LASER SPOT PROJECTOR

Abstract: Disclosed is a laser spot projector adapted for use with a laser coagulation system in which a laser beam is radiated as a spot into a selected portion (34) to be thermally coagulated, which comprises a laser source (40) for producing the laser beam, a focussing lens (30) for focussing the laser beam on the selected portion in the form of a laser spot, and a variator lens (43) displaceably arranged between the laser source (40) and focussing lens (30) for changing the magnification of the laser spot depending upon the displacement thereof. The variator lens (43) is displaceable to a position where one of two conjugate points at which the image point lies is an object point of the variator lens (43). This arrangement makes it possible to provide two focussed laser spots each having a different spot diameter.

Description: This invention relates to a laser spot projector, and more particularly to a laser spot projector adapted for use with a laser coagulation system in which a laser beam is radiated as a spot into a portion selected to be thermally coagulated. There have long been known laser coagulation systems in which during an ophthalmic operation against diseases such as retina detachment, glaucoma, etc., a patient's eye is irradiated with laser energy, which is absorbed by a biological organism such as retina to develop thermal coagulation thereon for ophthalmological treatment. For this purpose, the laser coagulation system includes a laser spot projector for producing a laser beam from an argon or krypton laser, which is condensed to a laser beam of a predetermined diameter, directed toward a predetermined portion of the eyeball to be coagulated, and then focussed thereon as a laser spot for thermally coagulating the portion selected. The laser coagulation system further comprises a slit image projector for forming a slit image on the eyeball to illuminate the background and define the predetermined portion of the eyeball to be coagulated, and an observation equipment for observing the slit image and laser spot in the eyeball. In such an arrangement, the laser spot from the laser spot projector must be changed in diameter depending upon how large the portion to be coagulated is. To adjust the diameter of the laser spot, the laser spot projector is conventionally provided with a magnification changing device of a type which has already been used in the field of the laser beam machining. However, such a laser spot projector in the prior art has the drawbacks that the magnification changing device is complicated in structure, not compact and very hard to operate. It is also known from WO-A-85/01870 to provide a laser spot projector with an afocal system including lenses which are displaceable to change the divergence angle. This enables the spot diameter to be changed but involves defocusing the laser beam. It is therefore an object of the present invention to provide a laser spot projector capable of easily adjusting the magnification of the laser spot projected on the portion to be thermally coagulated. It is another object of the present invention to provide a laser spot projector capable of being made compact, and easy to manufacture. According to the present invention, there is provided a laser spot projector adapted for use with a laser coagulation system in which a laser beam is radiated as a spot into a selected portion to be thermally coagulated, comprising a laser source for producing said laser beam, a focussing lens for focussing said laser beam on said selected portion in the form of a laser spot, and a variator lens displaceably arranged between said laser source and focussing lens for changing the diameter of said laser spot depending upon the displacement of said variator lens, characterized in that the variator lens is displaceable to a first position such that its object point corresponds to one conjugate point of the variator lens and its image point corresponds to the other conjugate point thereof so that the focussing lens forms a first focussed laser spot on the selected portion, and to a second position such that its object point corresponds to the other conjugate point and its image point corresponds to the one conjugate point so that the focussing lens forms a second focussed laser spot having a spot diameter different from that of the first focussed laser spot. Thus, the laser spot projector of the present invention makes it possible to provide two sizes of focussed laser spot each having a different spot diameter. It is possible that the variator lens is further displaceable to a position where the object or image point of the variator lens lies out of the conjugate points. In this position, the laser spot can be