PHOTOCOAGULATION APPARATUS

Abstract: A photocoagulation apparatus (20) is adapted for attachment to an ophthalmic slit lamp (30), the apparatus comprising at least one laser source (1) arranged to direct treatment laser light to the eye (31) of a patient via a beam splitter (11) mounted in a head part of the apparatus which is adapted to be located between the microscope (15) of a slit lamp and the eye of a patient, whereby in use of the apparatus a clinician may view the eye through the slit lamp microscope via the beam splitter during treatment without exposure to the treatment light. At least one adjustable or detachable lens (14) is arranged between the beam splitter and the eye of the patient for selectively varying together the working distance(s) at which the treatment laser beam and slit lamp microscope are focused in front of the head part of the apparatus, whereby the apparatus may be adjusted to accommodate different configurations of contact lens (34) on the eye.

Description: Photo-coagulation Apparatus This invention relates to photocoagulation apparatus incorporating lasers for ophthalmic use. Laser photocoagulation has become a standard procedure for the treatment of retinal disorders, and numerous types of apparatus have been disclosed for focusing and aiming a beam of laser light onto a desired area of the retina for this purpose. Various forms of such apparatus are disclosed in EP-A-0293126 all of which include an infra-red laser diode source and a dichroic beam splitter arranged to deflect the laser beam into the patient's eye such that a clinician may view the region of the eye being treated through the beam splitter without being exposed to the laser light. One embodiment of the apparatus is in the form of a unit adapted to be attached to an ophthalmic slit lamp, which is a standard piece of medical equipment comprising an illuminating system and a microscope, and is traditionally used for observing the interior of the eye. An advantage of this arrangement is that the photocoagulation apparatus may utilise the existing viewing optics of a standard slit lamp thus minimising the size, complexity and cost of the photocoagulation unit itself. As described in EP-A-0293126 the photocoagulating unit may conveniently be mounted such that the beam splitter through which the clinician observes the patient's eye is mounted in a head part of the apparatus disposed between the slit lamp microscope and the patient, the beam splitter deflecting the laser light from a diode source located below the optical path of the microscope into such optical path so that the viewing and treatment beams are substantially aligned between the beam splitter and the patient's eye. A slit- lamp traditionally incorporates a suitable chin and head rest whereby the patient's head is located such that the focal point of the slit-lamp microscope approximately coincides with the retina, fine adjustment in this respect being accommodated by adjusting the position of the microscope relative to the patient. Similarly, the photocoagulation unit may incorporate an adjustable optical system for focusing the infra-red laser beam to a point coincident with the focal point of the slit-lamp microscope. Experience has shown that with such an arrangement, the location of a head part of the photocoagulation apparatus can, in some circumstances, undesirably restrict the clinician's access to the patient's eye in particular for inserting and using a contact lens orr the eye as is usual in this type of treatment. To overcome this problem, a negative (i.e. diverging) lens is permanently mounted between the slit lamp microscope and the beam splitter of the known photocoagulation apparatus to move the focal point of the microscope further away from the microscope so as to increase the working distance available. Such a system has been successfully used where the treatment involves a contact lens such as the so-called Goldma -three mirror lens applied to the patient's eye which is designed to cancel the optical power of the eye to allow the laser and viewing beams to be focused directly on the retina. The Goldman lens is also usually used for anterial treatments in which treatment is carried out on parts of the eye in front of the retina e.g. glaucoma treatment. However, there are other.treatment configurations involving a different form of contact lens such as the so-called Mainster lens adapted to form a real image of the retina in front of the patient's eye, and it is necessary to accommodate such a configuration within the motion limits of the slit-lamp microscope. In such a system there is a need to focus the treatment beam and microscope in front of the patient's eye so that they can be refocused on the retina by the contact lens. With the prior art system described above these treatments cannot both be accommodated without modifying the slit lamp either to move the patient's head rest rearwardly and/or to increase the rearward travel of the microscope adjusting system. Such modifications required to the slit lamp would undermine the advantage of providing a photocoagulation apparatus as a straight forward add on attachment. Viewed from one aspect the invention provides a photocoagulation apparatus adapted for attachment to an ophthalmic slit lamp, the apparatus comprising at least one laser source arranged to direct treatment laser light to the eye of a patient via a beam splitter mounted in a head part of the apparatus which is adapted