United States Patent
`
`[19]
`5,993,438
`[11] Patent Number:
`[45] Date of Patent: Nov. 30, 1999
`Juhasz et al.
`
`
`
`U5005993438A
`
`[54]
`
`[75]
`
`[73]
`
`INTRASTROMAL PHOTOREFRACTIVE
`KERATECTOMY
`
`Inventors: Tibor Juhasz, Irvine, Calif; Josef F.
`Bille, Heidelberg, Germany
`
`Assignee: Escalon Medical Corporation,
`Skillman, N.J.
`
`Appl. No.: 08/916,082
`
`Filed:
`
`Aug. 21, 1997
`
`Related U.S. Application Data
`
`Continuation—in—part of application No. 08/516,581, Aug.
`17, 1995, which is a continuation—in—part of application No.
`08/151,726, NOV. 12, 1993, abandoned.
`
`Int. Cl.6 ....................................................... A61N 5/02
`U.S. Cl.
`...................................... 606/5; 606/3; 606/10
`Field of Search ................................. 606/3—6, 10—19
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`3,769,963
`4,309,998
`4,391,275
`4,538,608
`4,580,559
`4,601,288
`4,633,866
`4,653,495
`4,665,913
`4,669,466
`4,718,418
`4,732,148
`4,770,172
`4,773,414
`4,903,695
`4,907,586
`4,941,093
`4,976,709
`4,988,348
`
`.
`
`.
`
`.
`11/1973 Goldman et al.
`1/1982 Aron nee Rosa et al.
`7/1983 Frankhauser et al.
`.
`9/1985 L’Esperance, Jr.
`.
`4/1986 L’Esperance, Jr.
`.
`7/1986 Myers.
`1/1987 Peyman et al.
`3/1987 Nanaumi.
`.
`5/1987 L’Esperance, Jr.
`.
`6/1987 L’Esperance, Jr.
`1/1988 L’Esperance ............................... 606/5
`3/1988 L’Esperance, Jr.
`.
`9/1988 L’Esperance, Jr.
`.
`9/1988 L’Esperance, Jr.
`.
`2/1990 Warner et al.
`.
`3/1990 Belle et al.
`................................. 606/5
`7/1990 Marshall et al.
`.
`12/1990 Sand.
`1/1991 Bille .
`
`FOREIGN PATENT DOCUMENTS
`
`0 484 005
`WO 89/06519
`WO 94/09849
`
`5/1992 European Pat. Off .
`7/1989 WIPO .
`5/1994 WIPO .
`
`OTHER PUBLICATIONS
`
`Jr., Ophthalmic Lasers Photocoagulation,
`L’Esperance,
`Photoraa'iation, and Surgery, pp. 529—538, 1983, The CV.
`Mosby Company.
`Krauss et al., Contemporary Technology, pp. 37—52, Survey
`of Ophthalmology, vol. 31, No. 1, Jul—Aug, 1986.
`John Marshall et al., Photoablative reprofiling of the cornea
`using an excimer laser: Photorefractive keratectomy, pp.
`21—45.
`
`Primary Examiner—David M. Shay
`Attorney, Agent, or Firm—Nydegger & Associates
`
`[57]
`
`ABSTRACT
`
`A method for performing intrastromal photorefractive kera-
`tectomy in the cornea of an eye, using a pulsed, laser beam
`to photodisrupt a portion of the cornea, includes the initial
`step of focusing the beam to a focal spot at a selected starting
`point
`in the stroma. The starting point
`is located at a
`predetermined distance behind the epithelium of the cornea.
`While focused on the starting point, the laser beam is pulsed
`to disrupt a volume of the stroma which is approximately
`equal to the volume of the focal point. Subsequently, the
`beam is focused in a patterned sequence to focal spots at
`other discrete points in the stroma. At each point the stroma
`is photodisrupted. With this progressive pattern of
`photodisruption, each spot is placed substantially contiguous
`With adjacent a volume of previously disrupted tissue. The
`resultant photodisrupted tissue creates a layer which is
`substantially centro-symmetrical around the optical axis. A
`plurality of layers can be removed to create a cavity in the
`stroma. When the cavity collapses, the corneal curvature is
`changed as desired.
