Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Intracorneal Lens Placement Method and Apparatus
The present application is a continuation in part of copending U.S. Patent
Application No. 09/132,987, filed August 12, 1998, which is incorporated
herein by
reference.
RELATED APPLICATIONS
The present application is a continuation in part of U.S. Patent Application
No.
10/618,279, filed July 11, 2003 which is a divisional of U.S. Patent
Application 09/586,273,
filed June 2, 2000, now U.S. Patent 6,599,305 which is a continuation in part
of U.s. Patent
Application 09/132,987, filed on August 12, 1998 now U.S. Patent No.
6,083,236. It is also a
continuation in part of U.S. Patent Application 10/668,882, filed September
23, 2003 which is a
continuation in part of U.S. Patent Application 09/521,010, filed March 7,
2000 now U.S.
Patent No. 6,623,497 which is a continuation in part of U.S. Patent
Application 09/132,987,
filed August 12, 1998 now U.S. Patent No. 6,083,236. The content of each of
the
aforementioned applications and patents is incorporated herein by reference.
FIELD OF THE INVENTION
The present invention pertains to the general field of ophthalmologic surgery,
and in
particular to surgical methods and devices for corneal implantation of optical
lenses.
BACKGROUND
Numerous ophthalmic surgical procedures have been developed for correcting
imperfect visual acuity such as myopia or hyperopia. A variety of keratomes
have been
developed over recent decades, devices for performing corneal resectioning to
permit access
to inner portions of the cornea, where surgical reshaping may then be used to
permanently
correct vision defects.
Referring to Figs. 1 and 2a, a typical prior art resectioning operation will
separate
flap 6 of corneal (and epithelial) tissue 2 from eyeball 4. The outer layers
of cornea and
epithelial cells are separated and lifted away to expose the inner layers 12
of cornea 2, and
are let attached only as flap 6. Exposed interior layers 12 of cornea 2 will
to some extent
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adjust themselves, or their shape may be altered through further surgical
steps, such as laser
ablation or subsequent resectioning, to remove a contoured layer of corneal
tissue. At the
conclusion of the surgical procedure, flap 6 is typically replaced over inner
corneal tissues
12 to protect the healing tissues.
However, most such surgical reshaping is not reversible, resulting in some
risk of
creating permanent visual aberrations for the patient. A known alternative is
to surgically
prepare an opening in the cornea of an eye having visual abnormalities, and to
insert a lens
therein. Such surgery is difficult to perform accurately. Moreover, the lenses
which are
available for such vision correction are not entirely satisfactory for a
variety of reasons,
including a tendency to shift out of position after placement, to impair
transcorneal gas
diffusion, to be excessively thick, or to be unable to correct presbyopia or
astigmatism.
Accordingly, there exists a need for a method and device for correcting visual
abnormalities through surgical implantation of an appropriate corrective lens
within the
cornea an eye in such a way that the lens may be reliably placed and will
remain properly
positioned and oriented, to enable reversible correction of a wide range of
visual
abnormalities.
SUMMARY OF THE INVENTION
The present invention solves the above-noted need by providing a method and
devices for intracorneal lens placement. A specially adapted lens is implanted
in a corneal
pocket which has been precisely formed by a device which creates and shapes
the pocket to
accept and retain a lens in the cornea. Whereas in typical corrective surgery
an entire flap of
the cornea is lifted as shown in Fig. 2a to permit access for further surgical
modification of
the cornea, in vision modification according to the present invention a flap
of cornea is not
lifted, but rather a pocket is formed in the corneal tissue as shown in Fig.
2b. As much of
the corneal surface as practical is left intact to simplify healing and to
discourage movement
or loss of the inserted lens.
In order to position a lens within the cornea of an eye in a precisely
predictable and
repeatable manner, and to help retain the intended orientation and positioning
of the lens
while the eye heals from surgery, the present invention provides a corneal
pocket keratome
to create a pocket of precise dimensions in the cornea, and also a lens having
special features
to establish a close fit between the lens a.nd the corneal pocket. Both of
these pieces can be
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realized in a number of different embodiments. Moreover, the corneal pocket
keratome has
several subparts, each of which can be realized in many ways.
The lens size and shape matches the corneal pocket formed by the corneal
pocket
keratome, and provides desired focal modifications when disposed within
corneal tissue.
The lens permits sufficient gas diffusion to allow adequate oxygenation of
internal eye
tissues. In preferred embodiments, lens features create an interference fit
between the lens
and the corneal tissue at the edges of the corneal pocket to aid in retaining
the placement and
orientation of the lens. In addition to a precise fit, such retention features
of the lens may
include a material which swells when hydrated after placement within the
cornea, or
variations in the radius of the lens to form circumferential bumps. The lens
may accordingly
have an asymmetric, radially and/or axially varying focus to compensate for
the effects of
astigmatism or presbyopia, generally in addition to compensation for myopia or
hyperopia.
For some applications, lens thickness may be desirably reduced by employing a
Fresnel
intracorneal lens.
The corneal pocket keratome preferably includes a surgical unit having cutting
head
elements mounted on a keratome drive assembly, and also a control unit and a
footpedal.
During formation of a pocket in the cornea, the cutting head elements are in
intimate contact
with the subject eye, either to position the eye or to create an incision. The
control unit
supplies power and vacuum to control the surgical unit according to settings
entered by the
use, and in response to commands made using the footpedal. The surgical unit
is preferably
hand-held and easily positioned over the subject eye.
The preferred surgical unit may include four distinct elements. Three of these
are
"cutting head" elements which contact the eye during corneal surgery -- a
positioning ring
assembly, a corneal support assembly, and a corneal pocket blade assembly.
Preferably,
each of these three cutting head elements extends from the fourth element, a
keratome drive
assembly, wllich drives the corneal pocket blade assembly with respect to the
other two
cutting head elements in such a way that interference and rubbing between
parts of the
corneal pocket keratome is minimal or entirely absent near the surgical site.
It is also
preferred that each of the three cutting head elements is easily removed and
as easily
replaced onto the fourth element, the drive assembly, without a need for
tools, so the
surgeon can ensure sterility by simply replacing the cutting head elements.
Ease of
replacement also enables the surgeon to readily select different styles and
sizes of cutting
head elements, as desired for a particular operation.
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The subject eye is held in a position by a positioning device, which is
typically a
positioning ring attached to the keratome drive assembly. The positioning ring
is supplied
with vacuum which draws the eye into the ring causing the cornea to protrude
through the
ring. Then, in most applications the protruded cornea is pressed against a
corneal support
assembly which is also attached to the keratome drive assembly. The corneal
pocket blade
assembly is attached to a driving member of the keratome drive assembly such
that a corneal
pocket blade of the assembly is positioned near the corneal support assembly.
