U.S. patent number RE46,493 [Application Number 14/013,917] was granted by the patent office on 2017-08-01 for selective photocoagulation.
This patent grant is currently assigned to The General Hospital Corporation. The grantee listed for this patent is The General Hospital Corporation. Invention is credited to Charles P. Lin.
United States Patent |
RE46,493 |
Lin |
August 1, 2017 |
**Please see images for:
( Certificate of Correction ) ** |
Selective photocoagulation
Abstract
A method of scanning a laser beam across a set of cells includes
during a first interval, scanning a laser beam across a set of
cells; and during a second interval, deflecting the laser beam away
from the set of cells. The first interval is selected to cause
microcavitation in at least a portion of the cells from the set of
cells.
Inventors: |
Lin; Charles P. (Arlington,
MA) |
Applicant: |
Name |
City |
State |
Country |
Type |
The General Hospital Corporation |
Boston |
MA |
US |
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Assignee: |
The General Hospital
Corporation (Boston, MA)
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Family
ID: |
1000001857290 |
Appl.
No.: |
14/013,917 |
Filed: |
August 29, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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11428018 |
Jul 26, 2006 |
7763017 |
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10296417 |
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7115120 |
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PCT/US01/17818 |
Jun 1, 2001 |
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60209010 |
Jun 1, 2000 |
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Reissue of: |
12131612 |
Jun 2, 2008 |
8006702 |
Aug 30, 2011 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
A61F
9/008 (20130101); A61F 2009/00897 (20130101); A61F
9/00821 (20130101); A61F 2009/00863 (20130101); A61F
9/00823 (20130101); A61F 9/00802 (20130101); A61F
2009/00861 (20130101) |
Current International
Class: |
A61F
9/008 (20060101) |
Field of
Search: |
;606/4-6 ;607/88,89
;128/898 |
References Cited
[Referenced By]
U.S. Patent Documents
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2001-149403 |
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Jun 2001 |
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JP |
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99/65431 |
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Dec 1999 |
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WO |
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2001/91661 |
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WO |
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2004/043234 |
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May 2004 |
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WO |
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2005/065116 |
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Jul 2005 |
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WO |
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2007/053701 |
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May 2007 |
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WO |
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2007/092349 |
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Aug 2007 |
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WO |
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2008/049164 |
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May 2008 |
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WO |
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2009/092112 |
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Jul 2009 |
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WO |
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Primary Examiner: Farah; Ahmed
Attorney, Agent or Firm: Fish & Richardson P.C.
Government Interests
STATEMENT OF GOVERNMENTAL SUPPORT
This invention was made with Government support under Grant Nos.
F49620-96-1-0241 and F49620-00-1-0179 awarded by the United States
Air Force Office of Scientific Research and Grant No. EY012970
awarded by the National Institutes of Health. The Government has
certain rights in this invention.
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATION
This application is a divisional of U.S. application Ser. No.
11/428,018, filed Jun. 30, 2006, which is a continuation of U.S.
application Ser. No. 10/296,417, filed Jul. 9, 2003, which is the
U.S. national stage of PCT Application No. US01/17818, filed Jun.
1, 2001, which claims the benefit of U.S. Provisional Application
Ser. No. 60/209,010, filed Jun. 1, 2000. The contents of all the
foregoing applications are incorporated herein by this reference.
Claims
The invention claimed is:
1. A method of photocoagulating cells, the method comprising:
during a first interval, scanning a laser beam across a set of
cells, wherein one or more laser parameters and a length of the
first interval are selected to cause microcavitation in the set of
cells; during a second interval, deflecting the laser beam away
from the set of cells; detecting radiation from the set of cells;
determining an extent of the microcavitation occurring in the set
of cells based on the detected radiation; and ending the first
interval and beginning the second interval after a selected extent
of the microcavitation has occurred in the set of cells.
2. The method of claim 1, further comprising selecting the first
interval to have a length that is about 40% of the length of the
combined first and second intervals.
3. The method of claim 1, wherein scanning comprises scanning at a
scan rate between about 0.1 to about 10 microseconds per pixel.
4. The method of claim 3, wherein scanning comprises scanning at a
scan rate between about 0.5 to about 7 microseconds per pixel.
5. The method of claim 4, wherein scanning comprises scanning at a
scan rate between about 1 to about 5 microseconds per pixel.
6. The method of claim 1, wherein the radiation from the set of
cells forms a feedback signal indicative of microcavitation in the
set of cells.
7. The method of claim 6, wherein scanning comprises scanning at
least in part on the basis of the feedback signal.
8. The method of claim 1, wherein scanning and deflecting both
comprise modulating an acoustic-optical scanner.
9. The method of claim 1, wherein scanning and deflecting both
comprise rotating a polygonal mirror.
10. The method of claim 1, wherein scanning and deflecting both
comprise operating a resonance scanner.
11. The method of claim 1, further comprising changing a fluence of
the laser beam for a subsequent scan of the beam.
12. The method of claim 11, wherein changing the fluence comprises
changing the fluence in response to a parameter of light scattered
from the cells.
13. The method of claim 12, wherein changing the fluence in
response to a parameter comprises changing the fluence in response
to polarization of light scattered from the cells.
14. The method of claim 12, wherein changing the fluence in
response to a parameter comprises changing the fluence in response
to Doppler shift of light scattered from the cells.
15. The method of claim 12, wherein changing the fluence in
response to a parameter comprises changing the fluence in response
to the intensity of light scattered from the cells.
16. The method of claim 1, wherein the cells comprise retinal
cells.
17. The method of claim 1, wherein the microcavitation comprises
microbubble formation in the set of cells.
18. A method of treatment, comprising: using the method of claim 1
in treating at least one of glaucoma, ocular complications due to
diabetes, macular degeneration, and retinal detachment in a
patient.
19. A method of causing photocoagulation of cells, the method
comprising: scanning a laser across a set of cells at a scanning
frequency and laser power selected to cause microcavitation in the
set of cells; detecting microcavitation in the set of cells; and
terminating the scanning when a selected extent of microcavitation
has occurred, wherein scanning the laser comprises: defining a
first scan line; defining a second scan line; defining a third scan
line disposed between the first and second scan lines; scanning the
laser across the first scan line; skipping over the third scan
line; and scanning the laser across the second scan line, whereby
heat generated by scanning across the first scan line dissipates
into cells located along the third scan line.