`
`23 Claims, 2 Drawing Sheets
`
`
`
`Alcon Research, Ltd.
`Exhibit 1020 - Page 1
`
`Alcon Research, Ltd.
`Exhibit 1020 - Page 1
`
`

`

`US. Patent
`
`N0V.30, 1999
`
`Sheet 1 0f2
`
`5,993,438
`
`LASER UNIT
`
`28
`
`
`
`Alcon Research, Ltd.
`Exhibit 1020 - Page 2
`
`Alcon Research, Ltd.
`Exhibit 1020 - Page 2
`
`

`

`US. Patent
`
`N0V.30, 1999
`
`Sheet 2 0f2
`
`5,993,438
`
`Flg'4 39
`
`560
`
`56b 56c 56d ace 56f
`520
`52b 52c 52d 52c 52!
`
`50
`
`
`
`Alcon Research, Ltd.
`Exhibit 1020 - Page 3
`
`Alcon Research, Ltd.
`Exhibit 1020 - Page 3
`
`

`

`5,993,438
`
`1
`INTRASTROMAL PHOTOREFRACTIVE
`KERATECTOMY
`
`This Application is a continuation-in-part of co-pending
`US. patent application Ser. No. 08/516,581 filed Aug. 17,
`1995, for Intrastromal Photorefractive Keratectomy, which
`was a continuation-in-part of US. patent application Ser.
`No. 08/151,726 filed Nov. 12, 1993, which is now aban-
`doned. The contents of US. patent application Ser. Nos.
`08/516,581 and 08/151,726 are incorporated herein by ref-
`erence.
`
`FIELD OF THE INVENTION
`
`invention pertains to a method for using
`The present
`lasers to accomplish ophthalmic surgery. More particularly,
`the present invention pertains to methods for reshaping the
`cornea of the eye to improve a patient’s vision. The present
`invention is particularly, but not exclusively, useful as a
`method for
`intrastromal photorefractive keratectomy
`(hereinafter “ISPRK”).
`
`BACKGROUND OF THE INVENTION
`
`It is known that the cornea of an eye can, in certain
`instances, be surgically reshaped to correct and improve
`vision. Where the condition being corrected is myopia or
`near-sightedness, the cornea is relatively flattened, whereas
`if hyperopia is being corrected,
`the cornea is relatively
`steepened.
`In either case, as more fully set forth below, there are
`several different types of ophthalmic surgical procedures
`which can be employed for this purpose. Although the types
`of procedures may vary, the ultimate object in correcting
`myopia, for example, is the same. Namely, the object is to
`cause different types of tissues in the cornea. These include
`portions of the epithelium, Bowman’s membrane, and the
`stroma.
`
`The present invention recognizes that it is preferable to
`leave the epithelium and Bowman’s membrane intact and to
`limit the tissue removal to only the stroma. Removal of
`tissue from the stroma results in the creation of a specially
`shaped cavity in the stroma layer of the cornea. When the
`cornea deforms in the intended manner, the desired flatten-
`ing of the cornea results.
`internal
`Further,
`the present
`invention recognizes that
`tissue “photodisruption,” can be effectively accomplished
`using a pulsed laser energy if the irradiance of the beam, its
`focal spot size, and the proper layering of photodisruption
`sites are effectively controlled.
`Accordingly, it is an object of the present invention to
`provide an improved method for performing intrastromal
`photodisruption on the cornea of an eye. Still another object
`of the present invention is to provide a method for intras-
`tromal photodisruption which removes stromal tissue in a
`predetermined pattern to attain the desired flattening of the
`cornea. Yet another object of the present invention is to
`provide a method for intrastromal photodisruption which is
`relatively easy to perform and which is comparatively cost
`effective.
`
`SUMMARY
`
`In accordance with the present invention, a method for
`performing photodisruption and removal of tissue in a
`stroma in a cornea of an eye uses a pulsed laser beam which
`is sequentially focused to individual spots at a plurality of
`points in the stroma. Each focus spot has a finite volume,
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`rather than being a single point. Further, each spot has a
`central point at approximately the center of the finite vol-
`ume. Photodisruption of stromal tissue occurs at each spot
`where the beam is focused and the volume of stromal tissue
`disrupted at each spot is approximately equal to the volume
`of the spot. The photodisrupted tissue is absorbed into or
`removed from the cornea through well known means. The
`spots are arranged in successive spiral patterns to photodis-
`rupt and remove a plurality of layers of stromal tissue, with
`the diameters of the layers being properly sized to result in
`the desired diopter correction.
