U.S. patent application number 09/817083 was filed with the patent office on 2001-11-22 for visual acuity examination apparatus.
This patent application is currently assigned to NIDEK CO., LTD. Invention is credited to Hayashi, Akihiro, Kanazawa, Yuichiro, Nozawa, Noritsugu.
Application Number | 20010043309 09/817083 |
Document ID | / |
Family ID | 26589015 |
Filed Date | 2001-11-22 |
United States Patent
Application |
20010043309 |
Kind Code |
A1 |
Hayashi, Akihiro ; et
al. |
November 22, 2001 |
Visual acuity examination apparatus
Abstract
A visual acuity examination apparatus for examining a visual
acuity of an examinee by presenting an optotype to the examinee
includes an optotype presenting unit which selectively presents at
least one of a plurality of comparison optotypes expressed in
geometrical series, the optotypes being provided to be plural in
number for each visual acuity value, an input unit with which a
distinction answer of the examinee with respect to the presented
optotype is input, a storage unit in which an examination program
which sequentially determines an optotype to be next presented
based on whether the distinction answer with respect to the
presented optotype is right or wrong is stored, a control unit
which controls the optotype presenting unit in accordance with the
examination program, and a processing unit which determines a
visual acuity value of the examinee from a percentage of right
answers in the distinction answers with respect to an optotype for
a visual acuity value.
Inventors: |
Hayashi, Akihiro;
(Toyokawa-shi, JP) ; Kanazawa, Yuichiro;
(Okazaki-shi, JP) ; Nozawa, Noritsugu;
(Toyokawa-shi, JP) |
Correspondence
Address: |
OLIFF & BERRIDGE, PLC
277 S. WASHINGTON STREET, SUITE 500
ALEXANDRIA
VA
22314
US
|
Assignee: |
NIDEK CO., LTD
|
Family ID: |
26589015 |
Appl. No.: |
09/817083 |
Filed: |
March 27, 2001 |
Current U.S.
Class: |
351/243 |
Current CPC
Class: |
A61B 3/032 20130101 |
Class at
Publication: |
351/243 |
International
Class: |
A61B 003/02 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 31, 2000 |
JP |
2000-96087 |
Mar 31, 2000 |
JP |
2000-96090 |
Claims
What is claimed is:
1. A visual acuity examination apparatus for examining a visual
acuity of an examinee by presenting an optotype to the examinee,
the apparatus including: an optotype presenting unit which
selectively presents at least one of a plurality of comparison
optotypes expressed in geometrical series, the optotypes being
provided to be plural in number for each visual acuity value; an
input unit with which a distinction answer of the examinee with
respect to the presented optotype is input; a storage unit in which
an examination program which sequentially determines an optotype to
be next presented based on whether the distinction answer with
respect to the presented optotype is right or wrong is stored; a
control unit which controls the optotype presenting unit in
accordance with the examination program; and a processing unit
which determines a visual acuity value of the examinee from a
percentage of right answers in the distinction answers with respect
to an optotype for a visual acuity value.
2. The visual acuity examination apparatus according to claim 1,
wherein the examination program includes a step of sequentially
presenting all of optotypes belonging to a first visual acuity
value at which a majority of the distinction answers are right and
all or some of optotypes belonging to a second visual acuity value
which is higher by one level than the first visual acuity value,
and the processing unit determines the visual acuity value from the
percentages of right answers in relation to the first and second
visual acuity values.
3. The visual acuity examination apparatus according to claim 2,
wherein the presenting step included in the examination program
includes a step of sequentially presenting all of the optotypes
belonging to the first visual acuity value and then all of the
optotypes belonging to the second visual acuity value.
4. The visual acuity examination apparatus according to claim 2,
wherein the presenting step included in the examination program
includes a step of sequentially presenting the optotypes belonging
to the second visual acuity value when the majority of the
distinction answers in relation to the first visual acuity value
are right, and sequentially presenting unpresented optotypes
belonging to the first visual acuity value again when the majority
of the distinction answers in relation to the second visual acuity
value are wrong.
5. The visual acuity examination apparatus according to claim 1
further including a display unit which displays the visual acuity
value determined by the processing unit, the visual acuity value
being expressed in a form selected between a logarithmic visual
acuity value form and a decimal visual acuity value form.
6. The visual acuity examination apparatus according to claim 1,
wherein the optotype presenting unit includes: an optotype disc
plate on which a plurality of charts each provided with one
optotype or a plurality of optotypes is formed in a circle; a mask
disc plate on which a plurality of masks for presenting one
optotype or at least a part of the optotypes formed on the chart; a
rotating unit which individually rotates the optotype disc plate
and the mask disc plate, thereby to selectively present the
optotype; and the control unit controls the rotating unit in
accordance with the examination program.
7. The visual acuity examination apparatus according to claim 6,
wherein the plurality of optotypes formed on the chart are
configured in one line or three lines.
8. The visual acuity examination apparatus according to claim 7,
wherein the optotypes each having a small size corresponding to
decimal visual acuity values of 0.2 or less are configured in three
lines of five characters, while the optotypes each having a large
size corresponding to visual acuity values of more than 0.2 are
configured in one line.
