Abstract:
The present invention relates to a device and method for visual threshold measurement, which belongs to the field of optical precision measurement technology. The device comprises a first uniform plane light source system, a second uniform plane light source system, a first primary color adjusting system, a second primary color adjusting system, a first complementary color adjusting system, a second complementary color adjusting system, a first color mixture system, a second color mixture system, and a beam splitting system. The device can generate four observation targets with variable brightness (illumination), contrast, color difference, and periodic pattern frequency, by using a four-integrating sphere light source system and by multiplexing the color adjusting systems, the color mixture systems, and subsequent light paths, so as to implement multi-parameter measurement for a set of visual thresholds. One device can simultaneously measure visual illumination, contrast, and color difference thresholds, and achieve ease operation, wide range measurement, multi-measurement-parameter coverage, large color gamut adjustment range, and high light source output power.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to a device and method for visual threshold measurement, which belongs to the field of optical precision measurement technology. 
       BACKGROUND OF THE INVENTION 
       [0002]    More than 95% outside information consumed by human being are from the visual. Whether the visual characteristics are good is directly related to work and life. In clinical practices, the application of visual diagnostic equipments for early detection of visual disorders and early intervention treatments is very important. With the improvement of living standards, the emphasis on visual health is also increasing, and many new types of visual diagnostic equipments and testing technologies are developed, such as contrast sensitivity tester, chromatic meter and perimeter which are based on visual threshold measurement, and Electro-oculogram, Electroretinogram, Visual evoked potentiometer based on visual electrophysiological signals. 
         [0003]    The existing visual diagnostic equipments such as contrast sensitivity tester, chromatic meter and perimeter based on visual threshold measurement, mostly perform single parameter test and their measuring range is limited. Different kinds of instruments need to be switched to implement illumination, contrast and color vision threshold examination, which is therefore complex, time-consuming and low efficient. Moreover, without unified calibration and traceability method, it is lack of comparability between measurement results given by different instruments, and mutual recognition of test results cannot be achieved among hospitals. Although relevant metrological research has been carried out for some visual diagnostic equipment and several national standards are established for optometry equipments such as refractometer, focimeter, refractor heads and so on, the calibration and traceability for visual diagnostic equipment based on visual threshold hasn&#39;t been solved yet. Further in-depth study on calibration and traceability method for visual diagnostic equipments is key to medical metrology during China&#39;s “twelfth five-year” period. 
       SUMMARY OF THE INVENTION 
       [0004]    The present invention is to provide a multi-functional integrated device for measurement of both vision illumination, contrast and color difference threshold of human eye, with output parameters realizing real-time control and accurate calibration. The invention of the device for measuring visual threshold can produce four observable targets: luminance (illumination), contrast, chromaticity and frequency variable cycle pattern, for accurate examination of illumination, contrast and color difference threshold of human eye. 
         [0005]    The aim of the present invention is achieved by the following technical solutions. 
         [0006]    The device used to measure visual threshold includes the first uniform plane light source, the second uniform plane light source, the first primary color adjusting system, the second primary color adjusting system, the first complementary color adjusting system, the second complementary color adjusting system, the first color mixture system, the second color mixture system and beam splitting system. 
         [0007]    Among them, the first uniform plane light source includes the first light source and the first small integrating sphere; the second uniform plane light source includes the second light source and the second small integrating sphere; the first primary color adjusting system includes the first filter disc and the first block disc; the second primary color adjusting system is as same as the first one; the first complementary color adjusting system includes the second filter disc and the second block disc; the second complementary color adjusting system is as same as the first one; the first color mixture system includes the first big integrating sphere; the second color mixture system includes the second big integrating sphere; beam splitting system consists of a cubic splitting prism, target plate, the first reticle and the second reticle. 
         [0008]    Each small integrating sphere has one input port and two exit ports which are at 90° to each other. Each big integrating sphere has one exit port, one detector port and two input ports which are at 90° to each other. Moreover, two exit ports of the first and second big integrating sphere are oriented at 90° to each other in the horizontal plane. 
         [0009]    The connection relationship of the above parts is: The first light source is located at the input port of the first small integrating sphere and light enters into it through the input port. The first primary color adjusting system is located between the exit port of the first small integrating sphere and input port of the first big integrating sphere. The second primary color adjusting system is located between the other exit port of the first small integrating sphere and input port of the second big integrating sphere. Light with color and intensity of illumination based on three primary colors of red, green and blue is produced by joint action of color mixture system with the first and second primary color adjusting system. The second light source is located at the input port of the second small integrating sphere. The first complementary color adjusting system is located between the exit port of the second small integrating sphere and the other input port of the first big integrating sphere. The second complementary color adjusting system is located between the other exit port of the second small integrating sphere and the other input port of the second big integrating sphere. Another light with color and illumination is produced by joint action of color mixture system with the first and second complementary color adjusting system. However the three primary colors are not red, green and blue. 
