WO1987000748A1

WO1987000748A1 - Device for ophthalmologic surgery by photoablation

Info

Publication number: WO1987000748A1
Application number: PCT/FR1986/000268
Authority: WO
Inventors: Danièle Sylvie ARON-ROSA
Original assignee: Daniele Sylvie Aron Rosa
Priority date: 1985-07-31
Filing date: 1986-07-30
Publication date: 1987-02-12
Also published as: EP0232347A1

Abstract

Device intended for corneal surgery by photoablation comprising a laser source. According to the present invention, the laser being a solid laser (1), a multiplication of frequencies is effected by means of a crystal (27) in order to obtain an output wavelength of between 150 and 220 nanometers with a space-time distribution of the beam of which the energy is comprised between 100 and 1000 millijoules per cm2.

Description

DEVICE FOR OPHTHALMOLOGICAL SURGERY BY PHOTOABLATION

The present invention relates to an ophthalmological surgery device by photoablation, photodiεruption or ultraviolet linear photodissociation of living tissues directly accessible, by means of ultra short pulses whose duration is from 10 to 100 nanoseconds, originating from a laser light source. consistent and intended in particular, but not exclusively, for corneal and vitreous surgery.

More specifically, it relates to a device emitting, at the output, in a spatial or temporal mode, radiation whose wavelength is in the ultraviolet and in particular included in the range of 150 to 215 nanometers. Indeed, the radiation emitted must be outside the absorption band of human proteins and DNA deoxyribonucleic acid. For these reasons, the range of 230 to 260 nanometers should be avoided. Indeed, it has been observed that a KRF laser with a wavelength of 247 nm. corresponded to a frequency of DNA and could have a carcinogenic effect by breaking molecular chains. At the bottom of the UV spectrum, below 150 nm. the radiation is completely absorbed by the air and the addition of a vacuum radiation channel would prevent the permanent control necessary for precision surgery.

STATE OF THE ART

Lasers have been known for twenty five years and are now used in various areas of microsurgery.

Patent EP-A-0 007 256 describes an ophthalmological surgery device including a YAG laser (double garnet of yttrium and aluminum emitting pulses of a duration of the order of a few picoseconds with a length d wave of 1064 nanometers to achieve a closed globe endocular icosurgery. The ultra-fast emission of a small amount of emerging energy and the high concentration of light on a microsurface are at the origin of the optical breakdown and the formation of a plasma followed by the development of responsible shock waves disruption of the target tissue, regardless of its chemical nature and regardless of any coloring or pigmentation. These lasers are currently used in secondary cataract surgery, in particular after implantation of an artificial lens, in the treatment of glaucoma and to cut inside the eye all the superficial tissues and in particular the vitreous flanges responsible for some retinal detachments. The strong penetration of YAG radiation and the intensity of the wave produced prevent any direct surgery on the cornea. In addition, eight years of experience with a pulsed YAG laser, carried out by the Applicant have shown its limited effectiveness in vitreous surgery.

Argon lasers have also been used in continuous emission of light emitting radiation of 488 to 514.5 nanometers in order to carry out photocoagulations and krypton lasers of wavelength equal to 647 nm allowing photocoagulation of the choroid. through the retina itself.

However, these techniques require the presence of a medium constituted by the eye itself and cannot be used in the case of corneal surgery and, until now, no laser has been used to cut the cornea without coagulating it. This type of indication must use laser radiation strongly absorbed by the cornea and not penetrating inside the eye.

We know that the cornea consists by weight of about 80% water and 20% protein. The problem of photoablation consists in carrying out a pure photodissociation of water without altering the proteins. We have already used, to carry out a photodissociation, a laser emitting in the blue, in pre ^'presence of a metal catalyst with an energy of about 1.8 electron volt photon. But catalysis causes an action on proteins, which is absolutely to be avoided. On the other hand, the introduction of a catalyst onto or into the retina can pose problems, the oxygen resulting from the dissociation of water recomposing with another constituent of the retina. With the energies mentioned above (between 4 and 8 electronvolts / photon), only water is photodissociated and there is no danger of side effects on proteins for the energies indicated above. In addition, the fact of drawing the laser between 10 and 100 nanoseconds, that is to say well below the thermal relaxation time threshold of the water in the cornea, avoids the danger of diffusion of the thermal effects, and as a result of extensive tissue burns. The above data have been found experimentally in a closed tank under a nitrogen atmosphere and in the presence of reagents.