20. The method of claim 19, wherein the cells comprise retinal
cells.
21. The method of claim 19, wherein the microcavitation comprises
microbubble formation in the subset of cells.
22. A method of treatment, comprising: using the method of claim 19
in treating at least one of glaucoma, ocular complications due to
diabetes, macular degeneration, and retinal detachment in a
patient.
.Iadd.23. A method of treating tissue cells, the method comprising:
during a first interval, scanning a laser beam across a set of
tissue cells, wherein one or more laser parameters and a length of
the first interval are selected to cause changes in one or more
properties of the set of cells; during a second interval,
deflecting the laser beam away from the set of cells; detecting
radiation from the set of cells; determining an extent of the
changes in the one or more properties occurring in the set of cells
based on the detected radiation; and ending the first interval and
beginning the second interval after a selected extent of changes in
the one or more properties has occurred in the set of
cells..Iaddend.
.Iadd.24. The method of claim 23, further comprising selecting the
first interval to have a length that is about 40% of the length of
the combined first and second intervals..Iaddend.
.Iadd.25. The method of claim 23, wherein scanning comprises
scanning at a scan rate between about 0.1 to about 10 microseconds
per pixel..Iaddend.
.Iadd.26. The method of claim 25, wherein scanning comprises
scanning at a scan rate between about 0.5 to about 7 microseconds
per pixel..Iaddend.
.Iadd.27. The method of claim 26, wherein scanning comprises
scanning at a scan rate between about 1 to about 5 microseconds per
pixel..Iaddend.
.Iadd.28. The method of claim 23, wherein the radiation from the
set of cells forms a feedback signal indicative of the changes in
the one or more properties of the set of cells..Iaddend.
.Iadd.29. The method of claim 28, wherein scanning comprises
scanning at least in part on the basis of the feedback
signal..Iaddend.
.Iadd.30. The method of claim 23, wherein scanning and deflecting
both comprise modulating an acoustic-optical scanner..Iaddend.
.Iadd.31. The method of claim 23, wherein scanning and deflecting
both comprise rotating a polygonal mirror..Iaddend.
.Iadd.32. The method of claim 23, wherein scanning and deflecting
both comprise operating a resonance scanner..Iaddend.
.Iadd.33. The method of claim 23, further comprising changing a
fluence of the laser beam for a subsequent scan of the
beam..Iaddend.
.Iadd.34. The method of claim 33, further comprising changing the
fluence in response to an intensity of light scattered from the
cells..Iaddend.
.Iadd.35. The method of claim 34, further comprising changing the
fluence in response to a polarization of light from the
cells..Iaddend.
.Iadd.36. The method of claim 34, further comprising changing the
fluence in response to a Doppler shift of light from the
cells..Iaddend.
.Iadd.37. The method of claim 34, further comprising changing the
fluence in response to a fluctuation of light from the
cells..Iaddend.
.Iadd.38. The method of claim 23, wherein the cells comprise
retinal cells..Iaddend.
.Iadd.39. The method of claim 23, wherein scanning the laser beam
across the set of cells causes microbubble formation in the set of
cells..Iaddend.
.Iadd.40. A method of treatment comprising: using the method of
claim 23 in treating at least one of glaucoma, ocular complications
due to diabetes, macular degeneration, and retinal detachment in a
patient..Iaddend.
.Iadd.41. The method of claim 23, further comprising selecting the
one or more laser parameters and the length of the first interval
to cause microcavitation in the set of cells..Iaddend.
.Iadd.42. The method of claim 23, wherein the changes in the one or
more properties comprise a change in reflectivity of the
cells..Iaddend.
.Iadd.43. The method of claim 23, wherein the detected radiation
comprises a change in backscattered light intensity..Iaddend.
.Iadd.44. The method of claim 23, wherein the detected radiation
comprises fluctuations in light intensity..Iaddend.
.Iadd.45. The method of claim 23, wherein the detected radiation
comprises a change in polarization..Iaddend.
.Iadd.46. The method of claim 23, wherein the detected radiation
comprises a Doppler shift..Iaddend.
.Iadd.47. The method of claim 23, further comprising scanning the
laser beam across the set of tissue cells during the first interval
to at least partially photocoagulate the set of cells..Iaddend.
.Iadd.48. The method of claim 23, further comprising scanning the
laser beam across the set of tissue cells during the first interval
to kill at least some of the set of cells..Iaddend.
.Iadd.49. The method of claim 23, wherein the one or more
properties are optical properties..Iaddend.
.Iadd.50. The method of claim 23, wherein the cells comprise eye
tissue cells..Iaddend.
.Iadd.51. The method of claim 23, wherein the cells comprise brain
tissue cells..Iaddend.
.Iadd.52. A method of treating tissue cells, the method comprising:
scanning a laser across a set of tissue cells at a scanning
frequency and laser power selected to cause changes in one or more
properties of the set of cells; detecting the changes in the one or
more properties of the set of cells; and terminating the scanning
when a selected extent of changes in the one or more properties of
the set of cells has occurred, wherein scanning the laser
comprises: defining a first scan line; defining a second scan line;
defining a third scan line disposed between the first and second
scan lines; scanning the laser across the first scan line; skipping
over the third scan line; and scanning the laser across the second
scan line, whereby heat generated by scanning across the first scan
line dissipates into cells located along the third scan
line..Iaddend.
.Iadd.53. The method of claim 52, wherein the cells comprise
retinal cells..Iaddend.
.Iadd.54. The method of claim 52, wherein scanning the laser across
the set of cells causes microbubble formation in the set of
cells..Iaddend.
.Iadd.55. A method of treatment, comprising: using the method of
claim 52 in treating at least one of glaucoma, ocular complications
due to diabetes, macular degeneration, and retinal detachment in a
patient..Iaddend.
.Iadd.56. The method of claim 52, further comprising selecting the
scanning frequency and laser power to cause microcavitation in the
set of cells..Iaddend.
.Iadd.57. The method of claim 52, wherein the changes in the one or
more properties of the set of cells comprise a change in
reflectivity of the cells..Iaddend.
.Iadd.58. The method of claim 52, wherein detecting the changes in
the one or more properties of the set of cells comprises measuring
radiation from the set of cells..Iaddend.
.Iadd.59. The method of claim 58, wherein the measured radiation
comprises a change in backscattered light intensity..Iaddend.
