WO1995020920A1

WO1995020920A1 - A microkeratome and method and apparatus for calibrating a microkeratome

Info

Publication number: WO1995020920A1
Application number: PCT/US1995/000975
Authority: WO
Inventors: Raymond C. Clark; Hilton L. Grisel; Kent D. Reimann
Original assignee: Chiron Vision Corporation
Priority date: 1994-02-02
Filing date: 1995-02-01
Publication date: 1995-08-10
Also published as: AU1732095A

Abstract

A microkeratome (11) includes an annular base (18) adapted to set over the patient's corona, a skate (12) slidably mounted to the base, a blade (27) supported by the skate (12), and an adjustable foot (55). The foot (55) is interconnected to the skate (12) by a differential screw mechanism (43) for infinite adjustment of the foot (55) relative to the cutting edge of the blade (27). An apparatus (10) for calibrating the blade extension of a microkeratome (11) includes a magnifying device (16) and a fixture (14) for holding the microkeratome assembly adjacent thereto. The magnifying device (16) defines a line of sight and includes a reticle visible in the line of the sight. The fixture (14) supports the bottom surface of the shim (68) of the microkeratome (11) in a plane parallel to the line of sight of the magnifying device (16). In measuring the blade extension, the reticle is first aligned with either the cutting edge of the blade (27) or the bottom surface of the gauge member (55). Relative movement between the reticle and the fixture (14) is effected until the reticle is aligned with the other of the cutting edge (27) and bottom surface (61) of the gauge member (48). A measuring device monitors the relative movement. The reading of the measuring device equals the blade extension of the microkeratome (11).

Description

A MICROKERATOME AND METHOD AND APPARATUS FOR CALIBRATING A MICROKERATOME

This application is a continuation-in-part of co-pending patent application serial number 08/190,515, filed February 2, 1994. Field of the Invention

The present invention pertains to a microkeratome, and to a method and apparatus for calibrating the extension of a microkeratome blade. Background of the invention

A microkeratome is a surgical implement for performing lamellar refractive surgery, and in particular lamellar keratecto y. This procedure involves the resection of an outer layer of the patient's cornea. As can be appreciated, the depth of the resection must be carefully controlled to ensure a successful operation.

A microkeratome 200 as disclosed, for example, in U.S. Patent No. 5,133,726 to Ruiz et al. includes a blade 202 to remove an outer layer c' of the cornea C (Fig. 35) . Blade 202 is held by a skate 207 which is slidably attached to the top 209 of a ring 210 by a pair of dovetail runners 212. The ring 210 is set over the cornea such that an outer portion of the cornea extends upward above the ring. A shim member 215 is releasably received in a slot 217 along a bottom portion of the skate to engage the cornea. The thickness t of shim 215 sets the vertical distance d between the cutting edge 220 of blade 202 and the bottom surface 222 of shim 215, which in turn, sets the depth of the resection. Shims having different thicknesses can alternatively be received in slot 217 to vary the depth of the cut.

While the components of the microkeratome are fabricated according to precise manufacturing techniques, a surgeon needs to ascertain with certainty the actual depth of the cut which will be effected with a particular shim. Surgeons have not, heretofore, been able to consistently and accurately measure the blade extension; and therefore have been forced to rely solely upon the manufacturer's calibration of the shims.

Further, the use of replaceable shims enables only a finite adjustment of the blade extension. As a result, the options available to the surgeon for a prospective operation are limited. Also, the need for multiple alternative shims requires the manufacture of a number of additional parts—many of which are unused in any one operation. As can be appreciated, this manufacture of alternatively used parts increases the costs of making the microkeratome. Summary of the Invention

The present invention is directed to an adjustable microkeratome, and a method and apparatus for setting or measuring the blade extension of a microkeratome.

A microkeratome of the present invention includes a movable foot for engaging the exterior of the cornea. The foot is movable in a vertical direction to alter the distance the cutting edge of the blade extends beyond the bottom surface of the foot. This enables the surgeon to effect resection of the cornea at different desired depths. In the preferred construction, a _differential screw mechanism is used to provide infinite adjustment capabilities for the foot.

Also in accordance with the present invention, the extension of a microkeratome blade beyond its adjacent gauge member can be consistently and accurately measured, irrespective of whether the gauge member is a replaceable shim or an adjustable foot. To this end, a microkeratome assembly is supported adjacent to a magnifying device. The magnifying device defines a line of sight and includes a reticle which is visible in the line of sight. The microkeratome assembly is positioned so that the bottom surface of the gauge member lies in a plane parallel to the line of sight. The reticle is first aligned with either the cutting edge of the blade or the bottom surface of the gauge member. Thereafter, relative movement is effected between the reticle and the microkeratome assembly so that the reticle is next aligned with the other of the cutting edge of the blade or bottom surface of the gauge member. The relative movement is monitored by a measuring device. The reading of the measuring device equals the distance between the cutting edge and the bottom surface of the gauge member, which in turn, equals the extension of the blade.

