U.S. patent number RE40,184 [Application Number 10/621,105] was granted by the patent office on 2008-03-25 for refractive surgery and presbyopia correction using infrared and ultraviolet lasers.
This patent grant is currently assigned to SurgiLight, Inc.. Invention is credited to Jui-Teng Lin.
United States Patent |
RE40,184 |
Lin |
March 25, 2008 |
Refractive surgery and presbyopia correction using infrared and
ultraviolet lasers
Abstract
A method and surgical technique for corneal reshaping and for
presbyopia correction are provided. The preferred embodiments of
the system consists of a scanner, a beam spot controller and
coupling fibers and the basic laser having a wavelength of
(190-310) nm, (0.5-3.2) microns and (5.6-6.2) microns and a pulse
duration of about (10-150) nanoseconds, (10-500) microseconds and
true continuous wave. New mid-infrared gas lasers are provided for
the corneal reshaping procedures. Presbyopia is treated by a method
which uses ablative laser to ablate the sclera tissue and increase
the accommodation of the ciliary body. The tissue bleeding is
prevented by a dual-beam system having ablative and coagulation
lasers. The preferred embodiments include short pulse ablative
lasers (pulse duration less than 200 microseconds) with wavelength
range of (0.15-3.2) microns and the long pulse (longer than 200
microseconds) coagulative lasers at (0.5-10.6) microns. Compact
diode lasers of (980-2100) nm and diode-pumped solid state laser at
about 2.9 microns for radial ablation patterns on the sclera
ciliary body of a cornea are also disclosed for presbyopia
correction using the mechanism of sclera expansion.
Inventors: |
Lin; Jui-Teng (Coleman,
FL) |
Assignee: |
SurgiLight, Inc. (Orlando,
FL)
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Family
ID: |
23173174 |
Appl.
No.: |
10/621,105 |
Filed: |
July 10, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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Reissue of: |
09303673 |
May 3, 1999 |
06258082 |
Jul 10, 2001 |
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Current U.S.
Class: |
606/5; 372/37;
372/83; 606/10; 606/13; 606/4; 606/6; 607/89 |
Current CPC
Class: |
A61F
9/008 (20130101); A61F 9/00804 (20130101); A61F
9/00808 (20130101); A61F 2009/00865 (20130101); A61F
2009/00872 (20130101) |
Current International
Class: |
A61B
18/18 (20060101) |
Field of
Search: |
;606/4-6 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Other References
Thornton, Spencer P., Anterior Ciliary Sclerotomy (ACS), A
Procedure to Reverse Presbyopia, In "Surgery for Hyperopia and
Presbyopia", Oct. 1997, pp. 33-36 (chapter 4), published by
Williams & Wilkins. cited by other.
|
Primary Examiner: Cohen; Lee S.
Attorney, Agent or Firm: Knobbe, Martens, Olson & Bear
LLP
Claims
I claim:
1. A method of performing refractive surgery by reshaping a portion
of corneal tissue, said method comprising the steps of: selecting a
gas laser generated by transverse electrical discharge in a mixture
of neural gases including at least helium gas and having a pulsed
output beams of predetermined mid-IR wavelength of (2.7-3.2)
microns; selecting a beam spot controller mechanism, said spot
controller consisting of an internal magentic coupler integrated
inside the laser cavity having a pin-hole size of about (2-10) mm;
focusing the output beam to a spot size of about (0.05-2.5) mm on
the corneal surface; selecting a scanning mechanism for scanning
said selected laser output beam; coupling said laser beam to a
scanning device for scanning said laser beam over a predetermined
corneal surface area to remove corneal tissue, whereby a patient's
vision is corrected by reshaping the cornea.
2. A method of claim 1, in which the hydration level of said
corneal surface area is controlled by a gas blower such that a
consistent tissue ablation rate can be achieved.
3. A method for improving .[.presbyopic patient's vision by
removing a portion of the sclera tissue from an eye of a patient,
said method comprising the steps of.]. .Iadd.accommodation and/or
treating presbyopia, the method comprising.Iaddend.: selecting an
ablative laser for removing sclera tissue by focusing said ablative
laser to a spot size of about (5-800) microns on the corneal
surface; selecting a scanning mechanism for scanning said ablative
laser; coupling said ablative laser to a scanning device for
scanning said ablative laser over a predetermined area outside the
corneal limbus to remove said sclera tissue.Iadd.; removing sclera
tissue from outside the corneal limbus area, said removing
comprising forming a pattern of radial lines in the sclera to a
depth of 500-600 microns, .Iaddend.whereby a patient's near vision
is improved by the increase of the corneal lens accommodation.
4. A method of claim 3, in which said .Iadd.removing is performed
using an .Iaddend.ablative laser .[.is a gas laser.]. having an
output wavelength of about (2.7-3.2) microns, energy per pulse of
about (0.5-15) mJ on .Iadd.the .Iaddend.corneal surface and a pulse
duration less than 150 nanoseconds.
