GB2074343A

GB2074343A - Laser Ophthalmic Surgery Apparatus

Info

Publication number: GB2074343A
Application number: GB8112288A
Authority: GB
Original assignee: Institute of Ophthalmology
Current assignee: Institute of Ophthalmology
Priority date: 1980-04-18
Filing date: 1981-04-21
Publication date: 1981-10-28
Also published as: GB2074343B

Abstract

A laser ophthalmic surgery apparatus comprising a high-powered pulsed beam laser 1 and a low-power laser 9 providing a colinear continuous aiming beam. The high-power beam is subjected to a beam expansion system 6, 7 and to facilitate alignment of the laser mirror system, there is provided a pellicle 8 which directs part of the low-power beam back to the pulsed laser so that superimposed beams are passed through the beam expansion system. <IMAGE>

Description

SPECIFICATION Laser Ophthalmic Surgery Apparatus The invention relates to laser ophthalmic surgery apparatus which has particular value in the treatment of glaucoma.

The high transparency of the cornea of the eye enables surgery to be carried out through the intact cornea using a laser beam of visible wavelength. To be effective the beam power must be some three orders of magnitude greater than that of C. W. laser ophthalmic photo-coagulators and be in the form of a pulse of only a few microseconds duration. In order to ensure accurate location of the pulsed beam it is essential to provide a visible co-linear beam from a continuous low power laser. However, often beam expansion is required for the high-power beam.

This, as a result of reduction in laser pulse power density, avoids damage both to the system's optical elements and to the patient's cornea. A highly convergent cone of radiation is produced and this minimises the depth of focus and localises the region of laser damage.

The use of a beam expansion system introduces difficulty in aligning the pulsed laser with the expansion system. The present invention seeks to provide apparatus which facilitates alignment of the optical element of both laser and beam expander.

According to the invention there is provided laser ophthalmic surgery apparatus comprising a high-power pulsed laser having mirrors, a beam expansion system having lenses and situated to expand the beam from the high-power pulsed laser, a low-power laser for producing an aiming beam, means for superimposing the aiming beam on the high-power beam, a device for directing part of the low power beam back to the pulsed laser to be reflected thereby, the reflected beam being thus capable of use for the alignment of the laser elements and the expander lenses, and means for delivering the superimposed beams to a movable terminal where the beam paths and points of focus in the patient's eye can be observed. Preferably the movable terminal has the form and facilitites of an ophthalmic slit-lamp.

Preferably the said device is a beam splitter in the form of a pellicle. The alignment of the highpower laser mirrors and the expander may be observed by specialised reflection interferometry.

In accordance with a preferred feature of the invention the image of the aiming beam on the patient's eye is observed by way of a binocular microscope through a selective mirror. Preferably the selective mirror is solenoid-operated to twist out of the field of view of the binocular microscope so as to allow normal colour observation and photograph of the eye.

The invention will further be described with reference to the accompanying drawing, the sole figure of which is a schematic plan and elevation view of apparatus in accordance with the invention.

Referring to the drawing the apparatus comprises a high-powered pulsed laser having a pumping cavity 1 and mirrors 2 and 3 on a lower deck. The output from the laser is guided to an upper deck by mirrors 4 and 5 where it is expanded in a beam expander comprising lenses 6 and 7. Figure 1 is a schematic view of the apparatus and does not show the structural features. In fact, elements 5 to 8 and 11 would be mounted on the top of an upper deck, and elements 2, 3 and 4 would be suspended from beneath the upper deck. The optical pumping cavity 1 (with its associated systems) would be capable of being jacked up and down from the lower deck.

From lens 7 the light passes, via mirrors 1 1, 12, 14, 16 and 18, to an objective lens 19 and thence to the eye of the patient. Mirror 11 is temporarily removable to permit light beam alignments to be undertaken on a long straight path. Three low friction telescopic joints 13, 15 and 17 enable the surgeon to translate the terminal assembly in the horizontal plane, in a vertical direction and to rotate it about a vertical axis. These movements would be equivalent to those of an ophthalmic slit-lamp, and could be effected in the same way. The overhead delivery between mirrors 12, 14 and 16 is well above head height, permitting complete accessibility around the surgeon and patient. Mirror 18 is dichroic, with greater than 99% reflection for the wavelength of the high-powered pulsed laser radiation.

However a small fraction of the radiation (0.1%) passes through the mirror to be registered on a photodiode 20 which can record the power, duration and energy of the pulse.

An alignment and aiming system is provided which comprises a continuous low power heliumneon laser 9 which projects a beam onto a pellicle 8, generating an 8% reflection proceeding to the left. The 92% of the helium-neon laser radiation transmitted through the pellicle is reflected back to the helium-neon laser by the mirror 10 and, in so doing, generates a 7% reflection from the pellicle proceeding to the right.