9. The visual acuity examination apparatus according to claim 7,
wherein the plurality of masks include a single-character mask for
individually presenting the one optotype and a lateral mask for
presenting the optotypes per line among the optotypes configured in
three lines.
10. A visual acuity examination apparatus which switches and
displays an optotype in a screen, the apparatus including: an
optotype disc plate on which a plurality of charts each provided
with one optotype or a plurality of optotypes are formed in a
circle, the plurality of optotypes being configured in one line or
three line in the chart; a mask disk plate on which a plurality of
masks for presenting one optotype or at least a part of the
optotypes formed on the chart; and a rotating unit which
individually rotates the optotype disc plate and the mask disc
plate, thereby to selectively present the optotype.
11. A visual acuity examination apparatus for examining a visual
acuity of an examinee by presenting an optotype to the examinee,
the apparatus including: an optotype presenting unit which
selectively presents at least one of a plurality of comparison
optotypes expressed in geometrical series, the optotypes being
provided to be plural in number for each visual acuity value; an
input unit with which a distinction answer of the examinee with
respect to the presented optotype is input; a storage unit in which
an examination program which sequentially determines an optotype to
be next presented based on whether the distinction answer with
respect to the presented optotype is right or wrong is stored; and
a control unit which controls the optotype presenting unit in
accordance with the examination program.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a visual acuity examination
apparatus for examining the visual acuity of an examinee, or an eye
of the examinee, by presenting optotypes to the examinee.
[0003] 2. Description of Related Art
[0004] There have been known visual acuity examination apparatuses
for estimating the visual acuity of an examinee by sequentially
presenting a plurality of optotypes for different visual acuity
values (visual acuity levels or scales) to the examinee, or an eye
of the examinee, and determining the visual acuity of the examinee
based on whether the examinee could see (distinguish) or not the
presented optotypes. Heretofore, the visual acuity examination
apparatus of this type would generally perform a visual acuity
examination by the use of optotypes expressed in decimal values for
visual acuity.
[0005] However, the optotypes expressed in the decimal visual
acuity values differ in size difference according to visual acuity
values, and therefore accurate estimation could not be executed. To
be more specific, in the decimal visual acuity values, the
improvement in visual acuity from 0.2 to 0.3 and the improvement
from 0.9 to 1.0 are both considered as the improvement of one level
of visual acuity. However, if expressing in visual angle, the
increase from 0.2 to 0.3 corresponds to 1.5 times the visual angle,
while the increase from 0.9 to 1.0 corresponds to about 1.1
(1.0/0.9) times. Therefore, it would be difficult to make the same
estimation in the above cases.
[0006] In judgement of the visual acuity, if five optotypes for the
same visual acuity value are used, the maximum value among the
visual acuity values of the optotypes to which three or more right
answers are given (i.e., the largest value in decimal visual acuity
values) is directly regarded as the visual acuity value of the
examinee (the examinee's eye). Consequently, the estimation would
be rough and insufficient for the ophthalmologists and the like to
confirm treatment results and correction results.
SUMMARY OF THE INVENTION
[0007] The present invention has been made in view of the above
circumstances and has an object to overcome the above problems and
to provide a visual acuity examination apparatus capable of easily
and simply obtaining and estimating the visual acuity of an
examinee's eye.
[0008] Additional objects and advantages of the invention will be
set forth in part in the description which follows and in part will
be obvious from the description, or may be learned by practice of
the invention. The objects and advantages of the invention may be
realized and attained by means of the instrumentalities and
combinations particularly pointed out in the appended claims.
[0009] To achieve the purpose of the invention, there is provided a
visual acuity examination apparatus for examining a visual acuity
of an examinee by presenting an optotype to the examinee, the
apparatus including: an optotype presenting unit which selectively
presents at least one of a plurality of comparison optotypes
expressed in geometrical series, the optotypes being provided to be
plural in number for each visual acuity value; an input unit with
which a distinction answer of the examinee with respect to the
presented optotype is input; a storage unit in which an examination
program which sequentially determines an optotype to be next
presented based on whether the distinction answer with respect to
the presented optotype is right or wrong is stored; a control unit
which controls the optotype presenting unit in accordance with the
examination program; and a processing unit which determines a
visual acuity value of the examinee from a percentage of right
answers in the distinction answers with respect to an optotype for
a visual acuity value.
[0010] According to another aspect of the present invention, there
is provided a visual acuity examination apparatus which switches
and displays an optotype in a screen, the apparatus including: an
optotype disc plate on which a plurality of charts each provided
with one optotype or a plurality of optotypes are formed in a
circle, the plurality of optotypes being configured in one line or
three line in the chart; a mask disk plate on which a plurality of
masks for presenting one optotype or at least a part of the
optotypes formed on the chart; and a rotating unit which
individually rotates the optotype disc plate and the mask disc
plate, thereby to selectively present the optotype.
