Abstract:
A portable visual acuity examination device comprises a mounting unit that can be mounted in front of eyes either using or not using eyeglasses, a visual target displaying unit that uses an organic EL display panel, a display controlling unit that changes the visual target displayed on the displaying unit, an inputting unit for visual target viewing results, and a transmitting unit for measurement results. The portable visual acuity examination device comprises an optical system that can change the distance at which the visual target virtual image is visible. The portable visual acuity examination device detects whether eyeglasses are used and matches an uncorrected vision acuity examination and a corrected vision acuity examination. The portable visual acuity examination device switches between a C-type visual target and an E-type visual target. With data display, both the right and left display units are enabled.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a visual acuity test device and a visual acuity test system. 
       BACKGROUND ART 
       [0002]    Visual acuity tests are performed by letting a subject recognize a visual acuity chart on which are displayed C shape Landolt rings, which are commonly used in Japan, or E shape letters of a Tumbling E chart, which are commonly used in the United States, etc., or alphabets in a Snellen chart. Thereby far-vision visual acuity, near-vision visual acuity, etc., are measured. Use of automatic visual acuity test devices has been proposed in which, instead of a tester letting a subject read aloud the recognition result of a visual target of a visual acuity chart pointed by the tester, a visual target is displayed in a housing into which the subject can look, and a subject by himself/herself can input the recognition result of a visual target by operating a joystick lever (Patent Document 1). 
       LIST OF CITATIONS 
     Patent Literature 
     Patent Document 1: JP-A-2005-296402 
     SUMMARY OF THE INVENTION 
     Technical Problem 
       [0003]    However, there are yet many problems to be studied in relation to visual acuity test devices and visual acuity test systems. 
         [0004]    In view of the above, an object of the present invention is to provide improved visual acuity test devices and improved visual acuity test systems. 
       Means for Solving the Problem 
       [0005]    According to one feature of the present invention, a portable visual acuity test device includes a mount worn in front of an eye, a display which displays a visual target for a visual acuity test, a display controller which switches visual targets displayed on the display, an input unit to which the recognition result of a visual target is inputted, and a transmitter which transmits a measurement result. It is thereby possible to obtain a portable visual acuity test device that can be worn on a person&#39;s head. 
         [0006]    According to a specific feature, the display comprises an organic electroluminescence display panel. It is thereby possible to achieve display of black in display of a black and white visual target. 
         [0007]    According to another specific feature, the portable visual acuity test device includes an optical system which permits adjustment of a distance at which a virtual image of the visual target is seen. It is thereby possible to obtain a portable visual acuity test device that can measure far-vison visual acuity and near-vision visual acuity. 
         [0008]    According to another specific feature, the mount is mountable in front of the eye both in an eyeglasses-worn state and in a naked-eye state. It is thereby possible to obtain a portable visual acuity test device that can measure naked-eye visual acuity and corrected visual acuity. According to a more specific feature, the portable visual acuity test device includes a detector which detects whether or not eyeglasses are worn. According to an even more specific feature, the detector determines a relationship between whether an intended test is a naked-eye visual acuity test or a corrected visual acuity test and whether or not eyeglasses are worn. 
         [0009]    According to another specific feature, the display can switch between a C shape visual target and an E shape visual target. It is thereby possible to obtain a portable visual acuity test device that suits the use region. 
         [0010]    According to another specific feature, the display has a right-eye display and a left-eye display. In a visual acuity test, one of the right-eye display and the left-eye display is enabled, and in information display, the right-eye display and the left-eye display are both enabled. It is thereby possible to obtain a portable visual acuity test device that allows smooth measurement. According to yet another specific feature, in information display, the display displays in letters enlarged to be larger than a visual target. This also helps allow smooth measurement. 
         [0011]    According to another specific feature, the portable visual acuity test device autonomically performs a plurality of kinds of visual acuity tests. It is thereby possible to smoothly perform measurements for the right-eye, the left-eye, far-vision visual acuity, near-vision visual acuity, naked-eye visual acuity, corrected visual acuity, etc. 