In addition, recent developments have been conducted on corneal surgery. Professor José BARAKER made changes to the convexity of the cornea by cutting it, recti ication, then implanting the cut part as a graft. Professor FIODOROV laid down the principles of radial keratotomy. In this operation, a series of 4 to 32 radial incisions is made on the cornea in order to modify its shape. We were thus able to correct myopia from -1 to -8 diopters. By making linear incisions perpendicular to the axis of astigmatism, it was possible to correct certain astigmatisms. To maintain a definitive effect, the radial keratotomy must be extended to the DESMET membrane without reaching it, let alone the non-renewable endothelium. Currently, the incisions are made with a diamond knife. The results of this operation remain largely uncertain since, after a few incisions, the cornea deforms (corneal depression) so that, even with a knife fitted with a guard, the - _^ depth of incision can hardly be constant.

US-A-4,461,294 (BARON) describes a device and a method intended for performing radial keratotomies by means of a tracer device including a dye (riboflavin) on the cornea. After drawing the configuration of the cut lines, the marked lines are evaporated by means of an argon laser through a slit mask, the lines being drawn by a computer according to the change in convergence to be obtained. The dye having been introduced into the BOWMAN layer and into the stroma absorbs the light energy emitted by the laser, which causes the marked tissue to be cut. This solution is not satisfactory clinically insofar as it implements a thermal process which is always difficult to control and where it is not specified whether the laser emits continuously or not, the pulse speed and the length of the laser. wave being the two capital elements. Only an ultraviolet or C02 laser (12,000 nm) fully absorbed by water for the latter were possible for the cornea.

A first object of the present invention is a device making it possible to perform a photoablation of the cornea according to a defined configuration of incisions, performed simultaneously, or almost simultaneously, using a pulsed laser, without significant necrosis of the tissues ( epithelium, membrane of B0 MANN, stroma) at an exactly determined depth, making it possible to avoid the problems due to corneal depression and giving predictable and repetitive results.

A second object of the present invention is a device delivering an output laser beam whose radiation is completely absorbed by the cornea and cannot in any case diffuse into other tissues: lens, retina, choroid or in the vitreous humor. A third object of the present invention is a device for multipurpose uses allowing various ophthalmic surgery operations to be carried out with a single device.

According to the present invention, the device for linear photoablation of living tissue comprising at least one laser source is characterized in that it comprises means for concentrating and focusing the beam emitted by the laser source, and means for spatiotemporal distribution of the beam output whose wavelength is between 150 and 220 nanometers and the energy between 100 and 1000 millijoules per cm2.

It is thus possible, with a device according to the invention, not only to perform radiation keratotomies in complete safety, but also to carry out a set of operations each of which previously required a different installation, the device having possibilities of '' varied adaptation to perform all ophthalmic surgery operations. For example, this device can constitute, from a single source: a YAG photodisruptor laser operating in triggered (Q-switched) or thermal mode operating in "free running" mode, a photocoagulator argon laser, in particular an argon pulse laser for the treatment of glaucoma or a short ultraviolet laser for corneal or vitreous surgery.

For this we can:

1. Using one or more frequency doubling stages or a RAMAN tank, obtain an output laser beam suitable for its wavelength for corneal operations. However, the processing operations which the original beam is subjected to all exhibit poor yields, which results on the one hand in high heat dissipation, and on the other hand, by the need to have originally a very high power laser, that is to say to use an additional YAG bar as a power amplifier in the case of a YAG bar with The origin.

According to a characteristic of the present invention, the original laser bar is a rectangular YAG bar of the SLAB type.

Such a laser ensures propagation of the photons resulting from the emission stimulated by multiple reflections inside the cavity. This avoids on the one hand the thermal effects and, on the other hand, produces a very little expanded beam. Thus, at comparable power, the yield obtained with an SLAB bar is approximately 10 times higher than that obtained with an ordinary YAG bar. This beam is single-phase with a cleaner phase front which gives, if the frequency is doubled, using a KDP crystal (double potassium and deuterium phosphate) or, preferably, with a phosphate crystal triple known in the art under the name of KTP, a green laser beam, very clean, the frequency of which can again be doubled to obtain with better efficiency an ultraviolet radiation suitable for carrying out photoablation. Thus, it is no longer necessary to use a second YAG bar, serving as an amplifier for the first, an assembly which made it possible to obtain an output of the order of 5 joules at the output of the second bar.

