A COMPUTERIZED SELF VISUAL ACUITY TESTING SYSTEM
Method of the Optotype Presentation and Adjustment
WooBeom Lee and ChangYur Choi
School of Computer Information Enginnering, Sangji University, 660 woosan-dong, Wonju-si, Kangwon-do 220-702, Korea
Keywords: Visual-Acuity Testing, KS Optotype and its Presentation, Gesture Recognition, Renard Series, Randolt's
rings.
Abstract: This paper suggests the method of the optotype presentation and adjustment for a computerized self visual
acuity test. The proposed method is guaranteed credibility by ‘KS P ISO 8596’ in 2006. Also this system
provides convenience to people who take an eyesight test based on gesture recognition of them. And the
method of the optotype adjustment for a computerized self visual acuity test is able to measure objective
eyesight that excluded subjective judgment of inspector and conjecture of subject’s memorization.
According to result of experimental comparison between method of using real visual-acuity chart and the
system of a computerized self visual acuity test, Our system showed the 98% consistency in the limit of the
±1 visual-acuity level error.
1 INTRODUCTION
A visual-acuity test is fulfilled by using the visual-
acuity chart which arranged according to size, then
presenting the chart to subject in certain distance to
measure their eyesight in general. However, this
method is able to involve inspector’s subjective
point of view because the inspector measures vision.
Especially, the result from this method is lack of
credibility because same chart is used to test both
eyes, so subject might conjecture with one’s
memorization.
Therefore we propose a computerized self visual
acuity test system that is possible to solve those
problems(Bach et al., 2009). This system doesn’t
need inspectors because subjects can take a visual
acuity test by themselves to use computerized
program, so we can exclude those problems. And the
method of gesture recognition is similar to existing
visual acuity test that uses visual-acuity chart,
therefore subjects don’t show negative reaction
when they are taking the visual acuity test. Also, it
can possibly provide convenience to subjects by
inducing their interests for the test.
Especially, our system uses Landolt’s Ring
which is industry standards, also it uses P ISO
8596’s standard visual-acuity chart that suggested by
Korean Industrial Standards to measure a minimum
resolvable power KS P ISO 8596 (2006). Therefore
it is very useful for people who are lack of ability to
distinguish shape of object such as little child, the
old and the infirm. Also it minimizes a limit of
measuring environment by giving selective measure
distance. Furthermore measured vision is able to
save and maintain through database, so Electronic
Medical Record is not necessary.
2 KOREAN STANDARD
OPTOTYPE PRESENTATION
AND ADJUSTMENT METHOD
The shape and size of optotypes in the visual-acuity
chart, the distance and measuring method, and the
method of deciding vision level of the self visual
acuity test system in our paper is based on Korean
Industrial Standards(KS P ISO 8596, 2006).
This content follows ‘International Standard ISO
8596:1994(E) Ophthalmic Optic-Visual Acuity
Testing Standard Optotype and Its Presentation’ .
2.1 Visualization
The visualization fulfills functions that show shape,
size and direction of visual-acuity optotype on
subject’s screen by using adjustment information of
the optotype such as direction and gap size of the
432
Lee W. and Choi C..
A COMPUTERIZED SELF VISUAL ACUITY TESTING SYSTEM - Method of the Optotype Presentation and Adjustment.
DOI: 10.5220/0003289004320435
In Proceedings of the International Conference on Biomedical Electronics and Devices (BIODEVICES-2011), pages 432-435
ISBN: 978-989-8425-37-9
Copyright
c
2011 SCITEPRESS (Science and Technology Publications, Lda.)
optotype. Delivered information, size of logical
visual-acuity optotype and direction of its gap, is
made by computer that follows Korean Industrial
Standards. Then, this information displayed on
screen with pixel unit, which is a physical unit
displayed on subject’s screen on visualization
module by the transformation mapping.
The size transformation mapping means a
relation between logical coordinate and physical
coordinate. It performs a role that decides how to
relate an image that exists in computer as logical
coordinate to physical coordinate that we can see.
Even though calculated logical coordinate image is
realized by Korean Industrial Standards, to show
accurate size of visual-acuity optotype can be
difficult, because if a resolution of display (an output
device) or this device is changed, a physical
coordinate of the device also changed.
Therefore we transform 0.01mm unit of logical
coordinate to a physical coordinate, pixel, which
possibly display on screen by using HIMETRIC
mode that is one of mapping mode provides from
MFC library of Microsoft. By this process, the
image of optotype that displayed to subject is able to
show the optotype which has equal standards on
equal vision level to resolution of displaying device
or its model, because it can maintain a constant size
of the optotype no matter how many pixels in the
device that has various resolutions.