5. A method of claim 3, in which said ablative laser is a mid-IR
solid-state laser having a wavelength of about (2.7-3.2)
microns.
6. The method of claim 3, in which said .[.ablative laser
includes.]. .Iadd.removing is performed using .Iaddend.pulsed
radiation generated by .Iadd.a .Iaddend.transverse electrical
discharge carbon dioxide laser which is frequency-doubled into a
laser having a wavelength of about (5.6-6.2) microns, energy per
pulse of about (2-15) mJ on the corneal surface.
7. A method of claim 3, in which said .[.ablative laser is.].
.Iadd.removing is performed using .Iaddend.a diode laser having a
wavelength of about 980 nm.
8. A method of claim 3, in which said .[.ablative laser is.].
.Iadd.removing is performed using .Iaddend.a diode laser having a
wavelength of about (1.4-2.1) microns.
9. A method of claim 3, in which said .[.ablative laser is.].
.Iadd.removing is performed using .Iaddend.a diode-pumped Er:YAG
laser having a wavelength about 2.9 microns and a pulse duration
less than 500 microseconds.
10. A method of claim 3, in which said .[.ablative laser is.].
.Iadd.removing is performed using .Iaddend.an ultraviolet laser
having wavelength of about (190-310) nm.
11. A method of claim 3, in which said sclera tissue is coagulated
by a laser having a wavelength of about (0.5-3.2) microns, an
average power of about (0.1-5.0) W on the corneal surface, spot
size of about (0.1-1.0) mm, and a pulse duration longer than about
200 seconds.
12. A method of claim 3, in which said .Iadd.removing is performed
using an .Iaddend.ablative laser .[.is.]. fiber-coupled and
combined with a coagulation laser and delivered to the
.[.corneal.]. .Iadd.eye .Iaddend.surface.
13. A method of claim 3, in which said sclera tissue is ablated in
radial patterns having a length about (2.5-3.5) mm .[.and a depth
about (400-700) microns.]. .
14. A method of claim 3, in which said sclera tissue is ablated in
radial patterns by a computer-controlled scanning mechanism.
15. A method of claim 3, in which said sclera tissue is ablated in
radial patterns by a translation mechanism.
.Iadd.16. A method as in claim 3 wherein the radial lines are at
least 2.5 mm in length..Iaddend.
.Iadd.17. A method as in claim 3 wherein the removing is performed
using a pulsed laser having a pulse duration of about 10-500
microseconds..Iaddend.
.Iadd.18. A method as in claim 3 wherein the removing is performed
using a laser focused to a spot size of about 5-500
microns..Iaddend.
Description
.Iadd.The questions raised in reexamination request 90/006,089,
filed Aug. 21, 2001 have been considered and the results thereof
are reflected in this reissue patent which constitutes the
reexamination certificate required by 35 U.S.C. 307 as provided in
37 CFR 1.570(e), for ex parte reexaminations, or the reexamination
certificate required by 35 U.S.C. 316 as provided in 37 CFR
1.997(e) for inter partes reexaminations..Iaddend.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to refractive surgical systems using
low-power, infrared and ultraviolet lasers in a predetermined
scanning patterns in procedures of photorefractive keratectomy
(PRK), laser assisted in situ keratomileusis (LASIK) and laser
sclera expansion (LASE), a new procedure for presbyopia
correction.
2. Prior Art
Refractive surgeries (or corneal reshaping) including a procedure
called photorefractive keratectomy (PRK) and a more recent
procedure called laser assisted in situ keratomileusis, or laser
intrastroma keratomileusis (LASIK) have been performed mainly by
lasers in the ultraviolet (UV) wavelength of (193-213) nm. The
commercial UV refractive lasers include ArF excimer laser (at 193
nm) and other non-excimer solid-state lasers such as the one
patented by the present inventor in U.S. Pat. No. 5,144,630. Laser
corneal reshaping has been conducted by two major beam deliver
techniques: the broad beam systems based on patents of L'Esperance
et. al. In U.S. Pat. Nos. 4,773,441, 5,019,074, 5,108,338 and
5,163,934; and the scanning small-beam systems based on patent of
the present inventor, U.S. Pat. Nos. 5,520,679 and 5,144,630.
Precise, stable corneal reshaping require lasers with strong tissue
absorption (or minimum penetration depth) such that thermal damage
zone is minimum (less than few microns). Furthermore accuracy of
the procedure of vision correction depends on the amount of tissue
removed in each laser pulse, in the order of about 0.5 microns.
