U.S. patent application number 09/992400 was filed with the patent office on 2003-06-12 for devices and techniques for light-mediated stimulation of trabecular meshwork in glaucoma therapy.
Invention is credited to Shadduck, John H..
Application Number | 20030109907 09/992400 |
Document ID | / |
Family ID | 22290357 |
Filed Date | 2003-06-12 |
United States Patent
Application |
20030109907 |
Kind Code |
A1 |
Shadduck, John H. |
June 12, 2003 |
Devices and techniques for light-mediated stimulation of trabecular
meshwork in glaucoma therapy
Abstract
An apparatus and technique for transscleral light-mediated
biostimulation of the trabecular plates of a patient's eye in a
treatment for glaucoma or ocular hypertension. The apparatus
includes; (i) a working end geometry for contacting the anterior
surface of the sclera and cornea to insure that a laser emission
reaches the trabecular meshwork from a particular location on the
anterior surface of the sclera, (ii) a laser energy source
providing a wavelength appropriate for absorption beneath the
anterior scleral surface to the depth of the trabecular plates, and
(iii) a dosimetry control system for controlling the exposure of
the laser emission at the particular spatial locations. The device
uses a light energy source that emits wavelengths in the
near-infrared portion of the spectrum, preferably in the range of
about 1.30 .mu.m to 1.40 .mu.m or from about 1.55 .mu.m to 1.85
.mu.m. The depth of absorption of such wavelength ranges will
extend through most, if not all, of the thickness of the sclera
(750 .mu.m to 950 .mu.m). In accordance with a proposed method of
trabecular biostimulation, the targeted region is elevated in
temperature to a range between about 40.degree. C. to 55.degree. C.
for a period of time ranging from about 1 second to 120 seconds or
more.
Inventors: |
Shadduck, John H.; (Tiburon,
CA) |
Correspondence
Address: |
John H. Shadduck
1490 Vistazo West
Tiburon
CA
94920
US
|
Family ID: |
22290357 |
Appl. No.: |
09/992400 |
Filed: |
November 17, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09992400 |
Nov 17, 2001 |
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09102533 |
Jun 22, 1998 |
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6319274 |
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Current U.S.
Class: |
607/89 ; 604/20;
606/3 |
Current CPC
Class: |
A61N 2005/0659 20130101;
A61F 2009/00868 20130101; A61N 5/0613 20130101; A61F 2009/00844
20130101; A61N 5/067 20210801; A61F 2009/00891 20130101; A61N
2005/0644 20130101; A61F 9/008 20130101 |
Class at
Publication: |
607/89 ; 604/20;
606/3 |
International
Class: |
A61N 001/30; A61N
005/067 |
Claims
What is claimed is:
1. A method for delivering energy to trabecular meshwork in a
patient's eye, comprising: positioning a working face of a member
in contact with a patient's sclera overlying the trabecular
meshwork; and delivering at least one laser beam through the member
wherein said at least one beam is transmitted transclerally to
irradiate a region of said trabecular meshwork.
2. The method of claim 1 wherein said at least one beam has a
wavelength range from about of 1.30 .mu.m to 1.85 .mu.m.
3. The method of claim 1 further comprising the steps of: sensing a
temperature of the sclera overlying the trabecular meshwork with at
least one sensor in said member to provide a signal; and modulating
or terminating the delivery of said at least one laser beam in
response to said signal.
4. The method of claim 3 further comprising the step of elevating
the temperature of said trabecular meshwork to a range between
about 40.degree. C. to 55.degree. C.
5. A method for delivering energy to a patient's trabecular
meshwork to treat glaucoma, comprising the steps of: (a) placing a
laser emitter in contact with a portion of the sclera of the
patient's eye overlying the trabecular meshwork; (b) delivering
laser energy from the emitter at a wavelength ranging between about
1.30-1.40 .mu.m or 1.55-1.85 .mu.m; and (c) modulating the power
level, pulse duration and pulse intervals of the laser energy to
maintain the temperature of the trabecular meshwork at less than
about 60.degree. C. (d) wherein said laser energy delivery causes
substantially uniform thermal effects in all layers of the
trabecular meshwork.
6. The method of claim 5 wherein the laser emitter is carried in a
contact surface of a thermally conductive material having a surface
area greater that about 20 mm.sup.2 thereby conducting heat away
from surface sclera layers.
7. The method of claim 5 further comprising the steps of sensing
the temperature of the sclera overlying the trabecular meshwork
with at least one sensor carried within the working face to provide
a signal and modulating the laser energy delivery in response to
the signal.
8. A method for delivering energy to a patient's trabecular
meshwork to treat glaucoma, comprising the steps of: (a) placing a
laser emitter in contact with a patient's eye wherein the axis of
laser beam propagation is aligned with the trabecular meshwork; (b)
delivering laser energy from the emitter at a selected wavelength;
and (c) modulating the power level, pulse duration and pulse
intervals of the laser energy to maintain the temperature of the
trabecular meshwork at less than about 60.degree. C.; (d) wherein
said laser energy delivery causes substantially uniform thermal
effects in all layers of the trabecular meshwork.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a Continuation of U.S. patent
application Ser. No. 09/102,533 filed Jun. 22, 1998 titled "Devices
and Techniques for Light-Mediated Stimulation of Trabecular
Meshwork in Glaucoma Therapy."
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to the field of medical
therapeutics and more specifically relates to the field of glaucoma
and ocular hypertension therapy utilizing novel instruments and
techniques for opto-thermal mediation of a patient's trabecular
meshwork for enhancing the mitotic rate of endothelial meshwork
cells and for reduction of biostructural laxity within the
meshwork, which meshwork biocharacteristics may be subject to
cell-division inhibitions and/or other degradations.
[0004] 2. Description of the Related Art
[0005] Glaucomas comprise a group of debilitating eye diseases that
are the leading cause of blindness in the United States and around
the world. The pathophysiological mechanisms of glaucomas are not
fully understood. The principal sign of the disease is elevated
intraocular pressure (IOP). Such elevations of IOP ultimately can
cause damage to the optic nerve head and result in impairment to,
or loss of, normal visual function. It is known that elevated IOP
is caused by an excess of fluid or aqueous AQ within the eye, which
is continually produced by the ciliary body CB and drained through
the trabecular meshwork M to leave the eye or globe 5 (see FIGS.
1A-1D). The excess intraocular fluid generally results from
blockage or impairment of the normal drainage from the anterior
chamber AC via the trabecular meshwork M. The meshwork consists of
about 10 to 25 layers of perforated trabecular plates (TP.sub.1 . .
