Abstract:
A CCD camera captures an image of the lachrymal fluid layer in a prescribed position of a subject&#39;s eye to which a target substance is administered. Images are selected from a plurality of images captured, and the positions of the target substance in the selected images and the capturing times thereof are used to compute the movement speed of the target substance. The computed movement speed of the target substance is then outputted as the movement speed of the lachrymal fluid of the subject&#39;s eye. This arrangement allows the movement speed of lachrymal fluid to be reliably measured, assuring quantitative diagnosis even of severe dry eye.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to an ophthalmic measuring method and apparatus that can be used to screen dry eye and evaluate dry eye severity in a subject&#39;s eye.  
         [0003]     2. Description of the Prior Art  
         [0004]     The recent increase in the number of patients with dry eye is considered to be caused by an increased number of workers at VDTs (Visual Display Terminal),contact lens wearers or the dryness of air-conditioned rooms. Disorders in the corneal epithelium, conjunctival epithelium, and various other ophthalmic disorders can occur in conjunction with dry eye, and the diagnosis of dry eye has become an important subject of ophthalmic field.  
         [0005]     Configurations have been proposed in the past for an ophthalmic apparatus for capturing an image of the lachrymal fluid layer of a subject&#39;s eye and observing, analyzing, and measuring the image in order to quantitatively evaluate conditions of dry eye.  
         [0006]     Embodiments of known techniques include a technique (see Japanese Laid-open Patent Application Publication No. 1997-201334) for capturing an image of an interference pattern formed in the lachrymal fluid surface layer of a subject&#39;s eye, and evaluating dry eye conditions based on the hue of a plurality of areas in the image of the interference pattern; and a technique (see Japanese Laid-open Patent Application Publication No. 1999-267102) for projecting an image of an aperture having a prescribed shape onto the surface of lachrymal fluid accumulated in the lachrymal fluid meniscus along the lower eyelid, capturing an image of the aperture projected on the lachrymal fluid surface, finding the curvature radius of the lachrymal fluid surface from the magnification factor of the aperture image, and evaluating dry eye severity.  
         [0007]     In the conventional techniques, particularly the technique described in Japanese Laid-open Patent Application Publication No. 1997-201334, an image of the interference color of the lachrymal fluid layer is captured, and the image is observed, analyzed, and measured, but almost no interference color occurs in the normal eye and the eye experiencing the worst severity of dry eye, and this conventional technique suffers from drawbacks in that the normal eye or the eye experiencing the worst severity of dry eye cannot be observed, analyzed, and measured.  
         [0008]     In view of the foregoing drawbacks, an object of the present invention is to ensure that the movement speed of lachrymal fluid can be reliably measured, diagnosis can be quantitatively performed from the movement speed of the lachrymal fluid thus measured even on a severely dry eye, and the state of a normal eye can be reliably identified.  
       SUMMARY OF THE INVENTION  
       [0009]     The present invention provides an ophthalmic measuring method comprising the steps of administering a target substance to the lachrymal fluid of a subject&#39;s eye; irradiating the lachrymal fluid with illuminating light; electronically capturing a plurality of images of the illuminated lachrymal fluid of the subject&#39;s eye, the images being captured respectively at different times; measuring the movement speed of the target substance based on the positions thereof in the images selected among the plurality of captured images and the capturing times of the selected images; and outputting the measured movement speed of the target substance as the movement speed of the lachrymal fluid of the subject&#39;s eye.  
         [0010]     The present invention also provides an ophthalmic measuring apparatus comprising means for electronically capturing an image of the lachrymal fluid layer in a prescribed position of a subject&#39;s eye to which a target substance is administered; means for selecting images among a plurality of images captured; means for computing the movement speed of the target substance based on the positions thereof in the selected images and the capturing times of the selected images; and means for outputting the computed movement speed of the target substance as the movement speed of the lachrymal. fluid of the subject&#39;s eye.  
         [0011]     According to the present invention, an image of the lachrymal fluid layer in a specific position of the subject&#39;s eye to which a target substance is administered is electronically captured a plurality of times, the image signal captured each time is computed and comparatively analyzed, and the movement speed of the target substance is measured as the movement speed of the lachrymal fluid of the subject&#39;s eye. The severity of dry eye is thus quantitatively evaluated based on the results of measuring the movement speed of the lachrymal fluid of the subject&#39;s eye.  