`The physical characteristics of the laser beam, as well as
`the manner of focusing the laser beam, are important to the
`proper performance of the method of the present invention.
`As indicated above, these considerations are interrelated.
`First, insofar as the characteristics of the laser beam are
`concerned, several factors are important. The laser beam
`should have a wavelength that allows the light
`to pass
`through the cornea without absorption by the corneal tissue.
`Accordingly, the light in the laser beam will not be absorbed
`as the beam transits through the cornea until it reaches the
`focal spot. Generally, the wavelength should be in the range
`of three-tenths of a micrometer (0.3 pm) to three microme-
`ters (3.0 pm), with a wavelength of one thousand fifty-three
`nanometers (1,053 nm) being preferred. The irradiance of
`the beam for accomplishment of photodisruption of stromal
`tissue at the focal spot should be greater than the threshold
`for optical breakdown of the tissue. The irradiance which
`will cause optical breakdown of stromal tissue is approxi-
`mately two hundred gigawatts per square centimeter (200
`GW/cmz) at a pulse duration of approximately fifty pico
`seconds. Preferably, the irradiance should not be more than
`ten (10) times greater than the threshold for optical break-
`down . Further, the pulse repetition frequency of the pulsed
`laser beam is preferably in the range of approximately one
`Hertz to ten Hertz (1 kHz—10 kHz).
`Second,
`insofar as the focusing of the laser beam is
`concerned, spot size, spot configuration, and spot pattern are
`all important. The spot size of the focused laser beam should
`be small enough to achieve optical breakdown of stromal
`tissue at the focal spot. Typically, this requires the spot size
`to be approximately ten micrometers (10 pm) in diameter.
`Additionally, it is preferable that the spot configuration be as
`close to spherical as possible. To achieve this configuration
`for the spot it is necessary that the laser beam be focused
`from a relatively wide cone angle. For the present invention,
`the cone angle will preferably be in the range of fifteen
`degrees to forty-five degrees (15°—45°). Finally, the spots
`must be arranged in a pattern that is optimal for creating a
`cavity of the desired shape. The subsequent deformation of
`the cavity results in the ultimate reshaping of the cornea in
`the desired fashion to achieve a desired refractive effect.
`
`To perform intrastromal photodisruption in accordance
`with the method of the present invention the laser beam is
`focused at a first selected spot at a starting point in the
`stroma. For myopic corrections, the starting point is prefer-
`ably on the optical axis of the eye at a location behind the
`epithelium. The laser beam is then activated and the stromal
`tissue at
`the first spot
`is photodisrupted.
`Importantly,
`because spot size and configuration and the irradiance level
`of the laser beam are closely controlled for the present
`invention, the volume of stromal tissue which is photodis-
`rupted and removed at the focal spot is carefully controlled.
`Preferably, this volume is about the same as the volume
`occupied by the focal spot, and has a volume diameter of
`between about
`ten micrometers (10 pm) to twenty-five
`micrometers (25 um) diameter spherical volume.
`
`Alcon Research, Ltd.
`Exhibit 1020 - Page 4
`
`Alcon Research, Ltd.
`Exhibit 1020 - Page 4
`
`

`

`5,993,438
`
`3
`Next, the laser beam is focused at a second selected spot
`in the stroma, proximate the first focal spot. It should be
`noted, however, that during photodisruption of the stromal
`tissue, a cavitation bubble results which has a bubble radius
`which is approximately equal to or larger than the spot
`diameter of the focal spot. Therefore, the second focal spot
`is selected at a point in the stroma which is substantially
`adjacent to the cavitation bubble resulting from the first
`focal spot. Again, the laser beam is activated and stromal
`tissue at the second spot is photodisrupted to add to the
`volume of stromal tissue which had previously been pho-
`todisrupted. Because of the placement of the second spot
`relative to the cavitation bubble from the first spot, there
`preferably is some overlap between the cavitation bubbles at
`the two (2) spots. This process is continued, proceeding from
`point to point along a spiral through the stroma, until a ten
`micrometer (10 pm) thick layer of stromal tissue has been
`photodisrupted and removed. The layer of photodisrupted
`tissue is substantially symmetrical to the optical axis.
