Undercut diamond surgical blade and method of using the same

Surgical blades, knives and keratotomy procedures are provided which are capable of severing deep corneal tissue in the optical zone without penetrating the surface of this zone and causing optical glare. The blades of this invention include at least one cutting edge thereon which is shorter than about 0.5 mm and which includes a projecting cutting portion and/or recessed blunt edge to permit primary or secondary incisions beneath the surface of the optical zone.

FIELD OF THE INVENTION 
This invention is related to surgical knives having controllable extendable 
blades, and more particularly to gemstone blade configurations having at 
least one cutting edge which is suitable for radial and astigmatic 
keratotomy procedures. 
BACKGROUND OF THE INVENTION 
Radial keratotomy procedures are currently available for myopic patients 
having about 2-6 diopters of myopia. Such keratorefractive procedures 
attempt to flatten the cornea with radial incisions which begin 
paracentral to the cornea center and leave the central optical zone of 
about 3-4 mm unaffected. Two widely available techniques currently 
employed are known as the Russian (up hill) and the American (down hill) 
methods. In the Russian method, the incision is started in the cornea near 
the limbus and is directed to the edge of the optical zone. In the 
American technique, the initial incision is made at the optical zone, and 
then proceeds radially outward toward the limbus. With both procedures, 
approximately 4-16 radial incisions are made in the cornea. These 
incisions are designed to reconfigure the cornea so that the light 
entering the eye tends to focus more accurately on the retina. However, 
since the corneal thickness varies from patient to patient, and from one 
region of the cornea to the next, and since the skill level of surgeons 
varies from one surgeon to to the next, the predictability of 
keratorefractive surgery has typically been low. The lack of 
predictability and efficiency are especially true when employing the 
American style incisions, as these typically yield incisions of variable 
depth. 
Recently, as disclosed in U.S. Pat. No. 4,691,716, studies have shown that 
the efficacy of radial keratotomy and the final degree of refractive 
correction is significantly influenced by the depth of the incision. 
Procedures which produce a relatively shallow cut are known to produce the 
least amount of correction with the greatest degree of regression. 
Accordingly, surgeons must be careful to cut fully through approximately 
90% of the thickness of the cornea in order to provide effective results. 
Since the American style incisions do not provide uniform depth (producing 
shallower incisions centrally), and since the corneal periphery is thicker 
(0.580-0.600 mm) than the paracentral and central corneal zones (0.500 mm) 
in most patients, the surgeon must redeepen the peripheral cut in order to 
provide an incision at 90% of the corneal thickness over its entire 
length, following American style incisions. 
Redeepening the incision presents the formidable risk of puncturing the 
cornea and creating an entrance bacteria to enter the anterior chamber of 
the eye with attendant risks of infection and complications. Redeepening 
the incision also often requires lifting the blade and retracing or 
reversing the cutting motion. This is a very difficult procedure and can 
result in penetration into the optical zone, as well as inaccurate 
retracing of the bottom of the incision. Incisions invading the full 
thickness of the optical zone are associated with optical glare, since the 
resulting surface scarring has a different refractive index than the 
surrounding corneal tissue. While the Russian (up hill) incisions tend to 
provide uniform depth with resultant greater predictability, they are 
still fraught with the danger of invading the central optical zone. This 
is because slight irregular movements of the patient's eye or the 
surgeon's hand may result in optical zone incisions as the blade 
approaches the central zone. 
Accordingly, there is a present need for knive blades and keratotomy 
surgical procedures which permit carefully controlled keratorefractive 
incisions approaching 90% of the thickness of the cornea without risking 
puncture into the anterior chamber or scarring at the surface of the 
optical zone. 