. TP.sub.n) or sheets around the filtration angle FA of the
anterior chamber AC, having a width of about 1,000 .mu.m to 1,500
.mu.m (1.0 mm. to 1.5 mm.) in a circumference ranging from 35,000
to 40,000 .mu.m. FIGS. 1A-1B show electron micrographs of
trabecular plates TP with FIG. 1B including a representation of an
endothelial cell layer EC of trabecular beam B with the beam core
BC believed to be predominantly collagen and GAGs
(glucosaminoglycans) or ground substance. FIG. 1C illustrates that
each successively deeper plate (more anterior plate) of the
meshwork M has smaller perforations PF or openings between the
beams B than more exposed (posterior) trabecular plates. Further,
the intraplate spacing IPS diminishes with the successively deeper
plates (FIG. 1C). The meshwork M thus serves as a filtration
mechanism wherein cellular detritus, etc. in the aqueous outflow is
captured before it passes into Schlemm's canal SCH where the
aqueous is transported away form the eye (FIG. 1D). The meshwork M
lies about 750 .mu.m to 950 .mu.m beneath the anterior surface of
the sclera SC.
[0006] A number of ophthalmic disease conditions are related to the
trabecular meshwork and can be linked to distinct processes or
pathological conditions within a patient's eye. Any disease of the
trabecular meshwork shares the characteristic of elevating IOP.
Chandler et al. described many forms of glaucoma, the principal
ones being: primary open-angle glaucoma (POAG); progressive
low-tension glaucoma; pigment dispersion and pigmentary glaucoma;
angle-closure glaucoma; combined open-angle and angle-closure
glaucoma, exfoliation and open-angle glaucoma; angle-closure
glaucoma due to multiple system cysts of iris and ciliary body;
angle-closure glaucoma secondary to occlusion of the central retina
vein; angle-closure glaucoma secondary to bilateral transitory
myopia; ghost-cell glaucoma; lens-induced glaucoma; glaucoma due to
intraocular inflammation; neovascular glaucoma; glaucoma associated
with extraocular venous congestion; essential atrophy of the iris
with glaucoma. among others. (Chandler, et al., Glaucoma, 3.sup.rd
Ed., Lea & Febliger, Phila. (1986)) In all of the above-listed
glaucoma syndromes, elevated IOP results from an increase in
resistance to aqueous humor outflows through the trabecular
meshwork.
[0007] In terms of incidence, primary open-angle glaucoma (POAG) is
the most prevalent form of the disease affecting up to 0.5% of the
population between ages of 35 to 75. The incidence of glaucoma
rises with age to over 6% of the population 75 years are older. One
identifiable component of the POAG syndrome is the loss of
endothelial cells within the meshwork which is associated with a
degeneration of the normal trabecular biostructure. It is known
that the human aging process itself leads to a progressive loss of
trabecular endothelial cells EC which compromises normal aqueous
outflows therethrough. When examined in tissue cultures, degraded
endothelial tissue from POAG patients appears similar to that of
"aging" individuals.
[0008] Other characteristics believed common to POAG (as well as
many other glaucomas listed above) relate to a biostructural
obstructive syndrome of the trabecular plates TP, for example,
resulting from compression of the plates into a matt-like form that
reduces intraplate spacing IPS (FIG. 1C). This factor reduces the
capacity of the meshwork to act as a filtering mechanism and may
develop after the meshwork is clogged with cellular detritus,
pigments, etc. Such an obstructive syndrome, it is believed, also
is characterized by increased laxity of the trabecular beams B
allowing their collapse which thus reduces intraplate spacing. The
most likely causes of the meshwork degradations described above may
be cumulative stresses from various factors (e.g., oxidative,
phagocytic, glucocorticoidal stresses). The fact that increased
outflow resistance appears in the non-glaucoma "aging" population
further suggests that both trabecular endothelial cellular
processes and an obstructive meshwork syndrome play significant
roles in decreasing aqueous outflows.
[0009] The normal IOP for humans usually ranges from about 10 to 22
mm. Hg. (1.3-2.7 kilopascals) and is maintained by a balance in the
aqueous production by the ciliary body CB, inflows to the anterior
chamber AC and outflows therefrom. As described above, in a normal
eye, the aqueous drains from the anterior chamber through the
meshwork into Schlemm's canal SCH, through which it leaves the eye.
In patients in a glaucomous state, besides passing through
Schlemm's canal, the aqueous may also pass through the ciliary
muscle CM into the suprachoroidal space and finally leave the eye
through the sclera SC (FIG. 1D).
[0010] For purposes of description, the intraocular pressure (IOP)
in a human can be defined by a formula of the following type:
IOP=P.sub.e+(F.sub.t-F.sub.uv).times.R:(TM.sub.cep,TM.sub.sp,TM.sub.br)
[0011] where P.sub.e is the episcleral venous pressure (generally
regarded as being around 9 mm. Hg.); F.sub.t is the total outflow
of the aqueous humor from the anterior chamber, F.sub.uv is the
fraction of aqueous passing by the uveoscleral route; R is the
resistance to outflow of aqueous through the trabecular meshwork
into Schlemm's canal, which can be considered to be functionally
related to (i) the vitality of trabecular endothelial cellular
cellular and enzymatic processes (TM.sub.cep), (ii) the dimensions
of intraplate spacing between (TM.sub.ips) relative to a norm, and
(iii) the trabecular beam resiliency (T.sub.br) or biostructural
tension within the meshwork under the pressure of aqueous outflow
therethrough. Such a formula is useful for understanding the
targets of various prior art therapies, if not for use as an actual
mathematical model.
[0012] Among several therapies targeted at various elements of the
above equation, two forms of treatment are common: (i) medical or
drug therapies, and (ii) trans-corneal laser irradiation of the
trabecular meshwork via a goniolens (see FIG. 2A). In medication
therapies, the objective may be to lower IOP by either of several
routes: reducing the aqueous flow total (F.sub.t in the above
equation); increasing uveoscleral flow (F.sub.uv in above
equation); or altering resistance to outflow (R), by stimulating
endothelial cellular processes (TM.sub.cep) which is believed to
act on outflow resistance. Drug therapies have the disadvantages of
requiring a lifelong treatment; causing significant side effects;
being very costly (between $1,000-$2,000/yr.); and being
unavailable or unaffordable in lesser developed countries of the
world where the incidence of glaucoma is highest.