adjusted to any magnification although the laser spot is not focussed. The invention is illustrated, merely by way of example, in the accompanying drawings, in which:- Figure 1 is a perspective view showing a whole appearance of a laser coagulation system comprising the laser spot projector of the present invention; Figure 2 is an illustrative view showing the arrangement of an optical system for a laser spot projector according to the invention, a slit image projector and observation equipment used in the laser coagulation system; Fig. 3 is a perspective view showing the arrangement of the optical system in Fig. 2; and Figs. 4 and 5 are illustrative views each showing how the laser beam can be focussed depending upon the position of a variator lens used in the laser spot projector of the invention. Figs 6 and 7 are illustrative views each showing how a blurred laser spot image may be generated. Fig. 1 shows the appearance of a laser coagulation system including a laser spot projector according to the present invention. The laser coagulation system 1 includes a slider 11 mounted on a base plate 10 so as to be slidable relative to the base plate 10 in a direction X or Y by means of a manipulator 12 such as a joy stick. The displacement of the slider 11 relative to the base plate 10 can be effected by operating the manipulator 12 in the directions X and Y. The slider 11 supports thereon an instrument base 53 on which a slit image projector 20, a laser spot projector 21 (Fig. 2) and an observation equipment 50 are mounted as will be fully described later. The manipulator 12 is further provided with a handle 12a, the rotation of which allows the instrument base 53 to move upwardly or downwardly to displace the projectors 20 and 21 together with the observation equipment 50 vertically. Thus, the manipulator 12 can adjust the position of the instrument base 53 in the directions X and Y and in the vertical direction. The thus adjusted slider 11 can be locked on the base plate 10 by means of a lock 12b. The base plate 10 has on its front edge two poles 13 between which a chin support 14 and a forehead pad 15 are fixedly mounted. A patient sits down in front of the apparatus with his chin against the support 14 and his forehead against the pad 15 and pays an attention to an eye fixation lamp 16a which serves to fix the patient's eye during measurement or coagulation. Mounted on the rear end of the slider 11 is the slit image projector 20 which is turnable about the axis A (see Fig. 2) and serves to project a slit image onto the eyeball to illuminate the background and determine the portion of the eye to be measured or coagulated. As will be described later, the slit image projector 20 is arranged coaxially with the laser spot projector 21 for projecting a laser beam from a source 40 such as an argon or krypton laser through an optical fiber 41 onto that portion to be coagulated in the eyeball. The observation equipment 50 for observing the focussed laser spot or imaged slit in the eyeball is further arranged on the front edge of the slider 11 so as to be rotatable about the same axis as the turning axis A for the slit image projector 20. Figs. 2 and 3 show the detailed arrangement of an optical system for the laser spot projector 21, slit image projector 20 and observation equipment 50. The slit image projector 20 is arranged in a housing 22 mounted so as to be rotatable about the axis A and is provided therein with a lamp 24 which is adjustable in intensity by means of an adjusting knob 23 (see Fig. 1). The lamp 24 emits illuminating light, which is converged by condenser lenses 25 and 25' to illuminate a slit aperture 26. Arranged between the condenser lens 25 and slit aperture 26 are a roof-shaped prism 27, and infrared ray cutting filter 28 and a detachable blue filter 29. The illuminated slit aperture 26 is imaged, for example, onto a retina 34 of a patient's eye 33 as a slit image 34' by means of a focussing lens 30 including lenses 30a and 30b. To eliminate the imaging function of the eye itself, a special contact lens (not shown) is attached to the patient's eye. A mirror assembly 35 having three-divided mirror portions 35a to 35c is mounted between the patient's eye 33 and lens 30b. The central mirror portion 35a can, as described later, be turned upwardly, downwardly, leftwardly or rightwardly about an axis perpendicular to or within the paper surface (in Fig. 2) by means of an operating lever 12c of the manipulator 12. Arranged between the lens 30a and a prism 31 is a screen plate 36 which serves to interrupt the arrival of slit light to the central mirror 35a, while permitting it to reach the upper and lower mirrors 35b, 35c to the retina 34. To make the slit image on the retina 