Abstract:
A visual field testing apparatus for scanning the visual field of a human eye in great detail, precision, and clarity so as to detect the smallest blind area whereby allowing users the ability of early detection of glaucoma and other eye diseases of visual loss. The apparatus is small and inexpensive so that anyone can afford to purchase it and self-test without assistance so that the user can test frequently at home which further leads to early detection of eye diseases. Because of its great precision and detail in test results, the present invention is especially useful to doctors and researchers. One embodiment of the present invention is a visual field tester which comprises: (a) a recording surface having eye fixation means to fixate an eye&#39;s visual field relative to said recording surface; and (b) a handheld scanning device which has a test mark for detecting very small blind areas in said eye&#39;s visual field and marking means for mapping said detected very small blind areas onto said recording surface.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    Not Applicable 
       FEDERALLY SPONSORED RESEARCH 
       [0002]    Not Applicable 
       SEQUENCE LISTING OR PROGRAM 
       [0003]    Not Applicable 
       BACKGROUND OF THE INVENTION 
       [0004]    This invention relates to a device and a method for detecting and mapping the diseased blind areas in a person&#39;s vision. The most widely used visual field tester today is the Standard Automated Perimeter (SAP) which is used to perform a contrast sensitivity test. In this test, a person is usually seated in front of a hemispherical projection surface whereupon an optical projection system projects circular spots according to an algorithm, and the subject responds to the stimulus by pressing an input device such as a mouse. Usually the algorithm used to project the spots of light is written so that the location and the timing of the projected lights are random to the user. This is to keep the user from falling into a rhythm and expectantly clicking on the input device even when he or she does not see the projected light. However, these SAP tests suffer from a number of disadvantages.
       a) They are costly and most individuals would normally not be able to afford them. SAP equipment require an expensive projection system, software and hardware. The SAPs are usually only found at hospitals and eye physicians&#39; offices. As a result, SAPs are not easily accessible devices. If someone wanted to monitor the condition of one&#39;s own visual field, he or she would not be able to run a visual field test often and usually would have to make an appointment with a doctor to do so.   b) SAPs are large bulky machines. They are not mobile machines that can be transported anywhere. Current SAPs are large and heavy and once they are placed at a certain location they cannot be moved easily.   c) SAPs are prone to inaccuracies and sometimes do not detect problems in the visual field until noticeable deterioration has occurred. One of the problems with SAPs is that due to the random generation of projected lights, users do not know where the next light will appear; therefore, sometimes they will often miss identifying certain lights because they were not prepared. The SAP tests are time-constrained; while a user is pondering whether or not to click the button, the next light appears. Therefore, it is a man-machine contest with the user being quite nervous in taking the test. Also, some machines require the user to fixate his or her eye on a bright light in order to keep the eye from wandering. However, blinking often creates after-images which tricks subjects into seeing a projected light where none was projected.   d) The result from SAPs do not show decisive results for each location in the visual field. Due to the inaccuracies in the SAPs, their algorithm usually displays or prints out a map of the visual field with each area of the visual field given different probabilities of damage or problems. This is done to account for the user&#39;s errors in clicking or identifying random lights. If the user did not click the button when a light was projected, the result from the SAP would be inaccurate. Rather than identifying an area where the subject could not see as a problem area, the SAP might identify it as an area with medium probability, but not definite probability.   e) Current visual field testers are not good at early detection of glaucoma or other eye diseases. If glaucoma can be detected early on, medication such as pressure-reducing eyedrops can be given to stop the farther destruction of optical nerves in the eye. Often, when glaucoma is detected, excessive damage to the nerves in the eye has already occurred causing severe visual field loss. Because of the uncertain outputs from SAP testers, doctors and patients are often misled into believing glaucoma does not exist, when in actuality, it is already present. For example, a doctor may look at a result from a SAP and incorrectly conclude that an area with medium probability next to the natural blind spot is not problematic and is considered part of the natural blind spot when in reality, nerve cells have already begun to die in that region as is shown in the later section under the title “Accurate Detection of Diseased Blind Areas: FIGS.  15 A- 15 B.”       
 
       OBJECTS 
       [0010]    Accordingly, to overcome the disadvantages of current visual field testers as described above, and besides the objects of the visual field device described in our patent, several objects and advantages of the present patent are:
       a) To provide a visual field tester which can detect glaucoma and other eye diseases causing vision loss in their very early stages by scanning the visual field in even greater detail and accuracy, thus allowing early treatment.   b) To provide a visual field tester which can provide a decisive output, indicating which areas in the visual field are definitely good and which areas are definitely bad.   c) To provide an accurate visual field tester that allows the user to have total control so that he or she can retest certain areas of the visual field if he or she finds something unusual or feels that an area has been missed.   d) To provide an inexpensive visual field tester that anyone can afford and purchase readily.   e) To provide a small portable visual field tester that can be easily transported.   f) To provide precise and detailed visual field test results for a patient whereby his or her doctor can make a correct diagnosis.   g) To provide accurate and detailed visual field mapping results to help researchers track the progression of eye diseases under different treatments and to help them find new cures and root causes of eye diseases.       
 
       BRIEF SUMMARY OF THE INVENTION 
       [0018]    The object of the present invention is to provide a new visual field tester for detecting, with decisive accuracy, glaucoma and other eye diseases with vision loss at the very early stages, and to provide a portable, inexpensive visual field tester that anyone can afford. 