Therefore lasers at UV wavelength (193-213 nm) and at the
mid-infrared (2.8-3.2) microns are two attractive ranges which
match the absorption peak of protein and water, respectively. UV
lasers however have some concerns regarding to the long-term
mutagenic effects of the corneal tissue which is less concern in
infrared (IR) lasers, noting that the DNA absorption peaks at a UV
wavelength about 260 nm. Moreover, UV laser systems suffer problems
such as optical damage of the coated mirrors, unstable and short
lifetime of the lasing gases and high cost toxic gas of fluorine
(for excimer laser). Low beam delivery efficiency and complexity of
beam uniformity are other drawbacks of UV refractive lasers.
Refractive surgery using a scanning device and lasers in the
mid-infrared (mid-IR) wavelength was first proposed by the present
inventor in U.S. Pat. Nos. 5,144,630 and 5,520,679 and later
proposed by Telfair et. al., in U.S. Pat. No. 5,782,822, where the
generation of mid-IR wavelength of (2.5-3.2) microns were disclosed
by various methods including: the Er:YAG laser (at 2.94 microns),
the Raman-shifted solid state lasers (at 2.7-3.2 microns) and the
optical parametric oscillation (OPO) lasers (at 2.7-3.2 microns).
These mid-IR wavelength lasers are proposed as candidates for
corneal reshaping due to their strong water absorption.
The present inventor had spent more than five years without success
in an attempt to develop mid-IR laser systems based on the
above-described prior arts. At the present time, there is no any
commercial or clinically practical mid-IR refractive laser system
been developed based upon the prior arts because of the inherent
problems and difficulties to be discussed as follows.
Er:YAG lasers to long-pulse (or the fundamental mode without
Q-switched) were proposed and described for refractive surgery by
Seller and Wollensak in "Fundamental mode photoablation of the
cornea for myopic correction", Laser and Light in Ophthalmology,
pp. 199-203 (1993), and Cozen et al, in PCT Application No.
93/14817. No clinically acceptable results were obtained based on
these prior arts because of the following drawbacks: (a) the basic
Er:YAG laser having a pulse duration of about 200 microseconds,
which was too long to minimize the thermal damage down to that of
the UV laser range of few microns, thermal damage zone of about
20-100 microns were reported in long-pulse Er:YAG; b) only low
laser repetition rate of about (5-10) Hz are available which limits
the procedure speed and to a non-scanning mode; (c) uniform,
flat-top beam profiles are not available and only the fundamental
Gaussian-type profiles were used in vision corrections limited to
myopia only;, other uses of hyperopic and astigmatism corrections
can not be performed by the fixed Gaussian beam profile; (d) a 90%
Gaussian or better beam profiles without any hot spot are
critically required to achieve the expected corrections whose
profiles are not predictable, (e) system was operated by a broad
beam mode of spot (5-6 mm diameter) which required high laser
energy of at least 20 mJ on the corneal surface.
Q-switched Er:YAG lasers at short pulse duration as proposed by Lin
and Telfair et al., has not been developed with laser parameters
meeting the clinically desired criteria of short pulse width (less
than 80 nanoseconds for minimum thermal damage), high repetition
rate (at least 40 Hz for reasonable surgery speed) and reliable
system components. Development of Q-switched Er:YAG system was
inherently limited by factors of optical damage of the Q-switching
components, coating problems due to strong water absorption, and
the low repetition rate Oess than 25 Hz) due to the cooling
problems of the laser rod. To overcome all these inherent drawbacks
in an Er:YAG system will not be cost effective and a high
maintenance efforts will be required when it is used for refractive
surgery. The prior art of Telfari et al proposed a short pulse,
less than 50 nanoseconds, Er:YAG system has never been achieved so
far in any commercially available system. The reported Er:YAG pulse
duration was limited to about 200 nanoseconds.
Another alternative proposed by Lin and Telfail et al., the
OPO-laser also had technical difficulties in making a clinically
practical system. At this time only low repetition rate OPO-laser
(lower than 30 Hz) at low energy (less than 5 mi per pulse) was
tested due to the problems of: low conversion efficiency from
near-IR to mid-IR wavelength, crystal and optics coating damage at
high power and unstable output IR energy due to cooling problems.
Therefore a practical OPO-laser system for refractive surgery will
be either difficult to make or high cost at high maintenance
efforts.
In addition to the above-described OPO-laser, the present inventor
also had attempt at no success to develop a Raman-shifted laser due
to difficulties of: unstable IR output due to Raman gas flow,
optical damage of the coated windows and the inherent back
scattering of the Raman signals. Again, a Raman-laser for
refractive surgery will be of high cost and difficult to maintain.
In addition the system can not be compact in size due to the
one-meter long Raman cell.
Corneal reshaping may also be performed by laser thermal
coagulation currently conducted by a Ho:YAG laser (at about 2
microns in wavelength) which however, was limited to low-diopter
hyperopic corrections. A new procedure for presbyopic correction
has recently proposed by implant or diamond knife incision by
Schaker in U.S. Pat. Nos. 5,529,076 and 5,722,952. These prior
arts, however, have drawbacks of being complexity and time
consuming surgery and having risk of side effects. Using lasers for
presbyopic corrections or improvements have not been previously
proposed.