According to another aspect of the invention, the blade extension of a microkeratome having infinite adjustment capability can be accurately set. To set the blade extension, a microkeratome assembly is supported adjacent a magnifying device so that the bottom surface of the foot lies in a plane parallel with the line of sight of the magnifying device. Once the assembly is properly mounted, the cutting edge of the blade is aligned with the reticle of the magnifying device. Relative movement, monitored by a measuring device, is then effected between the reticle and the cutting edge. The relative movement is continued until the distance between the reticle and the cutting edge equals the desired extension of the blade. The foot of the microkeratome assembly is then adjusted so that the bottom surface of the foot is aligned with the reticle.

In the preferred construction, an apparatus for calibrating a microkeratome includes a fixture for holding the microkeratome assembly within the line of sight of the magnifying device. The fixture has jaws which engage and hold the runners of the microkeratome assembly parallel to the line of sight. This arrangement ensures that the bottom surface of the gauge member (i.e. the shim or foot) is oriented parallel to the line of sight. The jaws of the fixture define a three point mount for supporting and accurately setting the microkeratome assembly for the desired measurement. The jaws of the fixture are. further constructed to permit a quick mount and release of the microkeratome assembly, and to permit adequate lighting for visible observation of the blade and shim components.

Brief Description of the Drawings

Figure 1 is a perspective view of the present invention.

Figure 2 is a side elevational view of the present invention.

Figure 3 is a front elevational view thereof.

Figure 4 is a cross sectional view taken along line 4-4 in Figure 3, with the ocular components and post adjustment assembly omitted.

Figure 5 is a perspective view of a fixture of the present invention and a microkeratome.

Figure 6 is a front end view of the fixture.

Figure 7 is a front view of a support element of the fixture.

Figure 8 is a side view of the support element.

Figure 9 is a top view of the support element.

Figure 10 is a front view of the fixed jaw of the fixture.

Figure 11 is a top view of the fixed jaw.

Figure 12 is a front view of the movable jaw of the fixture.

Figure 13 is a side view of the movable jaw.

Figure 14 is a top view of the movable jaw.

Figure 15 is a cross sectional view taken along line 15-15 in Figure 6.

Figure 16 is the left side elevational view of the tray of the fixture.

Figure 17 is the right side elevational view of the tray.

Figure 18 is a top plan view of the tray.

Figure 19 is a front end view of the tray.

Figure 20 is a partial side view of the upper portion of the table of the present invention.

Figure 21 is a view as seen through the magnifying device of the present invention.

Figure 22 is a second view as seen through the magnifying device of the present invention.

Figure 23 is a side view of a microkeratome according to the present invention.

Figure 24 is an enlarged cross sectional view of a microkeratome assembly in accordance with the present invention.

Figure 25 is a front view of a portion of a skate according to the present invention.

Figure 26 is a cross sectional view taken along line 26-26 in Figure 25, with the cutting blade, differential screw mechanism, and foot included.

Figure 27 is a top plan view of an alternative table in accordance with the present invention.

Figure 28 is a cross sectional view taken along line 28-28 in Figure 27.

Figure 29 is an enlarged partial cross sectional view taken along line 29-29 in Figure 27.

Figure 30 is a rear elevational view of an alternative fixture with its threaded pin omitted in accordance with the present invention.

Figure 31 is a top plan view of the fixture.

Figure 32 is one side elevational view of the fixture with the pins omitted.

Figure 33 is an opposite side elevational view of the fixture. Figure 34 is an enlarged partial rear view of one side wall of the fixture.

Figure 35 is a cross sectional view of a prior art microkeratome. Detailed Description of the Preferred Embodiments

One aspect of the present invention relates to a microkeratome 11 (Figs. 23-26) . Microkeratome 11 preferably has much of the same construction as the microkeratome of U.S. Patent No. 5,133,726, which is incorporated by reference for the common structure and operation of the microkeratome not discussed in this application.

Microkeratome 11 includes a skate 12 provided with an upper section 12a and a lower section 12b. Upper section 12a includes a body 13 and a threaded segment 15a. Lower section 12b includes a pair of runners 17a, 17b, a threaded segment 15b, and a bridge structure 40. Sections 12a, 12b are atingly fit together so that segments 15a, 15b form a threaded rod on which is received a lock nut 25.

Skate body 13 includes an opening 21 adapted to movably receive therein a blade holder (not shown) attached to cutting blade 27. The blade holder is coupled to an eccentric (not shown) extending from a motor encased in handle 31 to laterally reciprocate the blade during the operation. Longitudinal bore 23 and transverse bore 35 are adapted to receive therein an endless pinion and a pinion-shaft respectively. The endless pinion and pinion-shaft cooperate to drive skate 12 across the base ring 39 as set forth in the '726 patent. Runners 12a, 12b slidably engage tracks 37 on ring 39 to guide skate 12 and blade 27 across the cornea. Preferably, runner 17a has a rectangular slot and runner 17b has a dovetail shape. The use of the rectangular slot alleviates binding which can occur with two dovetail runners and prevents improper positioning of the skate on the ring. Nonetheless, both runners may be dovetail shaped if desired.