Upon
direction from the operator, the keratome drive unit imparts a compound
movement to the
corneal pocket blade through the driving member, driving the blade forward
into the cornea
while also causing the blade to oscillate laterally.
The blade preferably travels within a cutting plane which is controlled with
respect
to the corneal surface. The corneal surface is typically disposed against the
corneal support
assembly. The precise position of the cutting plane with respect to the
corneal surface may
be controlled by a guide which is supported by, and travels along with, the
corneal pocket
blade assembly and directly contacts the cornea. Alternatively, the cutting
plane may be
maintained at a known distance from the corneal support assembly. The distance
may be
controlled by a guide portion of the corneal pocket blade assembly which
interferes with the
corneal support assembly during cutting. Such interfering guide, if used, may
contact the
cornea or may be positioned to avoid such contact. The cutting plane to
corneal support
distance may also be controlled directly by the mechanical connection between
the corneal
support surface, the keratome drive assembly, and the comeal pocket blade
assembly. by
thus controlling the cutting plane with respect to a reference plane of the
corneal support
assembly, contours may be formed in the corneal support assembly which will
translate into
variations in the depth of the pocket below the corneal surface, thus
controlling the shape of
the formed pocket.
For some applications, it is desirable to practice the invention omitting the
corneal
support assembly, leaving only the positioning ring and the corneal pocket
blade assembly
in intimate contact with the subject eye. In this event the positioning ring
is stationary with
respect to the subject eye, while the corneal pocket blade is driven with
respect thereto. In
embodiments thus omitting the corneal support assembly, the thickness of the
cut is
preferably controlled by a guide which is part of the corneal pocket blade
assembly and is in
direct contact with the corneal surface tissue.
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A feature of some embodiments of the present invention is a pivotable corneal
support assembly, which may be swung out of the way while the eye is retained
by the
positioning ring to permit examination and treatment of the eye with minimal
disturbance of
the surgical setup.
In order to allow insertion of the lens, and yet facilitate its retention, the
corneal
pocket keratome preferably creates a pocket having an opening in the corneal
surface tissue
which is narrower, measured laterally to the direction of the cut, than the
maximum lateral
width of the pocket which accommodates the widest part of the lens. This is
accomplished
in the preferred embodiment by increasing the amplitude of the lateral
oscillation imparted
to the corneal pocket blade as the blade moves farther into the corneal
tissue.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a cross-section of an eye.
Fig. 2a shows a cornea with a flap of epithelial tissue lifted as in the prior
art.
Fig. 2b shows a cornea with a pocket formed below the epithelial tissue
Fig. 3 shows a surgical unit for the invention, with the cutting head elements
on a drive
assembly.
Fig. 4 shows the control unit with connections to the surgical unit and to a
foot pedal.
Fig. 5 shows the surgical unit front with cutting head elements disengaged
therefrom.
Fig. 6a shows an eyeball held against the applanator shoe by the positioning
ring, and a
blade supported by a blade fork prepared to cut a corneal pocket.
Fig. 6b is like Fig. 6a, except the blade has a guide which contacts the
applanator.
Fig. 6c shows a blade assembly with a guide contacting the obverse side of the
applanator.
Fig. 6d shows a blade assembly and guide cutting a corneal pocket without an
applanator.
Fig. 7 is a top view of a blade in a corneal pocket of an eye retained by a
positioning ring.
Fig. 8a details ari embodiment of a corneal pocket blade with guide.
Fig. 8b is a section view of Fig. 8a.
Fig. 8c details a blade having only a circumferential cross-section, with a
guide.
Fig. 8d is a section view of Fig. 8c.
Fig. 8e details a blade on a blade fork asseinbly with an applanator obverse
guide.
Fig. 8f is a section view of Fig. 8e.
Fig. 8g is a section view of a blade without a guide.
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Fig. 9a shows an applanator extended and swung up and away from the
positioning ring.
Fig. 9b shows the same applanator in the fully restrained position.
Fig. 10a shows an alternative method of swinging the applanator away.
Fig. l Ob shows a releasable locking method for the applanator of Fig. 10a.
Fig. 11 a shows the positioning ring attached to the drive assembly.
Fig. 11 b shows the details of positioning ring restraint at section l lb-1 lb
of Fig. 11a.
Fig. 12 shows a cross-section of a surgical unit using motor driven blade
oscillation.
Figs. 14a-14e show details of lenses according to the present invention.
Fig. 15 shows a prospective view of a support for a pocket keratome for use in
making a
corneal pocket.
Fig. 16 shows a prospective view of a blade assembly employing the support of
Fig. 15.
Fig. 17 shows a front view of the blade assembly of Fig. 16.
Fig. 18 is a view through Section A-A of Fig. 17.
Fig. 19 shows the detail at B of Fig. 18.
Fig. 20 shows a bottom view of the support of Fig. 15.
Fig. 21 shows a top view of the blade assembly of Fig. 16.
Fig. 22 shows a prospective view of the blade.
Fig. 23 shows a prospective view of a support for an alternative pocket
keratome for use in
making a corneal pocket.
Fig. 24 shows a prospective view of a blade assembly employing the support of
Fig. 23.
Fig. 25 shows a front view of the blade assembly of Fig. 24.
Fig. 26 is a view through Section A-A of Fig. 25.
Fig. 27 shows the detail at B of Fig. 26.
Fig. 28 shows a partial bottom view of the support of Fig. 23.
Fig. 29 shows a prospective view of the blade.
Fig. 30 shows a prospective view of a support for another alternative pocket
keratome for
use in making a corneal pocket.
Fig. 31 shows a transparent prospective view of a blade assembly employing the
support of
Fig. 30.
Fig. 32 shows a front view of the blade assembly of Fig. 31.
Fig. 33 is a view through Section A-A of Fig. 32.
Fig. 34 shows the detail at B of Fig. 33.
Fig. 35 shows a prospective view of the blade.
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DETAILED DESCRIPTION
The present invention presents means to permanently, yet reversibly, correct
defects
of vision by disposing a lens in a pocket in a cornea. Various embodiments
correct myopia,
hyperopia, astigmatism, presbyopia, or a combination of these defects.
Appropriate lenses
are provided, as well as a device to create a corneal pocket to accept these
lenses. The
correction may be permanent, if it remains satisfactory, and may also be
reversed by
removing the lens from the cornea.
