AU7171200A

AU7171200A - Large beam scanning laser ablation

Info

Publication number: AU7171200A
Application number: AU71712/00A
Authority: AU
Inventors: Paul Phillip Van Saarloos
Original assignee: Q Vis Ltd
Current assignee: Q Vis Ltd
Priority date: 1997-06-16
Filing date: 2000-11-20
Publication date: 2001-02-08

Description

P/00/011 Regulation 3.2

AUSTRALIA

Patents Act 1990

ORIGINAL

COMPLETE SPECIFICATION STANDARD PATENT Invention Title: Large beam scanning laser ablation The following statement is a full description of this invention, including the best method of performing it known to us: IP Australia Documents received on: 0 2 0 NOV 2000

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BatGh No: Freehills Carter Smith BeadleMELC600371688.6 A LARGE BEAM SCANNING LASER ABLATION The present invention relates to the laser processing or ablation of materials, and in particular the invention is suitable for use in operations on the corneal tissue of the eye for the correction of myopia, astigmatism and hyperopia, examples of which are refractive correction operations such as photorefractive keratectomy (PRK) and laser in-situ keratomileusis (LASIK). The invention will be described with reference to these operations though it will be appreciated that other applications are possible and envisaged.

The most common laser used for operations on the corneal tissue is the excimer laser operating at a wavelength of 193 nanometres. Whatever the laser source, the laser system needs to control the laser output so that the/ appropriate shape is etched or ablated into the corneal material. Three distinct systems have evolved to control the laser output necessary to perform this task. The first method uses a large beam capable of ablating a large ooo surface area of between 5 and 10 millimetres. The beam is S...masked off to limit the area of corneal surface exposed oo* (see, for example, U.S. Patent 4,941,093). The mask size and shape is varied during the procedure to control the shape being ablated. Examples of masks include an iris diaphragm, ablated plastic forming an oval, or parallel blades forming an expanding slit. Sometimes the mask consists of shapes cut in spinning disks. The laser beam S 30 may also be rotated continuously using an image rotator about its central axis to smooth the ablated surface. The laser beam, after being shaped by the mask, is sometimes then scanned in a fixed pattern, as described in EP 0 628 298 Al and in Ophthalmic Excimer Lasers: Principles and Practice, edited by McGee, Taylor,

H.R.,

Gartry, Trokel, Martin Dunitz Limited, London (1997) when, for example, hyperopia is being corrected.

2 The other two methods involve scanning the beam across the surface of the material to be ablated. The first method involves scanning a long, narrow slit beam across an aperture of masks similar to that used in the large beam method. The configuration of the shape being ablated into the surface is also controlled in a similar fashion to that used to control the large beam method. The last method involves scanning a small beam with a diameter in the range of 2.5 mm or smaller (see U.S. Patent 5,520,679). The shape being ablated is controlled by having the scanned beam pass over the areas to be ablated more often than those areas where less material is required to be removed.

Scanning systems have the advantage that a lower energy laser source is required, with both cost and size advantages. The small beam scanning method also has the advantage that it is easier to control the laser system to ablate any arbitrary shape than it is using masks.

Scanning the laser beam also imparts some of the beam smoothing required for these operations.

The biggest disadvantage with scanning systems is their inability to maintain a uniform tissue hydration over the 25 area being treated. The ablation rate of tissue is strongly related to its state of hydration. Immediately after exposure to the laser the tissue is warm and dry, -and a second laser pulse will ablate more than expected. In the following seconds fluid will well up from deeper tissue 30 so that the surface tissue becomes very hydrated with a layer of fluid on top. In this case the next pulse will ablate much less than expected. Hence it is extremely difficult to create a desired shape, or to predict accurately the profile that a scanning laser will ablate.

Large beam systems have an advantage in that theycan expose the whole treated area at once and hence they can CD/00371624.2 3 maintain a uniform tissue hydration level over that area. It can also perform the operation quicker than scanning systems. However, it requires larger and more costly laser sources. The requirement for beam homogeneity is also more important in large beam systems.

It is an object of the present invention, therefore, to provide an improved beam control system that can more accurately and/or predictably ablate a desired shape into a material such as tissue in LASIK and PRK operations, while maintaining some or all of the advantages of both large beam systems and the scanning system.