2.2 Subject’s Gesture Recognition
Visualization fulfills functions that show shape, size
and direction of visual-acuity optotype on subject’s
screen by using adjustment information
Gesture recognition module extracts coordinate
of starting point Gs(Xs, Ys) and ending point Ge(Xe,
Ye) after subject gestures about the visual-acuity
optotype as shown in Fig. 1(a). If the starting point
and ending point are extracted, it set up an
intersection point Gp(Xp, Yp) which is an
intersection between a horizontal line that goes to X-
axis of the starting point and a vertical line that goes
to Y-axis of the ending point. After it gets Gs, Ge
and Gp, it calculates a vectorial angle ‘Ө’ from
subject’s gesture through below equation (1).
=
es
ps
GG
GG
1
cos
θ
(1)
Where,
epps
xxGG =
and ||
•||
: Euclide distance
In this equation (1), subject’s gesture angle ‘θ
corresponds to a vectorial angle (0≤θ≤2π) between a
horizontal line of the starting point and a segment
that connects the ending point Ge to the starting
point Gs. If y
e
is greater than y
s
, θ is computed as
2π- θ.
Figure 1: Subject Gesture Recognition.
To identify the visual-acuity optotype, calculates
the GOI(GOI: Gesture Orientation Index) value that
corresponds to selected visual-acuity optotype
direction on Landolt’s Ring gap direction 8 through
the equation (2) below.
+
=
I
O
GOI
)2,mod(
πωθ
,
where
2
I
O
=
ω
(2)
In the equation (2), O
I
means direction
separation distance, but it means π/4 that one
separated direction section of equal separation of 8-
direction in our paper(Fig. 5).
ω is a bias value for perceiving a invalid region
of the gesture orientation angle as shown in Fig. 1(b),
and is a floor(•) function.
2.3 Minimum Resolvable Power Test
When subject gestures with using pointing device
after seeing a gap orientation of Landolt’s Ring, a
minimum resolvable test module fulfills the test
process of P
0
P
2
in Fig. 2 by using GOI value from
gesture recognition module and presented optotype
information. The minimum resolvable test module
distinguishes coincidence between a gap
orientation(GOI) of Landolt’s Ring by subject and a
gap orientation of presented optotype(OGO:
Optotype Gap Orientation) through a result of GOI
value from gesture recognition module.
If GOI value and a gap orientation of optotype
coincided, it increases a value of TRUE CNT and
inspects number of presentation to equal level for
checking resolvable power. If the number of
presentation doesn’t exceed the max number of
presentation in equal level, it requests an optotype
adjustment module to reproduce only a gap
orientation of optotype randomly just for judging
vision without changing level of optotype. On the
A COMPUTERIZED SELF VISUAL ACUITY TESTING SYSTEM - Method of the Optotype Presentation and
Adjustment
433
contrary this, if the NOP exceeds the MNOP, it
requests a percentage of correct answers and a gap
orientation of optotype to an optotype adjustment
module for raising or reducing the level by the
percentage of correct answers.
Figure 2: Minimum Resolvable Testing and Optotype
Adjustment Process.
2.4 Adjustment of Optotype Level and
Visual Acuity Decision
Adjustment of Optotype level is controlled when
subject has been judged to obtain minimum
resolvable ability or not about the present level. In
Fig. 2, applicable process to P
3
P
5
, is comparing a
percentage of correct answers from minimum
resolvable module with an actual value of T. T is
judging that having an ability of visible resolution
which means actual value of 60% and if the value
did not exceed, we are expecting that it was not
having a visibility of resolvable power. In the case
of the percentage of correct answers is above the
actual value of T, sight level requests the Optotype
size change to upward rating of module by raised
rate. In this situation, parameter value of B, Boolean
type, is using as confirming and setting up to check
that previously offered Optotype rating has the
resolvable power of visualization. If the percentage
of correct answers is under the actual value of T,
sight level would become to downward readjustment
and confirms that B value is 1/0. Assuming that
downward readjusted sight level of B value is 1,
lower vision level adjudges to final vision level so it
sent management module of measuring sight data to
sight level information. Thus, subject will get the
complete result through visualization module.
However, if B value is 0, downward readjusted
level would have no sight measured record, and
consequently adjusting optotype of visualization
module is requested for suggestion of downward
readjusted optotype. At this moment, readjustment
of optotype level is adjusted by R10 series and KS
standard of ratio(KS Q ISO 3, 2002).
If we define current Optotype Diameter as OD
c
,
a bigger Optotype Diameter which adjusts to one
level reduce as OD
u
, a smaller Optotype Diameter
which adjusts to one level increased as OD
d
, and
R10 series as a constant of ratio R(=about 1.25), we
can define adjusting Optotype Diameter as the
equation (3) and (4) below.