         [0012]    According to another feature of the present invention, a portable visual acuity test device includes a mount worn in front of an eye, a display which displays a visual target for a visual acuity test, and an acceleration sensor. The recognition result of a visual target is inputted by a head movement. It is thereby possible to smoothly input the recognition result, and thus to smoothly proceed from the acknowledgment of display content to a visual acuity test. According to a specific feature, the recognition result of a visual acuity is determined based on a relationship between a direction of a visual target displayed on the display and a direction of a head movement. According to another specific feature, inability to recognize is inputted by a predetermined head movement. 
         [0013]    According to yet another feature of the present invention, a visual acuity test system includes a plurality of portable visual acuity test devices, and an administrator which can communicate with the portable visual acuity test devices. It is thereby possible to perform measurements with respect to a plurality of subjects concurrently. 
       Advantageous Effects of the Invention 
       [0014]    As will be seen from the above, in accordance with the present invention, it is possible to provide improved visual acuity test devices and improved visual acuity test systems. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0015]      FIG. 1  is a block diagram showing the overall configuration of a visual acuity test device and a visual acuity test system in Example 1 embodying the present invention (Example 1); 
           [0016]      FIG. 2  is a basic flow chart explaining the operation of an HMD controller in Example 1; and 
           [0017]      FIG. 3  is a flow chart showing the details of step S 36  of  FIG. 2 . 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
     Example 1 
       [0018]      FIG. 1  is a block diagram showing the overall configuration of a visual acuity test device and a visual acuity test system in Example 1 embodying the present invention. Example 1 is configured as a visual acuity test system that includes a visual acuity test device which is a google-type head-mounted portable visual acuity tester (hereinafter “portable visual acuity tester”)  2  and an administrator  4  which can perform near-field communication with the portable visual acuity tester  2 . Although, for the sake of simplicity,  FIG. 1  shows only one portable visual acuity tester  2 , the present invention is configured as a system in which a plurality of portable visual acuity testers having the same configuration are provided. The plurality of portable visual acuity testers are made capable of performing near-field communication with the administrator  4  so that visual acuity tests are concurrently performed with the portable visual acuity testers worn by a plurality of subjects on their heads respectively, and the results are transmitted to the administrator  4 , and thereby it is possible to concurrently process, in the administrator  4 , the results of the visual acuity tests taken by the plurality of subjects. As will be described later, the tests performed by the portable visual acuity testers are voluntarily taken by the subjects. Hereinafter, the configuration and function of the illustrated portable visual acuity tester  2  as a representative of the plurality of the portable visual acuity testers will be described together with those of the administrator  4 . 
         [0019]    The portable visual acuity tester  2  can be worn further in front of eyeglasses  10 , which a subject usually wears, worn in front of the subject&#39;s right and left eyes  6  and  8 , and in this state, corrected visual acuity can be measured. When the eyeglasses  10  are taken off and the portable visual acuity tester  2  alone is worn, uncorrected visual acuity can be measured. To that end, the portable visual acuity tester  2  comprises a body  2   a  and temples  2   b , and is configured such that, when the temples  2   b  are placed on the ears over the eyeglasses  10 , the body  2   a  is located in front of the lenses of the eyeglasses  10 . On the other hand, when the temples  2   b  are placed on the ears directly without the eyeglasses  10 , the portable visual acuity tester  2  is located in front of the eyes with an accommodation space left for the eyeglasses, and thus uncorrected visual acuity can be measured. In the body  2   a , an eyeglasses detector  11  is provided that detects whether or not the eyeglasses  10  are present; this makes it possible to automatically distinguish between measurement of corrected visual acuity and that of uncorrected visual acuity, and also to provide a function of giving a warning that a given state is not appropriately suitable for the purpose, for example, when the eyeglasses  10  are detected in preparation for measurement of uncorrected vision (for example, a function of displaying a warning to take off the eyeglasses) or the like. 
         [0020]    A right-eye display  12  and a left-eye display  14  inside the body  2   a  each comprise an OLED (organic light-emitting diode) display panel exploiting organic electroluminescence. The right-eye display  12  and the left-eye display  14  are each monochrome, and use an OLED (organic light-emitting diode) display panel, and this permits, when a black and white visual target for visual acuity test is shown with varying sizes and directions, black to appear distinct, contributing to visual acuity test. 