Bridge 40 defines a threaded central bore 41 into which is matingly received a differential screw mechanism 43. Screw mechanism 43 includes an outer, annular screw 45 provided with an axial bore 51 and an inner screw 49. Annular screw 45 is provided with inner and outer threads. The outer threads of screw 45 mate with the threads in bore 41. The inner threads along bore 51 mate with the threads of inner screw 49. As is well known with differential screws, the pitches of the different threads are selected so that substantial turning of outer screw 45 causes inner screw 49 to move axially only a small amount. The upper end of outer screw 45 is provided with a knurled handle 53 or other means to effect rotation of the screw.

A foot 55 is fixedly attached to the lower end of screw 49. Foot 55 defines a pair of side walls 59 and a bottom surface 61. Side walls 59 are lightly abutted against opposing inner walls 62 to prevent rotation of the foot during actuation of differential screw mechanism 43. A pair of leaf springs 57 are preferably positioned between the foot and the skate to alleviate the effects of backlash in connection with screw mechanism 43. Bottom surface 61 of foot 55 is adapted to engage the outer surface of the cornea and set the depth of the resection in cooperation with blade 27. As best seen in Figures 23 and 24, the vertical distance I between bottom surface 61 of foot 55 and cutting edge 63 of blade 27 is the blade extension of the microkeratome, or in other words, the depth of the resection to be made during the operation.

Another aspect of the present invention relates to a method and apparatus 10 for calibrating (i.e., measuring or setting) the blade extension of a microkeratome. In the preferred construction, apparatus 10 includes a fixture 14 for holding a microkeratome assembly and a magnifying device 16 for viewing the relevant components of the microkeratome (Fig. 1) . For purposes of illustration, the microkeratome is shown generally as structured in U.S. Patent No. 5,133,726. Of course, microkeratomes of other constructions, including microkeratome 11 discussed above, could be used with this aspect of the present invention.

Apparatus 10 further comprises a relatively broad base 18 and an upstanding post 20 (Figs. 1-3) . Magnifying device 16 is adjustably mounted to the top of the post for movement along the X-axis. To accommodate the desired movement, the top of the post is configured to define a rail 22 which extends along the X-axis (Figs. 2 and 4) . Rail 22 has a central head 24 and a pair of shoulders 26. A carriage 32 having a complementarily shaped base portion is movably mounted on the rail. Bearing guides 28, 29 are fixedly secured to shoulders 26 and carriage 32, respectively (Fig. 4). Guides 28, 29 each defines a V-shaped groove 33, 34 along one side. Grooves 33, 34 are placed in opposed relation to one another, to form a pair of channels 35. Cylindrical bearings 36 are placed in channels 35 in an alternating arrangement, such that each bearing is oriented ninety degrees re_lative to its adjacent bearings. This bearing structure ensures that carriage 32 moves in only the X-axis direction as indicated by arrows 38 (Figs. 1 and 3) .

Carriage 32 extends forward from rail 22 in a cantilevered manner to support the optical assembly of magnifying device 16 over fixture 14 (Figs. 1, 2 and 4) . The magnifying device includes a magnifying lens within barrel 47 and an eyepiece 46 (Figs. 1-3) . Barrel 47 defines a circular range of vision which is seen through eyepiece 46 (Figs. 21-22) . The outward longitudinal extension of this circular range from barrel 47 defines the line of sight for the magnifying device, as indicated by arrow 50 (Fig. 3) . Eyepiece 46 includes a reticle which defines a linear marking, preferably in the form of a cross hair 48 (Figs. 21-22).

Carriage 32 is linearly moved in the X-axis direction by preferably a screw mechanism 52 (Figs. 1 and 3) . Screw mechanism 52 comprises a screw threadedly received through nut 54 fixed to carriage 32 (Fig. 4) . As the screw is turned, the carriage is moved linearly along rail 22. A digital encoder 56 is used to measure the amount of movement caused by turning the screw (Figs. 1 and 3) . Of course a micrometer or other measuring device could also be used. A digital display 58 located in base 18 is provided to indicate the distance traveled by the carriage (Figs. 1 and 3) .