The above described prior arts which are not clinically practical
for refractive uses because of the inherent technical problems or
being not cost-effective. In this of this, it is an object of the
present invention to provide new laser sources for refractive
surgeries and offer the advantages of: compact, low-cost, easy to
maintain, operated at mid-IR wavelengths and matching most or all
of the clinically desired laser parameters (short pulse, high
repetition rate and high water/tissue absorption). These new lasers
proposed in this invention will match the two major water
absorption peaks at about (2.7-32.) microns and (5.6-6.2)
microns.
It is yet another object of the present invention to provide
refractive laser systems which offer smooth ablated corneal surface
by appropriate beam overlapping and scanning patterns. To further
reduce the thermal effects and even corneal hydration, specially
designed scanning patterns will be proposed in this invention.
Furthermore the exact IR laser beam profiles are not critical in a
scanning mode which provides smoother corneal surface by the
randomized averaging procedure than the non-scanning lasers which
require a 90% Gaussian or better profile without hot spot.
It is yet another object of the present invention to provide
refractive laser systems which offer variable beam spot size of
about (0.1-2.5) mm for flexible and accurate correction profiles.
In the proposed designs, one single system at variable laser beam
spots will provide multiple-application including PRK, LASIK and
laser sclera expansion (LASE) as introduced earlier. Variable spot
size (VSS) controller using electronic shutter or motorized
pin-hole will be used in the presently proposed novel devices. It
should be noted that the new procedure of LASE has not been
reported so far in any UV or IR laser systems because it requires a
scanning flexibility of the beam direction, position and the
controlled beam spot size and energy for accurate ablation depth on
the sclera tissue. We note that the LASE procedure is a method for
the treatment of presbyopic patient by corneal sclera expansion
caused by removal of a portion of the sclera tissue. After the LASE
treatment the patient's accommodation will increase to see both
near and far. One of the critical issues of LASE is the corneal
bleeding during the laser "cutting". Therefore it is yet another
objective of this invention is to combine a coagulation laser with
the ablation laser to prevent or minimize the bleeding in the LASE
procedure.
According to the discussion in Jacques, S. L., Laser-tissue
Interactions; Photochemical, Photothermal and Photomechanical,
Lasers in General Surgery, 72t3), 531-558 (1992), we note that
photoablation is associated with the UV excimer laser corneal
ablation, whereas photomechanical ablation is responsible for the
mid-IR laser interaction with the corneal tissue. In the present
invention, however, we shall just use the name of "ablation" for
the process of photomechanical ablation in describing the mid-IR
radiation interaction with the corneal, where corneal tissue
fragments was by the mid-IR lasers by its strong absorption in
water. We further note that a laser pulse duration of less than 50
nanoseconds for corneal thermal damage claimed by the prior art of
Telfair et al may be true for the PRK or LASIK procedures, in which
few microns of tissue are removed in each mid-IR pulse. However, an
Er:YAG laser Q-switched to a short pulse of 50 nanoseconds has not
The condition of short pulse less than 50 nanoseconds not required
in the present invention for PRK or LASIK procedures. We propose in
this invention that new mid-IR lasers with pulse duration of about
(10-100) nanoseconds instead. We also propose that when a laser
beam is tightly focused, for example less than 0.15 mm, a long
pulse laser may still ablate corneal tissue efficiently at a
minimum thermal damage. For the proposal LASE procedure, a much
longer laser pulse (in about 10 microseconds or longer) may be used
for efficient sclera tissue ablation, as far as the beam spot is
less than 150 microns on the corneal surface.
It is yet another object of this invention is to provide novel
devices with variable beam spot sizes and multi-stage scanning such
that the refractive surgical procedures can be performed within
(10-30) seconds without losing the profile accuracy.
It is yet another object of the present invention to provide
refractive laser systems which offer a "gas blower" on the corneal
surface during the surgery to maintain a controlled level of
corneal hydration, which is rather sensitive and critical to the
laser ablation rate which is mainly caused by the water absorption
in the tissue. The hydration condition of the corneal surface is
much more important in IR lasers than in U-V lasers for the process
of corneal reshaping.
SUMMARY OF THE INVENTION
The preferred embodiments of the basic refractive surgical lasers
to perform the PRK or LASIK procedures include mid-IR lasers of:
(a) neutral gas lasers which are governed by transverse electrical
(TE) pulse discharged, in the mixtures of xenon, krypton, nitrogen
or helium gases and generate wavelengths of about (2.7-3.2)
microns; (b) pulsed carbon-dioxide laser (in isotopes of carbon)
which is transverse electrical atmosphere (TEA) discharged and
frequency doubled into a wavelength of about (5.6-6.2) microns.
