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BACKGROUND OF THE INVENTION
This invention relates generally to intravitreal surgical techniques
uitilizing the direct application of a laser beam into the vitreous
cavity. In particular, this invention relates to the use of a surgical
instrument for vitreous surgery employing a CO.sub.2 laser probe
incorporating illumination of and viewing from within the eye. This
surgical instrument also includes the capability of aspiration for removal
of vitreous material together with the maintenance of intraocular pressure
by means of irrigation.
This invention is related to a co-pending application entitled "Articulated
Arm Radiation Guide" filed by T. J. Bridges and A. R. Strnad on the same
day as this application, Ser. No. 338,871.
The prior art is replete with a number of concepts together with reports in
the scientific literature evidencing limited instances of actual use of a
CO.sub.2 laser in ophthamalic procedures. The use of lasers as surgical
tools, and in particular, CO.sub.2 laser systems to accomplish
simultaneous cutting and cauterization, is now well established. Cutting
action, a result of intense local heating of the tissue due to absorption,
occurs when the focused laser beam impinges on the tissue. Cauterization
occurs simultaneously due to heating. The beam's energy is absorbed by the
medium and will not propagate through it.
The use of a CO.sub.2 laser, operating at 10.6 .mu.m wavelength, offers
both advantages and disadvantages in surgical procedures. CO.sub.2 lasers
have been particularly useful for the treatment of biological tissue
reached by surface application of the radiation directly onto the area
affected. Typical uses are dermatological, laryngological and
gynecological polyp excisions. The use of a CO.sub.2 laser for the
treatment of tissue located within an absorbing medium has, however, to
date been generally unsuccessful. This is because the laser radiation at
10.6 .mu.m is completely absorbed by the fluid or tissue that it first
impinges. That is, the beam will not penetrate through layers of tissue
without first vaporizing or damaging those outer layers. It is for this
reason that CO.sub.2 laser techniques have heretofore found application in
surface procedures.
The characteristic of complete absorption of the CO.sub.2 laser beam's
energy does however find unique application in vitreous surgery. This
microsurgery poses requirements for exact cutting of vitreoretinal
membranes and elimination of hemorrhage in situ at a precise point within
the spherical vitreous cavity. Present intravitreal techniques for the
removal of vitreous hemorrhage and cutting vitreoretinal adhesions have
utilized two approaches for entry into the vitreous cavity. One,
transcorneal, utilizes a corneoscleral incision and the removal of the
crystalline lens. The second, trans pars plana, utilizes an instrument
which is inserted through the ocular coates, at a point behind the lens.
Following removal of hemorrhagic vitreous and reattachment of the retina,
the vitreous cavity is, where necessary, filled with normal saline, human
vitreous or other suitable fluid such as Ringers. Vitreous surgery
utilizes mechanical cutters and suction probes to remove vitreous
hemorrhage and/or cut vitreoretinal membranes. Existing surgery frequently
requires manipulation of the vitreoretinal bands resulting in secondary
vitreous hemorrhage. The technique is performed utilizing an operating
microscope or indirect ophthalmoscope.
The two techniques referred to above have traditionally utilized various
mechanical cutting instruments. Vitrectomy instruments currently in actual
use are conventionally either motor, air or solenoid driven. Rotary,
oscillatory or guillotine-like cutters have been developed. The essential
concept of each is cutting and removal of the vitreous material from the
eye with suction and the replacement of aspirated vitreous with infusion
fluid. A hallmark deficiency of such mechanical cutting is that the
opening is not at the tip of the probe and thus cutting action is limited
when operations take place close to the retinal surface. Such cutting
instruments are also objectionable since they place added traction on the
vitreoretinal membrane at the point of attachment to the retina as a
result of shear during the cutting operation. Accordingly, there is a
propensity of retinal tears and hemorrhage during such mechanical cutting.
Another disadvantage of the trans pars plana and transcorneal approaches
using mechanical cutters is the inability to control hemorrhage within the
vitreous cavity. This deficiency is especially complicated in the case of
damaged or leaking vessels of diabetic patients. It is well established
that vitreous hemorrhage is a frequent complication of diabetic
retinopathy and retinal detachment. Once vitreous hemorrhage has occurred,
adhesions develop between the retina and the vitreous body. These
adhesions form adhesive bands similar to scars which tend to contract and
cause traction on neighboring retinal blood vessels and the retinal tissue
itself. The consequence is subsequent vitreous hemorrhage and retinal
detachments frequently leading to complete blindness.