The invention provides a method for ablating material, including: directing a pulsed laser beam through variable mask means to produce an incident beam of cross-section predetermined by the mask means; and scanning the incident beam in a predetermined pattern onto the material to thereby ablate the material; 15 wherein said predetermined cross-section is progressively increased by ••said mask means during said scanning in said predetermined pattern; and wherein said predetermined pattern includes multiple selected paths on and around said material, in each of which there are a plurality of pulses of said incident beam.

g 20 The invention also provides an apparatus for laser ablation of material including: a laser source for producing a pulsed laser beam; variable mask means; means for directing said beam through said mask means to produce an incident beam of cross-section predetermined by the mask means; and CD/00371624.2 4 a computer-controllable scanning unit for scanning said incident beam in a predetermined pattern onto said material to thereby ablate the material; wherein said mask means is varied to increase said predetermined crosssection as the incident beam is scanned; and wherein said predetermined pattern includes multiple selected paths on and around said material, in each of which there are a plurality of pulses of said incident beam; said apparatus further including computer means coupled to or incorporated in said scanning unit and to said mask means for jointly controlling both, said computer means having an installed program for effecting said predetermined scanning pattern and for varying said mask means to progressively increase said predetermined cross-section during said scanning in said predetermined pattern.

Thus, the mask means (or aperture therein) is used to control the deposition of 15 laser beam energy onto the material in any pattern.

'Preferably said mask means includes a variable mask, having a transparent or transmitting aperture of variable area for admitting or transmitting said beam.

Preferably the beam spot at the material is initially less than 2.5 mm 2 and in one embodiment may initially be less than 1 mm 2 2 20 Preferably said beam spot is increased to greater than 5 mm 2 and in one embodiment to greater than 10 mm 2 o, Preferably said laser beam is one of a plurality of laser beams.

Preferably said mask means includes an iris diaphragm.

The iris diaphragm may have a central hole with a variable diameter for producing CD/00371624.2 beam spots on said tissue from less than 0.5 mm to 1'0 mm in diameter.

In one embodiment, the central hole has a variable diameter for producing beam spots on said tissue between 0.5 mm and 6 mm in diameter.

After said iris the beam may go through optics to minify or magnify said beam size.

In one preferred embodiment, said beam is scanned over said tissue in a plurality of patterns sequentially, and in another preferred embodiment said pattern may be changed during a procedure.

In a particularly useful application, the material to be ablated is human or animal tissue, eg. corneal tissue.

Preferably said method and apparatus are used to fully or partially correct defects in eyesight.

The iris diaphragm may have a central hole with a variable diameter for producing beam spot sizes on said tissue from less than 0.5 mm to 10 mm in diameter.

15 In one embodiment, the central hole has a variable diameter for producing beam spot sizes on said tissue between 0.5 mm and 6 mm in diameter.

In all of the above aspects of the invention, the laser source or source of the laser beam is preferably an Argon-Fluoride excimer laser (193 nm), flash-lamp or laser pumped solid state laser (193 215 nm) such as quintupled Nd-YAG laser or a quadrupled Ti:Sapphire laser, Ho:YAG (2.1 micrometres), Er:YAG or Er:glass ge2.laser or tunable IR laser.

.ee.

Preferred embodiments of the invention will be described, by way of example with reference to the accompanying drawing, in which: Figure 1 is a schematic view of an apparatus according to the present CD/00371624.2 6 invention.

An apparatus for laser ablation is shown generally in Figure 1. The apparatus includes a laser source 1. This laser source produces a laser beam 2 which passes through beam smoothing components 3 before continuing through to a variable mask in the form of an iris diaphragm 4. The beam is then directed toward the scanning unit 5, before passing to the surface of the cornea 7. A computer 6 controls the operation of both the mask and the scanning device.

In use the computer 6 controls iris diaphragm 4. In the preferred method of operation, the iris 4 is used to vary the beam diameter in steps during a surgical procedure, initially being set to a small iris diameter and hence beam size (with a beam spot diameter of generally between 0.1 mm and 2.5 mm) and increasing to a larger iris setting (to produce a beam spot diameter of between 2.5 mm and 6 mm).

As the beam size is progressively increased, a number of pulses of each desired 15 size, scanned in the selected pattern or path, are applied to the cornea:

S.

1) For spherical corrections, the laser pulses are preferably evenly spaced around a circular path. Each circular path has at least pulses, but more than one circular path may be traced out at each beam size step; 2) For astigmatic corrections, the distribution around the path may be ~more concentrated in one axis than in another and/or the paths may be made elliptical; 3) For irregular astigmatism corrections, the scanning path will be SSirregular, the spacing between pules will be irregular and there may be only 1 pulse per beam size.

Where there are more than 5 pulses in a circular path, the pulses are applied in an CD/00371624.2 7 order such that the scanner transverses the path (be it circular, elliptical or irregular) in no more than about 0.5 s and will continue going around the path until all pulses are fired. Thus, for example, if there are ten pulses to be fired at 10 Hz, every second position is hit on the first pass around the path, and the intermediate positions are hit on the next pass of the laser beam around that path.