According to one aspect of the present invention, The preferable
scanning mid-IR laser energy per pulse on corneal surface is about
(2.0-5.0) mJ for a short pulse of about (10-50) nanoseconds, and
about (5-15) mJ for a long pulse of about (50-150) nanoseconds.
Focused spot size of about (0.5-2.5) mm will be needed in a
scanning system and pulse duration of about (10-150) nanoseconds
are also desired for minimum thermal effects.
The other preferred laser parameter of this invention is the laser
repetition rate of about (40-500) Hz which will provide reasonable
surgical speed and minimum thermal effects. We note that the above
preferred two embodiments of the mid-IR spectra, (2.7-3.2) microns
and (5.6-6.2) microns are based on the facts that they are the two
major water absorption peaks and will result in very efficient
corneal tissue removal with minimum thermal damage and precise
ablation. We also note that the 6.1 microns spectrum matches the
absorption peak of corneal protein. Unlike the UV excimer ArF
laser, these mid-IR lasers can be easily delivered through a
sapphire fiber at minimum loss.
In another aspect of the present invention is the use of novel,
devices for beam-spot-size control, where variable spot size (VSS)
are required for fast, efficient tissue removal in PRK, LASIK and
LASE. The VSS can be achieved by either a shutter at a fixed
pin-hole size or a motorized electronic shutter for adjustable beam
spot. Our objective in the present invention is to use these VSS
devices to achieve: (a) large beam spot of about (1.5-2.5) mm for
large area ablation at fast speed (shorter than 20 seconds), and
(b) small spot of about (0.1-0.5) mm for small area ablation such
as that of LASE correction without losing the accuracy.
Another preferred embodiment of the present invention is to control
the laser output spot size from the laser cavity by an internal
magnetic coupler which is used to select a pin-hole size inside the
cavity.
To keep the procedure speed, one can use a large spot beam of about
2.0 mm which, however, will lose the accuracy for the ablation of
small zone area less than about 3.0 mm range. Therefore VSS device
operated in multi-stage procedure is proposed in the present
invention. For example, a large beam with (1.5-2.5) mm spot will
ablation the first stage involving an corneal ablation zone size of
about (3.5-9.0) mm and followed by the second-stage ablation using
a small beam of about (0.3-0.6) mm for the remaining zone of about
3.4 nun.
We should also notice that the problems of central islands, caused
by uneven hydration level and shock-wave on the corneal surface,
would be mostly reduced by above-introduced VSS designs and
controlling these beams scanning in a counter-directions. Moreover,
it is another preferred aspect of the present invention to use a
random predetermined scanning pattern such that the thermal effect,
shock wave and uneven hydration level on the corneal surface can be
minimized. The random scanning can be easily achieved by a software
design based on the desired correction profiles which is governed
by myopic diopter, ablation zone diameter and the position
(coordinate) of each scanning beam on the corneal surface. The
pre-calculated positions of each scanning spot can be stored and
easily assigned to each scanning spot in a randomized means.
Details of the equation describing the refractive corrections can
be found in J. T. Lin, "Critical review of refractive surgical
lasers" in Optical Engineering, vol. 34, 668-675 (1995).
It is yet another preferred embodiment of the present invention to
provide refractive laser systems which offer a "gas blower", at a
controlled hydration gas mixture or pure predetermined gas of
helium or nitrogen, on the corneal surface during the surgery.
Controlling the corneal hydration is rather critical to the laser
ablation. The hydration control is much more important in IR lasers
than in LTV lasers. The gas blower may also reduce the thermal
effects on the corneal tissue caused by the mid-IR lasers.
For the purpose of smooth ablation corneal surface, a
computer-controlled galvanometer-pair coated with high-reflecting
at the main mid-IR beam is used in the present invention. Scanning
patterns including circular and oriented linear scan are used for
beam profile averaging (BPA) to achieve the smooth tissue surface.
We had tested hundreds of PMMA ablated sheets to conclude that only
rough surfaces can be obtained without this BPA design.
Quantitative comparisons are made in out laboratory by the diopter
readings of the ablated PMMA sheets in a lensmeter. The scanning
laser offers a clearly readable diopters (up to about 5.0) on the
ablated PMMA sheets whereas those from the conventional
non-scanning lasers are not readable at all due to the high surface
light scattering.
We should note that the idea refractive surgical laser should
perform and achieve: fast procedure to reduce the
eye-motion-effects, accurate ablation profile (particularly in the
presbyopia small zone application), good clinical results (smooth
ablated cornea surface, reduced haze and regression), low system
cost and easy maintenance. The proposed novel devices of VSS and
the multi-stage ablation patterns described in the present
invention provide us a unique means to achieve these
objectives.