RODOD
cu
×
=
(3)
R
ODOD
cd
1
×=
(4)
The OD
u
value which is one level reduced
Optotype Diameter equals to a value of multiplying
current Optotype Diameter(OD
c
) to a constant of
ratio(R) and it corresponds to 125% magnification of
OD
c
value. Also, if we multiply 1/R, a reciprocal of
R, to OD
c
, the OD
d
value which is an one level
increased Optotype Diameter becomes 80%
magnification of OD
c
value.
Figure 3: Scale Ratio of Optotype Diameter.
The function of measured distance change is
adjusting Optotype’s size of 1.0 sight level presented
according to originally subject inputted measured
distance through data management module.
Adjustable ratio also can be defined by R10 series of
R which is constant number of magnification as
blow equations (5) and (6).
×=
c
new
cnew
D
D
OGOG
,
where OG
c
= 1.5mm, D
c
= 5m (5)
newnew
OGOD
×
=
0.5
(6)
In above equation, D
c
is 5m which means
standard measure distance and OG
c
is 1.5mm which
means gap size of optotype that being one minute of
arc at the standard measure distance. D
new
is
measuring distance which is selected by subject and
values of OG
new
and OD
new
are indicated diameter of
ring and gap size of optotype of sight level that is
coordinative by subject measured distance.
BIODEVICES 2011 - International Conference on Biomedical Electronics and Devices
434
Figure 4: Visual Acuity 1.0 Level Size by selecting a
measure distance.
Thus, when the subject is selecting the measure
distance of D
new
, the standard measure distance of D
c
and ratio multiply by the standard optotype size of
OG
c
value so OG
new
is calculated which will be
using with gap size of optotype of the new 1.0 sight
level at the selected distance. If the value of OG
new
is
found, OD
new
would be calculating and sending to
visualization module of Optotype.
As shown by Fig. 5, another operation of
adjusting optotype is producing one of way from
eight ways of optotype gap randomly by a computer,
sending as visualization module for new Optotype
presentation with Adjusted Optotype diameter value.
Figure 5: The 8-orientation of Optotype Gap.
3 EXPERIMENTS
All process of the computerized self visual acuity
testing system is implemented to Visual C++(GDI:
Graphic Device Interface) of Microsoft Windows
XP. We used 32 inch normal monitor that applies
1024×768 pixel resolution display device. The
performance evaluation of the system is fulfilled by
100 subjects who compare our method to original
visual acuity test and the option of choosing distance
doesn’t evaluate to each distance so it evaluated to
standards distance. As the results (Table 1)
compared with two methods, 87% of subjects was
corresponded to test result of eyesight measured
table and the rest of discordant 13 of testers was
showing that 98% of credibility in the limit of ±1
visual acuity level error.
Table 1: Measurement Result of Implemented System
(: Margin of Error ±1 Visual Acuity Level).
Number
of
Subjects
consistency
inconsistency
inner of
error limit
outer of
error limit
100 87% 98% 2%
4 CONCLUSIONS
The Computerized Self Visual Acuity System
provides flexibility to measure environment by
choosing measure distance and Gesture Recognition
increases subject’s convenience also, it has less
negative reaction because it is similar to existing
method of measuring. Also the method of the
optotype adjustment for a computerized self visual
acuity is able to prevent presumption to
memorization of subject and prevent most of
subjective measurement of subject or inspector.
Especially it is able to apply to manage database
of estimating vision without any additive works on
EMR system anywhere such as ophthalmology and
optician's shop.
if it increases subject’s concentration by change
of measuring distance, change of visual-acuity chart
presentation location and visual-acuity chart type
and make up for tiredness of eyes to use an output
device such as electronic ink that using another
medium, our Self Visual Acuity Test System will be
effective.
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Bach, M. et al. (2009). Resolving the clinical acuity
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Harrison, E. R. (1953). Visual Acuity and the Cone Cell
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Kniestedt, C. and Stamper, R. L. (2003). Visual acuity and
its measurement. Ophthalmol. Clin. N. Am (16),
155-177.
KOREA INDUSTRIAL STANDARD. (2006). P ISO
8596:2006, Ophthalmic Optic - Visual Acuity Testing
- Standard Optotype and its Presentation.
KOREA INDUSTRIAL STANDARD. (2002). Q ISO 3:
2002, Preferred Number.
Lee, W. B. and Choi, C. Y. (2009). A Self-Visual Acuity
Testing System by the KS Standard Optotype.
Proceedings of the Korean Information Processing
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A COMPUTERIZED SELF VISUAL ACUITY TESTING SYSTEM - Method of the Optotype Presentation and
Adjustment
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