         [0010]    The exit port of the first big integrating sphere is directly facing one plane of the cubic splitting prism, and the exit port of the second big integrating sphere facing the other adjacent plane; the center of cubic splitting prism coincides with the intersection point of centerlines of exit port of the first and second big integrating spheres. The cubic splitting prism is used to generate observation targets by overlaying emergence light from the first and second big integrating sphere; Target plate is located close to the exit port of the first integrating sphere when taking contrast measurement. When taking color difference measurement, the first and second reticle, a set of conjugate reticle, is located close to two adjacent surfaces of cubic splitting prism with right angle. When observable for measurement of illumination and contrast threshold is generated, the target plate is used in the exit port of the first big integrating sphere, by switching different multiple target plates with different spatial frequency, observation targets with different spatial frequency can be generated. 
         [0011]    Described target plates are with different spatial frequencies. By switching different target plate different observation targets can be generated. 
         [0012]    The first and the second reticle described above have different patterns which are conjugate. They are used to generate two conjugate images with similar color for color difference measurement. 
         [0013]    The described first primary color adjusting system consists of the first filter disc and the first block disc which are in turn placed parallel; the second primary color adjusting system has the same structure as the first one; the first complementary color adjusting system consists of the second filter disc and the second block disc which are placed in parallel too; the second complementary color adjusting system has the same structure as the first one. 
         [0014]    The described first filter disc includes red filter, green filter and blue filter in order to generate red, green and blue primary colors. Each filter is fan shaped with 120° angle, and the plane constructed by the red, green and blue filter can completely block the exit port of first small integrating sphere and input port of the first big integrating sphere; The described second filter disc includes yellow filter, magenta filter and cyan filter in order to generate three other primary colors more than red, green and blue. Also the plane constructed by the yellow, magenta and cyan filter can completely block the exit port of second small integrating sphere and the other input port of the first big integrating sphere; The above six filters can be moved radially. The first block disc has the same structure as the first filter disc which includes three black light barriers, and the second block disc has the same structure as the second filter disc which also includes three black light barriers; the above six black light barriers can be moved radially too. By moving black light barriers radially of the first and second block discs the rays of light through the optical area will be changed, and then light with special color or illumination will be obtained at the exit port of big spheres. 
         [0015]    In the described visual threshold measurement device, all interfaces should ensure no light leakage. 
         [0016]    The method to realize the visual threshold measurement by the use of the device described in the present invention is. 
         [0017]    (1) Color difference threshold measurement, the following provides specific steps: 
         [0018]    The first light source light through the first small integrating sphere enters into the first primary color adjusting system. After the joint action of the first filter disc and block disc, light is into the first big integrating sphere. The second light source light through the second small integrating sphere enters into the first complementary color adjusting system. After the joint action of the second filter and block disc, the light is into the first big integrating sphere. Two beams of light are mixed by the first integrating sphere and a colored uniform light emits out of the exit port. The first light source light through the first small integrating sphere enters into the second primary color adjusting system. After the joint action of inside filter and block disc, the light is into the second big integrating sphere. The second light source light through the second small integrating sphere enters into the second complementary color adjusting system. After the joint action of inside filter and block disc, the light is into the second big integrating sphere. Two beams of light are mixed by the second integrating sphere and another uniform colored light emits out of the exit port. Then two beams of light pass through the first and second reticle respectively. After the action of cubic splitting prism observation target is generated for the measurement of color difference threshold. 
         [0019]    Illumination threshold measurement, the following provides specific steps: 
         [0020]    Method 1: The first light source light through the first small integrating sphere enters into the first primary color adjusting system. After the action of the color adjusting system, light is into the first big integrating sphere. Then light with special illumination emits out of its exit port. The uniform light shines on the target plate and observation target with different illumination for threshold measurement is obtained. 
         [0021]    Method 2: The second light source light through the second small integrating sphere enters into the first complementary color adjusting system. After the action of the color adjusting system, light is into the first big integrating sphere. Light with special illumination emits out of its exit port. The uniform light shines on the target plate and observation target with different illumination for threshold measurement is obtained. 
