The placement of a visual display may influ-
ence the neck symptoms, head posture, neck
muscle activity, eye symptoms, and eye function
of computer users (Daum et al., 2004; Hagberg &
Rempel, 1997). For example, an increased height
of the display is associated with a lower blink rate,
greater eye symptoms, and lower amplitude of
accommodation (Atchison, Claydon, & Irwin,
1994; Burgess-Limerick, Plooy, & Ankrum, 1998;
Jaschinski-Kruza, 1988; Saito, Miyao, Kondo,
Sakakibara, & Toyoshima, 1997; Villaneuva,
Sotoyama, Jonai, Takeuchi, & Saito, 1996).
Since a low display height is associated with
increased neck muscle activity and increased
neck pain (Hagberg & Sundelin, 1986; Seghers,
Jochem, & Spaepen, 2003; Sommerich, Joines,
& Psihogios, 2001; Turville, Psihogios, Ulmer, &
Mirka, 1998), it is generally recommended that the
center of the screen be between 15°and 25°below
the horizontal from the eye (Hagberg & Rempel,
1997; Sheedy & Shaw-McMinn, 2003; Sommerich
et al., 2001).
The distance from the display to the eyes is also
important and is the subject of this investigation.
Factors such as visual display size, character and
object size, screen resolution, and presbyopia (loss
of near focusing ability) in an aging population are
all factors that may influence optimal visual display
distance. In addition, the workstation and chair de-
sign, use of keyboard trays, desk depth, and display
The Effects of Visual Display Distance on
Eye Accommodation, Head Posture,
and Vision and Neck Symptoms
David Rempel and Kirsten Willms, University of California, Berkeley, California, Jeffrey
Anshel, Corporate Vision Consulting, Encinitas, California, Wolfgang Jaschinski,
Leibniz Research Centre for Working Environment and Human Factors, Dortmund,
Germany, and James Sheedy, College of Optometry, Pacific University, Forest Grove,
Objective: Determine the effects of display viewing distance on both the visual and
musculoskeletal systems while the text height is held constant across viewing dis-
tances. Background: The distance from the eyes to a computer display may affect
visual and neck comfort. If the angular size of the characters remains the same, it is
recommended that the display be placed at a farther viewing distance (e.g., 70–100 cm).
However, in common usage, the character sizes are not adjusted based on viewing
distance. Method: Participants under the age of 35 years (N = 24) performed visually
demanding tasks using a computer display for 2 hr each at three viewing distances
(mean: 52.4, 73.0, and 85.3 cm) while torso and head posture were tracked. At the
end of each task, eye accommodation was measured and symptoms were recorded.
Results:The near distance was associated with significantly less blurred vision, less
dry or irritated eyes, less headache, and improved convergence recovery when com-
pared with the middle and far distances. Participants moved their torsos and heads
closer to the monitor at the far distance. Conclusion: If the computer screen character
sizes are close to the limits of visual acuity, it is recommended that the computer mon-
itor be positioned between the near (52 cm) and middle (73 cm) distance from the eyes.
Application:The location of a computer display should take into account the size of
the characters on the screen and the visual acuity of the user.
Address correspondence to David Rempel, Ergonomics Program, University of California Berkeley, 1301 South 46th St., Bldg.
163, Richmond, CA94804; email@example.com. HUMAN FACTORS, Vol. 49, No. 5, October 2007, pp. 830–838. DOI:
10.1518/001872007X230208. Copyright © 2007, Human Factors and Ergonomics Society. All rights reserved.
VISUAL DISPLAY DISTANCE
depth and size will influence the available range of
display distance. Recommended ranges for display
distance are important for furniture and equipment
manufacturers, ergonomics consultants, facilities
designers, optometrists, and computer users. Rec-
ommendations for the distance from the display to
the eyes vary from a minimum of 30 cm (Human
Factors and Ergonomics Society, 1988) to a max-
imum of 1/3 of the farthest distance at which char-
actersof a given size can just be identified (Sheedy
& Shaw-McMinn, 2003).
The argument for a longer viewing distance is
that the longer distance may put less demand than
does near distance upon the ocular convergence and
accommodative mechanisms. Jaschinski-Kruza
(1988) showed that participants preferred work-
ing on a computer display at 100 cm, compared
with 50 cm, when the character size was adjusted
to provide equal visual angles for the two condi-
tions. In a subsequent study, Jaschinski-Kruza
(1990) showed that participants preferred the dis-
play at 70 cm, compared with 50 cm – even when
a reference document from which they worked
was fixed at 50 cm – indicating that they preferred
the longer viewing distance even if it required
them to change viewing distance to view the ref-
It has also been shown that in the absence of
any visual stimulation (i.e., in the dark), the ac-
commodation and vergence positions of the eye
generally assume resting positions of about 67 cm.