to be located between the microscope of a slit lamp and the eye of a patient, whereby in use of the apparatus a clinician may view the eye through the slit lamp microscope via the beam splitter during treatment without exposure to the treatment light, wherein at least one adjustable or detachable lens is arranged between the beam splitter and the eye of the patient for selectively varying together the working distance(s) at which the treatment laser beam and slit lamp microscope are focused in front of the head part of the apparatus. Thus, in accordance with the invention, a longer working distance may be selected in treatment configurations wherein the microscope and treatment beam are focused directly onto the retina, whereas the working distance may be reduced to accommodate treatments in which the focal points of the treatment beam and microscope need to coincide with a real image of the retina in front of the eye produced by a contact lens. It is important that the adjustable lens arrangement is located in front of the beam splitter of the phtocoagulation apparatus, i.e. between the beam splitter and the patient's eye so that the focal points of the treatment beam and slit lamp microscope are adjusted simultaneously. In this way the clinician may readily change the apparatus from one mode of operation to the other (as and when a contact lens on the patient's eye is changed) without having to refocus the treatment beam. The apparatus preferably comprises a single adjustable or detachable lens movably or detachably mounted by suitable means in front of the beam splitter. In one form, the lens is displacable into and out of the optical path on a movable carriage. In a.simple form of the apparatus, a single negative (i.e. diverging) lens may be provided which is located in the optical path when it is desired to increase the working distance as aforesaid, and is moved out of the optical path so that the working distance corresponds to that provided by the slit lamp microscope uncorrected for treatments in which the focal point coincides with a real image of the retina in front of the eye (in such configurations the total working distance available between the patient's eye and the apparatus is in any case increased as compared with the arrangement in which the treatment beam and microscope are focused directly on the retina) . Alternatively, a negative lens of increased focal length may be substituted when the alternative mode of operation is to be used, whereby the working distance is still increased but by a lesser extent. In an alternative, preferred embodiment a first negative lens is permanently disposed between the beam splitter and the slit lamp microscope, and is thus effective permanently to increase the distance of the focal point of the microscope in front of the apparatus by a predetermined amount. Adjustment of the working distance may then be achieved by locating either a converging or diverging lens in front of the beam splitter to move the focal points of the microscope and treatment beam towards or away from the apparatus as appropriate. In a particularly advantageous embodiment a diverging lens permanently located between the beam splitter and the microscope has a focal length selected to provide a working distance for the microscope suitable for treatments in which a contact lens creates an image of the retina in front of the patient's eye, and a diverging lens is ovably mounted in front of the beam splitter to increase the focal length by a predetermined amount to accommodate the alternative mode of treatment in which the treatment light is focused directly on the retina. Such an arrangement has a practical advantage in that, by appropriately selecting the focal lengths of the two negative lenses, it has been found that a substantially constant variation in the size of the "spot" formed on the retina by the treatment beam can be achieved by a predetermined displacement of the apparatus head out of a position in which the beam is precisely focused to a point on the retina, regardless of whether or not the removable lens is mounted to the apparatus. This is advantageous in that with many treatments of this type it is desirable to carry out the treatment with the treatment beam not precisely focused on the retina so as to produce a predetermined spot size. It is clearly advantageous that the spot size of the out of focus beam remains constant for the different modes of treatment without having to reposition the photocoagulation apparatus with respect to the slit lamp each time the working distance is adjusted. A permanent lens with a focal length of substantially -300mm combined with a displaceable one of substantially -83mm have been found advantageous for providing the desired working lengths together with substantially constant spot size variation within working limits. To minimise the effect of the adjusting lens or lenses reflecting light back into the slit lamp microscope it is preferred that the axis of the or each lens is slightly inclined (by e.g. 5-10°) or is slightly offset with respect to the optical axis of the microscope. In the case of a lens located in front of the beam splitter it is preferable that it is offset, since inclining the lens takes up slightly more of the working space in front of the lens. Certain embodiments of the invention will now be described, by way of example only, with reference to the drawings, in which: Fig. 1 is a schematic vertical cross section