2. It is easier to use a sodium borate crystal as a converter. It allows you to easily obtain the 5th harmonic of the YAG, economically without losing either energy or repetition rate, without having to go through a RAMAN tank. In this case, a simple removable housing placed in front of the YAG makes it possible to obtain a wavelength of 200 or 210 nm. Obviously, this device only allows a YAG wavelength photodiswitch and ultraviolet C pulsed and we can no longer simulate argon copper, but the device is miniaturized, handy and economical.

If we use a ruby laser source instead of the YAG bar, we can, by a simple frequency doubling, obtain a radiation of wavelength equal to 231 nanometers with very high powers, but very low rates .

According to another characteristic of the present invention, the device uses at least one phase conjugation mirror making it possible to clean the beam without changing the wavelength thereof.

Other characteristics and advantages of the present invention will appear during the description which follows of a particular embodiment, given solely by way of nonlimiting example, with reference to the drawings which represent:

- Fig.l, a device for implementing the invention, in a first embodiment using a YAG laser; _ Fig. 2, a diagram showing the device for implementing the invention with at least one YAG laser;

- Fig.3, an assembly diagram using at least one ruby laser;

- Fig.4, a fourth assembly including a phosphate laser;

- Fig.5, examples of incisions that can be made in the cornea using one of the above assemblies;

- Fig.6, an assembly in which a conjugate mirror is arranged at the output of the original laser; _ a Fig.7, a second assembly in which a conjugate mirror is arranged at the exit of the beam division stage. Among the laser sources currently on the market are known "EXCIMER" (EXCited dIMER) argon fluorine (ARF) lasers emitting at 193 nanometers. The excimer laser beam delivers pulses of 10 to 30 nanoseconds at 6 electron volts / photon. In the assembly shown in Fig.l, the device comprises a source laser 1, excimer argon fluorite, enclosed in a casing 8 resting on the ground by a support (not shown) or mounted on an optical bench. At the output of the laser 1 is mounted an electrically controlled shutter 2, the "curtain" of which is constituted by a glass slide "SCHOTT KG3", for example, controlled by a trip pedal 14 or even by a voice-controlled computer. After crossing the shutter, the laser beam 10 is directed onto the entry of an articulated arm 7 provided with a set of reflecting mirrors 9 adapted to the wavelength of the excimer. Of course, inside the casing 8 are mounted cooling devices (not shown) allowing the laser and the various components of the system to work at an adequate temperature. According to the invention, the beam 10 is not concentrated during its transfer to the operating head. It arrives at the outlet of the arm 7 on a convergence device 13, included in the operating microscope 3 (or in a slit lamp) which focuses the beam 10 at a point 12. The device also includes inside the casing 8 a Pockels cell (not shown) intended to ensure the blocking of modes. According to a characteristic of the invention, the lenses constituting the convergence system 13 are calcium fluoride (CaF2) or "SPECTROSIL B" lenses, bodies which are transparent for the wavelength of 193 nanometers emitted by the laser. 1. The beam 10 then has the shape of a line ten to two hundred microns wide by three to four millimeters long. A beam transducer or deflector 4, disposed in the vicinity of the line 12 is constituted either by an acousto-optical modulator with Brague fringes in the event of temporal distribution of the beam, or by a set of mirrors in the event of spatial distribution of the beam . In the case of an electroacoustic modulator, deflecting the beam in two horizontal and vertical planes respectively, the command is obtained by a microprocessor 5 programmed as a function of the configuration of the corneal incisions which it is desired to obtain. Inside the casing 8 is also an alignment laser 6, for example of the Helium-neon type with a power of 1 milli att, for example allowing to operate with precision and to arrange the incisions on the cornea, since, obviously, the UV beam is not visible. The laser 6 emits through a focal lens a continuous ray 11 which is superimposed on the ray 10 of the laser 1. The excimer laser 1 delivers pulses of 10 to 30 nanoseconds. From a slit adjustable from 4mm high by 0.1 to 0.2mm wide or less (for example from 10 to 200 microns), each line of incision is scanned in 30 nanoseconds. The surgeon's eye 01 observes the patient's eye 02 through the microscope 3, preferably through a protective plate (not referenced). With the EXCIMER laser, cell 27 does not exist.

