U.S. patent application number 13/732720 was filed with the patent office on 2013-05-09 for system and method for correcting higher order aberrations with changes in intrastromal biomechanical stress distributions.
The applicant listed for this patent is Josef F. Bille, Frieder Loesel, Luis Antonio Ruiz. Invention is credited to Josef F. Bille, Frieder Loesel, Luis Antonio Ruiz.
Application Number | 20130116675 13/732720 |
Document ID | / |
Family ID | 42169430 |
Filed Date | 2013-05-09 |
United States Patent
Application |
20130116675 |
Kind Code |
A1 |
Bille; Josef F. ; et
al. |
May 9, 2013 |
System and Method for Correcting Higher Order Aberrations with
Changes in Intrastromal Biomechanical Stress Distributions
Abstract
A method for correcting higher order aberrations in an eye
requires Laser Induced Optical Breakdown (LIOB) of stromal tissue.
In detail, the method identifies at least one volume of stromal
tissue in the eye, with each volume defining a central axis
parallel to the visual axis of the eye. Thereafter, a pulsed laser
beam is focused to a focal spot in each volume of stromal tissue to
cause LIOB of stromal tissue at the focal spot. Further, the focal
spot is moved through the volume of stromal tissue to create a
plurality of incisions centered about the respective central axis
of the volume. As a result, a predetermined selective weakening of
the stroma is caused for correction of the higher order
aberration.
Inventors: |
Bille; Josef F.;
(Heidelberg, DE) ; Loesel; Frieder; (Mannheim,
DE) ; Ruiz; Luis Antonio; (Bogota, CO) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Bille; Josef F.
Loesel; Frieder
Ruiz; Luis Antonio |
Heidelberg
Mannheim
Bogota |
|
DE
DE
CO |
|
|
Family ID: |
42169430 |
Appl. No.: |
13/732720 |
Filed: |
January 2, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
12360715 |
Jan 27, 2009 |
8366701 |
|
|
13732720 |
|
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|
|
Current U.S.
Class: |
606/5 |
Current CPC
Class: |
A61F 9/00827 20130101;
A61F 9/008 20130101; A61F 9/00829 20130101; A61F 2009/0088
20130101; A61F 2009/00897 20130101; A61F 2009/00895 20130101; A61F
2009/00857 20130101; A61F 2009/00872 20130101 |
Class at
Publication: |
606/5 |
International
Class: |
A61F 9/008 20060101
A61F009/008 |
Claims
1-17. (canceled)
18. A method for correcting unsymmetrical aberrations in an eye,
wherein the eye defines a visual axis and the method comprises the
steps of: identifying at least one volume of stromal tissue in the
eye, wherein the volume of tissue defines a central axis located at
a distance from the visual axis of the eye and oriented
substantially parallel thereto; focusing a pulsed laser beam to a
focal spot in the volume of stromal tissue to cause Laser Induced
Optical Breakdown (LIOB) of stromal tissue at the focal spot; and
moving the focal spot of the pulsed laser beam through the volume
of stromal tissue to create at least one incision centered about
the respective central axis of the volume, to cause a predetermined
selective weakening of the stroma for correction of the
unsymmetrical aberration.
19. A method as recited in claim 18 wherein the unsymmetrical
aberration is astigmatism.
20. A method as recited in claim 18 wherein the at least one
incision forms an arc segment on a cylindrical surface centered on
the central axis.
21. A method as recited in claim 18 wherein each volume of stromal
tissue is bounded by Bowman's membrane and wherein each incision is
at least ten microns from Bowman's membrane.
22. A method as recited in claim 21 wherein each volume of stromal
tissue is further bounded by the endothelium and wherein each
incision is at least 150 microns from the endothelium.
23. A method as recited in claim 18 wherein the at least one volume
of stromal tissue is two volumes of stromal tissue.
24. A method as recited in claim 18 wherein the at least one
incision is one incision.