SUMMARY OF THE INVENTION 
The present invention provides surgical knives which are designed for use 
in surgical procedures, especially delimiting, astigmatic and radial 
keratotomy, and the like. One group of preferred knives includes an 
elongated blade having proximal and distal ends and front and back 
opposing planar surfaces. These blades further include first and second 
longitudinal sides, which together with the planar surfaces, form 
generally rectangular blade configurations having an angular transverse 
distal end. At the distal end of these blades, first and second cutting 
edges are provided which extend distally from the first and second 
longitudinal sides of the gemstone to form a sharp apex for piercing into 
a cornea. The second cutting edge can be shorter than the length of the 
first cutting edge and can have a cutting depth of significantly less than 
the thickness of the cornea, about 0.500 mm and preferably less than about 
0.350 mm, with a critical minimum established at about 0.120 mm for the 
cleanest incisions. 
Accordingly, these surgical blades permit ophthalmologists to take 
advantage of the benefits of both the Russian and American radial 
keratotomy techniques. The initial incision can be performed employing the 
relatively safe American technique, while the redeepening procedure can be 
produced employing the Russian method with the second cutting edge. Since 
the second cutting edge is significantly shorter than the thickness of the 
cornea in the central corneal region, and a blunt edge is provided 
proximal to this cutting surface, the redeepening procedure presents no 
greater risk than that involved with the American technique. 
The knives of this embodiment are equipped to provide redeepening 
procedures without the surgeon lifting the knife. The incision is merely 
retraced with the second cutting edge, which tends to deepen the incision, 
while a blunt portion proximal to the second cutting edge prevents 
intrusion into the optical zone. These features substantially eliminate 
the risk of corneal puncture, as well as scarring of the superficial 
optical zone. 
In further embodiments of this invention, surgical knives are provided 
which include the above-described gemstone blades having first and second 
cutting edges located distally from the longitudinal sides of the blade. 
The blade is set in a blade holder which is sized to fit within a 
surgeon's hand and includes a foot portion for contacting and gliding over 
a peripheral portion of the cornea, while helping to maintain the blade at 
a selected incision depth. The surgical knife also preferably includes a 
micrometer for accurately setting the extension of the blade beyond the 
foot portion of the blade holder. 
This invention also provides surgical radial keratotomy procedures which 
include providing a surgical knife having a primary cutting edge and a 
second shorter cutting edge having a cutting depth of substantially less 
than the thickness of the cornea. The blade of the surgical knife is 
pierced into the cornea tissue with the sharp apex located at the distal 
tip, and an incision is made radially outward from about the optical zone, 
cutting toward the limbus. The bottom portion of the incision is then 
deepened with the second cutting edge of the blade by retracing back 
toward the optical zone, without puncturing the cornea or significantly 
optically interfering with the optical zone. The blades of this invention 
are also useful in post-radial-keratotomy enhancement procedures in which 
the blade is later reintroduced into the "old tunnels" of the wound and 
the verticle edge is used to scrape the bottom. 
Finally, blade designs are provided by this invention which are capable of 
"undercutting" the cornea beneath the optical zone at a preferred vertical 
orientation to provide further flattening of the cornea and for correcting 
as much as about 6-12 diopters, or more, of myopia. These blade 
constructions preferably include a recess along the longitudinal side of 
the blade cutting edge. This recess enables the redeepening incision to 
penetrate as much as 0.05 mm, or more, beneath the optical zone with 
potentially dramatic results in keratorefractive correction ability, 
without the associated problems of glare as no surface scarring occurs. 
The distal end of the blunt edge is spaced from a distal tip of said blade 
a distance no greater than a thickness of the corneal tissue, and is 
located distally beyond the proximal end of the primary cutting surface, 
so as to assist in minimizing penetration by the blade into the surface 
tissue of the optical zone.

DETAILED DESCRIPTION OF THE INVENTION 
Surgical blades, knives and radial keratotomy procedures are provided by 
this invention which provide ophthalmologists with equipment and 
techniques for corrective procedures having high efficacy with minimal 
risk of complications. Although keratorefractive surgical procedures are 
disclosed, the surgical blades of this invention can be used for any 
surgical, or microsurgical application which requires maneuverability and 
tactile sensitivity. 