`For effective vision correction of the eye using intrastro-
`mal photorefractive keratectomy techniques, it is preferable
`that tissue photodisruption be accomplished at a plurality of
`adjacent points in a patterned sequence to create a plurality
`of layers of tissue removal. The object is to create a dome
`shaped cavity within the stromal tissue. The dome shaped
`cavity subsequently collapses, reshaping the corneal surface.
`The present invention contemplates that the adjacent focal
`spots in a given cavity layer of the stroma can all be located
`in a plane which is perpendicular to the optical axis of the
`eye. Further, in this embodiment, the pattern of spots in each
`layer can be positioned in a spiral pattern which is substan-
`tially centro-symmetric to the optical axis of the eye. The
`result is a plurality of substantially flat layers of photodis-
`rupted stromal tissue, each layer being substantially perpen-
`dicular and substantially symmetric to the optical axis.
`Alternately, the present invention provides that the adja-
`cent focal spots in a given cavity layer of the stroma can be
`positioned so that each cavity layer has a substantially
`curved cross-section. The result is a plurality of curved
`cavity layers of photodisrupted stromal tissue, each cavity
`layer being substantially symmetric to the optical axis.
`the
`Importantly,
`to obtain effective vision correction,
`consecutive focal spots must be properly spaced apart. For
`example, if the focal spots are too close together, too much
`heat may develop in the eye. Alternately, if the consecutive
`focal spots are too far apart, the vision may not be properly
`corrected. As provided by the present
`invention, a spot
`distance between consecutive focal spots is preferably
`between approximately one (1) to two (2) times the bubble
`radius and more preferably between approximately one and
`one-half (1.5) to one and nine-tenths (1.9) times the bubble
`radius.
`
`In accordance with the present invention, a plurality of
`superposed photodisrupted layers can be created by first
`photodisrupting the layer which is to be farthest from the
`epithelium, followed by successive photodisruption of addi-
`tional layers in an anterior progression. Each successive
`layer in the anterior progression has a smaller outer diameter
`than the previous layer. The amount by which each layer is
`smaller than the previous one is determined by a particular
`geometric model which has been devised to result in the
`creation of the desired dome shaped cavity. Regardless of
`the number of layers created, it is important that every layer
`be at a safe distance form the epithelium, e.g., no closer than
`approximately thirty micrometers (30 um).
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`The novel features of this invention, as well as the
`invention itself, both as to its structure and its operation, will
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`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:
`
`FIG. 1 is a cross-sectional view of the cornea of an eye
`shown in relationship to a schematically depicted laser unit;
`
`FIG. 2 is a cross-sectional view of the cornea of an eye
`showing one embodiment of the cavity layers in the eye;
`
`FIG. 3 is a cross-sectional view of the cornea of an eye
`showing a second embodiment of the cavity layers in the
`eye;
`
`FIG. 4 is a schematic representation of the relative posi-
`tioning of adjacent
`laser beam spots and the resultant
`overlapping disruption of stromal tissue which occurs during
`implementation of the method of the present invention; and
`
`FIG. 5 is a plan view schematic representation of a
`predetermined spiral pattern of focal spots and the resultant
`layer in which stromal tissue is photodisrupted by imple-
`mentation of the method of the present invention.
`
`DESCRIPTION
`
`Referring initially to FIG. 1, a cross-section of part of an
`eye is shown and generally designated 10. For reference
`purposes, the portion of eye 10 which is shown includes the
`cornea 12,
`the sclera 14, and the lens 16. Further,
`in
`accordance with standard orthogonal ocular referencing
`coordinates, the z-axis or z direction is generally oriented on
`the optical axis of the eye 10. Consequently, the x and y
`directions establish a plane which is generally perpendicular
`to the optical axis.
