WO1987000037A1

WO1987000037A1 - Laser surgery device, particularly for the keratotomy of the cornea (ii)

Info

Publication number: WO1987000037A1
Application number: PCT/DE1986/000267
Authority: WO
Inventors: Reinhardt Thyzel; Eckhard SCHRÖDER
Original assignee: Thyzel Reinhardt Meditec
Priority date: 1985-06-29
Filing date: 1986-06-30
Publication date: 1987-01-15
Also published as: EP0229120A1; JPS62503151A; DE3523340A1

Abstract

A laser surgery device, used particularly for the keratotomy of the cornea, comprises for example a UV laser of which the beam may be applied to the tissue to be operated. An adjustable diaphragm (4) is arranged on the laser beam path in order to limit the illuminated tissue area. To increase the field depth, which is an indispensable condition to succeed in performing a radial keratotomy of the cornea, an adjustable diaphragm is arranged between two converging optical elements (3, 5) which form a telecentred arrangement. In a preferred embodiment, the laser beam is coaxially introduced in the beam path of a slot lamp of which the slot is used as a diaphragm.

Description

Device for laser surgery and in particular for keratotomy of the cornea (II)

Description

Technical field

The invention relates to a device for laser surgery and, in particular, for keratotomy of the cornea with a laser, in particular a UV laser, according to the preamble of claim 1.

State of the art

For example, from the article "Excimer-Laser surgery of the Cornea" by Stephen L. Trokel (American Journal of Ophthalmology, 1983, Volume 96, pages 710-715) it is known that in particular argon-fluoride excimer lasers with a wavelength of 193 nm are suitable for performing operations on the cornea. The aim of such operations is, for example, to correct abnormal corneal curvatures by applying a certain "cutting pattern".

Lasers of other wavelengths, for example RF lasers, which are used for; Keratotomy are known from the literature.

In the known devices for keratotomy of the corea, as described, for example, in the above-mentioned article and which are required in the formulation of the preamble of claim 1, a mask is used whose UV-light-permeable areas have the shape of the desired one Has "pattern". This mask is placed close to the eye to be operated and with -2-

UV laser light irradiated.

As a result of this structure, the known devices have a number of disadvantages according to the preamble of claim 1:

Since the diaphragm is arranged directly in front of the tissue to be operated on, it is not possible to visually check the success of the operation during the operation. It should be borne in mind that a large number of laser pulses are generally required to make a cut. For this reason, the integration of the known devices into examination devices, such as slit lamp devices etc., has not been considered.

The apparently obvious solution of arranging the diaphragm at a distance from the tissue to be operated on and optically imaging it on the tissue to be operated on has not been considered for the following reason: the surface of the eye as the image plane is not flat, but extremely curved; typically it shows a 45 ° inclination. This means that the contour sharpness of the diaphragm image is not retained in the known optical imaging measures.

Presentation of the invention

The invention has the object of providing a device according to the preamble of claim 1 such weiter¬ zubilden that the _^ optical image of a distant from the disposed to be operated tissue aperture such a large depth of field is that the iris image even at extremely curved tissue surfaces, such as it represents, for example, the cornea of eyes, has a high definition. According to the invention, this object is achieved by the features specified in the characterizing part of patent claim 1.

According to the invention, the device has two collecting optical elements which form a telecentric arrangement, i.e. the distance between the two optical elements is equal to the sum of their focal lengths. Since the laser beam, for example the UV laser beam, for example an excimer laser, illuminates the first collecting optical element as a parallel laser light bundle, the laser light is interposed and leaves the second collecting optical element again as a parallel bundle. Through this

Arrangement in connection with the important property of the laser light from lasers, namely the coherence, in contrast to the illumination of the arrangement provided according to the invention with incoherent light results in the extreme depth of field of the aperture image generated with laser light.

The depth of field of the aperture image is several millimeters, so that the aperture image remains sharp when viewed on the cornea of human eyes.

The device according to the invention can thus be easily integrated into examination devices, in particular eye examination devices, such as ophthalmoscopes or slit lamp devices.