.Iadd.60. The method of claim 58, wherein the measured radiation
comprises fluctuations in intensity..Iaddend.
.Iadd.61. The method of claim 58, wherein the measured radiation
comprises a change in polarization..Iaddend.
.Iadd.62. The method of claim 58, wherein the measured radiation
comprises a Doppler shift..Iaddend.
.Iadd.63. The method of claim 52, further comprising scanning the
laser across the set of tissue cells to at least partially
photocoagulate the set of cells..Iaddend.
.Iadd.64. The method of claim 52, further comprising scanning the
laser across the set of tissue cells to kill at least some of the
set of cells..Iaddend.
.Iadd.65. The method of claim 52, wherein the one or more
properties are optical properties..Iaddend.
.Iadd.66. The method of claim 52, wherein the cells comprise eye
tissue cells..Iaddend.
.Iadd.67. The method of claim 52, wherein the cells comprise brain
tissue cells..Iaddend.
Description
FIELD OF INVENTION
This invention relates to methods and devices useful in laser
surgical techniques. More particularly, the invention relates to
methods of determining therapeutic end points and preventing
collateral damage in laser surgical techniques.
BACKGROUND
Laser surgery has become a generally useful technique, requiring
specialized equipment and techniques. Laser surgery is indicated in
the treatment of many eye diseases. For example, lasers are used to
treat the ocular complications of diabetes. For glaucoma patients,
lasers help to control the pressure inside the eye when medications
alone do not succeed. Lasers are used to seal holes in the retina,
and prevent or treat retinal detachments. Macular degeneration is
another condition where lasers can sometimes help prevent vision
loss. Laser surgery is also used after cataract surgery to improve
vision, if necessary.
The retinal pigment epithelium (RPE) is a single cell layer,
situated in the back of the eye behind a sensitive neuroretinal
layer, with a high pigment density that can be targeted by laser
irradiation. Retinal laser surgery can be classified into
techniques which rely on thermal damage to the neuroretinal layer
(such as retinal welding), and those that desirably do not involve
damage to the neuroretinal layer (such as photocoagulative
treatment of central serous retinopathy, diabetic macular edema,
and drusen).
Conventional laser photocoagulation of the retina is performed with
long pulses (on the order of from about 10 to about 500 ms)
generated from a continuous wave laser, with the majority of the
energy absorbed by the RPE. Heat diffusion during the long exposure
to the laser pulse results in a relatively large zone of thermal
damage, causing irreversible thermally-induced damage of not only
the RPE cells, but also the photoreceptors and the
choroicapillaris, producing scotomas (blind spots) in the treated
areas.
Selective RPE photocoagulation is a recently developed therapeutic
approach that uses short (microsecond) laser pulses to, ideally,
target retinal pigment epithelial cells while not affecting
adjacent photoreceptors in the retina, as described in U.S. Pat.
No. 5,302,259 to Birngruber, and U.S. Pat. No. 5,549,596 to Latina.
These treatment methods do not produce blind spots, as does
conventional laser photocoagulation. In fact, these treatments do
not produce any visible changes in the fundus during treatment.
However, clinicians have to rely on post surgery fluorescein
angiography to determine if the treatment endpoint has been
reached, a procedure that requires approximately an hour and is
inconvenient for the patient.
SUMMARY
The invention results from the discovery that detection of
microbubbles within retinal pigment epithelial (RPE) cells formed
upon absorption of pulsed laser radiation by RPE cells can be used
to inhibit or prevent thermal and mechanical damage to cells
proximate to those undergoing laser treatment. Thus, the invention
allows substantially instantaneous control over the laser dosimetry
to ensure that laser energy reaches the threshold required for RPE
cell killing (a therapeutic endpoint), but avoids the
administration of laser energies sufficient to damage adjacent
cells, such as photoreceptors (collateral damage control).
As used herein, "microcavitation" refers to the sudden formation
and collapse of microbubbles in a liquid, events which are
primarily caused by the absorption of light by chromophores in the
liquid. This term also applies to bubbles formed transiently by
local heating. The term does not necessarily require pressure
changes to exist.
In one aspect, the invention features a method of scanning a laser
beam across a set of cells. The method includes, during a first
interval, scanning a laser beam across a set of cells; and during a
second interval, deflecting the laser beam away from the set of
cells. The first interval is selected to cause microcavitation in
at least a portion of the cells from the set of cells.
Some practices further include selecting the first interval to have
a length that is about 40% of the length of the combined first and
second intervals.
Other practices include causing the first interval to end upon
detecting a selected extent of the microcavitation.
Additional practices include those in which scanning includes
scanning at a scan rate between about 0.1 to about 10 microseconds
per pixel, those in which scanning includes scanning at a scan rate
between about 0.5 to about 7 microseconds per pixel, and those in
which scanning includes scanning at a scan rate between about 1 to
about 5 microseconds per pixel.
Other practices also include receiving a feedback signal indicative
of microcavitation in the set of cells. In some of these practices,
scanning is carried out at least in part on the basis of the
feedback signal.
Additional practices include those in which scanning and deflecting
both include modulating an acoustic-optical scanner, those in which
scanning and deflecting both include rotating a polygonal mirror,
those in which scanning and deflecting both include operating a
galvometric scanner, and those in which scanning and deflecting
both include operating a resonance scanner.
Additional practices include those in which the fluence of the
laser beam is changed for a subsequence scan of the laser beam.
These practices include those in which fluence is changed in
response to a parameter of light scattered from the target cells.
Exemplary parameters include those derived from or dependent on
polarization, intensity, and/or Doppler shift of light scattered
from target cells. As used herein, a parameter derived from, or
dependent upon, a value of some property of the light includes the
value itself.
In another aspect, the invention features an apparatus for scanning
a laser beam across an array of cells. Such an apparatus includes a
laser for providing a laser beam; a scanner disposed in the path of
the laser beam; and a controller for causing the scanner to scan
the laser beam across a cell array at a rate selected to cause
microcavitation in the cell array.
In some embodiments, the controller is configured to cause the
scanner to deflect the beam away from the cell array in response to
detection of a selected extent of microcavitation within the cell
array. In other embodiments, the controller is configured to cause
the scanner to scan the laser beam across the cell array during a
first interval and to deflect the laser beam away from the cell
array during a second interval.