         [0021]    As will be described later, a driver  16  drives selectively either the right-eye display  12  or the left-eye display  14  based on a video signal for visual target display fed from a display controller  22  to display a right-eye visual target or a left-eye visual target on its display surface. As indicated by broken-line arrows, virtual images of a visual target displayed on the display surfaces are directed to the right and left eyes  6  and  8  along lines of sight  6   a  and  8   a  by right-eye and left-eye eyepiece optical systems  18  and  20  respectively. The right-eye and left-eye eyepiece optical systems  18  and  20  adjust the distance at which the virtual images of the visual target are seen according to whether far-vision visual acuity measurement or near-vision visual acuity measurement is performed. 
         [0022]    The portable visual acuity tester  2  further includes a head-mounted display controller (hereinafter “HMD controller”)  24 , a global positioning system terminal (hereinafter “GPS”)  25 , an acceleration sensor  26 , a memory  28 , and a near-field communication unit  30 . The HMD controller  24  controls the various functions of the portable visual acuity testers  2  based on a program stored in the memory  28 . 
         [0023]    Now, a description will be given of the function of the HMD controller  24 . First, the result of detection by the eyeglasses detector  11  is transmitted to the HMD controller  24  so that corrected or uncorrected visual acuity measurement is performed as intended as described above. Then, the HMD controller  24  transmits an optical drive signal to the driver  16  via the display controller  22 , and thereby drives the right-eye and left-eye eyepiece optical systems  18  and  20  to set whether to perform far-vision visual acuity measurement or near-vision visual acuity measurement. Meanwhile, the GPS  25  detects the region where the portable visual acuity tester  2  is being used, and transmits the result of detection to the HMD controller  24  so that the visual target data to be used is automatically switched among the visual target data stored in the memory  28  such that, for example, when the use region is in Japan, a Landolt ring is displayed as a vision target, and when the use region is in the United States, a letter of the Tumbling E chart is displayed as a vision target. Then, the HMD controller  24  controls the display controller  22  based on the visual target data stored in the memory  28  with consideration also given to a signal received from the acceleration sensor  26  so as to make the driver  16  transmit a video signal for visual target display. 
         [0024]    More specifically, the acceleration sensor  26  detects the movement of the head of a subject indicating the recognition result of a visual target, and transmits a detection signal to the HMD controller  24 . For example, when the subject moves the head in any of the up/down/left/right directions in which a cut in a Landolt ring is open (for example, on recognizing a cut on the right side, the subject turns the head to the right), the acceleration sensor  26  detects the head movement, and transmits a detection signal to the HMD controller  24 , and thereby the HMD controller  24  recognizes the response of the subject. On the other hand, for example, when the subject cannot visually recognize where the cut is in the Landolt ring, and repeatedly turns the head left and right, the acceleration sensor  26  detects the movement, and this let the HMD controller  24  know that the subject cannot respond. This function will be described in detail later. 
         [0025]    The near-field communication unit  30  communicates with the administrator  4  for exchanging information related to starting of a test and transmission of test results. The arrangement of the blocks shown in  FIG. 1  is illustrated merely for the sake of convenience of description and thus does not show an actual arrangement. Specifically, the display controller  22 , the HMD controller  24 , the acceleration sensor  26 , the memory  28 , and the near-field communication unit  30  are, in fact, small components mounted inside the body  2   a . In the body  2   a , a power supply  32  including a battery is arranged to feed electric power to components of the portable visual acuity tester  2  as mentioned above. 
         [0026]    On the other hand, the administrator  4  has a near-field communication unit  34  for communicating, via near-field radio waves (or infrared rays)  34   a , with the near-field communication unit  30  of the portable visual acuity tester  2  configured as described above. The near-field communication unit  34  can communicate also with other portable visual acuity testers (unillustrated) having a similar configuration as the portable visual acuity tester  2  by near-field radio waves (or infrared rays)  34   b  and  34   c  and the like. An administrator controller  36  in the administrator  4  controls establishment and execution of communication with the portable visual acuity testers (hereinafter, the portable visual acuity tester  2  is taken as a representative of the plurality of portable visual acuity testers), and gives the portable visual acuity tester  2  an instruction to start measurement via the near-field communication unit  34 . An operation panel  38  and a display  40  are provided to allow setting and other operations for starting of the above-described measurement. The near-field communication unit  34  receives information on the result of detection from the portable visual acuity tester  2  and stores it in a memory  42 . The memory  42  stores, in addition to various data including information on the result of detection, a program for the function of the administrator  4  which operates in coordination with the portable visual acuity tester  2 . A power supply  44  feeds electric power to components of the administrator  4  as mentioned above. 