This mean value has a considerable interindividual
range, from about 40 cm to infinity in emmetrop-
ic participants (Owens, 1984; Owens & Wolf-
Kelly, 1987). It has been proposed that visual
work at this “dark” position should result in
greatest visual comfort. Most participants with
a distant dark vergence position experienced
stronger visual strain at short viewing distances
(Jaschinski & Heuer, 2004; Jaschinski-Kruza,
1991). Furthermore, most participants who prefer
a longer viewing distance have a larger vergence
error (fixation disparity) in near vision (Jaschin-
ski, 2002). However, Jaschinski-Kruza (1988)
has shown greater comfort at 100 cm than at 50 cm
regardless of the dark accommodation position
(which differs from dark vergence in most partic-
ipants) of the eyes.
If the visual display is too close, the increased
accommodation and convergence required of the
visual system, may, over time, lead to decreased
accommodative flexibility and capacity, possibly
to convergence concerns, and ultimately to eye
symptoms. The effect of distance from the mon-
itor to the eyes on eye function and symptoms has
been studied in the laboratory (Jaschinski, 2002).
Participants self-selected optimal distances while
performing a visually demanding task for 30 min.
The preferred viewing distance was 63 cm (±13)
with a range of 43 to 99 cm (Jaschinski, 2002).
However, the effects of monitor distance have not
been studied for longer durations. In addition, the
effects of monitor distance on head posture have
not been studied.
Thus, the physiological evidence appears to
support longer viewing distances, provided the
character size (in millimeters) is increased accord-
ingly. However, in common usage, the character
size remains fixed on a display regardless of the
viewing distance; thus the visual angle decreas-
es with increased viewing distance. The primary
concern is that if the visual display is placed too
far away, difficulty in resolving characters will
over time lead to a forward head posture or for-
ward leaning and ultimately neck symptoms.
The purpose of this study was to determine the
effects of visual display distance on both the visu-
aland musculoskeletal systems. In this study, the
text height was kept constant across viewing dis-
tances, hence reflecting common usage in which
the angular size decreases with increased view-
ing distance. Common usage was also simulated
with long performance trials. The null hypothesis
was that there would be no change in head pos-
ture, torso posture, accommodative capacity, ac-
commodative flexibility, convergence ability, eye
comfort, or neck comfort over a 2-hr period with
a visual display set to three different distances
from the eyes for computer users who are less
than 35 years of age.
This was a full-factorial, repeated measures
study with 24 participants. All participants expe-
rienced all three conditions of computer monitor
placement, in randomized sequence, while they
performed visually demanding tasks. The partic-
ipants were seated in front of the monitor and per-
formed the tasks with a computer mouse. The study
was approved by the University of California at
San Francisco Committee on Human Research.
Participants were recruited from flyers placed
832 October 2007 – Human Factors
on the campus and in the community. Interested
recruits were screened and were excluded if they
were left-handed; had less than 1 year of experi-
ence using a computer; reported current head, neck,
back, or arm injuries; had difficulty sitting and us-
ing a computer for 6 hr; had difficulty with their
vision; or used glasses when using a computer. Par-
ticipants were between the ages of 18 and 35 years
in order to limit the study to participants with ap-
propriate accommodation to the viewing distances
studied. Participants completed a demographic
For the three test conditions, the center of the
visual display was set to a near, middle, or far dis-
tance from the participants’eyes – target distances
of 46, 66, and 86 cm (18, 26, and 34 inches),
respectively–while the participants were seated in
a reference posture. The order of testing was block
randomized. Participants were not told of the spe-
cific distance tested. The monitor was centered
along a line that was 15° below the horizon from
the participant’s eyes. The monitor was positioned
directly in front of the participant. The viewing
distances were selected to encompass a preferred
viewing range (Jaschinski, 2002).
Each of the three test conditions was per-
formed for 2 hr, with a 30-min break between
conditions. Prior to the study and during the
breaks, participants were instructed to perform
no near vision tasks (e.g., reading). The comput-
er tasks involved document editing and Internet
searching. The tasks were performed using the
mouse so that head posture would not be influ-
enced by visual gaze to the keyboard for those
with poor touch typing skills.
The document editing task involved viewing
a screen filled with an array of random text char-
acters: 10 lines of text, 20 characters per line, and
“words” between 3 and 10 random characters
long, separated by blanks (Jaschinski, 2002).
