社会医学研究．第 34 巻 2 号．Bulletin of Social Medicine, Vol.34(2）2017

原著

Effects of Aging and Visual Acuity on the Legible Point Size
for a Single Character on an E-paper Display
電子ペーパーディスプレイの単一文字の読み取れる
ポイントサイズに対する加齢と視力の影響
R. Paul Lege1), Nobuhiro Ishio2), Ichizo Morita3), Takehito Kojima4), Ryota Kimura2), Kohei Iwata2),
Shigusa Matsunami2), Hiromu Ishio5), Hasegawa Satoshi6), Masaru Miyao2)
R. Paul Lege1)、石尾暢宏 2)、森田一三 3)、小嶌健仁 4)、木村瞭太 2)、岩田光平 2)、
松波紫草 2)、石尾広武 5)、長谷川聡 6)、宮尾克 2)
1) Nagoya University, Graduate School of Law, Program for Leading Graduate Schools
2) Nagoya University, Graduate School of Information Science, Department of Information Engineering
3) Japanese Red Cross Toyota College of Nursing, Faculty of Nursing, Department of Nursing
4) Chubu Gakuin University, Faculty of Nursing & Rehabilitation Sciences, Department of Nursing5) Fukuyama City University, Faculty of Urban Management, Department of Urban Management
6) Nagoya Bunri University, School of Information and Media Studies
1) 名古屋大学大学院法学研究科
2) 名古屋大学大学院情報科学研究科
3) 日本赤十字豊田看護大学
4) 中部学院大学看護リハビリテーション学部
5) 福山市立大学都市経営学部
6) 名古屋文理大学情報メディア学部
Abstract
In recent years, manufacturers have increased the number of electronic book reading terminals with e-ink
displays to meet consumer demand. Also called e-papers, these products have achieved high resolution on thedisplay panels. The aim of this research was to collect basic data on the legibility of displayed characters of
e-papers because many manufacturers have claimed that their products are close to paper text. We carried out
an experiment of the effects of ageing, visual acuity, and cataract cloudiness on the legibility of different size
characters on an e-paper device. The participants in the experiment included 133 males and females between theages of 17 and 79 years. The participants read from a string of random set of capitalized letters whose font size
declined from large (18pt) down to small (2pt). We used Times New Roman and Helvetica for the experiment.
We asked each participant to read out loud the character string, and we used a systematic evaluation method
to calculate for the correct reading each character. The participants were tested 20times for each font size inthe trial. If the reader could recognize a letter of a font 16out of 20times (80% ), then we defined the specific fontsize as sufficiently legible. When a reader reached this 80% point, then this was defined as the minimum legible
character size for the participant. The results showed that with higher than 50cm visual acuity, the participants
could read the smallest sizes for both font types. However, for older people with 50cm visual acuity above 1.0, theresults indicate that they have greater difficulty reading the smaller characters compared to younger participants.
Our study found that participants could read the smaller font points for Helvetica better than Times New Roman.
This research, suggests that in the future we should compare the legible smallest character size among different
types of font using character height (mm) instead of point size.
－ 19 －