[0013] In the laser therapies, ALT (argon laser trabeculoplasty)
and SLT (selective laser trabeculoplasty) have been developed which
both rely on a trans-corneal approach to the posterior surface of
the meshwork. Introduced in the 1980's, ALT uses an argon laser
operating at a wavelength (.lambda.) of 488 nm to 514.5 nm with a
long pulse duration of about 0.10 second and a power range of from
500-1000 mW to irradiate a series of about 50 spots only around the
180.degree. of the meshwork (see FIG. 2A). In ALT, the
ophthalmologist utilizes a goniolens to direct laser beam strikes
on the exposed surface of the trabecular plates TP. The causative
mechanisms of ALT have never been clearly understood. It has been
proposed that each ALT beam's incidence on the meshwork causes a
burn or a melt and results in the formation of scar tissue that
contracts (or tensions) a portion of the meshwork around the burn
(cf. TM.sub.br or resiliency of beam B in above formula). According
to another view, the ALT meshwork burns cause a wound healing
response resulting in significant cell division and the transient
repopulation of endothelial meshwork cells, at least in zones
around the burns (cf. TM.sub.cep above). FIG. 2B shows an electron
micrograph of an ALT meshwork burn indicated at 6, which may
tension the meshwork at the burn periphery indicated at 7. A
principal disadvantage of ALT is that it can only be performed
twice on an eye--once in the superior (or nasal) 180 degrees of the
meshwork and once in the inferior (or temporal) 180 degrees. The
laser melts are too significant to repeat the treatment in the same
portion of the meshwork.
[0014] The more recently developed trans-corneal laser approach is
SLT, which uses a short-pulse, frequency-doubled, 530 nm Nd:YAG
laser with pulse duration of 3 nanoseconds and energy levels that
range from 0.60 mJ to 1.20 mJ. The SLT modality is called
"selective photothermolysis" by its inventor (Dr. M. Latina)
wherein the proposed wavelength is absorbed by endogenous pigment
within the meshwork which kills (or lyses) the pigmented cells
without damaging the non-pigmented cells (see U.S. Pat. No.
5,549,596). In theory, the short pulses allow heat to dissipate
from the absorbing pigmented cells before killing adjacent cells
(see FIG. 3). The SLT inventor proposes that the causative
mechanisms of increasing aqueous outflows relate to (i) an
inflammatory response in the meshwork that results in activation of
enzyme systems that clean up the meshwork, and (ii) a mild
expansion of the meshwork plates or perforations by killing
pigmented cells with a photothermal or microcavitation effect (FIG.
3). The following table compares the ALT and SLT parameters.
1 Pulse Beam Treatment .lambda. Duration Power Size Area ALT
488-514.5 nm 0.1 second 500-1000 mW 50 .mu.m 50 spots/180.degree.
SLT 530 nm 3 nanoseconds 0.6-1.2 mJ 300-400 .mu.m 50
spots/180.degree.
[0015] Several disadvantages are associated with the ALT/SLT
modalities. First, both systems approach the meshwork through the
anterior chamber AC by means of a goniolens. For this reason, the
wavelengths must be selected from a portion of the spectrum that
penetrates through the cornea C and aqueous AQ without the light
energy being absorbed and extinguished--a distance of about 4 mm.
to 8 mm. (4000 .mu.m to 8000 .mu.m). This factor greatly limits the
choice of possible wavelengths--each of which has a different
absorption coefficient in water (see FIG. 4A). The requirement of
using a goniolens along with a laser aiming beam also makes the
ALT/SLT approach technique dependent--making the therapy available
only to highly skilled surgeons.
[0016] A second disadvantage the ALT/SLT modalities relates to the
lack of exact understandings of the causative mechanisms for
improving outflow facility. Since ALT has effects that last for
about 5 years at most--and can be repeated only once--the medical
and surgical communities have not developed a consensus about
sequencing medical and surgical therapies. Glaucoma is a disease
state that requires lifelong management. Some physicians propose
that ALT be resorted to only after drug therapies have lost their
effectiveness; other physicians propose ALT as a first line of
defense in order to delay a lifetime of drug therapy and the
attendant side effects.
[0017] Other significant disadvantages of ALT/SLT relate to the
fact that both deliver similar photothermal effects to a limited
depth within the trabecular plate structure. That is, the ALT/SLT
causative mechanisms--no matter what they are--probably only
operate within the trabecular plates TP most exposed to the
incident beam which thus absorb the beam's photonic energy. This
factor suggests that only the first few plates (most posterior
plates) exposed to the anterior chamber AC are affected by such
energy delivery--perhaps only about 10%-20% of the larger
dimensioned trabecular plates. It is postulated that the underlying
(anterior) trabecular plates that have smallest dimensioned
perforations PF and the least intraplate spacing IPS are degraded
to the greatest degree and thus play the most significant role in
increasing IOP by clogging the pathways to Schlemm's canal (see
FIG. 1D). Yet, these most anterior meshwork regions probably remain
untreated by ALT and SLT.
[0018] Further, studies have shown that ALT is not effective in all
patients, and actually increases IOP in over 20% of patients.
Additionally, in recent SLT patients, the following complications
have been documented: uveitis in the form of iritis in virtually
all treated eyes; corneal burns in up to 25% of treated eyes; and
anterior synechiae or adhesions due to the significant absorption
of light energy in the pigmented cells of the meshwork.
[0019] What is needed is an improved technique for effecting
biostructural changes in the trabecular meshwork to facilitate
aqueous outflows that provides: (i) means for stimulating
endothelial cell division to cause cell repopulation and
rejuvenation within the trabecular plate structure; (ii) means for
inducing a slight inflammatory or wound healing response to
activate enzymatic systems such as stromolysin and metalloproteases
that may help clean up the meshwork; (iii) means for causing the
desired biostimulative effects without photocoagulation,
photodisruption or photothermolysis of endothelial layers of the
meshwork as in ALT/SLT; (iv) MIS (minimally invasive surgical)
means for causing the desired effects in a repeatable maintenance
therapy that can continue over the lifetime of the glaucoma
patient; (v) MIS means for meshwork treatment that can be evaluated
in all patients before resorting to drug therapies; (vi) MIS means
for treating 360.degree. of the meshwork instead of 180.degree. or
less; (vii) means for causing the desired effects substantially
equally on all trabecular plates from the most posterior to the
most anterior, (viii) MIS means simultaneous treatment of a
substantial arc of the meshwork with a device in a single treatment
position rather than time-consuming treatment in a series of spots;
(ix) MIS means for biostimulating the trabecular structure in the
many forms of glaucoma (other than POAG) that are not possible with
a goniolens and laser strikes through the anterior chamber, (x) MIS
means for treating the meshwork without risk of any corneal burns;
and (xi) MIS means for treating the trabecular structure that is
not technique-dependent and capable of being performed by
optometrists or other lesser-skilled health care professionals in
the lesser developed countries of the world.