With reference to the figures, and particularly to FIGS. 1-5 thereof, there 
is shown a preferred micrometer surgical knife 100 having a blade 10 and a 
knife body 11. As shown in the enlarged view of FIG. 2, the blade is 
affixed to the distal end 14 of the knife body 11 and is positioned at a 
preselected depth through the feet 12, which can be of the Russian, 
American, or the depicted Universal design. The micrometer 13 is helpful 
for less sensitive surgical applications and gross calibration 
measurements. This setting is generally further fine-tuned with a 
calibrating microscope to provide closer tolerances for keratotomy 
procedures. 
In the first preferred blade configuration embodied in FIGS. 3-5, a 
surgical blade 10 is provided. The blade includes a hard, corrosion 
resistant material capable of being honed or lapped into a sharp cutting 
edge. Such materials include stainless steel, glasses, ceramics, and 
crystalline materials containing natural or synthetic stones, such as 
diamonds, rubies, sapphires or similar materials of sufficient hardness. 
Although the term "gemstone" is used, the stones need not be "gem" 
quality, as industrial quality stones may be sufficient in certain 
applications. Preferably, however, the gemstone contains a natural diamond 
of a grade and internal molecular structure suitable for making flat slabs 
with proper orientation with respect to the cleaving planes. The gemstone 
is typically provided in a rough shape which is developed by laser cutting 
or sawing into a generally flat configuration. The more precise facet and 
cutting edge dimensions are thereafter applied to the diamond slab by 
cleaving and lapping. 
The preferred surgical blade 10 includes a pair of longitudinal sides and a 
distal end containing first and second cutting edges. The first cutting 
edge is desirably configured into an angled cutting edge 24 having a 
leading edge portion 27 and a trailing edge portion 21. The trailing edge 
portion 21 preferably ends at the distal end portion of the blade 10. The 
angled cutting edge 24 is provided by a pair of faces or facets 18 which 
define therebetween an angle .gamma.. The second cutting edge preferably 
includes a sharpened vertical edge 22 which forms the distal apex of the 
blade 10 and tapers proximally along tapered portion 25. The sharpened 
vertical edge 22 is defined by a pair of faces 16 which form therebetween 
an angle .OMEGA.. (As used herein, the term "vertical" is not limited to 
an edge which is perpendicular or co-planar with blunt side edge 20 or 
tapered portion 25, and this term is used generally to provide a 
comparative orientation with the disclosed angled cutting edges.) 
The blunt side edge 20 begins at transition point 23, and extends 
proximally along the second longitudinal side of the gemstone. The tapered 
portion 25 is preferably defined by faces or facets 28 having an included 
angle of about 30.degree.-55.degree.. The tapered portion 25 also presents 
a substantially blunt surface and may be cut to form a plane, or facet, 
extending at an angle of about 1.degree.-15.degree., preferably about 
3.degree.-7.degree., from blunt side edge 20 shown in FIG. 4. 
The sharpened vertical edge 22 preferably forms an angle of about 
+/-90.degree. and more preferably, an acute angle .alpha. with the second 
longitudinal side, and preferably with the blunt side edge 20 or tapered 
portion 25 of the blade 10. The angled cutting edge 24, on the other hand, 
forms a preferred acute angle .beta. formed with a perpendicular line 
drawn from the second longitudinal side. The surgical blade 10 further 
includes a length dimension C, a width dimension B and a thickness D, the 
preferred ranges of which are described in Table I further in this text. 
Alternatively, a blade 110 can be provided with most of the above features, 
including an angled cutting edge 124 and a blunt side edge 120 situated 
proximally from a sharpened vertical edge 122, but with a slight taper 
along the entire vertical edge 122 or most of the vertical edge 122. In 
this tip variation of the blade configuration of FIG. 3, the vertical edge 
122 preferably forms an angle .alpha.' of about 1.degree.-15.degree. and 
more preferably about 3.degree.-7.degree. with the blunt side edge 120, 
with the faces of the vertical edge 122 and angled cutting edge forming a 
preferred included angle of about 25.degree.-55.degree., and more 
preferably about 33.degree. and 35.degree. respectively. 
An alternative preferred surgical blade 30 will now be described with 
reference to FIGS. 6-9. The alternative surgical blade 30 includes many of 
the features associated with blade 10, but noticeably includes a recess, 
having depth measurement I, located along its second longitudinal side. 