[0011] According to another aspect of the present invention, there
is provided a visual acuity examination apparatus for examining a
visual acuity of an examinee by presenting an optotype to the
examinee, the apparatus including: an optotype presenting unit
which selectively presents at least one of a plurality of
comparison optotypes expressed in geometrical series, the optotypes
being provided to be plural in number for each visual acuity value;
an input unit with which a distinction answer of the examinee with
respect to the presented optotype is input; a storage unit in which
an examination program which sequentially determines an optotype to
be next presented based on whether the distinction answer with
respect to the presented optotype is right or wrong is stored; and
a control unit which controls the optotype presenting unit in
accordance with the examination program.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] The accompanying drawings, which are incorporated in and
constitute a part of this specification illustrate an embodiment of
the invention and, together with the description, serve to explain
the objects, advantages and principles of the invention.
[0013] In the drawings,
[0014] FIG. 1 is a schematic front view of a main unit of a visual
acuity examination apparatus in an embodiment according to the
present invention;
[0015] FIG. 2 is a schematic view of an optical system disposed in
the main unit seen from side;
[0016] FIG. 3 is a schematic view of the optical system disposed in
the main unit seen from front;
[0017] FIG. 4 is a front view of an optotype disc plate in the
embodiment;
[0018] FIG. 5 is a front view of a mask disc plate in the
embodiment;
[0019] FIG. 6 is an explanatory view of charts on which Landolt
ring optotypes are provided in the embodiment;
[0020] FIG. 7 is a front view of a remote control unit in the
embodiment.
[0021] FIG. 8 is a block diagram of a control system (an electric
system) of the apparatus in the embodiment;
[0022] FIG. 9 is an explanatory view showing an example of a manner
of determining a visual acuity value;
[0023] FIG. 10 is an explanatory view showing another example of a
manner of determining a visual acuity value;
[0024] FIG. 11 is a flowchart of a judgment routine to be executed
in response to depression of a YES switch;
[0025] FIG. 12 is a flowchart of another judgment routine to be
executed in response to depression of a NO switch; and
[0026] FIG. 13 is a flowchart of a Log judgment routine.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0027] A detailed description of a preferred embodiment of a visual
acuity examination apparatus embodying the present invention will
now be given referring to the accompanying drawings. FIG. 1 is a
schematic front view of the visual acuity examination apparatus in
the embodiment.
[0028] Numeral 1 is a main unit provided, at its front upper
portion, with a window 2 made of a glass plate on which an
antireflective film is provided. An examinee is allowed to view
through this window 2 optotypes which should be presented in a
center of the main unit 1. This window 2 may be made of a filter
instead of the glass plate. The interior of the main unit 1 is
painted in black color so that the examinee can hardly look the
interior structure of the main unit 1.
[0029] Numeral 3 is a power switch, and 3a is an indication lamp
for informing that the power switch 3 has been turned on. Numeral 4
is a window for transmission and receipt of optical signals with
respect to a wireless remote control unit 40 which will be
mentioned later.
[0030] Next, an optical system disposed in the main unit 1 is
explained with reference to FIGS. 2 and 3. FIG. 2 is a schematic
right side view of the main unit 1 with the optical system seen
therethrough. FIG. 3 is a schematic front view of the main unit 1
with the optical system seen therethrough.
[0031] An alphabet E denotes an eye of an examinee. Numeral 20 is
an optotype disc plate made of glass. On this disc plate 20, many
optotypes for visual acuity examination such as optotypes for
various visual acuity values and others are formed in a circle by
chrome evaporation and the like. The optotype disc plate 20 is
rotated by a motor 21 to change optotypes (charts) to be presented
to the examinee. Numeral 22 is a mask disc plate for partially
masking the optotypes. This mask disc plate 22 is rotated by a
motor 23 to cover a desired part of the disc plate 20. The details
of the optotype disc plate 20 and the mask disc plate 22 will be
described later.
[0032] Numeral 24 is an illumination lamp for illuminating the
optotypes (charts) provided on the optotype disc plate 20; 25 is a
mirror; 26 is a beam splitter; and 27 is a concave mirror. The
concave mirror 27 in the present embodiment is designed to have a
focal distance so that an optical distance between the optotype and
the examinee's eye E is adjusted to an examination distance of 5 m
when the distance between the eye E and the window 2 is 0.9 m.
[0033] Luminous flux of the optotype illuminated by the
illumination lamp 24 is reflected upward by the mirror 25,
permitted to transmit through the beam splitter 26, and reflected
by the concave mirror 27. The optotype luminous flux reflected by
the mirror 27 is then reflected by the beam splitter 26 toward the
eye E through the window 2. Since the beam splitter 26 is fixed to
a rotating shaft 28, an inclination angle of the beam splitter 26
is changed in accordance with the rotation of the shaft 28 caused
by a motor 29. Thus, the optical path of the optotype luminous flux
reflected by the beam splitter 26 is shifted in an up or down
direction to be adjusted to the positional height of the eye E, so
that the optotype light is properly delivered to the eye E.
[0034] Numeral 30 is a detection optical system for detecting the
positional height of the eye E. This optical system 30 includes a
light condensing lens 31 and a two-dimensional position detecting
element 32, which are disposed in the inside of the main unit 1 on
right and left sides of the window 2. An infrared light emitted
from a light-emitting section of the remote control unit 40
mentioned later is condensed by the condensing lens 31 onto the
position detecting element 32 which outputs a detection signal.