SUMMARY OF THE INVENTION
[0020] The laser system and handpiece of the present invention are
particularly adapted for use in elevating the temperature of a
patient's trabecular meshwork for purposes of stimulating cellular
processes. The system is adapted for a novel transscleral approach
(instead of trans-corneal) and is called opto-thermal transscleral
trabeculoplasty (or OT.sup.3). The present invention provides
cooperating means to develop biostimulative opto-thermal effects in
a patient's trabecular meshwork, including a working face for
contacting the sclera and aligning the axes of a plurality of
beams' propagation toward the meshwork, and a laser energy source
having a wavelength range appropriate for penetration to the
meshwork. Further, the invention includes an optional dosimetry
control system for terminating or controlling energy delivery based
on feedback signals from a temperature sensor array in the working
face.
[0021] The working face has a 1.sup.st corneo-spherical receiving
portion and a 2.sup.nd sclero-spherical receiving portion for
positioning the face in contact with the globe with a footprint
dimension that is large enough to stabilize the working face at a
proper treatment angle. Within the working face are a plurality of
light beams emitters connected with fiber optics to the laser
source. The emitter axes at which the beams propagate are provided
at a predetermined angle relative to the 1.sup.st and 2.sup.nd
part-spherical receiving portions of the working face, for example
a tangent to the sclera.
[0022] Research and modeling indicates that the preferred
wavelength ranges for opto-thermal biostimulation of the trabecular
plates lie in the near-infrared portion of the spectrum, preferably
in ranges of about 1.30 .mu.m to 1.40 .mu.m or about 1.55 .mu.m to
1.85 .mu.m. It is believed that absorption coefficients related to
the above ranges, or a subset of the such ranges, will prove best
suited for such trabecular meshwork stimulation. The depth of
absorption of such wavelength ranges will extend through most, if
not all, of the thickness of the sclera (750 .mu.m to 950 .mu.m).
For the proposed method of trabecular biostimulation, the targeted
region is elevated in temperature to a range between about
40.degree. C. to 55.degree. C. for a period of time ranging from
about 1 second to 120 seconds or more. More precisely, the desired
range would be between about 40.degree. C. to 50.degree. C. for
such time periods. The optimal therapeutic effects will result from
a balance of appropriate light energy wavelength, power level,
exposure duration, together with the thermal absorption
characteristics of the heat-sink working face.
[0023] The light-mediated trabecular biostimulation techniques
proposed herein differ greatly from other common laser-tissue
interactions. The proposed technique develops only low energy
densities in the absorbing medium as can be seen in the chart of
FIG. 4C where various temperature levels indicate different effects
on tissue. Such biostimulative effects are caused by a
photoexcitation modality proposed herein which differs
significantly from typical modalities of laser-tissue interactions:
the photocoagulation and photodisruption modalities. In the
photocoagulation modality, photons elevate tissue temperatures
sufficient to coagulate, denature, shrink, desiccate or cause
thermolysis of tissues such as in ALT and SLT (see FIG. 4B). In the
photodisruption modality, photons of a light energy beam disrupt
the chemical bonds of atoms or molecules making up the medium, with
the end result being that the medium is vaporized as indicated in
FIG. 4B. In the present invention, the objective is to elevate
meshwork to temperatures well below those used to practice the
photodisruption or photocoagulation modalities. The photoexcitation
modality proposed herein uses far less energetic photons in the
above-described ranges which will cause atoms and molecules in the
meshwork or aqueous AQ engulfing the meshwork to vibrate or
resonate. The excitement or resonant effect will elevate the
temperature within the absorbing medium (meshwork) without
disrupting any intramolecular or intermolecular chemical bonds,
such as would occur temperatures above about 60.degree. C. which
can cause denaturation of tissue.
[0024] The dosimetry control component of the invention can be
adapted to control exposure duration, power levels and timing of
energy delivery in various operational modes. A basic mode of
operation can follow a pre-set program of timing and power based on
treatment experience. A preferred operational mode is based on a
feedback-control system that receives signals from a thermal sensor
in the working end of the device. Another preferred operational
mode is based on a feedback-control system and a beam sequencing
controller that sequences beam delivery between or among
non-adjacent emitter locations to optimize temperature elevation in
the meshwork while minimizing temperature elevation in the anterior
and mid-sclera.
[0025] In general, the present invention advantageously provides a
system having an arrangement of a plurality of n spaced-apart beam
emitters in a radius that corresponds to that of the trabecular
meshwork of a patient's eye for transsclerally treating an angular
portion of the meshwork with a single energy delivery.
[0026] The invention advantageously provides a device having a
working face with geometry and part-spherical receiving forms for
receiving portions of a patient's cornea and sclera to insure the
light energy beams are directed toward the trabecular plates.
[0027] The invention advantageously provides a device having n lens
elements to insure that the light energy beams penetrate and are
absorbed substantially about the region of the trabecular
meshwork.
[0028] The invention advantageously provides a device and method
for creating a reverse thermal gradient in the sclera by lowering
the temperature of the anterior surface of the scleral with a
heat-sink working face to protect the scleral epithelium.
[0029] Additional features and advantages of the device and method
of the present invention will be understood from the following
description of the preferred embodiments, which description should
be taken in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0030] FIGS. 1A is an electron micrograph of the trabecular
meshwork of a patient's eye.
[0031] FIG. 1B is an enlarged electron micrograph of the trabecular
meshwork of FIG. 1A with a schematic sectional view of a trabecular
beam.
[0032] FIG. 1C is a sectional representation of the trabecular
plate layers of meshwork of FIG. 1A.
[0033] FIGS. 1D-1E are sectional views of a patients' eye or globe
showing the location of the trabecular meshwork.
[0034] FIG. 2 is a view of a prior art method of laser treatment of
trabecular plates.
[0035] FIG. 2B is an electron micrograph of a laser melt of
trabecular plates in the prior art method of FIG. 2A.
[0036] FIG. 3 is a schematic view of another prior art method of
laser treatment of a trabecular plate.
[0037] FIG. 4A is a graph showing light wavelengths with absorption
coefficients in water.