         [0019]    The invention includes a recording surface (typically a visual field grid sheet), a handheld scanning device, and an optional head support for reproducible test results. 
         [0020]    The head support is comprised of a flat rigid frame with a T-shaped opening for a face and two rotating U-shaped support members. Under normal operation, the user would be seated or standing at a table with the visual field tester placed near the edge of the table. A user inserts his or her face into the T-shaped opening of the head support and positions the head using a mirror to align the center of the face with a line or notch on the bottom-side of the head support. In this way, the head support allows the head to be positioned exactly the same distance and orientation from a recording surface or visual field grid sheet each time, so that the test is repeatable and the progression of the eye disease can be evaluated by comparing results of each test. 
         [0021]    A visual field grid sheet is clamped beneath the head support by use of a base board so that both the visual field grid sheet and head support are immobile. The base board is made of a rigid flat material and it has a clip on one side to clamp the visual field grid sheet and U-shaped support members of the head support. The base board can be made to fold to facilitate storage. The visual field grid sheet itself is in polar coordinates comprised of an eye fixation mark at the center, radial lines, and concentric circles centered about the eye fixation mark. The concentric circles corresponding to the visual angles of the eye under test. We shall refer to the blind area in a person&#39;s eye that corresponds to the area where the optic nerve joins the eye as the “natural blind spot” to follow conventional naming, and we shall refer to very small test areas that cannot be seen by the eye within the natural blind spot as “very small natural blind areas.” We shall refer to very small test areas that cannot be seen by the eye outside of the natural blind area as “very small diseased blind areas.” Likewise, we shall refer to a cluster of very small diseased blind areas as a “diseased blind area.” Also, we shall use the term “very small blind area” to refer to a very small blind area which could either be a very small diseased blind area or a very small natural blind area. During scanning, the user would focus one eye on the eye fixation mark of the visual field grid sheet while the other eye is closed, and he or she would use a handheld scanning device to scan through all areas of the visual field and find areas of very small diseased blind areas and very small natural blind areas. The handheld scanning device has a block for a hand to hold. Protruding from the block is a thin resilient stick with a small test mark, usually a small dot, on the top surface at the end of the stick. Directly below the test mark is a stamp the same size and shape as the test mark. During scanning whenever the test mark disappears from view, the user would push down on the stick with the index finger and stamp a corresponding mark or dot onto the visual field grid sheet. The user could follow one of several methodological ways of scanning the visual field grid sheet without missing any areas. The visual field grid sheet is divided by circles of visual angles and radial lines of polar angles into many small sections which facilitates the user to search thoroughly for diseased blind spots in a particular section. Unlike tests done with SAPs which are controlled by the machine, in the present invention, users can spend as much time as they need to scan a particular spot so that they are sure the spot is a very small diseased blind area before stamping a dot or mark on the visual field grid sheet. At the end of the test, the user will have an extremely detailed map of the visual field. When the test mark is in a completely blind area, including both the diseased blind area and the natural blind spot, the user cannot see the test mark at all. As soon as the test mark is moved away from a completely blind area, the user can see the test mark clearly. Thus the user can map the contours of both the diseased blind area(s) and the natural blind spot clearly and precisely, and be able to distinguish the two areas easily as will be shown later. Furthermore, the test mark can be made as small as the user can see; thus, very small diseased blind areas, typically in the early stage of the disease, can be detected. Therefore, the present invention enables early detection of glaucoma and other eye diseases with vision loss and the ability to monitor progression of eye diseases. 
       ADVANTAGES 
       [0022]    In some cases a diseased blind area may not be completely blind, that is, the area has both dead and intact optical nerves intermingled together. In this case, to the user&#39;s eye, the test mark would appear to be grey if the test mark is black, or the test mark would twinkle as it is moved around slowly, and the user would use a different color to stamp a mark to map the very small blind area on the visual field grid sheet. Thus, our visual field tester can map both the areas of complete blindness and the areas of partial blindness. This is especially important when later the user finds that a partially blind area becomes completely blind indicating his/her disease is getting worse, although the overall blind area does not grow larger. 
         [0023]    From the description above, a number of advantages of our visual field tester become evident.
       a) With our visual tester, the user can detect and locate a very small diseased blind area. That is, glaucoma and other eye diseases with vision loss can be detected at a very early stage, enabling the disease to be treated at a very early stage and preventing the eye from further vision loss beyond this early stage.   b) Furthermore, the visual field tester can be cheaply made so that everyone can afford to possess it and use it as frequently as he or she wants, which increases the chance for early detection of the disease.   c) The head support of our visual field tester can be folded, thus allowing the visual field tester to be extremely compact. The head support and handheld scanning device are small enough to be stored or carried around in a briefcase.   d) The user can re-scan certain regions of his or her visual field and use smaller test marks or dots to obtain a visual field map with even finer resolution. In certain spots in the visual field that seem to be trouble spots, the user can retest those areas several times to ensure accurate results.   e) The output from our visual field tester shows exactly which areas of the visual field have problems and does not arrive at results based on a probability.   f) With our visual field tester the user can map not only completely blind areas, but also partially blind areas. Therefore, if a user&#39;s partially blind area becomes completely blind even though the overall blind area does not get larger, he or she will know the eye disease is getting worse.       