Based on this detection signal from the position detecting element
32, the height of the examinee's eye E is detected. The detail
method of adjusting the optical path of the optotype luminous flux
to the height of the examinee's eye is referred to U.S. Pat. No.
5,485,231 (corr. to Japanese Patent Unexamined Application No.
7-236612).
[0035] Next, the optotype disc plate 20 is explained in detail with
reference to FIG. 4.
[0036] The optotypes such as Landolt rings and others to be used
for the conventional visual acuity examination apparatuses are
represented in decimal visual acuity values. As the optotypes to be
used in the present embodiment, on the other hand, a visual angle
of the minimum separation threshold is expressed in common
logarithm (comparison optotypes expressed in geometrical series,
which is hereinafter referred to as LogMAR (the logarithm of the
minimum angle of resolution) optotype).
[0037] In the conventional decimal values for visual acuity, which
are expressed as 0.1, 0.2-0.8, 0.9, 1.0 . . . , a visual acuity
level changes by 0.1 each in decimal. Therefore, the improvement of
visual acuity from 0.2 to 0.3 and the improvement from 0.9 to 1.0
are both regarded as one-level improvement of the visual acuity. In
this conventional case, however, if expressing the visual acuity in
terms of visual angle, the former corresponds to 1.5 times the
visual angle, while the latter corresponds to 1.0/0.9=1.1 times.
Consequently, it can not be said that the estimation of the visual
acuity is accurately executed.
[0038] On the other hand, the LogMAR optotypes used in the present
embodiment are formed in increments of 0.1 in a range of -0.3 to
+1.4 on condition that the logarithmic visual acuity value of a
Landolt ring optotype corresponding to decimal visual acuity value
of 1.0 is regarded as zero. As a result of this, the size
differences of optotypes according to visual acuity values are
equal. On the other hand, the visual acuity values in the LogMAR
optotypes are expressed as the decimal visual acuity values
converted therefrom for the purpose of making them clearly
understandable for examinees.
[0039] As shown in FIG. 4, the optotype disc plate 20 is provided
thereon with a chart section 50 including thirteen charts each
having Landolt ring optotypes in the LogMAR, a chart section 51
including five charts each having Hiragana character optotypes
(which may be replaced by Alphabetical character optotypes) in the
LogMAR, and a chart section 52 including seven charts to be used
for a red and green test, a balance test of both eyes, and others.
Thus, total twenty-four charts are formed on the disc plate 20 in a
circle. A predetermined one of the above charts is placed on the
optical path of the lamp 24 to be presented as a screen in the
window 2.
[0040] The chart section 50 is explained below in detail, referring
to FIG. 6. In FIG. 6, small optotypes (Landolt ring optotypes for
decimal visual acuity values of 0.25-2.0) are illustrated in
enlarged sizes for convenience of explanation.
[0041] Charts 50a and 50b are each formed with a Landolt ring
optotype for a decimal visual acuity value of 0.04 (a logarithmic
visual acuity value of +1.4). Charts 50c and 50d are each formed
with a Landolt ring optotype for a decimal visual acuity value of
0.05 (a logarithmic visual acuity value of +1.3). The Landolt ring
optotypes formed on the charts 50a to 50d each have a slit formed
in one direction selected from among four upper, lower, right, and
left directions so that the slit directions are different from one
another among the charts 50a-50d.
[0042] A chart 50e is formed with two Landolt ring optotypes for a
decimal visual acuity value of 0.063 (a logarithmic visual acuity
value of +1.2), which are laterally aligned. A chart 50f is formed
with two Landolt ring optotypes for a decimal visual acuity value
of 0.08 (a logarithmic visual acuity value of +1.1), which are
laterally aligned as in the case of the chart 50e. The total four
Landolt ring optotypes formed on the charts 50e and 50f each have a
slit formed in one direction selected from among four upper, lower,
right, and left directions so that the slit directions are
different from one another among those four optotypes.
[0043] Charts 50g to 50i are each formed with three Landolt ring
optotypes for a decimal visual acuity value of 0.1 (a logarithmic
visual acuity value of +1.0), for 0.125 (+0.9), and for 0.16
(+0.8), respectively. The three Landolt ring optotypes in each
chart are laterally aligned.
[0044] Charts 50j to 50m are each formed with Landolt ring
optotypes for three kinds of visual acuity values, in which five
Landolt ring optotypes are prepared for each visual acuity value.
Each of the charts 50j to 50m therefore has total fifteen Landolt
ring optotypes.
[0045] To be more specific, the chart 50j has three optotype groups
for three decimal visual acuity values of 0.2, 0.25, and 0.32
(corresponding to logarithmic visual acuity values of +0.7, +0.6,
and +0.5); the chart 50k has three optotype groups for decimal
visual acuity values of 0.4, 0.5, and 0.63 (corr. to logarithmic
visual acuity values of +0.4, +0.3, and +0.2); the chart 501 has
three optotype groups for decimal visual acuity values of 0.7, 0.8,
1.0 (corr. to logarithmic visual acuity values of +0.1, 0);
[0046] the chart 50m has three optotype groups for decimal visual
acuity values of 1.25, 1.6, and 2.0 (corr. to logarithmic visual
acuity values of -0.1, -0.2, and -0.3).
