Title: Applanation lens and method for ophthalmic surgical applications
Abstract: An improved applanation lens and method for use in an interface between a patient's eye and a surgical laser system does not discolor or lose light transmittance when subjected to gamma radiation. The improved applanation lens has an applanation surface configured to contact the eye upon application of a pressure. The lens is formed of high purity silicon dioxide (SiO2) with purity great enough to resist discoloration upon prolonged irradiation by high-energy radiation such as UV, x-rays, gamma rays or neutrons, and is preferably a fused silica.
Patent Number: 6,899,707 Issued on 05/31/2005 to Scholler, et al.
| Inventors:
|
Scholler; Gordon Scott (Poway, CA);
Webb; R. Kyle (Escondido, CA)
|
| Assignee:
|
Intralase Corp. (Irvine, CA)
|
| Appl. No.:
|
896429 |
| Filed:
|
June 29, 2001 |
| Current U.S. Class: |
606/5; 606/4; 606/166 |
| Intern'l Class: |
A61B 018/18 |
| Field of Search: |
606/4- 6,166
|
References Cited [Referenced By]
U.S. Patent Documents
| 5171254 | Dec., 1992 | Sher.
| |
| 5282088 | Jan., 1994 | Davidson.
| |
| 5336215 | Aug., 1994 | Hsueh et al.
| |
| 5359373 | Oct., 1994 | Koester et al.
| |
| 5549632 | Aug., 1996 | Lai.
| |
| 5556417 | Sep., 1996 | Sher.
| |
| 5984915 | Nov., 1999 | Loeb et al.
| |
| 6140630 | Oct., 2000 | Rhodes.
| |
| 6254595 | Jul., 2001 | Juhasz et al.
| |
| 6325792 | Dec., 2001 | Swinger et al.
| |
| 2002/0103481 | Aug., 2002 | Webb et al.
| |
| Foreign Patent Documents |
| WO 01/4487/1 | Jun., 2001 | WO.
| |
Other References
Edmund Optics ‘Tech Spec for Fused Silica windows, High Performance UV
Optics-PCV; High Performance UV Optics-DCV; High Performance UV Optics-DCX; and
High Performance UV Optics-PCX.’ . http://www.edmundoptics.com/onlinecatalog/search/index.cfm.*
Dynasil "Precision Optics Materials Fabrication." http://www.dynasil.com/.*
PCT Search Report dated Sep. 12, 2002.
Mitsutoshi Ito, et al.; "Picosecond Laser In Situ Keratomileusis With a 1053-nm
Nd: YLF Laser", Journal of Refractive Surgery vol. 12 Sep./Oct. 1996.
Specifications on Lens Material from Dynasil Website, available at least as early
as May 19, 2001.
Marketing Materials for Fused Silica.
Information on the Optical Properties of Dynasil Synthetic Fused Silica, available
at least as early as May 30, 2001.
|
Primary Examiner: Farah; A.
Attorney, Agent or Firm: Fulbright & Jaworski L.L.P.
Parent Case Text
CROSS REFERENCE TO RELATED APPLICATIONS
The present application is a continuation-in-part of co-pending U.S. patent application
Ser. No. 09/772,539 filed Jan. 29, 2001, which is commonly owned by the assignee
of the present application, the entire contents of which are expressly incorporated
by reference.
Claims
1. An improved applanation device specifically adapted for forming a mechanical
interface structure between the anterior surface of a patient's cornea and a surgical
laser, the improved device comprising:
(a) a frame for holding an applanation lens onto the outer surface of the patient's
cornea;
(b) the lens being sized and shaped to be held in the frame and having an applanation
surface configured to contact the outer surface of the patient's cornea and provide
a reference surface from which the laser is able to compute a depth of focus characteristic,
said lens being formed of high purity synthetic fused silicon dioxide (SiO
2)
such that said lens does not discolor or lose light transmittance when subjected
to gamma radiation.
2. The improved applanation lens of claim 1, wherein said applanation lens has
a transmittance of greater than 90% for wavelengths of light from 275 nm-2500 nm.
3. The improved applanation lens of claim 2, wherein said applanation lens has
a transmittance of greater than 90% for a wavelength of about 1053 nm.
4. The improved applanation lens of claim 1, wherein said applanation lens has
an index of refraction of approximately 1.46.
5. The improved applanation lens of claim 1, wherein said applanation lens is
formed of an SiO
2 with a purity great enough to resist discoloration
upon prolonged irradiation by high energy radiation such as gamma rays or neutrons.
6. The improved applanation lens of claim 5, wherein said high purity SiO
2
is noncrystalline.
7. A method for applanating an anterior surface of a patient's eye and coupling
the eye to a surgical laser, the method comprising the steps of:
a. providing an interface that has been sterilized with gamma radiation, the
interface including a central orifice, and an applanation lens having top and bottom
surfaces;
b. removably coupling a suction ring to the bottom surface of the interface;
positioning the interface over an operative area of an eye, such that the suction
ring comes into proximate contact with the surface of the eye;
c. applying a suction to the suction ring to thereby stabilize the position of
the interface relative to the operative area of the eye;
d. positioning the applanation lens in proximate contact with the operative area
of the eye, said applanation lens having an applanation surface configured to contact
the eye said applanation lens being formed of high purity synthetic fused SiO
2,
such that said applanation lens does not discolor or lose light transmittance when
subjected to gamma radiation; and
e. coupling the applanation lens to the interface to thereby stabilize the position
of the lens relative to the operative area of the eye.