 
       CONCLUSION, RAMIFICATIONS AND SCOPE 
       [0030]    Accordingly, a visual field test can be performed by anyone anywhere using the visual field tester described in this patent. In addition, the visual field tester of the present invention has the additional features in that: 
         [0031]    it allows production of visual field testers at low cost, allowing individuals, rather than only hospitals and doctors to purchase them. 
         [0032]    it permits a visual field tester to be compact and portable. 
         [0033]    it provides a visual field tester that will give extremely accurate results as patients can rerun the test themselves on trouble spots by using a smaller test mark for finer resolution. 
         [0034]    it gives decisive results on whether a specific area in the visual field has problems. 
         [0035]    Although the description above contains many specifications, these should not be construed as limiting the scope of the invention but as merely providing illustrations of some of the presently preferred embodiments of the invention. Thus, the scope of the invention should be determined by the appended claims and their legal equivalents rather than by the examples given. 
     
     
       BRIEF DESCRIPTIONS OF THE DRAWINGS 
         [0036]      FIG. 1  illustrates the major components of the visual field tester according to the present invention and how it is used by a user; 
           [0037]      FIG. 2  is a perspective view of the head support and visual field grid sheet (recording surface); 
           [0038]      FIG. 3  is a perspective view of the head support of the visual field tester in an opened position; 
           [0039]      FIG. 4  is a perspective view of the head support of the visual field tester in a compact folded position; 
           [0040]      FIG. 5  is a perspective view of the base board of the visual field tester; 
           [0041]      FIG. 6A  is a perspective view of the handheld scanning device of the visual field tester; 
           [0042]      FIG. 6B  is a view of the underside of the resilient stick of the visual field tester where a stamp is located; 
           [0043]      FIG. 6C  is a side view of a user rewetting ink to the stamp on the handheld scanning device; 
           [0044]      FIG. 7  is a top view of the visual field grid sheet (recording surface) of the visual field tester where optional vertical guide lines and horizontal guide lines are shown; 
           [0045]      FIG. 8A  is a perspective view of an alternate embodiment of the visual field tester in which the head support is not foldable; 
           [0046]      FIG. 8B  is an exploded view of an alternate embodiment of the visual field tester shown in  FIG. 8A ; 
           [0047]      FIG. 9A  is a perspective view of an alternate embodiment of the visual field tester in which the head support only has support members close to the forehead; 
           [0048]      FIG. 9B  is an exploded view of an alternate embodiment of the visual field tester shown in  FIG. 9A ; 
           [0049]      FIG. 10A  is a perspective view of an alternate embodiment of the visual field tester in which the head support only has support members close to the chin positioner; 
           [0050]      FIG. 10B  is an exploded view of an alternate embodiment of the visual field tester shown in  FIG. 10A ; 
           [0051]      FIG. 11A  is a top view of an alternative embodiment of the visual field tester in which the handheld scanning device comprises a substantially flat object and a marking tool; 
           [0052]      FIG. 11B  is a top view of the alternative embodiment of  FIG. 11A  where a user is aligning the marking tool&#39;s marking tip to the flat object&#39;s test point; 
           [0053]      FIG. 11C  is a top view of the alternative embodiment of  FIG. 11A  where a user has placed a mark onto the recording surface; 
           [0054]      FIG. 11D  is a top view of another alternative embodiment of the visual field tester in which the handheld scanner comprises only a marking tool; 
           [0055]      FIG. 12A  is a top view of a user performing a horizontal scan using the rectangular guide with the test mark pointed downwards from the hand holder; 
           [0056]      FIG. 12B  is a top view of a user performing a horizontal scan using the rectangular guide with the test mark pointed upwards away from the hand holder; 
           [0057]      FIG. 13A  is a top view of a user performing a diagonal scan using the rectangular guide with the test mark on the right side of the hand holder; the same method can be applied for a vertical scan; 
           [0058]      FIG. 13B  is a top view of a user performing a diagonal scan using the rectangular guide with the test mark on the left side of the hand holder; the same method can be applied for a vertical scan; 
           [0059]      FIG. 14A  is a test result of a normal eye of one of the present inventors using the present invention, which shows that a natural blind spot is a polygon; 
           [0060]      FIG. 14B  is a test result of a normal eye of another present inventor using the present invention, which shows that a natural blind spot is a polygon; 
           [0061]      FIG. 15A  is a test result of a glaucoma patient obtained from a SAP machine; the name of the patient will not be revealed to protect privacy; 
           [0062]      FIG. 15B  is a test result using the present invention of the same patient from  FIG. 15A ; 
           [0063]      FIG. 16A  is a top view of a visual field grid sheet modified for people with macular degeneration or other eye disorders with central vision loss; and 
           [0064]      FIG. 16B  is a close-up top view of the visual field grid sheet of  FIG. 16A . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Description: FIGS. 1-13 
       [0065]    A preferred embodiment of the present invention is illustrated in  FIG. 1  and  FIG. 2 . A user positions his or her head using a head support  40 . The preferred embodiment&#39;s head support  40  can position the head the same orientation and location relative to a recording surface (typically visual field grid sheet)  100  each time the test is performed. Thus, each time the user takes a visual field test with the present invention, the visual field tester&#39;s mapping results would be reproducible, and any changes in the visual field would show up as a change in the test results as compared to the previous one. If the user chooses, he or she could run the test without using the head support. He or she would place visual field grid sheet  100  (recording surface) on a flat surface such as a table, keep the head a fixed distance from sheet  100 , and hold the head still while performing the test. The disadvantage of not using the head support is that if the user later wishes to perform additional tests, results would not be reproducible in that the map of the blind spots would not have the same reference point. Head support  40  consists of a rigid frame  41 , a tilting mirror  50 , and a base board  47 . 