[0038] FIG. 4B is a chart indicating laser-tissue effects at
various temperature levels in tissue, including the modality of
photoexcitement proposed herein; the photocoagulation modality
wherein tissue is caused to coagulate, denature or shrink; and the
photodisruption modality wherein tissue is vaporized.
[0039] FIG. 5 is a perspective view of the handpiece of the present
invention together with a block diagram of the components and
control systems of the invention.
[0040] FIG. 6 is an enlarged perspective view of a the distal
working end of the handpiece of FIG. 5 depicting a plurality of
emitter locations and light energy beams emitting therefrom.
[0041] FIG. 7 is a sectional view of the working end of FIG. 6
taken along line 7-7 of FIG. 6 showing particular working end
geometry.
[0042] FIG. 8 is a plan view of working end of FIG. 6 showing other
particular working end geometry.
[0043] FIG. 9 is an enlarged sectional view of the working end of
FIG. 7 showing a lens element.
[0044] FIG. 10 is an enlarged sectional view of a sclera and cornea
and showing various transcleral angles-of-attack.
[0045] FIG. 11 is a partial sectional view of an eye showing the
footprint of the working end of FIGS. 6, 7 & 8.
[0046] FIGS. 12-12B are sectional representations of a patients
sclera and trabecular meshwork regions depicting a manner of
utilizing the apparatus of FIG. 5 in performing a method of the
invention in elevating the temperature of the meshwork; FIG. 12A
indicating the thermal effect of a light beams' incidence on tissue
at the instant of energy absorption; FIG. 12B indicating the
thermal effect of the light beams a number of nanoseconds
later.
DETAILED DESCRIPTION OF THE INVENTION
[0047] Referring now to FIG. 5, the laser system 8 with handpiece
10 of the present invention is shown which is adapted for the novel
technique of elevating the temperature of a patient's trabecular
meshwork for biostimulation purposes. The system of the invention,
for convenience, may be at times referred to as an OT.sup.3 system
("OT-Cubed system") for the practiced technique of opto-thermal
transscleral trabeculoplasty.
[0048] The present invention includes cooperating means for
projection of energy beams at particular penetration angles in
particular spatial locations on the anterior surface of the sclera,
together with wavelength means for transscleral penetration of such
energy beams to reach the patient's trabecular meshwork. The
OT.sup.3 device thus provides (i) a working end with particular
geometry for propagating light beam(s) relative to the sclera's
anterior surface, (ii) a laser energy source operating within
selected wavelength domains, and (iii) an optional dosimetry
control system for controlling (or terminating) laser energy
delivery based on a temperature feedback signals. These systems and
aspects of the invention will be described in order below, and
subsequently in their use in performing the technique of the
invention in stimulating cellular and other processes of the
trabecular meshwork.
[0049] 1. Working End Beam Propagation Geometry. As can be seen in
FIG. 5, handpiece 10 comprises a working end portion 12 that
extends along axis 15 and which is coupled to body portion 16. The
working end 12 is fabricated of any suitable transparent material,
such a transparent medical grade plastic. The body is formed of any
suitable material such as metal or plastic and is adapted for
gripping with a human hand. Preferably, working end 12 and body 16
are of inexpensive and disposable injection-molded parts. The body
16 has proximal and distal ends, indicated at 17a and 17b,
respectively, with end 17a having a detachable coupling 18 for
connecting fiber optic cable 20 thereto for operative connection to
laser energy source 25 described below.
[0050] FIGS. 6-8 show perspective, sectional and plan views of
working face 30 of working end 12 with a plurality of emitter
locations 31A-31n and lens elements 33A-33n from which beams
35A-35n are be emitted. The preferred embodiment shows a plurality
of 6 emitter locations 31A-31n, but it should be appreciated the
number of emitters may range from about 1 to 10 per any 10.degree.
to 45.degree. of radial angle distance RAD of working face 30 (FIG.
8) described below (i.e., n=1 to 10). The number of emitter
locations 31A-31n also will vary depending on selected beam
diameter described below. FIG. 6 shows that individual optic fibers
40 (collectively) are connected by any suitable means (e.g., cement
or a clamping mechanism) at each emitter location and more
particularly to each lens element 33A-33n. FIG. 9 shows an enlarged
sectional view of a lens element 33A which is adapted as a
plus-type lens to converge the beam generally at depth D which is
about the depth of meshwork M (about 750 .mu.m to 950 .mu.m) as is
known in the art. It should be appreciated that the lens element
33A is represented as a part-hemispheric lens but that any flat
field or convergent lens may be appropriate for opto-stimulation of
the meshwork M and falls within the scope of the invention.
[0051] The light beams 35A-35n may be generated and emitted by the
emitters from any suitable source of light, either coherent or
non-coherent, and may be from a pulsed or CW laser source in the
wavelength domain described below. It should be appreciated that
the term "emitter" is used herein to describe the location or point
at which beams 35A-35n are emitted from working end 12 and lens
elements 33A-33n into the sclera, and as such, the emitter is
considered to be a combination of elements including, but not
limited to, the laser source 25 together with optics, fiber optics,
lenses, mirrors, filters, splitters, combiners, energy attenuators,
beam shapers and other arrangements operatively connected between
the laser source 25 and the lens elements 33A-33n. FIG. 5 shows
beam splitter 44 that is known in the art for splitting output from
one or more light sources 25 to pump the light energy into each
individual optic fiber 40.
[0052] Turning now to FIGS. 10-11, very particular beam-angle
propagation means are formed into working face 30 of working end 12
that comprises a balance between several considerations and several
potential transscleral angles-of-attack to reach the trabecular
meshwork M. Referring back to FIG. 7, the working face 30 in its
treatment position is adapted to interface with globe 5 generally
in surface contact with three portions of the globe: the sclera SC,
the limbus 36 and the cornea C. In other words, the working face
has a first corneal-spherical receiving portion 45A and a second
scleral-spherical receiving portion 45B with annular
limbus-interface portion 47 therebetween. The limbus 36 herein is
defined as the particular annular transition region from 0.5 mm. to
2.0 mm. between the sclera and cornea. Further, the working face 30
extends a minimum radial angular distance RAD when measured in
degrees as will be described below (see FIG. 8). Thus, the
footprint dimensions of working face are large enough to stabilize
the working face 30 against the globe, as well as for functioning
as a heatsink as described below.