         [0022]    Method 3: The first light source light through the first small integrating sphere enters into the first primary color adjusting system and the first big integrating sphere in turn; the second light source light through the second small integrating sphere enters into the first complementary color adjusting system and the first big integrating sphere in turn; two beams of light is mixed by the first big integrating sphere and light with illumination emits out of the exit port. The uniform light shines on the target plate and observation target with different illumination for threshold measurement is obtained. 
         [0023]    When taking illumination threshold measurement, filter discs in primary and complementary color adjusting systems should be all moved out and only black light barriers are in the optical path. 
         [0024]    Contrast threshold measurement, the following provides specific steps: 
         [0025]    Method 1: The first light source light through the first small integrating sphere enters into the first primary color adjusting system and the first big integrating sphere in turn. Light with special illumination emits out and shines on the target plate with different spatial frequency, and then enters into the cubic splitting prism. Observation targets with different spatial frequency can be obtained by switching different target plates. The second light source light through the second small integrating sphere enters into the second complementary color adjusting system and the second big integrating sphere in turn. Another light with special illumination emits out and enters into the cubic splitting prism. Two beams of light mix in the splitting system and observation target for contrast threshold measurement is obtained. 
         [0026]    Method 2: The first light source light through the first small integrating sphere enters into the first primary color adjusting system and the first big integrating sphere in turn. Light with special illumination emits out and shines on the target plate with different spatial frequency, and then enters into the cubic splitting prism. Observation targets with different spatial frequency can be obtained by switching different target plates. The first light source light through the first small integrating sphere enters into the second primary color adjusting system and the second big integrating sphere in turn. Another light with illumination emits out and enters into the cubic splitting prism. Two beams of light mix in the splitting system and observation target for contrast threshold measurement is obtained. 
         [0027]    Method 3: The second light source light through the second small integrating sphere enters into the first complementary color adjusting system and the first big integrating sphere in turn. Light with special illumination emits out and shines on the target plate with different spatial frequency, and then enters into the cubic splitting prism. Observation targets with different spatial frequency can be obtained by switching different target plates. The second light source light through the second small integrating sphere enters into the second complementary color adjusting system and the second big integrating sphere in turn. Another light with special illumination emits out and enters into the cubic splitting prism. Two beams of light mix in the splitting system and observation target is obtained for contrast threshold measurement. 
         [0028]    Method 4: The second light source light through the second small integrating sphere enters into the first complementary color adjusting system and the first big integrating sphere in turn. Light with special illumination emits out and shines on the target plate with different spatial frequency, and then enters into the cubic splitting prism. Observation targets with different spatial frequency can be obtained by switching different target plates. The first light source light through the first small integrating sphere enters into the second primary color adjusting system and the second big integrating sphere in turn. Another light with illumination emits out and enters into the cubic splitting prism. Two beams of light mix in the splitting system and observation target is obtained for contrast threshold measurement. 
         [0029]    When the contrast threshold measurement is performed, filter discs in primary and complementary color adjusting systems should be all moved out and only black light barriers are in the optical path. 
         [0030]    Beneficial Effects 
         [0031]    1. The present invention relates to a device and method for visual threshold measurement. By the use of the four integrating sphere system, color adjusting system, color mixture system and subsequent optical path, four observable targets including luminance (illumination), contrast, chromaticity and frequency variable cycle pattern can be generated. The device realizes measurement of illumination, contrast and color difference threshold simultaneously with the advantage of convenient operation, large color adjustment range and big light output power. 
         [0032]    2. The present invention relates to a device and method for visual threshold measurement. Output parameters of the device can be real-time controlled and accurately calibrated by the use of metrological instruments such as spectrometer, illuminometer and so on. As a result, the calibration and traceability of the whole device can be realized and measurement results can be guaranteed to be accurate and reliable. On the basis of the achievement, standard device for visual threshold measurement can be established and calibration or traceability of visual threshold diagnostic equipments can be realized. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0033]      FIG. 1  is a left view of the spatial structure of the visual threshold measurement device in present invention; 
           [0034]      FIG. 2  is a top view of the spatial structure of the visual threshold measurement device in present invention; 
           [0035]      FIG. 3  is a schematic diagram for the visual threshold measurement device in present invention; 
           [0036]      FIG. 4  is an inside structure of primary and complementary color adjusting system; where, “a” is for primary color adjusting system and “b” is for complementary color adjusting system; 
           [0037]      FIG. 5  is an example for one application of the visual threshold measurement device in present invention; 
           [0038]      FIGS. 6A-6C  is an example for optical path design to generate observation targets of color difference measurement;  FIG. 6A  is pattern of the first reticle,  FIG. 6B  is pattern of the second reticle, and  FIG. 6C  is the schematic optical system; 
           [0039]      FIG. 7  is an example for the design of target plates used for contrast threshold measurement. 
       