25. A method as recited in claim 18 wherein each incision is
created to form a rectangular cylinder centered on the respective
central axis.
26. A method for correcting unsymmetrical aberrations in an eye,
wherein the eye defines a visual axis and the method comprises the
steps of: identifying at least one volume of stromal tissue in the
eye, wherein the volume of tissue defines a central axis located at
a distance from the visual axis of the eye and oriented
substantially parallel thereto, and wherein each volume has an
anterior surface located at least ten microns from Bowman's
membrane and a posterior surface located approximately 150 microns
from the endothelium of the cornea; focusing a laser beam to a
focal spot in the volume of stromal tissue to cause Laser Induced
Optical Breakdown (LIOB) of stromal tissue at the focal spot; and
moving the focal spot of the laser beam within the volume of
stromal tissue to create at least one incision centered about the
respective central axis of the volume, to cause a predetermined
selective weakening of the stroma for correction of an
unsymmetrical aberration.
27. A method as recited in claim 26 wherein the unsymmetrical
aberration is astigmatism.
28. A method as recited in claim 26 wherein the at least one
incision forms an arc segment on a cylindrical surface centered on
the central axis.
29. A method as recited in claim 26 wherein the at least one volume
of stromal tissue is two volumes of stromal tissue.
30. A method as recited in claim 26 wherein the at least one
incision is one incision.
31. A method as recited in claim 26 wherein each incision is
created to form a rectangular cylinder centered on the respective
central axis.
32. A system for correcting unsymmetrical aberrations in an eye,
wherein the eye defines a visual axis, the system comprising: a
means for identifying at least one volume of stromal tissue in the
eye, wherein the volume of tissue defines a central axis located at
a distance from the visual axis of the eye and oriented
substantially parallel thereto; a means for generating a pulsed
laser beam, wherein the duration of each pulse in the beam is less
than one picosecond; a means for focusing the laser beam to a focal
spot in each volume of stromal tissue to cause Laser Induced
Optical Breakdown (LIOB) of stromal tissue at the focal spot; and a
means for moving the focal spot of the laser beam within each
volume of stromal tissue to create at least one incision centered
about the respective central axis of each volume, to cause a
predetermined selective weakening of the stroma for correction of
the unsymmetrical aberration.
33. A system as recited in claim 32 wherein the unsymmetrical
aberration is astigmatism.
34. A system as recited in claim 32 wherein the at least one
incision forms an arc segment on a cylindrical surface centered on
the central axis.
35. A system as recited in claim 32 wherein each volume of stromal
tissue has an anterior surface located at least ten microns from
Bowman's membrane and a posterior surface located approximately 150
microns from the endothelium of the cornea.
36. A system as recited in claim 32 wherein the at least one volume
of stromal tissue is two volumes of stromal tissue.
37. A system as recited in claim 32 wherein the at least one
incision is one incision.
Description
[0001] This application is a continuation of application Ser. No.
12/360,715 filed Jan. 27, 2009, which is currently pending. The
contents of application Ser. No. 12/360,715 are incorporated herein
by reference.
FIELD OF THE INVENTION
[0002] The present invention pertains generally to methods for
performing intrastromal ophthalmic laser surgery. More
particularly, the present invention pertains to laser surgery to
correct higher order aberrations in an eye. The present invention
is particularly, but not exclusively, useful as a method for
correcting higher order aberrations in an eye wherein incisions
centered about a plurality of axes parallel to the visual axis
cause a predetermined selective weakening of the stroma via changes
in intrastromal biomechanical stress distributions.
BACKGROUND OF THE INVENTION
[0003] The cornea of an eye has five (5) different identifiable
layers of tissue. Proceeding in a posterior direction from the
anterior surface of the cornea, these layers are: the epithelium;
Bowman's capsule (membrane); the stroma; Descemet's membrane; and
the endothelium. Behind the cornea is an aqueous-containing space
called the anterior chamber. Importantly, pressure from the aqueous
in the anterior chamber acts on the cornea with bio-mechanical
consequences. Specifically, the aqueous in the anterior chamber of
the eye exerts an intraocular pressure against the cornea. This
creates stresses and strains that place the cornea under
tension.
