LASER COAGULATION SYSTEM

Abstract: Disclosed is a laser coagulation system adapted for use in an ophthalmological treatment comprising an optical system including reflecting means (35) for directing a focussed laser beam toward a predetermined portion (34) to be coagulated in the eyeball (33) of a patient, and a manipulator (12) for generating a desired value representative of a desired position of the reflecting means (35) for thermal coagulation. The actual position of the reflecting means (35) is detected and compared with the desired value to derive therefrom a control signal, which activates means (93, 98) for driving the reflecting means (35) to a position corresponding to the desired value for thermal coagulation.

Description: BACKGROUND OF THE INVENTION Field of the Invention This invention relates to a laser coagulation system, and more particularly to a laser coagulation system adapted for use in an ophthalmological treatment in which a laser beam from a laser source is radiated into a patient's eye to develop great heat causing thermal coagulation at a predetermined portion of the biological organism in the eyeball of a patient. Description of the Prior Art 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 in a biological organism such as retina to develop thermal coagulation thereon for ophthalmological treatment. For this purpose, the laser coagulation system includes a laser beam 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 thermal coagulation. The laser coagulation system further comprises a slit image projector for forming a slit image on the eyeball to illuminate the background and determine the predetermined portion of eyeball to be coagulated, and an observation equipment for observing the slit image and laser spot in the eyeball. With such arrangement, the slit image projector is rotatably mounted on an instrument base about the vertical axis and includes two mirrors for directing slit light toward the patient's eye to form the slit image on the extension of the vertical axis. The laser beam projector is, on the other hand, arranged above the slit image projector and includes a mirror arranged adjacent to said two mirrors to project the laser spot in the vicinity of the slit image. The observation equipment is arranged outside of the slit image projector and mounted turnably about the vertical axis. The mirror of the laser beam projector arranged adjacent to the mirrors of the slit image projector is displaceable or turnable vertically or horizontally using an operating lever mechanically linked to or wire-connected to the mirror to displace or scan the laser spot in the vicinity of the slit image. This operating lever extrudes rearwardly from the observation equipment for easy access. The operating mechanism for the mirror is called a manipulator. Such coagulation systems in the prior art have the drawbacks that the operating lever of the manipulator is mechanically dependent on the driving link or wire mechanism and disturbs the turning operation of the slit, image projector or observation equipment. The manipulator is additionally provided with a spring for preventing the operating lever from falling down by gravity and returning it to a reference position. This disadvantageously makes it impossible to hold the operating lever to a position different from the reference position for a long time and to accurately displace the laser spot position in the eyeball. The operating lever is further arranged away from a control panel for controlling the instrument as a whole, thus requiring sophisticated operations. It is, therefore, an object of the present invention to provide a laser coagulation system capable of displacing the laser spot precisely to a predetermined position to be coagulated in the eyeball of a patient. It is another object of the present invention to provide a laser coagulation system enabling the easy turning operation of a slit image projector or observation equipment. It is still another object of the present invention to provide a laser coagulation system capable of making the displacement of the laser spot mechanically independent from the operation of a manipulator. In WO-A-85/00010 there is disclosed a laser coagulation system adapted for use in an ophthalmological treatment comprising a support member which supports reflecting means, means for causing a focussed laser beam to be directed by the reflecting means toward the eyeball of a patient to develop great heat causing thermal coagulation at a selected portion in said eyeball, and driving means for moving the reflecting means to a desired position; and means for generating a desired value signal representative of the said desired position of said reflecting means for thermal coagulation. According, however, to the present invention, there is provided a laser coagulation system adapted for use in an ophthalmological treatment comprising a support member which supports reflecting means, means for causing a focussed laser beam to be directed by the reflecting means toward the eyeball of a patient to develop great heat