[0047] It is to be noted that the Landolt ring optotype for the
decimal visual acuity value of 0.7 is not a LogMAR optotype shown
in the present embodiment. However, the decimal visual acuity value
of 0.7 is used as a reference visual acuity value for driver's
licenses or the like, and therefore the optotype group for the
decimal visual acuity value of 0.7 is added in the present
embodiment.
[0048] In the chart section 51, five charts formed with Hiragana
optotypes for decimal visual acuity values of 0.1 to 1.6 (corr. to
logarithmic visual acuity values +1.0 to -0.2) are prepared. The
optotype configuration in each of the charts is the same as that of
the Landolt ring optotypes mentioned above, and its explanation is
omitted.
[0049] Next, detailed explanation is made on the mask disc plate 22
for masking a desired portion of the optotype groups on the above
charts, referring to FIG. 5. Dash-single-dot lines in the drawing
correspond to centerlines of the charts in respective longitudinal
and lateral directions.
[0050] Numeral 60 is an opening for allowing the entire face of a
chart to be presented without masking. Numeral 61 denotes openings
(lateral masks) for presenting the optotypes aligned in a lateral
direction (corr. to a line in which the optotypes for the same
visual acuity value are arranged) in each optotype group including
three lines of five characters as shown in the charts 50j-50m,
thereby separately presenting an upper, medium, and lower lines.
Numeral 62 denotes openings (longitudinal masks) for presenting the
optotypes aligned in a longitudinal direction (corr. to a column in
which the optotypes for different visual acuity values are
arranged) in the optotype group including three lines of five
characters (five columns), thereby separately presenting a left,
center, and right columns.
[0051] Numeral 63 denotes openings (single-character masks) for
individually presenting the optotypes of the charts 50e and 50f in
each of which the optotypes are formed in one line of two
characters. Numeral 64 denotes openings (single-character masks)
for individually presenting the optotypes of the charts 50g-50i and
the like in each of which the optotypes are formed in one line of
three characters. Numeral 65 denotes openings (single-character
masks) for individually presenting the optotypes of the charts
50j-50m and the like in each of which the optotypes are formed in
three lines of five characters.
[0052] Meanwhile, in the case where detailed estimation is made
using the LogMAR optotypes as mentioned above, the kinds of
optotypes for lower visual acuity values than a decimal visual
acuity value of 0.2, that is, the kinds of large-sized optotypes,
need to be increased. In order to examine an accurate visual acuity
value, it is preferable to prepare different optotypes for the same
visual acuity value (such as Landolt ring optotypes having
different slit directions) in a larger number as much as possible.
Accordingly, in the present embodiment, if one chart can have only
one optotype due to its large size, at least two charts are
prepared for providing two or more different optotypes for the same
visual acuity value. If one chart can have plural optotypes for the
same visual acuity value, each chart is formed with optotypes in
the maximum number (with an upper limit of five optotypes in each
line) with sufficient intervals between the adjacently arranged
optotypes, thereby preventing interference with each other during
the visual acuity examination.
[0053] To form different optotypes in a large number as much as
possible in one chart with the increase of the optotypes for lower
visual acuity, the kinds of configuration patterns of the optotype
group formed on one chart should be increased. Therefore, without
contrivance of the configuration patterns, many openings need to be
formed on the mask disc plate 22 as compared with those in the
conventional apparatus. That is, if one chart is provided with
different optotypes in a large number as much as possible, the
following configuration patterns are conceivable; for example, one
line of one character, one line of two characters, two lines of
three characters, three lines of five characters, and others.
However, this needs many types of masks to apply single-character
masks and lateral masks to all patterns, and therefore such the
masks could not be formed in a single disc plate (mask disc).
[0054] In the present embodiment, as mentioned above, small-sized
optotypes such as those in the charts 50j-50m are configured in
three lines of five characters in one chart, while large-sized
optotypes are configured in one line in one chart. Thus, even if
many optotypes for lower visual acuity are formed in one chart, an
optotype group in one lateral line per visual acuity value and one
optotype can be presented in any of the charts, while the number of
types of masks can be reduced to a minimum. This makes it possible
to efficiently form masks in a single disc.
[0055] Next, the remote control unit 40 is described below in
detail with reference to FIG. 7.
[0056] Numeral 41 denotes a power switch; 42 is a group of chart
changing switches for selecting the chart; 43 is a mask switch for
selecting the type of the mask to be applied to the optotypes; and
44 is a group of optical path changing switches for changing the
direction of the optical path of an optotype presented to the
examinee. This switch group 44 when operated transmits infrared
light signals representative of positional detection for adjustment
of the height of the examinee's eye E or the switch group 44 is
used for manual operation to drive the motor 29, thereby changing
the direction of the optical path. Numeral 46 is a display for
displaying the optotype to be presented in the main unit 1 and its
visual acuity value; 47 is a group of optotype changing switches
for changing the optotypes to be presented by changing the position
of the masks. Numeral 48 is a display changing switch for selecting
the expression of the visual acuity value to be displayed in the
display 46 between decimal and logarithm.