         [0012]     In the present invention, a target substance is administered to the subject&#39;s eye and its movement in the lachrymal fluid can be monitored even when an interference color does not occur. Therefore, the movement speed of lachrymal fluid can be quantified regardless of the state of the subject&#39;s eye, and there is no occurrence of the drawback of the prior art in which it was difficult to distinguish between a normal eye and a severely dry eye. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]      FIG. 1  is a block diagram showing one embodiment of an ophthalmic measuring apparatus according to the present invention;  
         [0014]      FIG. 2  is a diagram showing the operation in the configuration shown in  FIG. 1 ;  
         [0015]      FIG. 3  is a block diagram showing another embodiment of an ophthalmic measuring apparatus according to the present invention; and  
         [0016]      FIG. 4  is a diagram showing the operation in the configuration shown in  FIG. 3 . 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0017]     Embodiments of the present invention will be described hereinafter with reference to the drawings.  
         [0018]      FIG. 1  shows the simplified structure of an ophthalmic measuring apparatus according to the present invention. In this drawing, the reference numeral  1  indicates a white light source composed of a halogen lamp or the like for illuminating a subject&#39;s eye E. Light radiated from the white light source  1  passes through a mask  2  for limiting the field of illumination, and then illuminates a prescribed point P on the subject&#39;s eye E via a lens  3 , an exciter filter  3   a,  a half mirror  4 , and a lens  5 . The position selected for this prescribed point P is the lipid layer of the outermost lachrymal fluid layer on the cornea of the subject&#39;s eye E. The intensity of the white light source  1  can be adjusted by a dimmer circuit (not shown in the drawing).  
         [0019]     The light reflected from point P enters a color CCD camera  7  via the lens  5 , the half mirror  4 , and a lens  6 , and the RGB (color) video signal thus captured is inputted to an image processing device  20 .  
         [0020]     The image processing device  20  can be configured so as to utilize a personal computer (PC) or other hardware. This image processing device  20  has a video storage device  8  that is composed of a video capture interface and an HDD or other external storage device and is capable of real-time image output and the like to a monitor  12 ; an image processor  9  composed of a CPU and memory (ROM and RAM) or other computing resources; an output display controller  11  that uses the monitor  12  and controls the output display described hereinafter; and a timer  13  used for controlling the image acquisition timing of the video storage device  8 , the timing of image output to the monitor  12 , and other timings.  
         [0021]     The image processing device  20  also has a keyboard, a pointing device (mouse or the like), or another common operating device not shown in the drawings. The monitor  12  is used as described hereinafter for output displays relating to ophthalmic measurement, and the abovementioned operating device and monitor  12  constitute a user interface for ophthalmic measurement.  
         [0022]     The operation according to the configuration described above will next be described.  
         [0023]     In the present embodiment, a target substance (tracer, marker, or other particulate substance, colorant, or the like that is not harmful to the test subject/subject&#39;s eye) is directly or indirectly administered to the lachrymal fluid of the subject&#39;s eye, the illuminating light of the white light source  1  is radiated, an image of the lachrymal fluid of the subject&#39;s eye is electronically captured two or more times at different times by the CCD camera  7 , each image signal thus captured is computed and comparatively analyzed, and the movement speed of the target substance is measured as the movement speed of the lachrymal fluid of the subject&#39;s eye. The severity of dry eye can be quantitatively evaluated based on these results of measuring the movement speed of the lachrymal fluid of the subject&#39;s eye.  
         [0024]     The target substance is administered to the subject&#39;s eye by administering the subject&#39;s eye with an eye drop or ointment that includes the target substance, or by using another method. When a fluorescent target substance is used, the exciter filter  3   a  is inserted in the optical path, and a barrier filter (not shown) is inserted in the optical path along the CCD camera  7 .  
         [0025]     After the target substance is administered to the subject&#39;s eye, measurement is performed according to the control sequence shown in  FIG. 2 .  FIG. 2  shows the control sequence in the configuration of  FIG. 1 , and the state of the output display on the monitor  12 . The control sequence of  FIG. 2  is stored in advance in the ROM (or HDD or the like) storage device of the image processor  9  shown in  FIG. 1 .  
         [0026]     After the target substance is administered to the subject&#39;s eye, and blinking is confirmed in the subject&#39;s eye, the user performs a prescribed operation (using a keyboard or other device not shown in the drawing) to initiate imaging. In step S 11  of  FIG. 2 , the illuminating light of the white light source  1  is directed to the subject&#39;s eye, and an image of the illuminated location is received by the video storage device  8  of the CCD camera  7 .  