causing thermal coagulation at a selected portion in said eyeball, and driving means for moving the reflecting means to a desired position; and means for generating a desired value signal representative of the said desired position of said reflecting means for thermal coagulation, characterised in that a manipulator is provided with an operating lever so that the support member may be moved in X and Y directions by said manipulator and the operation of the operating lever causes the desired value signal to be generated; there being sensor means for detecting the actual position of said reflecting means, the sensor means generating an actual value signal representative of said actual position; controller means for generating a control signal in response to a deviation of the actual value signal from the desired value signal; and said driving means are responsive to the control signal for displacing the reflecting means until the laser beam reaches a predetermined position corresponding to the desired value signal where the deviation disappears. With such arrangement according to the present invention, the manipulator is operable to generate a desired value signal to which the reflecting means can be set by controller and driving means, thus displacing the laser spot precisely to a predetermined portion to be coagulated in the eyeball of a patient. Thus, the manipulator is not mechanically, but electrically connected with driving means and is free from the mechanical connection therewith, assuring an easy operation for the slit image projector and observation equipment. According to the invention, the manipulator is provided therein with an operating lever for displacing the laser spot. This allows the operating lever to be held stably in the manipulator and makes it possible for an operator to operate the manipulator without stopping the operation of the slit image projector. BRIEF DESCRIPTION OF THE DRAWINGS The objects and features of the present invention will become more apparent from a consideration of the following detailed description taken in conjunction with the accompanying drawings in which: Fig. 1 is a perspective view showing a whole appearance of a laser coagulation system of the present invention; Fig. 2 is an illustrative view showing the arrangement of an optical system for a laser beam projector, slit image projector and observation equipment used in the laser coagulation system of the present invention; Fig. 3 is a perspective view showing the arrangement of the optical system in Fig. 2; Fig. 4 is a side view showing the inner construction of a manipulator for the laser coagulation system of the present invention; Fig. 5 is a perspective view showing the manipulator in Fig. 4 in a disassembled state; Fig. 6 is a side view showing the arrangement of a driving mechanism for displacing a mirror in a laser beam projector together with detectors for detecting the actual position of the mirror; Fig. 7 is a perspective view showing the arrangement of the driving mechanism corresponding to that in Fig. 6; Fig. 8 is a block diagram showing an electrical arrangement of the laser coagulation system; and Fig. 9 is a flow chart showing the control flow in the laser coagulation system of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Fig. 1 shows the appearance of a laser coagulation system according to the present invention which 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 beam projector 21 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 beam 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 beam or imaged slit in the eyeball is further arranged on the front edge of the slider 11 so as to be rotated 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 beam 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 rotated 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, an 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 to 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 beam 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 50µm to 1mm 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', a 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 and 5 show the detailed construction of the manipulator 12 which includes the operating lever 12c having a spherical portion 12d, which is provided with a pin 12e inserted into a hole 71a in a cylindrical member 71. The operating lever 12c has its lower part 12f brought into engagement with a cutout portion 70a in an L-shaped lever 70. This lever 70 is provided with a pin 70b which intrudes into a hole 72a in a C-shaped block 72 fixedly mounted in the housing for connection with a pinion gear 73. Thus, the turning of the operating lever 12c in the direction X in Fig. 5 causes the L-shaped lever 70 to be swung about the pin 70b to rotate the pinion gear 73 and a crown gear 74 engaging therewith. The turning of the crown gear 74 allows the rotation of the shaft 76a of an X-potentiometer 76 held in a holder 75, so that the displacement of the operating lever 12c in the direction of X can be converted into an electrical signal through a terminal 76b