OPHTHALMIC DISEASE DETECTION APPARATUS

Abstract: An apparatus for detecting ophthalmic diseases such as an inflammation in a patient's eye (11) includes means of focusing a laser beam (L) at a selected spot (P) in the eye. The light scattered from the eye is photoelectrically detected through a mask (26) with a slit (26a) and converted into an electrical signal which is subsequently used to determine the protein concentration essential to ophthalmic disease detection in the patient's eye. A light shield member (61) for blocking diffused light from the eye or scattered light from the laser beam is provided in the slit (26a) to improve the S/N ratio of the electrical signal to be processed.

Description: BACKGROUND OF THE INVENTION Field of the Invention This invention relates to an apparatus for detecting ophthalmic diseases in a patient's eye, and more particularly to an apparatus for detecting opthalmic diseases in which laser light is radiated via an optical system at one spot in the camera oculi of the patient's eye, particularly in the anterior chamber thereof, and the laser light scattered therefrom is analyzed to measure the protein concentration for ophthalmic disease detection in the camera oculi. Description of the Prior Art The camera oculi is comprised of the camera oculi anterior (anterior chamber) and the camera oculi posterior (posterior chamber). The camera oculi anterior is defined by a space surrounded by the rear surface of the cornea, a part of the ciliary body, the iris, and the front surface of the crystalline lens, while the camera oculi posterior is defined by a space surrounded by the rear surface of the iris, the inner surface of the ciliary body, and the front surface of the crystalline lens. The camera oculi is filled with transparent humor aqueous, which has chemical and physical characteristics that are different from those of lymphatic liquid and has a close relation with the metabolism of the cornea or crystalline lens. The humor aqueous contains proteins the increase of which causes turbidity in the camera oculi when it becomes inflamed. In this respect, the measurement of protein concentration in the camera oculi of the patient's eye is of great importance in determining whether the camera oculi is inflamed, that is, whether a blood-aqueous barrier functions normally or not. To measure the protein concentration in the camera oculi, a slit lamp microscope is very often used to determine the turbidity by grading via the naked eye. This is, however, disadvantageous because the judgment depends upon the person who performs the measurement. On the other hand, a photographic measuring method has been developed to make a quantitative measurement of the protein concentration. This method is, however, highly complicated to analyze, and is thus very difficult to apply in a clinical examination. To overcome this problem, an apparatus for detecting opthalmic diseases has been proposed which includes means for focusing a laser beam at a selected spot in the camera oculi of an eye. In the apparatus, the light scattered from the eye is photoelectrically detected and converted into an electrical signal which is subsequently used to determine the protein concentration essential to ophthalmic disease detection in the camera oculi of the patient's eye. See, for example, Japanese Patent Laying-open No. 120834/87. In such apparatus in the prior art, the light laterally scattered from the eye is detected through a mask with a slit to limit the scattered light that impinges on the mask. In this apparatus, the scattered light from the laser beam and the diffused light from eye organs such as the crystalline lens, vitreous humor, retina, implanted artificial crystalline lens, etc. are simultaneously observed, thus resulting in an inadequate S/N ratio and unsatisfactory measurement accuracy. It is therefore an object of the present invention to provide an apparatus for detecting ophthalmic diseases in the patient's eye which is capable of measuring the diseases in the eye precisely and easily. Another object of the present invention is to provide an apparatus for detecting ophthalmic diseases which enable the noise from diffused light from the eye or reflected or scattered light which may impinge on the spot to be measured in the patient's eye to be reduced or removed. According to the present invention there is provided an apparatus for detecting ophthalmic diseases in a patient's eye comprising a laser source for producing a laser beam, a laser beam projector for projecting the laser beam from the laser source and focusing the laser beam at a selected point to form a measuring spot in the patient's eye, photoelectric converting means for receiving light scattered from the patient's eye and photoelectrically converting it into an electrical signal which is processed to derive therefrom a measure of the protein concentration in the camera oculi of the patient's eye for ophthalmic disease detection, and a mask disposed in front of the photoelectric converting means and formed thereon with a slit having a predetermined width to limit the scattered light that impinges on the photoelectric converting means, characterised in that the slit is provided with light shield means for blocking the light scattered from the selected spot, that the light shield means is constructed as a line-shaped stop several times wider than the of the measuring spot in the slit, said light shield means being