The recess defines a recessed blunt side edge 36 more clearly described in 
FIG. 9. 
Surgical blade 30, as with predecessor blade 10, further includes a 
sharpened vertical edge 32 which forms a piercing distal tip with angled 
cutting edge 34 at the distal tip of the blade 30. The blade 30 includes 
an overall width F, and a recessed portion width H. The overall length of 
this blade is provided by measurement G, and the thickness of the blade is 
provided by measurement J. The angled cutting edge 34 has a leading and 
trailing edge portion similar to that for blade 10, and forms an angle 
.beta.' with a perpendicular line drawn from the sharpened vertical edge 
32. The faces of the angled cutting edge 34 form an included angle 
.gamma.', and the faces of the sharpened vertical edge 32 form an included 
angle .OMEGA.'. 
In the further variation of the tip configuration of the blade construction 
of FIG. 6, a blade 130 can be provided having the similar features of a 
sharpened vertical edge 132, angled cutting edge 134, and recessed blunt 
side edge 136. With this particular development, however, a small radius R 
is provided between the sharpened vertical edge 132 and the recessed blunt 
side edge 136 to provide a smooth transition between these elements. In 
practice, this will facilitate! the removal of the knife blade 130 
following redeepening of the incision. 
In still a further variation of the tip design the blade configuration 
described in FIG. 6, a blade 230 can be provided with similar features of 
a sharpened vertical edge 232, angled cutting edge 234, and recessed blunt 
side edge 236. In this embodiment, a taper is provided between the 
sharpened vertical edge 232 and the recessed blunt side edge 236. This 
taper can have an angle .theta. of approximately 3.degree.-90.degree.. In 
both of the embodiments described in FIGS. 6a and b, undercut capability 
can be provided as with blade 30. 
The alternative configurations exhibited by blades 30, 130, and 230 are 
easier to manufacture since the recessed blunt side edges can be 
configured with a laser or by conventional sawing and/or grinding methods. 
The length E of the sharpened vertical edges can thus be more precisely 
and economically controlled by employing more automated methods, than by 
the more time-consuming and less accurate lapping wheel procedures 
employed to configure the cutting facets of blade 10. 
Blades 30, 130, and 230 also provide heretofore unprecedented "undercut" 
capability, since the projected sharpened vertical edges can be directed 
beneath the optical zone 52, illustrated in FIG. 12, without creating 
optical interference or scarring at the surface of optical zone 52. As 
used herein, the "optical zone" refers to the approximate 2.5-4 mm 
diameter section of the corneal center, or the corneal region which is 
immediately above the maximum pupil diameter. Undercutting must be made 
below the surface of the cornea, since it is believed that this will avoid 
surface scarring and provide tremendous corrective ability. This 
observation is based, in part, upon radial keratotomy procedures that 
have, by erroneous manipulation of the blade, transected the optical zone. 
It has been determined that these "mistakes" created far more flattening 
of the cornea than an equivalently sized incision outside the optical 
zone. The presently described undercutting blades permit nearly perfect 
perpendicular incisions beneath the surface of the cornea, where glare is 
less of a problem, and thus, take advantage of the more significant 
corrective abilities available when flattening occurs in the optical zone 
itself. The sharpened vertical cutting edges of this invention are 
"completely" vertical (disposed at about 90.degree. with the corneal 
surface), or, are less than 15.degree., preferably less than 8.degree., 
and ideally about 3.degree.-7.degree. from being completely vertical, so 
that they can either cut perpendicularly into the cornea, or be adjusted 
slightly within the blade holder to provide a vertical cutting edge. 