We begin with an overview of a device for preparing a corneal pocket to retain
an
appropriate lens in a subject eye. Referring to Figs. 3, 4, and 5, such a
device is preferably
embodied in three separate components: surgical unit 100, footpedal 300, and
control unit
400. Surgical unit 100 has four subsections including drive assembly 110 and
three cutting
head elements: positioning ring assembly 20, optional applanator assembly 40,
and blade
fork assembly 60. Footpedal 300 communicates user commands to control unit 400
via
cable 310, and surgical unit 100 is connected to control unit 400 by
electrical cable 410 and
vacuum hose 412. Each of these items are discussed in more detail below.
Control Unit
Electrical and vacuum control are preferably provided by control unit 400 as
shown
in Fig. 4. Control unit 400 is a microprocessor-controlled unit enabling the
user to direct
operation of the actuators within drive assembly 110 and the level of vacuum
supplied to
positioning ring assembly 20 of surgical unit 100. The user may control
operation, for
example, by means of two pedal switches including in footpedal 300, in
conjunction with
three rotary input devices 450, 452, and 454 and two pushbuttons 456 and 458
on the front
panel of control unit 400. Operating parameters are displayed on the front
panel for the user
by means of numeric readouts 412, 414, and 416 and by multiple character alpha-
numeric
display 440, while speaker 434 gives audible inforination.
A microprocessor on printed circuit board 460 executes operating firmware
which is
held in reprogrammable non-volatile memory and can be reprogrammed in the
field. The
firmware allows the microprocessor system to read switch closures and the
rotation of the
rotary controls. These electronics translate operator actions into tool
control voltages which
are applied to the drive unit actuators and can be stored as presets to be
recalled as required
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by the operator. The microprocessor system also interprets the sensors and
controls the
actuators to maintain vacuum at a level set by the user.
Control unit 400 provides electric control signals to surgical unit 100 via
cable 410.
Vacuum pressure for positioning ring assembly 20 is supplied from control unit
400 via
vacuum hose 412. Control unit 400 contains vacuum reservoir 422 in which
vacuum
pressure is established by vacuum pump 420 and released by vacuum release
solenoid 426,
and the vacuum pressure is sensed by vacuum transducer 424 to give feedback to
the control
electronics. Electric control for the actuators (not shown) within drive
assembly 110 is
provided by electronic switches 436-438. Persons skilled in the art will
appreciate that there
is no limit to the variations by which control unit components may control the
surgical unit
actuators and vacuum.
Surgical Unit
Referring to Fig. 3, surgical unit 100 includes drive assembly 110 for
supporting and
driving three cutting head elements which contact the eye during surgery. The
cutting head
elements include positioning ring assembly 20, applanator assembly 40, and
blade fork
assembly 60. Surgical unit 100 is supplied electrically via cable 410, and
vacuum is
supplied to positioning ring 30 via vacuum hose 412 which attaches to vacuum
connection
tube 22.
Fig. 5 clearly delineates the three cutting head elements, including
positioning ring
assembly 20, applanator assembly 40 (not used in all embodiments), and blade
fork
assembly 60, as they are separated from drive assembly 110. Since each of
these cutting
head elements ordinarily comes into direct contact with an eye being operated
upon, it is
preferable that they be easily removed from, and replaceable on, drive
assembly 110, in
order to facilitate the use of clean and sterile elements. For the same
reason, it is also
preferable that these cutting head elements be either sterilizable or sterile
disposable.
Blade fork 70, and blade support 65 which is suspended from blade fork arms
68, are
all part of blade fork assembly 60. Blade support 65 in turn supports (or may
be one part
with) blade 67. Blade fork 70 is connected to blade fork drive arm 140 which
impels the
entire blade fork assembly 60. A dovetail or trapezoidal attachment mechanism
between
blade fork 70 and blade fork drive arm 140 is shown. Threaded spring-ball
assembly 64 in
blade fork 70 causes a ball to press into a complementary detent, not shown,
in drive arm
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140 to properly position blade fork 70 to drive arm 140. The attachment
mechanism may be
made removable with a thumbscrew 142, as shown, or by other means.
Blade fork 70 is preferably composed of titanium but many other materials are
suitable, including stainless steel. For a steam sterilization blade fork,
dimensionally stable
plastics such as polycarbonate or polysulfone are suitable, and gas or gamma
ray
sterilization is compatible with additional plastics, such as polypropylene.
Surgical Cutting Action
Figs. 6a-6d show the cutting head elements in use resectioning cornea 2.
Vacuum
pressure delivered to vacuum chamber 36 of positioning ring 30 will draw
sclera 3 and
cornea 2 of eye 4 upward such that cornea 2 is retained, and in applanator
embodiments is
pressed against the applanator shoe 50. The forward travel of blade fork arm
70 continues
until the formation of the pocket is completed. In this embodiment, blade 67
is guided
without using a guide, as in Fig. 8k.
Fig. 7 is a top view of corneal pocket 56. Blade fork assembly 70 has blade
fork
arms 68 which suspend blade support 65. Blade 67, in this case, is of a piece
with blade
support 65. Cornea 2 is held by positioning ring 30. Blade 67 has entered into
the corneal
tissue, opening the incision line 59, and has proceeded into the cornea. Blade
67 is
oscillated laterally - left and right in Fig. 7 - while it is simultaneously
driven into cornea 2
(vertically ascending in Fig. 7) at least until it reaches the point shown. As
blade 67 traveled
into cornea 2 from incision line 59 to the position shown, the amplitude of
the lateral
oscillation of the blade was increased gradually, until the blade lateral
oscillation amplitude
is maximum in the position shown, where it defines the widest portion of
pocket 56. Entry
channel edges 57 of pocket 56 are closer together at incision line 59 and
farther apart hen
they join pocket circumferential edge 55. (The small flat region of the pocket
shown at the
tip of blade 67 can be substantially eliminated, if desired, by progressively
reducing the
amplitude of the lateral oscillation of the blade while moving the blade
slightly farther into
the cornea 2.) The narrowing channel for lens insertion formed between edges
57
discourage an inserted lens from slipping out of cornea 2.
Corneal Pocket Wall Thickness Control
It is clearly desirable to precisely control the thickness of corneal
epithelial tissue
which remains above the pocket. Generally, a constant thickness of pocket wall
is desired,
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except in some cases of corneal irregularities. Returning to Figs. 6a-6d, four
embodiments
are shown which each control pocket wall thickness in a different manner.
In Fig. 6a, precise control of the spacing between applanator shoe 50 and
blade 67 is
maintained during the cut. The position of blade 67 is preferably maintained
within 0.050
mm, and even more preferably within 0.030 mm, of a selected distance from a
surface
reference plane of applanation shoe 50. In the presence of a guide (e.g. 63,
69) this distance
from blade 67 is preferably maintained within 0.5 mm and even more preferably
within 0.1
mm or less, but tolerances even larger than 0.5 mm may be acceptable,
particularly in
embodiments using a guide (e.g. 63, 69).