displaceable within the slit perpendicularly to the direction along which the light shield means extends; and that the light shield means is arranged to be positioned in the slit such that it shields the light scattered from the selected spot so that the signal produced by the unwanted diffused background light is subtractable to improve the signal to background ratio of the output signal. As indicated above, on the aperture in the slit there may be observed the scattered light from the laser beam and the diffused light from the various organs in the eye. The light shield member is provided in the slit to block the diffused light from the eye. This makes it possible to increase the effective signal, that is, the component of the scattered light from the eye, and to reduce the noise due to the diffused light from the eye, thus improving the S/N ratio and measurement accuracy. The invention is illustrated, merely by way of example in the accompanying drawings in which: Figure 1 is a perspective view of an apparatus according to the present invention; Figure 2 is an illustrative view showing the arrangement of the optical system of the apparatus; Figure 3 is an illustrative view showing the arrangement of the optical axes of a laser projector and light receiving portion; Figure 4 is an illustrative view showing the configuration of a mask; Figure 5 is an illustrative view showing the detailed configuration of a mask with a light shield member; and Figures 6 (A) and 6(B) are plan and side views each showing a driving mechanism for the light shield member. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention will now be described in detail with reference to the drawings. In Figures 1 and 2, which show an arrangement of the ophthalmic disease detection apparatus according to the present invention, reference numeral 1 denotes a laser light source,such as, for example, a helium-neon or argon laser source. The laser light source 1 is disposed on a stand 2. Light from the laser light source 1 is passed through a laser beam filter 3 and via a prism 4, prisms 5 and 6, a lens 7, a beam splitter 8, a condenser lens 9 and a prism 10 to converge on the eye under examination 11 at a spot in the anterior chamber 11a thereof. The laser beam projector is provided with a slit light source 12. Light from the slit light source 12 passes via a slit light shutter 13 and a slit 14 and goes via the beam splitter 8, lens 9 and prism 10 to form a slit image on the anterior chamber 11a. With the light from the laser light source being converged to a spot P, this slit image is for illuminating the surrounding area to facilitate confirmation of the position of the spot of converged light. The width and length of the slit 14 can be adjusted by an adjusting knob 15 and a switching knob 16, respectively, which are shown in Figure 1. A portion of the laser light scattered from the measuring spot P in the anterior chamber 11a passes through an objective lens 20 of a detection section 29 and is split by a semitransparent mirror or beam splitter 21. One part of the light thus split passes through a lens 22, a mask 26 provided with a slit 26a and a shutter 26′ and impinges on a photomultiplier 27 used as the photoelectric converter. The other part of the scattered light split by the beam splitter 21 passes via a lens 30 and prisms 31 and 34 to an eyepiece 32 by means of which an examiner 33 can carry out observations. The output from the photomultiplier 27 is passed through an amplifier 28 and is fed to a counter 40 and the intensity of the scattered light detected by the photomultiplier is counted as numbers of pulses per unit time period. The output of the counter 40, i.e. the number of samplings or the total pulse count, is stored in a memory 25 allocated for each unit time period. The data stored in the memory 25 is processed by an evaluating device 41 which, as explained below, computes the concentration of protein in the anterior chamber on the basis of the count value stored in the memory 25. The detector 29 is affixed to a support 70. The support 70 and the laser beam projector are provided so as to be rotatable, with respect to each other, about a spindle 71, so as to allow the angle between the optical axes of the laser beam projector and the light receiving means to be adjusted to the required setting. In the preferred embodiment, detection is carried out with this angle set at about 90 degrees. Thus in accordance with this embodiment, as illustrated in Figure 3, the light receiving means and the laser beam projector are disposed so that their optical axes cross at around 90 degrees. At this time an image 26'' of the mask formed by the lens in the light receiving means is formed at the beam waist 80 on the optical axis of the light receiving means at a position which is a conjugate with that of the mask. Figures 4 and 5 show the slit 26a of the mask 26 provided with a light shield member 61 for blocking light diffusing from the eye, i.e. the light scattered from the selected spot P. The light shield member 61 is constituted as a line-shaped stop that is several times thicker than the image 1a which is formed by the laser beam in the selected spot P and which appears in the slit 26a. As illustrated by Figure 6, the light shield member 61 can be driven, for example by a motor 63, along side rails 62, 62' to scan in a direction perpendicular to the laser beam 1a and thus perpendicular to the direction along which the