The device according to the invention can, for example, be integrated into the microscope carrier arm of a laser slit lamp. In such a laser slit lamp, the beam of the laser is first introduced into the common axis of rotation of the slit lamp and of the microscope, then reflected out of it at a 90 ° angle, deflected by 90 ° into the vertical part of the microscope carrier arm and then projected onto the human eye.

A particularly simple design results, however, when the laser beam, e.g. an Exeimer laser according to claim 2 is introduced coaxially into the beam path of a slit lamp, the slit of which serves as an aperture. This not only results in a substantial reduction in the structural outlay, since the usual adjustment mechanisms of the slit of the slit lamp act in terms of length, width and orientation simultaneously on the visible and the UV light; moreover, the visible slit image is the "target beam" for the invisible UV light, so that the orientation of the invisible UV light can be easily checked. However, it is expressly pointed out that the visible light (if incoherent visible light is used) does not show the high contour sharpness of coherent light.

The use of UV achromats in the beam path of the slit lamp according to claim 3 ensures that when UV lasers are used, the UV image and the visible image are absolutely congruent, with the exception of the lower contour sharpness of the visible image.

Of course, it is possible to mechanically rotate the slit of the slit lamp or the diaphragm in order to influence the alignment of the diaphragm image on the tissue to be operated on, for example in order to make radial keratotomy cuts.

However, this presupposes that the gap is illuminated "areally", so that the gap or the diaphragm only allows a small part of the tissue to be operated on from the available UV light; this significantly increases the operating times. A solution to this problem is given in claim 4: The gap or the diaphragm remain fixed with regard to their orientation and are only adjusted in terms of length and height. To rotate the diaphragm or gap image on the tissue to be operated, an optical rotary element is arranged between the diaphragm and the tissue to be operated, which rotates the beam around the optical axis. Since the gap is no longer adjusted in terms of its orientation, it is sufficient to essentially illuminate the gap. It is of great advantage here that the beam profile of an excimer laser is elongated without measures that change the beam cross section and thus supports widening in one direction.

Claim 5 specifies a preferred arrangement of the rotary element by means of which the overall length of the entire device is reduced.

In claim 6, a particularly advantageous rotary element is characterized, which has the advantage over the known rotary elements that the beam penetrates all entry and exit surfaces vertically and no dividing line in reflection surfaces "disturbs" the gap image.

Brief description of the drawing

The invention is described below by way of example with reference to the drawing, in which:

1 shows a longitudinal section through part of a device according to the invention, and

Fig. 2 shows a preferred embodiment of an optical rotary element. Way of carrying out the invention

1 shows a longitudinal section through a device according to the invention, specifically through a slit lamp known per se. In a manner known per se, the slit lamp has a lamp together with optical elements, such as condensers, etc. These elements are generally referred to with the reference symbol 1 and are not described in more detail below. The light of a UV laser (not shown in FIG. 1) is introduced into the beam path s of the slit lamp by means of a beam splitter 2 which is transparent to visible light and reflective to UV light. In the direction of the light path in front of and behind the slit 4 of the slit lamp, which is designed in a manner known per se, there are collecting optical elements 3 and 5 which form a telecentric arrangement, ie their distance is equal to the sum of their focal lengths. The optical element 3 can be arranged either outside the "normal" beam path of the slit lamp (position 3) or in the beam path of the slit lamp (position 3 ¹ ). Furthermore, a deflection mirror 6 is provided in a manner known per se, which deflects the beam path of the slit lamp onto the tissue 7 to be operated, for example the cornea of a human eye.

In addition, the slit lamp according to the ^* . Gap 4 an optical rotating element 8 may be arranged, which is preferably arranged in front of the collecting optical element 5, since this can shorten the overall length.