         [0066]      FIG. 3  shows rigid frame  41  in an opened position while  FIG. 4  shows rigid frame  41  in a closed position for storage. In the opened position, a user inserts his or her face into a face opening  44  that is located on rigid frame  41 . At one end of face opening  44 , a chin positioner  42  protrudes vertically from rigid frame  41 . On the opposite side of face opening  44  is a notch  43  that the user aligns with the center line of the user&#39;s face as he or she looks at mirror  50 . A dark line  52  ( FIG. 4 ) protruding from notch  43  on the bottom of rigid frame  41  further aids in alignment of the center line of the user&#39;s face. A soft pad  60  is affixed on the top side of rigid frame  41  where a user would place his or her forehead. During test, much of the weight of the head is placed against the forehead so that soft pad  60  alleviates any discomfort. Situated at the four corners of rigid frame  41  are a front left insertion hole  57 , a front right insertion hole  56 , a rear left insertion hole  59  and a rear right insertion hole  58  ( FIG. 4 ). A front U-shaped support member  54  plugs into holes  56  and  57  while a rear U-shaped support member  55  plugs into holes  58  and  59 . A hook  65  is attached to a leg of U-shaped support member  55 , and a hook  64  is attached to a leg of U-shaped support member  54 . Bulges  51  and  53  on U-shaped support members  54  and  55  hold the hooks  64  and  65  in place so they do not slide up or down the legs. When rigid frame  41  is opened, hook  65  is inserted into a left hook hole  61  and hook  64  is inserted into a right hook hole  62 . Hooks  64  and  65  lock U-shaped support members  54  and  55  in place so they are immobile when rigid frame  41  is in an opened position for use. At the center of the bottom segments of U-shaped support members  54  and  55  are alignment marks  66  and  67 , respectively. When folded, rigid frame  41  becomes substantially flat and compact allowing easy carriage and storage. As shown in  FIG. 4 , rotatable hooks  64  and  65  are unplugged from their holes  61  and  62 , thus allowing the two U-shaped support members  54  and  55  to freely rotate. U-shaped support members  54  and  55  are rotated inwards towards the bottom of rigid frame  41  for storage. 
         [0067]      FIG. 5  illustrates a base board that is a preferred embodiment of the present invention. In this embodiment, two flaps  74  and  75  are joined by folds, hinges, or creases  76  and  77 , respectively, to a main board  203 . Attached to the top-side of board  203  is a clip  201 . Flaps  74  and  75 , when unfolded outwards from main board  203 , will create a flat surface for placing visual field grid sheet  100  (recording surface) ( FIG. 1 ). During storage or carriage, flaps  74  and  75  are folded inwards to save space. On the top of base board  203  is a base board alignment line  205  which is used to align the y-axis of visual field grid  100  and alignment marks  66  and  67  on U-shaped support members  54  and  55  of head support  40 . 
         [0068]      FIGS. 6A-6C  show a preferred embodiment of a handheld scanning device  91 . It consists of a hand holder  92 , a resilient stick  95  inserted into an insertion hole  93  of hand holder  92 , and an inkpad  30 . On one end of resilient stick  95  is an enlarged area  98 , typically the shape of a circular disc. A test mark  97  is at the center of the top side of enlarged area  98 . A stamp  99  is affixed directly beneath test mark  97  on the bottom side of enlarged area  98 . Resilient stick  95  is slightly curved down so that when hand holder  92  rests on visual field grid sheet  100 , stamp  99  is only slightly elevated above visual field grid sheet  100  (recording surface). Resilient stick  95  can be changed to another stick with test mark  97  of different size and corresponding stamp  99  of corresponding size if the user wishes to; For example, if the blind area in the user&#39;s visual field is quite large, he or she may use a resilient stick with a larger test mark or dot for faster scanning and then change to a stick with a smaller mark or dot for detailed scanning on the contour of the blind area. 
         [0069]      FIG. 7  shows visual field grid sheet  100  (recording surface). An eye fixation mark  101  is located at the center of sheet  100 . Centered about fixation point  101  are several concentric circles corresponding to the visual angles of the eye under test. The visual angle can be calculated from the formula: 
         [0000]      Visual angle=tan −1 ( r/h ) 
         [0000]    where r is the radius of a circle of a given visual angle and h is the vertical distance between the tested eye and the fixation point  101  where the tested eye is approximately vertically above the fixation point  101 . For example, a circle  35  corresponds to visual angle 35 degrees. Lines radiating from the eye fixation mark correspond to the polar angles of the test eye. For example, a radial line  150  corresponds to polar angle 150 degrees. Optional horizontal lines  70  and vertical lines  71  can be used to aid in scanning which will be explained in more detail in the operations section. 