It would be very difficult for any non-scanning lasers to perform
the new application of laser sclera expansion (LASE) for presbyopia
correction which requires small beam spot, low-energy and flexible
scanning patent to ablate the sclera tissue. The preferred
embodiments of the basic ablative lasers to perform the LASE
procedures by removing portion of the sclera tissue include lasers
of: (a) diode laser at about 980 nm, 1.5 microns, and 1.9 microns,
(b) diode-laser pumped Er:YAG laser at about 2.94 microns, (c) the
mid-IR gas lasers of about (2.7-3.2) microns and (5.6-6.2) microns
and (d) short wavelength ultraviolet lasers of about (190-310) nm
including ArF(193 nm) and XeCl (at 308 nm) excimer lasers and (e)
solid-state OPO-lasers of about (2.7-3.2) microns. We propose that
when a laser beam is tightly focused, for example less than 0.15
mm, a long pulse laser can still ablate corneal sclera tissue
efficiently with minimum thermal damage. Thermal damage zone size
of about (5-20) microns is clinically acceptable for the sclera
ablation which has a typical ablation depth of about (400-700)
microns. Therefore laser pulse duration for diode lasers at
quasi-continuous wave (QCW) mode or diode-pumped free-running
Er:YAG laser with a typical pulse duration of about (10-500)
microseconds are proposed in the invention.
The preferred embodiments of the basic coagulation lasers to
prevent or minimize the corneal bleeding during the LASE procedures
include the following lasers at long pulse duration: (a) visible
lasers with wavelength of (500-690) nm, (b) infrared lasers at
wavelength of about 1.0, 1.5, 2.0 and 2.9 microns, in which the
corneal tissue absorption of these radiation will cause the thermal
effects for coagulation to occur.
The ophthalmic applications of the IR laser systems described in
the present invention should include, but not limited to,
photorefractive keratectomy (PRK), phototherapeutic keratectomy
(PTK), intrastroma photokeratectomy, laser assisted in situ
keratomileusis (LASIK) for myopic, hyperopic, astigmatism and laser
sclera expansion (LASE) for presbyopia corrections.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram of a refractive laser system consisting
of an mid-IR laser couple to a beam spot controller, scanning
device, and reflector for refractive surgery.
FIG. 2 presents the schematics of the internal magnetic coupler for
the selection of output beam spot size.
FIG. 3 presents the schematics of the external pin-hole spot size
controller.
FIG. 4 shows schematics for a gas blower to control the hydration
level of the corneal surface during the laser ablation.
FIG. 5 illustrates the dual beam device for presbyopia
correction.
FIG. 6 shows the schematics of fiber-coupled diode lasers or
diode-pumped laser for presbyopic correction system.
FIG. 7 shows the presbyopia correction patterns on the sclera
area.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
We should first briefly present some of the theoretical background
of the present invention regarding to the ablation efficiency or
the procedure speed, and the ablation threshold, fluency and
intensity, two of the main objectives of the present invention.
Greater detail regarding to the theoretical aspects can be found in
a paper published by the present inventor in: "Critical Review of
Refractive Surgical Lasers", Optical Engineering, Vol. 34,
pp.668-675, (1995).
Given a laser energy per pulse of E (in mJ), a fluency of F (in
mJ/cm.sup.2) may be achieved by focusing the beam into an area of F
and F=E/A. For corneal tissue ablation, either photoablation or
photomechanical ablation (defined by reference of Jacques, S. L.,
"Laser-tissue Interactions; Photochemical, Photothermal and
Photomechanical," Lasers in General Surgery, 72(3), 531-558,1992).
For an ablation to occur, the laser intensity I (in MW/cm.sup.2)
must be higher than the an ablation threshold (AT) of about (10-20)
MW/cm.sup.2 for UV-laser, and about (50-100)MW/cm.sup.2 for IR
lasers where I-Ft/t, t being the pulse duration. Therefore it is
always possible to tightly focus a pulsed-laser beam and achieve
the AT value even for a low-energy laser of (0.1-1.0) mJ for UV
lasers and (0.5-5) mJ for mid-IR lasers.
Taking a typical mid-IR laser of 15 nanosecond pulse width as an
example, small spot size of about 1.0 mm is needed on the corneal
surface when the available mid-IR energy is limited to about 3 mJ
range, whereas about 9 mJ will be needed when spot size of 2 mm is
used.
In addition to the above described ablation threshold (governed by
laser intensity and pulse width), the procedure speed (governed by
laser averaged power) is another important concept needed to be
addressed. The drawback of using a low-energy, small-spot laser for
refractive procedures is that the operation time will be longer
than that of a large-spot but high-power laser. However, the
operation time may be shortened by using a high repetition-rate
laser. It is important to note that given an averaged power P, the
laser intensity must be above the ablation threshold (AT) by either
beam focusing or increasing the laser energy or keeping the laser
pulse short enough.
