Surgery – Instruments – Light application
Patent
1995-03-28
1999-08-17
Shay, David M.
Surgery
Instruments
Light application
606 3, 606 10, 606 12, 606 17, A61N 502
Patent
active
059386568
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a process for correcting the shape of a lens, in which the surface of the lens is acted upon by the radiation of a pulsed radiation source through a shutter in specific regions exposed by the shutter and thereby removing material from the lens by the radiation effect during the impingement of each radiation pulse, wherein the radiation is concentrated in a bundle of rays, the cross section of which is smaller when striking the lens surface than that of the lens surface exposed by the shutter, and wherein the bundle of rays is moved such that the entire lens surface exposed by the shutter is irradiated by radiation pulses consecutively impinging on the lens surface.
Furthermore, the invention relates to a device for performing this process.
With the described process, it is possible to form the shape of the surface of a lens, for example a contact lens or also the cornea of the eye by so-called photo-ablation, such that an optical correction of the surface can be achieved. Usually lasers are used for this purpose as radiation sources, namely pulsed lasers which repeatedly emit radiation pulses in timed succession. These radiation pulses are directed onto the lens surface via shutters corresponding with the desired correction and remove a very small amount of material from the lens surface at each impingement.
It is known in processes of this type to have the entire area of the lens surface exposed by the shutter completely irradiated by each radiation pulse, i.e. the cross section of the bundle of rays directed onto the shutter is then larger at each radiation pulse than that of the area exposed by the shutter. In this respect, problems concerning intensity can result, since the entire radiation generated by the laser must possibly be distributed over a relatively large area.
On the other hand, it is known to concentrate the radiation energy generated by the laser in a bundle of rays having a very small cross section, wherein this bundle of rays scans the lens surface exposed by the shutter in a manner similar to a scanner. In this respect, it is very difficult to achieve a uniform irradiation of the entire area, since the positions of the radiation pulse have to adjoin each other exactly.
In a further known process, the radiation is concentrated in a beam-shaped area which is guided stepwise over the area exposed by the shutter. In this respect, only a portion of the exposed area is irradiated at each irradiation, the connection of these portions to each other, however, is easier to accomplish.
In all the described processes, the area exposed by the shutter is ultimately struck at every point by a radiation pulse, thus, a more or less uniform ablation results in the entire region exposed by the shutter, the depth of this ablation corresponding with the ablation of one radiation pulse.
When a greater ablation is desired, it is normally necessary to repeat the procedure as a whole.
The object of the invention is to perform a process of the type described at the outset such that already during a first irradiation procedure, an ablation depth can also be attained which corresponds with multiple irradiation.
This object is accomplished in accordance with the invention in a process of the type described in the beginning, in that the bundle of rays is moved between successive radiation pulses only to such an extent that the regions of the lens surface struck by the radiation pulses consecutively impinging on the lens surface partially overlap. Depending on the extent of the overlapping, radiation pulses repeatedly impinge on the lens surface to be shaped in the overlapping region so that a greater ablation depth can also be achieved. For example, two radiation pulses strike in each region with an overlap of adjacent radiation cross sections of 50%, three radiation pulses with an overlap of 67%, etc. Thereby, it is possible to achieve an ablation to the desired depth in one procedure.
In principle, such a process can be performed with every form of cross section of the bundle of rays which
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patent: 5284477 (1994-02-01), Hanna et al.
Aesculap-Meditec GmbH
Hoppin Ralph F.
Lipsitz Barry R.
Shay David M.
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