[0004] Structurally, the cornea of the eye has a thickness (T) that
extends between the epithelium and the endothelium. Typically, "T"
is approximately five hundred microns (T=500 .mu.m). From a
bio-mechanical perspective, Bowman's capsule and the stroma are the
most important layers of the cornea. Within the cornea, Bowman's
capsule is a relatively thin layer (e.g. 20 to 30 .mu.m) that is
located below the epithelium, within the anterior one hundred
microns of the cornea. The stroma then comprises almost all of the
remaining four hundred microns in the cornea. Further, the tissue
of Bowman's capsule creates a relatively strong, elastic membrane
that effectively resists forces in tension. On the other hand, the
stroma comprises relatively weak connective tissue.
[0005] Bio-mechanically, Bowman's capsule and the stroma are both
significantly influenced by the intraocular pressure that is
exerted against the cornea by aqueous in the anterior chamber. In
particular, this pressure is transferred from the anterior chamber,
and through the stroma, to Bowman's membrane. It is known that how
these forces are transmitted through the stroma will affect the
shape of the cornea. Thus, by disrupting forces between
interconnective tissue in the stroma, the overall force
distribution in the cornea can be altered. Consequently, this
altered force distribution will then act against Bowman's capsule.
In response, the shape of Bowman's capsule is changed, and due to
the elasticity and strength of Bowman's capsule, this change will
directly influence the shape of the cornea.
[0006] It is well known that all of the different tissues of the
cornea are susceptible to LIOB. Further, it is known that different
tissues will respond differently to a laser beam, and that the
orientation of tissue being subjected to LIOB may also affect how
the tissue reacts to LIOB. With this in mind, the stroma needs to
be specifically considered.
[0007] The stroma essentially comprises many lamellae that extend
substantially parallel to the anterior surface of the eye. In the
stroma, the lamellae are bonded together by a glue-like tissue that
is inherently weaker than the lamellae themselves. Consequently,
LIOB over layers parallel to the lamellae can be performed with
less energy (e.g. 0.8 .mu.J) than the energy required for the LIOB
over cuts that are oriented perpendicular to the lamellae (e.g. 1.2
.mu.J). It will be appreciated by the skilled artisan, however,
that these energy levels are only exemplary. If tighter focusing
optics can be used, the required energy levels will be
appropriately lower. In any event, depending on the desired result,
it may be desirable to make only cuts in the stroma. On the other
hand, for some procedures it may be more desirable to make a
combination of cuts and layers.
[0008] As implied above, reshaping of the cornea by weakening
tissue in the stroma can be an effective way to provide refractive
corrections that will improve a vision defect. Not all vision
defects, however, are caused by aberrations that are symmetrical
with respect to the visual axis. Indeed, the higher order
aberrations are typically asymmetrical. Accordingly, it may be
necessary to weaken tissue in volumes that are offset from the
visual axis. With all of this in mind, and as intended for the
present invention, refractive surgery is accomplished by making
incisions in the stroma centered about axes parallel to the visual
axis to induce a redistribution of bio-mechanical forces that will
reshape the cornea.
[0009] In light of the above, it is an object of the present
invention to provide methods for correcting higher order
aberrations through changes in intrastromal biomechanical stress
distributions for improvement of a patient's vision. Another object
of the present invention is to provide methods for correcting
higher order aberrations that require minimal LIOB of stromal
tissue. Still another object of the present invention is to provide
methods for performing ophthalmic laser surgery that create
incisions having a same pattern at selected locations about the
visual axis. Yet another object of the present invention is to
provide methods for correcting higher order aberrations via
ophthalmic laser surgery that are relatively easy to implement and
comparatively cost effective.
