Neodymium-YAG laser, for ophthalmological treatment

Details Neodymium-YAG laser, for ophthalmological treatment Neodymium-YAG laser, for ophthalmological treatment

1985-06-27

1987-03-24

Corbin, John K.

G02B 1300, G02B 1700, G02B 2700

Patent

active

046520929

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

The invention relates to a neodymium-YAG laser for ophthalmological treatment.


BACKGROUND

Neodymium-YAG lasers with laser beam guides and focusing optics are used for operations on the human eye. Since in the case of such operations, the so-called optical opening is larger than the laser beam spot, hitherto no attention has been paid to the variation in the spot size and consequently also to the associated variation in the angle of the marginal beams of the focused beam, i.e. the variation of the so-called divergence angle. Thus, known neodymium-YAG lasers are constructed in such a way that the laser beam is focused with a given fixed divergence angle.


DISCLOSURE OF THE INVENTION

However, it has been recognised that for safety reasons it would be desirable to be able to vary the angle of the marginal beams of the focused beam, i.e. to vary the divergence angle. Thus, the divergence angle should be as large as possible, so that there is a rapid decrease in the energy density of the operating beam upstream and downstream of the operating plane in the eye on which the laser is focused.
However, the angle of the marginal beams is limited by the size of the pupil. In order to be able to operate with the maximum possible divergence angle in all cases, it will be necessary to vary the angle and consequently vary the spot size of the focus. The displacement of the focal plane of the focused beam must thereby be as small as possible.
In the case of argon lasers, it is known to adjust the spot size without displacing the focal plane using zoom optics, which is very complicated and costly.
However, in the case of neodymium-YAG lasers, such zoom optics are not only undesirable for cost reasons, but also for the following reasons. When using neodymium-YAG lasers as operating lasers, whose light is not visible, a helium-neon laser is frequently additionally used as the collimating or target laser. As the beam of the helium-neon laser is to be focused in the same plane as the beam of the neodymium-YAG laser, it is necessary to bring about a very good color correction of the zoom optics over a wide range, so that its construction is necessarily very complicated.
The object of the invention is to bring about simple optical beam guidance for a neodymium-YAG laser, which permits an adjustment of the divergence angle without any detectable displacement of the focal plane.
Using a neodymium-YAG laser with a laser beam guide in which the laser beam is guided as a parallel beam over a long distance and with focusing optics which focus the laser beam onto the operating plane following the distance, this object is met by placing an afocal system with a plurality of optical components in the parallel beam path at a distance of more than about 50 cm from the focusing optics. In its normal position the afocal system substantially brings about no change to the parallel beam. An optical component in the afocal system is displaceable for varying the angle of the marginal beams of the focused beam.
In most neodymium-YAG lasers used for ophthalmological treatment, for some reason or the other such as, for reflecting into the optical path of a slit lamp, the laser beam is guided over a long distance often for more than 1 meter and is only then focused in the human eye.
In the case of a neodymium-YAG laser with such a beam guidance, the divergence angle can easily be made adjustable in that an afocal system is placed in the parallel optical path at an adequate distance in front of the focusing optics. In its normal position, this afocal system does not modify the parallel beam, i.e. the diameter thereof. It is sufficient for increasing or decreasing the divergence angle to move one of the two optical components of this additionally introduced system slightly out of the normal position, in which said system is afocal. As a result of this small movement of one of the two components, the parallel beam is no longer imaged in a parallel beam and instead the latter leads to a slightly convergent or divergent beam. As a resu

REFERENCES:
patent: 3817604 (1974-06-01), Watt
patent: 4203652 (1980-05-01), Hanada
patent: 4499897 (1985-02-01), Roussel
patent: 4592625 (1986-06-01), Uehara et al.

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