[0057] Numeral 49 is a group of automation switches for execution
of a visual acuity examination program which will be mentioned
later. This switch group 49 is also used for inputting whether the
answer of the examinee about the optotype presented in the main
unit 1 is right or wrong. The switch group 49 includes a YES switch
to be used for the right answer of the examinee and a NO switch for
the wrong answer or the case where the examinee answered he could
not see or distinguish the presented optotype. The remote control
unit 40 is also provided, at its front portion, with a signal
transmittance/receipt portion 40a for transmitting/receiving pulse
signals of infrared light.
[0058] Operation of the apparatus constructed as above will be
explained below with reference to FIG. 8.
[0059] The examiner instructs, first, the examinee to take a
predetermined position (which is at a distance of 0.9 m from the
window 2 in the present embodiment) in front of the main unit 1.
Then, the examiner manipulates the remote control unit 40 to start
the visual acuity examination. The examiner operates the switch
group 42, the switch 43, and the switch group 47 to present one or
plural desired optotypes. The signal representative of the
information on the selected optotypes and the mask, emitted from
the signal transmittance/receipt portion 40a is received at a light
receiving section 36 disposed in the main unit 1 through the signal
transmittance/receipt window 4. The signal received at the light
receiving section 36 is transmitted to a processing and control
section 38 through a signal processing circuit 33. Upon receipt of
the signal from the signal processing circuit 33, the processing
and control section 38 causes the motors 21 and 23 to set the chart
and the mask opening corresponding to the received signal onto the
optical path. The processing and control section 38 then causes a
light emitting section 37 to transmit a signal representative of
the information on the presented optotype via a signal processing
circuit 34. The transmitted signal is received at the signal
transmission/receipt portion 40a of the remote control unit 40. The
optotype information is displayed in the display 46 along with the
visual acuity value, thereby to prevent inconsistency from
occurring between the displayed optotype(s) and the presented
optotype(s).
[0060] Next, explanation is made on an automatic examination for
automatically presenting next optotypes by only input of a
decision, right or wrong, with respect to the answer of the
examinee by means of the switch group 49.
[0061] The examiner operates the switch group 42, the switch 43,
and the switch group 47 to present an optotype regarded as being
appropriate (distinguishable) for the examinee (this visual acuity
value may be determined based on results of an objective
examination and the like). The examiner asks the examinee to answer
whether he can see (distinguish) or not the presented optotype,
namely, a distinction result thereof. Confirming whether the answer
of the examinee is right or wrong, the examiner presses the YES
switch or NO switch of the switch group 49 in accordance with the
confirmation result. Upon depression of the YES/NO switch, the
automatic examination program mentioned below is executed.
Furthermore, the information on the right or wrong answer, inputted
with the switch group 49, is all recorded in a memory 35 and used
for subsequent judgement routines and calculation of a final visual
acuity value of the examinee.
[0062] The judgement routines of the automatic examination program
in the present embodiment are explained below with reference to
FIGS. 11, 12, and 13. Using those judgement routines, an example of
a manner of determining a visual acuity value is explained with
reference to FIG. 9. It is to be noted that the automatic
examination program is stored in a storage circuit of the
processing and control section 38.
[0063] In FIG. 9, numerals (-0.2 to +0.3) written at the left are
the logarithmic visual acuity values of the optotypes to be
presented. A mark .smallcircle. denotes a right answer. A mark X
denotes a wrong answer or the case where an examinee answered he
could not distinguish a slit of a presented optotype. Circled
numerals indicate the order of examination procedures.
[0064] If the answer of the examinee with respect to the optotype
first presented (in the example shown in FIG. 9, the optotype for a
logarithmic visual acuity value of +0.3 (corr. to a decimal visual
acuity value of 0.5)) is right, in other words, if the YES switch
is pressed, the estimation is made as follows in accordance with
the judgement routine shown in FIG. 11 to decide the next optotype
to be presented.
[0065] The processing and control section 38 confirms whether Log
judgement is in progress (Step 1). The Log judgement in progress
means the condition that, as a result of distinction made over
several times, the maximum value among the visual acuity values
(the smallest value for a logarithmic visual acuity value) at which
the majority of examinee's answers about the optotypes for the same
acuity value were right and the minimum value among the visual
acuity values (the largest value for a logarithmic visual acuity
value) at which the majority of examinee's answers about the
optotypes for the same acuity value were wrong have already been
obtained, and the next stage is only the distinction with respect
to the unpresented optotypes for those two visual acuity values. In
this example, since it is the first optotype distinction, the
processing and control section 38 determines that the Log judgement
is not in progress.
[0066] Successively, in Step 2, it is judged whether the visual
acuity value has been decreased by two levels (to a logarithmic
visual acuity value of +0.2). If NO in step 2, a decision is made
as to whether there is no wrong answer in the examinations made
until now (Step 3).