The excimer lasers make it possible to carry out photoablation by photodissociation of the material without there being, at the periphery of the vaporized zone, too marked deterioration by thermal effect. The incident energy diffuses little and is mainly used to locally cut the material. Unfortunately, the beam of these lasers is not clean, that is to say that it is of a highly random geometry, it is not pure, it is multimode, and difficult to focus. In addition, gas lasers are difficult to mass produce, and pose safety problems in the event of leaks, especially when the gas used is a compound as active as fluorine, although precautions are taken by the automatic regeneration of gas and stabilization measures to avoid frequent recharging despite repeated work.

Also, according to another characteristic of the invention, the laser source is advantageously a solid-state laser. But there are no solid lasers emitting in a length wave suitable and with a power suitable for corneal surgery.

The laser source 1 can then be a YAG source, advantageously of the SLAB type, the assembly diagram being that shown in FIG. 1 and which corresponds to that described in EP-A-0 007 256, with the exception of scanning. final spatiotemporal. Of course, the nature of the mirrors is adapted to the wavelength of the YAG radiation.

The only difference in the assembly consists in the interposition before or after the scanning of a cell 27 of sodium borate which transforms the wavelength of the beam from 1064 nm to 200-210 nm, that is to say say a practically ideal wavelength for corneal surgery.

In accordance with the invention, the desired results could also be obtained as indicated below.

Figs 2 to 4 show mounting methods for obtaining laser radiation for the previously defined wavelength range (150 - 215 nm) from a bar laser source. In these diagrams, only the main elements and the shutters, the cooling devices and the Pockels cell ensuring active Q-s itching have been deliberately omitted. Fig. 2 shows a second arrangement in which the original beam is emitted by a YAG laser whose wavelength (1064 nm) is much greater than the wavelength of the ultraviolet laser used in the first embodiment .

The device comprises, in this case, a first laser YAG 1 (double garnet of aluminum and of Yttrium doped with neodymium) followed by a second laser YAG 21, amplifier connected in series with the first. There is thus obtained, at the output of the laser 10, an energy of approximately 5 Joules. The YAG beam is pulsed at a frequency such that the duration of the pulses is between 10 and 100 nanoseconds. Of course, the power required for the output must always be between 0.1 and 1 Joule for the desired biophysical result. However, it will be necessary to increase the original frequency to fall within the absorption range of the cornea. To this end, the device comprises: an electrically controlled shutter composed of a glass slide Schott KG3, an optical system called afocal making it possible to adjust the convergence of the alignment beam and the main beam so that the two beams coincide in the operating area and a Pockels cell ensuring active Q-switching.

Behind this set is a first cell 22 of KDP or KTP (double or triple phosphate of deuterium and potassium) allowing a tripling of the frequency by selecting the 3rd harmonic so that at the output of cell 22 the length of the emerging beam is 266 nanometers. Of course, this result can be obtained, as shown in Fig.2, by having two frequency doublers in series, the first 22 of which selects the first harmonic and the second 23 selects of the third harmonic. We know that by adjusting parameters such as the orientation of the crystal, the polarization of the incident wave and the temperature, we currently obtain, with such cells, yields of up to 80% but decreasing very quickly with the rank of the harmonic. The excess of the light of the beam 10 (1064 nm) is mixed by the link 25 with the third harmonic in a RAMAN tank 24 whose output delivers a radiation of wavelength equal to 217 nm, and a maximum energy of 800 mJ / cm2.

As in the previous example, the device is mounted on an operating microscope via an articulated arm and contains a beam deflector similar to that which was described in the previous embodiment for the fluoride excimer laser d 'argon. It is thus possible to obtain a device producing ultraviolet laser radiation from one or two YAG lasers, the aim of this device being to avoid heavy maintenance, to reduce the cost of assembly and to avoid the insecurities due fluorine leakage and the instabilities inherent in the excimer laser. It is thus possible to obtain in the short ultraviolet a laser beam of better quality than that of the excimer.