[0053] FIGS. 10-11 show that a particular limited range of
angles-of-attack (or beam propagation) relative to anterior surface
48 that is indicated to reach meshwork M. Among the considerations
for determining the most preferable angle-of-attack are (i) the
reduction of incident beam reflection off the anterior surface 48
of the sclera SC; (ii) the reduction of unnecessary photon
scattering in the mid-sclera 53, and (iii) the elimination of any
angle-of-attack that might align with anatomic structures that one
would not want to irradiate unnecessarily. To meet these
objectives, the working face 30 is formed with a geometry for
angular positioning the axes 50 (collectively) of propagation of
beams 35A-35n within a defined angle--for example angle .beta.
which measures the angle between an axis 50 of beam propagation and
a tangent T to the sclera in an incident zone Z outside the limbus
centerline 51. In other words, axis 50 extends from the zone Z in
which a light beam penetrates the anterior 48 of the sclera to hit
meshwork M. As can be seen in FIG. 10, any beam propagation at
other angles along other lines (e.g., lines X.sub.1 or X.sub.2)
that are more oblique relative to tangent T may cause photonic
energy to be absorbed in undesirable locations like ciliary body CB
or iris 52 and thus damage tissue outside the meshwork M. The
correct beam propagation angle .beta. can be defined in a number of
different geometric manners relative to surfaces, radii, axes etc.
of globe 5, and for that reason the ranges of radii of curvature of
a normal globe are shown in FIG. 10. Preferably, as shown in FIG.
8, beam angle .beta. is within a range of about 10.degree. on
either side of a line drawn perpendicular to tangent T in the zone
Z of the sclera and limbus. Incident zone Z has in lesser diameter
of about 0.0 mm. to 0.5 mm. from the centerline 51 of limbus 36 and
an outer diameter to 3.0 to 5.0 mm. from the centerline 51 of the
limbus 36. Thus, the working end geometry in its "contact position"
or "treatment position" against globe 5 orients beams 35A-35n to
(i) allow about the least distance of travel possible through the
sclera SC to the meshwork M to correspond to wavelength domains
described below; (ii) allow reduction of photon scattering and heat
within the mid-sclera 53 by minimizing the beams' propagation
length through the sclera; and (iii) allow light beams 35A-35n
delivery at close to a 90.degree. angle relative to anterior
surface 48 of sclera SC to reduce surface photon reflection.
[0054] Of particular interest to the invention, the compound
curvatures 45A and 45B (first corneal-spherical receiving portion
45A and second scleral-spherical receiving portion 45B) of working
face 30 allow the ophthalmologist to gently fit the working face
against the globe 5 about the corneal-scleral junction to insure
the optimal beam spatial location and beam angle-of-attack. The
ophthalmologist first may move the working face laterally back and
forth as shown in arrow A1 in FIG. 10 until it fits comfortably
against the eye. Thereafter, the ophthalmologist may tilt working
face 30 against the curvature of the sclera and cornea as indicated
by arrow A2 as shown in FIG. 10 to establish the correct angle
.beta. relative to globe 5. In the previous view of the working
face in FIG. 7, it can be seen that first part-spherical receiving
form 45A has a meridional or first cross-sectional radius R1 of
about 6.4 mm. to 7.8 mm. which represents a meridian of corneal
curvature. The working face 30 has second part-spherical receiving
form 45B with a second cross-sectional radius R2 of from about 8.0
mm. to 12.0 which represents a meridian of scleral curvature (or
greater) with the forms 45A and 45B meeting along partial annular
junction 47. The width of first part-spherical receiving form 45A
may range from about 0.5 mm. to 4.0 mm., indicated at W1 in FIG. 8.
The width of second part-spherical receiving form 45B may range
from about 2.0 mm. to 5.0 mm., indicated at W2 in FIG. 8.
[0055] FIG. 8 shows a plan view of working face 30 indicating that
it is adapted to extend a particular angular or radial angle
distance RAD around globe 5 and is shown in this preferred
embodiment with a radial extension RAD of about 60.degree. out of
360.degree.. It should be appreciated that other embodiments are
possible and fall within the scope of the invention and such radial
extension may range between about 10.degree. and 180.degree. (see
FIG. 8). In terms of circumferential dimensions, the dimension
along partial annular junction 47 of working face may range from
about 2.5 mm. to 2.0 cm. The footprint 54 defining the surface area
of working face 30 preferably has an area of at least 20 mm..sup.2
to meet the requirements of stabilizing the working face against
globe 5 to provide the correct angle of beam propagation, and to
provide sufficient heat absorption characteristics for any of the
materials of working face described herein. More preferably, the
footprint 54 of working face 30 has an area of at least 40
mm..sup.2 to meet above requirements. Still more preferably, the
footprint 54 of working face 30 has an area of at least 60
mm..sup.2 to meet such requirements.
[0056] The dosimetry control system 55 will be described in detail
below in Section 3. Some aspects of the dosimetry control system
can be fed by a signal from sensors 57 (collectively or sensor
array) in working face 30. Therefore, referring back to FIGS. 6
& 8, it can be seen that sensor array 57 is provided which
comprises thermisters or thermocouples carried in a spaced apart
relationship close to lens elements 33A-33n in face 30. The sensors
may be in actual contact with the sclera SC or may measure the
temperature of the material of face 30 that is in contact with the
sclera. Each thermocouple or thermister (a temperature sensor that
has resistances that vary with the temperature level) is any
suitable type known in the art and may consist of paired dissimilar
metals such as copper and constantan which form a T-type
thermocouple.
[0057] Referring back to FIG. 5, a block diagram of the controllers
of the system 8 is included and further shows a visible aiming beam
(e.g., a HeNe laser) indicted at 58 operating at 630.8 nm or any
other suitable visible laser wavelength. The system includes
dosimetry control system indicated at 55 and optional beam sequence
controller 59, which computer controllers are adapted to operate in
cooperation (as will be described below) to control the power of
beams 35A-35n, as well as the timing, of laser energy delivered
from laser source 25.
[0058] 2. Laser Source Wavelength Selection. The preceding section
described the working end geometry or positioning mechanisms of the
novel OT.sup.3 device to insure that the physician can easily and
consistently locate the working face 30 in suitable "treatment
positions" on or about the anterior scleral surface. This section
and FIGS. 12A-12B describe the means provided by the invention for
controlling penetration of light beams 35A-35n beneath the anterior
scleral surface 48 to provide the desired photon absorption within
the trabecular meshwork M. The biostimulative effect is caused by
the beam's photonic energy being absorbed and exciting (or
vibrating) molecules within the meshwork, and for that reason the
energy delivery effect may be called herein a photoexcitation
modality to distinguish it from various high-energy laser delivery
modalities described in the section above titled "Summary of the
Invention".