In order to meet these overall positioning tolerances, in embodiments without
guide
63 or 69, blade fork assembly 60 is preferably constructed to position blade
67 within Ø03
mm, and even more preferably within 0.015 mm of an intended plane known with
respect to
the surfaces where fork 70 attaches to drive arm 140. In use with guide 76,
blade fork
assembly 60 is preferably constructed to position blade 66 within 0.3 inm, or
more
preferably within 0.15 mm, of an intended plane known with respect to the
surfaces where
fork 70 attaches to drive arm 140. However, it is within the scope of the
present invention
to permit tolerances twice as large as those enumerated as preferred.
In Fig. 6b, guide 631eads just above blade 67, sliding between cornea 2 and
applanator shoe 50. The spacing between guide 63 and blade 67 thus controls
the corneal
pocket wall thickness. The perimeter of the cross-section of guide 63 is
advantageously
small, preferably less than 2 mm or at least less than 6 mm. A small cross-
sectional
perimeter conveys several advantages: it reduces the frictional interaction
between the guide
and the cornea, it localizes a deformation of the cornea to avoid pressure on
the eye
generally, and it reduces the likelihood of trapped bubbles distorting the
cornea to cause
inaccurate cuts.
In Fig. 6c, guide feature 69 rides along the obverse side of applanator shoe
50
opposite cornea 2. The spacing between guide feature 69 and blade 67, along
with the
thickness of applanator shoe 50, thus control the corneal pocket wall
thickness. It should be
noted here that in some instances it may be desirable to contour a thiclcness
of the corneal
pocket. By shaping the thickness of applanator shoe 50 as shown, the thickness
of the
resulting pocket can be shaped as desired (the pocket wall thickness will be
inverse to the
corresponding applanator shoe thickness).
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Fig. 6d shows an embodiment in which the applanator is not used. Guide 63
provides a controlled spacing from blade 67 which in turn controls the corneal
pocket wall
thickness. In Figs. 6c and 6d, the corneal tissue of the pocket can be seen
returning to
contact after passage of blade 67. In this embodiment, of course, distance
tolerances to an
applanator surface reference plane are of no concern.
Blade and Guide Construction
Figs. 8a-8g show details of various blade constructions. Blade support 65 in
each
figure is suspended between blade fork arms 68, though any means of supporting
the blade
accurately may be used. As shown in Fig. 8a and sectional view Fig. 8b, blade
67 may be
simply an edge on stainless steel blade support 65, or may be a separate
material, such as
sapphire, bonded to support 65. Blade guide 63 preferably follows the cutting
edge contours
of blade 67. The angle shown for the edge of blade 67 helps to reduce blade
drift, at least in
the case where corneal tissue is distorted by the passage of guide 63 as can
be seen in Fig.
6b. However, various blade edge geometries may be used depending on the
overall surgical
cutting circumstances.
Fig. 8c, with sectional view Fig. 8d, shows blade 67 formed as a narrow edge,
rather
than continuous with blade support 65. In this particular embodiment, blade
strip 67 is
attached by glue or welding to one side of blade support 65, while blade guide
63 is
similarly attached but to the opposite side of support 65. However, any method
of effecting
proper spacing between blade and guide is satisfactory. Both blade and guide
may, for
example, be stainless steel. Blade guide 63 in this embodiment have an oval
cross section to
increase strength to match that of blade 67. This embodiment is preferred for
forming
corneal pockets without using an applanator, and the alternative edge of blade
67 shown is
effective with the correspondingly reduced of corneal tissue distortion of
that method.
Fig. 8e and sectional view Fig. 8f detail blade construction for cutting as
shown in
Fig. 6c. Guide feature 69 rests across the top side of blade support arms 68,
and protrusion
70 rests on the obverse side of applanator shoe 50 (Fig. 6c). There is no
guide near to blade
67 in this embodiment. Although not shown, one skilled in the art will have no
difficulty
understanding that guide feature 69 may be made readily removable to allow
access to the
eye being operated on (after also moving the applanator, as described later).
Fig. 8g is very similar to Fig. 8f, with guide 69 removed. In this
configuration,
corneal pockets may be made accurately by a precision surgical unit and
precision cutting
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head elements, without a need for a guide at all. Blade 67 is supported by
blade support fork
arms 68, which are driven by the surgical unit which also supports the
applanator.
Applanator Assembly
Referring to Figs. 5, 6a, 9a, 9b, and 10a, applanation shoe 50 is that part of
applanator assembly 40 which includes the surface for restraining the cornea
during incision.
Applanator assembly 40 as shown in Figs. 5, 9a and 9b includes applanator
retention insert
42, optional hinge 44, applanation shoe support 46, and applanation shoe 50.
Applanation
shoe 50 is preferably made of a transparent and abrasion-resistant material
such as glass or
sapphire, and marked with crosshair 52, to make the cutting operation visible
to the surgeon.
If the applanator is not hinged, then insert 42 and support 46 may be subparts
of the same
part.
Applanator retention insert 42 and shoe support 46 preferably have trapezoidal
edges, and slide into mating recess 108 of drive assembly 110, where they are
located by a
threaded captive-ball spring assembly on one side, and secured by thumbscrew
114 on the
other side, in a manner similar to that described below in regard to
positioning ring retention
feature 34 of positioning ring assembly 20 (Fig. 1 lb).
As discussed above with respect to blade fork assembly 60, various materials
may be
used to construct applanator retention insert 42, applanation shoe support 46,
and
applanation shoe 50. For versions in which a guide 76 does not contact
applanation shoe 50,
abrasion resistance is less important. As above, the material chosen must be
compatible
with the method to be used to assure sterility of the element, whether a
method such as heat,
steam, gas, or gamma is used, or the element is sterile disposable. All of the
same materials
as for blade fork assembly 60 may be used, including preferably clear
materials for
applanation shoe 50.
Applanator assembly 40 is preferably able to swing out of the way to expose
the
cornea of an eyeball held in the retaining ring 30. One preferred mechanism to
permit such
swinging is shown in Figs. 9a and 9b. In Fig. 9a, applanator assembly 40 is
partly
withdrawn from recess 108 in drive assembly 110 into which it is mounted, so
that hinge 44
is exposed and applanation shoe 50, along with support 46, is enabled to swing
up,
preferably about 60 degrees, relative to applanator retention insert 42 which
remains in
recess 108. In Fig. 9b, applanator assembly 40 is fully home so that hinge 44
is captive in
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recess 108. Applanator assembly 40 is secured to drive assembly 110 by
thumbscrew 114,
which impinges on applanator retention insert 42.