When the required treated size is larger than the maximum beam size and/or the desired shape cannot be created using an iris alone, the varying sized beam is scanned in an appropriate pattern to produce the desired shape. The beam control may be optimized such that is always scans the largest beam possible so that the treatment time is minimized and the tissue hydration is maintained as uniformly as possible.

The apparatus of the present invention therefore provides for accurate ablation, providing an alternative beam control method, while maintaining the advantages associated with two prior methods of laser ablation.

15 Modifications within the spirit and scope of the invention may readily be effected by person skilled in the art. it is to be understood, therefore, that this invention is not limited to the particular embodiments described by way of example hereinabove.

Claims

1. A method for ablating material, including: directing a pulsed laser beam through variable mask means to produce an incident beam of cross-section predetermined by the mask means; and scanning the incident beam in a predetermined pattern onto the material to thereby ablate the material; wherein said predetermined cross-section is progressively increased by said mask means during said scanning in said predetermined pattern; and wherein said predetermined pattern includes multiple selected paths on and around said material, in each of which there are a plurality of pulses of said incident beam. ee

2. A method for ablating material as claimed in claim 1, wherein said mask means includes a variable mask, having a transparent or transmitting aperture of variable area for admitting or transmitting said beam.

3. A method according to claim 1 or 2 wherein said predetermined cross- section is increased in successive steps as the incident beam is scanned. ooooo S4. A method according to claim 3 wherein there are a plurality of pulses of said incident beam at each of said steps in said predetermined cross-section.

5. A method according to any one of claims 1 to 4 wherein said pattern and said mask means are arranged so that said cross-section produces a beam spot at said material of a diameter which is increased during said scanning from between 0.1 and 2.5 mm to between 2.5 and 6 mm.

6. A method for ablating material as claimed in any one of claims 1 to 4, wherein said mask means is arranged so that said cross-section produces a beam spot at said material which is initially less than 5 mm 2 CD/00371622.3 9

7. A method for ablating material as claimed in claim 5 or 6 wherein said mask means is arranged so that said cross-section produces a beam spot at said material which is initially less than 1 mm 2

8. A method for ablating material as claimed in any one of claims 1 to 4, wherein said mask means is arranged so that said cross-section produces a beam spot at said material which is increased during said scanning to greater than 2 mm.

9. A method for ablating material as claimed in claim 8, wherein said beam spot is increased to greater than 10 mm 2

10. A method for ablating material as claimed in any one of the preceding claims, wherein said laser beam is generated by an Argon-Fluoride excimer laser, flash-lamp or laser pumped solid state laser.

11. A method for ablating material as claimed in any one of claims 1 to 9, wherein said laser beam is generated by a quintupled Nd:YAG laser, a quadrupled Ti:Sapphire laser, a Ho:YAG, Er:YAG or Er:glass laser, or a tunable IR laser.

12. A method for ablating material as claimed in any one of the preceding claims, wherein said laser beam is one of a plurality of laser beams.

13. A method for ablating material as claimed in any one of the preceding claims, wherein said mask means is computer controlled.

14. A method for ablating material as claimed in any one of the preceding claims, wherein said mask means includes an iris diaphragm. A method for ablating material as claimed in claim 14, wherein said iris diaphragm has a central hole with a variable diameter for producing beam spots on said material from less than 0.5 mm to 10 mm in diameter.

16. A method for ablating material as claimed in claim 15, wherein said iris CD/00371622.3 diaphragm has a central hole with a variable diameter for producing beam spots on said material of between 0.5 mm and 6 mm in diameter.

17. A method for ablating material as claimed in any one of the preceding claims, including passing said beam through minifying or magnifying optics to minify or magnify the size of said beam, after said beam has passed through said mask means.

18. A method for ablating material as claimed in any one of the preceding claims, including changing said pattern during a procedure.

19. A method for ablating material as claimed in any one of the preceding claims, wherein said pattern is one of a plurality of patterns. An apparatus for laser ablation of material including: a laser source for producing a pulsed laser beam; variable mask means; means for directing said beam through said mask means to produce an 15 incident beam of cross-section predetermined by the mask means; and a computer-controllable scanning unit for scanning said incident beam in a predetermined pattern onto said material to thereby ablate the material; wherein said mask means is varied to increase said predetermined cross- section as the incident beam is scanned; and wherein said predetermined pattern includes multiple selected paths on and around said material, in each of which there are a plurality of pulses of said incident beam; said apparatus further including computer means coupled to or incorporated in said scanning unit and to said mask means for jointly controlling CD/00371622.3 11 both, said computer means having an installed program for effecting said predetermined scanning pattern and for varying said mask means to progressively increase said predetermined cross-section during said scanning in said predetermined pattern. 21 An apparatus as claimed in claim 20, wherein said mask means includes a variable mask, having a transparent or transmitting aperture of variable area for admitting or transmitting said beam.