         [0027]      FIG. 2  is a basic flow chart explaining the operation of the HMD controller  24  in Example 1 described above. The flow starts when electric power starts to be supplied to the portable visual acuity tester  2  by the power supply  32 . At step S 2 , a standby process for communicating with the administrator  4  is performed, and the flow then proceeds to step S 4 . At step S 4 , whether or not communication with the administrator  4  is established is checked, and if the communication is established, the flow proceeds to step S 6 . 
         [0028]    At step S 6 , based on detection by the GPS  25 , whether or not the use region of the portable visual acuity tester  2  is in Japan is checked. If the use region is in Japan, the flow proceeds to step S 8 , where a Landolt ring in a C shape is chosen as a visual target, and the flow then proceeds to step S 10 . On the other hand, if, at step S 6 , it is not detected that the use region is in Japan, an assumption is made that use is made in the United States or the like, and the flow proceeds to step S 12 , where a letter of the Tumbling E-chart in an E shape is chosen as a visual target, and the flow then proceeds to step S 10 . 
         [0029]    At step S 10 , whether or not there is a measurement start signal is detected. As will be described later, once the portable visual acuity tester  2  receives the first measurement start signal from the administrator  4 , it autonomically performs a scheduled measurement in a predetermined order. For example, suppose that, on receipt of, at step S 10 , a right-eye measurement start signal as the first measurement start signal from the administrator  4 , measurement operation is started and right-eye measurement is completed; then, the next time when the flow proceeds to step S 10 , by the autonomic operation of the HMD controller  24 , left-eye measurement is started based on a left-eye measurement start signal prepared by the HMD controller  24  by itself. 
         [0030]    If, at step S 10 , a measurement start signal is detected, the flow proceeds to step S 14 , where whether or not there is a near-vision measurement signal is detected. This near-vision measurement signal is autonomically prepared by the HMD controller  24  by itself according to the measurement schedule as initially instructed from the administrator  4 . At step S 10 , when measurement is started based on the first measurement start signal from the administrator  4 , measurement for far vision is started first, and thus, at step S 14 , no near-vision measurement signal is detected. 
         [0031]    If, at step S 14 , no near-vision measurement signal is detected, the flow proceeds to step S 16 , where the right-eye and left-eye eyepiece optical systems  18  and  20  are adjusted to set the distance at which virtual images of a visual target can be seen at, for example, 5 meters so that far-vision visual acuity measurement is set, and the flow then proceeds to step S 18 . On the other hand, if, at step S 14 , a near-vision measurement signal is detected, the flow proceeds to step S 20 , where the right-eye and left-eye eyepiece optical systems  18  and  20  are adjusted to set the distance at which virtual images of a visual target can be seen at, for example, 30 centimeters so that near-vision visual acuity measurement is set, and the flow then proceeds to step S 18 . 
         [0032]    At step S 18 , whether or not there is a naked-eye measurement signal is detected. This naked-eye measurement signal is autonomically prepared by the HMD controller  24  by itself according to the measurement schedule as initially instructed from the administrator  4 . At step S 10 , when measurement is started based on the first measurement start signal from the administrator  4 , measurement for naked-eye is started first, and thus, at step S 18 , a naked-eye measurement signal is detected. 