A second preferred embodiment to enable swinging is shown in Fig. 10a. There,
hinge 44 permits applanation shoe 50 and support 46 to pivot away from
applanator
retention insert 42 while remaining in the same plane as insert 42. Fig. l0a
shows shoe 50
with support 46 pivoted away from applanator retention insert 42, exposing
latch feature 47.
When closed, latch feature 47 will engage spring ba1148, thereby releasably
securing the
applanator in the closed position. Fig. 10b shows a cross-sectional detail of
engaged
latching mechanism 48.
The corneal restraining surface of applanation shoe 50 may be perfectly flat,
or it
may be contoured. The blade is generally guided a controlled distance from
a"surface
reference plane" of the applanation shoe, which is the plane which "just
touches" the corneal
restraint surface, and which is parallel to the desired cutting plane.
Positioning Ring Assembly
Figs. 11 a and 11 b depicts details of positioning ring assembly 20.
Positioning ring
30 is provided with vacuum to vacuum chamber 36 so that an eyeball placed
against it may
be drawn in, distending the cornea which is then typically pressed against
applanation shoe
50 as shown in Figs. 7a - 7d. The vacuum is furnished through vacuum
connection tube 22,
with the vacuum hose (not shown) placed over vacuum connection nipple 24 and
stopped by
vacuum tube stop 26. Alternatively, vacuum may be ducted through ring support
32 and
drive assembly 110 to obviate vacuum connection tube 22, the vacuum hose 412
connected
then only to drive assembly 110 and optimally consolidated with electrical
control cable
410.
Referring to Fig. 11 a, which is a bottom view, and cross-section Fig. 11b,
positioning ring support 32 preferably includes retention feature 34 having
detent 35.
Retention feature 34 slides into matching recess 120 in drive assembly 110.
Captured ball
117 settles into detent 35 under the pressure of captured spring 115 to
properly locate
positioning ring assembly 20. Then, thumbscrew 118 secures retention feature
34, seating it
firmly against the sides of recess 120 formed in head 112 of drive assembly
110. (Note that
Fig. 11 a omits thumbscrew 114, located in head 112 opposite thumbscrew 118,
and used for
securing the applanation assembly.)
As discussed with regard to blade fork assembly 60 and applanator 40, a
variety of
materials may be used for positioning ring 20. The choice depends on whether
sterility is to
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be ensured by reuse of the element in conjunction with a sterilization method,
or by using
sterile disposable elements. Suitable materials include metals, such as
stainless steel, and
plastics, such as polycarbonate, polysulfone, polypropylene or others.
Drive Assembly
Figs. 12 & 13 show details of a preferred embodiment for surgical unit 100,
and in
particular shows details of a preferred embodiment for drive assembly 110,
which is largely
enclosed by drive assembly cover 160.
Referring to Fig. 12, the primary actuators within drive assembly 110 are
travel
motor 180 and oscillation motor 170. Travel motor 180 drives shaft 184 through
gear train
182. Clutch 190 couples a limited torque to screw 192. The rotational motion
of screw 192
is converted to linear motion by threaded traveller 194. Pivot assembly 196
couples the
motion from the forward end of traveller 194 to blade fork drive arm 140,
while permitting
drive arm 140 to oscillate rotationally about the pivot of pivot assembly 196.
Blade travel
stop adjust knob 150 preferably rotates a threaded member which adjustably
stops blade fork
drive arm 140 travel.
Drive arm 140 preferably includes portions of its top and bottom surface which
are
made closely parallel to each other and a controlled distance apart (the top
and bottom
surfaces are those most distal from the center of the drive arm 140 in the
direction parallel to
the pivot axis of pivot assembly 196, with the top surface being the farther
from positioning
ring 30). Drive arm 140 top and bottom surfaces are preferably flat to within
0.005 mm over
their travel range of 1.5 cm, and are slidably captured by bearing surfaces
136 and 138 of
drive assembly head 112. The bearing surfaces limit top-to-bottom play of
drive arm 140 to
preferably 0.01 mm or even more preferably to 0.05 mm.
Drive assembly head 112 holds applanator assembly 40 and blade fork drive arm
140
such that blade 66 is maintained a known distance away from applanation shoe
50 as it
travels, as described above in the section entitled "Blade Fork Assembly." The
tolerances
needed to establish precise relative positioning between the drive arm and the
applanator
mounting surface are preferably established by either placing shims, or by
machining head
112 (see Figs. 5, 6). This procedure may adjust either the position of bearing
surfaces 136,
138 for drive arm 140, or the position of recess 108 for applanator assembly
40. Control of
the actual blade travel and applanation shoe reference planes then further
depends on the
precise construction of those cutting head elements, discussed in their
respective sections
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above. In embodiments utilizing guide 76 (not shown) parallel to blade 66 on
blade for 70,
the distance between blade 66 and applanation shoe 50 is preferably controlled
to within +/-
0.5mm, or more preferably with +/- 0.25 mm.
Oscillation may be imparted to drive arm 140 by slider 176 which oscillates in
a
direction perpendicular to the page. Slider 176 interferes with the edges of a
groove in drive
arm 140, while the groove allows drive arm 140 to travel in and out of drive
assembly 110.
Slider 176 receives oscillation drive from oscillation motor 170 via shaft 172
and eccentric
pin 174. Eccentric pin 174 rides in a slot in slider 176 which absorbs the
vertical component
of eccentric pin 174, but transmits the lateral motion.
In order to cause a widening opening to the comeal pocket, the oscillation
lateral
travel must be gradually increased through much of the blade forward travel.
In this
embodiment, oscillation motor 170 is preferably a stepper motor, which does
not travel a
full half circle, but rather reverses direction to form gradually increasing
arcs.
Fig. 13 shows an alternative embodiment of means to impart oscillating motion
to
drive arm 140. In this embodiment drive arm 140 incorporates ferromagnetic
material 144
which is acted on by magnetic fields generated by coils 175 positioned along
the sides of
drive arm 140. A position feedback sensor may be used to precisely control the
amplitude
of the lateral oscillation. In this embodiment, if position feedback is not
used, then it is
preferred that the drive arm lateral travel be controlled by an interference
piece having a
ramped shape which allows wider travel as the drive arm extends, so that
travel is
progressively less limited (i.e. ahs a progressively increasing amplitude) as
the drive arm
extends from surgical unit 100.
Surgical Device Alternative Embodiments
It will be appreciated by those skilled in the art that many alternative
embodiments
are envisioned within the scope of the present invention. Some possible
variations of the
blade fork assembly are discussed in the blade fork assembly section above.