Other embodiments include those in which the controller is
configured to cause the first interval to be about 40% of the sum
of the combined first and second intervals, those in which the
controller is configured to cause the scanner to scan the laser
beam though an angle between about 0.1 degrees and about 5 degrees,
those in which the controller is configured to cause the scanner to
scan at a rate of between about 0.1 microseconds per pixel to about
10 microseconds per pixel, those in which the controller is
configured to cause the scanner to scan at a rate of between about
0.5 to about 7 microseconds per pixel, and those in which the
controller is configured to cause the scanner to scan at a rate of
between about 1 to about 5 microseconds per pixel.
Additional embodiments further include a detector for receiving a
signal indicative of microcavitation in the cell array.
In other embodiments, the controller is configured to control the
scanner at least in part on the basis of a signal indicative of
microcavitation in the cell array.
Embodiments also include those in which the scanner includes an
acousto-optic scanner, those in which the scanner includes a
polygonal mirror, those in which the scanner includes a galvometric
scanner, and those in which the scanner includes a resonance
scanner.
Unless otherwise defined, all technical and scientific terms used
herein have the same meaning as commonly understood by one of
ordinary skill in the art to which this invention belongs. Although
methods and materials similar or equivalent to those described
herein can be used in the practice or testing of the present
invention, suitable methods and materials are described below. All
publications, patent applications, patents, and other references
mentioned herein are incorporated by reference in their entirety.
In case of conflict, the present specification, including
definitions, will control. In addition, the materials, methods, and
examples are illustrative only and not intended to be limiting.
The present invention allows selective photocoagulation to be
carried out without the need for an inconvenient post-operative
determination of a therapeutic endpoint. The present invention
allows the photocoagulation of RPE cells without complications and
tissue destruction that can occur with conventional laser retinal
surgery. The present invention provides an apparatus that is
specifically suited for determination of a real-time therapeutic
endpoint, and feedback based on this determination to minimize
collateral damage which can arise from mechanical and thermal
damage associated with photocoagulation therapies.
Other features and advantages of the invention will be apparent
from the following detailed description, and from the claims.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic of a representative laser surgery system
according to a particular embodiment of the invention.
FIG. 2 is an oscilloscope trace of reflectivity versus time.
DETAILED DESCRIPTION
The invention is based on the optical measurement of the onset of
laser-induced cavitation and feedback to the laser source or to the
operator to control the delivered laser energy based on the
measurement. The absorption of laser energy by chromophores
(specifically melanosomes) within, or proximate to, cells produces
transient (lifetimes on the order of nanoseconds to microseconds)
microcavitation bubbles with diameters on the order of micrometers.
The bubbles arise since the laser excitation of the chromophores
can rapidly produce local heating in the immediate vicinity of the
chromophores. It has been observed that the local heating can be
intense enough to vaporize a thin layer of liquid in intimate
contact with the chromophores. Detection of the presence of
microbubbles is a way to determine the amount of heating caused by
laser energy. Microcavitation causes a temporary and measurable
change in the reflectivity of the cells being irradiated. This
change is used to adjust the energy of the laser source and thereby
minimize damage to proximate cells that are not desirably exposed
to the same laser energies used to cause photocoagulation or
thermal energies that can kill those proximate cells.
Selective RPE photocoagulation with the feedback of the present
invention provides useful therapeutic outcomes. While not bound by
any particular theory of operation, it is believed that the
selective killing of diseased RPE cells can stimulate neighboring
RPE cells to proliferate and form a new and properly functional RPE
cell layer to replace those killed by selective photocoagulation.
Thus, selective RPE photocoagulation can serve as a method of
treatment for diseases believed to be associated with the RPE, such
as central serous retinopathy, diabetic macular edema, and
drusen.
Referring to FIG. 1, a representative laser surgery system is
shown. Treatment laser source 10 sends treatment laser beam 12 to
dichroic beam splitter 14. Dichroic beam splitter 14 is adapted to
allow transmittance of treatment beam 12. Treatment beam 12 is
focused by focusing lens 22 to impinge on mirror 24 that directs
treatment beam 12 through contact lens 26 into eye 28. Scanner 64
can be used to controllably scan the electromagnetic radiation
across the cells of eye 28. The position of scanner 64 is variable,
and an illustrative example of a position is provided in FIG. 1.
Optional probe laser 30 produces probe beam 32, which is directed
onto polarizing beam splitter 34, directing probe beam 32 toward
quarter wave plate 36. Probe beam 32 impinges on dichroic beam
splitter 14, which is adapted to reflect probe beam 32 along
substantially the same path as treatment beam 12. Probe beam 32 is
reflected back along the same path and a fraction of probe beam 32
passes through polarizing filter 34, through focusing lens 38, and
into detector 40. The probe laser and beam is optional. The
interior of eye 28 is illuminated by slit lamp 42. Detector 40
sends detector signal 44 to discriminator 46 for determination of
the presence of signal peak 48. Determination of the presence of
signal peak 48 leads to signal 50 being sent to converter 52 which
either sends signal 54 to laser source 10 immediately, or stores
the current treatment laser energy value and, according to a
multiplier value input to the converter, sends signal 54 to laser
source 10 when the treatment laser energy reaches a value equal to
the current treatment laser energy value plus some fraction of that
value, determined by the multiplier value. Signal 54 can be a stop
ramp signal, or can be a signal to input into controller 62, to
modulate the electromagnetic radiation.
In some embodiments, interferometer 60 can be introduced between
eye 28 and detector 40. in such embodiments, probe beam 32
(alternatively, treatment laser beam 12) is divided, so that a
first portion of the beam impinges eye 28, and a second portion of
the beam impinges interferometer 60. The position of interferometer
60 is variable, and an illustrative example of a position is shown
in FIG. 1. Detector 40 operates to detect interference between
these portions of the beam, for example frequency or intensity
interferences.
Treatment Laser Source
The treatment laser source provides a treatment beam having the
following characteristics. The wavelength of light (that is, the
energy of light) of the treatment beam is chosen to be selectively
absorbed by the target tissue. The wavelength of the light source
is desirably within the absorption spectrum of the chromophore
present within or proximate to the cell or group of cells to be
treated. For example, a treatment laser that produces visible light
can be used in the practice of the invention. Visible light is
generally light having a wavelength of from about 400 nm to about
800 nm. For retinal pigment epithelial cells, preferred wavelengths
for the treatment beam range front about 400 nm to about 600 nm,
for example, from about 450 nm to about 550 nm.