         [0033]    If, at step S 18 , a naked-eye measurement signal is detected, the flow proceeds to step S 22 , where whether or not the eyeglasses  10  are detected by the eyeglasses detector  11  is checked. If there are no eyeglasses detected, a naked-eye measurement state is confirmed, and thus the flow proceeds to step S 24 . On the other hand, if, at step S 22 , detection of the eyeglasses by the eyeglasses detector  11  is confirmed, the flow proceeds to step S 26 , where a warning requesting removal of the eyeglasses  10  unnecessary for naked-eye measurement is displayed on each of the right-eye and left-eye displays  12  and  14 , and the flow then returns to step S 18 . Then, the loop of steps S 18 , S 22 , and S 26  is repeated until the naked-eye measurement signal is no longer detected at step S 18  or the eyeglasses  10  are removed and are no longer detected at step S 22 . 
         [0034]    If, at step S 18 , no naked-eye measurement signal is detected, corrected visual acuity measurement is assumed to be performed, and the flow proceeds to step S 28 . At step S 28 , whether or not the eyeglasses  10  are detected by the eyeglasses detector  11  is checked, and if the eyeglasses  10  are detected, a corrected visual acuity measurement state is confirmed, and thus the flow proceeds to step S 24 . On the other hand, if, at step S 28 , detection of the eyeglasses by the eyeglasses detector  11  is not confirmed, the flow proceeds to step  30 , where a warning requesting wearing of the eyeglasses  10  necessary for corrected visual acuity measurement is displayed on each of the right-eye and left-eye displays  12  and  14 , and the flow then returns to step S 18 . Then, the loop of steps S 18 , S 28 , and S 30  is repeated until the naked-eye measurement signal is detected at step S 18  or the eyeglasses  10  are worn and are detected at step S 28 . 
         [0035]    Through the processes described above, when an intended measurement state is confirmed, the flow proceeds to step S 24 , where a message of instructions for use of the portable visual acuity tester  2  is displayed on each of the right-eye and left-eye displays  12  and  14 , and the flow then proceeds to step S 32 . In this state, a person who has poor eyesight may be in a naked-eye state, and thus the message is displayed in enlarged letters so as to be visually recognized with both eyes. The same applies to the warning display at step S 30 , and a person who has poor eyesight may be in the naked-eye state, and thus the warning is displayed in enlarged letters so as to be visually recognized with both eyes. 
         [0036]    At step S 32 , by the acceleration sensor  26 , whether or not an acceleration change based on the nodding movement (repeated up/down movement) of the head of a subject indicating his/her acknowledgment of the usage is detected is checked. If, at step S 32 , the acknowledging acceleration is detected, the flow proceeds to step S 34 . On the other hand, if the acknowledging acceleration is not detected, the flow returns to step S 24 , and thereafter, until the acknowledging acceleration is detected, steps S 24  and S 32  are repeated, and the message of instructions for use continues to be displayed. 
         [0037]    When the flow proceeds to step S 34 , a measurement program starts, and the flow proceeds to step S 36 , where a measurement process is performed. The details will be described later. When the measurement process at step S 36  is completed, the flow proceeds to step S 38 . If, at step S 4 , establishment of communication with the administrator  4  cannot be confirmed, the flow immediately jumps to step S 38 . Also, if, at step S 10 , no measurement start signal is detected, the flow immediately jumps to step S 38 . Cases in which no measurement start signal is detected at step S 10  include, in addition to a situation where a measurement start signal has not yet been received from the administrator  4 , a situation where all the scheduled measurements have been completed and thus no more measurement start signal is autonomically prepared by the portable visual acuity tester  2 . 
         [0038]    At step S 38 , whether or not electric power continues to be supplied to the portable visual acuity tester  2  is checked. If it is confirmed that electric power is being supplied, the flow returns to step S 4 , and thereafter, steps S 4  through S 38  are repeated to perform a scheduled measurement while coping with various situation changes. On the other hand, if, at step S 38 , it is not confirmed that electric power is being supplied, the flow ends. 
         [0039]      FIG. 3  is a flow chart showing the details of the measurement process at step S 36  in  FIG. 2 . When the flow starts, at step S 42 , whether or not there is a near-vision measurement signal is checked. If no near-vision measurement signal is detected, a normal far-vision visual acuity measurement state is assumed, and the flow proceeds to step S 44 , where a setting is made to record the result of the far-vision visual acuity measurement, and the flow then proceeds to step S 46 . On the other hand, if, at step S 42 , a near-vision measurement signal is detected, the flow proceeds to step S 48 , where a setting is made to record the result of the near-vision visual acuity measurement, and the flow then proceeds to step S 46 . 