         [0070]    As stated above, the tested eye is approximately vertically above the fixation point  101 . This is because the middle point between two eyes is vertically above the fixation point  101 , and, hence, each eye is only approximately vertically above the fixation point  101 . It does not affect the performance of our visual field tester at all. It does not affect any of the advantages of the present invention stated above in the section under the title “Brief Summary of the Invention”. 
       Alternative Embodiments 
     FIGS.  8 - 10   
       [0071]    Additional embodiments are shown in  FIGS. 8A-8B ,  FIGS. 9A-9B ,  FIGS. 10A-10B , and  FIGS. 11A-11D . Referring to  FIG. 8A , head support  40 , instead of having two rotatable or folding support members, has unfoldable support members  81  to facilitate manufacturing. As shown in  FIG. 8B , base board  47  has an indentation  80  to fit mirror  50  snugly in place and four indentations  83  to fit support members  81 . Clip  201  has an alignment line  204  in addition to center line  205  to align with the y-axis of the visual field grid sheet  100  (recording surface). 
         [0072]      FIGS. 9A-9B  show another embodiment which has one or more support members, typically two support members  81 , affixed near soft pad  60  on rigid frame  41 , but which has no support member(s) near chin rest  42 . Two diagonal support structures  85  keep rigid frame  41  from drooping down under downward pressure when a user places his or her head onto head support  40 . Support members  81  are affixed to base board  47  by any fasteners, typically by screws  82  through threaded holes  84 . 
         [0073]      FIGS. 10A-10B  show another embodiment which has one or more support members, typically two support members  81 , affixed to rigid frame  41  near chin positioner  42 , and which has no support member(s) near soft pad  60 . Here, rigid frame  41  is modified so that soft pad  60  is no longer used. Diagonal support structures  85  give support to rigid frame  41 , and support members  81  are affixed to base board  47  by any fastener, typically by screws  82  through threaded holes  84 . Since there are no notch  43  and alignment line  52  on rigid frame  41  to align the center line of a user&#39;s face, the alignment is accomplished by having an alignment line  63  on mirror  50 , which is to be aligned with the center line of the user&#39;s face as he or she looks at mirror  50 .  FIG. 10B  shows that mirror  50  fits snugly into indentation  80  in base board  47  and mirror  50  can only be tilted up and down so that line  63  on mirror  50  always aligns with center line  205  on base board  47 . 
         [0074]    So far, the head support described above can produce reproducible test results. If the user&#39;s only concern is to detect diseased blind spots but not care about the reproducible test results, then a simple head support can be used, which is described as follows. A typical simple head support includes a vertical rod with one end attached to the visual grid sheet (recording surface) and the other end propped against the user&#39;s forehead. This head support does not need to have a mirror or base board. 
         [0075]      FIGS. 11A-11C  show another embodiment of the handheld scanning device, and  FIG. 11D  shows yet another embodiment of the handheld scanning device. In the present invention, the handheld scanning device includes anything that has a test mark, which a user can perceive with his or her peripheral visual field, and that can place a corresponding mark on the visual field grid sheet (recording surface) at the location of the test mark. Referring to  FIGS. 11A-11C , one alternative embodiment comprises a flat object  401  such as a piece of paper or thin strip of plastic. Located on the top surface of flat object  401  is test mark  97 . In addition, a marking tool or marking apparatus  402  such as a pencil, pen, or marker which has a marking tip  403  will be used to place a mark  404  whenever the user cannot see test mark  97 . Referring to  FIG. 11D , a simpler alternative embodiment of the scanning device is shown where marking tip  403  on marking apparatus  402  also functions as the test mark. The operation of these embodiments will be discussed in greater detail in the operations section. 
       Operation: FIGS. 1-12 
       [0076]    To use the present invention, the user first clamps visual field grid sheet  100  (recording surface) onto base board  47  as shown in  FIGS. 1-2 . The user would align a y-axis  270  (that is, 90° radial line and 270° radial line) of visual field grid sheet  100  (recording surface) with alignment line  205  on base board  47 , and then clamp the bottom part of U-shaped support member  55  with clip  201  such that alignment marks  66  and  67  of both U-shaped support members align with the y-axis of visual grid sheet  100  (recording surface). In the alternate embodiments in  FIGS. 8-10 , line  204  on clip  201  and line  205  on base board  47  would align with y-axis  270  on visual field grid sheet  100  (recording surface). The user would then look at tilting mirror  50  and position the head until the center line (symmetric line) of the face aligns to notch  43  and/or line  52  (shown in  FIG. 3  and  FIG. 4 ) underneath rigid frame  41  or line  63  on mirror  50  ( FIG. 10A ). An image  300  in the mirror in  FIGS. 1 ,  8 A,  9 A,  10 A illustrates a head aligned correctly. Once the head is positioned, the user stares with one eye (the other eye is closed) at fixation point  101  located at the center of visual field grid sheet  100  (recording surface). 
         [0077]    The user could also use the head support without the baseboard which would give less stability. Here, the user would place the rigid frame on top of the recording surface. Also, a user may also not use a head support at all if he or she is not interested in reproducible results. The user would simply need to hold the head a predetermined distance from the recording surface and hold the head still while running the test. Results from such a test would still be useful in that diseased blind areas would be detectable and any changes in the shapes of the diseased blind areas would be detectable, but the disadvantage is that the exact coordinates of these diseased blind areas would not be known. 