         [0027]     An imaging period of about six seconds, for embodiment, is set at this time, and about 10 to 100 images are automatically and continuously captured. When 100 images are captured in six seconds, the image capture interval is 0.06 seconds. The appropriate imaging period is considered to be at least several seconds, since it is preferred that the target movement speed be able to be measured after blinking of the subject&#39;s eye following administration of the target substance. The timer  13  is used to control the capture timing described above, and the capture time data of each image are stored in the video storage device  8  after being correlated with the captured images.  
         [0028]     After image acquisition is completed in step S 12 , in step S 13 , the image processor  9  controls the monitor  12  via the output display controller  11  and creates an output display such as the one shown in the upper right of  FIG. 2 . In this arrangement, the screen  12   a  of the monitor  12  is divided into top and bottom portions, the top portion is the main display area  121 , the bottom portion is the thumbnail display area  122 , and a plurality of size-reduced thumbnail images of the captured images are displayed in the thumbnail display area  122 .  
         [0029]     In the thumbnail display area  122 , cursors  122   a  and  122   b  are displayed, and two images used for measuring the lachrymal fluid movement speed can be selected by matching these cursors  122   a  and  122   b  with the bottom of a thumbnail in the thumbnail display area  122  using a keyboard or pointing device (mouse or the like) not shown in the drawing and performing a prescribed selection operation.  
         [0030]     In the embodiment depicted in the drawing, a state is shown in which images t 2  and t 5  are selected among five thumbnail images t 1  through t 5 , and images t 2  and t 5  (comparison images) corresponding to these thumbnail images t 2  and t 5  are displayed in the main display area  121 .  
         [0031]     Target substances  124  and  125  are displayed in the images t 2  and t 5 , respectively, in the main display area  121 . It is apparent that since the same target substance must be used to measure the movement speed of the lachrymal fluid, the user is required to select two images that show target substances  124  and  125  which are considered to be the same.  
         [0032]     When the user can determine that target substances  124  and  125  are displayed that are considered to be the same, then in step S 14 , the user specifies the images of the target substances  124  and  125  by clicking them using the pointing device (mouse or the like) as indicated by the reference symbol C in the lower right of  FIG. 2 .  
         [0033]     Thus, in step S 15 , the lachrymal fluid movement speed is computed based on the distance between the target substances  124  and  125  considered to be the same in the two comparison images t 2  and t 5 , and on the elapsed time found from the imaging time data of the comparison images t 2  and t 5 . In order for a prescribed image magnification to be obtained in this distance computation, the measuring apparatus shown in  FIG. 1  is aligned in advance with the subject&#39;s eye so that the actual distance is reliably obtained from the distance in the image, or a device capable of stereo imaging is used as the CCD camera  7  so that the actual distance is obtained from the distance in the image.  
         [0034]     According to the operation described above, the movement speed of lachrymal fluid can be computed, and the results thereof can be displayed as shown in the lower right of  FIG. 2 . The bottom portion of the screen  12   a  in this arrangement is changed to a measurement results area  123 , and the lachrymal fluid movement speed in the transverse direction and lachrymal fluid movement speed in the longitudinal direction are numerically displayed in the measurement results area  123 .  
         [0035]     According to the present embodiment as described above, the target substance is administered to the lachrymal fluid of the subject&#39;s eye, the illuminating light of the white light source  1  is radiated, an image of the lachrymal fluid of the subject&#39;s eye is electronically captured two or more times at different times by the CCD camera  7 , the lachrymal fluid movement speed found from the images thus obtained can be displayed, and based on these results, the user can evaluate the severity of dry eye.  
         [0036]     Since the target substance is administered to the lachrymal fluid of the subject&#39;s eye and imaged according to the present embodiment, the movement of the lachrymal fluid can be monitored even when an interference color does not occur, the movement speed of lachrymal fluid can be quantified regardless of the state of the subject&#39;s eye, and it is possible to overcome the drawback of the conventional configuration in which it was difficult to distinguish between a normal eye and a severely dry eye.  
         [0037]     In the embodiment above the target substance was administered to the lachrymal fluid of the subject&#39;s eye, and the surface of the lachrymal fluid on the cornea of the subject&#39;s eye was imaged, but it is also possible to adopt a configuration in which the layer of lachrymal fluid accumulated in the lachrymal fluid meniscus along the lower eyelid of the subject&#39;s eye is imaged, as in the following embodiment.  