Not only is the recessed blunt side edges of the "undercut" configurations 
easier to prepare, but the carefully tailored shape of these surfaces 
provides more resistance to trespassing the original incision point at the 
optical zone than blade 10, since a more controlled flat rectangular 
surface is provided. Compare, for example, FIG. 9 with FIG. 4. The tapered 
portion 25 of blade 10 has very little flat surface area just proximal of 
the sharpened vertical edge 22. This provides little assurance that the 
redeepening procedure will terminate at the original incision point. The 
controlled, large surface area of the recessed blunt side edge 36, on the 
other hand, provides much more flat surface where it is needed at its most 
distal portion closest to the sharpened vertical edge 32. This provides a 
blunter, and less intrusive configuration deeper in the corneal incision. 
The recessed blunt side edge 36 can be carefully configured by varying the 
angle .OMEGA. and depth I, to provide a myriad of sharpened vertical edge 
configurations carefully tailored to provide selected undercut and optical 
zone resistance capabilities. Preferred dimensional tolerances for the 
blades 10 and 30 of this invention are provided in Table I below. 
TABLE I 
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Preferred Diamond Dimensional Ranges 
Genesis Modified 
Dimension 
Broad Narrow Dimension 
Broad Narrow 
__________________________________________________________________________ 
A .050-.400 mm 
.120-.350 mm 
E .025-.400 mm 
.120-.350 mm 
(.215 mm target) (.215 mm target) 
B .7-2.5 mm 
1 mm F .7-2.0 mm 
1 mm 
C 3-8 mm 6 mm G 3-8 mm 6 mm 
D .1-.25 mm 
.12 mm H .695-1.5 mm 
.95 mm 
.alpha. 
1-8.degree. 
3-7.degree. 
I .005-1.5 mm 
.05 mm 
.beta. 
25-78.degree. 
45.degree. 
J .1-.25 mm 
.12 mm 
.OMEGA. 
25-45.degree. 
33.degree. 
.beta.' 
25-78.degree. 
45.degree. 
.gamma. 
30-55.degree. 
45.degree. 
.OMEGA.' 
25-45.degree. 
33.degree. 
.gamma.' 
30-55.degree. 
45.degree. 
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The preferred surgical blades 10, 110, 30, 130, and 230 of this invention 
include sharpened vertical edges 22, 122, 32, 132, and 232 and angled 
cutting edges 24, 124, 34, 134, and 234. The width measurement of the 
diamond blades B and H and the angles .beta. and .beta.' are important 
parameters in determining the depth of the primary incision created by the 
angled cutting edges during American-style radial keratotomy procedures. 
The initial radial incisions of an American procedure are about equal to 
the depth of the exposed angled cutting edge. It can be readily observed 
that larger cutting angles .beta. and .beta.' will proportionally increase 
the cutting depth for a given knife setting and blade width. Accordingly, 
the depth dimensions A and E for the preferred vertical cutting edges of 
these blades are designed to lie within the broad range of about 0.05-0.35 
mm. The lower limit, 0.05 mm, is defined by the current level of 
manufacturing ability, and the upper limit is set at a level which will be 
more than sufficient to "clear up" the remainder of corneal tissue left by 
typical American technique procedures, but safely beneath the 0.500 mm 
full corneal thickness. An upper limit of no more than about 400 mm should 
almost guarantee against superficial scarring. 
From a physician's perspective, the lower limit for the vertical edge is 
desirably no less than about 0.120 mm. This is due to the fact that 
reverse cutting edges significantly below 0.120 mm require larger .alpha. 
angles which render the vertical cutting edge difficult to maneuver by the 
surgeon. Vertical cutting edges significantly below 0.120 mm tend to plow 
rather than cleanly sever the corneal tissue. With such blades, if the 
operating surgeon does not maintain the blade precisely in the original 
incision, for example, if the blade is twisted or tilted from the 
perpendicular, the redeepening procedure may fail to retrace the bottom of 
the incision, and result in double cuts or additional trauma. 
In the American technique, the angles .beta. and .beta.' generally 
determine the depth of penetration for the primary incision for any given 
setting of the surgical blade through the feet 12. It is known, for 
example, that sharp blades having large .beta. angles approaching 
78.degree., or more, can be fabricated with known manufacturing 
techniques, but such configurations, like blades with a large .alpha. 
measurement, tend to be difficult to maneuver in the cornea. Accordingly, 
the angled cutting edge is preferably disposed at an angle .beta. and 
.beta.' of about 40.degree.-60.degree.. Such cutting edges are capable of 
severing through approximately 0.400-0.420 mm of the corneal tissue with a 
0.500 mm setting. The redeepening procedure for these types of blades 
would therefore require an exposed vertical edge of something just less 
than about 0.080-0.100 mm. 
