Optics: eye examining – vision testing and correcting – Spectacles and eyeglasses – Ophthalmic lenses or blanks
Patent
1987-07-13
1989-12-12
Arnold, Bruce Y.
Optics: eye examining, vision testing and correcting
Spectacles and eyeglasses
Ophthalmic lenses or blanks
350 64, 350 69, 351209, 351221, 1283031, G02B 2610, A61B 310
Patent
active
048870196
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
1. Technical Background
The invention relates to a device for the generation of a laser beam spot with adjustable size.
In working processes or in therapeutic processes with lasers, for example in cutting processes or in operations in the human eye, there exists the general problem of adjusting the laser beam, which will have a certain cross-section depending on the type of laser used, to the surface to be worked or to be treated.
2. State of the Art
To do this, particularly in the medical technique sector, beam-expanding optical elements are used in conjunction with elements, for example, vario-lenses, which alter the magnification. In this way, it is, for example, possible to vary the beam spot area of the operation laser on the fundus between certain diameters. However, this raises the problem that at the same time the aperture cone of the beam is also varied. If this aperture cone becomes too small, then the energy density is already so great before the actual operation site that it may cause injury. In addition, it is not possible with these known devices to set more or less any desired beam spot areas such as, for example, are required for incisions in the cornea which can, for example, be performed by EXIMER lasers.
REPRESENTATION OF THE INVENTION
The object of the invention is to describe a device for the generation of a laser beam spot with which, for example, injuries to the cornea or the iris due to high radiation intensity can be safely avoided even with spot sizes of greatly differing size and with which, in addition, any desired spot forms can be generated.
In accordance with the invention, burns etc. on areas in front of the area to be treated are avoided by working with a laser beam with an aperture cone of constant size while the area to be irradiated on the object is not irradiated with a stationary laser beam of relatively high energy but is swept over by the laser beam in accordance with a predetermined pattern. According to the setting of this sweep-over movement spot sizes of different sizes can thus be realized. The size of these beam spots can be varied infinitely in accordance with the selected scanning pattern which ensures a zoom-like adjustability. In this way an adjustable zoom optical system can be dispensed with and it is even perhaps possible to have a smaller adapter construction. But injuries are still effectively prevented as the aperture angle of the irradiation cone always remains constant and thus the energy density in front of the coagulation area does not vary.
For coagulations on the fundus, a laser beam spot size of 50 .mu.m, with which a larger laser beam spot is scanned, has proved to be particularly useful. Depending on the type of optical system used, on the laser source and also on the application sector, other spot sizes are, of course, also possible and sensible.
Particularly in eye operations, a circular beam spot is preferred. Here the relationship of the irradiated area to the area to be treated is particularly favourable; this spot configuration is, in addition, particularly advantageous for heat dissipation. However, depending on each application case, other spot forms, for example square forms, can also be selected.
The scanning of the spot can, for example, be in a linear form. In accordance with the invention it is, however, also preferred to process a circular beam spot with a rotating laser beam, i.e. the laser beam rotates on a ring-shaped path. By increasing the path diameter, the desired spot size is obtained. The adjustment of the spot size can be done automatically or manually in full accordance with the requirements. The rotation movement of the laser beam is advantageously done automatically with a normal rotation time being around 8 msec. However, this value should not be understood as a limitation.
To obtain a certain distribution of the power over the beam spot area, for example a Gaussian distribution or a homogeneous or uniform illumination of the beam spot, a number of different measures can be taken. In particular, it
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Bisle Werner
Reis Werner
Arnold Bruce Y.
Ben Loha
G. Rodenstock Instruments GmbH
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