[0067] If there is no wrong answer, it is determined in Step 4
whether the currently presented optotype is an optotype for a
visual acuity value higher by one-level (a logarithmic visual
acuity value of +1.3) than the minimum visual acuity value, and
then in Step 5 whether it is an optotype for the minimum visual
acuity value (a logarithmic visual acuity value of +1.4). If NO in
both Steps 4 and 5, in Step 6, the processing and control section
38 causes the optotype disc plate 20 and the mask disc plate 22 to
rotate, thereby presenting an optotype for a visual acuity value
higher by two-levels (a logarithmic visual acuity value of +0.1; a
decimal visual acuity value of 0.8) to the examinee. If the answer
of the examinee with respect to this optotype is right, the control
section 38 controls, through the same steps as above, to present an
optotype for a visual acuity value higher by another two-levels (a
logarithmic visual acuity value of -0.1; a decimal visual acuity
value of 1.25).
[0068] If the distinction answer with respect to the optotype for
the logarithmic visual acuity value of -0.1 is wrong, the examiner
depresses the NO switch. Upon depression of the NO switch, the next
optotype to be presented is determined in accordance with the
judgement routine shown in FIG. 12 (the judgement routine to be
executed when the NO switch is depressed). Like in FIG. 11, after
Step 1', it is determined in Step 2' whether the visual acuity
value has been increased by two-levels (to a logarithmic visual
acuity value of -0.2). In this example, since the visual acuity
value has been increased by two-levels, the processing and control
section 38 operates to present an optotype for a visual acuity
value lower by one-level (to a logarithmic visual acuity value of
0; a decimal visual acuity value of 1.0) to the examinee in Step
7'.
[0069] If the distinction answer about the optotype for the
logarithmic visual acuity value of 0 is right, a decision is made
again in accordance with the judgement routine of FIG. 11. After
Steps 1 and 2, the flow advances to Step 3. In this example, the
distinction answer about the previously presented optotype for the
logarithmic visual acuity value of -0.1 was wrong, and therefore it
is determined in Step 8 whether there have been three right answers
among the distinction answers about the optotypes for that visual
acuity value. In this example, there are not three right answers
and the processing and control section 38 presents a different
optotype for the same visual acuity value (the logarithmic visual
acuity value of 0).
[0070] In the above way, when the examinee distinguishes the
optotypes for the logarithmic visual acuity value of 0 and gives
right answers three times with respect to that visual acuity value,
after Step 8, it is determined in Step 9 whether the optotypes are
for the maximum visual acuity value (a logarithmic visual acuity
value of -0.3). If it is not for the maximum visual acuity value,
an optotype for a visual acuity value higher by one-level (a
logarithmic visual acuity value of -0.1) in Step 10.
[0071] In Step 11, it is judged whether there have been three wrong
answers among the distinction answers about the optotypes for the
logarithmic visual acuity value of -0.1. If no three wrong answers,
a different optotype from the previously presented optotypes is
presented to the examinee. If the examinee gives a right answer
with respect to the presented optotype, a different optotype for
the same visual acuity value is presented in accordance with the
judgment routine of FIG. 11. If the examinee gives a wrong answer
with respect to the presented optotype, alternatively, a different
optotype for the same visual acuity value is presented in
accordance with the judgement routine of FIG. 12.
[0072] In the above manner, distinction is made several times with
respect to the optotypes for the logarithmic visual acuity of -0.1.
For the third wrong answer, the flow advances through Steps 1', 2',
3', 8', and 9' to Step 10' where an optotype for a lower visual
acuity value by one-level (a logarithmic visual acuity value of 0)
is presented. It is then determined whether there are three right
answers (Step 1'). If YES, the Log judgement routine is executed
from that visual acuity value.
[0073] FIG. 13 shows a flowchart of the Log judgement routine. At
this time, right answers have already been obtained about three
optotypes which are the majority of five optotypes for the
logarithmic visual acuity value of 0, and wrong answers have been
obtained about three optotypes which are the majority of five
optotypes for the logarithmic visual acuity value of -0.1. Thus,
the subsequent optotype distinction is treated as the Log judgement
in progress.
[0074] In this Log judgement routine, the unpresented optotypes
(the remainder optotypes are two in this example) of the visual
acuity value (the logarithmic visual acuity value of 0) at which
three right answers have been obtained are presented in sequence.
After all the optotypes (five in this example) are presented, the
unpresented optotypes (the remainder is one in this example) for
the visual acuity value (a visual acuity value higher by one-level
(the logarithmic visual acuity value of -1)) at which three wrong
answers have been obtained are presented in sequence to the
examinee, allowing him to answer whether he can distinguish each of
the optotypes.
[0075] When the distinction answers (right or wrong) are obtained
about all the optotypes in relation to the two visual acuity
values; the maximum value of the visual acuity values at which the
three right answers have been obtained and the minimum value of the
visual acuity values at which three wrong answers have been
obtained, the processing and control section 38 determines the
visual acuity value of the examinee based on the information on the
right/wrong answers stored in the memory 35.
[0076] Processing of the visual acuity value in the present
embodiment is performed in the following manner. In the case where
there are five optotypes for the same visual acuity value, each
optotype is assigned 0.02 each in logarithmic visual acuity value.