    
    
       [0040]    Where,  1 —the first light source,  2 —the first small integrating sphere,  3 —the second light source,  4 —the second small integrating sphere,  5 —the first big integrating sphere,  6 —the second big integrating sphere,  7 —the first primary color adjusting system,  8 —the second primary color adjusting system,  9 —the first complementary color adjusting system,  10 —the second complementary color adjusting system,  11 —cubic splitting prism,  12 —target plate,  13 —the first reticle,  14 —the second reticle,  15 —the first filter disc,  16 —the first block disc,  17 —the second filter disc,  18 —the second block disc,  19 —red filter,  20 —greeen filter,  21 —blue filter,  22 —black light barrier,  23 —yellow filter,  24 —cyan filter,  25 —magenta filter,  26 —illuminometer,  27 -spectrometer,  28 —the first probe,  29 —the second probe,  30 —optical fiber. 
       DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0041]    The invention is further explained with the combination of accompanying figures and example. 
         [0042]    The device for visual threshold measurement consists of the first uniform plane light source (including the first light source  1  and the first small integrating sphere  2 ), the second uniform plane light source (including the second light source  3  and the second small integrating sphere  4 ), the first primary color adjusting system  7 , the second primary color adjusting system  8 , the first complementary color adjusting system  9 , the second complementary color adjusting system  10 , the first color mixture system (including the first big integrating sphere  5 ), the second color mixture system (including the second big integrating sphere  6 ) and beam splitting system (including cubic splitting prism  11 , target plate  12 , the first reticle  13  and the second reticle  14 ), as shown in  FIG. 1 ,  FIG. 2  and  FIG. 3 . 
         [0043]    Each small integrating sphere has one input port and two exit ports which are at 90° to each other. Each big integrating sphere has one exit port, one detector port and two input ports which are at 90° to each other too. Moreover, two exit ports of the first and second big integrating spheres are oriented at 90° to each other in the horizontal plane. 
         [0044]    The first light source  1  is located at the input port of the first small integrating sphere  2  and light enters into it through the input port. The first primary color adjusting system  7  is located between the exit port of the first small integrating sphere  2  and input port of the first big integrating sphere  5 . The second primary color adjusting system  8  is located between the other exit port of the first small integrating sphere  2  and input port of the second big integrating sphere  6 . Light with color and intensity of illumination based on the three primary colors of red, green and blue is produced by the joint action of color mixture system with the first and second primary color adjusting system. The second light source  3  is connected with the input port of the second small integrating sphere  4 . The first complementary color adjusting system  9  is located between the exit port of the second small integrating sphere  4  and the other input port of the first big integrating sphere  5 . The second complementary color adjusting system  10  is located between the other exit port of the second small integrating sphere  4  and the other input port of the second big integrating sphere  6 . Light with color and illumination is produced by the joint action of color mixture system with the first and second complementary color adjusting system. However the three primary colors are not red, green and blue. The exit port of the first big integrating sphere  5  is directly facing one plane of the cubic splitting prism  11 , and the exit port of the second big integrating sphere  6  facing the other adjacent right angle plane. The center of the cubic splitting prism  11  is coinciding with the intersection point of centerlines of exit port of the first  5  and second big integrating spheres  6 . 
         [0045]    The probe of illuminometer  26  is located at the exit port of the first big integrating sphere  5  in order to detect the exit surface illumination at real time. Dual-channel spectrometer  27  has two probes: the first probe  28  and the second probe  29 . The first probe  28  is located at the detector port of the first big integrating sphere  5  and the second probe  29  is located at the detector port of the second big integrating sphere  6 . Two probes are connected with spectrometer  27  with optical fiber  30 , so that the spectral distribution of the light emitted from the first big integrating sphere  5  and the second big integrating sphere  6  can be real-time monitored, as shown in  FIG. 5 . 
         [0046]    The first primary color adjusting system  7  consists of the first filter disc  15  and the first block disc  16  which are in turn placed parallel; the second primary color adjusting system has the same structure as the first one and inside structure is shown in  FIG. 4A ; the first complementary color adjusting system  9  consists of the second filter disc  17  and the second block disc  18  which are in turn placed parallel too; the second complementary color adjusting system has the same structure as the first one and inside structure is shown in  FIG. 4B . 
         [0047]    The first filter disc  15  includes red filter  19 , green filter  20  and blue filter  21  in order to generate red, green and blue primary colors. Each filter is fan shaped with 120° angle, and the plane constructed by the red  19 , green  20  and blue filter  21  can completely block the exit port of first small integrating sphere  2  and input port of the first big integrating sphere  5 ; The second filter disc  17  includes yellow filter  23 , cyan filter  24  and magenta filter  25  in order to generate three other primary colors more than red, green and blue. Also the plane constructed by the yellow  23 , cyan  24  and magenta filter  25  can completely block the exit port of the second small integrating sphere  4  and the other input port of the first big integrating sphere  5 ; The above six filters can be moved radially. The first block disc  16  has the same structure as the first filter disc  15  which includes three black light barriers  22 , and the second block disc  18  has the same structure as the second filter disc  17  which also includes three black light barriers; the above six black light barriers can be moved radially too. By radially moving black light barriers of the first  16  and second block discs  18 , the light through the optical areas can be changed, and then light with special color or illumination can be obtained at the exit port of big spheres. 