SUMMARY OF THE INVENTION
[0010] In accordance with the present invention, methods for
correcting higher order aberrations in an eye via intrastromal
ophthalmic laser surgery are provided that cause the cornea to be
reshaped under the influence of intrastromal bio-mechanical stress
distributions. Importantly, for these methods, at least one volume
of stromal tissue is identified for operation. Structurally, each
operational volume extends posteriorly from about ten microns below
Bowman's membrane to a substantial depth into the stroma that is
about 150 microns from the endothelium. Further, each operational
volume defines a central axis that is parallel to and located at a
distance from the visual axis of the eye.
[0011] In general, the method of the present invention requires the
use of a laser unit that is capable of generating a so-called
pulsed, femtosecond laser beam. Stated differently, the duration of
each pulse in the beam will approximately be less than one
picosecond. When generated, this beam is focused onto a focal spot
in the volume of stromal tissue. The well-known result of this is a
Laser Induced Optical Breakdown (LIOB) of stromal tissue at the
focal spot. In particular, and as intended for the present
invention, movement of the focal spot within each volume of stromal
tissue creates a plurality of incisions that are centered about the
respective central axis of the volume. The purpose here is to cause
a predetermined selective weakening of the stroma for correction of
the higher order aberration. Preferably, each incision has a same
pattern. For purposes of the present invention, "incision" may
refer to a location of weakened or eliminated tissue along the path
of the focal point.
[0012] In certain embodiments, various volumes of stromal tissue
with corresponding central axes are identified. For each
embodiment, the central axes are arranged equidistant from the
visual axis. Geometrically, the respective incisions may form
concentric cylinders that are centered on the respective central
axis. Other incision shapes may, however, be used. For example, the
incisions may be concentric cylinder sections centered on the
central axis, or they may be rectangular cylinders centered on the
central axis, or they may be crosses that are centered on the
central axis. In certain embodiments, the incisions will each have
a thickness of about two microns.
[0013] In accordance with the present invention, various procedures
can be customized to treat identifiable refractive imperfections.
Specifically, in addition to specific incisions alone, the present
invention contemplates using combinations of various types of
incisions. In each instance, the selection of incisions will depend
on how the cornea needs to be reshaped.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] The novel features of this invention, as well as the
invention itself, both as to its structure and its operation, will
be best understood from the accompanying drawings, taken in
conjunction with the accompanying description, in which similar
reference characters refer to similar parts, and in which:
[0015] FIG. 1 is a cross-sectional view of the cornea of an eye
shown in relationship to a schematically depicted laser unit;
[0016] FIG. 2 is a cross-sectional view of the cornea showing a
defined operational volume in accordance with the present
invention;
[0017] FIG. 3 is a front view of a stroma centered on the visual
axis and illustrating a plurality of operational volumes, with each
operational volume having a plurality of incisions.
[0018] FIG. 4 is a perspective view of a plurality of cylindrical
surfaces where laser incisions can be made by LIOB;
[0019] FIG. 5 is a cross-sectional view of incisions on the
plurality of cylindrical surfaces, as seen along the line 5-5 in
FIG. 4, with the incisions shown for a typical treatment of
presbyopia;
[0020] FIG. 6A is a cross-sectional view of the plurality of
cylindrical surfaces as seen along the line 6-6 in FIG. 4 when
complete incisions have been made on the cylindrical surfaces;
[0021] FIG. 6B is a cross-sectional view of the plurality of
cylindrical surfaces as seen along the line 6-6 in FIG. 4 when
partial incisions have been made along arc segments on the
cylindrical surfaces for the treatment of astigmatism;
[0022] FIG. 6C is a cross-sectional view of an alternate embodiment
for incisions made similar to those shown in FIG. 6B and for the
same purpose;
[0023] FIG. 6D is a cross-sectional view of an alternate embodiment
for incisions;
[0024] FIG. 6E is a cross-sectional view of an alternate embodiment
for incisions; and
[0025] FIG. 7 is a cross-sectional view of a cornea showing the
bio-mechanical consequence of making incisions in the cornea in
accordance with the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0026] Referring initially to FIG. 1, it will be seen that the
present invention includes a laser unit 10 for generating a laser
beam 12. More specifically, the laser beam 12 is preferably a
pulsed laser beam, and the laser unit 10 generates pulses for the
beam 12 that are less than one picosecond in duration (i.e. they
are femtosecond pulses). In FIG. 1, the laser beam 12 is shown
being directed along the visual axis 14 and onto the cornea 16 of
the eye. Also shown in FIG. 1 is the anterior chamber 18 of the eye
that is located immediately posterior to the cornea 16. There is
also a lens 20 that is located posterior to both the anterior
chamber 18 and the sclera 22.