`
`As can best seen in FIGS. 2 and 3, the anatomy of the
`cornea 12 of an eye 10 includes five (5) different identifiable
`tissues. The epithelium 18 is the outermost tissue on the
`exterior of the cornea 12. Behind the epithelium 18, and
`ordered in a posterior direction along the Z-axis, are Bow-
`man’s membrane 20, the stroma 22, Descemet’s membrane
`24, and the endothelium 26. Of these various tissues, the
`region of most interest to the present invention is the stroma
`22.
`
`Returning for the moment to FIG. 1, it will be seen that
`the method of the present invention incorporates a laser unit
`28 which must be capable of generating a pulsed laser beam
`30 having certain characteristics. Importantly,
`the pulsed
`laser beam 30 should be monochromatic light having a
`wavelength (X) which will pass through all tissues of the
`cornea 12 without interacting with those tissues. Preferably,
`wavelength (A) of laser beam 30 will be in the range of from
`three tenths of a micrometer to three micrometers ()L=0.3 pm
`to 3.0 pm). Also, the pulse repetition rate of laser beam 30
`should be approximately in the range of from one hundred
`Hertz to one hundred thousand Hertz (0.1 kHz to 100 kHz).
`
`An additional factor of great importance to the present
`invention is that the irradiance of laser beam 30 must be
`circumscribed and well defined. The main concern here is
`
`that the irradiance of beam 30 will, in large part, determine
`the photodisruptive capability of pulsed laser beam 30 on
`tissue of the stroma 22.
`
`Irradiance, or radiant flux density, is a measure of the
`radiant power per unit area that flows across a surface. As
`indicated by the following expression, the irradiance of laser
`beam 30 is a function of several variables. Specifically:
`
`Alcon Research, Ltd.
`Exhibit 1020 - Page 5
`
`Alcon Research, Ltd.
`Exhibit 1020 - Page 5
`
`

`

`5,993,438
`
`5
`
`(pulse energy)
`,
`Irradiance =+
`(pulse duration)(spot Size)
`
`From the above expression for irradiance it can be appre-
`ciated that, for a constant level of irradiance, the irradiance
`is proportional to the amount of energy in each pulse of
`beam 30. On the other hand, irradiance is inversely propor-
`tional to pulse duration and spot size. The significance of this
`functional relationship stems from the fact that the irradi-
`ance of pulsed laser 30 should be approximately equal to the
`optical breakdown threshold for stromal
`tissue 22. This
`threshold is known to be about two hundred gigawatts per
`square centimeter (200 GW/cmz) for a pulse duration of
`approximately fifty pico seconds (50 psec). Insofar as each
`factor’s contribution to irradiance is concerned, it is impor-
`tant to recognize that no one (1) factor can be considered
`individually. Instead, the pulse energy, pulse duration, and
`focal spot size of laser beam 30 are interrelated and each
`characteristic is variable.
`
`For purposes of the present invention, the pulse duration
`of pulses in laser beam 30 is preferably in the range of from
`one hundred femtoseconds (100 fs) to ten nanoseconds (10
`ns). As for the spot size to which each pulse is focused, the
`determinative consideration is that the spot size should be
`small enough to achieve optical breakdown in a volume of
`stromal
`tissue 22 which is approximately equal
`to the
`volume of the focal spot. This relationship is perhaps best
`seen in FIG. 4.
`
`In FIG. 4, a succession of focal spots 32a—32f are shown.
`All focal spots 32a—32f are substantially spherical or slightly
`ellipsoidal and have substantially the same volume. As such,
`they can each be characterized as having a spot diameter 34.
`Focal spots 32a—32f are shown arranged in a straight line 50
`for the sake of simplicity of the drawing, but as will be
`explained, for the present invention, it is preferable for the
`focal spots 32a—32f to be arranged on a spiral path. FIG. 4
`also shows the general relationship between each focal spot
`32a—32f and the associated cavitation bubble 36a—36f which
`results when laser unit 28 is activated to irradiate a focal spot
`32a—32f. The cavitation bubble 36a—36f, like the associated
`focal spot 32a—32f, will be generally spherical and can be
`characterized by a bubble diameter 38 and a bubble radius
`39.