In the preferred construction, a sensor device 65 is attached to the underside of carriage 32 to project in a downward direction next to barrel 47 (Figs. 1-3) . As described more fully below, the sensor device is included to provide an easy, reliable way of performing a delicate measurement. Sensor device 65 comprises a bracket 67 which is fixed to carriage 32 and a switch 69. Switch 69 is preferably a precision limit switch, such as model no. MY-COM-G75N80L, manufactured by Applied Motion Products, of 8039 24th Ave. S, Bloomington, MN 55425-1224. Nevertheless, other switches and other sensing devices having sufficient sensitivity could also be used. In any event, switch 69 includes an actuator for sensing engagement with an object. The free end 71a of actuator 71 is positioned to be in precise alignment with cross hair 48. The switch is coupled to a lamp 73 which is lit upon engagement of actuator 71 with an object.

To facilitate measurement of the blade extension, the handle and ring components of the microkeratome are removed. For purposes of illustration, a microkeratome assembly in accordance with the prior art is shown mounted in fixture 14 (Figs. 1 and 5) . Nevertheless, a microkeratome 11 with infinite adjustment capabilities could be mounted in the fixture in the same way. In any event, the remaining assembly 60 includes a skate 64, a blade holding unit 66 and a shim 68 (Figs, l and 5) . In Figure 5, shim 68 is shown as being partially inserted into skate 64 in order to illustrate its bottom surface 70. In actual use with apparatus 10, the shim would be fully inserted such that tenon 72 would be fully received into mortise 74. Skate 64 includes a pair of parallel dovetail runners 76 adapted to slidably mount the skate to the ring (not shown) . Blade holding unit 66 includes a blade holder (not shown) and a blade 77 with a cutting edge 78 (Figs. 21 and 22) . Microkeratome assembly 60 is mounted in fixture 14 for viewing through eyepiece 46 (Figs. 1 and 5) . In particular, skate 64 is engaged by jaws 80, 82 and held so that dovetail runners 76 are positioned parallel to the line of sight. Jaws 80, 82 are attached to a U-shaped support 84 having upstanding legs 86, 88 and a lower bight portion 90 (Figs. 5-15). The gap 91 defined between legs 86, 88 of support 84 permits a portion of the surrounding light to shine on blade 77 and shim 68. An auxiliary lamp 92, supported by arm 94, is preferably also provided for increased lighting (Fig. 1) . Further, bight portion 90 is recessed relative to front faces 96, 98 of legs 86, 88 to permit increased lighting to shine up from the main lamp (not shown) in table 100 (Figs. 5 and 9).

Fixed jaw 80 is secured to leg 86 by a pair of screws 87 (Figs. 5-11 and 15) . Movable jaw 82 is preferably pivotally attached at its bottom end to leg 88 by a screw 89 (Figs. 5-6 and 12-15). A slot 101, defined in the upper end of jaw 82, is received over a projection 102 to provide support and clearance for the jaw's movement. A spring 119 works to bias jaw 82 into its closed position and thereby supply the gripping force necessary to hold microkeratome assembly 60 (Figs. 6 and 12-15) . In the preferred construction, a cavity 121 is defined in front face 98 of leg 88 to receive a lug 123 extending rearwardly from jaw 82. Spring 119 presses against lug 123 to normally rotate jaw 82 toward fixed jaw 80. A stop 125 projects from face 98 to properly position the microkeratome assembly. A lever 116 extends laterally outward from jaw 82 to facilitate manual pivoting of the jaw (Figs. 5, 6 and 12). The movable jaw may also have other constructions. For instance, the movable jaw may be a block member provided with a transverse channel and a gripper member which is mounted for movement towards and away from the fixed jaw. The gripper member would be spring biased towards the fixed jaw, but manually movable in a rearward direction for release of the microkeratome assembly. Of course, other jaw arrangements could also be used.

Jaws 80, 82, along their inner edges 106, 108, are beveled in order to matingly engage dovetail runners 76 of microkeratome assembly 60. The jaws form a three point mount to ensure accurate positioning of assembly 60. Preferably, inner end 106 of jaw 80 has an undulated configuration which defines two spaced contact points 111, 112. Inner end 108 of jaw 82 defines an opposed single contact point 113 located between points 111, 112.

Support 84 is secured to the front end 132 of a relatively flat, elongated tray 130 by a pair of screws 89, 133 (Figs. 5-6 and 16-19) ; although other attachment means could be used. Front end 132 is preferably notched at 134 in order to provide ample clearance for positioning of the tray when it is used with certain pre-existing inspection microscopes; that is, to permit proper placement of the microkeratome assembly within the line of sight of the magnifying device. Also, as seen in Fig. 6, tray 130 is wider than support 84 to accommodate the channel defined in certain pre-existing inspection microscopes. The presence of the notch and enlarged width is, of course, not essential to the invention. The front end of the microscope is also preferably provided with a recess for accommodating the construction of certain microkeratomes. The rear end 136 of tray 130 is _bifurcated into a pair of legs 142, 143 to form a suitable handgrip. Each leg 142, 143 is provided with an angled groove ₁₄4, 145 for better manipulation of the fixture. Of course other handles or gripping arrangements could be employed.