         [0048]    In the example of the invention, the first light source  1  and the second light source  3  both use halogen lamp. 
         [0049]    As shown in  FIG. 5 , the steps to generate four observables used for measurement of visual threshold are listed below: 
         [0050]    First, open the power supply of the first  1  and second light source  3 . Light and preheat the halogen lamps to illuminate stably. The first light source  1  and the first small integrating sphere  2  form the first uniform plane light source, and the second light source  3  and the second small integrating sphere  4  form the second uniform plane light source, which are used to produce uniform emergent light with continuous spectrum. 
         [0051]    (1) The steps for color difference threshold measurement: 
         [0052]    The first light source  1  light through the first small integrating sphere  2  enters into the first primary color adjusting system  7 . After the joint action of the first filter disc  15  and block disc  16 , the light is into the first big integrating sphere  5 . The second light source  3  light through the second small integrating sphere  4  enters into the first complementary color adjusting system  9 . After the joint action of the second filter disc  17  and block disc  18 , the light is into the first big integrating sphere  5 . Two beams of light are mixed by the first integrating sphere  5  and uniform colored light emits out of the exit port. The first light source  1  light through the first small integrating sphere  2  enters into the second primary color adjusting system  8 . After the joint action of inside filter and block disc, the light is into the second big integrating sphere  6 . The second light source  3  light through the second small integrating sphere  4  enters into the second complementary color adjusting system  10 . After the joint action of inside filter and block disc, the light is into the second big integrating sphere  6 . Two beams of light are mixed by the second integrating sphere  6  and another uniform colored light emits out of the exit port. Light emitted from the first big integrating sphere  5 , through a frosted glass, shines on the first reticle  13  and a colored pattern is produced. Light emitted from the second big integrating sphere  6 , through another frosted glass, shines on the second reticle  14  and another colored pattern is produced. Two beams of light pass through the cubic splitting prism  11  and mix. Observation target for color difference threshold measurement is then generated. A pattern with mixing color can be seen or detected by eyes or equipment under test. 
         [0053]    By the use of fiber optic spectrometer, the specific color parameters of the two patterns can be measured, such as Lab chromaticity coordinate, X/Y/Z value and so on. Then the color difference ΔE for these two colors is calculated with computer. With the control of the color of emitted light from the first and second uniform plane light source, the color difference ΔE can be changed close to the threshold of eye or equipment under test, as shown in  FIG. 6C . 
         [0054]    The conjugate pattern on two sets of reticles is shown in  FIGS. 6A and 6B ,  6 A is the pattern on the first reticle and  6 B is that on the second reticle. Wherein the white part is the transparent glass substrate and black part is the opaque coating. 
         [0055]    With the first probe  28  and the second probe  29  of dual-channel spectrometer connected, the color of emitted light from the first  5  and second big integrating sphere  6  is real-time monitored. With the feedback to the first primary color adjusting system  7 , the second primary color adjusting system  8 , the first complementary color adjusting system  9  and the second complementary color adjusting system  10 , light through the optical area is changed by radially moving the inside black light barriers and corresponding color light is obtained. 
         [0056]    (2) The steps for illumination threshold measurement: 
         [0057]    The first light source  1  light through the first small integrating sphere  2  enters into the first primary color adjusting system  7 . With the action of block disc  16 , light with special illumination is emitted out of the exit port of the first big integrating sphere  5  and observation target with different illumination for threshold measurement is obtained. 
         [0058]    Light emitted from the first big integrating sphere  5  is real-time monitored by illuminometer  26 . With the feedback of the light illumination to the first primary color adjusting system  7 , light through the optical area is changed by radially moving the inside black light barriers and as a result corresponding illumination is obtained. 
         [0059]    (3) The steps for contrast threshold measurement: 
         [0060]    The first light source  1  light through the first small integrating sphere  2  enters into the first primary color adjusting system  7 . With the action of the first block disc  15 , light with special illumination emitted from the first big integrating sphere  5  shines on the target plate  12  with different spatial frequency, and then enters into the cubic splitting prism  11 . The second light source  3  light through the second small integrating sphere  4  enters into the second complementary color adjusting system  10 . With the action of the inside block disc, another light with special illumination emits out of the second big integrating sphere  6  and enters into the cubic splitting prism  11 . Two beams of light mix in the splitting system and observation target is obtained for contrast threshold measurement. In the example of this invention, a kind of transmissive grating optotype is designed for contrast threshold measurement according to the Weber-Fechner law, which includes five different spatial frequency listed in table 1. They are scored on five target plates and there are four different direction (0°, 45°, 90° and 135°) of grating strips for each spatial frequency target. An example of the target plate is shown in  FIG. 7 . 
         [0000]    
       