[0027] In FIG. 2, five (5) different anatomical tissues of the
cornea 16 are shown. The first of these, the epithelium 24 defines
the anterior surface of the cornea 16. Behind the epithelium 24,
and ordered in a posterior direction along the visual axis 14, are
Bowman's capsule (membrane) 26, the stroma 28, Descemet's membrane
30 and the endothelium 32. Of these tissues, Bowman's capsule 26
and the stroma 28 are the most important for the present invention.
Specifically, Bowman's capsule 26 is important because it is very
elastic and has superior tensile strength. It therefore,
contributes significantly to maintaining the general integrity of
the cornea 16.
[0028] For the methods of the present invention, Bowman's capsule
26 must not be compromised (i.e. weakened). On the other hand, the
stroma 28 is intentionally weakened. In this case, the stroma 28 is
important because it transfers intraocular pressure from the
aqueous in the anterior chamber 18 to Bowman's membrane 26. Any
selective weakening of the stroma 28 will therefore alter the force
distribution in the stroma 28. Thus, as envisioned by the present
invention, LIOB in the stroma 28 can be effectively used to alter
the force distribution that is transferred through the stroma 28,
with a consequent reshaping of the cornea 16. Bowman's capsule 26
will then provide structure for maintaining a reshaped cornea 16
that will effectively correct refractive imperfections.
[0029] While referring now to FIG. 2, it is to be appreciated that
an important aspect of the present invention is the identification
of operational volumes 34 which are defined in the stroma 28.
Although the operational volumes 34 are shown in cross-section in
FIG. 2, they are actually three-dimensional, and extends from an
anterior surface 36 that is located at a distance 38 below Bowman's
capsule 26, to a posterior surface 40 that is located at a distance
41 from the endothelium 32. Both the anterior surface 36 and the
posterior surface 40 essentially conform to the curvature of the
stroma 28. For a more exact location of the anterior surface 36 of
the operational volumes, the distance 38 will be about ten microns.
For the posterior surfaces 40, the distance 41 will be about
one-hundred-fifty microns.
[0030] In FIG. 3, incisions 44a-44f are made in a plurality of
operational volumes 34a-34f as envisioned for the present
invention. Although six different volumes 34a-34f are shown in FIG.
3 (also FIGS. 6D and 6E) it will be appreciated by the skilled
artisan, this is only exemplary and presented here for purposes of
disclosure. More specifically, for third order aberrations only
three volumes 34 need to be identified. In any event, the exact
number of volumes 34, and their respective radial distances from
the visual axis 14 for any specific higher order aberration can be
ascertained from the well known Zernike polynomials. As shown, for
each operational volume 34a-34f, a plurality of incisions 44', 44''
and 44''' are made, though there may be more or fewer incisions 44,
depending on the needs of the particular procedure. With this in
mind, and for purposes of this disclosure, the plurality in a
selected volume 34 will sometimes be collectively referred to as
incisions 44. Further, as shown in FIG. 3, six operational volumes
have been identified. However, any number of operational volumes 34
may be used for the present invention.
[0031] As shown in FIG. 3, the exemplary incisions 44 for each
operational volume 34 are made on respective cylindrical surfaces.