For other medical procedures which can benefit from selective
photocoagulation, such as treatment of neural tissue by laser
surgery, other lasers can be utilized. For example, if a
chromophoric material such as lamp black, or other laser light
absorbing material, were delivered within, or bound to the surface
of, tumor cells or other cells to be killed, the laser wavelength
could be a longer wavelength light source tailored to the
chromophoric material. The chromophore can be delivered to be
absorbed within a cell, or can be bound to the surface of the cell,
for example, by antibodies, or by covalent or ionic bonding.
Chromophores which can be used in the practice of the invention can
be any which will produce heat upon laser irradiation sufficient to
create microbubbles, e.g., melanin, carbon black, gold, iron oxide,
and other laser phototherapy chromophores known to those of skill
in the art.
Light of significantly shorter wavelength than visible light can be
absorbed directly by a wide variety of proteins, nucleotides, and
many other cellular materials that tend to be distributed
throughout cells generally. Thus, a treatment beam of a wavelength
much shorter than 400 nm, for example, below 360 nm, does not tend
to selectively affect cells containing visible-light chromophores,
and thus should be avoided. Further, a treatment beam of
significantly longer wavelength than visible light is not
particularly strongly absorbed by the chromophores of the RPE, and
therefore penetrates deeper into the choroid, effectively creating
a thicker heat reservoir under the photoreceptors. This thicker
heat reservoir takes longer to cool (since the cooling time
increases as the square of the layer thickness), and releases more
energy into the adjacent tissue. Thus, photoreceptors are more
likely to be damaged with a treatment beam of near infrared
wavelength, even if the pulse duration is shortened.
A laser which produces pulsed light can be used in the new methods.
For example, pulses of pulse widths less than about 10 microseconds
(.mu.s) are desirable, for example less than about 5 .mu.s, 1
.mu.s, 100 nanoseconds (ns), 1 ns, or 100 picoseconds (ps). Pulse
width (that is, pulse duration) of the laser is chosen to be
sufficiently short that heat conduction away from the absorbing
tissue to the surrounding tissue is minimized.
Alternatively, a laser that produces continuous light can be used.
In such embodiments, the continuous light can be "chopped," for
example, by an opto-acoustic modulator, which produces pulsed
light. Such a chopper can be placed immediately in front of the
laser source, so as to produce the same "chopped" light in both the
through and reflected beam fractions.
In some embodiments, the laser energy is delivered to particular
tissue areas, even to the limit of individual cells, as a train of
short pulses. Each pulse within the train does not contain enough
energy to cause mechanical disruption, but the effect of all short
pulses cumulatively creates selective thermal damage at the RPE.
Such trains are characterized, in part, by a repetition rate. In
particular methods of treating tissue within the eye, the
repetition rate is desirably high enough so that the pulse train be
delivered to the tissue within less than about 1 second, so that
the effects of eye movement car be minimized. On the other hand,
the repetition rate is desirably not so high as to be substantially
equivalent to continuous wave excitation, which can produce heating
effects in the bulk tissue. The repetition rate varies from about
10 Hz to about 500 Hz, for example, from about 50 Hz to about 2000
Hz, or from about 100 Hz to about 1000 Hz.
In traditional photocoagulation, with pulse widths of from about 50
to 500 ms, laser-tissue interaction is well described by thermal
processes; absorption of light energy by the RPE is accompanied by
heat diffusion away front the absorbing layer to the adjacent
tissue, producing a zone of thermal damage which is visible under
opthalmoscopic examination as a coagulated lesion on the retina.
This thermal process remains for pulse widths down to the
sub-millisecond range. For shorter pulse widths (ns and ps) on the
other hand, very little thermal diffusion can take place on the
timescale of the laser pulse. The laser energy is selectively
deposited into the melanin granules within the RPE, creating a
situation in which the temperature distribution in the cell is
highly non-uniform. Discrete hot spots are created within the cell,
at the energy absorbing granules, while the rest of the cell
experiences little heating. Thermal diffusion creates temperature
equilibrium on the timescale of microseconds after the laser pulse
(for a melanosome of approximately 1 .mu.m, the thermal relaxation
takes place in approximately 1 .mu.s). The average temperature of
the whole cell after thermal relaxation is much lower than the
initial temperature spikes created upon excitation. RPE killing is
observed only when the laser fluence exceeds a threshold for
initiating microscopic cavitation bubble formation inside the RPE
cells. Transient heating alone below bubble formation does not
appear to lead to cell killing.
Microbubbles originate from explosive vaporization of a thin (less
than about 0.1 .mu.m) layer of fluid surrounding the individual
heated particles. The explosive growth of microbubbles is observed
within less than a nanosecond after the particles are irradiated
with a 30 picosecond laser pulse, but the bubbles are not stable.
After an initial expansion to a maximum diameter of a few
micrometers, the bubbles collapse with a lifetime of about 0.1 to 1
microsecond, the lifetime being fluence dependent. For fluences up
to a few times the microcavitation threshold, coalescing bubbles
can form from individual bubbles, and can collapse entirely within
the cell, that is, the cell is not blown apart by the
microexplosion. The cell retains its shape with little apparent
change in morphology. Laser induced microcavitation is described
generally in Kelly et al., "Microcavitation and cell injury in RPE
cells following short-pulsed laser irradiation," Proc. SPIE 2975
(1997), and in Lin et al., "Selective Cell Killing by Microparticle
Absorption of Pulsed Laser Radiation," IEEE J. Sel. Topics Quantum
Elect., Vol. 5, No. 4, July/August 1999, pp 963-8.
At laser fluences of approximately five times the cavitation
threshold, irradiated cells undergo a remarkable expansion which
does not burst the cells, but distends them severely. At lower
fluences, the bubbles are smaller, and the morphology of the cells
changes very little after bubble collapse. Individual melanosomes
also undergo cavitation in a similar manner. After bubble collapse,
the melanosomes can remain intact.