         [0078]    Using the right hand or left hand, the user would grasp handheld scanning device  91 , and slide it systematically on visual field grid sheet  100  such that the movement of test mark  97  would encompass the whole visual field. As the user moves handheld scanning device  91 , he or she would keep the test eye staring at fixation point  101  while using the test eye&#39;s peripheral vision to see test mark  97 . If test mark  97  disappears from the test eye&#39;s peripheral vision, then the user stops moving handheld scanning device  91  immediately and presses down resilient stick  95  which will in turn cause stamp  99  to stamp a mark or dot on visual field grid sheet  100  (recording surface). The user can either use a finger of the hand that is holding handheld scanning device  91  or any finger of the other hand to press resilient stick  95 . The user not being able to see test mark  97  with the peripheral vision indicates that the user has a very small blind area in the visual field, and by stamping the corresponding mark on visual field grid sheet  100 , the user maps the very small blind area onto visual field grid sheet  100 . 
         [0079]    After test mark  97 &#39;s movement covers the entire visual field grid sheet  100  and all very small blind areas found have been stamped, the complete map of very small blind areas in the visual field of the eye just tested is obtained. In the course of scanning, instead of test mark  97  completely disappearing, the user may find that test mark  97  does not disappear completely at a particular spot. This is because the very small blind area is smaller than test mark  97 . For better resolution, the user would change resilient stick  95  (shown in  FIG. 6A ) to one with a smaller test mark  97 . For this purpose, the present invention includes several resilient sticks  95  with different sizes of test marks  97 , and resilient stick  95  can be easily changed by pulling out existing resilient stick  95  from hole  93  in hand holder  92  in  FIG. 6A  and pushing in another resilient stick  95  into hole  93 . Thus the present invention can detect a very small blind area in the earliest stage of eye disease with vision loss. 
         [0080]    If the user finds that test mark  97  twinkles as it is moved around slowly, then the area being scanned is an incompletely or partially blind area. That is, there are many dead optical nerves and intact optical nerves intermingled. In this case, the user would use a different color to stamp the very small blind area on the visual field grid sheet. Later, if the user cannot even see test mark  97  twinkling in that area, then the user and the eye doctor would know that the area became completely blind, and that the eye disease is getting worse even though the overall blind area did not enlarge. 
         [0081]    To rewet stamp  99  with ink, the user tilts hand holder  92  up slightly so that stamp  99  is tilted up to allow inkpad  30  to slide beneath stamp  99  as shown in  FIG. 6C . The user presses down resilient stick  95 , and stamp  99  touches inkpad  30  to rewet stamp  99  with ink. Resilient stick  95  is made of resilient material, typically metal or plastic so that it will rebound and return to the original shape after being pressed down and released either to rewet stamp  99  with ink or to stamp a dot on visual field grid sheet  100  when a very small blind area is perceived. Once stamp  99  is rewetted, it can stamp several times before it needs to rewet again. Therefore, it can stamp very fast in a blind region. 
         [0082]    Stick  95  and enlarged area  98  (excluding test mark  97 ) have the same color as visual field grid sheet  100 , typically white, to allow them to camouflage with the visual field grid sheet during scanning. The reason for having enlarged area  98  is that during scanning, the user will only perceive the movement of test mark  97 , and all surrounding stamped marks and grid lines will be blocked out by enlarged area  98 . 
         [0083]    The ink used for inkpad  30  can be any color. One way of tracking the progression of an eye disease is to use different colored ink every time the test is performed. Thus, on subsequent tests, by using the same visual field grid sheet  100  previously used, the new very small diseased blind areas can be differentiated from the previous areas because the colors will be different. 
         [0084]    In order to obtain more precise scanning,  FIGS. 12 and 13  show the use of a rectangular guide  96 . The purpose of using rectangular guide  96  is to assist the user in scanning an area in doubt with very fine detail.  FIGS. 12A-12B  show a method for horizontal scanning.  FIG. 12A  illustrates how to scan the lower part of test grid sheet  100  and  FIG. 12B  illustrates how to scan the upper part of visual field grid sheet  100 . In both cases, the method is as follows. First, the user places rectangular guide  96  on visual field grid sheet  100  parallel to horizontal lines  70  on visual grid sheet  100  ( FIG. 7 ). Then the user uses his or her thumbs and index fingers of both hands to hold hand holder  92  and presses a back edge  94  of hand holder  92  against guide  96  in the case of  FIG. 12A , or a front edge  20  of hand holder  92  against guide  96  in the case of  FIG. 12B . All the other fingers are used to press down rectangular guide  96  firmly so that it will not move. Then the user slides hand holder  92  slowly along rectangular guide  96  to scan for very small blind areas. When the user perceives a very small blind area, he or she stops sliding hand holder  92  immediately. While holding hand holder  92  and rectangular guide  96  firmly with one hand, he or she uses any finger of the other hand to press down resilient stick  95  to stamp a mark on visual field grid sheet  100 . 