The preferred embodiments disclosed in the present invention will
be based upon the above described theory. Beam focusing and
scanning are always required to achieve the ablation threshold and
ablation smoothness for the proposed low-energy lasers. The
individual beam profile in the scanning system is not as critical
as that of prior non-scanning systems which require a uniform
overall profile.
Referring to FIG. 1, a refractive laser system in accordance with
the present invention comprises a basic laser 1 having wavelength 2
was focused by a beam spot controller 4 into the scanning device 4
and reflected by a coated (high-reflecting at the wavelength 2 of
IR beam) mirror 5 into the target, patient's cornea surface 6.
Still referring to FIG. 1, the basic laser 1, according to the
present invention, the preferred embodiments of the basic
refractive surgical lasers to perform the PRK or LASIK procedures
include mid-IR lasers of: (a) neutral gas lasers which are governed
by transverse electrical (TE) pulse discharged, in the mixtures of
xenon, krypton, nitrogen or helium gases and generate wavelengths
of about (2.7-3.2) microns; Co) pulsed carbon-dioxide laser (in
isotopes of carbon) which is transverse electrical atmosphere (TEA)
discharged and frequency doubled into a wavelength of about
(5.6-6.2 microns). According to one aspect of the present
invention, the preferable scanning mid-IR laser energy per pulse on
corneal surface is about (2.0-5.0) mJ for a short pulse of about
(10-50) nanoseconds, and about (5-15) mJ for a long pulse of about
(50-150) nanoseconds. Focused spot size of about (0.5-2.5) mm will
be needed in a scanning system and pulse duration of about 150
nanoseconds or shorter are also desired for minimum thermal
effects. The other preferred laser parameter of this invention is
the laser repetition rate of about (40-500) Hz which will provide
reasonable surgical speed and minimum thermal effects.
Referring to FIG. 2, the basic mid-IR gas laser cavity 1 has a pair
of reflecting windows 7 and 8 to generate the output beam of 2
which has a beam spot size of about (2-10) mm diameter controlled
by the internal magnetic coupler, or pin-hole 9. This magnetic
coupler when is at the "on" position will limited the internal beam
propagation to a small area and generate a circular output beam
which can be easily focused into a small spot on the corneal
surface about (0.05-0.5) mm. On the other hand when the magnetic
coupler is at the "off" position, a larger output beam, with higher
energy, can be generated for situation that a larger beam, size of
about (0.5-2.5) mm is desired for a faster procedures in PRK or
LASIK. We note that the small beam spot of less than 0.15 mm is
normally needed in the new procedure of LASE to be discussed
later.
As shown in FIG. 3, the beam spot external controller 3 consisting
of a motorized electronic shutter 10 and a focusing lens 11, where
the pin-hole size of the electronic shutter (made by, for example,
Melles Griod) are continuously adjustable in the range of about
(1.5-10) mm to reduce the output beam from the laser cavity 2 to a
spot size of about (0.05-2.5) mm on the corneal surface.
Referring to FIG. 4, the output beam from the laser cavity 2 is
reflected by a mirror 5 onto the corneal surface 6 in which the
hydration level is controlled by a gas blower 12. The preferred
embodiments of this invention is to use gases 13 which include
nitrogen or helium and apply to the target area of the cornea.
These gases 13 will have a controlled speed and hydration level.
Furthermore, another preferred embodiment of this invention is to
use cool gases 13 to minimize the thermal effects on the corneal
surface caused by the mid-IR lasers.
FIG. 5 shows the schematics of a system for presbyopia correction
by laser sclera expansion (LASE). The selected basic ablative laser
14 having wavelength 15 is coupled to a coagulation laser 16 having
wavelength of 17 by a beam splitter 18 and focused by a spot
controller 3 into a scanner device 4. These two beams 15 and 17 are
then reflected by a dual-band coated high-reflecting mirror 5 onto
the limbo area of the cornea 6.
In FIG. 5, the preferred embodiments of the basic ablative lasers
14 to perform the LASE procedures include lasers of: (a) diode
laser at about 980 nm, 1.5 microns, and 1.9 microns, (b)
diode-laser pumped Er:YAG laser at about 2.94 microns, (c) the
mid-IR gas lasers of about (2.7-3.2) microns and (5.6-6.2) microns
and (d) short wavelength ultraviolet lasers of about (190-310) nm
including ArF(193 mn) and XeCl (at 308 nm) excimer lasers and (e)
solid-state OPO-lasers of about (2.7-3.2) microns. We propose that
when a laser beam is tightly focused, for example less than 0.15
mm, a long pulse laser can still ablate corneal sclera tissue
efficiently with minimum thermal damage. Thermal damage zone size
of about (5-20) microns is clinically acceptable for the sclera
ablation which has a typical ablation depth of about (500-600)
microns. Therefore laser pulse duration for diode lasers at
quasi-continuous-wave (QCW) mode or diode-pumped free-running
Er:YAG laser with a typical pulse duration of about (10-500)
microseconds are proposed in the invention.