社会医学研究．第 34 巻 2 号．Bulletin of Social Medicine, Vol.34(2）2017

抄録
近年、情報機器メーカーは、消費者の需要に合わせて、e －インクを用いた電子書籍端末の出荷を増加させている。
また、電子ペーパーと呼ばれるこれらの製品は、高い解像度のディスプレイパネルを実現した。この研究の目的は、情報機器メーカーが電子ペーパーを紙の上に書かれた文字列に近いと主張しているように、電子ペーパーに表示された文字が、そのように読みやすいのかという点を明らかにするための基礎資料を収集することであった。我々は、
電子ペーパー端末の種々の文字サイズの読みやすさに、加齢、視力、および水晶体白濁度がいかに影響するかという実験を実施した。実験の参加者は、133 人の男女で、年齢は 17 歳から 79 歳に分布した。参加者は、大文字で書かれたランダムなアルファベットの文字列で、フォントサイズが大きい方（18pt）から小さい方（2pt）に順に 1pt
ずつ小さくなっていく 17 文字の文字列を、大きい文字から順に読んだ。私達は実験のアルファベット文字に、タイ
ムズ・ニュー・ローマンとヘルヴェティカの 2 種類を用いた。このようなサイズが漸減する文字列を、2 種のフォントごとに、20 行ずつ作製した。そして、参加者は、大きいサイズから順に、文字列を読める限界の小さいサイズ
まで１行ごとに読み、2 種のフォントごとにそれぞれ 20 行、読むこととした。こうした手順によって、我々は、文字サイズごとの可読性を算出する体系的な評価方法を確立した。参加者は 1 つのフォントサイズごとに 20 回の試験のうち、80％以上の正解率を得た場合に、そのサイズが可読であると定義した。そして、1 人ずつの参加者について、それぞれが可読であったもののうち最小のサイズを、その参加者の読み取れる最小の文字サイズと定義した。結果は、50cm 視力が高い参加者は、2 種のフォントの両方で、最も小さいサイズを読み取ることができた。しかし、同じ視力 1.0 以上の参加者のみで、比較すると、高齢者は、視力は同じでも、若い参加者よりも文字サイズが大きくないと読めない傾向を示した。我々の研究によって、ヘルヴェティカの方が、タイムズ・ニュー・ローマンよりも小さい
サイズの文字を読み取ることができることを、明らかにした。読み取りやすさのフォント間の比較をポイントではなく、文字高（mm）で行うことが今後必要と思われる。
Key words: E-paper, E-book, the smallest legible size, E-Ink, 50cm visual acuity, ageing
キーワード : 電子ペーパー、電子書籍、最小可読文字サイズ、e インク、近見視力、加齢

1. Introduction

2. Methods

In 2013, the amount of money spent on books was

2.1 Participants$121.5 billion. Business forecasters predict that such

This study included the participation of 133

1)

spending expected to reach a plateau of 1.1% by 2018 .

people aged 17 to 79 years old. All participants

Meanwhile, expenditures for e-books represented about

signed a consent form and approval for experiment

12% of the book market in the years 2013-14 but should

was received from the Ethical Review Board of the

1,2)

increase to 25% by 2018 .

Graduate School of Information Science at Nagoya

One of the concerns for readers has been with

University.

the reading of characters on small screens with low

Individuals who needed to wear corrective lens

resolution displays. Since 2007, Amazon’s e-paper

during the procedure were allowed to do so in orderproducts such as Kindle Paperwhite have grown

to complete the tests. All participants, regardlessin popularity. One of the reasons for this growingof whether or not they needed corrective lenses,

appeal has been due to the improvement in thewere measured for binocular near visual acuity

device’s resolution, going from 167 ppi to 300 ppi,

for 50cm 3). The near visual acuity was expressed

and at a lower price. While e-paper devices havein the following way: 0.1, 0.3, 0.5, 0.7, 1.0, or 1.2. We

become increasingly popular, they include numerous

calculated the visual function of a single eye with

font types with multiple sizes that need testing for

cataract cloudiness (CC) in the lens3-6) with the use

legibility. Therefore, we conducted an experiment toof an anterior ocular segment measuring instrumentcompare and evaluate the smallest point sizes thatcalled the EAS-1000TM (NIDEK Inc.). There were

could be read from two main types: Helvetica and

256 levels of cataract cloudiness (0= no cloudiness andTimes New Roman.

255=the maximum)6). We defined an individual’s level－ 20 －

社会医学研究．第 34 巻 2 号．Bulletin of Social Medicine, Vol.34(2）2017of cloudiness based on the lens clarity in the best eye;experimental room. Figure 2 below presents anfor example, if a person had a level 100 in the left eye

example of the Paperwhite displaying English

and 150 in the right eye, then we considered them as

Figure3 1.below
Photoshowsof the how
experimentcharacters. Figure
the task washaving a 100 for cloudiness.

performed.