         [0085]    The advantages of using rectangular guide  96  are as follows. First, the user can move hand holder  92  very slowly and at a steady pace, so that his or her eye can perceive the disappearance of test mark  97  very clearly when a very small blind area is encountered. Secondly, after one line is scanned, the user can proceed to scan another line by moving rectangular guide  96  up (or down, if the scanning starts from the top of the area to be scanned) in very small increments with a distance slightly smaller that the diameter of test mark  97  while still keeping rectangular guide  96  horizontal, that is, parallel to the horizontal lines on test grid sheet  100 . This process would be repeated until the area in doubt is completely scanned. Thus no blind spots in that area would escape detection. 
         [0086]      FIGS. 13A-13B  show a method for scanning vertically or in a slanted direction.  FIG. 13A  shows how to scan the right part of the visual field grid sheet  100  and  FIG. 13B  shows how to scan the left side of visual field grid sheet  100 . The user first places rectangular guide  96  either parallel with vertical lines  71  ( FIG. 7 ) or in a slanted direction. In  FIG. 13A , the user uses a right hand  21  to hold down rectangular guide  96 . A left hand  22  holds hand holder  92  using the thumb, index finger and middle finger and places back edge  94  against rectangular guide  96 . In this way, the user can slowly slide hand holder  92  along rectangular guide  96  and use the index finger of left hand  22  to press down resilient stick  95  to stamp a mark. In  FIG. 13B , the user uses left hand  22  to hold down rectangular guide  96  and right hand  21  to grasp hand holder  92  with its index finger, thumb and middle finger. Here, the user can slowly slide hand holder  92  along rectangular guide  96  using right hand  21  and stamp a mark with the index finger of right hand  21 . 
         [0087]    In the case of the alternate embodiment of the scanning device in  FIGS. 11A-11C , the user would grasp flat object  401  and slide it around the visual field grid sheet (recording surface). Whenever test mark  97  disappears from view, the user moves marking tool  402  such that marking tip  403  is directly above or below test mark  97  ( FIG. 11B ). Then the user removes flat object  401  slightly away so that marking tip  403  can make a mark  404  on the visual field grid where test mark  97  had originally been ( FIG. 11C ). 
         [0088]    In the case of the alternative embodiment of the scanning device in  FIG. 11D , the marking tip  403  on marking tool  402  also is the test mark. In this way, when a user moves marking tool  402  about the visual field grid sheet and marking tip  403  disappears from view, the user would stop moving the tip and make a mark on the visual field grid sheet or recording surface at the location where marking tip  403  disappears. 
       Natural Blind Spot and New Discovery: FIGS. 14A-14B 
       [0089]    It is well known that everyone has a blind spot at the location where the optic nerve from the brain enters the eye. Because this natural blind spot is not covered with retinal cells, it cannot perceive light. Eye diseases such as glaucoma, macular degeneration, and so forth will cause visual loss in other parts of the visual field. These visual loss areas caused by diseases will be called “diseased blind areas.” 
         [0090]    Before the present invention, only the approximate location of the natural blind spot in the visual field was known, and there was no visual field tester that was accurate enough to map out the shape of the natural blind spot in the visual field grid sheet. The natural blind spot is only known to exist between the 10 degree and 20 degree visual angles, on around the negative x-axis for the left eye and on around the positive x-axis for the right eye. 
         [0091]    With the present invention, for the first time, the exact shape, size, and location of the natural blind spot has been found by the present inventors as shown in  FIGS. 14A and 14B .  FIGS. 14A and 14B  are reduced copies from the original test grid sheet of 11″×17″ for the right eye natural blind spot. Inside the natural blind spot, nothing can be seen; hence, test mark  97  cannot be seen when scanning inside a natural blind spot  103 . When test mark  97  is moved across the boundary of natural blind spot  103  to the outside, the user&#39;s perception of test mark  97  changes from being completely invisible to being clearly visible, with no transition or blurred image in between. Thus, the boundary of natural blind spot  103  can be precisely located and mapped (stamped) on visual field grid sheet. 
         [0092]      FIGS. 14A and 14B  show that the shape and the size of natural blind spot  103  are different from person to person. It is not a circle, rather a polygon of five sides ( FIGS. 14A and 14B ) or four sides ( FIG. 15B ). Note that in  FIG. 14A , one side (the upper side) of the polygon is not straight. 
         [0093]    The ability of the present invention to precisely map the natural blind spot will help doctors diagnose the progression of patients&#39; eye diseases and help researchers correlate blind spot shape and/or size with some diseases including eye diseases, brain tumors, and so forth, because changes to blind spot shape and/or size are important in the detection of such diseases. 
       Accurate Detection of Diseased Blind Areas: FIGS. 15A-15B 
       [0094]    The prominent advantages of the present invention are the detailed and clear scanning results, which enables one to early detect vision loss related to eye diseases such as glaucoma, macular degeneration, . . . etc. In visual field tests with SAPs, the light appears at only a limited number of points in the visual field. Therefore, the whole visual field is not covered by the test and some very small blind areas which occur at early stages of the disease will most likely be undetected. In the present invention, test mark  97  can be moved continuously as described above by using rectangular guide  96  to scan closely line by line the entire visual field so that no very small diseased blind area will escape from detection. 