With reference to FIGS. 10-12, preferred keratotomy procedures offered by 
this invention will now be described. As shown in FIG. 10, the knife blade 
10 extending from the preferred universal feet 12 is inserted into the 
cornea 50, and an initial incision is made starting at the optical zone 52 
and cutting toward the limbus of the eye in a first direction X. Without 
lifting the knife, the incision is retraced in a second direction Y, to 
redeepen the wound. This provides a uniform incision depth along the 
entire incision length, unlike the American-style incision. Furthermore, 
this procedure ensures a more squared-off central or leading edge at the 
base of the wound enabling not only increased efficacy, but more 
predictable results as well. The sharpened vertical edge 22 deepens the 
incision while the blunt side edge 20 prevents intrusion into the optical 
zone 52 during the retracing of the blade. 
As shown in the enlarged view of FIG. 11, the blade 10 is carefully 
configured so that the sharpened vertical edge 22 of blade 10 does not 
enter into the optical zone 52. However, in certain keratorefractive 
surgical procedures, it may be desirable to penetrate the cornea 50 
beneath optical zone 52, as shown in FIG. 12. In this application, the 
sharpened vertical edge 32 of blade 30 becomes a valuable asset. When used 
in the above-described surgical procedure, sharpened vertical edge 32 will 
not only provide a redeepening of the wound, but will penetrate beneath 
the optical zone 52 for a distance equal to the dimension I, (assuming the 
knife is held substantially perpendicularly with the surface of the cornea 
50), wherein contact of the edge of the optical zone 52 with recessed 
blunt side edge 36 prevents further penetration. This tunnels beneath the 
optical zone to lengthen the incision at its base, thereby elongating the 
incision to provide a greater degree of flattening. 
From the foregoing, it can be realized that this invention provides 
improved keratotomy procedures and blades for minimizing optical glare and 
reducing the possibility of puncturing corneal tissue. Although radial 
keratotomy procedures are described, this invention would also be suitable 
for astigmatic and other techniques. The blades of this invention are 
suitable for use with the American, Russian or combined techniques and 
provide blade designs suitable for undercutting the optical zone without 
causing glare. The specific dimensional configurations are approximate 
measurements only and the disclosed ranges are applicable to all of the 
disclosed blade configurations, despite the fact that specific ranges are 
preferred for each blade. Although various embodiments have been 
illustrated, this was for the purpose of describing, but not limiting the 
invention. Various modifications, which will become apparent to one 
skilled in the art, or within the scope of this invention described in the 
attached claims. 
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LIST OF REFERENCE NUMERALS 
______________________________________ 
10 Blade 
11 Knife Body 
12 Feet 
13 Micrometer 
14 Distal End 
16 Sharpened Vertical Edge Face 
18 Angled Cutting Edge Face 
20 Blunt Side Edge 
21 Trailing Edge Portion 
22 Sharpened Vertical Edge 
23 Transition Point 
24 Angled Cutting Edge 
25 Tapered Portion 
26 Blunt Side Edge 
27 Leading Edge Portion 
28 Tapered Portion Face 
30 Blade 
32 Sharpened Vertical Edge 
34 Angled Cutting Edge 
36 Recessed Blunt Side Edge 
50 Cornea 
52 Optical Zone 
100 Micrometer Surgical Knife 
110 Blade 
120 Blunt Side Edge 
122 Sharpened Vertical Edge 
124 Angled Cutting Edge 
130 Blade 
132 Sharpened Vertical Edge 
134 Angled Cutting Edge 
136 Recessed Blunt Side Edge 
230 Blade 
232 Sharpened Vertical Edge 
234 Angled Cutting Edge 
236 Recessed Blunt Side Edge 
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