The pars plana incision requires viewing of the procedure using an
operating microscope positioned above the eye and through a corneal
contact lens. Accordingly, there is loss of visibility of the cutting
instrument as it approaches the posterior region of the vitreous cavity in
a case of massive vitreous hemorrhage. Moreover, if a cataract is present,
viewing is impaired.
This deficiency in prior art vitreous procedures becomes further
complicated when the hemorrhage may be so dense that the surgeon cannot
adequately differentiate a neovascularized vitreoretinal membrane from
retinal tissue with its normal vascular supply. Internal illumination by
means of fiber optics has generally been developed; however, there is no
instrument which currently allows a surgeon to view as well as illuminate
the operative site from within the vitreous cavity. Accordingly, while
significant advances have occurred in vitreous surgery, significant
problems remain.
In response to these problems, the use of a CO.sub.2 laser for
simultaneously accomplishing both photo-transection and photocoagulation
has been proposed as a cutting tool. A second unique advantage of a
CO.sub.2 laser operating at 10.6 .mu.m is its absorption by almost all
biological tissue at the point of contact. While this characteristic may
be a deficiency in other procedures, it is a material advantage in
vitreous surgery since little damage to neighboring or remote ocular
tissue occurs. The propensity for damage to retinal tissue is minimized.
The problem of propagation through the vitreous cavity, striking the optic
nerve is eliminated. Fine et al, in "Preliminary Observations on Ocular
Effects of High-Power, Continuous CO.sub.2 Laser Irradiation", Am. J.
Ophth. 64:209, August 1967 report that utilizing CO.sub.2 laser radiation
on the cornea resulted in little effect on underlying ocular structures.
Data By Karlin et al in "CO.sub.2 Laser in Vitreoretinal Surgery",
Ophthamology 86:290, February 1979 indicates that the depth of penetration
of 10.6 .mu.m radiation is about 10 microns. This minimal depth of
penetration is in direct contrast to laser radiation occurring in the
visible spectrum, for example, in argon and ruby lasers where propagation
occurs through the vitreous over long distances potentially damaging the
retina and the optic nerve. Given the high absorption at the point of
contact, the CO.sub.2 laser beam can therefore be used to achieve
simultaneous cutting and coagulation while other types of lasers cannot.
In vitreous surgery, this advantage minimizes the possibility of
hemorrhage when neovascular membranes are severed, a problem common in
current mechanical cutters.
Investigations have already attempted to determine the feasibility of
utilizing a CO.sub.2 laser in vitreoretinal surgery. One report, Karlin et
al, supra. investigates four potential applications of this technology.
These applications include photo-transection and photocoagulation,
intravitreal biopsy, full thickness sclera-chorioretinal wall resection
and, radiation effects on the lens. Other reports in the literature such
as Campbell et al, "Laser Photocoagulation of the Retina", Tr. Am. Acad.
Ophth. Otolaryng. 70:939, November-December 1966; Miller et al,
"Transvitreal Carbon Dioxide Laser Photocautery and Vitrectomy", Tr. Am.
Acad. Ophth. Otolaryng. 85:1195, November 1978 indicate that evaluation of
CO.sub.2 lasers for vitreal surgery have taken place. To date, however,
those reports and experiments have been done utilizing rudimentary
instruments primarily concerned only with investigating photo-transection
and photocauterization. The development of a CO.sub.2 laser instrument
capable of widespread ophthalmic clinical use has yet to be achieved.
The definition of such an instrument requires a careful matching of
surgical requirements with the level of engineering and scientific
knowledge necessary to actually build the device. Hence while the surgeon
can define his goals, the level of engineering know-how has not to date
been sufficient to achieve them. Laser power requirements, precise focus,
minimum instrument size, levels of illumination and field of view angles
are all problems that remain.
The prior art is also replete with patents describing laser instruments
that conceptually find utility for eye surgery. One, L'Esperance, Jr.,
U.S. Pat. No. 3,982,541 relates to the use of a CO.sub.2 laser probe
coupled to a laser source by means of articulated couplings. One probe
configuration utilizes a series of circumferential segmented chambers for
the introduction of a stabilizing fluid to maintain eye inflation, that
is, an irrigation channel, and an aspiration channel to evacuate debris.
The probe size is unacceptably large.
This patent perceives that a fiber optic bundle can be utilized in place of
the articulated segments each having mirror elements, given the
propagation losses in such articulated arms. However, in such a case, the
CO.sub.2 laser cannot be utilized and the patent affirmatively recognizes
that some other type, such as argon, should be utilized. Accordingly, the
U.S. Pat. No. 3,982,541 patent perceives the difficulties of transmitting
CO.sub.2 10.6 .mu.m radiation through fiber bundles.