8. The method of claim 7, wherein said applanation lens has a transmittance of
greater than 90% for wavelengths of light from 275 nm-2500 nm.
9. The method of claim 8, wherein said applanation lens has a transmittance of
greater than 90% for a wavelength of about 1053 nm.
10. The method of claim 7, wherein said applanation lens has an index of refraction
of approximately 1.46.
11. The method of claim 7, wherein said applanation lens is formed of an SiO
2
with a purity great enough to resist discoloration upon prolonged irradiation by
high energy radiation such as gamma rays or neutrons.
12. The method of claim 7, wherein said high purity SiO
2 is noncrystalline.
Description
FIELD OF THE INVENTION
The present invention relates to an improved applanation lens for an interface
device for ophthalmic laser surgery and, more particularly, an applanation lens
formed of a material that is biocompatible with the cornea and does not discolor
and/or have reduced transmittance with respect to its ability to transmit light
energy generated by a laser beam during ophthalmic surgery. An applanation lens
is a lens with an applanation surface configured to contact the eye and applanate
or flatten the anterior surface of the eye upon application of a pressure. An applanation
lens for use with laser surgery must be relatively free from aberrations, both
spherical aberrations (which relates to points on the optical axis of the laser
beam) and coma (which relates to points that are off-axis).
BACKGROUND OF THE INVENTION
In recent years, significant developments in laser technology have led to its
application in the field of ophthalmic surgery. In particular, laser surgery has
become the technique of choice for ophthalmic surgical applications. In certain
ophthalmic laser procedures, surgeons use a mechanical device termed a microkeratome
to cut a layer of the anterior surface of the cornea in order to expose the underlying
corneal stroma to which the laser is applied. However, complications surrounding
the use of the microkeratome and its metal blade have resulted in research into
improved techniques that are performed exclusively by a laser system. Such all-laser
techniques obviate the need for mechanical devices pre- or post-operatively, and
provide significantly improved precision.
Despite these advances in laser technology, the use of such systems for ophthalmic
surgical procedures remains fraught with substantial mechanical limitations, particularly
in the area of developing a stable interface between an incident laser beam and
the eye of a patient. Ophthalmic surgery is a precision operation and requires
a very precise coupling between the surgical tool (i.e., the laser beam) and the
region to be disturbed (i.e., a portion of the patient's eye). Even a very small
movement of the eye with respect to the intended focal point of the laser beam
can not only lead to non-optimal results, but might even result in permanent damage
to non-renewable tissue within the eye, leading to precisely the opposite result
than that desired. Given that eye movement is often the result of autonomic reflex,
it should be understood that there must be some means of stabilizing the position
of a patient's eye with respect to an incident laser beam in order to avoid the
intolerable consequence of relative movement.
Heretofore, the major technique used to compensate for relative eye motion
with respect to an incident laser beam has been to have the patient focus on a
stationary target. This involves providing a visual target to the eye undergoing
surgery, and requiring that the patient retain focused on the perceived target
feature. While this technique has provided some small benefit, it places all of
the burden of minimizing relative motion upon the patient, and does not allow for
any gross autonomic reflex motions, e.g., as when the patient might be startled.
In this technique, the target provides optical interface, while the patient's conscious
responses provide the feedback mechanism.
An additional technique involves the use of an optical eye tracking apparatus,
whereby a selected eye feature is targeted for monitoring by an optical device,
and as the targeted feature displaces as the result of eye movement, its displacement
is characterized and fed into the incident laser beam control apparatus as a compensation
signal. This second technique offers a substantial improvement over the first,
particularly when it is implemented in addition to a patient-driven target focusing
mechanism. However, such systems are inordinately expensive since a second, completely
independent optical path must be provided between a patient's eye and a surgical
apparatus in order to accommodate the eye tracking apparatus. Further expense and
complexity are incurred when it is considered that an eye tracking apparatus requires
an additional software component in order to be operative, which software component
must be integrated into a laser delivery system. Considerations of interoperability
must be met as well as the provision for an automatic shutdown of the laser system
in the event of the loss of target feature lock.
Accordingly, a simple mechanical system, if properly designed, is able
to best meet the imperatives of interfacing a laser delivery system with a target
object. If the goal is to minimize relative analog motion, an analog stabilization
device would necessarily offer the most advantageous solution.
In this regard, certain mechanical stabilization devices have been proposed,
particularly,
a corneal applanation device which is the subject of U.S. patent application Ser.
No. 09/172,819, filed Oct. 15, 1998 and commonly owned by the assignee of the present
invention, the entire contents of which are expressly incorporated herein by reference.
Such a mechanical device directly couples a patient's eye to the laser's delivery
system being affixed to both the laser and the anterior surface of a patient's
cornea. The corneal coupling, in these devices, is typically implemented by lowering
an applanation fixture over the anterior surface of the cornea under pressure.
It is assumed in these forms of devices that pressure applied normal to the corneal
surface will restrict conventional motion of the cornea thereby stabilizing the
eye along a major access normal to the device.
However, although this assumption may hold true in a large number of cases,
it certainly does not have universal application. Moreover, in the cases where
it does hold, the device/cornea interface should be established with the iris centered,
for best results. The actual establishment of an effective device/corneal interface
is an exercise in trial-and-error, resulting in a great deal of frustration to
doctor and patient, as well as considerable eye fatigue. For ophthalmic laser procedures
where eye tissue is to be photodisrupted, it is extremely important for the laser
beam to be properly focused to a specific focal spot in the tissue that is to be
effected. Not only is it extremely important to have good focal definition, but
also for the focal point to have the proper dimensionality (i.e., the correct spot
diameter and shape). In order to accommodate this, it is necessary for the laser
beam to be as free from aberrations as possible. In particular, for ophthalmic
laser procedures involving the cornea, it happens that the spherical geometry of
the cornea introduces optical aberrations as a result of its shape, which are separate
and distinct from aberrations introduced by the laser's own optical system. Significantly,
these corneal induced aberrations distort the definition of the focal spot of a
laser beam as the beam is focused to a position within corneal tissue.