illustrating apparatus in accordance with the invention; Figs. 2 to 5 illustrate schematically the beam splitter of the apparatus and the effect, on the working distance by "the inclusion of an adjustable lens system in accordance with the invention; Fig. 6 is a front view on an enlarged scale of the head part of the aparatus, illustrating the mounting arrangement for the movable lens. As shown in Fig. 1, a photocoagulation apparatus 20 is adapted for use as an add-on demountable attachment for a standard slit lamp 30. The slit lamp, which may take a number of standard forms, traditionally incorporates a tonometer mount 14 and a microscope 15. An illuminating light source 16 is arranged above the slit lamp mirror 17, whereby, in normal use of the slit lamp, a clinician may view a patient's retina via the microscope 14. As shown schematically in Fig. 1 the photocoagulation apparatus may be mounted onto the tonometer mount 14 of the slit lamp by suitable means. As described in EP-A-0293126 the photocoagulation apparatus includes one or more high power infra-red laser diodes 1, light from which is collimated by a high numerical aperture lens 2 and is then expanded by an anamorphic prism pair 3 along the long axis of the infra- red laser diode output whereby to reduce the image size on that axis. Where higher powers or intensities are required than can be achieved with a single laser diode, then the beam from a second infra-red laser diode can be combined with that of the illustrated one using a polarising cube as described in EP-A-0293126. A beam of visible laser light for aiming the infra-red beam is produced by a visible laser diode 4 and collimated by a lens 5, the visible beam being combined with the infra¬ red beam by a dichroic cube 7. The combined visible a_d infra-red beams are then relayed and expanded by telescope lenses 8, 9 and are focussed to a point substantially confocal with the slit lamp microscope 15 by a lens 10. These telescope lenses may be adjusted by the clinician to ensure that the focal points of the infra-red and visible laser light and of the slit lamp microscope are coincident. A wavelength selective mirror 11 acts as the beam splitter adapted to reflect all of the infra-red laser light into the patient's eye 31, but to enable a clinician to view the eye via the microscope 15 and beam splitter 11 without the risk of the clinician's eyes being exposed to the treatment light. For this purpose aligned windows 32,33 are provided in the upper or head part of the apparatus 20. As described in more detail below, the windows are provided with suitable means for mounting therein negative (i.e. diverging) lenses. As shown schematically in Fig. 1 a contact lens such as the so-called Goldman lens is arranged on the patient's eye to cancel out the optical power of the eye so that the treatment and aiming laser beams are focussed directly on the retina. In such a system the slit lamp microscope 15 must therefore also be focussed directly on the retina. Accordingly, the working distance between the head part of the apparatus 20 and the patient's eye is restricted by the maximum focal length of the slit lamp microscope. Access to the patient's eye for the clinician is therefore limited, and it is difficult for the clinician to apply and use the contact lens 34 on the lens with the patient's head supported on the slit lamp head and chin rest. The restriction of the working distance W between the focal point F of the slit lamp microscope and treatment beam is illustrated schematically in Fig. 2 (in which certain parts of the apparatus have been removed for clarity) . As shown in Fig. 3, the preferred apparatus is provided with a first negative lens 40 which is permanently located between the slit lamp microscope 15 and the beam splitter 11 in window 33. The effect of this diverging lens is to move the focal point F away from the microscope 15 whereby the working distance W is increased. The telescope lenses are adjusted to refocus the laser light at the new focal point of the microscope. As described above, in alternative treatments a different form of contact lens is applied to the patient's eye, such as the Mainster lens, which is adapted to produce a real image of the retina in front of the patient's eye. In this case the slit lamp microscope and treatment and aiming beams need to be focussed at a point in front of the eye, so that they are re-focussed on the retina by the contact lens. In a preferred embodiment of the invention the first negative lens 40 has a focal length selected for providing a working distance W suitable for accommodating this form of treatment. As shown in Fig. 4, in the preferred embodiment, when it is desired to adapt the apparatus to the other mode of treatment in which the light is focussed directly on the retina a longer working distance W is required, and this is achieved by locating a second negative lens 41 adjacent the window 32 i.e. between the beam splitter 11 and the patient's eye 31. As shown in Fig. 4 this is effective to increase the focal lengths simultaneously both of the microscope 15 and of the treatment and aiming laser beams. Thus, the clinician can effectively switch the apparatus from one mode of treatment to the other simply by moving the second diverging lens 41 into and out of the optical path. Figure 6 illustrates the preferred mounting arrangement for the movable lens 41, which comprises a slidable carriage 50 movable upwardly and downwardly on