The device shown in Fig.3 uses a single ruby laser 1 pulsed in nanoseconds whose wavelength is 694 nanometers. We know that in lasers of this type the active medium consists of an alumina crystal (A1203) doped with 0.05% chromium ions. Such a laser makes it possible to obtain a gain equal to two to four times the gain of a YAG laser, which avoids the use of an amplifier laser. But this wavelength is too large to be used as it is in corneal surgery. As before, we carry out a first frequency doubling at 22, then a second doubling at 23. Preferably, the KDP crystals are replaced by crystals of ADP (double phosphate of ammonium and deuterium) or of KTP . A first harmonic of wavelength equal to 347 nm is thus obtained, which cannot be used because it is too penetrating and a second harmonic whose wavelength is 175.5 nm. whose wavelength falls within the useful radiation range for corneal surgery.

If an amplifier is necessary, an assembly similar to the previous one is carried out with two ruby lasers 1,

21, one of which serves as a power amplifier for the emitting laser.

In Fig. 3 the ruby laser 1 delivers a power of around 20 Joules at the outlet and is followed by two doublers

22, 23 in ADP. As before, the output beam of the doubler 22 is directed onto a slot followed by an electroacoustic or even purely optical beam deflector. Indeed, the power at the output of the second doubler selecting the third harmonic can vary from approximately 5 to 10 Joules. By a set of four or eight mirrors, it is possible to transfer the image of the slit to the cornea, according to an appropriate configuration. All cut designs on the cornea are thus made possible. In addition, the cost price of the device is very low.

A fourth device uses a phosphate laser source emitting radiation whose wavelength is 1054 nm. In the same way as before, the original beam is processed to separate the third harmonic therefrom, on slides 22, 23 in ADP, KDP or KTP, the wavelengths being as follows: 1st harmonic 527 nm; 2nd harmonic 263.5 nm and third harmonic 131.7 nm. The wavelength of the third harmonic is too small for it to be used directly (absorption by air). Also, at the output of the third doubler, there is a RAMAN tank 24 on which the third harmonic and a deviated part 25 of the original beam are simultaneously applied, so as to cause a frequency beat. The first antistoke frequency radiated along a cone focused on the main beam is established at 193 nm. or the wavelength of the argon fluoride excimer laser.

The blades of ADP or KDP or of sodium borate crystal, are mounted articulated on a support so as to be removable and out of the beam path. Thus, from one of the devices described above, it is possible to carry out a multiplicity of ophthalmological operations using laser beams of different wavelengths. With the assembly of Fig. 2, one can either open a posterior capsule by inhibiting the action of the blades 22 and 23 of KDP or 27 of sodium borate, or make corneal incisions.

Fig. 5a shows a first example of a radial incision of the cornea C obtained using the method according to the invention. The cut lines T are arranged radially so as to allow a correction of the convexity of the cornea. Sure Fig.δb shows a second mode of photoablation incision, the T incision lines being arranged in an octagon, it was found that this arrangement practically eliminated postoperative astig atisms in keratoplasties. These configurations, as well as all the other desirable configurations are obtained by deflecting the beam 10 which is distributed into a plurality of secondary beams either by means of an acousto-optical transducer, or by means of a set of mirrors.

In Figure 6, there is a solid laser source 1 which emits a beam oriented towards a first doubler stage 22 of KTP. The beam used at the output of stage 22 has a frequency doubled compared to the frequency emitted by the laser 1 and consequently emits substantially in the green. Part of the energy of this output beam, of the order of 1 / 100th for example, is taken by the optical path 25 and then applied to the stage 24, at the output thereof. This sample is intended to constitute the aiming beam. The cell 22 is followed by a second cell 23 advantageously constituted by a KTP crystal. The beam, after passing through the doubling cell 23, is then routed on the stage 24 allowing a distribution, either spatial or temporal, of the beam.

In FIG. 6, the mirror 26 is arranged directly at the outlet of the laser cavity 1, and it is the beam thus purified which is directed on the doubling cells 22 and 23.

However, the conjugate mirror 26 can be placed anywhere in the path of the beam and, for example, as in FIG. 7, at the exit from stage 23 or on the distribution stage 24 of the beam, before the division of this one or at the entrance to floor 24.