Due to the spherical geometry of the anterior surface of the cornea, two specific
types of aberrations are of particular importance with regard to beam distortion;
spherical aberration (which relates to points on the optical axis of the laser
beam) and coma (which relates to points that are off-axis). Spherical aberration
and coma are similar to one another in that they both arise from a failure to image
or focus optical ray traces onto the same point. Spherical aberration relates to
a distortion that can be characterized as radial in nature, with some radial directions
being stretched while other radial directions are shrunk, converting thereby, an
ideally circular spot into an elliptical spot. Coma distortion, on the other hand,
implies an elongation along one radius in the shape of a circle, resulting in a
"cometlike" shape. Accordingly, any structure which interfaces between a curved,
anterior surface of the cornea and laser delivery system must be applanatic in
nature. By definition, an applanatic lens is one that is free from both spherical
aberration and coma.
As is recognized by the present invention, applanatic refraction at the anterior
surface of the cornea can be effectively accomplished by flattening the anterior
surface. With such a corneal reconfiguration, the beam will be free of aberrations
(other than chromatic) which would otherwise result from an interface with the
cornea's native spherical anterior surface.
Because of the foregoing considerations, a simple mechanical interface device
was developed which is the subject of copending parent application Ser. No. 09/772,539.
That device is able to stabilize the eye against relative motion with respect to
a laser beam used for ophthalmic surgical procedures without relying on secondary
mechanical considerations, such as surface tension, friction, or the like. Such
a device should be able to present an optical feature to an incident laser beam
in a stable, well-characterized location, such that the beam is able to interact
with the feature without regard to opto/electronic feedback mechanisms. In addition
to maintaining a proper orientation between the eye and a laser delivery system
during ophthalmic laser surgery, such a device should applanate the eye during
surgery while reducing inter-ocular pressure during the surgical procedure. Such
a device should be easy for a clinician to affix, as well as being simple and cost
effective to manufacture and use.
Aside from structural differences, applanation lenses are unlike many other
types of lenses used in lens systems such as those described in U.S. Pat. Nos.
5,359,373 and 6,142,630, because an applanation lens is not part of an expensive
lens system and can easily be removed from mechanical interface devices. As such
applanation lenses used in the past have been disposable. Because of cost considerations
they have been formed of a polymer materials.
The preferred method of sterilization for such lenses is by gamma sterilization.
Gamma sterilization is relatively inexpensive and does not leave a residue, as
some sterilizing gases tend to do. However, it has been found that gamma radiation
at levels sufficient for sterilization (e.g., 25 kGy-40 kGy) causes problems because
it discolors polymers and certain glasses, or otherwise lowers the transmittance
of light through these materials. Transmittance as used herein refers to optical
efficiency or the ability of a material to transmit light.
Because the dose of radiation may be variable between sterilization lots,
the amount of transmittance loss is not uniform. Thus, sterilization of these materials
using gamma radiation introduces an uncontrolled variable into the system. This
is a serious problem because of the need to be able to focus the laser beam at
precise locations in or on the cornea, and to consistently deliver, a predetermined
level of energy to that location.
The variability caused by sterilization has the effect of significantly reducing
the predictability from one surgical procedure to another, and adds to the time
of a surgical procedure because the system must be recalibrated for each use. The
loss of transmittance also requires greater power depending on the reduction in
the lens's ability to transmit light.
Thus, there is also a need for an applanation lens that remains stable when
gamma radiation is applied and does not discolor or lose transmittance below 90%
for wavelengths of light from 275 nm to 2500 nm, particularly at about 1053 nm
which is the near infrared wavelength of the femtosecond laser that is preferably
used in the system in this application.
Because the applanation lens is in direct contact with the cornea of the
eye, it must be composed of a material that is biocompatible with corneal tissue.
In addition, the applanation lens material must be able to withstand the applied
laser energy without melting, oxidizing, or creating byproducts that are not compatible
with corneal tissue.
SUMMARY OF THE INVENTION
The problems described above have been solved by an improved applanation lens
for use in an interface between a patient's eye and a surgical laser system that
does not discolor or lose light transmittance when subjected to gamma radiation.
The improved applanation lens has an applanation surface configured to contact
the eye and applanate or flatten the anterior surface of the eye upon application
of a pressure. The lens is formed of high purity silicon dioxide (SiO
2).
The improved applanation lens must have a transmittance of greater than 90% for
wavelengths of light from 275 nm-2500 nm, particularly for a wavelength of about
1053 nm. The improved applanation lens is formed of SiO
2 with purity
great enough to resist discoloration upon prolonged irradiation by high-energy
radiation such as UV, x-rays, gamma rays or neutrons, and is preferably a fused silica.
The invention also includes an interface, adapted to couple a patient's eye to
a surgical laser, in which the interface includes an attachment apparatus adapted
to overlay the anterior surface of an eye and for stable engagement to the eye.