34 brighter and sharper, the deflection prism 27 has one surface 27a angled deflect light toward the lower mirror 35b and the other surface 27b also angled to deflect light toward the upper mirror 35c. Thus, the deflection prism functions to form the filament image of the lamp 24 at two points existing on the entrance pupil of the focussing lens 30. It is to be noted that the slit width and length of the slit aperture 26 are adjustable by adjusting knobs 37 and 38 and the intensity of the lamp 24 by an adjusting knob 23. The laser spot projector 21 is, on the other hand, arranged in the same housing 22 as the slit image projector 20. The laser beam passing through the optical fiber 41 from the laser source 40 is deflected rectangularly at a prism 42 toward a variator lens 43 and a lens 44, reflected at the prism 31 and then advanced along the same optical path as the slit image projector 20 through the lens 30b, mirror 35a and contact lens to radiate the laser spot of a predetermined diameter on the retina 34 for thermal coagulation. The spot diameter of the laser beam can be adjusted in the range of about 50 µm to 1 mm by turning a knob 45 and adjusting the variator lens 43. The instrument base 53 (Fig. 1) is provided with the housing 22 for accommodating the projectors 20 and 21 and a housing 52 for accommodating the observation equipment 50, and is displaceable vertically using the handle 12a of the manipulator 12 as mentioned before. Further, the housings 22 and 52 are turnable to each other about the axis A, so that the projectors 20, 21 and the observation equipment 50 can effect upward, downward or turning movement, respectively. The observation equipment 50 includes an optical system comprised of an objective 55, variator lenses 56 and 56', safety filter 61, a focussing lens 57, erecting prisms 58 and 58', and eyepieces 51, 51'. The observation equipment 50 allows the observation of the slit image and laser spot formed in the eyeball. The adjustment of a knob 60 causes the variator lens 56 to be adjusted to provide an enlarged or reduced slit image or laser spot. The safety filter 61 is used to interrupt the laser beam reflected back from the irradiated portion of eye or cornea and protect the eyes of an observer. For this purpose, the safety filter 61 is automatically inserted into the optical path of the observation equipment 50 immediately before the laser source 40 is activated to produce a stronger laser beam. It should be noted that the optical elements following the objective 55 are provided in pairs respectively to allow binocular observation. Figs. 4 to 7 show a main portion of the laser spot projector 21. For an optical system where light from a point A is repeatedly reflected or refracted and focussed on a point A', the point A is commonly designated as an object point and the point A' as an image point. If the light is caused to advance reversely from the image point A', then the light is focussed on the object point A. In this case, the point A serves as the image point and the point A' as the object point, so that the object and image points are exchangeable in its function. In this connection, a pair of object and image points are called conjugate points, respectively. In the case of the embodiment in Fig. 4, the top edge A of the fiber 41 forms the object point with respect to the variator lens 43, and a position A' on which an image is formed is the image point. Thus, the distance between both the points A and A' is kept the same even is the variator lens 43 is displaced with its conjugate points reversed, for example, as shown in Fig. 5. Now assume that a point A" is a focal point which exists on the retina and on which an image is focussed by the focussing lenses 44 and 30 through the variator lens 43. The selection of the variator lens 43 forming a relation A'/A=0.707 with the object point A of 60 µm diameter results in the formation of an image having a diameter of 42.42 µm on the image point A'. The selection of the focussing lenses 44 and 30 forming a relation A"/A'=1.179 then causes the formation of an image having a diameter of 50 µm on the point A". If, on the other hand, the variator lens 43 is shifted to the object point A as shown in Fig. 5 in the reversed position with respect to the object and image points as shown in Fig. 4, then A'/A is equal to 1.414 with an image diameter of 84.84µm at the point A' and a spot diameter of 100 µm on the point A" on the supposition that the focussing lenses 44 and 30 are used forming a relation of A"/A'=1.179. Thus, the utilization of a relation between the object and image points in the optical system allows the formation of a focussed clear spot image. If the variator lens 43 is further displaced