Surgery – Instruments – Light application
Patent
1996-10-07
1999-04-20
Hindenburg, Max
Surgery
Instruments
Light application
606 4, A61B 1736
Patent
active
058953841
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a device for shaping the cornea according to the generic part of claim 1.
STATE OF THE ART
There are devices for shaping the cornea commerically available using an excimer laser as the laser. Excimer lasers emit light in the UV range, and in ophthalmology, excimer lasers emitting light with a wavelength of 193 nm are often employed.
Light with such a short wavelength can only be shaped and guided with some difficulty in the beam-shaping and beam-guiding device required in cornea laser treatment: for instance, tiny particles of dust on the surface of the lens cause "burnt-in spots" on these lens surfaces.
Furthermore, speculations have been published that light with the aforementioned wavelengths may be carcinogenic and/or mutagenic.
For this reason, it was proposed some time ago to use lasers emitting light in the infrared spectral range with wavelengths of about 3 .mu.m in the respective applications instead of excimer lasers, because water in this spectral range has a strong absorption band. Most of the lasers emitting in this spectral range are YAG lasers, the laser beam of which has a cicular mode of distribution. In order that the circular mode of distribution is not imaged as a "circular" cornea ablation, it is necessary that in the devices for shaping the cornea on which the generic part of claim 1 is based, the energy density is homogenized over the cross section of the beam.
A relatively complicated beam-shaping device for excimer lasers, not having a circular mode of distribution, in which a light guide having an oblong cross section is used, is known from DE-A-40 04 423.
DESCRIPTION OF THE INVENTION
The object of the present invention is to provide a device for shaping the cornea according to the generic part of claim 1 in such a manner that a homogeneous laser beam is placed at disposal with simple means even if using a laser having a circular mode of distribution.
An element of the present invention is that the beam-shaping device for homogenizing the energy density over the cross section of the beam is provided with plane of the focusing optic and the diffraction maxima of which interfere with the minima of the mode of distribution, conjugate to the cornea.
The diffraction element is made respectively disposed in the beam path in such a manner that its diffraction maxima interfere at the site of the image-field diaphragm with the minima of the mode structure. In this way, the energy density can be homogenized with simple means over the beam cross section. Moreover, the beam-shaping device can be easily adapted to the radial distribution of the mode structure different from laser to laser by moving the diffraction element in a direction on the optical axis.
The diaphragm provided for delimiting the image field is disposed in the plane of the beam homogenization and is imaged via a (further) optic onto the cornea. In other words, the image-field diaphragm is optically conjugate to the cornea. (Optically conjugate values refer, in accordance with the prevailing definition, to values which are disposed in pairs, in that one value relates to the object respectively the object space and the other value relates to the image respectively the image space.)
Various elements can be utilized as diffraction elements. Two possibilities, in which the use of an aperture diaphragm has cost advantages compared to the use of a grid, are described in claim 2.
In a preferred embodiment of the present invention, an expansion optic is provided before the focusing optic which widens the laser beam. In this way, the diameter of the laser beam is widened (approximately) to the diameter value or a larger value, as is required for shaping the cornea in such a manner that all "beam manipulations" can be executed at the "exactly required beam cross section" or at a larger beam cross section then with greater accuracy.
This is especially advantageous in the invented improvement of the present invention described in claim 4: According to this claim, a radial-forming el
REFERENCES:
patent: 5336216 (1994-08-01), Dewey
patent: 5376086 (1994-12-01), Khoobehi et al.
patent: 5395356 (1995-03-01), King et al.
patent: 5461212 (1995-10-01), Seiler et al.
patent: 5571107 (1996-11-01), Shaibani et al.
Leiacker Richard
Steiner Rudolf
G. Rodenstock Instrumente GmbH
Hindenburg Max
Yarnell Bryan K.
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