An applanation lens, which is adapted to be mounted on the attachment apparatus,
has an applanation surface configured to contact the eye and applanate or flatten
the anterior surface of the eye upon application of a pressure. The surface is
bounded by a plane and coupled to a delivery tip of the surgical laser such that
the delivery tip is referenced to the plane. The applanation lens is formed of
high purity SiO
2 and has an index of refraction of approximately 1.46.
The applanation lens must have a transmittance of greater than 90% for wavelengths
of light from 275 nm-2500 nm, particularly for a wavelength of about 1053 nm. The
applanation lens is formed of a SiO
2 with purity great enough to resist
discoloration upon prolonged irradiation by high-energy radiation such as UV, x-rays,
gamma rays or neutrons, and is preferably a fused silica.
The invention also includes a method for applanating an anterior surface of a
patient's eye and coupling the eye to a surgical laser. The method includes the
steps of (1) providing an interface, the interface including a central orifice,
and having top and bottom surfaces; (2) removably coupling a suction ring to the
bottom surface of the interface; (3) positioning the interface over an operative
area of an eye, such that the suction ring comes into proximate contact with the
surface of the eye; (3) applying a suction to the suction ring to thereby stabilize
the position of the interface relative to the operative area of the eye; (4) positioning
an applanation lens in proximate contact with the operative area of the eye, the
applanation lens having an applanation surface configured to contact the eye and
applanate or flatten the anterior surface of the eye upon application of a pressure,
the applanation lens being formed of high purity SiO
2; and (5) coupling
the applanation lens to the interface to thereby stabilize the position of the
lens relative to the operative area of the eye. The applanation lens must have
a transmittance of greater than 90% for wavelengths of light from 275 nm-2500 nm,
particularly for a wavelength of about 1053 nm. The applanation lens is formed
of SiO
2 with purity great enough to resist discoloration upon prolonged
irradiation by high-energy radiation such as UV, x-rays, gamma rays or neutrons,
and is preferably a fused silica.
BRIEF DESCRIPTION OF THE DRAWINGS
These and other features, aspects and advantages of the present invention will
be more fully understood when considered in connection with the following specification,
appended claims and accompanying drawings wherein:
FIG. 1, is an exploded, perspective illustration of the component portions of
an ocular stabilization and applanation device in accordance with the present invention;
FIG. 2, is a simplified, top plan view of the gripper/interface structure suitable
for use in connection with the ocular stabilization and applanation device of FIG. 1;
FIG. 3, is a simplified, side view of the gripper/interface structure suitable
for use in connection with the ocular stabilization and applanation device of FIG. 1;
FIG. 4, is a perspective illustration of a lens cone, interfacing with a gripper/interface
structure, and incorporating an applanation lens in accordance with the invention;
FIG. 5, is a simplified, cross-sectional illustration of an attachment ring,
suitable for use in connection with the ocular stabilization and applanation device
of FIG. 1;
FIG. 6, is a simplified, cross-sectional illustration of the attachment ring
of FIG. 5, illustrating the coupling of the attachment ring to the anterior surface
of a patient's eye, and indicating applanation of the corneal surface;
FIG. 7, is a simplified, cross-sectional illustration of a first embodiment
of an applanation lens disposed within an attachment ring;
FIG. 8, is a simplified cross-sectional illustration of the ocular stabilization
and applanation device of FIG. 1, showing operation of the device to applanate
the corneal surface of an eye.
FIG. 9, is a simplified, cross-sectional illustration of a second embodiment
of an applanation lens disposed within an attachment ring;
FIG. 10, is a simplified, semi-schematic illustration of the top surface of
a gripper/interface device and showing radial alignment guides, in accordance with
the present invention.
DETAILED DESCRIPTION OF THE INVENTION
The present invention is directed to an improved applanation lens and method
using such a lens. The improved lens can be used in any system that uses such a
lens, particularly a mechanical apparatus that performs the functions of coupling
the anterior surface of a target eye to a surgical laser and applanating said eye.
The apparatus is termed mechanical because it directly couples the mechanical surface
of an operative target, such as human corneal tissue, to a mechanical fixture of
a surgical laser system, such as the distal tip of a laser beam's delivery system.
Simply put, and in the context of a particular embodiment which will be described
in greater detail below, the apparatus is affixed to the anterior surface of a
human cornea and is affixed to the laser delivery system.
Referring initially to the exemplary embodiment of FIG. 1, an illustrative
ocular fixation and applanation device is shown in an exploded, perspective view,
and is generally indicated at
10. The ocular fixation and applanation device
(referred to herein as simply an applanation device or alternatively, a patient
interface) is an apparatus that attaches to a human eye and holds (fixes) the eye
in all three axes (x, y and z) from translational and rotational movement with
respect to the incident beam of a laser surgical device. In addition, the applanation
device allows for the cornea of the eye to be applanated by a lens (laser optic)
for efficient ophthalmic surgery. Once the eye is applanated by an external force,
the applanation device grips, holds or affixes the eye to the applanation lens,
or laser optic, during a laser surgical procedure, so as to minimize or preclude
differential motion of the human eye with respect to the laser optical path during
the laser procedure.
With regard to the exemplary embodiment of FIG. 1, the applanation device
10
comprises a number of component parts. In this regard, the applanation device
10
suitably comprises an ocular attachment ring
12, by means of which the applanation
device
10 is coupled to the eye, a gripper fixture
14, a lens cone
fixture
16 and an applanation lens
18, which in combination with
the lens cone
16 is used to applanate a patient's cornea and establish an
appropriate optical path alignment between the cornea and a laser optical path.