Variations of
other parts are discussed below, but do not represent an exhaustive survey of
possibilities;
rather, they serve as examples to show that a wide variety of mechanisms are
encompassed
within the scope of the invention.
Myriad physical configurations of the connection interface surfaces which
removably attach the blade fork assembly to the blade fork drive arm can
provide the
predictable positioning needed to practice the invention. The mating parts of
the interface
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are described herein as trapezoidal or "dovetail" but may take any form having
locating
features, including sawtooth, rectangular, eccentric oval, keyhole, or other
shapes too
numerous to enumerate.
Similarly, the means for securing the connection interface is shown herein as
a
thuinbscrew, but may be a cam locking lever, or could be accomplished by means
of:
magnetic attraction, spring-loaded detents, or tapered engaging pieces fitted
into a recess
formed partly from each of the mating parts. Any method known in the art to
disengageably
secure two pieces in a closely predictable relationship could be used.
A preferred embodiment of the applanator includes a pivot so the applanator
can be
pivoted away from the cornea. Hinges and pivots of all known types are well
within the
scope of this invention. A flexible chain, cable, strap or string could retain
the applanation
shoe when the rigid attachment is disconnected; or the applanator could be
made retractable.
Any blade fork can be used which is able to support the blade (and blade
guide, if
use) in a well-controlled position with respect to the mounting surface of the
connection
interface. The blade fork need not be a fork at all, but could support the
blade from a single
arm attached to the drive mechanism, rather than from dual arms.
A corneal support device may be a positioning ring, as discussed above, or an
applanator, or some other device to prevent the eye form moving during
surgery, while yet
permitting access to the cornea by the corneal pocket bade. For example, a
transparent
cornea support device may be shaped somewliat like a baseball batting helmet,
with the bill
pointing toward the keratome drive mechanism to permit access into the corneal
tissue, and
the edges surrounding the corneal tissue and the sclera to securely restrain
the eye. The
inside of such corneal support device, against which the central portion of
the cornea is
disposed for cutting, is then shaped as descried for the bottom of the
applanator as described
above. The top of such a corneal support device may be flat to accommodate a
guide 69 for
a corneal pocket blade as shown in Fig. 8f. Thus, a single cornea support
device may
function as both the presently preferred positioning ring and applanator
together.
It is also possible to provide a corneal pocket blade assembly which is
guided, for
example, by following channels which are rigidly connected to a corneal
support device.
Thus the present invention is not necessarily limited to the blade and support
structure which
is described herein by way of example.
A preferred embodiment of this invention includes sterile disposable or
sterilizable
disposable cutting head elements. A non-limiting variety of material choices
suitable for
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WO 2006/007545 PCT/US2005/023466
such an embodiment is- discussed above with respect to each cutting head
element. There is
no need for the various cutting head elements to be all disposable or all
permanent, but a
mixture of types is also suitable.
User commands may be recognized in any known way, including voice command
reception, and sensing user activation of sensors or switches located on the
surgical unit or
in other convenient places. The commands thus recognized may exert control
through any
combination of control elements, which may include mechanical means, direct
electrical
control, or intelligent electrical control with intelligence provided by any
means known to
the art. The command recognition and control elements could be physically
located any
accessible place, and as an example could be placed largely or entirely within
the surgical
unit.
Lenses
Figs. 14a-14e show several embodiments of lenses suitable for the present
invention.
It is not essential, but is preferred that the lens have a feature which will
cause it to remain in
the corneal pocket. In many instances, such as when astigmatism must be
corrected, it is
desirable that the lens retain the orientation it is given upon insertion.
Fig. 14a shows a lens having refractive materia1202 within a generally
circular
shaped perimeter 204. In order to both transport oxygen and create a snug fit
in a corneal
pocket, it is desirable that this lens be made of a hydrophilic material which
swells
somewhat when hydrated. Such materials, for example hydrogels, are used in
some present
contact lenses. The lens may be fully hydrated to elastically fit in the
pocket, or while at
least partly dehydrated such that subsequent hydration helps secure the fit in
the pocket.
Fig. 14b shows a lens which is preferably semi-rigid, such that interference
features
206 will interfere with corneal tissue and thus resist loss or movement within
the corneal
pocket. Fig. 14c shows an example of another shape which may be used to resist
shifts in
position after insertion. In practice, features 206, are not sharp.
The lenses shown in Figs. 14a-14c are limited somewhat in the range of vision
coiTection they can effect, due to their limited index of refraction, and
limited thicleness.
Such lenses are particularly limited in their ability to correct presbyopia.
The lens shown in
Fig. 14c is a Fresnel lens, and includes an annular series of lens sections
208 between
perimeter 204 and the central portion 209. Fresnel lenses may not be practical
as contact-
type lenses on the surface of corneas, due to their rigid surface, but may be
used within
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corneal tissue where they cannot irritate epithelial surfaces. The greater
range and control of
refraction permitted by a Fresnel lens is particularly useful for correction
of presbyopia by
the method and apparatus of the present invention. Of course, a Fresnel lens
may also be
give retention features as shown in Figs. 14b and 14c; and the annular ridges
of the Fresnel
lens will themselves resist lateral displacement.
Lenses having a single focal length are generally sufficient to correct simple
myopia
or hyperopia, and may of course be used to practice the present invention.
However, lenses
having variations in either refractive index or lens shape, or both, may be
used
advantageously as part of the present invention to establish a multifocal
lens. The focal
length of such lens is not constant, but varies across the expanse of the
lens. Such
multifocality can be used to compensate for presbyopia, by causing one portion
of the light
incoming to the eye to be focused if the source is far away, while another
portion of the light
is focused when the source is close (as when reading). Varying focal length of
toric surfaces
of the lens can be used to correct astigmatism. The present invention may be
practiced using
multifocal lenses to simultaneously correct or compensate various combinations
of defects
including myopia, hyperopia, astigmatism, and presbyopia.
The effectiveness of such varying focal lengtli lenses relies upon reliable
positioning
of the lens, as is provided by the present invention, in order to avoid
misalignment of the
lens, and to simplify adaptation to a plurality of focal lengths by the visual
processing
facilities. For example, presbyopia may be compensated by situating a small
area,
preferably less than 3 mm diameter, of focal-length reducing lens at the
center of the cornea.
Such location will have greater effect in high-light conditions (as are
typical for reading),
when the pupil is small, and proportionally less effect under lower lighting
conditions, such
as night driving, when the pupil is large. Thus the lens location with respect
to the pupil
must be maintained; and the brain will adapt more easily to a non-uniform
focus of the eye
which is at least constant.