Table 100 defines a channel 149 which matingly receives tray 130 (Figs. 1, 2 and 20). The sides of tray 130 and channel 149 are configured to temporarily hold the tray in place and to enable the tray to be quickly inserted into and removed from the channel (Figs. 2 and 16-19) . Specifically, one side 152 of tray 130 includes a longitudinal groove 153 which is received over a complementary ridge 161 defined on channel side wall 159. The opposite side 155 of tray 130 is formed with chamfered corners 157, but not a groove. The opposite side wall 163 of the channel defines a planar surface set at a right angle to the bottom 165 of the channel.

To insert tray 130 into channel 149, the tray is first inclined at an angle of about 45 degrees with side 152 facing generally downward toward channel 149. Fixture 14 is next moved into the channel so that groove 153 is partially received over ridge 161. Fixture 14 is then rotated until bottom 167 of tray 130 lies against bottom 165 of channel 149. Chamfered corners 157 provide the clearance necessary to effect the rotation of the tray into and out of the channel. The tray is securely held in place for measurement of the blade extension by a bolt 169 received into a threaded bore (not shown) defined in the bottom 165 of channel 149. Of course, fixture 14 could be secured into channel 149 in other ways.

Table 100 is movably supported on block 173 (Figs. 1-3) with t_he same bearing construction as described above for rail 22 and carriage 32. The bearing construction (not shown) connecting table 100 to block 173, however, is orthogonal to the orientation of bearing guides 28, 29. In this way, table 100 is restricted to movement only along the Y-axis, as indicated by arrows 175 (Figs. 1-2) . A screw mechanism 177 effects the movement of the table along block 173 (Figs. 1-3) . Such movement of the table is used to bring microkeratome assembly 60 into the line of sight for magnifying device 16 and to facilitate inspection of the entire cutting edge 78 for damage.

Block 173 is fixedly attached to a bracket 179 which is movably connected to post 20 (Figs. 1-3) . Bracket 179 includes a mounting leg 181 which lies against post 20 and a support leg

183 which projects outward over base 18. Support leg 183 supports block 173 underneath magnifying device 16 to enable viewing of microkeratome assembly 60. Mounting leg 181 is coupled to a screw adjustment mechanism 185 positioned within post 20. Screw adjustment mechanism 185 extends through passage

184 defined in rail 22, carriage 32 and post 20. The screw adjustment mechanism moves bracket 179 vertically along post 20 to enable focusing of magnifying device 16.

Alternatively, table 250 and fixture 252 are preferably used to support a microkeratome assembly for calibration (Figs. 27- 34) . More specifically, table 250 is a generally rectangular member with a top 254, a bottom 256, a pair of sides 258, 259, a front 261 and a rear 263 (Figs. 27-28) . The bottom of table 250 is fixedly secured via bolting or the like to a bracket member (not shown) . The bracket member supports the bearings and drive elements needed for moving the table along the Y-axis. These elements are the same as in the above-described embodiment.

The top of table 250 includes a channel 265 which opens in front wall 261 and extends in a direction parallel to the Y-axis (Figs. 27-29) . Channel 265 includes a side wall 267 provided with the same type of contour for the same purpose as side wall 159 of table 100. A hole 268 for the main lamp (not shown) of table 250 lies adjacent channel 265. While the lamp may be mounted in table 250, it is preferably positioned below table 250 and adapted to shine up through hole 268. The top flats 271a, 271b are preferably recessed relative to the remainder of the top surface 254 to provide the necessary clearance for the mounting of certain microkeratome assemblies.

Fixture 252 includes a tray 275 and an upstanding support 277 (Figs. 30-34) . Tray 275 is adapted for receipt in channel 265 in the same manner as tray 130 in channel 149. As seen in Figures 30 and 34, tray 275 includes a side wall 279 adapted to cooperatively engage the contoured side wall 267 of channel 265. Tray 275 is secured within channel 265 by a set screw (not shown) received through tapped bore 281.

Support 277 extends outward beyond side wall 279 (Figs. 30- 31). Support 277 includes a pair of legs 283, 284 and an intermediate bight portion 285 to generally define a U-shaped configuration (Figs. 30-32). Bight portion 285 is recessed slightly with respect to the legs to define a gap through which light from the main lamp shines (Fig. 31) . Leg 283 includes a pair of inclined holes 289 in face 291 for receiving a pair press fit pins 293. Pins 293 are adapted to engage one side of the microkeratome assembly. Specifically, the ends of the pins are preferably matingly received into the contour of the microkeratome runners. Leg 284 includes an extended portion 295 which defines a tapped bore 297 extending parallel to the Y-axis. Tapped bore 297 movably receives a threaded pin 299 adapted to extend outward and engage the opposing side of the microkeratome assembly. The free end of pin 299 is preferably shaped to matingly engage the runner on the corresponding side of the microkeratome. In use, threaded pin 299 is manually rotated for movement toward or away from the microkeratome assembly.