The component parts of the applanation device
10 are illustrated in exploded
view, and are intended to be collapsed vertically, such that each of the individual
portions of the device are in mechanical engagement with appropriate other portions,
such that the completed device is provided in a generally unitary structure. This
is not to say that the device's component parts are permanently affixed to one
another: indeed, the component parts are separable and interchangeable at will.
Rather, the applanation device
10 is intended to form a single composite
interface structure between a human cornea and a surgical laser once the component
parts have been aligned with a patient's eye and with respect to the laser delivery
system, as will be described in detail below.
As illustrated in the exemplary embodiment of FIG. 1, the attachment ring
12
forms the mechanical interface between the anterior surface of a human cornea and
the remaining structure of the applanation device. The attachment ring
12
is constructed of a flexible, hypoallergenic material such as rubber, hypoallergenic
plastic, silicone, or the like. The attachment ring
12 is substantially
annular in shape, having a generally smooth exterior surface and a highly articulated
and functional inner surface, as will be described in greater detail below. Being
annular in shape, the attachment ring
12 necessarily defines an outer diameter
(OD) and inner diameter (ID), with the inner diameter circumscribing a central
target opening
13. The absolute value of its outer diameter is not particularly
relevant to practice the principles of the present invention, but the value of
the inner diameter is suitably chosen such that when the attachment ring
12
is placed over a patient's eye, the attachment ring's central opening, defined
by the inner diameter, completely circumscribes a sufficient area of corneal tissue
such that a surgical laser procedure may be completely performed within the exposed
area without having to displace the attachment ring.
The attachment ring
12 is disposed and retained within an appropriately
shaped female-type receptacle provided in the underside of the gripper/interface
structure
14. Since the attachment ring
12 is constructed of a flexible
material, the female receptacle of the gripper structure
14 need only have
an ID of a dimension slightly smaller than the OD of the attachment ring, such
that the attachment ring may fit within the receptacle and be held in place by
compressive force.
The gripper/interface structure
14 of the exemplary embodiment of FIG.
1 is detailed in the top plan view illustration of FIG.
2 and the side view
illustration of FIG.
3. In general, the gripper/interface
14 functions
much like a clothes pin, and is constructed with a gripper portion
19, overlaying
a receiver portion
20 that is designed to receive and contain the attachment
ring
12 within a central opening
21 that passes through both the
gripper portion and the receiver portion. The gripper portion
19 is constructed
as a lever, characterized by two lever handles
22 and
24 separated
by a closure spacing
25. As the lever handles are squeezed together, the
closure spacing
25 closes and a deformation force is transmitted to two
jaws
26 and
27 surrounding the central opening
21. Applying
a deformation force causes the jaws
26 and
27 to further separate,
in turn causing the central opening to increase in area. Pinching the lever handles
22 and
24 together forces the jaws
26 and
27 to widen
sufficiently for a cylindrical object to be inserted into the now-widened central
opening
21. Once the pressure on the lever handles is relaxed and the jaws
close to their nominal position, the inside surfaces of the jaws
26 and
27 compress against the object and retain the object in position in the
central opening
21. The gripper/interface device
14 must couple the
attachment ring
12 to the lens cone fixture
16 in a relatively secure
manner and with a characterizable geometric relationship.
The receiver portion
20 is disposed below the jaws of the gripper portion
and lays in a plane parallel to that of the gripper portion. The receiver portion
is cantilevered forward from the space between the lever handles and the jaws and
is separated from the gripper jaws by a slight spacing. The receiver portion is
substantially annular in shape with the central opening
21 extending therethrough.
Thus, it will be noted that when the gripper portion jaws
26 and
27
are opened, only the central opening portion defined in the gripper portion
19
is widened. The central opening portion extending through the receiver portion
20 maintains its diameter. This particular feature allows the attachment
ring
12 to be maintained within the central opening portion of the receiving
portion, when the gripper jaws are opened. Likewise, the gripper jaws may be opened
to receive, for example, the lens cone, without disturbing or displacing the attachment ring.
In this regard, and in connection with the perspective illustration of FIG. 4,
the lens cone fixture
16 is suitably constructed as an open-sided truncated
cone-like structure, with an open, annular base ring
28 affixed to an open,
cylindrical apex ring
30 by a set of support struts
32 which extend
between the base ring
28 and the apex ring
30. The base ring
28
is larger than the apex ring
30 thereby giving the lens cone
16 its
characteristic truncated cone-like shape.
Being cylindrical in construction, the apex ring
30 will be understood
to comprise an inner
20 diameter (ID) and an outer diameter (OD), wherein
the OD is dimensioned such that it is only slightly larger than the ID of the central
opening portion
21 of the gripper portion
19 of the gripper/interface
structure
14. The lens cone structure
16 is constructed of a substantially
rigid material such as a rigid, extruded plastic, aluminum, or the like, such that
the OD of the apex ring
30 would not be expected to substantially deform
under pressure, particularly not under the compression forces applied by the jaws
of the gripper.
Accordingly, the lens cone fixture
16 would not precisely fit
into the ID of the central opening
21 of the gripper/interface structure
14 under normal circumstances. However, once compressive force is applied
to the lever handles
22 and
24, that force is applied to the remainder
of the structure, causing the jaws
26 and
27 to open and the interior
diameter of central opening
21 to increase in consequence. The OD of the
apex ring
30 of the lens cone structure
16 is able to then be inserted
into the central opening
21 of the gripper/interface structure I
4
and, when pressure is released on the lever handles
22 and
24, the
jaws
26 and
27 close upon the apex ring
30 thereby grasping
the apex ring and establishing a fixed relationship between the lens cone
16
and the gripper/interface structure
14. Since the gripper/interface structure
14 is in geometric engagement with the attachment ring
12, and since
the attachment ring
12 is coupled to corneal tissue, it should be understood
that the lens cone fixture
16 is now held in a particular spatial relationship
(alignment) with the surface of the cornea.
