Assembly and Method for Performing Surgical Laser Treatments of the Eye

Abstract

An arrangement for carrying out surgical laser treatments of the eye is adapted to emit pulsed treatment radiation with a wavelength of between about 190 nm and about 380 nm and a pulse duration in the femtosecond range. Such treatment radiation allows nonaggressive corneal or intraocular laser treatment of the eye, for example in order to make corneal cuts or deliberately ablate corneal tissue.

Description

BACKGROUND

The invention relates to an arrangement and a method for carrying out surgical laser treatments of the eye.

It is known in the prior art to use so-called femtosecond lasers, i.e. pulsed lasers with pulse durations in the femtosecond range, for ophthalmological surgery, particularly in order to separate tissue structures on or in the eye. For example, femtosecond lasers are used to perform so-called flap cuts, i.e. incisions into the eye from the side in order to produce a small flap which is folded to the side, for example for a LASIK intervention. Femtosecond lasers are also employed in so-called keratoplasty.

Femtosecond lasers previously used in ophthalmological surgery have generally emitted radiation with wavelengths in the IR range or in the visible range of the electromagnetic spectrum.

U.S. Pat. No. 5,984,916 relates to corneal and intraocular laser surgery, employing pulsed laser radiation whose pulse duration lies between 10 fs and 2 ps with a wavelength of about 400 nm upwards.

U.S. Pat. No. 5,656,186 describes a method for determining a suitable pulse duration for processing a very wide variety of materials with pulsed laser radiation. According to this method, the dependency of the threshold for optical penetration of the material on the pulse duration is initially determined experimentally for a given wavelength. In a curve describing the dependency which is found, a point is then determined from which, towards shorter pulse durations, a quadratic dependency of the penetration threshold on the pulse duration no longer applies. The laser processing per se is then carried out with a pulse duration on the other side of this transition point. Pulse durations in the femtosecond and picosecond range are indicated for this.

The method described in U.S. Pat. No. 5,656,186 is intended to be applicable in an extremely wide wavelength range, which covers virtually the entire laser spectrum used in practice. In any event, a wavelength range of from 200 nm to 2 μm is mentioned in this document. As examples of the variety of materials for which the method is intended to be applicable, metals such as gold and aluminium, glass materials but also living tissue are mentioned, in particular the cornea. For laser treatment of the cornea, a wavelength of 770 nm is specifically indicated.

SUMMARY

It is an object of the invention to provide an arrangement and a method for carrying out surgical laser treatments of the eye, with which improved operation results are achievable. In particular, the arrangement and the method should allow undesired modifications in the tissue structures of the eye to be avoided better, for example damage to the lens or the retina during interventions in the cornea.

The invention is based on the discovery that by the action of pulsed treatment radiation with a wavelength of between about 190 nm and about 380 nm and a pulse duration in the femtosecond range, undesired impairments of eye regions which are not intended to be affected by the electromagnetic radiation during the operation can be avoided better.

When using radiation in the infrared range or in the visible range, however, such damage cannot (always) be ruled out.

The arrangement according to the invention preferably comprises means for focusing the treatment radiation on or in a cornea. It is thereby possible to surgically intervene only on the cornea, in particular by a photoablation and/or photodisruption, for instance in order to ablate superficial or intratissue corneal material and/or make cuts in the cornea, for example in order to produce a corneal flap in the scope of a LASIK treatment. It is thus possible to avoid significantly affecting other structures of the eye, for example the lens and/or the retina.

DETAILED DESCRIPTION

According to a preferred configuration of the invention, the wavelength of the emitted treatment radiation lies between about 190 nm and about 200 nm or between about 260 nm and about 280 nm or between about 340 nm and about 360 nm. In particular, the wavelength of the emitted treatment radiation may be about 193 nm or about 267 nm or about 347 nm. The latter wavelength may be generated for example by frequency tripling from a basic wavelength of 1040 nm. The wavelength 193 nm may for example be generated from a basic wavelength of 1064 nm. The person skilled in the art is familiar with frequency conversion concepts, for which reason details of the frequency conversion need not be discussed in detail here. Suitable converters may be constructed for example with components such as optical parametric generators/oscillators, sum-frequency generators and generators for the second, third, fourth or fifth harmonic. Femtosecond lasers which emit the two aforementioned basic wavelengths, as well as other wavelengths in the near infrared range, are readily available commercially. The wavelength 267 nm may for example be generated as a third harmonic of the emission wavelength of a Ti:Sa laser.

It has been found that when using laser pulses with the said wavelengths and pulse durations in the femtosecond range for corneal treatment, for instance in order to produce a flap, virtually all of the incident radiation is converted in the cornea, and any radiation passing through the cornea as residual transmission is absorbed by the human lens and not in the retina.

As a result of relatively high pulse repetition rates, is also possible to reduce the so-called ablation threshold beyond which—statistically speaking—photoablation takes place to a significant extent. At least for a wavelength of the emitted treatment radiation between about 340 nm and about 360 nm, a pulse repetition rate for the treatment radiation is therefore preferably at least about 10 kHz in the invention, preferably between about 100 kHz and about 500 kHz. A pulse repetition rate into the MHz range may of course also be selected, even for example in the two-digit MHz range.

At least for a wavelength of the emitted treatment radiation between about 340 nm and about 360 nm, the pulse energy for the treatment radiation is preferably between about 0.1 nJ and about 5 μJ in the invention, preferably at most about 10 nJ. For example, pulse energies of not more than 0.8 nJ per pulse may be set, in particular not more than 0.7 nJ per pulse and more particularly not more than 0.5 nJ per pulse. The minimum energy limit values depend in this case on the repetition rate and the numerical aperture, and they are respectively to be adjusted so that the desired effect takes place, i.e. for example the ablation threshold is reached.