         [0095]    Furthermore, the detail and clarity in the scanning result of the present invention enables one to differentiate the diseased blind area from the natural blind spot around the natural blind spot area as in contrast to the SAP test which shows the diseased blind area and the natural blind spot as one fuzzy lump, causing doctors to misdiagnose as described in the following.  FIG. 15A  is the test result taken with a SAP of the left eye of a glaucoma patient, whose name will not be revealed to protect privacy. Note that in this machine plot of  FIG. 15A , doctors knew that two fuzzy lumps  104  and  105  were actually one single fuzzy lump, which was just separated by the negative x-axis and its scale. Two of the patient&#39;s doctors, including one glaucoma specialist, knew that fuzzy lumps  104  and  105  were at the approximate location of the natural blind spot. Therefore, both doctors told the patient that fuzzy lumps  104  and  105  were just the natural blind spot and that there was no diseased blind area there. A week prior to the doctor&#39;s tests, the patient used the present invention to scan the same eye, and the result is shown in  FIG. 15B . It was a trial test with no charge to the patient. The result as shown in  FIG. 15B  was amazing.  FIG. 15B  clearly shows two distinct blind areas: (1) A normal left eye natural blind spot  107  which is about the same size but in the opposite location of the right eye&#39;s natural blind spot  103  of  FIG. 14 . (2) A diseased blind area  106  which has no definite shape and is clearly distinguishable from natural blind spot  107 . Thus it is seen that the present invention is able to detect the diseased blind areas in the vicinity of the natural blind spot, and because of its detail and clarity, doctors will be able to properly diagnose a diseased eye that would have been misdiagnosed as a healthy eye by SAPs. 
       Macular Degeneration: FIGS. 16A-16B 
       [0096]    In the early stages of macular degeneration, one&#39;s vision may have small diseased spots which may appear as (1) blank spots or blind spots (2) blotches, that is, gray or black stain-like spots, (3) blurred spots, or (4) distortion spots where straight lines appear wavy. 
         [0097]    The present invention can be used to detect the above-mentioned types (1), (2), and (3) diseased spots from the early stages of macular degeneration. In this test, a bright color, say red, will be used for test mark  97  so that it is clearly distinguishable from type (2) diseased spots, that is, gray or black stain-like spots. Different colored inkpads can be used for different types of diseased spots. The user should write a note or legend on visual field grid sheet  100  as to which ink color is used for what type of diseased spot. 
         [0098]    In the later stages of macular degeneration, the diseased spots may cover eye fixation mark  101  at the center of visual field grid sheet  100 . Therefore, eye fixation mark  101  cannot be seen by the test eye; hence it cannot be used to fix the test eye in this special case. To fix the test eye for this case, the natural blind spot will be used as follows. As mentioned above, the boundary of the natural blind spot is very sharp and when test mark  97  is moved across the boundary from the outside to the inside of the natural blind spot, the eye will perceive test mark  97  from being clearly visible to being completely invisible with no fuzzy transition image in between. Furthermore, the present invention has clearly identified the location and size of the natural blind spot; therefore, referring to  FIG. 16A  and  FIG. 16B , we can put two marks  305  and  301  adjacent to one another aligned horizontally on visual field grid sheet  100 . Mark  305  is outside and mark  301  is inside of an expected natural blind spot  304  of the left eye. Note that since the shape of the natural blind spot differs from person to person, in  FIG. 16B , we shall approximate that natural blind spot  304  is represented by a circle. Marks  305  and  301  are slightly below the negative x-axis, that is, at about the 185 degree polar angle and about the 18 degree visual angle. Eye fixation using these two dots  305  and  301  can be done as follows. Since the patient&#39;s central vision is diminished, he or she should use his or her peripheral vision to perceive two marks  305  and  301  by turning the left eye from the left to the right. At first, two marks  305  and  301  will both appear, indicating that they are on the right side of natural blind spot  304 . Then the two marks disappear indicating that they are inside the natural blind spot  304 . Then the two dots appear again. At that moment, two marks  305  and  301  are just outside the left edge of the natural blind spot. Then, the user fine-tunes the position by turning his or her left eye very slowly to the left until one of two marks, that is mark  301 , disappears. That is, mark  301  is just inside natural blind spot  304  and mark  305  is just outside. Holding this position to perform the diseased spot scanning would ensure proper fixation. 
         [0099]    The test eye can be further fixed in the vertical direction by having another two marks  302  and  303  adjacent to one another on visual field grid sheet  100  aligned vertically across the upper edge of the natural blind spot. Two marks  302  and  303  are located slightly above the negative x-axis, that is, 173 degree polar angle and at the 16 degree visual angle. After the user has horizontally fixed the left test eye with marks  305  and  301 , he or she would then move the eye slowly up or down until mark  303  disappears from view while 302 remains. In this position, only marks  305  and  302  are visible. Holding this position, the user would then be able to scan without requiring a fixation point. This method of using horizontally aligned marks  305  and  301  and vertically aligned marks  302  and  303  for the eye fixation is more difficult to perform and can only be used by skillful users. For the unskillful user, using only horizontally aligned marks  305  and  301  is sufficient. 
         [0100]      FIG. 16A  also shows two horizontally aligned marks  309  and  306  and two vertically aligned marks  307  and  308  for testing the right eye. These marks are symmetrical about the y-axis with the dots mentioned above for the left eye testing and would be used to fix the right eye in the similar manner as described above. That is, marks  309  and  306  are located about the 18 degree visual angle and about the 355 degree polar angle, and marks  307  and  308  are located at about the 16 degree visual angle and about the 7 degree polar angle for right eye scanning.