Still referring to FIG. 5, the proposed LASE procedure with
efficient sclera tissue ablation, the preferred embodiments of the
invention for the pulse duration of the ablative laser 16 are: (a)
about (10-200) microseconds for quasi-continuous-wave (QCW) diode
lasers at wavelength of about 980 nm, 1.5 microns, and 1.9 microns,
(b) about (50-500) microseconds for diode-pumped Er:YAG laser, (c)
about (10-200) nanoseconds for pulsed mid-IR gas or solid-state
lasers at about (2.7-3.2) microns and (5.6-6.2) microns and (d)
short pulse laser of about (1-100) nanoseconds for the ultraviolet
lasers with wavelength of about (190-310) nm. For minimum thermal
damage and minimum scars on the corneal surface after the LASE
procedure, the preferred embodiments of this invention include a
laser beam spot size of about (5-500) microns on the ablated sclera
tissue. Depending on the pulse duration, beam spot size and
wavelength, the laser energy per pulse needed for sclera ablation
will be about (0.5-15) mJ on the corneal surface.
The preferred embodiments in FIG. 5 for the basic coagulation laser
16 to prevent or minimize for corneal bleeding during the LASE
procedures include the following lasers at long pulse duration or
continuous wave (CW): (a) visible lasers with wavelength of
(500-690) nm, (b) infrared lasers at wavelength of about 0.98, 1.5,
2.0 and 2.9 microns, in which the corneal tissue absorption of
these radiation will cause coagulation to occur. The preferred
embodiments of the invention for the selected coagulation lasers
include pulse duration of at least 100 microseconds and averaged
power on the corneal surface of about (0.1-5.0) W, for spot size of
about (0.1-1.0) mm. We note that the coagulation features of a
laser are mainly governed by the long pulse duration and large spot
size (or lower fluency) on the corneal surface. For a given
wavelength longer than about 980 nm, a laser may be an ablative one
or a coagulation one. When a laser is tightly focused, less than
about 100 microns, the high fluency or peak power may start to
perform ablative than coagulation in its interaction to tissues.
For ultraviolet lasers shorter than 310 nm, however, coagulation
effects will be minimum even at a large beam size.
FIG. 6 shows the LASE procedures performed by selected diode lasers
or diode-pumped laser which are fiber-coupled on to the corneal
surface. The basic ablative laser 19 is coupled to a fiber 21 and
combined by another fiber jacket 23 with the coagulation laser 20
after it is coupled to a fiber 22, where fibers 21 and 22 are
highly transparent (better than 85% in about one meter long) to the
wavelength of laser 19 and 20, respectively. The combined output
two wavelengths laser is then used to ablation and coagulate the
sclera tissue to achieve ablation patterns to be described in FIG.
7.
FIG. 7 shows the LASE patterns, where the selected lasers are
focused onto the cornea surface around the limbus area 24. Radial
ablation patterns are performed in the anatomic limbus area of the
sclera ciliary body. The ablation depth of the sclera ciliary
tissue is about (400-700) microns with each of the radial length 25
of about 2.5-3.5) mm adjustable according to the optimal clinical
outcomes including minimum regression and maximum accommodation for
the presbyopic patients. The preferred radial ablation shall start
at a distance about (4.0-5.5) mm from the corneal center out to the
limbus area.
Referring to FIG. 7, the preferred embodiments to generate the
radial patterns on the sclera area include: (a) using the computer
controlled scanning mirrors which move in x and y directions; (b)
using a mechanical translator which is attached to the fiber end of
the coupled ablative and coagulation lasers and cause the lasers to
move along the predetermined patterns, and (c) manually move the
fiber-coupled lasers along a line to generate the linear patterns.
For precise and controllable ablation depth of the sclera tissue,
methods (a) and (b) are preferred.
We also propose that overlapping of the scanning or translating
beam is preferred for smooth, uniform and controlled depth of the
ablated sclera. Calibration on materials including PMMA plastic
sheet is preferred in order to clinically pretest the ablation
depth of the sclera tissue. Measurement the depth of the ablated
sclera tissue can be conducted by preset diamond knife instrument
or ultrasound.
In this invention, we define the refractive surgeries by performing
either PRK for corneal surface ablation or LASIK for intrastroma
ablation and in general we name these procedures as corneal
reshaping. The presbyopia correction, however, is referred as the
removal of the sclera tissue.
While the invention has been shown and described with reference to
the preferred embodiments thereof, it will be understood by those
skilled in the art that the foregoing and other changes and
variations in form and detail may be made therein without departing
from the spirit, scope and teaching to the invention. Accordingly,
threshold and apparatus, the ophthalmic applications herein
disclosed are to be considered merely as illustrative and the
invention is to be limited only as set forth in the claims.
* * * * *