U.S. Pat. No. 4,122,853 also relates to laser photocautery for use in
vitreous surgery. A CO.sub.2 laser is utilized in combination with an
articulated arm having mirrored joints. The probe is inserted in the pars
plana region to a depth where the tip contacts the vascular tissue to be
cauterized. A number of probe embodiments are shown, with the embodiments
shown in FIGS. 9-11 of the U.S. Pat. No. 4,122,853 patent having a laser
light guide tube 34, an irrigation channel 45, an aspiration channel 78,
and, an illuminating light conduit 44. The particular embodiment shown in
FIGS. 9-11 of the U.S. Pat. No. 4,122,583 patent does not provide for
fiber optic viewing. However, this patent in FIG. 4 perceives an
endoscope-like embodiment utilizing simultaneous illumination and viewing.
Moreover, while five functions are shown in the various probe
configurations of the U.S. Pat. No. 4,122,583 reference, they are not
combined into a single functional unit.
An important criterion for probe configuration is to reduce the size to
minimize trauma to the eye occasioned by large incisions. The probe should
also match the geometry of the incision. Probes having a gauge greater
than an 18-20 gauge hypodermic needle are considered unsuitable for
vitreous procedures. Given this requirement for minimization of
cross-sectional size, the optimization of the probe presents one area of
continuing research. If the cross-sectional size is decreased, it becomes
increasingly difficult to provide adequate illumination at the probe end.
Problems of cold light and laser beam attenuation become significant and,
when coupled with insufficient resolving power in the optic viewing
segment tend to render those combined features unworkable. Such problems
are compounded in the case of procedures within the vitreous cavity where
the field of view is frequently clouded by hemorrhage.
Another problem not adequately addressed in prior art systems is the power
loss attendant to transmission of the laser beam from the laser to the
probe. This problem is particularly acute in the case of CO.sub.2 lasers
where absorption occurs at the point of contact. Hence, special
arrangements are necessary to transmit a CO.sub.2 laser beam along an
irregular path.
U.S. Pat. No. 4,170,997, is directed to this problem and relates to a laser
for surgical applications and specifically, a CO or a CO.sub.2 laser
having illumination through fiber bundle 13 and viewing through fiber
optic bundle 16. An axial hollow tube 18 contains a flexible infrared
transmitting fiber optical waveguide 19 coupled to a laser source 20. An
aiming or target beam produced by HeNe laser is utilized with transmission
selectively coupled by means of an optical shutter 22 interposed in the
path of the CO.sub.2 laser beam.
An important problem in the delivery of infrared laser radiation is the
provision of a flexible radiation path between the laser source and the
non-fixed probe. In the prior art, a number of solutions have been
suggested. Among them are conventional articulating arms, as in U.S. Pat.
No. 4,122,853 and illustrated in Herriott, "Application of Laser Light",
Scientific American, 219, 144 (1968); flexible metal waveguides in Garmire
et al, "Low Loss Propagation and Polarization Rotation in Twisted Infrared
Metal Waveguides", Appl. Phys. Letters 34(1), 35 (1979); and infrared
transmitting fibers in Pinnow, U.S. Pat. No. 4,170,997; Pinnow et al,
"Polycrystalline fiber Optical Waveguides for Infrared Transmission",
Appl. Phys. Letters 33(1), 28 (1978); Bridges et al, "Single-Crystal AgBr
Infrared Optical Fibers", Optics Letters 5, 85 (1980). These techniques
all have serious difficulties.
In both metal waveguides and infrared fibers, as known in the art, the
guides are multimode. The single mode radiation from the laser, when
launched, rapidly degrades into a multimode pattern. The pattern changes
in form and the beam wanders as the guide is moved to follow movements of
the probe. Hence, the beam does not remain centered, a critical factor in
ophthamalic surgery. Such degradation considerably reduces the maximum
intensity that can be obtained by focusing the output radiation.
Prior art articulating arms while preserving the single mode suffer from
alignment problems. Unless the input beam is precisely launched on axis
and the arm mechanism is precisely correct, the output beam will wander in
a complicated manner as the arm is manipulated. In the context of a
surgical procedure this is unacceptable. Moreover, such arms have
heretofore been large and cumbersome making them unsatisfactory linkages
for hand-held probes.