For this experiment, we used the Amazon Paperwhite which has a screen size of 6 inches

andresolution
300 ppi [7].Environment
We set the illuminance level at 750 lx as recommended by the
2.2aDevices
andof
Experimental
For this experiment,
we usedthe Amazon (ISO) [8] and the Japan Industrial Standards (JIS)International
Organizationfor Standardization

Paperwhite which has a screen size of 6 inches

which recommends higher than 500 lx for reading books [9].

and a resolution of 300 ppi7). We set the illuminancelevel at 750 lx as recommended by the International

2.3 Procedures

Organization for Standardization (ISO)8) and the Japan
Industrial Standards (JIS) which recommends higher

Figure 1 below represents a photo of the experimental room.Figure 2 below presents anthan 500 lx for reading books9).

exampleof the Paperwhite displaying English characters.Figure 3 below shows how the task was
2.3 Procedures
performed.
Figure 1 below represents a photo of the
Figure 2. Photo of e-paper device

Figure 2. Photo of e-paper device

Figure 3. Example of the reading task
Figure 3. Example of the reading task

The participants were asked to read a string of English alphabetic letters out loud. There
The participants were asked to read a string of English alphabetic letters out loud. There
were 20 lines and each line contained a random selection of seventeen English letters in upper case
FigureExamplethereading
Figure
1. Photoof the 20
experiment
Figure 3.
3. Example
ofofthetasktask English letters in upper casewereand each line contained a random
selection
ofreadingseventeen
Figure
1. Photo
thelines
experimentfor ofboth
fonttypes.Seventeen letters were displayed left to right, from 18 pt to 2 pt.While there afor bothfontasked
types.Seventeen
were
to right,
from18readpt to2inpt.WhilethereaThe participants
were
to read alphabet,a stringlettersof we excluded
fromdisplayed
18 pt
toletters
2 leftpt. While
there
areletterstheTheparticipants
were
asked
to
ato
stringof English
alphabet
26 lettersin the English
the“I” and
“J”
in26
order
avoid
any confusio
English alphabetic
letters
There
were 20we excluded
Englishexcludedthe inletters“I”
and“J” ofwere 20alphabet,lineslettersand weeach
lineandcontaineda order
randomseventeenEn
26 lettersin outthe loud.
Englishalphabet,
the
“I”
“J”
toselection
avoid
any
confusiofor the participants.We used Helvetica, which is a sans serif font type (fig 4-a), and Times New
lines and each line contained a random selection of
infororder
to avoid
any confusion
for were
the participants.
both font
types.Seventeen
letters
displayed left to right, from 18
for the participants.We used Helvetica, which is a sans serif font type (fig 4-a), and Times New
Roman
as theserifcase
typefor(fig4-b).
seventeen English
letters
in upper
both
font
We
used Helvetica,
which
is a sansfont thetypeletters(fig “I” and “J” in or
26 lettersin the English
alphabet,
weserif
excluded
Roman
as
the
serif
type
(fig
4-b).
types. Seventeen letters were displayed left to right,4-a), and Times New Roman as the serif type (fig 4-b).

for the participants.We used Helvetica, which is a sans serif font type (fiRoman as the serif type (fig 4-b).

(a)(a) Helvetica

Helvetica(a) Helvetica
Figure 2. Photo of e-paper
device(b) Times New Roman(b)Times New Roman(b)Times New Roman

Figure 4. Examples of both font types

Figure 4. Examples of both font types
Figure 4. Examples of both font types － 21 －5(a) Helvetica(b)Times New Roman

Figure 4. Examples of both font types

The participants sat down in a chair and held the reading device

visual distance from the eye to the device was limited to 50 cm. The parti

aloud thetestheldletters
thatreadingwere displayed
Reading The
from left
The participants sat down in a chairandthedeviceonatthea screen.
set distance.

would start at 18 pt and read down to 2 pt. Meanwhile, the tester recorded the answers whether
correct or error depending on what was read.
社会医学研究．第 34 巻 2 号．Bulletin
Social the
Medicine,
Vol.34(2）2017
For eachoffont,participants
had to read twenty lines; therefore, they read a total of 40lines for both font types. In order to exclude
for the effect of ordering, each reader started with aparticipant A could read 16 of 20 letters at the 4point

The participants sat down in a chair and held thedifferent
type,The
andvisualthe lettersselected.
As15long
reading device
at a set fontdistance.
distancewere randomly
character size
(80% ) but
of 20asat thethe participant
3pt size (75% ),could read afrom the eyefont
to thewas limited
50cm. The legible.
then
the definition
smallest pointof legibility
would havebeenspecific point
at device
80% thenit was toconsideredTheof smallest
legibility
is theparticipants were asked to read aloud the test lettersat the 4point size.