`
`As indicated above, it is preferable that diameter 38 of
`each of the cavitation bubbles 36a—36f be the same as the
`diameter 34 of the corresponding focal spot 32a—32f. This,
`however, cannot always be achieved. In any event,
`it is
`important that the volume of cavitation bubble 36a—36f not
`be significantly larger than the volume of the focal spot
`32a—32f. For the present invention, it is important that the
`diameter 34 of focal spots 32a—32f be less than about one
`hundred micrometers (1 00 um) and preferably about ten
`micrometers (10 pm). It is preferable that the diameter 38 of
`cavitation bubbles 36a—36f be no more than about twice the
`diameter 34 of focal spots 32a—32f.
`As indicated above, the focal spots 32a—32f are substan-
`tially spherical. To configure focal spots 32a—32f as close as
`possible to a sphere, rather than as an elongated ellipsoid, it
`is necessary for laser beam 30 to be focused through a rather
`wide cone angle 40 (See FIG. 1). For purposes of the method
`of the present invention, cone angle 40 should be in the
`range of from fifteen degrees to forty-five degrees
`(15°—45°). Presently,
`the best results are known to be
`achieved with a cone angle of about thirty-six degrees (36°).
`For the practice of the method of the present invention, it
`is first necessary for the physician to somehow stabilize the
`
`6
`eye 10. A suitable device for stabilizing the eye 10 is
`provided for in US. Pat. No. 5,336,215, issued to Hsueh et
`al. and entitled “Eye Stabilizing Mechanism for Use in
`Ophthalmic Laser Surgery.” After the eye 10 has been
`stabilized, laser beam 30 is focused on a focal spot 32a at a
`first selected focal spot central point 42a in the stroma 22.
`Specifically, for many procedures, the first focal spot central
`point 42a is located generally on the z-axis 44 behind the
`Bowman’s membrane 20. As used here, “behind” means in
`a posterior direction or inwardly from the Bowman’s mem-
`brane. Once laser beam 30 is so focused, the laser unit 28 is
`activated to irradiate the focal spot 32a at first focal spot
`central point 42a. The result is that a cavitation bubble 36a
`is formed in stromal tissue 22, and a corresponding volume
`of stromal tissue is disrupted and removed from the stroma
`22.
`
`The physical consequences of photodisruption of stromal
`tissue 22 at the first focal point 42a and at other focal points
`42b—42f is, of course, removed. Additionally, however,
`by-products such as carbon dioxide (C02), carbon monoxide
`(CO), nitrogen (N2) and water (H20) are formed. As stated
`above, these by-products create a cavitation bubble 36a—36f
`in the tissue of stroma 22. The volume of tissue removed is
`approximately the same as the volume of the cavitation
`bubble 36a—36f.
`As indicated in FIG. 4, once the cavitation bubble 36a has
`been created, the laser beam 30 is repositioned for refocus-
`ing at another point 42b. In FIG. 4, it is shown that the
`second focal spot central point 42b is substantially adjacent
`to the first focal spot central point 42a and that both the
`second focal spot central point 42b and first focal spot
`central point 42a lie on a path 50. Importantly, the distance
`along path 50 between first focal spot central point 42a and
`second focal spot central point 42b is selected so that the
`adjacent volumes of disrupted tissue in cavitation bubbles
`36a, 36b will preferably overlap. In effect, the size of the
`cavitation bubbles 36a—36f of disrupted tissue volume will
`determine the separation distance between selected focal
`spot central points 42a—42f along the path 50.
`As implied here, subsequent focal points 426 et seq. will
`also lie on the predetermined path 50 and the disrupted tissue
`volume at any respective focal spot central point 42 will
`preferably overlap with the volume of tissue disrupted at the
`previous focal point in stroma 22. Consequently, a separa-
`tion spot distance 51 between focal spot central points 42 on
`path 50 must be established so that tissue removal along the
`path 50 will be substantially continuous. As provided herein,
`the spot distance 51 between consecutive focal spots is
`preferably between approximately one (1) to two (2) times
`the bubble radius 39 and more preferably between approxi-
`mately one and one-half (1.5) to one and nine-tenths (1.9)
`times the bubble radius 39.
`
`FIG. 5 shows a plan view of a photodisrupted layer 52 as
`seen looking toward the eye 10 along z-axis 44. Also, FIG.