[0059] Turning back to FIG. 10, the perspective and partial
sectional view of globe 5 shows the beams 35A-35n incident within
zone Z at a particular moment in time that represents a technique
of the invention. FIG. 11 also shows the approximate location of
zone Z over the trabecular meshwork with the footprint 54 of
working face 30 and the working end 12 in phantom view in a second
treatment location. FIG. 12A illustrates an enlarged fill-thickness
sectional view of the sclera SC and meshwork M taken along an
arc-like section of FIG. 11. Sclera SC has a number of layers
including epithelial layer 60 with the total scleral thickness
ranging from about 750 .mu.m to 950 .mu.m.
[0060] The object of the invention, transscleral opto-thermal
biostimulation, requires identification of a specific light
wavelength domain that may be produced by laser source 25 to
penetrate substantially to the depth of about 750 .mu.m-950 .mu.m.
As background, when light energy is incident upon tissue, five
effects may result: (i) the beam, or some or all of the photons
thereof, may be reflected off the tissue surface; (ii) the photons
thereof may be transmitted entirely through the tissue medium,
(iii) the photons thereof may be absorbed along the beam's
propagation in the tissue medium by absorption within a
chromophore, (iv) the photons thereof may be absorbed along the
beam's path of propagation by varied processes of scattering; or
(v) some of beam may be scattered within the tissue beyond the
region of the beams path as it propagates within the tissue
medium.
[0061] To provide photon absorption to a depth in tissue of about
750 .mu.m-950 .mu.m, two of the above factors are of interest to
cause biostimulation of the trabecular meshwork M. Of particular
interest are the photon absorption effects (iii) and (iv) listed
above. Preferably, the photons of the energy beams 35A-35n will be
absorbed by the H.sub.2O content of the meshwork acting as a
chromophore, and also be absorbed by photon scattering processes,
thus elevating meshwork temperature. (As noted previously, photon
reflection off anterior surface 48 is minimized to the extent
possible, and deeper absorption is allowed, by orienting axes 50 of
the beams substantially perpendicular to the anterior scleral
surface which relates to beam incident effect (i) above).
[0062] Since the sclera is about 75%-80% water with little or no
cellular pigmentation, FIG. 4A is relevant as it depicts an
absorption coefficient of water as a function of wavelength
(.lambda.). As can be seen in FIG. 4A, the absorption coefficient
of water varies by a factor of about 10,000,000 from a peak light
transmission where .lambda.=500 nm (not shown) in the visible
spectrum to peak light absorption where .lambda.=at 2.8 .mu.m in
the infrared portion of the spectrum. Tissue research and
mathematical modeling of various wavelengths indicates that the
preferred wavelength range for light-mediated meshwork
biostimulation lies in the near-infrared, the laser source 25
preferably operating at a wavelength ranging from about 1.30 .mu.m
to 1.40 .mu.m or from about 1.55 .mu.m to 1.85 .mu.m. The
wavelength ranges correspond to an absorption coefficient (.alpha.)
in H.sub.2O ranging between about .alpha.=2.0 cm.sup.-1 to 10.0
cm.sup.-1, which is similar to the sclera. Such a range of
absorption coefficients would result in the photonic energy being
absorbed to a depth of about 750 .mu.m to 1100 .mu.m--in other
words the depth of the trabecular meshwork or slightly beyond. It
is not important if the absorption is somewhat deeper than the
meshwork, for the aqueous AQ will absorb or extinguish the energy
beam. Unlike ALT and SLT wavelengths that are absorbed by a pigment
(melanin) or chromophore in the meshwork, the proposed wavelengths
rely on H.sub.2O as the chromophore which is in the trabecular
plates TP and the aqueous AQ which allows a substantially uniform
temperature elevation in the entire region of the meshwork for
biostimulation purposes.
[0063] The temperature targeted for meshwork biostimulation is in
the range of about 40.degree. C. to 55.degree. C. for a period of
time ranging from about 1 second to 120 seconds, with the
temperature inversely related to the duration of exposure. More
preferably, the target temperature is within a range of 40.degree.
C. to 50.degree. C. It would be preferable to achieve an energy
profile that photoexcites the region of the meshwork without
over-elevating the temperature levels in the sclera overlying the
meshwork. For example, it is preferable that the opto-thermal
effects do not cause excessive cell death in epithelial layer 60 or
in the mid-sclera region 53. Such excessive cell death along the
light beam's propagation through the sclera could induce an
inflammatory response or wound healing response which would be
undesirable, although not serious threat to the patient's health.
Cell damage in the sclera is to be expected to some extent, but
since the inventive technique is transscleral there should be few
undesirable side effects. This is to be contrasted with the
trans-corneal approach of SLT which causes corneal burns in
significant numbers of cases resulting in at least a transient
effect on corneal clarity.
[0064] The present invention provides protection means for
preventing over-elevation of temperatures in the epithelial layer
60 and the midscleral region 53, by: (i) balancing wavelength
selection along with a low laser power level to penetrate the
sclera; (ii) balancing exposure duration with temperature which
exposure can be terminated with feed-back control; and most
importantly (iii) providing heat-absorption characteristics
incorporated in working face 30. In other words, a transient
reverse thermal gradient in the sclera can be achieved by use of
the heat-sink working face 30. Due to the relatively low target
temperatures, the heat-sink of even a plastic working face 30
around the lens elements will carry a significant amount of heat
away from the anterior regions of the sclera. It should be
appreciated that other heat-sink materials known in the art may be
used for portions of the working face 30, such as sapphire, quartz
or heat-absorbing ceramics (other than lens elements). FIG. 12A
depicts a sectional view of the propagation of beam 35A through the
sclera exactly at the moment of its incidence on anterior surface
48 with exemplary isotherms 70a-70c indicating the effects of
photon absorption; FIG. 12B depicts the same scleral location in as
little as several nanoseconds after energy delivery has been
terminated. In particular, FIG. 12B indicates that substantially
all heat has been conducted away from anterior surface region 48 of
the sclera to the heat-sink with exemplary isotherms 70a-70c
indicating the surface cooling effect that concentrates temperature
in the region of meshwork M. Such modeling shows how a transient
reverse thermal gradient (cooler at anterior surface 48 than
mid-sclera 53) can be developed to cause thermal meshwork
biostimulation without raising temperatures excessively in the
anterior 48 and mid-sclera 53.