A train of pulses with respect to particular areas of tissue can be
produced by using a continuous wave laser and rapidly scanning the
beam over the area of tissue, so that each RPE cell effectively is
exposed only to a short pulse, such as a microsecond pulse. The
cells or tissue to be treated can be repetitively exposed to such
scans, to simulate multiple pulse exposures. Single pulses can
produce unwanted mechanical perturbation of the cells or tissue
being treated. The desired pulse width and repetition rate can be
obtained by proper setting of the scanning speed (pixels/second)
and scanning range. Scanning ranges can be any dimensions less than
about 1000 .mu.m.times. about 1000 .mu.m, for example about 300
.mu.m.times. about 300 .mu.m. The scanning fields need not be
square, but can be rectangular, or any shape convenient to scan.
The scan lines need not be contiguous. Separated scan lines can
further minimize thermal build-up in the bulk tissue. The exact
dimensions will depend on the particular optics utilized in the
surgical setup, as can be recognized and optimized by those of
skill in the art.
In some embodiments, the laser beam is scanned by an opto-acoustic
deflector, Which can deflect a continuous wave laser. The
continuous wave laser is able to remain "on" essentially 100% of
the time. The scanning methodology can be defined by parameters of
scanning speed and scan angle. Useful scanning speed can range from
about 0.1 to about 10 .mu.s per pixel, for example, from about 0.5
to about 7 .mu.s per pixel, or from about 1 to about 5 .mu.s per
pixel. The scan angle can range from about 0.1 to about 5 degrees,
for example, from about 0.5 to about 2 degrees.
Scanning can be carried out by a number of different scanning
devices, such as two-dimensional acousto-optic deflectors (2D-AOD),
galvometric scanners, rotating polygons, and resonance scanners. In
some embodiments, acousto-optic deflectors are useful, because of
their speed, linearity across the scan, and variable scan ranges,
leading to more efficient data collection than is available with
some other scanning devices. In addition, because 2D-AOD scanning
uses sound waves in a crystal, there are no moving parts. Suitable
AOD scanners are commercially available, for example, from Brimrose
Corp. Suitable scanners include a two orthogonal AO crystals to
scan the optical beam in x and y directions. Scanning can be
carried up to 1.6 degrees on either axis, equivalent to a scan of
480 .mu.m by 480 .mu.m on the fundus of the eye if no contact lens
is used.
Desirable laser fluences for selective photocoagulation are
dependent on the detection of microcavitation, the particular pulse
width for pulsed lasers or chopped beams, the wavelength of laser
light employed, the type of cell irradiated, and the concentration
of chromophore irradiated. For example, for treatment of RPE cells
using 8 ns pulse widths of 532 nm light, the treatment laser
fluences which are desirable range from about 0.08 to about 0.16
J/cm.sup.2. For treatment of RPE cells using 3 .mu.s pulse widths
of 532 nm light, the treatment laser fluences which are desirable
range front about 0.22 to about 0.44 J/cm.sup.2.
Particular treatment lasers which can be used in the practice of
the invention include continuous wave lasers, including gas lasers
such as argon ion, krypton ion lasers adjusted to produce visible
light, as well as solid state lasers which produce visible light,
such as Nd-YAG lasers. A variety of excimer-pumped or YAG
laser-pumped dye lasers can also be used to readily produce pulsed
visible excitation. In some embodiments, the treatment laser source
utilized is an Nd-YAG laser operating at 532 nm.
Probe/Detection
As shown in FIG. 1, the invention can also utilize a probe source
that provides a probe beam. The wavelength of the probe beam can
vary, but it should be recognized that generally, it is considered
desirable to filter the generally intense treatment laser beam so
that it does not saturate the detector, and that filter means are
generally not extremely selective, so that spectral information in
the immediate wavelength vicinity of the treatment beam may not be
available for monitoring. Therefore, it may be preferable to use
probe source which can illuminate in spectral regions somewhat
removed from the treatment source wavelength, for example, at least
about 3 nm, 5 nm, or 7 nm away.
Detection of bubbles formed with a scanning excitation laser beam
can be done with the probe beam scanned together with the
excitation beam. Alternatively, the probe beam can be left
stationary somewhere within the scanning field, for example near
the center of the scanning field. In such a configuration, the
stationary probe beam will detect a bubble only when the excitation
beam imparts enough energy to the spot covered by the probe beam to
produce a bubble, giving rise to a time-dependent signal
synchronized with the scan. Alternatively, back-scattering of the
excitation beam itself can be used to monitor bubble formation. In
such a configuration, the back-scattering intensity is detected by
a detector and compared with a reference intensity generated from
the excitation beam itself. Below the bubble formation threshold,
the back-scattering signal will be proportional to the reference
intensity, with some variation as the beam scans over the treatment
area. Above the bubble formation threshold, the back-scattering
signal will be enhanced and show much greater fluctuation due to
the expansion and collapse of bubbles. The increase in light
fluctuation can be used as a signature for the onset of bubble
formation.
The intensity of the probe beam must be sufficient to allow
monitoring of the transient events within the cell or tissue of
interest. The optical properties of the sample can dictate the
intensity considerations for the probe source. On the other hand,
the intensity should not be so great as to independently cause
heating within the cell or tissue. The adjustment of the intensity
of the probe source to meet these criteria is within the
capabilities of one of ordinary skill in the art.
The particular absorbance and reflectance properties can dictate
the geometry of the probe and detection instruments. Any geometry
which allows detection of scattered light can be used. In
particular embodiments, the probe source can be used in a
through-sample or reflective (back-scattering) geometry. For in
vivo applications, through-sample will not generally be possible.
Back-scattering geometries are generally more useful for in vivo
treatment. In some embodiments, the geometry is a back-scattering
detection of an optical probe beam. For example a helium neon
(HeNe) laser can be focused to a 10 .mu.m diameter spot on the
tissue to be treated. The probe laser power should be adjusted to
prevent heating of the tissue by the probe beam, and can be from
about 0.01 to about 1 mW, for example, from about 0.05 to about 1
mW, or from about 0.1 to about 1 mW.
The probe beam can be continuous wave or pulsed. If the probe beam
is pulsed, and the treatment beam is scanned, the probe beam is
desirably synchronized with the treatment beam to improve signal
quality.
Detection of an optical probe can be accomplished by photodiodes,
photomultiplier tubes (PMT), and other similar and associated
devices known in the art. The various advantages and capabilities
of optical detection systems are discussed in numerous references
known to those of skill in the art. For the present purposes,
important capabilities of an optical detection system are speed and
sensitivity. In particular embodiments, an avalanche-type
photodiode can be used, with a confocal aperture placed in front of
the opening. Bandpass filters can be employed to substantially
eliminate the signal from reaching the detector and overloading or
possibly damaging the detector.