`5 shows that the first focal spot central point 42a and the
`sequence of subsequent points 42b—42f all lie along the path
`50. Further, FIG. 5 shows that the path 50 can be set as a
`pattern 62 and, as shown in FIG. 5, this pattern 62 can be a
`spiral pattern. It is to be appreciated that the spiral pattern 62
`can be extended as far as is desired and necessary to create
`the layer 52 of disrupted tissue volumes 36. Further, it is to
`be appreciated that layer 52 may be curved to generally
`conform to the shape of the cornea’s external surface. It is
`also to be appreciated that
`the final pattern 62 will be
`approximately centro-symmetric with respect to the optical
`axis (z-axis 44) of the eye 10.
`in one embodiment of the
`Referring back to FIG. 2,
`present invention, it will be seen that a plurality of disrupted
`
`5
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`Alcon Research, Ltd.
`Exhibit 1020 - Page 6
`
`Alcon Research, Ltd.
`Exhibit 1020 - Page 6
`
`

`

`5,993,438
`
`7
`tissue volumes 36 can be juxtaposed to establish a continu-
`ous layer 52 of disrupted stromal tissue. Only a few of the
`disrupted tissue volumes 36 are shown in layer 52, for the
`sake of clarity of the drawing, but it should be understood
`that the entire layer 52 is disrupted as discussed above. As
`shown in FIG. 2, a plurality of layers can be created in
`stroma 22 by the method of the present invention. FIG. 2
`shows a layer 54 which is located in front of the layer 52 and
`a layer 56 which is located in front of the layer 54. Layers
`58 and 60 are also shown, with layer 60 being the most
`anterior and smallest in diameter. As with layer 52, layers
`54, 56, 58, and 60 are entirely created by a plurality of
`disrupted tissue volumes 36. At least approximately ten (10)
`of these layers can be so created, if desired.
`
`it is
`Whenever a plurality of layers is to be created,
`preferable that the most posterior layer be created first and
`that each successive layer be created more anteriorly than
`any previously created layer. For example, to create layers
`52, 54, 56, 58, and 60, it is necessary to start first with the
`creation of the layer 52. Then, in order, layers 54, 56, 58, and
`60 can be created.
`
`As shown in FIG. 2, each cavity layer 52, 54, 56, 58, and
`60 is substantially flat, substantially planer, and substantially
`perpendicular to the optical axis 44 of the eye 10. Further,
`each cavity layer has a cavity outer diameter 61.
`
`There are limitations as to how close any layer can be to
`the epithelium, 18 in order to avoid unwanted photodisrup-
`tion of Bowman’s membrane 20 and the epithelium 18.
`Accordingly, no disrupted tissue volume 36 in any layer
`should be closer to the epithelium 18 than approximately
`thirty microns (30 um). Therefore, because it is anticipated
`that each layer will effectively encompass approximately a
`ten microns (10 pm) to fifteen microns (15 um) thickness of
`tissue, it is necessary that the first layer 52 be created at an
`appropriate location so that neither layer 52 nor any subse-
`quent
`layer should eventually be located closer to the
`epithelium 18 than thirty microns (30 pm).
`
`For a required myopic correction, it is desired to decrease
`the amount of corneal curvature by a given number of
`diopters (D), by increasing the corneal radius of curvature.
`Such a change in corneal curvature is accomplished by
`removing certain layers of the stromal tissue to create a
`dome shaped cavity entirely within the stromal layer 22.
`This cavity will then collapse, resulting in a flattening of the
`corneal anterior surface. This flattening will achieve the
`desired corneal curvature change. The desired corneal cur-
`vature change D in diopters can be computed according to
`the following equation:
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`8
`
`
`
`_ 2(._1)[..[1_[1{gqu
`Grit—NIT
`[Poll-[1%
`E
`
`where N is the selected number of intrastromal layers to be
`used to achieve the curvature change. The thickness of each
`layer, such as ten microns (10 82 m) in the example given,
`is represented by t. The index of refraction of the cornea is
`represented by n. The corneal radius of curvature is p, with
`p0 being the preoperative radius. The selected cavity outer
`diameter of the intrastromal cavity to be created, keeping in
`mind the minimum required separation from the epithelium
`18, is given by do. This selected outer diameter becomes the
`outer diameter 61 of the first layer to be created. More effect
`is produced with smaller cavity outer diameters and with
`more layers. The sensitivity to cavity diameter decreases
`sharply over a cavity diameter of approximately five milli-
`meters (5 mm).
