Surgery – Instruments – Light application
Reexamination Certificate
1995-12-13
2001-09-11
Shay, David M. (Department: 3739)
Surgery
Instruments
Light application
C606S003000, C606S010000, C606S013000
Reexamination Certificate
active
06287296
ABSTRACT:
FIELD OF THE INVENTION
The invention concerns a device for the removal of tissue from the cornea of an eye using a laser beam generator for the production of a laser beam, including an optical device by means of which, during the removal of the tissue, the laser beam is directed onto the cornea to be treated, with a beam cross section and a defined removal profile for the beam energy that is transferred to the corneal tissue to be removed, and a control device for controlling the optical device.
BACKGROUND OF THE INVENTION
Such a device is known from DE 4,103,615 C2. The device serves in the removal of deficient vision that results, in particular, as a consequence of a refraction anomaly in the eye. Thereby, a laser beam is directed onto the cornea, which has a removal profile over its cross section, i.e., its beam cross section has a beam energy profile that is to be transferred to the corneal tissue. Previously known surgical treatment devices are problematic, especially for myopia correction with high vertex power, especially over six diopters, in that the cornea has to be treated using a relatively high depth of removal in order to obtain adequate correction of the refraction anomaly. A risk of scar formation in the postoperative healing process hereby arises, especially at the edge of the field removed. A scar adversely influences vision, especially in the case of an enlarged pupil aperture with bad illumination or subdued light or, at night.
SUMMARY OF THE INVENTION
The object of the invention is to generate a device of the type designated at the beginning in which a considerable reduction in the depth of removal is achieved during the correction of a refraction anomaly, especially myopia.
According to the invention, this object is accomplished in that the radial section, starting out from the central beam axis of the beam cross section, the removal profile formed by the optical device, has an approximately spherical or concave course in an inner radial region that changes into a point of inflection and an outer radial region that joins the point of inflection, with a convex or, monotonic decreasing course.
A considerable reduction in the depth of removal is achieved as a result of the removal profile that is formed in this way for the beam energy within the beam cross section that is transferred by the laser beam to the corneal tissue that is to be removed.
Starting out from the central axis of the beam, the point of inflection of the removal profile lies at approximately 40-60% or, especially, approximately 50% of the respective radial dimension of the beam cross section.
In a preferred way, the optical device in which the removal profile is set up is charged by a laser beam that has a constant intensity distribution over its beam cross section. In order to produce a constant intensity distribution, use can be made, for example, of a beam integrator in the form known from DE 4,103,615 C2.
One achieves a reduction in the depth of removal of approximately 30% relative to the approximately spherically formed removal profiles that are known. Thereby, the danger of scar formation is considerably reduced, especially in the edge region, and removal diameters between 6 and 8 mm can be implemented during corneal transfer.
The beam cross section can be circular, approximately circular and, for astigmatism correction, oval or approximately elliptical.
In order to achieve the desired removal profile, a diaphragm device can be used that simultaneously forms several beam spots on the tissue surface to be treated. These beam spots can be circular and can have differing diameters. In addition, it is possible to utilize beam spots with a regular shape, e.g., a polygonal shape (e.g. hexagonal, octagonal), or those with an irregular geometry that has been assembled, for example, from fractals. The beam spots or spot that are/is formed in this way can produce the desired structuring of the corneal tissue with the removal profile according to the invention by rotation of the diaphragm aperture or rotation of the beam spot that is formed on the tissue. Such a device is known from EPO 651,982 A1. The wavelength of the laser beam to be used lies in the short wave ultraviolet region (EP-A-0,111,080 or Trokel et al., Excimer Laser Surgery of the Cornea, American Journal of Ophthalmology 96:710-715, December 1983).
It is also possible to form a beam spot that is guided over the tissue surface to be treated. In this connection, a laser beam is, in essence, guided over the tissue surface to be treated, especially the stroma, using the means that are present in the case of the known device, whereby the laser beam forms a beam spot on the tissue surface with a fraction of the surface dimension of the tissue surface to be treated. The surface dimension of the beam spot amounts to approximately {fraction (1/30)} to {fraction (1/10)} that of the tissue surface to be treated. In addition, the beam spot formed on the tissue to be treated has a regular polygonal or an irregular geometrical shape, especially at its edge. This irregular geometrical shape can be formed from several round spots of differing diameter in an irregular arrangement that are formed simultaneously or by a spot that is, in particular, star-shaped with uneven lines limiting the edges of the aperture or a spot with irregular ramifications that are formed by fractal geometry elements according to the mathematical theory based on the work of B. Mandelbrot, Les objets fractals [Fractal objects], Flammarion Publishers, Paris, 1974-1984, and The fractal geometry of nature, W. H. Freeman and Company, San Francisco, 1977-1982. In order to obtain this geometrical shape of the beam spot that is formed on the tissue surface, the region of the aperture in the diaphragm device has to be correspondingly constructed. For this purpose, several circular apertures can be provided in the form shown in EP0,651,982 A1, or a diaphragm aperture can be provided that exhibits ramifications and branches at its edge or is constructed in an irregular star shape.
This beam spot that has been formed and rotated in this way is guided over the tissue surface to be treated, with the help of a deflection device. It is certainly known from EPO 151,869 A1 that one can form a beam spot on the tissue surface to be treated with the laser beam supplied by the laser beam source and that, with this, one can scan the tissue region to be treated. However, use is not made of a diaphragm with which the beam spot is brought into an irregular geometrical shape, especially a geometrical shape that is formed by fractal geometry elements.
During beam, i.e., especially in the form of pulses, the beam spot is rotated about its center (axis). This can take place by rotating the laser beam that exits from the diaphragm with the help of one or more prisms or mirrors. Rotation can be achieved without additional expense by rotating the diaphragm aperture. One or more, especially, two to ten beam pulses can be produced in each scanning or deflection position. Deflection or scanning of the beam spot takes place relative to a fixed line that is formed by, for example, a fixed laser (EPO 651,982 A1), whereby the eye that is to be treated is aligned with its line of vision along the fixed line. In this way, deflection can take place in planes that are oriented vertically to the fixed line according to the X and Y coordinates or by swivelling the laser beam directed onto the corneal tissue with respect to the fixed line.
In the device according to the invention, use can be made of a laser beam source with a reduced laser output level. As a result of the beam geometry that is irregular, especially at the edge of the diaphragm aperture region and formed especially by fractal geometry elements, virtually all types of vision corrections can be achieved with the help of, in particular, a regular or irregular star-shaped diaphragm aperture, especially a fractal edge configuration. Especially astigmatism corrections and, above all, irregular astigmatisms can be corrected. Relative to an untrea
Borrmann Andreas
Seiler Theodor
Crowell & Moring LLP
Herbert Schwind GmbH & Co. KG
Shay David M.
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