The output of the detector is fed into a monitoring device, such as
an oscilloscope, a cathode ray-type monitor, a pen recorder, or
other monitoring device. In particular embodiments, the output of
the detector is fed into a digital oscilloscope, which is
synchronously triggered by the laser source producing the
excitation beam.
Methods of Treatment
The invention includes methods of treating tissue by killing cells,
individually and in groups. These methods are carried out by
administering laser energy sufficient to photocoagulate the cells
within particular tissue, or regions of tissue, while avoiding harm
to adjacent or neighboring tissue, or regions of tissue. These
methods involve the formation of microbubbles within the individual
target cells or groups of target cells, but without allowing heat
transfer sufficient to cause significant damage to cells proximate
the target cells. Bubble formation is used as a treatment endpoint
monitor. Even if bubble formation occurs at a fluence above the
threshold for RPE cell killing, it can still be used to mark the
treatment endpoint as long as the degree of tissue damage at this
fluence is well confined to the RPE and spares the
photoreceptors.
For example, methods of treating particular cells in RPE tissue
involve exercising substantially precise control over the laser
dosimetry administered. Such control is achieved by a real-time
monitor that reflects the state of affairs within the tissue being
treated. The control is based on the use of microbubble detection
to determine the end-point of laser therapy for target cells, and
to prevent damage to cells proximate the target cells.
As a first step to carry out therapeutic treatment involving the
inventive method, target cells are identified. Target cells can be
any which can benefit from selective photocoagulation treatment.
Target cells must be able to absorb laser energy selectively, or be
treated to be able to absorb laser energy selectively (e.g., by the
introduction of a chromophore). Suitable target cells for selective
photocoagulation are those target cells which are proximate to
cells which should not be photocoagulated. For example, retinal
pigment epithelial cells, which are proximate to neuroretinal
cells, are well suited for selective photocoagulation. Brain tumor
cells, which are proximate to normally functioning cells, can also
be target cells. Target cells are prepared for exposure to a
treatment laser beam by positioning focusing optics, such as a
contact lens for RPE cell treatment. The application of a contact
lens for laser eye surgery is well known to those of skill in the
art. The treatment laser is activated to operate initially at a low
beam intensity, for example, from about 10% to about 80%, for
example, from about 25% to about 80%, or from about 50% to about
75%, of the ED.sub.50 threshold determined for a particular pulse
width and cell type. For example, for selective RPE
photocoagulation, the laser can be initially operated at beam
fluences of from about 0.008 to about 0.064 J/cm.sup.2, for an 8 ns
pulse width, or from about 0.022 to about 0.176 J/cm.sup.2 for a 3
.mu.s pulse. The laser beam fluence can be slowly increased While
monitoring parameters of the scattered treatment beam, as
determined from a back-scattering geometry, for example. One useful
parameter is the intensity of the treatment beam scattered from
target cells. Other useful parameters can be polarization of light
scattered from target cells, or Doppler shifts of light scattered
from target cells, which arise due to the expansion and other
movement of microbubbles.
The monitoring should be carried out so as to determine if there is
any change, for example, a positive change, in the reflectivity of
the target cells. As used in this context, a "change" refers to a
difference in signal which is detectable by a sustained change in
the slope in a plot of target cell reflectance versus time, by a
sustained change in relative target cell reflectance signal as
compared to a baseline reflectance, or by observation of a visually
apparent peak in a plot of target cell reflectance versus time. In
embodiments which monitor changes in a scanning treatment beam, the
background reflectance may fluctuate as the treatment beam passes
over the relatively inhomogeneous surfaces of target cells, which
can include structures such as blood vessels, which can show
changes in reflectivity even in the absence of bubble formation.
The formation of microbubbles is expected to be discernable over
this fluctuating background, so that peaks due to bubble formation
may be somewhat more difficult to detect, but not prohibitively
difficult. The detection of microbubbles correlates with the laser
beam energy which is referred to as ED.sub.50, that is the laser
dose necessary to result in death of 50% of target cells.
Upon detection of a change in reflectivity, by digital, analog, or
manual means, the treatment laser beam intensity can be immediately
or subsequently modulated, that is, by discontinuing the increase
in treatment laser beam energy. In some embodiments, the detection
of microbubbles signifies an immediate or substantially immediate
halt in the ramp of beam intensity increase. In some embodiments,
the detection of microbubbles will cause the beam intensity to be
noted, as a digital or analog value (as a threshold value, that is
ED.sub.50) and the ramp of beam intensity will be continued until a
value of ED.sub.50+xED.sub.50 is reached, where x is greater than
zero, and less than about two.
Bubble formation can form near the end of the laser pulse, if the
laser energy is initially selected to be low relative to the bubble
formation threshold. and gradually increased to reach this
threshold. Therefore, the back-scattered signal intensity should
show a sudden increase near the end of the laser pulse if a bubble
is produced. By comparing the incoming pulse shape with the
scattered pulse shape, the onset of bubble formation can be
determined.
Particular diseases in the retina are associated with retinal
pigment epithelium. The RPE has as a primary function the exchange
of nutrients to and from neuroretinal and other cells. These
diseases include, for example, central serous retinopathy, diabetic
macular edema, and drusen. The invention provides a means of
treatment of such diseases by selective RPE photocoagulation.
EXAMPLES
The following examples illustrate certain properties and advantages
inherent in some particular embodiments of the invention.
Example 1
Ex Vivo Transient Bubble Formation
Porcine eyes of approximately 20 mm diameter were prepared 0 to 4
hours after enucleation. The eyes were dissected, and the vitreous
was removed. A sheet of 1 cm.sup.2 was cut out of the equatorial
region of the eye and the sample was suspended in 0.9% saline
solution. After 20 minutes the retina could be easily peeled off.
The sample was flattened at the edges using a plastic ring. The RPE
was covered with diluted Calcein AM (Molecular Probes) 1:1000 in
PBS or Dulbecos modified eagle medium (Gibco). A cover slip was
applied on top. After 20 minutes, viable cells accumulated enough
fluorescent Calcein to be distinguished from dead cells by
fluorescence microscopy. Calcein fluorescence was excited at 488 nm
and detected from 540 nm to 800 nm. One fluorescence image was
taken before and a second 15-30 minutes after irradiation.