Although the incisions 44 are shown as circular cylindrical
surfaces, these surfaces may be oval. When the plurality of
incisions 44 is made in the stroma 28, it is absolutely essential
that it be confined within the respective operational volume 34.
With this in mind, it is envisioned that incisions 44 will be made
by a laser process using the laser unit 10. And, that this process
will result in Laser Induced Optical Breakdown (LIOB). Further, in
the illustrated embodiment, it is important these cylindrical
surfaces be concentric, and that they are centered on a respective
central axis 45a-45f distanced from and parallel to the visual axis
14.
[0032] Cross-referencing FIG. 3 with FIGS. 4 and 5, it can be seen
that each incision 44 has an anterior end 46 and a posterior end
48. Further, the incisions 44 (i.e. the circular or oval
cylindrical surfaces) have a spacing 50 between adjacent incisions
44. Preferably, this spacing 50 is equal to approximately two
hundred microns. FIG. 5 also shows that the anterior ends 46 of
respective individual incisions 44 can be displaced axially from
each other by a distance 52. Typically, this distance 52 will be
around ten microns. Further, the innermost incision 44 (e.g.
incision 44'' shown in FIG. 4) will be at a radial distance
"r.sub.c" that will be about 1 millimeter from the central axis 45.
From another perspective, FIG. 6A shows the incisions 44 centered
on the central axis 45 to form a plurality of rings. In this other
perspective, the incisions 44 collectively establish an inner
radius "r.sub.ci" and an outer radius "r.sub.co". Preferably, each
incision 44 will have a thickness of about two microns, and the
energy required to make the incision 44 will be approximately 1.2
microJoules.
[0033] As an alternative to the incisions 44 disclosed above, FIG.
4 indicates that only arc segments 54 may be used, if desired.
Specifically, in all essential respects, the arc segments 54 are
identical with the incisions 44. The exception, however, is that
they are confined within diametrically opposed arcs identified in
FIGS. 4 and 6B by the angle ".alpha.". More specifically, the
result is two sets of diametrically opposed arc segments 54.
Preferably, ".alpha." is in a range between five degrees and one
hundred and sixty degrees.
[0034] An alternate embodiment for the arc segments 54 are the arc
segments 54' shown in FIG. 6C. There it will be seen that the arc
segments 54' like the arc segments 54 are in diametrically opposed
sets. The arc segments 54', however, are centered on respective
axes (not shown) that are parallel to each other, and equidistant
from the central axis 45.
[0035] As an alternative to the incisions 44 disclosed above, FIG.
6D indicates that incisions 44 may be created to form rectangular
cylinders centered on the respective central axes 45. Similarly,
FIG. 6E indicates that the incisions 44 may be created to form
crosses centered on the respective central axes 45. As shown in
FIGS. 6D and 6E, the rectangular cylinders and crosses are also
aligned with the visual axis 14.
[0036] FIG. 7 provides an overview of the bio-mechanical reaction
of the cornea 16 when incisions 44 have been made in the
operational volume 34 of the stroma 28. As stated above, the
incisions 44 are intended to weaken the stroma 28. Consequently,
once the incisions 44 have been made, the intraocular pressure
(represented by arrow 56) causes a change in the force distribution
within the stroma 28. This causes bulges 58a and 58b that result in
a change in shape from the original cornea 16 into a new
configuration for cornea 16', represented by the dashed lines. As
intended for the present invention, this results in refractive
corrections for the cornea 16 that improves vision.
[0037] While the particular System and Method for Correcting Higher
Order Aberrations with Changes in Intrastromal Biomechanical Stress
Distributions as herein shown and disclosed in detail is fully
capable of obtaining the objects and providing the advantages
herein before stated, it is to be understood that it is merely
illustrative of the presently preferred embodiments of the
invention and that no limitations are intended to the details of
construction or design herein shown other than as described in the
appended claims.
* * * * *