SUMMARY OF THE INVENTION
Given the deficiencies in various prior art systems, the present invention
provides a vitreous surgical system utilizing a single probe to introduce
CO.sub.2 laser energy directly into the vitreous cavity to accomplish
photo-transection and produce photocoagulation. The probe also allows
simultaneous illumination and viewing of the vitreous cavity using
illumination within the eye. Irrigation and aspiration functions are also
accomplished. Accordingly, a single, miniaturized, multi-function probe
for intravitreal surgery is defined by the present invention.
This invention also incorporates a novel articulating arm using straight
hollow dielectric waveguides of the Marcatili-Schmeltzer type. Such an arm
is disclosed in co-pending application "Articulated Arm Radiation Guide"
by T. J. Bridges and A. R. Strnad. Single mode propagation is maintained
while arm size is reduced and precision assembly criteria are diminished.
The transparent waveguide tube also acts as a light pipe to carry visible
light from a source to the probe for internal illumination of the surgical
site.
Accordingly, it is an object of the present invention to provide for an
improved CO.sub.2 laser system for use in vitreous surgery.
Another object of the present invention is to provide a laser surgical
system incorporating simultaneous illumination and viewing of the vitreous
cavity from within the eye.
A further object of the present invention is to provide for a single
miniaturized multi-function probe for use in intravitreal surgery.
Yet another object of this invention is to provide for an improved surgical
probe optimized to provide maximum functional operation within a probe of
minimum size, thereby reducing the propensity of damaging ocular tissue.
Still another object of this invention is to define a CO.sub.2 laser
surgical system having an improved flexible radiation path coupling the
energy source to the probe.
Additional objects, advantages and features of this invention will become
apparent from the following detailed description of the preferred
embodiment when considered in conjunction with the accompanying drawings.
In the drawings, like reference numbers are utilized to identify the same
parts throughout.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram of the multi-function laser vitrectomy system of
this invention;
FIG. 2 is an elevational view, partially cut-away, showing the laser
delivery system including the articulated arm used in accordance with this
invention;
FIG. 2A is a cut-away view showing operation of the mechanical shutter
element;
FIG. 2B is a cut-away view showing the internal elements of the articulated
arm including its coupling to the laser source;
FIG. 3 is an enlarged partial section of a laser coagulator probe in
accordance with the present invention;
FIG. 4 is an enlarged end view of a probe including additional functions of
aspiration, illumination, irrigation and internal viewing; and
FIG. 5 is a section view of the probe of FIG. 4 for the multi-function
vitreous probe.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now to FIG. 1, a schematic diagram of the CO.sub.2 system in
accordance with this invention is shown. FIG. 1 in schematic form shows
the arrangement of the components utilized relative to a surgical
procedure or an eye 10. In a conventional manner, the patient is
positioned supine, with an operating microscope positioned directly above
the face. The surgeon, working from behind and generally overhead,
performs the microsurgery by viewing through the operating microscope 12.
Such microscopes are well known in the technology and utilize foot pedals
to operate focus and zoom controls allowing viewing of the vitreous
through the iris of the eye 10. In accordance with one embodiment of the
present invention, the operating microscope is also coupled to the probe
14 to allow direct viewing of the operative site from within the eye.
The probe 14 is inserted into the vitreous cavity through an incision in
the pars plana. One embodiment is shown in FIG. 3 for coagulation. The
probe 14, to be described in detail with respect to the embodiment of
FIGS. 4 and 5 is constructed utilizing a series of generally annular
channels. The probe has preferably an elliptical shape.
Referring now to FIG. 2, a schematic diagram of the overall laser delivery
system is shown. The primary laser power system forms a first major
subsystem of this invention. A CO.sub.2 laser, for example, a Sylvania
Model 948, is shown schematically in FIGS. 1 and 2 as element 40. A laser
attenuator 42, typically a Sylvania Model 485, is used to control the
power over a range of 2-95% of laser output. The attenuator is adjustable
by means of control knob 43. Power readout is by means of a readout module
having a meter, now shown, and employs a power meter head 45 receiving the
laser radiation beam 50 diverted from the radiation source 49 by mirror
44. As indicated in FIG. 2A, the laser radiation beam from the CO.sub.2
laser is reflected by means of mirror 44 onto the power head 45 as a
result of action of the mechanical shutter 46.
The mechanical shutter 46, typically a Uniblitz Model 114, when closed,
reflects laser radiation via mirror 44 onto the power head 45. This allows
a power output reading to be made. The shutter, when opened, transmits the
laser beam to the delivery system. The shutter may be programmed to have
an opening time in the range of 50 milliseconds to 100 seconds.