The first step in the alignment procedure is to adjust the mirror 10 so that the reflected beam, transmitted again through the pellicle, is exactly superimposed on the exit aperture of the heliumneon laser 9. Since the pellicle is only seven microns thick, this adjustment ensures that the reflections proceeding to the left and right are colinear. The pellicle is then adjusted in angle until the reflected beam is horizontal and at right angles to the output beam of the helium-neon laser. With the beam expander lenses 6 and 7 removed and the pulsed laser mirrors 2 and 3 removed, the helium-neon beam reflected to the left is manipulated by adjustment of mirrors 4 and 5 so that it travels in reversed direction beneath and parallel to its path between elements 5 and 8.

Mirror 11 is then removed and a screen placed as far from the apparatus as possible to receive a reference helium-neon beam reflected to the right by pellicle 8. The pulsed laser mirrors 2 and 3 are placed in position and adjusted utnil their reflections on the screen are superimposed with the helium-neon reference beam.

Element 1 is then jacked vertically upwards and positioned so that the helium-neon beam maintains its same path through the system, whilst now passing along the axis of the pulsed lasing medium which possesses air interfaces at 90% relative to its axis. Each beam expander lens, 6 and 7, is then placed in position and adjusted for tilt and transverse positions until the Newton's rings they image on the screen are maximised in intensity and are concentric with the image of the helium-neon beam reflected to the right. The expanded pulsed laser beam is now colinear with the helium-neon laser beam.

To summarize the alignment technique, it can be regarded as setting up an optical refrence beam, or "keel" from the He-Ne laser on which the pulsed laser resonator components as well as the elements in the optical train can be centralised. Thus, the He-Ne beam is propogated colinearly in two directions; into the pulsed laser and to a point where the reflections can be superimposed. The alignment procedure involves the observaton of (a) discs of light and (b) Newton's rings.

With a lens in its approximately correct position one observes two discs of light. By transverse adjustment in the vertical and horizontal plane one can superimpose these on the reference point. One then adjusts in two orthogonal planes the tile of the lens to superimpose the Newton's rings on the reference point.

As either process can disturb the result achieved by the other process, one has to repeatedly and alternately adjust the transverse translation and orthogonal tilt procedures until both discs of light and Newton's rings are all superimposed on the reference point.

Mirror 11 is placed in position and adjusted along with mirrors 12, 14 and 16 so that the helium-neon beam does not change its position relative to the dichroic mirror 18 when the telescopic joints 13, 15 and 17 are activated by the surgeon through general movement of the terminal. The image of the aiming beam produced at the focus of the objective lens 19 can be seen by the surgeon through the binocular eyepiece 21, which is focussed for infinity, via the mirror 18 that has 50% reflectivity and transmission for the wavelength of the helium-neon laser. In view of the alignment system the point of focus of the high-powered pulse laser beam is the same as that of the aiming beam.

When appropriate positioning has been accomplished by means of the aiming beam the surgeon initiates the operation by a foot operated switch. This momentarily brings in a safety shutter 22 that terminates the surgeon's view and then activates the pulsed laser. On release of the foot switch the shutter is removed and the selective mirror 18 is swung into the horizontal position, illustrated by the broken line 23, to enable the microscope to be used for ordinary natural colour observation and photography of the eye.

The invention is not restricted to the details of the embodiment shown in the drawing. For example, it may be more convenient for the patient-surgeon axis of Figure 1 to be turned through 900. The drawing is schematic and omits the slit-lamp's illuminator arm (which could have a decentering facility where the light is emitted).

The illumination source for the slit-lamp could be coupled by a fibre-optic guide and could include a flash lamp for photography.

Normally, between the safety shutter and the dichroic mirror would be accommodated ( 1 ) A magnification changer (2) A binocular beam splitter system for the purpose of photography (3) A mirror (small enough not to intrude on the paths of the binocular viewing and photogrpahic system) set at 450 to provide axial illumination for gonoiscopic work.

As with slit-lamp illuminator light for the purpose of viewing and flash photography would be fed to this element in the microscope assembly via a fibre-optic bundle.

Claims

1. Laser ophthalmic surgery apparatus comprising a high-power pulsed laser having mirrors, a beam expansion system having lenses and situated to expand the beam from the highpower pulsed laser, a low-power laser for producing an aiming beam, means for superimposing the aiming beam on the highpower beam, a device for directing part of the low-power beam back to the pulsed laser to be reflected thereby, the reflected beam being thus capable of use for the alignment of the laser elements and the expander lenses, and means for delivering the superimposed beams to a movable terminal where the beam paths and points of focus in the patient's eye can be observed.

2. Apparatus as claimed in claim 1 wherein the movable terminal has the form and facilities of an ophthalmic slit-lamp.

3. Apparatusas claimed in claim 1 or claim 2 wherein the beam splitter is a pellicle.

4. Apparatus as claimed in any of the preceding claims wherein there is provided a binocular microscope and selective mirror arrangement whereby the image of the aiming beam on the patient's eye is observed.

5. Apparatus as claimed in claim 4 wherein the selective mirror is solenoid-operated to twist out of the field of view of the binocular microscope so as to allow normal colour observation and photograph of the eye.

6. Laser ophthalmic surgery apparatus substantially as herebefore described with reference to the accompanying drawings.