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

 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).

⎟

⎠

⎞

⎜

⎝

⎛

−

cos

(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

is greater than y

, 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.

⎥

⎦

⎥

⎢

⎣

⎢

GOI

)2,mod(

πωθ

where

(2)

In the equation (2), O

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

∼P

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

∼P

, 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

a bigger Optotype Diameter which adjusts to one

level reduce as OD

, a smaller Optotype Diameter

which adjusts to one level increased as OD

, 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

(3)

ODOD

×=

(4)

The OD

value which is one level reduced

Optotype Diameter equals to a value of multiplying

current Optotype Diameter(OD

) to a constant of

ratio(R) and it corresponds to 125% magnification of

value. Also, if we multiply 1/R, a reciprocal of

R, to OD

, the OD

value which is an one level

increased Optotype Diameter becomes 80%

magnification of OD

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).

⎟

⎠

⎞

⎜

⎝

⎛

×=

new

cnew

OGOG

where OG

= 1.5mm, D

= 5m (5)

newnew

OGOD

0.5

(6)

In above equation, D

is 5m which means

standard measure distance and OG

is 1.5mm which

means gap size of optotype that being one minute of

arc at the standard measure distance. D

new

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

and ratio multiply by the standard optotype size of

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

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

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.

REFERENCES

Bach, M. et al. (2009). Resolving the clinical acuity

categories "hand motion" and "counting finger" using

the Freiburg Visual Acuity Test(FrACT). Graefes

Arch Clin Exp Ophthalmol 247, 137-142.

Harrison, E. R. (1953). Visual Acuity and the Cone Cell

Distribution of the Retina. Brit. J. Ophthal. 37, 38-542.

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

Society Fall Conference, 16(2), 893-894.

A COMPUTERIZED SELF VISUAL ACUITY TESTING SYSTEM - Method of the Optotype Presentation and

Adjustment

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