light shield member 61 extends. An eye fixation light source 90 constituted by a light-emitting diode or the like powered by electricity supplied from a power source 91 is disposed at a position that permits the examiner to fix the patient's eye. The light selected for the eye fixation light produced by the light source 90 is of a different colour than the light of the laser light source 1. For example, when the light from the laser light source is red, a green light is selected. The eye fixation light from the light source 90 can be turned in the direction indicated by the arrow by means of a link mechanism 92 to enable it to be adjusted so that it is always in an optimum position with respect to the patient's eye. Provided on the base 2 is an input means, such as a joystick 45 equipped with a push-button 46, and this can be operated to insert the laser filter 3, the slit light shutter 13 and the photomultiplier shutter 26' into, or retract the said elements from, the respective optical system. The operation of the apparatus arranged thus will now be described. In conducting the measurement, the slit light source 12 is actuated and an image of the slit 14 is formed, via the beam splitters 8 and 10 and the lens 9, on a part of the anterior chamber 11a that includes the measurement point P. Following this, light from the laser light source 1 is converged on the measurment point P via the said optical system. A portion of the light from the measurement point P is simultaneously directed by the beam splitter 21 to the examiner 33 for observation and through the lens 22 and the mask 26 to impinge on the photomultiplier 27. In the measurement, the light shield member 61 is scanned from the upper edge of the aperture slit to the lower edge (i.e. in the direction denoted by X in Figure 5). When the light shield member 61 is in the vicinity of the upper edge of the aperture slit, scattered laser light and light diffusing within the eye is observed and the intensity I v of the sum of this light is measured. When the light shield member 61 is in the central part of the slit, scattered laser light is blocked, only light diffused from within the eye is observed and the intensity of the light I c is measured. When the light shield member 61 is in the vicinity of the lower edge of the slit, again scattered laser light is observed and the intensity I d of light diffusing from within the eye is measured. Therefore, the intensity I s of the scattered laser light can be obtained by deducting I c from the arithmetic mean of I v and I d Thus the light shield member 61 can be arranged in the slit 26a in a position in which it shields the light scattered from the selected spot P so that the signal produced by the unwanted diffused background light can be subtracted to improve the signal to background ratio of the output signal. The photoelectric converter 27 receives light via the slit 26a and converts the light into a corresponding series of pulses which are counted by the counter 40 as numbers of pulses per unit time and the count values are stored in the memory 25 allocated for each unit time period. The evaluating device 41 processes the data contained in the memory 25, and uses equation (1) to calculate the protein concentration in the anterior chamber. When the line-shaped stop is not scanned, the stop acts as a shield member to block light diffusing from within the eye, increasing the precision of the measurement of protein in the anterior chamber. 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 and equivalents may be substituted for elements thereof without departing from the scope of the invention as defined in the claim. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof as defined in the claim. 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 claim.

Claims: An apparatus for detecting ophthalmic diseases in a patient's eye comprising a laser source (1) for producing a laser beam, a laser beam projector (7,8,9,10) for projecting the laser beam from the laser source and focusing the laser beam at a selected point to form a measuring spot (P) in the patient's eye (11), photoelectric converting means (20,22,27) for receiving light scattered from the patient's eye and photoelectrically converting it into an electrical signal which is processed to derive therefrom a measure of the protein concentration in the camera oculi of the patient's eye for ophthalmic disease detection, and a mask (26) disposed in front of the photoelectric converting means and formed thereon with a slit (26a) having a predetermined width to limit the scattered light that impinges on the photoelectric converting means, characterized in that the slit (26a) is provided with light shield means (61) for blocking the light scattered from the selected spot, that the light shield means is constructed as a line-shaped stop several times wider than the image of the measuring spot in the slit, said light shield means being displaceable within the slit (26a) perpendicularly to the direction along which the light shield means extends; and that the light shield means is arranged to be positioned in the slit such that it shields the light scattered from the selected spot so that the signal produced by the unwanted diffused background light is subtractable to improve the signal to background ratio of the output signal.

Inventors: MIZUTA, SUSUMU
Applicants: KOWA CO. LTD.
Application year: 1988
Main classification: A61B3
IPC codes: A61B3