Characters were black on a white background,
Arial, all capitals, with a height of 3.3 mm (10
points). The characters were selected so that to
the left and right of a blank they were identical for
about 50% of blanks. The participant clicked on
each pair of words with the same character on
either side of the blank. The Internet search task
involved participants searching the Internet to
find answers to a series of very specific geograph-
ic questions (e.g., “What is the tallest mountain
in Columbia?”). For each test condition, partici-
pants performed 15 min of document editing, fol-
lowed by 90 min of Internet searching, followed
by 15 min of document editing.
The chair, monitor, and mouse surface were
adjusted to the participant’s anthropometry at the
beginning of the study. At the beginning of each
test condition, participants were required to sit
with their backs against the chair backrest while
looking at a mark on the wall at their eye level.
Posture data were collected for this reference
position, and then participants performed the
computer tasks for 2 hr. During the 2-hr period,
participants could assume any posture they pre-
ferred, but the chair and monitor could not be
The chair (Leap model, Steelcase, Grand
Rapids, MI) was secured to the floor, and the
backrest was maintained at an inclination angle
of 110°. The participant sat comfortably in the
chair, and the seat pan depth and height were
adjusted to his or her leg dimensions. The seat
pan was locked so that it would not slide forward.
The heights of the armrests on the chair were
adjusted to comfortably support the forearm
while the participant used a mouse. The partici-
pant practiced the computer tasks prior to the
start of the experiment and made small adjust-
ments to the chair height and depth for comfort.
After the experiment started, participants could
not make additional adjustments to the chair, but
they were allowed to move their bodies to what-
ever position was comfortable and allowed them
to complete the tasks. The mouse work surface
height and location were positioned to allow the
forearm to be level with the floor with minimal
shoulder flexion or abduction.
Acustom-made monitor stand was secured to
the floor. The stand allowed for movement of the
monitor toward or away from the participant
along an adjustable axis, which was set to a line
15°below the horizontal (vertical gaze angle). The
monitor and support arm were also adjustable in
height. The monitor was an 18-inch (45.7-cm)
LCD flat panel monitor (Model 9494-T860,
IBM) with digital quality set at 75 Hz refresh rate
and a resolution of 1280 × 1024. The video card
was an NVIDIAQuadro2 Pro.
VISUAL DISPLAY DISTANCE
Head and Torso Posture
Participants wore a tank top shirt to expose
their sternum. The head and torso postures were
recorded continuously at 1 Hz with an Optotrack
motion analysis system (Northern Digital, On-
tario, Canada) (see Figure 1). To measure head
posture, an active infrared marker was secured to
the right side of the face adjacent to the canthus
of the eye and a second marker was positioned
just forward of the tragus (i.e., forward of the
ear). In addition, two markers were placed verti-
cally along the midline of the sternum to record
the torso angle, the upper marker just below the
sternal notch and the second marker approxi-
mately 5 cm below the upper marker. A marker
was also secured to the center of the right side of
the monitor. The 3-D location of each active
marker was sampled using 2 Optotrak 3020 sen-
sor banks (accuracy ±0.1 mm).
Reference postures for the head and torso
were collected for 10 s prior to the testing of each
condition. The reference posture measurements
were made while the participants were seated
with their back and bottom against the chair
backrest and while they looked straight ahead
(vertical gaze angle of 0°) at a mark on the wall
positioned at their sitting eye height. The mean
reference posture was the average of the three
reference postures collected prior to each test
Summary measures for each participant were
calculated from the 2 hr of data for each test con-
dition for the following outcome measures: head
flexion angle relative to mean reference posture,
head flexion angle relative to torso angle, head
horizontal position relative to torso (i.e., head for-
ward), torso angle relative to mean reference pos-
ture, and torso height relative to mean reference
posture (i.e., measure of slouch). In addition, the
mean viewing distance (from the eye plane to
the monitor) was calculated.
Vision Function and Symptoms
At the end of each test condition, speed of
accommodation and ocular convergence and di-
vergence abilities were measured with computer
administered tests (Vision Therapy Assessment,
Home Therapy Systems, Noblesville, IN).
Speed of accommodation was measured by
having participants view targets at a viewing dis-
tance of 41 cm with alternating +1.50- and –1.50-
diopter lenses. Targets were squares with a small
dot located in one of four locations within the
square. The participant indicated the location of
the dot with the arrow keys, at which time the
lenses were switched and a new target appeared.
The test lasted 60 s, and the measure of perfor-
mance was the number of lens cycles.
The magnitude of ocular divergence and con-
vergence (in that sequence) over which fusion
with stereopsis could be maintained was measured
using random dot stereo pairs in which one of four
targets appeared in stereo depth. Paired images
were shown, one to each eye, with red and blue
channel separation at a viewing distance of 41 cm.