The diagrams of FIGS. 6 and 7 represent an assembly with a solid laser (for example with a ruby) emitting a radiation of wavelength equal to 694 nanometers, including the quadrupling of the frequency for a KTP cell (22) gives a second harmonic of wavelength equal to 173.5 nanometers. In the case of a YAG SLAB laser emitting a radiation of 1064 nm, a 3rd harmonic is mixed with part of the beam taken at the output of laser 1 in a RAMAN tank.

Of course, in corneal surgery the device is mounted on an ultrasound pachymeter for measuring the thickness of the cornea. A computer makes it possible to know the depth of the incision and a stop device immediately stops the operation of the source laser in the event of eye movement greater than four microns. The incision depth is currently around 1 micron per stroke, the laser being drawn at a rate of 2 to 100 Hertz. The depth of the tissue to be cut is, according to the operations, at most equal to approximately 600 microns.

When the operation is long, it is possible to immobilize the eye by means of a UV opaque plastic contact lens, having slots distributed according to the configuration desired for the operation.

Claims

1. An ophthalmological surgery device, in particular for corneal keratotomy, comprising a laser source emitting an original beam and means for focusing and blocking modes, characterized in that it further comprises means (4, 5) for division of the output beam and spatiotemporal distribution of the divided secondary beams, the wavelength of the output beam being. between 150 and 220 nanometers, the energy of the beam being between 100 and 1000 millijoules per cm2.

2. Device according to claim.1, characterized in that the source laser (l) is constituted by an argon fluoride excimer laser emitting radiation of 193 nanometers, pulsed at a rate of 5 to 30 nanoseconds, a system of lenses of calcium fluoride (12) or "SPECTROSIL B" concentrating the beam in a line of 10 to 200 microns in width, on a height of 3 to 4mm, the line being applied on an acousto-optic modulator (4) controlled by a microprocessor (5), deflecting the output beam according to the desired configuration.

3. Device according to claim 1, characterized in that the source laser (1) is a solid bar laser emitting radiation of wavelength from 1064 to 500 nanometers, the frequency of the emitted wavelength being divided by a factor determined using at least one KDP, KTP or ADP crystal cell (22,23) or a sodium borate crystal (27).

Device according to claim 3, characterized in that a beat is made between the selected harmonic and part of the original beam in a RAMAN tank (24).

5. Device according to claim 3, characterized in that the source laser (1) is a YAG laser doped with neodymium, of the SLAB type, emitting radiation of wavelength equal to 1064 nm, the output beam being applied to a sodium borate converter (27) making it possible to obtain the fifth harmonic.

6. Device according to Claim 3, characterized in that the source laser (1) is a neodymium-doped YAG laser emitting radiation of wavelength equal to 1064 nanometers, connected in series with a second YAG laser (21) amplifier, the laser output beam (21) being applied to a first doubling stage consisting of a doubling crystal (22) of KDP, KTP or ADP, then to a second frequency doubling stage (23) delivering radiation of length d wave equal to 266 nanometers, said radiation being mixed with a part (25) derived from the original beam in a RAMAN tank (24), so that the output beam has a wavelength of 212 nanometers and a energy substantially equal to 800 milliJoules / cm2.

7. Device according to claim 3, characterized in that the source laser (1) is a ruby laser emitting a radiation of length equal to 694 nanometers, the second harmonic with a wavelength of 175.5 nanometers being selected using at least one cell of double ammonium and deuterium phosphate (ADP), KDP or KTP.

8. Device according to claim 4, characterized in that the source laser (1) consists of a phosphate laser emitting a radiation whose wavelength is equal to 1054 nanometers, from which the third harmonic is taken which is mixed with a part (25) of the original beam in a RAMAN tank (24) to obtain a radiation whose wavelength is equal to 193 nanometers.

9. Device according to claim 1, characterized in that the space-device beam splitting is constituted by a set of at ^'least four mirrors distributed symmetrically around the axis of the main beam (10)

10. Device according to claim 1, characterized in that the beam splitting means consist of a set of eight octagonal slots.

11.Device according to claim 10, characterized ^'in that at least one conjugate mirror (26) is disposed in the path of the original beam.

12.Device according to one of claims 10 or 11, characterized in that means arranged at the outlet of the cell (22) take from the optical path (25) part of the beam directed directly onto the outlet stage ( 24), in order to constitute a targeting beam.