Support 277 further includes a narrow ledge 302 beneath pins 297, 299 for engaging the rear end of the skate of the received microkeratome assembly (Figs. 31-32) . The engagement between the skate and ledge 302 ensures that the bottom surface of the gauge member lies in a plane parallel to the line of sight of magnifying device 16. Further, a groove 304 is defined across the top surface of tray 275 in alignment with bight portion 285. Groove 304 provides clearance for the extension of sensor device 65 projecting downward from carriage 32.

The blade extension of a microkeratome is measured by first placing assembly 60 into jaws 80, 82 so that cutting edge 78 faces upward toward magnifying device 16. Preferably, fixture 14 is already mounted onto table 100 when microkeratome assembly 60 is attached, but it could be mounted afterward. If necessary, screw adjustment mechanism 177 is turned to place assembly 60 within the line of sight for magnifying device 16. Screw mechanism 52 is adjusted so that cross hair 48 is aligned with the cutting edge 78 of blade 77 (Fig. 21) . This is accomplished by looking through the magnifying device and adjusting the screw mechanism until visual alignment is attained. Encoder 56 is then zeroed by pushing button 186. Screw mechanism 52 is again rotated so that magnifying device 16 is moved along the X-axis until cross hair 48 is aligned with the bottom 70 of shim 68 (Fig. 22) . Sensor device 65 is positioned such that actuator 71 engages shim 68 when the bottom surface of the shim is precisely aligned with cross hair 48. Sensor device 65 then lights lamp 73 to indicate when to stop adjusting the screw mechanism. Of course, the bottom of shim 68 may also be aligned by looking through magnifying device 16, instead of using the sensor. Alternatively, cross hair 48 can be first aligned with bottom surface 70 of shim 68 and then moved to cutting edge 78. In the case with microkeratome 11, the reticle is successively aligned with the cutting edge of the blade and the bottom surface of the foot, or vice versa. In any event, the reading in display 58 is the distance the blade extends beyond the bottom surface of the gauge member 55 or 68.

Apparatus 10 can also be used to accurately set the blade extension of microkeratome 11. In this process, handle 31 and ring 39 of microkeratome 11 are removed to form a microkeratome assembly 11'. Assembly 11' is mounted to fixture 14 with the runners 17a, 17b of skate 12 engaged by jaws 80, 82. The beveled jaw is able to securely hold runner 17a by engaging the corner of the rectangular slot. As with measuring the blade extension, the bottom surface 61 of foot 55 is held vertically in a plane parallel with the line of sight of magnifying device 16. Additionally, blade 27 is oriented such that cutting edge 63 faces upwardly. Although fixture 14 is preferably mounted to table 100 before assembly 11' is attached, the fixture may be so mounted after the attachment of assembly 11'.

Once fixture 14 with assembly 11' is properly mounted to table 100, screw mechanism 177 is adjusted, if necessary, to bring assembly 11' within the line of sight of magnifying device 16. Screw mechanism 52 is next adjusted so that cross hair 48 is aligned with the cutting edge 63 of blade 27. At this juncture, encoder 56 is zeroed. Using encoder 56 and screw mechanism 52, carriage 32 is adjusted so that cross hair 48 is moved away from the cutting edge of blade 27 a distance equal to the desired extension of the blade. Thereafter, differential screw mechanism 43 is actuated so as to adjust the position of foot 55. The movement of foot 55 is continued until its bottom surface 61 is aligned with cross hair 48. In the preferred construction, alignment is indicated when bottom surface 61 engages actuator 71 and lights lamp 73. Nonetheless, alignment may also be achieved by looking through magnifying device 16. The foot and blade now define the desired cutting depth for the operation.

The above discussion concerns the preferred embodiments of the present invention. Nevertheless, as can be appreciated, apparatus 10 can be constructed in a number of different ways without departing from the present invention. For instance, the X and Y axis adjustments could be reversed such that the fixture is moved along the X-axis and the carriage along the Y-axis. In addition, the adjustments could be accomplished solely by moving either the fixture or the carriage in both directions. Also, the line of sight could be arranged horizontally instead of vertically. Further changes and alterations may also be made without departing from the spirit and broader aspects of the invention as defined in the claims.

Claims

1. A method for measuring the blade extension of a microkeratome assembly having a blade defining a cutting edge and a gauge member defining a bottom surface spaced from the cutting edge, said method comprising: positioning the microkeratome assembly adjacent a magnifying device defining a line of sight for the user and including a reticle visible in the line of sight, said reticle defining a linear marking, said microkeratome assembly being positioned within the line of sight such that the bottom surface of the gauge member lies in a plane parallel to the line of sight; aligning the linear marking with one of the cutting edge or the bottom surface of the gauge member; causing relative movement between the reticle and the microkeratome assembly in a direction perpendicular to the linear marking so that the linear marking is aligned with the other of the cutting edge or the bottom surface of the gauge member; monitoring the relative movement with a measuring device; and reading the amount of movement recorded by the measuring device to obtain the blade extension.