size where a person can read a font size correctly at 80% [10]. For example, if participant A could

that were displayed on the screen. Reading from

16 of 20 lettersat thepoint
size (80%) but 15 of 20 at the 3 pt size (75%), then theleft to right, readthe participant
would startat 418pt
andcharacter
3 Results
read down tosmallest
2pt. Meanwhile,thelegibility
tester recorded
thehave been
point ofwould
at the 54 andpoint
size. the correlation between
Figures
6 shows
answers whether correct or error depending on what

50 cm visual acuity and the smallest legible font

was read.

size for the Helvetica and Times New Roman. As

3 Results

For each font, the participants had to read twenty

illustrated in the figures, the results found that the

Figures
6 shows
the correlation
between50 cm forvisualacuity andlines; therefore, they reada total 5ofand
40linesfor bothsmallest pointof legibility
the Helvetica
fontthewassmallest legibl

font types. In
for the andeffectofan Roman.
average ofAs
3.75
pt + 0.95 (heightmm) andfontorder
size toforexclude
the Helvetica
Times
New
illustrated
in the 0.94
figures,the forresults found thaordering, each reader started with a different fontTimes New Roman 4.27 pt + 1.08 (height 0.99 mm).

type, and the letters were randomly selected. As

This means that most of the readers with 50 cm

the smallest point of legibility for the Helvetica font was an average of 3.75 pt + 0.95 (height 0.94

(heightmm).
meansthat most of themm) and could
for Times
4.27 pt visual+ 1.08long as the participant
read a New
font atRoman
80% thenacuitycould0.99
not readtheThisfont sizefor Helvetica

it was consideredlegible.
definition
smallest
on readaveragefor Timeson
New
Roman below 3.75 pt
readers
withThe50 cm
visualofacuity
could notthebelowfont 3.75
sizeptforand
Helvetica
averagelegibility is the specific point size where a person canbelow 4.27 pt.
and for Times New10)Roman below 4.27 pt.

read a font size correctly at 80 %. For example, if

40
30
20
10
8

10
0

6

0.1 0.2 0.3

0.4 0.5 0.6

4

0.7 0.8 0.9

1

2

Smallestlegiblefontsize

Nnumberofpeople50

1.1 1.2

50cmvisualacuity
Figure 5. Correlation between
50cm visual acuity and font size for Helvetica
Figure 5. Correlation between 50 cm visual acuity and font size for Helvetica
40
30
20
10
8

10

7

0
0.1 0.2 0.3

0.4 0.5 0.6

0.7 0.8 0.9

1

6
4
2

Smallestlegiblefontsize

Nnumberofpeople50

1.1 1.2

50cmvisualacuity
Figure 6. Correlation between
50cm visual acuity and font size at the Times New Roman
Figure 6. Correlation between 50 cm visual acuity and font size at the Times New Roman－ 22 －

Table 1 provides a nonparametric correlation coefficient and comparison between theFigure 6. Correlation between 50 cm visual acuity and font size at the Times New Roman

Table 1 provides a nonparametriccorrelation
andcomparison
the社会医学研究．第34 巻coefficient
2 号．Bulletinof Social
Medicine,between
Vol.34(2）2017
independent variables (age, 50 cm visual acuity, cataract cloudiness)and the smallest legible font

Table1 provides a nonparametric correlation

legible font size had a positive correlation with age andsize. As shown, the smallest legible font size had
a positive correlation with age and cataract
cataract cloudiness (p<0.01) and a negative correlation

coefficient and comparison between the independent

cloudiness(p<0.01)
a negative
correlationwith
with50cm
50 cm
visualacuity(p<0.01).
variables (age,50cm visualacuity,andcataract
cloudiness)visualacuity(p<0.01).
and the smallest legible font size. As shown, the smallest
1. Coefficient between smallest legible font size and independent variables
Table 1.Table
Coefficient
between smallest legible font size and independent variables