         [0040]    At step S 46 , whether or not there is a naked-eye measurement signal is checked. If a naked-eye measurement signal is detected, normal naked-eye measurement is to be performed, and thus the flow proceeds to step S 50 , where a setting is made to record the result of the naked-eye visual acuity measurement, and the flow then proceeds to step S 52 . On the other hand, if, at step S 46 , no naked-eye measurement signal is detected, corrected visual acuity measurement is assumed to be performed, and the flow proceeds to step S 54 , where a setting is made to record the result of the corrected visual acuity measurement, and the flow then proceeds to step S 52 . 
         [0041]    At step S 52 , whether or not there is a right-eye measurement signal is checked. If a right-eye measurement signal is detected, the flow proceeds to step S 56 , where a setting is made to record the result of the right-eye visual acuity measurement, and then to step S 58 , where a visual target is displayed only on the right-eye display  12 , the flow then proceeding to step S 60 . Here, nothing is displayed on the left-eye display  14 , which is thus in a dark state. On the other hand, if, at step S 52 , no right-eye measurement signal is detected, left-eye measurement is assumed to be performed, and the flow proceeds to step S 62 , where a setting is made to record the result of the left-eye visual acuity measurement, and then to step S 64 , where a visual target is displayed only on the left-eye display  14 , the flow then proceeding to step S 60 . Here, nothing is displayed on the right-eye display  12 , which is thus in a dark state. 
         [0042]    At step S 60 , an initial visual target of a predetermined size is displayed. As this initial visual target, one based on standard visual acuity is adopted, but if there is history data of the subject, a visual target based on the latest visual acuity is adopted. Then, the flow proceeds to step S 66 , where whether or not a predetermined time (the time taken to assume that the subject cannot visually recognize, for example, two seconds) has elapsed since the start of display is checked. If the predetermined time has not yet elapsed, the flow proceeds to step S 68 , where whether or not an acceleration change based on the head-shaking movement (repeated left- and rightward movement of the head) of the subject is detected is checked. This corresponds to the subject voluntarily admitting his/her inability to recognize the visual target before the lapse of the above-mentioned predetermined time. If, at step S 68 , the head-shaking acceleration is not detected, the flow proceeds to step S 70 . 
         [0043]    At step S 70 , whether or not responding acceleration is detected is checked. A responding movement that produces such acceleration is performed by a subject according to the instructions for use. For example, having found a cut in a Landolt ring at the top, the subject performs a movement involving relatively quickly moving the head slightly up and then returning the head slowly. Likewise, having found a cut in a Landolt ring at the bottom, the subject performs a movement involving relatively quickly moving the head slightly down and then returning the head slowly. Having found a cut in a Landolt ring at the right, the subject performs a movement involving relatively quickly moving the head slightly to the right and then returning the head slowly. Having found a cut in a Landolt ring at the left, the subject performs a movement involving relatively quickly moving the head slightly to the left and then returning the head slowly. If, at step S 70 , any such acceleration is detected, the flow proceeds to step S 72 . On the other hand, if, at step S 70 , no responding acceleration is detected, the flow returns to step S 66 , and thereafter, until the predetermined time has elapsed, head-shaking acceleration is detected, or responding acceleration is detected, steps S 66  through S 70  are repeated to receive any response. 
         [0044]    At step S 72 , whether or not the detected responding acceleration coincides with the direction of the cut in the Landolt ring, that is, whether or not a correct response is detected, is checked, and if so, the flow proceeds to step S 74 , where the fact of the correct response is recorded along with the size of the visual target. On the other hand, if the predetermined time has elapsed at step S 66 , or if head-shaking acceleration is detected at step S 68 , or if a correct response is not detected at step S 72 , the flow proceeds to step S 76 . 
         [0045]    At step S 76 , visual targets are changed, and a visual target enlarged to the next level size according to a visual acuity test criterion is displayed to permit easier recognition, and the flow returns to step S 66 . Thereafter, until a correct response is detected at step S 72 , steps S 66  through S 72  and step S 76  are repeated, and the visual target is sequentially enlarged until it can be visually recognized. 