2. A method in accordance with claim 1 in which said causing of the relative movement includes moving the magnifying device in a direction perpendicular to the linear marking.

3. A method in accordance with claim 2 in which said moving of said magnifying device is effected by a screw mechanism.

4. A method in accordance with claim 1 in which said monitoring of the relative movement is effected by an encoder.

5. A method in accordance with claim 1 in which said causing of the relative movement includes moving the microkeratome assembly in a direction perpendicular to the linear marking.

6. A method in accordance with claim 1 in which said causing and measuring of the relative movement is effected by a micrometer.

7. A method in accordance with claim 1 in which said gauge member is a replaceable shim.

8. A method in accordance with claim 1 in which said gauge member is an adjustable foot.

9. A method in accordance with claim 1 in which said aligning of the bottom surface of the gauge member with the linear marking is indicated by a sensor device.

10. A method for setting the blade extension of a microkeratome assembly having a blade defining a cutting edge and an adjustable foot defining a bottom surface spaced from the cutting edge, said method comprising: positioning the microkeratome assembly adjacent a magnifying device defining a line of sight for the user and including a reticle visible in the line of sight, said reticle defining a linear marking, said microkeratome assembly being positioned within the line of sight such that the bottom surface of the foot lies in a plane parallel to the line of sight; aligning the linear marking with the cutting edge of the blade; causing relative movement between the reticle and the microkeratome assembly in a direction perpendicular to the linear marking until said linear marking is spaced from the cutting edge of the blade a distance equal to the desired extension of the blade; monitoring said relative movement by a measuring device so as to determine when the linear marking has been spaced from the cutting edge a distance equal to the desired extension of the blade; and adjusting the foot of the microkeratome until the bottom surface of the foot is aligned with the linear marking.

11. A method in accordance with claim 10 in which said causing of the relative movement includes moving the magnifying device in a direction perpendicular to the linear marking.

12. A method in accordance with claim 11 in which said moving of said magnifying device is effected by a screw mechanism.

13. A method in accordance with claim 10 in which said monitoring of the relative movement is performed by an encoder.

14. A method in accordance with claim 10 in which said causing of the relative movement includes moving the microkeratome assembly in a direction perpendicular to the linear marking.

15. A method in accordance with claim 10 in which said causing and measuring of the relative movement is effected by a micrometer.

16. A method in accordance with claim 10 in which said adjusting of the foot is effected by operating a differential screw mechanism.

17. A method in accordance with claim 10 in which said adjusting of the foot is continued until alignment of the bottom surface of the foot with the linear marking is indicated by a sensor device.

18. An apparatus for calibrating the blade extension of a microkeratome assembly having a blade defining a cutting edge, a gauge member defining a bottom surface and a skate having a pair of runners, said apparatus comprising: a magnifying device defining a line of sight and including a reticle visible in said line of sight, said reticle defining a linear marking; a fixture for holding the microkeratome assembly adjacent said magnifying device and within said line of sight, said fixture including means for receiving and holding the microkeratome assembly so that the bottom surface of the gauge member lies in a plane parallel to said line of sight; an adjustment assembly for causing relative movement between said reticle and said fixture in a direction perpendicular to said linear marking; and a measuring device for measuring the distance said reticle is moved relative to said fixture.

19. An apparatus in accordance with claim 18 which further includes a post and in which said magnifying device includes a magnifying lens, an eyepiece and a carriage movably mounted to said post for movement in a direction perpendicular to said linear marking.

20. An apparatus in accordance with claim 19 in which said adjustment assembly includes a screw attached to one of said carriage and said post and a nut attached to the other of said carriage and said post.

21. An apparatus in accordance with claim 20 wherein said measuring device is an encoder associated with said screw to measure the movement of said magnifying device in a direction perpendicular to said linear marking.

22. An apparatus in accordance with claim 19 which further includes a second adjustment assembly associated with said fixture for moving said fixture in a second direction parallel with said linear marking, whereby the microkeratome assembly can be positioned within the line of sight and the cutting edge can be fully inspected for damage.

23. An apparatus in accordance with claim 18 in which said adjustment assembly and said measuring device are cooperatively formed as a micrometer.

24. An apparatus in accordance with claim 18 further including a table supporting said fixture adjacent said magnifying device and a block movably supporting said table for movement in a direction perpendicular to said linear marking.

25. An apparatus in accordance with claim 24 in which said adjustment assembly includes a screw attached to one of said table and said block and a nut attached to the other of said table and said block.

26. An apparatus in accordance with claim 25 wherein said measuring device is an encoder associated with said screw to measure the movement of said table in a direction perpendicular to said linear marking.