If the answers about all the optotypes for the same visual acuity
value are right, it is assumed that the same visual acuity value
can be obtained. If there are wrong answers, on the other hand,
0.02 each in the logarithmic visual acuity value by the number of
wrong answers is added to the visual acuity value. This is applied
to the maximum value among the visual acuity values at which the
examinee could distinguish and the minimum value among the visual
acuity values at which the examinee could not distinguish. Thus, a
further minute visual acuity value is found based on those two
visual acuity values. Then, the two found visual acuity values are
averaged to determine a final visual acuity value, which is treated
as the visual acuity value of the examinee.
[0077] In the example shown in FIG. 9, at the logarithmic visual
acuity value of 0 that is the maximum value of the visual acuity
values at which the examinee could distinguish, there are four
right answers and one wrong answer. Therefore, the minute visual
acuity value at this level is 0+0.02.times.1=0.02. On the other
hand, at the logarithmic visual acuity value of -0.1 that is the
minimum value of the visual acuity value at which the examinee
could not distinguish, there are two right answers and three wrong
answers. As a result thereof, the minute visual acuity value at
this level is -0.1+0.02.times.3=-0.04. The two visual acuity values
are averaged and a resultant final visual acuity value of the
examinee is -0.01.
[0078] This result is displayed as the logarithmic in the display
46. If a corresponding decimal visual acuity value is desired, the
switch 48 is depressed, whereby causing the processing and control
section 38 to convert the logarithmic visual acuity value to the
corresponding decimal visual acuity value, which is displayed on
the display 46. In this example, this decimal visual acuity value
displayed is 1.023.
[0079] As described above, in the present embodiment, the
information on the right and wrong answers (a percentage of right
answers) with respect to all the optotypes for the maximum value of
the visual acuity values at which the examinee could distinguish
and the information on the right and wrong answers with respect to
all the optotypes for the minimum value of the visual acuity values
at which the examinee could not distinguish are used to determine
the visual acuity of the examinee. Consequently, the visual acuity
examination apparatus in the present embodiment can provide a more
accurate and minute visual acuity value as compared with the
conventional estimation for a visual acuity value.
[0080] The present invention may be embodied in other specific
forms without departing from the spirit or essential
characteristics thereof. For instance, in the above embodiment, the
right/wrong answers about three among five optotypes for the same
visual acuity value are used to judge whether the examinee could
distinguish that visual acuity value. Alternatively, based on
whether the majority (or 60% or more) of answers about the
optotypes for the same visual acuity value are right, it may be
judged whether the examinee could distinguish the optotypes for
that visual acuity value. For example, for four optotypes for the
same visual acuity value, it may be determined that the examinee
could distinguish the optotypes for that visual acuity value if
only two or three among the answers are right. In this case, each
of the optotypes is assigned 0.025 in the logarithmic visual acuity
value. For only two optotypes for the same visual acuity value, it
may be decided that the examinee could distinguish the optotypes
for that visual acuity value only if all of the answers are
right.
[0081] The examination procedure in the case where the next
optotype is automatically presented in accordance with the answer
of the examinee is not limited to the above. Any examination
procedures may be adopted if only the maximum value among the
visual acuity values at which the examinee could distinguish and
the minimum value among the visual acuity values at which the
examinee could not distinguish can be finally determined and the
information on the right/wrong answers about all the optotypes for
the two visual acuity values can be obtained.
[0082] For instance, as shown in FIG. 10, the following procedure
may be used; when the answer with respect to one optotype (e.g., an
optotype for a logarithmic visual acuity value of -0.1) is wrong,
the examinee is asked to individually distinguish all the optotypes
for a visual acuity value lower by one-level (a logarithmic visual
acuity value of 0) and then distinguish all the optotypes for the
previous visual acuity value at which the examinee gave the wrong
answer. In this case, if there are three wrong answers about the
optotypes for the logarithmic visual acuity value of 0, the
optotypes for a visual acuity value further lower by one-level (a
logarithmic visual acuity value of +0.1) is presented and the same
procedure is conducted.
[0083] In the above embodiment, the present invention is applied to
the visual acuity examination apparatus capable of presenting
optotypes in small space, but not limited thereto. The present
invention may be applied to any visual acuity examination
apparatuses capable of individually presenting optotypes under
electrical control.
[0084] The answer results of the examinee may be input with a
joystick or the like. In this case, the steps up to the right/wrong
judgment with respect to the presented optotypes may be conducted
in accordance with the automatic examination program, whereby more
easily performing the examination.
[0085] According to the present invention, the visual acuity of the
examinee's eye can accurately and easily be obtained and
estimated.
[0086] The foregoing description of the preferred embodiment of the
invention has been presented for purposes of illustration and
description. It is not intended to be exhaustive or to limit the
invention to the precise form disclosed, and modifications and
variations are possible in light of the above teachings or may be
acquired from practice of the invention. The embodiment chosen and
described in order to explain the principles of the invention and
its practical application to enable one skilled in the art to
utilize the invention in various embodiments and with various
modifications as are suited to the particular use contemplated. It
is intended that the scope of the invention be defined by the
claims appended hereto, and their equivalents.
* * * * *