         [0046]    If, at step S 74 , the correct response is recorded, the flow proceeds to step S 78 , where whether or not the correct response recorded at step S 74  is the third correct response to a visual target of the same size is checked. If correct responses have not yet been detected three times, the flow proceeds to step S 82 , where a visual target reduced to the next level size according to the visual acuity test criterion is displayed, and the flow then returns to step S 66 . Thereafter, as long as, despite size reduction of the visual target, correct responses continue to be detected at step S 74 , steps S 66  through S 74 , step S 78 , and step S 82  are repeated with sequential size reduction. As long as this continues, the correct responses recorded at step S 74  are correct responses to visual targets of different sizes, and thus the flow proceeds from step S 78  to step S 82  repeatedly. 
         [0047]    By contrast, as a result of size reduction of the visual target at step S 82 , if, at step S 72 , a correct response can no longer be detected, the flow proceeds to step S 76 , where, this time, the visual target is enlarged. As a result, if, the next time the flow proceeds to step S 72 , a correct response is detected, the correct response can be a correct response to a visual target having the same size as that of the visual target to which the correct response was detected previously. As a result of the visual target being repeatedly enlarged or reduced around the size of the limit of visual recognition in this way, if, at step S 78 , it is recognized that correct responses have been detected three times to visual targets of the same size, the flow proceeds to step S 80 , where the visual acuity is determined based on the size of the visual targets to which correct responses have been detected three times, and the flow then proceeds to step S 84 . 
         [0048]    At step S 84 , whether or not all the scheduled measurements have been completed based on the instructions from the administrator  4  is checked. Then, if there is an uncompleted measurement, the flow proceeds to step S 86 , where a subsequent measurement start signal is prepared, and the flow then ends. As a result, the flow returns, via step S 38  in  FIG. 2 , to step S 4 , and if a subsequent measurement start signal is detected at step S 10 , the flow proceeds, through the intervening steps, to step S 36 , and measurement proceeds according to the flow in  FIG. 3 . For example, in  FIG. 3 , right-eye measurement is completed, and a measurement start signal for left-eye measurement is prepared at step S 86 ; then, in  FIG. 2 , when the flow reaches step S 10  again, the measurement start signal for left-eye measurement is detected, and the flow then proceeds again to step S 36 , where a measurement process for the left-eye is performed. On the other hand, if, at step S 84 , it is detected that all the scheduled measurements have been completed, the flow proceeds to step S 88 , where the results of all the measurements are transmitted to the administrator  4 , and the flow then ends. In this case, no subsequent measurement start signal is prepared, and thus even when the flow returns to step S 10  in  FIG. 2 , the flow immediately proceeds to step S 38 , where the portable visual acuity tester  2  ends the autonomic measurement. The potable visual acuity tester  2  then waits to receive a subsequent measurement start signal. 
         [0049]    The above-described various features and advantages of the present invention are not limited to those specifically described by way of a practical example above. For example, the instructions for use at step S 24  and the warnings at step S 26  and at step S 30  are not limited to those visually displayed like the ones mentioned in the practical example. For example, a configuration may be adopted in which an earphone is provided in the portable visual acuity tester  2  so that, by driving the earphone by the HMD controller  24 , instructions and warnings are given with a voice that can be heard only by a subject. 
         [0050]    Although, in the practical example, the C shape visual target and the E shape visual target are automatically switched with each other by the GPS  25 , it is also possible to adopt a configuration where, instead of a GPS or the like being provided in the portable visual acuity tester  2 , visual targets are switched according to instructions from the administrator  4 . Although, in the practical example, the communication between the administrator  4  and the portable visual acuity tester  2  is performed wirelessly, the communication may be performed on a wired basis. With a wired cable, electric power can be supplied across it; this makes it possible to adopt a configuration in which electric power is supplied via the cable from the power supply  44  of the administrator  4  without any power supply or the like provided in the portable visual acuity tester  2 . 
         [0051]    &lt;Synopsis&gt; 
         [0052]    To follow is a comprehensive description of the various features disclosed herein. 