`For myopic correction, the outer diameter 61 of each layer
`52, 54, 56, 58, and 60 is smaller than the outer diameter 61
`of the layer previously created,
`to create a dome shaped
`cavity with its base oriented posteriorly, and its crown
`oriented anteriorly. A geometric analysis of the change in
`corneal curvature upon collapse of an intrastromal cavity has
`revealed the optimum shape of the cavity. The appropriate
`diameter for each layer, d, to achieve a desired correction of
`the anterior corneal curvature, is calculated according to the
`following equation:
`
`di=2pol—
`
`(p0D+n—l)(p0—t(i—l/2))2+
`
`(p0 — Nr)[<poD + n —1)(P0 — NI) — 2m —1)Pol
`zméD—Nrmwm— 1W0 —r<i— 1/2»
`
`21/2
`
`where i designates the layer for which the diameter is being
`calculated and i=1,2,3, .
`.
`.
`, N.
`Table 1 lists the layer diameters, in millimeters, which
`would result from the selection of an outer treatment zone
`
`diameter, or cavity diameter, of six millimeters (6.0 mm),
`where N, the number of intrastromal layers, varies from two
`to ten (2—10). The first layer has the same diameter as the
`treatment zone. The preoperative corneal radius of curvature
`is assumed to be eight millimeters (8.0 mm) and each layer
`is assumed to have a thickness of ten micrometers (10 pm).
`The expected resultant change in corneal radius of curvature
`is listed at the bottom of each column.
`
`TABLE 1
`
`N=3 N=4 N=5 N=6 N=7 N=8 N=9 N=10
`
`6.000
`4.285
`2.490
`
`6.000
`4.779
`3.721
`2.159
`
`6.000
`5.051
`4.286
`3.334
`1.932
`
`6.000
`5.223
`4.622
`3.920
`3.047
`1.765
`
`6.000
`5.343
`4.847
`4.288
`3.635
`2.824
`1.635
`
`6.000
`5.430
`5.009
`4.543
`4.017
`3.404
`2.644
`1.530
`
`6.000
`5.497
`5.130
`4.731
`4.289
`3.792
`3.213
`2.495
`1.444
`
`6.000
`5.550
`5.225
`4.875
`4.495
`4.075
`3.602
`3.051
`2.368
`1.370
`—7.62
`
`Layer N = 2
`6.000
`3.044
`
`OOOQQQL’IkaJNb—KH
`
`—1.50
`
`2.26
`
`—3.02
`
`—3.78
`
`—4.54
`
`—5.31
`
`—6.08
`
`—6.85
`
`Alcon Research, Ltd.
`Exhibit 1020 - Page 7
`
`Alcon Research, Ltd.
`Exhibit 1020 - Page 7
`
`

`

`5,993,438
`
`9
`In Other embodiment shown in FIG. 3, a plurality of
`disrupted tissue volumes 36 are again juxtaposed to establish
`a continuous layer 52 of disrupted stromal tissue. Again,
`only a few of the disrupted tissue volumes 36 are shown in
`layer 52, for the sake of clarity of the drawing, but it should
`be understood that the entire layer 52 is disrupted as dis-
`cussed above. Similar to FIG. 2, layer 54 is located in front
`of the layer 52 and layer 56 is located in front of the layer
`54. Layers 58 and 60 are also shown, with layer 60 being the
`most anterior and smallest in diameter.
`
`In the embodiment shown in FIG. 3, each layer 52, 54, 56,
`58, and 60 has a substantially curved cross-section and is
`substantially symmetrical with the optical axis 44 of the eye.
`Stated another way, each layer 52, 54, 56, 58, and 60 is
`shaped somewhat similar to a segment of a sphere.
`Preferably, each layer has a curve which is substantially
`similar to the curve of the eye 10.
`While the particular method for performing intrastromal
`photorefractive keratectomy on the cornea of an eye using a
`pulsed laser beam 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
`o