A particularly preferred embodiment for the optical rotary element 8 is shown in FIG. 2. Since the inclinations of the individual reflection surfaces R1, R2, R3 and the beam passage surfaces D1, D2 and the beam guidance are given in FIG. writing of the optical rotary element can be dispensed with. The optical rotary element according to FIG. 2 has the advantage that the entrance surface E, the exit surface A and the two through surfaces D1 and D2 are each penetrated vertically by the beam and no dividing lines between parts of the prism in reflection surfaces interfere with the imaging of the gap. The two separating surfaces D1 and D2 of the prism shown in FIG. 2 for one-sided image reversal with three total reflections are spaced apart or optically blasted with an air gap, but are not canted.

The device according to the invention shown in FIGS. 1 and 2 has a number of advantages:

The depth of field of the slit image generated on the tissue to be operated on, for example the cornea, is very large: for example, it is about 200 mm at a focal length of the optical element 3 and about 50-100 mm, preferably 60, at a focal length of the optical element 5 mm, a few millimeters, so that the UV aperture image on the cornea shows the full contour definition. The visible aperture image, which is generated with incoherent light, does not show the full contour definition, but can be used as a target beam for the UV aperture image, in particular if the optical elements arranged in the common beam path of visible light and UV light UV- Achromats from CaF_ and Si0 ₂ , for example.

Due to the easily possible optical rotation of the diaphragm image, not only the most varied sectional figures can be generated using the usual adjustment mechanisms of the gap in terms of length and width, but also the power of the UV excimer laser can be used almost completely for the operation.

The invention has been described by way of example above. Various modifications are possible within the scope of the general idea of the invention to generate an image with a high depth of field by using a telecentric arrangement:

It is not necessary to integrate the telecenter arrangement according to the invention into a slit lamp. Of course, an additional gap or an additional adjustable diaphragm can also be used for UV imaging. It is also not necessary to make the diaphragm adjustable; instead, interchangeable diaphragms, for example complete cutting patterns, which consist of several lines, can also be used.

The UV laser light can be guided in front of the slit lamp in a manner known per se: the UV laser beam is first guided in the axis of rotation of the slit lamp, reflected from it at a 90 ° angle and then reflected into the slit lamp. Furthermore, it is also possible to use a new arrangement, as described in a parallel patent application, in which the slit lamp is only linearly displaceable and the chin rest is additionally adjustable for the patient.

In any case, it is particularly advantageous if tempered prisms are used as mirror elements for the UV laser light, since in these prisms compared to simple mirror layers, the tempering is easier and the degree of reflection is higher. Of course, the telecenter arrangement presented is also advantageous for lasers of other wavelengths if the image is to have a large depth of field.

Claims

Patent claims

1. Device for laser surgery and in particular for keratotomy of the cornea, with a laser, in particular a UV laser, the beam of which can be imaged on the tissue (7) to be operated on and a diaphragm (4) is arranged in the beam path (s), which delimits the illuminated area of the tissue, characterized in that the diaphragm (4) is arranged between two collecting optical elements (3, 5) which form a telecentric arrangement.

2. Device according to claim 1, characterized in that the beam of the laser is introduced coaxially into the beam path (s, s') of a slit lamp, the gap (4) serves as an aperture.

3. Apparatus according to claim 2, characterized in that when using a UV laser, the optical elements (5) of the telecentric arrangement, which are in the beam path of an observation device, e.g. a slit lamp are arranged, are UV achromats.

4. Device according to one of claims 1 to 3, characterized in that for rotating the diaphragm image between the diaphragm (4) and the tissue to be operated (7) an optical rotating element is arranged, which the beam about the optical axis (s *) rotates.

5. The device according to claim 4, characterized in that the rotary element (8) between the diaphragm (4) and the second optical element (5) is arranged.

6. The device according to claim 4 or 5, characterized in that the rotating element (8) is a two-part prism, the entrance (E) and exit surface (A) are perpendicular to the optical axis, and the three surfaces that totally reflect the beam and enclose its surface normal with the optical axis at an angle of 67.5 °, 90 ° and 112.5 °, and has two passages (D1, D2) between the two parts through which the beam passes perpendicularly ¬ occurs.