of the X-potentiometer 76. To the shaft 71b of the cylindrical member 71 there is fixed a pinion gear 77 which engages with a crown gear 79 fixed to the shaft 78a of Y-potentiometer 78. When the operating lever 12c is displaced into the direction Y perpendicular to the direction X, the L-shaped lever 70 can be turned about the center 12g within the range defined by the cutout 70a. This allows the shaft 78a of the Y-potentiometer 78 to be turned, thereby converting the displacement of the operating lever 12c in the direction Y into a corresponding signal through its terminal 78b. It is to be noted that an elastic member such as a spring plate 81 is provided to cooperate with a block 80 to urge the operating lever 12c leftwardly. Figs. 6 to 8 show the mechanical and electrical arrangement for converting the displacement of the operating lever into the electrical signal to control the mirror 35a to a desired position. In Figs. 7 and 8 the center mirror 35a abuts against one end of a mirror lever 90 urged downwardly by a spring. The mirror lever 90 is connected at the other end with one end of an interconnecting rod 91 which is rotatably mounted in a housing 95 and the other end of which is connected to a gear 92 provided with a helicoid screw 92a. The gear 92 engages with the pinion gear 93a of a Y-directional motor (DC motor with reduction gears) 93 and abuts at its lower end 92b on one end of a detection lever 94 which bears a magnet 94b at its other end and is mounted rotatably about an axis 94a. A spring is attached to the detection lever 94 to urge it to come into contact with the end of the gear shaft. The activation of the Y-directional motor 93 causes the rotation of the pinion gear 93a to displace the helicoid gear 92a due to the engagement of the gear 92 with the pinion gear 93a, thereby lifting the interconnecting rod 91 vertically to rotate the mirror 35a about an axis 96 as shown in Fig. 7 by a double arrow Y. The detection lever 94 turns about the axis 94a as the mirror 35a rotates. This causes the displacement of the magnet 94b relative to a Hall element 97 and allows the indirect detection of the turning movement of the mirror 35a. The interconnecting rod 91 is further provided at one end with a lever 91a having a pin shaft 91b coming into a longitudinal slot 90a formed in the mirror lever 90 and also provided at the other end with a lever 91c having a pin shaft 91d coming into engagement with a longitudinal slot 99c formed on a lever 99. The lever 99 is urged by a spring to absorb the backlash of gear engagements. An X-directional motor 98 having a construction similar to the Y-directional motor 93 is provided for turning displacement of the mirror 35a in the other axis. The motor 98 has a pinion gear 98a engaging in a rack of teeth 99a on a lever 99. The operation of the directional X motor 98 causes the lever 99 supported in a housing 95 to rotate about the same axis as the interconnecting rod 91 to turn the mirror 35a horizontally about a shaft 101 in the direction of the double arrow X because the pin shaft 91b engaging with the mirror lever 90 rotates about the axis of the rod 91. The turning displacement of the mirror 35a about the shaft 101 can be detected by a Hall element 102 relative to which a magnet 99b provided on the other end of the lever 99 is displaced as the mirror 35 turns about the shaft 101. As mentioned above, the displacement of the operating lever 12c in the direction X is detected by the X-potentiometer 76, the signal from which is applied to an analog to digital converter 112 in a controller 111 through an amplifier 110 and converted into a digital signal. The displacement of the mirror 35a in the direction X is, on the other hand, detected by the Hall element 102, the signal from which is similarly fed to the analog to digital converter 112 for digital conversion. The analog to digital converter 112 is connected to a storage 114 for storing the desired value corresponding to the displacement signal of the operating lever 12c and the actual position signal of the mirror 35a detected by the Hall element 102. Both the desired and actual signals are compared by an operational amplifier 115 to derive therefrom a deviation. In response to the deviation a CPU 116 generates a control signal, which is applied to a driver 117 to drive the X-directional motor 98 and rotate the mirror 35a until the deviation disappears. In Fig. 8 there is shown only the control system for the direction X. It will, however, be appreciated that a control system for the direction Y can be arranged similarly to the control system X. 