22. An apparatus as claimed in claim 21, wherein said area is variable from less than 5 mm 2

23. An apparatus as claimed in claim 22, wherein said area is variable to less than 1 mm 2

24. An apparatus as claimed in any one of claims 21 to 23, wherein said area is variable to greater than 5 mm 2 An apparatus as claimed in claim 24, wherein said area is variable to 15 greater than 10 mm 2

26. An apparatus as claimed in any one of claims 20 to 25, wherein said laser source is an Argon-Fluoride excimer laser, flash-lamp or laser pumped solid state laser.

27. An apparatus as claimed in any one of claims 20 to 25, wherein said laser source is a quintupled Nd:YAG laser, a quadrupled Ti:Sapphire laser, a Ho:YAG, Er:YAG or Er:glass laser, or a tunable IR laser.

28. An apparatus as claimed in any one of claims 20 to 27, wherein said laser source is one of a plurality of laser sources.

29. An apparatus as claimed in any one of claims 20 to 28, wherein said mask means includes an iris diaphragm. C/00371622. 12 A method according to any one of claims 1 to 19 wherein said material is human or animal tissue.

31. A method as claimed in claim 30, wherein said tissue is corneal.

32. A method as claimed in either claim 30 or 31, wherein said method is used to fully or partially correct defects in eyesight.

33. A method as claimed in claim 30, 31 or 32 including depositing on said tissue a series of evenly spaced pulses of said incident beam around said pattern, wherein said pattern is circular, for spherical correction of corneal tissue.

34. A method as claimed in claim 33, wherein said series includes at least pulses. A method as claimed in claim 30, 31 or 32 including depositing on said tissue a series of pulses of said incident beam around said pattern, wherein said pattern is elliptical and/or said pulses are more concentrated in one portion of said pattern, for astigmatic correction of corneal tissue.

36. A method as claimed in claim 30, 31 or 32 including depositing on said tissue a series of irregularly spaced pulses of said incident beam around said pattern, wherein said pattern is irregular, for irregular astigmatic correction of corneal tissue.

37. A method as claimed in claim 36, including depositing one beam pulse per 20 mask or beam cross-section size.

38. Apparatus according to any one of claims 20 to 29 and 49 to 51 adapted for laser ablation of animal or human tissue, said laser source producing a beam of far ultraviolet or infra-red light.

39. An apparatus as claimed in claim 38, wherein said tissue is corneal.

40. An apparatus as claimed in either claim 38 or 39, wherein said apparatus is CD/00371622.3 13 adapted for the full or partial correction of defects in eyesight.

41. An apparatus as claimed in any one of claims 38 to 40, including minifying or magnifying optics located after said mask, wherein said beam may be minified or magnified in size by being passed through said optics.

42. An apparatus as claimed in any one of claims 38 to 41, including means for changing said pattern during a procedure.

43. An apparatus as claimed in any one of claims 38 to 42, wherein said pattern is circular and said computer means is programmed to control said beam to be directed in a series of evenly spaced pulses around said pattern for spherical correction of corneal tissue.

44. An'apparatus as claimed in claim 43, wherein said series includes at least pulses.

45. An apparatus as claimed in any one of claims 38 to 42, wherein said computer means is programmed to control said beam to be directed in a series of 15 pulses around said pattern, and said pattern is elliptical and/or said pulses are more concentrated in one portion of said pattern, for astigmatic correction of corneal tissue.

46. An apparatus as claimed in any one of claims 38 to 42, wherein said computer means is programmed to control said beam to be directed in a series of irregularly spaced pulses around said pattern, and said pattern is irregular, for irregular astigmatic correction of corneal tissue.

47. An apparatus as claimed in claim 46, wherein said computer means is programmed to control said beam to direct one beam pulse per mask or beam size.

48. An apparatus as claimed in any one of claims 38 to 47, wherein said pattern is one of a plurality of patterns. CD/0037162.3. 14

49. An apparatus according to any one of claims 20 to 29, 38 to 48, wherein said program is arranged for increasing said predetermined cross-section in successive steps as the incident beam is scanned. An apparatus according to claim 49 wherein said program is arranged whereby there are a plurality of pulses of said incident beam at each of said steps in said predetermined cross-section.

51. An apparatus according to any one of claims 20 to 29, 38 to 40, 49 and wherein said program and said mask means are arranged so that said cross-section produces a beam spot at said material of a diameter which is increased during said scanning from between 0.1 and 2.5 mm to between 2.5 and 6 mm. Q-Vis Limited 20 November 2000 By its Registered Patent Attorneys Freehills Carter Smith Beadle