rail members 51 by means of knobs 52 which project outside a casing (not shown) of the apparatus for manual engagement by a clinician. The rail members 51 engage in slots formed in the sides of the carriage 50. As shown in Fig. 5, the lens 40 is tilted with respect to the optical axis so as to reduce the effect of light being reflected back into the microscope 15. The lens 41 may also be similarly tilted, although, as shown in Fig. 5, it its central axis may instead be slightly offset from the optical axis in the lateral direction. This avoids reducing the working distance by tilting the lens 41. The offsetting of the lens 41 with respect to the optical axis A results in upward displacement of the focal point F, as shown in Figure 5, but this can easily be compensated for by the clinician. Other arrangements of adjustable lenses may be provided. In a simple form, the lens 40 may be omitted, and the working distance W shown in Figure 2 used for treatments in which the focal point is at a real image of the patient's retina in front of the eye. In some cases there may be sufficient working distance with such an arrangement for this sort of treatment. A single displaceable negative lens 41 is therefore provided to increase the working distance W when the focal point F needs to be on the retina itself. Alternatively the power of the permanent lens 40 may be increased to provide a longer working distance similar to that shown in Fig. 4. In this case the movable lens 41 may instead be a converging lens of suitable power adapted suitably to reduce the working distance W to be similar to that shown in Fig. 3. However, the arrangement of two negative (i.e. diverging) lenses has a particular practical advantage. As described above, in practice many treatments are carried out with the treatment beam not precisely focussed with respect to the retina. In the preferred embodiment the "spot" size is adjusted by shifting the photocoagulation apparatus back and forth. By selecting a suitable combination of diverging lenses a constant spot size variation for a particular displacement of the apparatus may be achieved regardless of whether the second diverging lens 41 is in the optical path. This cannot be achieved in practice by using a movable negative lens on its own (at least whilst at the same time providing desired working lengths W) . This is clearly of advantage in that the clinician may adjust the apparatus to provide a predetermined spot size with the treatment.beam directly focussed on the retina, for example, and then when the apparatus is switched to an alternative mode of operation by the movement of the second lens 41 into the optical path, a similar spot size is provides at the plane of the virtual image of the retina defined in front of the patient's eye. There is therefore no need to adjust the position of the apparatus 20 each time the mode of treatment is changed. A combination of focal lengths of -300mm for the lens 40 and -83mm for the lens 41 are convenient for providing the appropriate working distances together with the constant spot size variation within the working range. With such an arrangement the movement of the second lens 41 into the optical path increases the working distance by about 15 mm. Other combinations of focal length are however possible.

Claims: \ \ CLAIMS 1. A photocoagulation apparatus adapted for attachment to an ophthalmic slit lamp, the apparatus comprising at least one laser source arranged to direct treatment laser light to the eye of a patient via a beam splitter mounted in a head part of the apparatus which is .adapted to be located between the microscope of a slit lamp and the eye of a patient, whereby in use of the apparatus a clinician may view the eye through the slit lamp microscope via the beam splitter during treatment without exposure to the treatment light, wherein at least one adjustable or detachable lens is arranged between the beam splitter and the eye of the patient for selectively varying together the working distance(s) at which the treatment laser beam and slit lamp microscope are focused in front of the head part of the apparatus. 2. Apparatus as claimed in claim 1 wherein the adjustable or detachable lens comprising a lens which is arranged for movement into or out of the optical path between the beam splitter and the eye of a patient. 3. Apparatus as claimed in claim 2 wherein said lens is mounted on a movable carriage. 4. Apparatus as claimed in claim 2 or 3 wherein said lens is a negative (diverging) lens. 5. Apparatus as claimed in claim 2,3 or 4 wherein said lens is arranged so that when located in the optical path its central axis is tilted or offset with respect to the central optical axis of the slit lamp microscope. 6. Apparatus as claimed in any preceding claim further comprising a negative lens arranged in the optical path between the beam splitter and the slit lamp microscope. 7. Apparatus as claimed in claim 6 wherein the negative lens is arranged such that its central axis is tilted or offset with respect to the central optical axis of the slit lamp microscope. 8. Apparatus as claimed in claims 4 and 6 wherein the focal lengths of said lenses are substantially -83mm for the movable lens and -300mm for the lens located between the beam splitter and the microscope.

Inventors: RAVEN ANTHONY, RAVEN, ANTHONY
Applicants: SCIENT GENERICS LTD, SCIENTIFIC GENERICS LIMITED
Application year: 1990
Main classification: A61F9
IPC codes: A61B3, A61B18, A61F9