The smallest legible font size above the㩷㩷correct response rate of 80%

㩷㩷Helvetica

Age (years)

Correlation Coefficient

0.438**

0.395**

Significance (bilateral)

0.000

0.000

133

133

Correlation Coefficient

**

0.383

0.359**

Significance (bilateral)

0.000

0.000

133

133

Correlation Coefficient**-0.500-0.527**Significance (bilateral)

0.000

0.000

No. of Participants
Less Cataract
CloudinessNo. of Participants

Visual acuity

Times New Roman

smallest 䋨Binocular䋩
legible characters
were 3.48 pt + 0.70 (character height:
0.88 mm) for Helvetica,
and 4.00 pt
No. of Participants
133
133+ 0.77mm) for Times New Roman.
**:(0.93
p<0.01Table
2 provides
nonparametriccomparison
betweenthe
After making thesecomparisons,weadecided
to look correlation
variablescoefficient(age, 50cm andvisualacuity, cataract
cloudiness)Aftermakingdecidedto look atlegible
the 105
participants
who font
hadforgood
at the 105
participantsvariables
who hadgood
visualandthe cloudiness)andsmallest
fontsize. As
shown,
independent(age,tothese
50excellent
cmcomparisons,visualacuity,we
cataractthesmallest
legibleacuity (above
1.0). Table2visual
belowacuity
providesthe 1.0).
results
the smallest
legiblefrom
font thissize analysis.
had a positive
to excellent(aboveTable 2 Helvetica,
below provides
the results
The

size. As shown, for Helvetica, the smallest legible font size had a positive correlation with age andfrom this analysis. The smallest legible characters werecorrelation
with age and cataract cloudiness (p<0.05)
8cataract cloudiness(p<0.05)
a negative
50 cm
visual acuity
ForacuityTimes
3.48pt+0.70(characterheight:0.88mm) forand
Helvetica,
and correlation
and a withnegativecorrelation
with (p<0.01).
50cm visual
4.00pt+0.77(0.93mm)
forthere
Times
New
Roman. correlation with
(p<0.01).
Times
New(p<0.01).
Roman, there was a negative
New Roman,wasa negative
50 cmForvisualacuityTable2 provides a nonparametric correlation

correlation with 50cm visual acuity (p<0.01).

coefficient and comparison between the independent

Table 2. Coefficient of font sizes and independent variables for those with 50 cm visual acuity above
Table 2. Coefficient of font sizes and independent variables for those with 50 cm visual acuity above 1.0
1.0
㩷㩷

㩷㩷

㩷

㩷

Age (years)

The smallest legible font size above thecorrect response rate of 80%
Helvetica

Correlation Coefficient

0.238*

0.189

Significance (bilateral)

0.014

0.053

105

105

Correlation Coefficient

0.216*

0.166

Significance (bilateral)

0.027

0.091

105

105

Correlation Coefficient-0.255**㩷

-0.328**Significance (bilateral)

0.009

0.001

105

105

Participants
Less Cataract
Cloudiness

Visual acuity
䋨Binocular䋩Times New Roman

ParticipantsParticipants*: p<0.05, **: p<0.01

4 Discussion－ 23 －In this experiment, we had a large sampling of participants. Most of them have been in社会医学研究．第 34 巻 2 号．Bulletin of Social Medicine, Vol.34(2）2017

4 Discussion

similar to conventional paper, they have the added

In this experiment, we had a large sampling ofadvantage of allowing the reader magnify the size ofparticipants. Most of them have been in engaged incharacters manually. As a result, these devices are

our human experiments for more than 10 years andbecoming more popular for the elderly.

are very skilled individuals in working with near

The results of this study suggests that the fontvision experiments. Most of these individuals havetype might change the legibility of e-paper devices.

appropriate glasses for 50 cm visual distance. In

However, in order to compare the various font types,

this experiment, the smallest point of legibility fora more accurate approach to looking at fonts isthe Helvetica font was an average of 3.75 pt + 0.95

necessary. Further study is needed to investigate the(height 0.94 mm) and for Times New Roman 4.27

effects of font type and character height on legibility.

pt + 1.08 (height 0.99 mm). For these readers, thesmallest font sizes were surprisingly legible. When

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