As will be described in greater detail below, the apex ring
30 defines
a receptacle for receiving and retaining an applanation lens
18. The applanation
lens
18 is intended to be placed in proximate contact with a human cornea,
and since it is the function of the attachment ring
12 to mechanically interface
with a human eye, it should be understood that the gripper/interface structure
14 functions to provide an alignment and coupling interface between the
lens cone fixture, including the applanation lens
18, and the attachment
ring
12, and thereby the patient's eye.
The applanation lens
18 must have good transmittance (e.g., above 90%)
for wavelengths from 275 nm to 2500 nm, preferably at 1053 nm which is the near
infrared wavelength of the preferred femtosecond laser used in conjunction with
the system described in this application. Because the applanation lens is in direct
contact with the cornea of the eye, it must be composed of a material that is biocompatible
with corneal tissue. In addition, the applanation lens material must be able to
withstand the applied laser energy without melting, oxidizing, or creating byproducts
that are not compatible with corneal tissue.
The lens
18 must also be compatible with gamma sterilization and not lose
transmittance when exposed to levels of gamma radiation used in the sterilization
process (e.g., 25 kGy-40 kGy). Gamma radiation is the preferred method of sterilization
to make a lens
18 disposable. Also, the lens
18 must be economically
available in quantities and with consistent quality to make production of a disposable
lens viable. In view of these considerations, it has been found that an applanation
lens
18 formed of high purity SiO
2, preferably fused silica,
has all of these characteristics. In particular, synthetic fused silica manufactured
by Dynasil Corporation, as Dynasil 4000 Fused Silica, is a preferred material.
With regard to the laser delivery system, it will be understood that the base
ring portion
28 of the lens cone fixture
16 is adapted to be affixed
to the distal end of a laser optical delivery system, such that the delivery system
need only be concerned with focusing an incident laser beam at a particular point
in space. As will be further described below, the surface of the applanation lens
in contact with corneal tissue (the applanation surface) is disposed at a specific
distance from the interface between the base ring and the laser delivery system,
such that the anterior corneal surface, or at least that portion in contact with
the applanation lens, is at a known specific distance from the laser delivery tip.
The surface of the cornea now resides along a plane at a distance known to the laser.
An exemplary embodiment of an attachment ring, generally indicated at
12,
is illustrated in the exemplary, cross-sectional diagrams of FIGS. 5 and 6, where
FIG. 5 illustrates the attachment ring alone, and FIG. 6 illustrates the attachment
ring as it would be applied to the anterior surface of a patient's eye. Recall
that it is the function of the attachment ring
12 to provide a primary interface
with an operative target, such as a human eye, and a laser delivery system. In
this regard, the operative target is represented as the corneal portion
34a
of a human eye
34 in the exemplary embodiment of FIG. 6, and to which
the attachment ring
12 is illustrated as being affixed. In the exemplary
embodiment of FIG. 5, the attachment ring
12 is illustrated as having an
interior and exterior portion, the exterior portion of which is characterized by
a lower skirt
36 which functions as a shroud that comes into intimate contact
with the anterior portion of the human eye
34. The shroud
36 has
a relatively thin cross-section and is deformable so as to establish and maintain
conformal contact with the anterior corneal surface. The shroud or skirt portion
36 extends upwardly into a crown surface
38 which maintains a substantially
uniform ID against deformations of the lower shroud portion
36 in response
to pressure against the shroud portion by the human eye.
The attachment ring
12 further includes an interior, annular ring member
40 which is disposed on and protrudes outwardly from the interior surface
of the attachment ring. The annular ring member
40 protrudes outwardly in
a direction normal to the interior surface of the attachment ring, on its top surface,
but is formed with a bottom surface that includes an upwardly extending cavity
42, with the cavity formed between a bottom portion of the annular ring
member
40 and a proximate portion of the interior surface of the attachment
ring
12. Thus, it should be understood that the cavity
42 formed
by the shape of the annular ring member
40 defines an annular cavity, with
its opening pointing towards the bottom, shroud or skirt portion of the attachment ring.
In the particular exemplary embodiment of FIGS. 5 and 6, the attachment ring
12
further
10 includes an attachment fitting
44 which extends, in a
radial direction, from the exterior surface of the attachment ring. The attachment
fitting
44 includes a central orifice
46, disposed along its entire
length, and which passes through the material of the attachment ring's skirt portion
36, such that a communication path is opened between the annular channel
42, at one end, and the distal end of the attachment fitting
44.
The attachment fitting
44 might be constructed of the same material as the
attachment ring; indeed the entire apparatus might be formed or molded as single
piece. Alternatively, the attachment fitting
44 might be a separate small
piece of plastic, metal, or some other material that is coupled to the attachment
ring
12 at any stage in the manufacturing or assembly process of the applanation
device
10. It should also be noted that if the attachment fitting
44
were to be constructed from the same pliant, flexible rubber, silicone or plastic
material as the attachment ring, a suitable female receptacle can be provided on
the underside of the gripper structure
14 in proximity to and extending
from the central opening
21 thereof. As the attachment ring
12 is
friction-fit into place within the gripper
14, the attachment fixture
44
is also press-fit into its corresponding female receptacle, thereby orienting and
retaining the entire attachment ring structure within the gripper
14, by
compressive force.