         [0038]      FIG. 3  depicts the manner in which measurement is performed in this embodiment. The hardware of the measuring apparatus in  FIG. 3  is the same as in  FIG. 1 , but the illumination and optical axis of imaging by the measuring apparatus are aligned so that imaging is performed in the location of the lachrymal fluid layer (lachrymal fluid meniscus) accumulated in the lachrymal fluid meniscus along the lower eyelid of the subject&#39;s eye. The lachrymal fluid moves along the edge of the lower eyelid when the subject&#39;s eye blinks.  
         [0039]     In this type of configuration as well, the target substance is administered to the lachrymal fluid of the subject&#39;s eye, and the severity of dry eye can be evaluated from the movement speed of the target substance that is moving in the lachrymal fluid meniscus on the edge of the lower eyelid of the subject&#39;s eye.  
         [0040]     The overall sequence of the measurement operation in the present embodiment is substantially the same as in the previously described embodiment, except that the illumination and optical axis of imaging by the measuring apparatus are aligned in the vicinity of the lachrymal fluid meniscus along the lower eyelid of the subject&#39;s eye.  
         [0041]      FIG. 4  shows the manner in which measurement control and output display are performed in the present embodiment, and uses the same format as  FIG. 2 . The flowchart portion on the left side of  FIG. 4  is the same as in  FIG. 2 , and the format of the output display on the right side of  FIG. 4  is the same as in  FIG. 2 .  
         [0042]     In the same manner as in the previously described embodiment, the target substance is administered to the subject&#39;s eye by administering the subject&#39;s eye with an eye drop or ointment that includes the target substance, and after the target substance is administered to the subject&#39;s eye, measurement is performed according to the control sequence shown in  FIG. 4 .  
         [0043]     After the target substance is administered to the subject&#39;s eye, and blinking is confirmed in the subject&#39;s eye, the user performs a prescribed operation (using a keyboard or other device not shown in the drawing) to initiate imaging. A prescribed number of images are then captured within the prescribed imaging period in steps S 11  and S 12 . The imaging interval and number of images captured are the same as in the previously described embodiment.  
         [0044]     In step S 13 , the comparison images (t 2  and t 5 ) are displayed in the main display area  121  when two comparison images (t 2  and t 5 ) are selected using the thumbnail display area  122  of the screen  12   a  of the monitor  12  in the same manner as in the previously described embodiment.  
         [0045]     At this time, the user selects the two images that show target substances  124  and  125  which are considered to be the same.  
         [0046]     When the images of the target substances  124  and  125  are specified by being clicked on with the pointing device (mouse or the like) as indicated by the reference symbol C in step S 14 , the computation routine of step S 15  is executed, and the lachrymal fluid movement speed is computed based on the distance between the target substances  124  and  125  considered to be the same in the two comparison images t 2  and t 5 , and on the elapsed time found from the imaging time data of the comparison images t 2  and t 5 .  
         [0047]     According to the operation described above, the lachrymal fluid movement speed can be computed, and the results can be displayed as shown in the lower right of  FIG. 4 .  
         [0048]     According to the present embodiment as described above, the target substance is administered to the lachrymal fluid of the subject&#39;s eye, the illuminating light of the white light source  1  is radiated, an image of the lachrymal fluid meniscus of the subject&#39;s eye is captured two or more times at different times by the CCD camera  7 , the lachrymal fluid movement speed found from the images thus obtained can be displayed, and based on these results, the user can evaluate the severity of dry eye.  
         [0049]     Since the target substance is administered to the lachrymal fluid of the subject&#39;s eye and is imaged according to the present embodiment, the movement of the lachrymal fluid can be monitored even when an interference color does not occur, the movement speed of lachrymal fluid can be quantified regardless of the state of the subject&#39;s eye, and it is possible to overcome the drawback of the conventional configuration in which it was difficult to distinguish between a normal eye and a severely dry eye.  
         [0050]     The ophthalmic measuring apparatus of the present invention includes many components in its hardware that are shared by common configurations of ophthalmic imaging devices, and can therefore be implemented easily and at low cost using an existing ophthalmic imaging device. The ophthalmic measuring method of the present invention can also be easily and inexpensively implemented in the same manner in existing ophthalmic imaging hardware, or in partially modified hardware.