Multifocality may be accomplished using a Fresnel lens, as described above, or
using
a non-Fresnel lens having a varying refractive shape and/or a varying
refractive index. An
non-Fresnel lens having both varying refractive index and also varying
refractive shape is
shown in cross section in Fig. 14e. The lens of Fig. 14e is preferably made of
hydrogel
material, and the refractive index of the material is changed in annular rings
from outer
annular ring 221 to central portion 234. (A top view of such a lens would
appear very much
as Fig. 14d; the lines between annular sections would be present, but not
visible.)
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The refractive index of the lens material varies slightly between each
adjacent
annular section of the lens, for example by changing the water content of the
lens as is
known. For example, outermost annular ring 221 may have a very high water
content, and a
refractive index of approximately 1.37 (to match that of the surrounding
corneal tissue).
Innermost section 234 of the lens has a lower water content, and a refractive
index of
approximately 1.46. In between, the refractive index changes between adjacent
sections in
about 0.01 refractive index steps. Thus, the refractive index of annular ring
221 is about
1.37, that of second outermost ring 222 is 1.38, and the increase continues at
each annular
ring until by annular ring 230, the index of refraction is about 1.46. This
higher index
enhances the refraction feature 214 so that a shorter focal length is effected
by that feature.
Next, the indices of refraction of annular ring 231 is about 1.445, of ring
232 about 1.43, and
of ring 233 about 1.445, and of central portion 234 about 1.46 as mentioned
above.
Representative dimensions for the lens of Fig. 14e are 0.9 mm diameter for
central section
234; 0.15 mm radius for each of annular rings 221-220 and 232-233; and 0.75 mm
radius for
annular section 231.
The variations in refractive index across the lens may enhance the focal
length
variations caused by lens contour features such as 210, 211, 212, 213, and
214. For
example, feature 210 provides a focal-length reducing section at the center of
the cornea,
which, as described above, is desirable to compensate for presbyopia by
yielding an area of
'reading' focus at the center of the pupil, and this effect is enhanced by the
relatively high
refractive index of central portion 234. Features 212 and 214 may provide
further rings of
short focal length, or may be part of a toric variation of focus to compensate
for astigmatic
defects of the subject eye, and their effects may again be aided by the
corresponding
variations in refractive index of the lens material. It will be understood by
those skilled in
the art that the actual choice of refractive contour depends upon the defects
of the eye to be
coiTected, and that Fig. 14e merely demonstrates combinations of refractive
index and
contour variations.
Variation in refractive index down to that of corneal tissue, as described,
has a
particular advantage in reducing edge glare effects. Light bounces off the
edges of lenses
(interfaces having a substantial discontinuity of index of refraction where
light hits at a
shallow angle), and may cause glare as this essentially random light enters
the eye.
However, by establishing the lens edge at an index of refraction matching that
of the
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surrounding corneal tissue, such reflected or bouncing light, and the
resulting glare, may be
reduced or eliminated.
The annular rings of varying refractive index may be established by
application of
successive layers of material to form a tubular section of lens material, from
which
individual lenses will be cut. After each successive layer of material is
disposed on the core,
cross-linking of the lens material of adjacent sections should be effected to
unify the
sections; this may be accomplished, for example, using ultraviolet or other
high energy
irradiation. In the lens of Fig. 14e, exemplary dimensions include central
portion 216 (high
index material) having a diameter of 3 mm. Ten annular rings, each 0.15 mm
thick, step the
refractive index down to that of the cornea over a radius of 1.5 mm, so that
the overall
diameter of this lens is 6 mm.
FURTHER EMBODIMENTS FOR A POCKET KERATOME
Further developments of the pocket keratome without the need for an applanator
is
discussed in U.S. Patent No. 6,623,497, the content of which is incorporated
by reference
herein (see RELATED APPLICATIONS above)
A FIRST EMBODIMENT FOR A POCKET KERATOME
In a further development the invention is a pocket keratome that will cut a
pocket in
the cornea into which a lens or other device can be inserted.
The pocket keratome has a blade support and guide member constructed as a
unitary
part to mount on a drive mechanism of the type described above that can drive
it forward
while reciprocating laterally. The term unitary part as used herein means that
it is made
from one piece of material, preferably stainless steel. In particular the
blade support and
guide member are made from one piece. The blade is mounted on the blade
support for
precise positioning with respect to the guide. Also a positioning ring as
described above is
provided.
In accordance with a major goal of a pocket keratome, the blade support and
guide
member is configured such that when assembled with the blade, it will enable a
very precise
and precisely controllable depth of cut in the cornea. The depth of cut is
controlled by
dimensions defining the distances from the guide member to the blade. Those
distances are
the vertical distance of the blade edge below the guide surface and the
spacing of the blade
edge from the rear peripheral surface of the guide.
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An embodiment of the pocket keratome is shown in Figs. 21-28. The blade
assembly is similar in some respects to those described above. For purposes of
the present
description the blade cartridge assembly 500 comprising a support 502, a blade
504 and a
screw 506. The cartridge 500 has a forward portion 508 and a rearward portion
510 which
are joined together by posts 512(a) and 512(b).
The rearward portion 510 of the blade assembly has a female dovetail
configuration
for attachment to the drive mechanism that is described above. It also has a
dependant
centrally located blade support post 514. A slot 516 is formed through the
floor 518 of the
dovetail and part way into the blade support post 514. The slot 516 allows the
dovetail to
flex so that it can be made to fit snugly and precisely on the drive
mechanism.
The posts 512 extend spaced apart at a downward slant from the rearward
portion
510 to the forward portion 508. The forward portion 508 has lower terminal
ends 520a and
520b. Extending transversely between the lower terminal ends 520a and 520b is
a guide 522
that with ends 524a and 524b being attached to the lower terminal ends 520a
and 520b
respectively. The guide 522 has a front edge 526 from which a transition
surface 528
extends to a lower surface 530 that is flat and extends transversely across
the guide 522.
Located transversely in the center of the guide 522 is a well 532 that is
semicircle and '
merges on either side with the rear surfaces 534a and 534b. The well 532 is
laterally aligned
with a slot 536 at the bottom of the blade support post 514 as further
explained below.
The slot 536 at the bottom of the blade support post 514 has a surface 540 and
opposite walls 542a and 542b, and a threaded hole 544.
The cartridge 500 has a blade 504. The blade 504 has at its rear end a fitting
stud
546 with a hole 548 and a shaft 550 extending forwardly and terminating in a
cutting edge
552. The cutting edge 552 is aligned with and is at the end of the lower
surface 554.
Behind the cutting edge 552 are fillets 560a and 560b which provide for smooth
passage of
the blade 504 into the cornea. The blade 504 has contact shoulders 556 that
help to achieve
the precise location of the blade 504 as will be appreciated. The blade 504 is
fixed to the
support 502 by the screw 506 threaded into the threaded hole 544. The blade
has a lower
surface 558.