27. An apparatus in accordance with claim 18 further including a table defining a channel releasably receiving and holding said fixture in said line of sight of said magnifying device.

28. An apparatus in accordance with claim 18 in which one of said jaws is fixed and one of said jaws is movable so that the microkeratome assembly may be quickly and easily mounted and removed from said apparatus.

29. An apparatus in accordance with claim 28 wherein said movable jaw is normally biased toward said fixed jaw.

30. An apparatus in accordance with claim 18 in which said means for holding the microkeratome assembly includes a plurality of jaws at least one of which has a beveled inner edge for receiving and holding at least one of said runners of the microkeratome assembly.

31. An apparatus in accordance with claim 18 in which said means for holding the microkeratome assembly includes a plurality of pins shaped to securely engage said runners of said microkeratome assembly.

32. An apparatus in accordance with claim 18 further including a sensor device for indicating the alignment of the bottom surface of the gauge member with said linear marking.

33. An apparatus in accordance with claim 32 in which said sensor device is a precision limit switch provided with an actuator which has a free end aligned with said linear marking.

34. An apparatus in accordance with claim 32 in which said sensor lights a lamp to indicate alignment of the bottom surface of the gauge member with said linear marking.

35. A microkeratome comprising: a base adapted to set over a patient's cornea; a skate movably attached to said base for movement thereacross; a foot having a bottom surface adapted to engage the exterior of the patient's cornea; a blade having a cutting edge extending beyond said bottom surface of said foot, such that the extension of said cutting edge relative to said bottom surface of said foot defines the depth of the cut to be made on the patient's cornea; and an adjustment device interconnecting said foot to said skate for movement in a direction perpendicular to said movement of said skate, said adjustment device including a differential screw mechanism having the capacity to provide infinite adjustment of said foot relative to the extension of said cutting edge of said blade to thereby vary the depth of the cut to any desired dimension, said differential screw mechanism including an annular screw and an inner screw threadedly interconnected, one of said screws being threadedly received in said skate and the other of said screws being attached to said foot.

36. A microkeratome in accordance with claim 35 in which said skate includes a pair of opposed inner walls and said foot includes a pair of side walls which engage said inner walls to prevent rotation of said foot during actuation of said differential screw mechanism.

37. A microkeratome in accordance with claim 35 further including at least one spring between said skate and said foot to alleviate the effects of backlash in connection with said differential screw mechanism.

38. A microkeratome comprising: an annular base adapted to set over the patient's cornea such that the cornea extends upward through said base, said base including a pair of spaced apart linear tracks; a skate slidably mounted to said base, said skate including a pair of runners in engagement with said tracks and a pair of opposed walls defining a recess therebetween; a blade holder movably supported by said skate; an assembly for laterally reciprocating said blade holder within said skate; a foot having a bottom surface adapted to contact the exterior surface of the cornea and a pair of side surfaces in engagement with said opposed walls of said skate; a blade held by said blade holder, said blade including a cutting edge extending outwardly beyond said bottom surface of said foot, said extension of said cutting edge defining the depth of the cut to be made on the cornea; and an adjustment device including a differential screw mechanism for moving said foot in a direction perpendicular to said lateral movement of said blade and to said sliding movement of said skate to thereby vary the depth of the cut.

39. A microkeratome in accordance with claim 38 further including at least one spring between said skate and said foot to alleviate the effects of backlash in connection with said differential screw mechanism.

40. A system for calibrating a microkeratome for a lamellar resection of a cornea comprising a microkeratome assembly and a calibrating apparatus, said microkeratome assembly comprising: a skate a gauge member supported by said skate having a bottom surface adapted to engage the exterior of the patient's cornea; and a blade mounted to said skate having a cutting edge extending beyond said bottom surface of said gauge member such that the extension of said cutting edge relative to said bottom surface of said gauge member defines the depth of the cut to be made on the patient's cornea; and said calibrating apparatus comprising: a magnifying device defining a line of sight and including a reticle visible in said line of sight, said reticle defining a linear marking; a fixture for holding the microkeratome assembly adjacent said magnifying device and within said line of sight such that said bottom surface of said gauge member lies in a plane parallel to said line of sight; an adjustment assembly for causing relative movement between said reticle and said fixture in a direction perpendicular to said linear marking; and a measuring device for measuring the distance said reticle is moved relative to said fixture.

41. A system in accordance with claim 40 in which said microkeratome assembly further includes an adjustment device which interconnects said gauge member to said skate for movement so that said adjustment device has the capacity to provide infinite adjustment of said gauge member relative to the extension of said cutting edge of said blade to thereby vary the depth of the cut to any desired dimension.

42. A system in accordance with claim 40 in which said calibrating device further includes a sensor device for selectively engaging said bottom surface of said gauge member and indicating when said bottom surface is aligned with said linear marking.