[0065] Another aspect of the OT.sup.3 system for effective
biostimulation of the meshwork M relates the preferred diameter of
scanned beams 35A-35n to provide temperatures within the particular
ranges described above. Either a CW (continuous wave) or fast
pulsed laser is suitable to perform the biostimulation technique of
the present invention utilizing a beam width ranging from about 25
.mu.m to 1 mm. for reasons that can be explained by the mechanisms
of heat transfer in tissue. In the preferred wavelengths described
above, when the light beam is absorbed in tissue medium (both by
chromophores and by photon scattering) the energy in the beam is
imparted to the scleral absorbing medium along the path of beam
propagation. The photonic energy that is absorbed by the medium
heats the absorbing volume instantly, for example in a period
ranging from femto-seconds to pico-seconds. Essentially, all of the
energy in the light beam is deposited in the tissue within about
one extinction length (which is directly related to the absorption
coefficient a of the sclera). Thus, it can be calculated that a
three-dimensional volume of the medium will be elevated in
temperature and is dependent on (i) the beam diameter, and (ii) the
extinction length of the particular wavelength (with some
adjustment for photon scattering). To optimize the meshwork
biostimulation, it is necessary to deposit enough energy into the
absorbing volume to elevate the volume to the desired temperature
range before it diffuses into surrounding tissue volumes. The
process of heat diffusion, called thermal relaxation, describes
such process of conduction and defines the absorbing volume's
thermal relaxation time (often defined as the time over which
photothermal temperature elevation is reduced by one-half). Such
thermal relaxation time scales with the square of the diameter of
the irradiated absorbing volume in a spherical volume, decreasing
as the diameter decreases. For a cylindrical-shaped irradiated
volume (see FIG. 12A) with diameter d and length L, such thermal
relaxation time is determined by the lesser of the two dimensions.
Thus, in the laser wavelengths and tissue absorption coefficients
described above, it is preferable to have the heat thermal
relaxation time in the anterior and mid-sclera as low as possible
to diffuse and reduce temperature elevations in those regions. For
these reasons, it is postulated that beam diameters in that range
of about 25 .mu.m to 1 mm. would be best suited for meshwork
stimulation, with a similar spaced-apart dimension SA from about 25
.mu.m to 1 mm. between the individual beams and lens elements
33A-33n (see FIG. 6).
[0066] 3. Dosimetry Control System of OT.sup.3 Device and Methods
of the Invention. The OT.sup.3 device 8 includes a dosimetry
control system indicated at 55 in FIG. 5 that is adapted to control
the power level of laser energy delivered through the emitter
locations 31A-31n in various operational modes. In utilizing the
device of FIG. 5 to perform the method of the invention, the
ophthalmologist gently positions the working face 30 of the device
against the patient's eye as shown in FIGS. 7, 10 & 11 above
following administration of a topical anesthetic. As described
above, after moving the working face laterally about the surface of
globe 5 and tilting the device back and forth, the physician will
have a tactile feel of the correct position of the working face, at
which time he may actuate the device by means of a footpedal (not
shown) or any other suitable trigger mechanism to deliver laser
energy under a number of different optional operational modes. The
ophthalmologist repeats the biostimulative treatment in successive
and slightly overlapping location in an arc around the entire
360.degree. of the globe. The dosimetry control system 55 typically
includes microprocessor 65 together with appropriate software
programs 66 and may be designed to modulate the power level of the
laser source 25 at any level among a continuous range of power
levels as the emitters project beams 35A-35n. The software 66 that
is part of the dosimetry control system, as the term is used
herein, includes a conventional software program, a program within
a programmable chip, or any other form of algorithm carried in any
form of memory storage system. Within the hardware portion of
dosimetry control system 55, there may be a keyboard, disk drive or
other non-volatile memory system, displays as are well known in the
art for operating such a system (see FIG. 5).
[0067] The dosimetry control system can operate in a "basic" mode
of operation, which means that the physician utilizes a
pre-selected program to control to (i) the particular power level
of laser source 25; (ii) the particular exposure duration of beams
35A-35n. The power level may range from about 1 mJ to 100 mJ for
the above-described beam diameters, with a CW source or a rapidly
pulsed source with pulse length ranging from 1-1000 ms. As
described above, the total duration of treatment may range from
about 1 second to 120 seconds.
[0068] Another operational mode, and a preferred mode, relates to
use of a feedback-controlled mode based on signals from thermal
sensor(s) 57 shown in FIGS. 6 & 8. In a first
feedback-controlled mode, surface temperature at the anterior
scleral surface 48 may be monitored by sensor array 57, such that
dosimetry control system 55 may simply terminate laser energy
delivery upon a detected surface temperature reaching a pre-set,
for example any temperature in pre-selected from a range of about
42.degree. C. to 55.degree. C., each such temperature also
optionally including a pre-selectable time period ranging from
about 1 ms to 30 seconds. Thus, the detected temperatures at the
anterior surface 48 of the sclera can be modeled (e.g., using Monte
Carlo modeling as is known in the art) to predict the temperature
in the region of the meshwork M for creating the biostimulation
temperature parameters described above. In another feedback
controlled-operational mode, the dosimetry control system 55 can be
programmed to modulate power to one or more emitter locations based
on feedback from the sensor array 50.
[0069] In yet another operational mode of the invention, herein
called the time-sequenced (or gated) operational mode, the
dosimetry control system 55 and more specifically the beam sequence
controller 59 which is adapted to sequentially deliver laser energy
at any given power level between the individual emitter locations
31A-31n. Such "sequential" delivery can provide energy delivery to
only one particular spot in the meshwork M at a time, or any spot
substantially remote from an adjacent spot (either in distance or
time of delivery) to allow the thermal relaxation time relative to
a particular to spot to diffuse the temperature within the
absorbing medium. For example, the beam sequence controller 59 may
randomly, or in a pre-set sequence, select only one single emitter
to emit a beam at any moment in time thus sequencing between any
adjacent or non-adjacent emitters; or controller 59 may select from
2 to n non-adjacent emitters to emit beam simultaneously while
sequencing between or among another single emitter or any
combination of emitters 31a-31n. By this beam delivery sequencing
means, and thermal modeling as is known in the art such as Monte
Carlo modeling, beam sequencing patterns can be developed as a
function of both the thermal relaxation time about a beam's
propagation and the heat aborption characteristics of working face
30 to optimize the biostimulative temperature elevation in the
trabecular meshwork.
[0070] Specific features of the invention are shown in some
drawings and not in others, and this is for convenience only and
any feature may be combined with another in accordance with the
invention. Further variations will be apparent to one skilled in
the art in light of this disclosure and are intended to fall within
the scope of the appended claims.
* * * * *