Non-fluorescing cells where classified as dead. For 12 ns
experiments, the sample temperature was 20.degree. C. For 6 .mu.s
pulses, the sample was kept at 35.degree. C. The thresholds were
calculated using a PC program for probit analyses (Cain et al., "A
Comparison of Various Probit Methods for Analyzing Yes/No Data on a
Log Scale," US Air Force Armstrong Laboratory, AL/OE-TR-1996-0102,
1996) after Finney ("Probit Analysis," 3rd ed. London: Cambridge
University Press; 1971). A 20.times. objective (NA 0.42, 25 mm
working distance) was used to image the cells onto a CCD camera.
The spatial resolution of the setup was approximately 1 .mu.m. A
frequency-doubled, Nd:YAG Laser (Continuum, SEO 1-2-3, .lamda.=532
nm, 6 mm beam) was used for 12 ns irradiation. A 200 .mu.m section
from the center of the beam was imaged on the sample to give a flat
top image of 20 .mu.m diameter. The intensity variations at the
sample due to hot spots in the beam were below 15%, as determined
by a fluorescing target within the area of irradiation. 6 .mu.s
Pulses were chopped from a cw frequency doubled Nd:YAG Laser
(Verdi, Coherent, .lamda.=532 nm). The Gaussian-shaped spot had
FWHM of 16 .mu.m on the sample. To probe the bubble formation, the
collimated beam of a diode laser (SF830S-18, Microlaser Systems,
830 nm, 1.5.times.2 mm beam diameter) was focused (7.times.10 .mu.m
FWHM) onto the RPE cell with a maximum power of 1 mW at the sample.
The average Nd:YAG power was 75 mW. The probe beam was switched on
for less then 10 .mu.s and switched off (1% power) 2-4 .mu.s after
the end of the pulse. The light was detected in a confocal geometry
and also slightly off the optical axis to reduce back reflectance
and scattering from the optical system and from tissue layers other
than the RPE. The detector used was an avalanche photodiode
(Hamamatsu C-5460), including a high-speed amplifier with 10 MHz
bandwidth.
For 12 ns pulses, 4 samples from 4 different eyes were taken, on
which a total of 117 spots were irradiated at different fluences
(40 controls with Nd:YAG only, 77 including probe beam). The
threshold for cavitation and cell death were the same, as displayed
in Table 1. FLL refers to the fluence lower threshold level, FUL is
the fluence upper threshold level, and Fluence is the mean of these
two determinations. The # cells is the number of cells exposed to
irradiation.
TABLE-US-00001 TABLE 1 12 Nanosecond Thresholds for Cavitation and
Cell Death Fluence FLL Fluence FUL Fluence # (mJ/cm.sup.2)
(mJ/cm.sup.2) (mJ/cm.sup.2) slope cells cell death 71 66 75 17 77
cavitation 71 67 75 16 77 control 71 66 81 14 40
FIG. 2 is an oscilloscope trace of a reflectance signal at 1.1
times threshold with a minimal lifetime of 200 ns. The diode laser
was switched on at 0.2 .mu.s and switched off at +3.4 As to
minimize sample heating. The Nd:YAG laser was fired at 1.2 .mu.s,
which caused a detectable increase in probe beam back scattering in
a single RPE cell.
Example 2
In Vivo Treatment of RPE Tissue
A total of six eyes of three chinchilla gray rabbits are used. The
rabbits are anesthetized with ketamine hydrochloride (30 mg/kg) and
xylazine hydrochloride (6 mg/kg). The eyes are dilated with 1 drop
of cyclopentolate hydrochloride and 1 drop of 5% phenylephrine
hydrochloride, then a -67 diopter Goldmann planoconcave lens is
placed on the eye.
For laser irradiation, the output of a Q-switch, frequency doubled
Nd:YAG laser at a wavelength of 532 nm is used. The pulse width is
controlled by shaping the high voltage pulse applied to the
Pockel's cell while actively monitoring the intracavity energy
build up. Without the active feedback, the normal Q-switch output
pulse width is typically 250 ns with pulse energies of several mJ
at a repetition rate of 500 Hz. A probe beam is provided by a HeNe
laser at 0.5 mW. The back scattered probe beam is detected by an
avalanche photodiode. The output of the detector is fed into an
oscilloscope.
Under slitlamp examination, four 100 .mu.m marker lesions are
placed outside the corners of a designated 300 .mu.m.times.300
.mu.m treatment area, using 100 ms of continuous laser exposure
each (approximately 100 mW). Then the treatment beam is turned on,
and 100 successive scans are delivered to the treatment area. Each
eye receives four such treatment spots with laser power settings of
0.5, 1, 2, and 3 times the ED.sub.50 threshold as determined above.
All laser treatment procedures are recorded with a CCD camera and a
video tape recorder. Fundus imaging and fluorescein angiography is
performed at 1 hour after irradiation. Changes in probe beam
scattering are detected and displayed on the oscilloscope. The
detection of microbubbles is accompanied by stabilization of laser
fluence at 1.5 ED.sub.50. Treatment is further carried out at this
fluence.
At the completion of the treatment, the animals are sacrificed with
pentobarbital injection. The eyes are enucleated and processed for
light and electron microscopy examination. The total time from
laser exposure to enucleation is approximately 2 hours. Each
enucleated eye is fixed in phosphate-buffered 2% glutaraldehyde for
24 hours. The anterior segments and vitreous are removed, and the
posterior eye is postfixed in phosphate-buffered 2% osmium
tetroxide, dehydrated, and embedded in epoxy resin. Thick sections
(approximately 1 .mu.m) for light microscopy are stained with
toluidine blue. Thin sections for electron microscopy are stained
with uranyl acetate/lead acetate. Areas treated by the scanning
laser are compared with control areas and with marker lesions
(coagulated with continuous wave laser) for damage to the
photoreceptors, RPE, Bruch's membrane, and the choriocapillaris.
Comparison is made to verify that the RPE cells are photodamaged
and the photoreceptors, Bruch's membrane, and the choriocapillaris
are undamaged and viable.
Other Embodiments
It is to be understood that while the invention has been described
in conjunction with the detailed description thereof, the forgoing
description is intended to illustrate and not limit the scope of
the invention, which is defined by the scope of the appended
claims. Other aspects, advantages, and modifications are within the
scope of the following claims:
* * * * *