Additionally, and as best seen with respect to Fig. I, the attachment
fixture
44 might be accessed by inserting one side of a male-to-male fitting
coupler
45 (FIG. 1) into the central orifice
46 and coupling the
other side to a length of small diameter, medical grade tubing. The tubing is then
coupled to a vacuum source which, in turn, is then able to apply a vacuum to the
annular channel
42 through the attachment fixture
44. Alternatively,
attachment ring
12 may be configured with projections, such as "teeth",
"bumps", or some such other gripping or friction inducing structure, that would
serve to attach the attachment ring to the eye without the need for suction. In
operation, and with regard to the particular exemplary embodiment of FIG. 6, the
ocular attachment ring
12 is placed around the limbus of a patient's eye
34, such that its lower, skirt portion
36 surrounds the anterior
surface of the cornea
34a, thereby leaving free optical access to
the cornea
34a. A slight compressive force is applied to the attachment
ring, thereby deforming the skirt portion
36 in an outwardly direction,
such that it tends to conform to the shape of the corneal surface. A slight vacuum
is developed by a vacuum source or suction pump and coupled to the attachment ring
through the attachment fitting
44. As suction is applied to the attachment
fitting
44, its internal orifice
46 couples the suction to the annular
channel
42 which is now sealed-off from the external ambient environment
by corneal contact with the skirt portion
36 (forming one side of the channel)
and a contact edge
50 of the annular ring member
40 (forming the
other surface of the channel). A vacuum is thereby developed within the annular
channel
42 which, in turn, couples the attachment ring
12 to the
corneal surface
34a, thereby fixing the eye to the attachment ring
which, when it is itself coupled to the rest of the structure, as will be described
in greater detail below, fixes the eye against relative movement.
It should be noted, in connection with the embodiment of FIG. 6, that in its
preferred
form, the attachment ring
12 is affixed to the gripper structure
14,
prior to the attachment ring's being coupled to an eye. The gripper is not shown
as being already attached to the attachment ring in order that the particular structural
and functional details of the attachment ring may be shown simply and without regard
to additional and potentially confusing structure. Further, and as will be described
in greater detail below, two corneal surface shapes are depicted in the illustrated
embodiment of FIG. 6, a rounded surface
34a, indicating the normal
shape of the cornea, and a flattened surface
34b indicating the effects
of applanating the corneal surface. Applanation is discussed further in this specification,
but it is worth noting that as the gripper/ring structure is affixed to the eye
34, the structure surrounds the limbus, leaving the corneal area open to
access. The corneal surface remains substantially rounded, at this point, and is
only contoured or flattened after introduction of the applanation cone
16
into the gripper and contact is made between the applanation lens
18 and
the cornea
34a. The applanated corneal surface
34b then
takes on a shape imposed by the shape of the contact surface (applanation surface)
of the applanation lens.
In the particular exemplary embodiment of FIG. 6, the vacuum or suction developed
by the vacuum source or suction pump is transmitted to the attachment fitting
44
by small-bore tubing. The suction might be applied by coupling the tip of a syringe
to the attachment fitting
44 and by introducing a vacuum in the body of
the syringe. That vacuum is transmitted to the attachment ring by a small-bore
tubing, a blunt canula, or the like. All that is required is that a vacuum (partial
or otherwise) be formed within the annular channel
42 such that it is able
to provide a coupling force between the attachment ring and the corneal surface.
Turning now to FIG. 7, it will be appreciated that the lens cone
16
affords similar functionality to the attachment ring
12, in that the lens
cone
16 provides the primary interface and attachment between the applanation
device (
10 of FIG. 1) and the delivery tip of a surgical laser system. In
this regard, the base ring
28 is rigidly coupled to the laser delivery system.
Attachment between the two structures may be made in a number of ways, while remaining
within the scope of the invention. In particular, the base ring
28 may be
provided with slot-shaped cutouts which are mated with retaining pins provided
on the delivery system, with the base ring being inserted over the pins and rotated
in order to create an interlock. Alternatively, the base ring can be screwed into
place on the delivery tip or, the delivery tip might be provided with rotatable
"dogs" which are rotated into place over the base ring
28 thereby securing
the base ring into position. The means by which the base ring and thus the lens
cone
16 are affixed to the delivery tip is not particularly material to
practice the principles of the invention. All that is required is that the lens
cone
16 be affixed to the delivery tip such that it is incapable of independent
relative movement with respect to the delivery tip. In this regard, it should be
noted that the base ring has a top surface defining a generally horizontal plane
(an x, y plane). The delivery tip is provided with a similar planar surface which
is mated with the planar base ring surface. An x, y plane defining one aspect of
ocular applanation is thereby established.
As illustrated in the exemplary, cross-sectional diagram of FIG. 7, the lens
cone's
apex ring
30 extends downwardly away from the base ring
28 and is
held in a particular spatial relationship by struts
32, extending between
the apex ring
30 and the base ring
28. The base ring
30 is
a substantially cylindrical structure with outer and inner wall surfaces and with
a wall thickness sufficient to support reasonable rigidity under compressive stress.
An applanation lens
18 is disposed within the apex ring
30 and has
an OD substantially the same as the ID of the apex ring such that it fits into
the apex ring and rests against the ring's interior wall surface. The applanation
lens
18 is then bonded into place forming a generally unitary structure
with the lens cone
16. The applanation lens
18 is formed with an
anterior surface
64 and an applanation surface
66. It is to be appreciated
that both the anterior surface
64 and the applanation surface
66
are substantially flat and substantially parallel to one another.
