding of the blade 36 into the handle 32 or the blade 36 may be bonded into the aperture 40 and handle 32 by a suitable glue. Accordingly, the

15 blade 36 is securely affixed to the handle 32 and is prevented from moving axially and angularly relative to the handle 32.

To set a depth of cut, the scalpel 30 includes a sleeve 42, preferably of molded plastic, adapted to

20 be fixed to the handle 32 near the tip 34. The sleeve 42 is semi-cylindrical having a forward end 43 and having an internal diameter adapted to mate with the outside diameter of the handle 32. During the manufacture of the scalpel 30, as describe below,

25 the sleeve 42 is precisely positioned along the handle 32 and is thereafter fixed to the handle 32 by sonic welding, by a suitable adhesive, or by other means. Accordingly, the sleeve 42 once fixed to the handle 32 is prevented from moving relative thereto.

30 The sleeve 42 holds and supports a gauge member or foot 44 which preferably is fashioned from metal to prevent deflection such as by bending and twisting during the surgical procedure. Deflection of the foot 44 would tend to unpredictably alter the depth

35

of cut. Additionally, by being fashioned from metal, the foot 44 can be made relatively narrow so as not to obscure the surgeon's vision.

To hold the foot 44, and for other purposes which will hereinafter become evident, the sleeve 42 includes a radially outwardly projecting mount 46. As shown in the drawings, the mount 42 is preferably rectangular and extends longitudinally along the sleeve 42 at approximately the circumferential midpoint from the forward end 43 to a point repre¬ senting approximately one-half the longitudinal length of the sleeve 42. It is to be understood, however, that the mount 46 can have other configura¬ tions and orientations suitable for operation of the scalpel 30 as herein set forth.

To hold the foot 44, the foot 44 may be insert molded into the mount 46, or the mount 46 may be provided with a receptacle to receive the foot which is thereafter bonded into the recepticle by a suitable glue or the like. Accordingly, the foot 44 and sleeve 42 are positioned and fixed along the handle 32 as a unit.

The foot 44 projects from the mount 46 substan¬ tially parallel to the taper of the handle tip 34 to a point spaced posteriorly from but near the tip of the blade cutting edge 38. At the aforementioned point, the foot 44 is bent to define an elbow 48 and, as shown in the drawings, particularly at FIG. 3, an upwardly extending guard 50. The angle of the bend of the elbow 48 is such that the guard 50 is substan¬ tially transverse to the longitudinal axis of the handle 32.

During a radial keratotomy procedure, the surgeon places and maintains the guard 50 against the cornea to, as described below, produce the desired incision having the proper depth of cut.

To accommodate the blade 36 for making the incisions the guard 50 is bifurcated to define a pair of parallel arms 52 spaced apart by a gap 54. The arms extend to either side of or "straddle" and are positioned transversly of the blade cutting edge 38. The blade 36, and more particularly the cutting edge 38, extends through the guard 50, and more particularly the gap 54, to define the depth of cut shown as "d" in FIG. 3. The arms 52 have a length adequate to project past the blade 36 so that the cutting edge 38 can freely pass through the gap 54.

As can be appreciated from FIGS. 4 and 5, the longitudinal axis of the foot 44 lies in the plane defined by the cutting edge 38. Additionally, the mount 46 is oriented to have its longitudinal axis coplanar with the axis of the foot 44. Therefore, the mount 46 has a longitudinal axis coplanar with the cutting edge 38.

To set the depth of cut "d" for the scalpel 30, the sleeve 42 is precisely positioned along the handle 32 such that the relative position of the guard 50 to the cutting edge 38 establishes the depth of cut "d" to within 10 microns of the selected setting. For radial keratotomy, the selected depth of cut typically falls between 0.435mm and 0.755mm. Since the positioning of the sleeve 42 along the handle 32 is done during manufacture rather than in the hospital operating room or the like, precise positioning to within 10 microns can be obtained. After the sleeve 42 has been located at the selected position, it is fixed to the handle 32 by sonic welding, glue, or the like.

As can be appreciated, the scalpel 30 is relatively inexpensive since both the handle 32 and sleeve 42 are molded- from plastic. The only metallic parts are the foot and blade. Due to the inexpensive nature of the scalpel 30, it is disposable. Since the scalpel 30

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is disposable, the problem of dull blades encountered by repeated use of scalpels, such as the adjustable scalpel 10, is not encountered. Furthermore, since the setting of the sleeve on the handle is done at the factory, the depth of cut "d" can be accurately determined. As an added advantage, the scalpel 30 can be sterilized and prepackaged, dispensing with the need for sterilization.

Turning to FIGS. 6 and 7, a further advantage of scalpel 30 is shown. In holding the scalpel 30, the surgeon grasps it between the index and middle fingers and the thumb. With prior art scalpels having a cylindrical shape at the point of grasp, the fingers and thumb could only support the scalpel at basically three points around its circumference. Accordingly, the scalpel would be subject to rotation within the surgeons hand which, in turn, disorients the blade. Furthermore, when picking up a cylindrical scalpel, the surgeon cannot determine by feel in which direc- tion the cutting edge is oriented. By providing the sleeve 42 with the mount 46, it has been found that the scalpel 30 can be more securely and comfortably held and that the direction of orientation of the cutting edge 38 can easily be determined by feel when the scalpel is picked up. As shown in FIG. 7, the mount 46, sleeve 42, and handle 32 cooperate to approximate a triangular periphery which securely and comfortably mates with the index and middle finger and thumb during the normal grasp of the scalpel 30. The mount also provides means for easily determining by feel the direction of cut by virtue of having its longitudinal axis oriented coplanar with the cutting edge 38.

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While individual pre-set scalpels may be separately provided, the present invention also contemplates providing a number of sets of scalpels 30 in a kit, the scalpels of each set having the same depth of cut and the depth of cut varying from set to set. The kit may include the same number of scalpels in each set. However, this would not be cost effective since some required depths of cuts are rarely encountered whereas others are frequently used simply due to the normal distribution of variances of cornea thicknesses and other pertinent factors determination of desired depth of cut.

To make the kit of scalpels 30 more cost effective, the number of scalpels provided in each set is based upon the probability that a particuliar depth of cut will be required. It has been found, based upon empirical data from 533 cases that due to variations in the thicknesses of corneas from patient to patient and other pertinent factors, the probable depth of cut varies from between 0.435mm and 0.755mm. It has further been found that the population distribution of required depths of cut is not random, but approxi¬ mates a Gaussian or normal distribution as shown in FIG. 8. For example, for any particular patient, the probability or likelihood that the required depth of cut will be 0.60mm is extremely more likely than that the required depth of cut will be 0.45mm.

Therefore, the kit of scalpels, according to the present invention, will contain sets of scalpels, all of the scalpels of each set having a particular depth of cut and the number of scalpels in any one set being determined by the probability that that particular depth of cut will be required. In other words, the number of scalpels in any particular set in the kit is based, approximately the probability distribution of required use.

The preceding description sets forth the pre¬ sently preferred embodiment of this invention and the presently known best mode of practicing this invention. That description is not exhaustive of all forms and modes of practicing the invention. Workers skilled in the act to which the invention pertains will understand that the invention can be differently embodied or practiced without departing from, and while still relying upon, the essential aspects of this invention.

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