As an example, the invention makes it possible to produce a corneal flap of the highest quality for the LASIK operation using pulsed UV radiation with only 0.5 nJ/pulse. A time of from 30 seconds to 1 minute for producing in the flap is thereby achievable.

The term femtosecond range in the scope of the invention is also intended to include pulse lengths of several hundred fs, i.e. for example pulse lengths with an FWHM length of 230 fs. In particular, this term is also intended to include pulse lengths in the single-digit picosecond range up to about 10 ps. For example, the pulse lengths with FS lasers may be stretched to 1 ps by using suitable optical means.

An exemplary embodiment of the invention will be described below with reference to the single appended figure. The Figure schematically shows a laser treatment system with a pulsed femtosecond laser 10.

The laser 10 delivers a wavelength of 347 nm by generating the third harmonic from a basic wavelength of 1040 nm. The emitted radiation pulses 12 have pulse lengths of 250 fs (FWHM) with a repetition rate of 20 MHz. The power is 27 mW. Beam shaping and guiding means are indicated overall by the block 14, and are known per se to the person skilled in the art. These means are adapted in particular to steer the radiation pulses so that the entire target region is covered. The means 14 are also equipped with a focusing function which makes it possible to focus the radiation pulses onto a desired point, which may for example lie on the surface of the target tissue or in its depth. The radiation pulses which are thus controlled in time and space by the means 14, and which are now denoted by 16, are directed in the represented exemplary case onto a cornea 18, for instance in order to produce a flap.

If so desired, the beam shaping and guiding means may also contain an objective lens arrangement. This, however, is not compulsory in the scope of the invention.

Good ablation results may for example be achieved by a wavelength of 347 nm with repetition rates in the range of 20 MHz, a maximum energy of 1 nJ per pulse and by using a UV focusing objective (100×). This corresponds approximately to a fluence of 2 J/cm².

With the aforementioned parameters, virtually complete radiation absorption is possible in the cornea together with extremely small radiation penetration into other eye regions. High-quality flaps can be produced in an acceptable time of less than 1 minute with a very low pulse energy.

Claims

1. Arrangement for carrying out surgical laser treatments of the eye, the arrangement being adapted to emit pulsed treatment radiation with a wavelength of between about 190 nm and about 380 nm and a pulse duration in the femtosecond range.

2. Arrangement according to claim 1, characterised by means for focusing the treatment radiation on or in a cornea.

3. Arrangement according to claim 1, characterised in that the wavelength of the emitted treatment radiation lies between about 190 nm and about 200 nm or between about 260 nm and about 280 nm or between about 340 nm and about 360 nm.

4. Arrangement according to claim 3, characterised in that the wavelength of the emitted treatment radiation is about 193 nm or about 267 nm or about 347 nm.

5. Arrangement according to claim 1, characterised in that at least for a wavelength of the emitted treatment radiation between about 340 nm and about 360 nm, the pulse energy of the treatment radiation is between about 0.1 nJ and about 5 μJ, preferably at most about 10 nJ.

6. Arrangement according to claim 1, characterised in that at least for a wavelength of the emitted treatment radiation between about 340 nm and about 360 nm, the pulse repetition rate of the treatment radiation is at least about 10 kHz, and preferably lies between about 100 kHz and about 500 kHz.

7. Method for carrying out a surgical laser treatment of an eye, comprising the step of emitting pulsed treatment radiation, with a wavelength of between about 190 nm and about 380 nm and a pulse duration in the femtosecond range, in the direction of the eye to be treated.

8. Method according to claim 7, furthermore comprising the step of focusing the treatment radiation on or in a cornea.

9. Method according to claim 7, wherein the wavelength of the emitted treatment radiation lies between about 190 nm and about 200 nm or between about 260 nm and about 280 nm or between about 340 nm and about 360 nm.

10. Method according to claim 9, characterised in that the wavelength of the emitted treatment radiation is about 193 nm or about 267 nm or about 347 nm.

11. Method according to claim 7, wherein at least for a wavelength of the emitted treatment radiation between about 340 nm and about 360 nm, the pulse energy of the treatment radiation is between about 0.1 nJ and about 5 μJ, preferably at most about 10 nJ.

12. Method according to claim 7, wherein at least for a wavelength of the emitted treatment radiation between about 340 nm and about 360 nm, the pulse repetition rate of the treatment radiation is at least about 10 kHz, and preferably lies between about 100 kHz and about 500 kHz

13. A system for laser treatment of the eye, the system comprising: a laser source adapted to emit a radiation;a frequency converter for converting the radiation to a treatment pulse with a wavelength of between about 190 nm to about 380 nm; andcontrol means for controlling the treatment pulse to a duration in a range from approximately 1 ps to 250 fs.

14. The system of claim 13, wherein the control means controls the treatment pulse to a repetition of between about 10 kHz to 20 MHz.

15. The system of claim 14, wherein the frequency converter converts the radiation to a treatment pulse wavelength selected from one of about between 190 nm to 200 nm, 260 nm to 280 nm, or 340 nm to 360 nm.

16. The system of claim 15, wherein the frequency converter converts the radiation to a treatment pulse wavelength selected from one of about 193 nm, 267 nm, or 347 nm.

17. The system of claim 13, wherein for the wavelength of the treatment pulse between about 340 nm to about 360 nm, a pulse energy of the treatment pulse is between about 0.1 nJ and about 5 μJ.

18. The system of claim 17, wherein the pulse energy is less than 10 nJ.

19. The system of claim 14, wherein for the wavelength of the treatment pulse between about 340 nm and about 360 nm, the control means controls the treatment pulse to the repetition of between about 10 kHz to 500 kHz.

20. The system of claim 19, wherein a pulse energy of the treatment pulse is less than 10 nJ.