         [0053]    A feature disclosed in the present specification provides a portable visual acuity test device including a mount worn in front of an eye, a display which displays a visual target for a visual acuity test, a display controller which switches visual targets displayed on the display, an input unit to which the recognition result of a visual target is inputted, and a transmitter which transmits a measurement result. It is thereby possible to obtain a portable visual acuity test device that can be worn on a person&#39;s head. 
         [0054]    According to a specific feature, the display comprises an organic electroluminescence display panel. It is thereby possible to achieve display of black in display of a black and white visual target. 
         [0055]    According to another specific feature, the portable visual acuity test device includes an optical system which permits adjustment of a distance at which a virtual image of the visual target is seen. It is thereby possible to obtain a portable visual acuity test device that can measure far-vison visual acuity and near-vision visual acuity. 
         [0056]    According to another specific feature, the mount is mountable in front of the eye both in an eyeglasses-worn state and in a naked-eye state. It is thereby possible to obtain a portable visual acuity test device that can measure naked-eye visual acuity and corrected visual acuity. According to a more specific feature, the portable visual acuity test device includes a detector which detects whether or not eyeglasses are worn. According to an even more specific feature, the detector determines a relationship between whether an intended test is a naked-eye visual acuity test or a corrected visual acuity test and whether or not eyeglasses are worn. 
         [0057]    According to another specific feature, the display can switch between a C shape visual target and an E shape visual target. It is thereby possible to obtain a portable visual acuity test device that suits the use region. 
         [0058]    According to another specific feature, the display has a right-eye display and a left-eye display. In a visual acuity test, one of the right-eye display and the left-eye display is enabled, and in information display, the right-eye display and the left-eye display are both enabled. It is thereby possible to obtain a portable visual acuity test device that allows smooth measurement. According to yet another specific feature, in information display, the display displays in letters enlarged to be larger than a visual target. This also helps allow smooth measurement. 
         [0059]    According to another specific feature, the portable visual acuity test device autonomically performs a plurality of kinds of visual acuity tests. It is thereby possible to smoothly perform measurements for the right-eye, the left-eye, far-vision visual acuity, near-vision visual acuity, naked-eye visual acuity, corrected visual acuity, etc. 
         [0060]    Another feature disclosed in the present specification provides a portable visual acuity test device including a mount worn in front of an eye, a display which displays a visual target for a visual acuity test, and an acceleration sensor. The recognition result of a visual target is inputted by a head movement. It is thereby possible to smoothly input the recognition result, and thus to smoothly proceed from the acknowledgment of display content to a visual acuity test. According to a specific feature, the recognition result of a visual acuity is determined based on a relationship between a direction of a visual target displayed on the display and a direction of a head movement. According to another specific feature, inability to recognize is inputted by a predetermined head movement. 
         [0061]    Yet another feature disclosed in the present specification provides a visual acuity test system including a plurality of portable visual acuity test devices, and an administrator which can communicate with the portable visual acuity test devices. It is thereby possible to perform measurements with respect to a plurality of subjects concurrently. 
         [0062]    Yet another feature disclosed in the present specification provides a portable visual acuity test device including a right-eye display and a left-eye display. In a visual acuity test, one of the right-eye display and the left-eye display is enabled, and in information display, the right-eye display and the left-eye display are both enabled. It is thereby possible to appropriately test visual acuity for the right and left eyes individually, and to enhance the communicating ability by use of both eyes for the purpose of information communications. 
         [0063]    According to a specific feature, in information display, the right-eye display and the left-eye display in letters enlarged to be larger than a visual target. It is thereby possible also to enhance the ability to communicate information, and thus to achieve smooth measurement. 
         [0064]    According to a specific feature, the portable visual acuity test device includes an acceleration sensor. The information display and display for the visual acuity test are switched by a head movement. It is thereby possible to smoothly proceed from the acknowledgement of information display to a visual acuity test. 
       INDUSTRIAL APPLICABILITY 
       [0065]    The present invention is applicable to visual acuity test devices. 
       LIST OF REFERENCE SIGNS 
       [0000]    
       
         
           
               2   b  mount 
               12 ,  14  display 
               22  display controller 
               26  input unit 
               30  transmitter 
               18 ,  20  optical system 
               11  detector 
               26  acceleration sensor