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 displacement of the operating lever 12c in the direction X, for example, in Fig. 5 (Step S1 in Fig. 9) causes the axis 76a of the X-potentiometer 76 to rotate due to the engagement of the pinion gear 73 with crown gear 74. This allows an analog signal representative of a desired value for location of the laser beams focus to be produced from its terminal 76b. This analog signal is amplified by the amplifier 110 (Fig. 8), converted into the digital signal by the analog to digital converter 112 and then stored in the storage 114. The signal corresponding to the position of the operating lever 12c is always stored in the storage successively. Thus, the renewed operation of the lever 12c provides a new desired value different from the preceding one. This difference is calculated in terms of magnitude and sign by the operational amplifier 115 in the controller 111(Step S2). This calculation results in the formation of a deviation signal, which is applied to the driver 117 to drive the X-directional motor 98 (Step S3) to rotate the lever 99 and the pin shaft 91b about the axis of the rod 91. This causes the turning of mirror 35a about the shaft 101 and the scanning of the laser spot in the direction X. The actual position of the mirror 35a detected by the Hall element 102 is stored in the storage 114, and compared with the preceding positional signal to derive therefrom the deviation. This activates the motor 98 which displaces the mirror 35a in the direction X until it reaches the new desired position determined by the operation of the lever 12c and the deviation disappears(Steps S4 and S5). These procedures apply also for the displacement of the laser spot in the direction Y. The displacement of the operating lever 12c in the direction Y causes the Y-potentiometer 78 to produce a desired value, which is compared with the actual signal representative of the position of mirror 35a obtained from the Hall element 97 to derive therefrom a control signal. This causes the Y-directional motor 93 to be driven to rotate the mirror 35a about the axis 96 by means of the interconnecting rod 91. This continues until the mirror 35a reaches the desired value. It should be noted that the mirrors as mentioned above are realized as reflecting means, and therefore include all kinds of reflectors such as total reflection mirrors, half mirrors or reflecting surfaces of prisms. While the invention has been described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes may be made. Therefore, it is intended that the invention should not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out the invention, but that the invention will include all embodiments falling within the scope of the appended claims.

Claims: A laser coagulation system adapted for use in an ophthalmological treatment comprising a support member (11) which supports reflecting means (35a), means for causing a focussed laser beam to be directed by the reflecting means (35a) toward the eyeball (33) of a patient to develop great heat causing thermal coagulation at a selected portion (34) in said eyeball, driving means (93,98) for moving the reflecting means (35a) to a desired position, and means for generating a desired value signal representative of the said desired position of said reflecting means (35a) for thermal coagulation, characterised in that a manipulator (12) is provided with an operating lever (12c) so that the support member (11) may be moved in X and Y directions by said manipulator (12) and the operation of the operating lever (12c) causes the desired value signal to be generated; there being sensor means (97,102) for detecting the actual position of said reflecting means (35a), the sensor means generating an actual value signal representative of said actual position; controller means (111,115,116) for generating a control signal in response to a deviation of the actual value signal from the desired value signal; and said driving means (93,98) are responsive to the control signal for displacing the reflecting means (35a) until the laser beam reaches a predetermined position corresponding to the desired value signal where the deviation disappears. A laser coagulation system as set forth in claim 1, wherein said desired and actual value signals each are converted into a digital signal, stored in a storage (114) and compared by a comparator (115) to derive therefrom said control signal. A laser coagulation system as set forth in claim 1 or 2, wherein said manipulator (12) includes at least one potentiometer (76,78) for converting mechanical movement of said operating lever (12c) into an electrical signal representative of said desired value signal for location of the focussed laser beam. A laser coagulation system as set forth in any preceding claim, wherein said detecting means (97,102) is a Hall element relative to which a magnet (94b,99b) is caused to move corresponding to the displacement of said reflecting means, thereby generating said actual value signal representative of the actual position of said reflecting means. A laser coagulation system as set forth in any preceding claim, wherein said operating lever (12c) is displaceable in a first direction and in a second direction perpendicular to said first direction to displace said reflecting means (35a) in first and second directions.

Inventors: ISHIDA, MAKOTO, KOIKE, CHIKASHI, MCCALLUM, DONALD THOMAS, PATAKI, STEPHAN
Applicants: COHERENT, INC., KOWA COMPANY, LTD.
Application year: 1986
Main classification: A61B17
IPC codes: A61F9, A61B18, A61B17, A61B3