The unit of angular measurement is the prism di-
opter, essentially equal to 1/100 radian or 0.57°for
the range of angles tested. The vergence require-
ment was increased in a stepwise manner until
two incorrect stereo responses were obtained; the
vergence magnitude of the last correct response
was taken as the “break” limit. The vergence mag-
nitude was then reduced in a stepwise manner
until a correct response was obtained, and this mag-
nitude was recorded as the “recovery” finding.
Figure 1.Diagram of participant and monitor with loca-
tion of 3-D markers.Viewing distance=square root [(Ex–
Ax)2+ (Ey– Ay)2]; head flexion angle = the angle between
vector BAand the Xaxis; torso flexion angle = the angle
between vector CD and the x axis; torso height = (Cy+
Dy)/2; torso forward position: (Cx+ Dx)/2; head forward
distance: the difference between the mean x location of
Markers Aand B and the mean x location of Markers C
834October 2007 – Human Factors
Following each vision test, participants also
completed a questionnaire that assessed their
experience following the computer task for the
following five symptom groups: eyestrain or eye
fatigue, blurred vision, neck ache, dry or irritat-
ed eyes, and headache (Sheedy, Hayes, & Engle,
2003). Participants rated the severity of the
symptoms on a 100-mm visual analog scale with
5 verbal anchors (none, mild, modest, bad,
Given the randomized order of conditions and
the breaks between the conditions, we assumed
that the vision functions and the symptoms
before each condition have the same group mean
values. Therefore, we confined the visual func-
tion and symptom testing to the moment after
each condition in order to represent the effect of
a particular viewing distance.
Differences among the three test conditions
(monitor distances) for all outcome measures were
initially evaluated using repeated measures
ANOVA. Significant findings were followed up
with the Tukey test for multiple comparisons.
Because participants were permitted to adjust
their body position after the start of a condition,
the mean distance from the eyes to the monitor
was not identical to the assigned condition. In
order to evaluate the effect of actual distance on
vision symptoms and vision test results, we applied
a regression analysis to distance as a continuous
predictor while adjusting for nonindependence of
the three observations for the same participant
(xtreg command, STATA, College Station, TX).
The mean age of the 24 participants was 25.4
(±4.1, range 19–35) years, and 16 (67%) were
male. The ethnic distribution was 46% Cauca-
sian, 29% Latino, and 25% Asian. Four partici-
pants used corrective lenses for distant vision but
did not normally use lenses for computer use. All
participants used the mouse with the right hand.
The mean number of years of experience using a
computer was 9.5 (±2.8). The mean height and
weight of participants were 171.2 (±8.7) cm and
69.6 (±13.4) kg, respectively. The mean adjusted
seat pan height, sitting elbow height, and sitting
eye height were 47.1 (±3.0) cm, 65.8 (±5.2) cm,
and 113.0 (±12.6) cm, respectively.
The mean postures during the 2-hr tasks
demonstrate that overall, participants did not
maintain the initial distance between their eyes
and the monitor, nor did they maintain the initial
reference posture (i.e., leaning back against chair
back support and gazing straight ahead). The
mean reference posture viewing distances were
52.4, 73.0, and 85.3 cm, respectively, for the near,
middle, and far distance (Table1). For each of these
viewing distances, the participants moved, on av-
erage, closer to the display during the task. When
the display was set to the far viewing distance,
the participants moved their heads and torsos for-
ward during the task so that the viewing distance
decreased from a reference distance of 85.3 cm
to 77.5 cm during the task (∆ viewing distance =
7.8 cm). Participants moved further forward dur-
ing the task for the far viewing distance than for
the near and middle viewing distances.
The torso and head posture data explain how
the changes in viewing distance were achieved.
The 3-D torso position changed from the initial
reference posture to the posture during the task
by rotating forward (∆ torso flexion angle) and
moving down in height (∆ torso height) for all
three viewing distances. The forward rotation
was 10°more for the far monitor location (11.7°)
than for the near monitor location (1.7°), and there
was more of a decline in torso height at the far
viewing distance (3.5 cm) than at the near view-
ing distance (2.5 cm). In addition, for the far
viewing distance the torso moved 4.8 cm forward
of the reference posture, toward the monitor,
whereas for the near distance it moved slightly
away from the monitor (0.4 cm).
The head flexion angle was close to the initial
reference head flexion angle throughout the tasks
(only 2.3°–3.8° more) and was not significantly
different among the three viewing distances (p =
.36). However, the head moved forward of the
torso during the tasks and moved the most for-
ward (3.4 cm) at the far viewing distance.