A focusing lens 47 is fixed on the threaded mount 47' shown in FIG. 2, to
vary to focal length by rotational adjustment relative to block 47". The
lens is typically made from zinc selenide material. The output, a focused
beam, is then directed through a support tube 48 to the work illumination
subsystem. The laser radiation beam passing through the opened shutter
into and through the support tube 48 is shown as beam 51.
The work illumination system functions to inject visible light into the
system for illumination of the surgical site. For this purpose, an
ellipsoidal mirror 52 focuses incandescent light from a fiber optic light
pipe into the fused quartz waveguide tube in the articulating arm
structure to be discussed herein. An auxiliary focusing lens 53 receives
light from a fiber optic light pipe 54. The light pipe is used in
conjunction with a quartz halogen illuminator, not shown, to supply the
visible light into the system. The auxiliary focusing lens 53 matches the
light beam from the light pipe 54 into the ellipsoidal mirror 52. The
mirror 52 has an opening to allow the laser beam to pass through into the
articulating arm.
The articulating arm 60 is coupled to the work illumination system by means
of a threaded ring disconnect 55. This disconnect mounting allows
interchangeability of arms so that, for example, sterilization of
individual elements can take place.
The articulating arm in accordance with the present invention solves a
particularly crucial problem in the use of laser instruments for surgery
by allowing single mode transmission, yet reducing in size prior art
systems and eliminating beam wander as the arm is manipulated. The
articulating arm comprises a series of straight precision bore quartz
Marcatili-Schmeltzer waveguides which carry radiation in the hollow
circular bore of a dielectric tube. The articulating arm 60, shown in FIG.
2B, comprises eight segments partially identified as 62, 64, 66, 68, and
70. In such systems, the dielectric need not be transparent to the
radiation being guided. The mechanism of guiding through the waveguides
can be considered as a continual glancing angle Fresnel reflection from
the dielectric walls. While this reflection is not total, it is close to
100% for very shallow incident angles to the walls.
The modes of propagation of such waveguides have been calculated as for
example in Marcatili et al, "Hollow Metallic and Dielectric Waveguides for
Long Distance Optical Transmission and Lasers", Bell System Tech. J. 43,
1783 (1964). These waveguides are also described in detail in U.S. Pat.
No. 3,386,043. As reported, the lowest loss mode is EH.sub.11.
The approximate waveguide size is in the range of 50-200 wavelengths in
diameter, this size being large enough to provide low loss, but still
retain adequate guiding, so that straightness of the tube is not an
important factor.
Because the dielectric need not be transparent to the radiation
transported, glass or quartz tubing, readily obtainable in precision bore
form, can be used to transport the 10.6 .mu.m radiation. Single mode laser
radiation is conveniently launched into the waveguide by means of the
focusing lens 47. The focal length of the lens is chosen to closely match
the Gaussian beam to the guided beam with small loss. This technique is
described in Smith, "A Waveguide Gas Laser", Appl. Phys. Letters, 19, 132
(1971).
In such a system, small gaps in the waveguide tube are tolerated with
minimal losses so that turning mirrors basic to the operation of the
infrared articulating arm can be used in a simple arrangement. As shown in
FIG. 2B, each link has an outer sheath 61 and is coupled to the succeeding
link by means of swivel elbow members 72, 74, 76, 78, 80, and 82. The
partial cutaway cross-section shows that each of the swivel elbows
incorporates a 45.degree. mirror 84 accurately fixed and mounted under a
protective cap member 86. The dielectric waveguide, for example, those
waveguides incorporated in members 62 and 64, protrude into the swivel
elbow member 86. The dielectric waveguides are placed in close proximity
to each other without actually contacting the mirror element 84. The
mirror itself may be fabricated from silicon coated with silver and a
transparent protective layer.
At each of the corners, swivelling is accomplished on precision
ball-bearing mechanisms 88 and 90. If, for example, the total length of
the articulated arm segments is in the range of 40 cm, the arm can then
access any point in an 80 cm diameter sphere. Such an arm can have a
transmission in the range of 80% and it has been demonstrated that a 1.55
mm diameter beam in the output tube will be transmitted in substantially
single mode and focused to a near defraction limited spot.
In order to allow the transparent waveguide to act as a light pipe carrying
visible light from the fiber optic light pipe 54, the mirror segments 84
should be highly reflecting in the visible as well as the infrared
wavelengths. For this reason, evaporated silver is the coating material of
choice. The | | |