The cutting edge 552 is shaped so as to be concentric with the well 532, in
this
exemplary form being semi-circular. The blade cutting edge extends in a semi-
circle about
180 , the same as the well 532, and having a tolerance of +0 and -10 .
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The support 502 is machined from a single piece of stainless steel. This
enables only
two tolerances to accumulate to determine the spacing of the blade cutting
edge 552 from
the well 532. In this way very close tolerances are achieved in the device.
This results in
great precision and consistency in forming the corneal pocket. In this
example, the blade
cutting edge is spaced below the wel1532 by 0.300mm +0, -0.025 and away from
the well
532 by 0.5mm 0.02. The gap thereby defined between the lower corner of the
well 532
and the blade cutting edge 552 controls the depth of the pocket cut into the
cornea. It is
possible to make this device with sufficient precision that a very exact and
consistent depth
can be achieved in the corneal pocket that is formed.
Also, by providing an elongated shaft 550 for the blade 504, and fixing it at
the rear
of the support 502 on the post 514, the blade 504 can enter the cornea away
from the center
of the eye, close to the cornea's periphery. This allows the entry cut for the
corneal pocket
to be distant from the center of the cornea where it is more benign.
In use the cartridge 500 is fitted to the drive mechanism, which also has a
positioning
ring all as described above. The positioning ring is fitted by suction to the
patient's eye.
The amount of protrusion of the cornea over the suction ring will determine
the point of
entry of the blade cutting edge 552 into the cornea. As noted, a point of
entry well away
from the center is now allowed by the long shaft 550. As the drive mechanism
moves
forward and oscillates side-to-side the cornea is prepared under the guide 522
for entry of
the cutting edge 552. The spacing of the cutting edge 552 with the well 532
will determine
the depth of the pocket cut, and the lower the tolerances that are achievable
in that spacing
the greater will be the precision and consistency of the depth of the pocket
into the cornea.
The amplitude of oscillation and blade width will ultimately determine the
width of the
pocket cut.
AN ALTERNATE POCKET KERATOME
An alternate embodiment of a corneal pocket keratome is shown in Figs. 29-35.
As
before this embodiment fits onto the drive mechanism described above that
moves forward
oscillates and side-to-side; and has a positioning ring.
The blade cartridge assembly 600 has a support 602, a blade 604, a screw 606
and
locating pins 608.
The support 602 has a rearward portion 610 with a dovetail configuration 612
to
attach it to the drive mechanism. Extending below the dovetail 612 is a blade
support post
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614 that has a mounting surface 616 on which the blade 604 is mounted. From
the rearward
portion 610, laterally spaced posts 618a and 618b extend to lower terminal
ends 620a and
620b. Supported between the lower terminal ends 620a and 620b is a guide 621
having a
curved, preferably circular transition surface 622 that merges with a lower
surface 624
extending rearward and terminating in a well 626 that merges with rear edges
28. The well
626 is preferably circular and extends to a semi-circle.
The blade 604 has an attachment zone 630 that extends vertically and is fitted
to a
vertical mounting surface 616 by use of the screw 606 and locating pins 608.
Extending at a
right angle to the attachment zone 630 is the shaft 632 that ends in the
cutting edge 634.
Because the blade support post 614 depends from the rearward portion 610, as
is the case
with the embodiment next described above, and is therefore spaced from the
well 626, a
long pocket is possible and entry away from the center of the cornea is
allowed. The cutting
edge 634 is slightly wider than the width of the shaft 632 and is in a semi-
circular shape
extending 180 . The cutting edge 634 is formed by a double bevel 636 and 638
and has
fillets 640 and 642.
The support 602 is machined from a single piece of stainless steel and is so
dimensional that the blade edge 634 is 0.15mm 0.025mm below the lower surface
624 of
the guide 621, and is concentrically 0.5 0.1 mm away from the well 626.
The pocket keratome is used in the same way described above. The positioning
ring
is set in place to allow the cornea to protrude above it and the drive is
turned on to propel the
cartridge 600 forward, as well as moving oscillating side-to-side. The guide
621 prepares
the cornea so that it is precisely positioned for entry of the blade edge 634
at a controlled,
precise, and consistent depth in the cornea.
ANOTHER ALTERNATE POCKET KERATOME
Another alternate form of the pocket keratome is shown in Figs. 36-41.
As in the above forms of the pocket keratome, this one has a blade cartridge
assembly 700 having a support 702, a blade 704 and screws 706.
The support 702 has a rearward portion 708 that has a dovetail configuration
to
attach it to the drive mechanism. Extending downwardly from the rearward
portion 708 are
spaced apart posts 710a and 710b ending in terminal ends 712a and 712b which
have
threaded holes in them or holes to allow a tight fit of a retaining element. A
guide 714
extends transversely between the terminal ends 712a and 712b. Here again the
support 702
and the guide are made from a single piece, preferably machined from a single
piece of
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stainless steel. The leading edge 716 of the guide 714 is straight and has a
curve 718 at its
lower edge to guide the cornea under its lower surface 720 to prepare the
cornea for entry of
the blade. The trailing edge of the guide 714 has a well 722 defined by
protrusion 724a and
724b.
The blade 700 has an attachment zone 726 that has curved legs 728a and 728b
attached at their extremities to the terminal ends 712a and 712b by screws or
drive-fit posts
or the like. The legs 728a and 728b merge into a central leg 730 and which
then curves
downwardly into a reverse bight 732. The blade shaft 734 extends forwardly
ending in a
cutting edge 736. The cutting edge 736 is circular and slightly wider than the
shaft 734 and
is double beveled.
When assembled, the blade cutting edge 736 will fit concentrically to the well
722.
It will be below the lower surface 720 by 0.15 0.025 mm and concentrically
spaced from
the well 722 by 0.50 0.025 mm.
In use as described above as the drive mechanism moves the blade cartridge
assembly 700 forward and oscillates from side to side the guide 714 presses on
the cornea,
into contact with the lower surface 720, preparing it for entry of the blade.
Then the blade
cutting edge 736 cuts the pocket consistently and predictably at a depth
determined by the
closely held dimensions that define the space between the lower surface 720 of
the well 722
and the blade cutting edge 736.
Exemplary embodiments of the invention are disclosed herein. Thus it will be
appreciated that various modifications, alternatives, variations, etc. may be
made without
departing from the spirit and scope of the invention as defined in the
appended claims and
equivalents. It is, of course, intended to cover by the appended claims all
such modifications
as fall within the scope of the claims literally or as equivalents.
24