Manufacture of the lens cone involves bonding and alignment of the applanation
lens
18 to the apex ring
30. Both of these operations (bonding and
alignment) are performed at substantially the same time. The lens cone
16
is placed in registration with an alignment and bonding fixture, termed a "golden
pedestal". The golden pedestal has a horizontal alignment plane (an x, y plane)
which is positioned parallel to the x, y plane defining the base ring
28.
An applanation lens
18 is positioned on the golden pedestal such that its
parallel anterior and applanation surfaces lie in the x, y plane defined by the
pedestal and, thus the base ring. The lens cone is lowered over the lens until
the lens is positioned within the apex ring portion, all the while maintaining
the relationship between the various x, y planes. When the lens is in position,
it is bonded, with a suitable glue, such as a UV curing cement, to the inside surface
of the apex ring, thereby fixing the applanation lens in a specific plane, with
respect to the base ring, and at a specific distance from the base ring. Accordingly,
it will be appreciated that the applanation lens is established in a specific x,
y plane and at a specific z distance from the base ring, itself established in
a specific x, y plane and at a specific z distance from the delivery tip of a surgical
laser. A known spatial relationship between the laser and the applanation surface
of the applanation lens is thereby defined.
The lower, contact, or applanation, surface of the applanation lens is disposed
in space in a particular relationship with the laser delivery tip. The contact
surface provides a reference surface from which the laser system is able to compute
a depth of focus characteristic. Since the position of the contact surface is known,
with respect to the delivery tip, so too is the position of the applanated corneal
surface. It is, therefore, a relatively straightforward matter to focus a laser
beam to any point within the cornea. One needs only to calculate the focal point
with respect to the contact surface of the lens, in order that the same focal point
be obtained within the eye.
Aligning the lens into position with respect to the lens cone structure
by use of a "golden pedestal" allows alignment tolerances which are substantially
tighter than those currently obtainable by conventional microkeratome techniques.
Conventional microkeratomes typically exhibit off-plane errors in the range of
about +/-30 to +/-40 microns. This alignment error leads to planar tilt in the
corneal flap, and to potentially dangerous flap thickness variations. For example,
if a flap were created with a 30 to 40 micron error, in the positive thickness
direction, there exists the possibility that the remaining corneal bed would not
be sufficiently thick to safely conduct a laser ablation procedure. Instead the
cornea would tend to bulge outward, in response, leading to a less than optimum
surface shape being presented for subsequent laser surface ablation. Indeed, it
is the very scale of microkeratome depth uncertainty that contributes to the significant
percentage of conventional laser surgery failures.
The "golden pedestal" registration and alignment system allows for planar (in
both the x, y plane and the z direction) alignment tolerances no greater than that
of a conventional microkeratome, i.e., in the range of about +/-30 microns, and
preferably in the range of about +/-10 microns. This is measured with respect to
both the planar "tilt" and the z position of the applanation surface of the applanation
lens with respect to the defined plane of the base ring and, therefore, with respect
to the laser's delivery tip. This is particularly advantageous when it is considered
that the applanation surface is devised to be co-planar with the anterior surface
of the cornea, thereby defining a corneal surface which is mathematically calculable
and precise with respect to the laser delivery tip: the x,y plane of the corneal
surface is known and the z distance from the tip to the surface is also known.
Thus, a precise cut may be made within the corneal material without concern for
potentially dangerous depth variation.
Turning now to FIG. 8, an exemplary embodiment of the complete ocular fixation
device
10, as it would be attached to a human eye, is illustrated in cross-sectional
form. The lens cone
16 is coupled to the attachment ring
12, thereby
coupling a patient's eye
34 to the laser delivery system, by interfacing
the two structures together by the gripper/interface
14. As previously mentioned,
the apex ring
30 has an OD sized just slightly larger than the ID of the
gripper's annular mating portion
20, such that the apex ring
30 can
be inserted into the central opening
21 of the gripper
14, when the
jaws of the gripper are opened. The apex ring is inserted into the central opening,
pressure released on the gripping structures
22 and
24 thereby allowing
the jaws to relax and to close around and grip the apex ring
30 securely
within the gripper's central opening. As illustrated in the exemplary embodiment
of FIG. 8, as the apex ring
30 is inserted into the central opening of the
gripper, the applanation surface of the applanation lens makes contact with a presented
portion of the anterior surface of the cornea
34b, As the lens cone
is lowered into proximity with the cornea, the applanation surface of the lens
makes contact with the cornea and applies a pressure to the cornea such that when
the lens cone is fully lowered into position, the corneal anterior surface
34b
and the applanation surface
66 of the lens are in intimate contact with
one another over a substantial portion of the applanation surface. Mechanical pressure
of the lens causes the corneal surface to conform to the shape of the applanation
surface of the lens. Although depicted in the exemplary embodiment of FIG. 8 as
being flat, the cornea may be formed as a concave or convex surface, depending
only on the shape of the contact surface of the applanation lens.
In summary, the attachment ring
12 is placed around the limbus of the
eye,
i.e., centered
10 about the cornea and the pupillary aperture. The gripper
14 has been previously affixed to the attachment ring
12, such that
positioning the ring with respect to the eye also positions the eye with respect
to the gripper's central opening, with the pupillary aperture generally centered
within the gripper's opening. Suction is then applied to the ring in order to attach
the ring onto the eye. With the eye so presented and held in place by the attachment
ring
12, it becomes a relatively simple matter to lower the lens cone and
applanation lens into proximate contact with the cornea, and