toward the object point out of its conjugation, then the spot image on the point A" becomes blurred and has a diameter of 500µm or 1000 µm, for example, as shown in Fig; 6, and 7. This makes it possible to produce a spot image having any diameter, although it appears to be out of focus. It is to be noted that an operating lever may be provided in the housing or lens barrel to displace or adjust the variator lens 43 in accordance with a scale provided thereon. The operation of the laser coagulation system according to the present invention will now be described. The patient first sits down with his chin against the support 14 and his forehead against the pad 15 and pays the attention to the eye fixation lamp 16. The lamp 24 of the slit image projector 20 is then turned on to form the slit image 34' on the retina 34 of the patient's eye 33 through the contact lens set thereon. The slit light has its central flux inhibited to arrive at the central mirror 35a by means of the screen plate 36 and is reflected only at the upper and lower mirrors 35b and 35c to form the slit image 34' on the retina 34. In this case, the deflection prism 27 is used to deflect the slit light towards the mirrors 35b and 35c effectively. The intensity of the slit image can be adjusted by the knob 23, and the slit width and length by the adjusting knobs 37 and 38. If the slit image 34' deviates from the desired place in the above-mentioned slit image formation, the manipulator 12 may be operated to displace the slider 11 and the housings 22 and 52 in the directions X, Y and Z and turn the projectors 20, 21 or observation equipment 50 about the axis A relative to each other until the slit image is formed on the desired portion for coagulation. The thus formed slit image 34' can be observed by the optical system of the observation equipment including the objective 55, variator lens 56, imaging lens 57, erecting prism 58 and eyepiece 51. After the portion of eye to be coagulated has been determined, the laser source 40 is activated to emit a weak laser beam, which is caused to pass through the prism 42, variator lens 43, lens 44, prism 31, and lens 30b , reflected at the central mirror 35a and then focussed as a spot onto the retina 34. For coagulation a stronger laser beam is generated from the laser source 40 by changing power. When said stronger beam is activated, the safety filter is automatically inserted into the optical path of the observation equipment 50 to protect the eyes of the observer from the laser beam reflected from at the irradiated portion of the patients eye or retina. For fine and precise coagulation the laser spot on the retina 34 can be displaced by scanning the central mirror 35a vertically or horizontally, that is, in the direction X or Y using the operating lever 12c of the manipulator 12. The adjustment of the knob 45 allows the variator lens 43 to be displaced to adjust the spot diameter of the laser beam, as described in conjunction with Figs. 4 and 5. It will also appreciated that the variator lens 43 may comprise not only one lens, but also a plurality of lenses and/or reflecting means such as mirrors for deflecting the optical path.

Claims: A laser spot projector adapted for use with a laser coagulation system in which a laser beam is radiated as a spot into a selected portion to be thermally coagulated, comprising a laser source (40) for producing said laser beam, a focussing lens (30) for focussing said laser beam on said selected portion in the form of a laser spot, and a variator lens (43) displaceably arranged between said laser source (40) and focussing lens (30) for changing the diameter of said laser spot depending upon the displacement of said variator lens, characterized in that the variator lens (43) is displaceable to a first position (Figure 4) such that its object point (A) corresponds to one conjugate point of the variator lens and its image point (A') corresponds to the other conjugate point thereof so that the focussing lens (30) forms a first focussed laser spot (A") on the selected portion, and to a second position (Figure 5) such that its object point (A) corresponds to the other conjugate point and its image point (A') corresponds to the one conjugate point so that the focussing lens forms a second focussed laser spot (A") having a spot diameter different from that of the first focussed laser spot. A laser spot projector as set forth in claim 1, wherein the focussing lens (30) is held at a fixed distance with respect to the position of the selected portion.

Inventors: HENNINGS, DAVID ROBERT, NAKANISHI, TAKAJI, NIINO, MASAO
Applicants: COHERENT, INC., KOWA COMPANY, LTD.
Application year: 1986
Main classification: A61B17
IPC codes: A61F9, G02B27, A61N5, A61B18