Surgery – Instruments – Light application
Patent
1997-10-21
2000-05-02
Dvorak, Linda C. M.
Surgery
Instruments
Light application
606 4, 606 3, 606 10, A61B 1736
Patent
active
060567414
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to the laser processing or ablation of tissue, in particular human or animal tissue. This invention is applicable for use in operations on the corneal tissue of the eye for the correction of myopia, myopic astigmatism, hyperopia and other visual problems. These operations are known as photorefractive keratectomy or phototherapeutic keratectomy, and the present invention will therefore be described with reference to its use in such an operation. It is however to be appreciated that other applications are also envisaged.
Currently this operation is performed using excimer lasers operating at wavelengths of 193 nm. The extremely high absorption of excimer laser beams of this wavelength in corneal tissue, and the high photon energy which can directly break molecular bonds therein allows this laser to ablate with very high precision and with virtually no damage to the remaining tissue. However, excimer lasers are bulky and expensive lasers that require significant maintenance and costs to run. These lasers also use a very corrosive gas.
There would therefore be significant benefits in replacing the excimer laser with an alternative laser source. Solid state lasers are available which can produce laser beams at reduced wavelengths of around 200 nm. However, these solid state lasers do not have enough energy to ablate tissue over a large enough area to be useful for this operation. Other lasers are available, such as the Holmium or Erbium laser, which produce a laser beam having very high absorption in corneal tissue and having enough energy to ablate the tissue over a large enough area. However, because the photon energy at the infra-red wavelength of the laser beam produced by these lasers is not high enough to directly break molecular bonds, the tissue adjacent to the ablated zone is damaged to too great an extent to be useful for this operation.
It is therefore an object of the present invention to provide an improved method and apparatus for laser ablation of tissue.
With this in mind, according to one aspect of the present invention, there is provided a method for laser ablation of corneal tissue, including directing at least one first pulsed unfocused laser beam of ultraviolet light and at least one second pulsed unfocused laser beam of infrared light to an area on the tissue to thereby ablate said tissue. The use of pulsed laser beams facilitates the ablation of the tissue while minimising any damage to the surrounding tissue.
The pulses of each said at least one first and second laser beam preferably arrives at the area of the tissue at least substantially simultaneously. This provides for the most efficient ablation of the area of the tissue.
The wavelength of the ultraviolet light may be in the range of between 180 to 225 nm, and the wavelength of the infrared light may be in the range of between 1.4 to 11.0 .mu.m and most preferably around 3.0 .mu.m. This is the wavelength closest to the absorption peak of water and hence facilitates the ablation of tissue.
A single first laser beam and/or a single second laser beam may be provided. It is however envisaged that more than one first laser beam and/or second laser beam be provided.
The method may include shifting the frequency of a laser beam of infrared light into the ultraviolet range to thereby provide said first laser beam.
The method may further include producing said first and second laser beams from a first and second laser means respectively, and preferably respectively smoothing, shaping and/or scanning said first and second laser beams.
The first and second laser beams may be mixed or combined to thereby provide a combined laser beam for said ablation. The combined laser beam may also or alternatively be smoothed, shaped and/or scanned.
It is alternatively envisaged that the method may include directing the first and second laser beams from different directions to the ablation area of the tissue.
It is also envisaged that the method may include producing a single laser beam from a laser means and splitting said sin
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Dvorak Linda C. M.
Harris-Ogugua Sonya
Lions Eye Institute
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