         
               
             
               
               
               
             
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Spatial frequency and cycle 
               
             
          
           
               
                 No. 
                 spatial frequency c/d 
                 cycle (mm) 
               
               
                   
               
             
          
           
               
                 1 
                 1.5 
                 3.49 
               
               
                 2 
                 3.0 
                 1.75 
               
               
                 3 
                 6.0 
                 0.87 
               
               
                 4 
                 12.0 
                 0.44 
               
               
                 5 
                 18.0 
                 0.36 
               
               
                   
               
             
          
         
       
     
         [0061]    When observable for measurement of illumination and contrast threshold is generated, only black light barriers in the primary and complementary color adjusting systems are used and inside filters are all moved out of the optical path completely. 
         [0062]    The present invention relates to a device and method for visual threshold measurement by generating four observable targets including luminance (illumination), contrast, chromaticity and frequency variable cycle pattern. By comparison with other test methods it has the advantage of convenient operation, simple structure, large color adjustment range and big light output power. Moreover, output parameters of the device can be real-time controlled and accurate calibrated, which is very important for realization of calibration and traceability for quantity values. In this way measurement results are guaranteed to be accurate and reliable. 
         [0063]    Above in connection with the accompanying figures, an example of the invention has been explained; however these instructions should not be construed as scope limitation of the invention. The protection scope of the invention is defined and limited by the appended claims, and any modifications based on the claims are within the protection scope of the invention.