Mean visual, neck, and head symptom inten-
sity scores after each test condition are summa-
rized in Figure 2. There was a trend for lowest
symptom intensity at the near location of the
monitor. Based on the repeated measures ANOVA,
differences among test conditions were signifi-
cant for blurred vision (p=.01), dry or irritated eyes
(p = .03), and headache (p = .01) but not for eye-
strain or eye fatigue (p = .15) or neck ache (p =
.62). The Tukey follow-up test found significant
VISUAL DISPLAY DISTANCE
differences between the near and far condition for
blurred vision and for dry or irritated eyes and
between the near and middle condition for
Alinear, random-effects model was applied to
the data in order to test the effect of the actual view-
ing distance on visual symptoms. The results of this
analysis were similar to those of the repeated meas-
ures ANOVA: Distance had a significant effect
on blurred vision (p = .003, coefficient = .0012),
dry or irritated eyes (p= .006, coefficient = .0014),
and headache (p = .003, coefficient = .0011) but
not on eyestrain or eye fatigue (p = .10) or neck
ache (p = .48).
The convergence and divergence test results
after each test condition are summarized in Fig-
ure 3. There appeared to be a trend associated
with distance for convergence recovery with im-
proved measures at the near distance. Based on the
repeated measures ANOVA, distance had a sig-
nificant effect on convergence recovery (p = .05)
but not on divergence break (p= .64), divergence
recovery (p= .88), or convergence break (p= .29).
The Tukey follow-up test for multiple comparisons
TABLE 1: Initial Reference Body Posture, Mean Posture During 2-Hr Computer Task, and Differences (∆)
Between the Two
Reference posture (cm)
During task (cm)
∆ Viewing distance (cm)a
∆ Head flexion angleb
∆ Torso flexion anglec
∆ Torso height (cm)d
∆ Torso horizontal position (cm)e
∆ Head forward distance (cm)f
Note. Mean viewing distance during task differs from reference posture viewing distance because participants were allowed to
change posture during the study. However, participants were not allowed to change the chair or monitor location during the study
(N = 24). Standard deviations in parentheses.
aDistance from eyes to screen during task relative to initial reference posture. bHead forward flexion angle relative to reference pos-
ture. Reference posture is mean of relevant measure across the three reference postures collected at the beginning of each test con-
dition. cTorso flexion angle relative to reference posture; with larger value, torso is more upright. dTorso height relative to reference
posture; with larger values, torso is lower. eTorso horizontal shift relative to reference posture; with larger values. torso moves for-
ward. fDistance head is forward of torso relative to reference posture; with larger values, head has moved farther forward of torso.
Figure 2.Vision, neck, and head symptom intensity following 2-hr task with computer display set to three different
distances. Significant (Tukey follow-up test) differences between distances are marked (----*----). N= 24. Error bars
indicate standard deviations.
836October 2007 – Human Factors
for convergence recovery found a significant dif-
ference only between near and far distances.
Alinear, random-effects model was applied to
the data in order to test the effect of the actual
viewing distance during the task on the vision test
results. Based on this analysis, viewing distance
(in centimeters) had a significant effect on con-
vergence break (p = .03, coefficient = –.01) and
convergence recovery (p = .01, coefficient =
–.02) but not on divergence break (p = .84) or
divergence recovery (p = .88). Viewing distance
had no significant effect (p = .86) upon the speed
of accommodation test, with values of 25.3 ±5.2,
24.0 ± 6.1, and 26.1 ± 7 cycles/min at the near,
middle, and far distances respectively.
This study found that the viewing tasks on a
computer display led participants to make pos-
tural adjustments to their torsos and heads that
moved them closer to the display; the amount of
the postural adjustment and foreshortening of the
viewing distance increased with farther viewing
distances. In addition, the farther viewing distance
caused an increase in visual symptoms and head-
ache pain and a decrease in convergence recovery.
The decrease in convergence recovery indicates
greater visual fatigue with the longer viewing dis-
tance. These outcomes may be attributable to the
smaller angular size of the text at the longer view-
ing distances. The longer viewing distance causes
visual discomfort and fatigue as well as postural
adjustment as the participants apparently try to
mitigate the problem.
In common usage, the size of the characters
is fixed on the computer display; therefore
the angular visual size decreases with increased
viewing distance. A properly corrected eye
(20/20 visual acuity) can identify characters with
a size threshold of 5 minutes of arc (arcmin).
However, the angular size of characters must
exceed 5 arcmin because not all people have opti-
mal correction. Even if they did, several studies
(Legge, Pelli, Rubin, & Schleske, 1985; Legge,
Rubin, Pelli, & Schleske, 1985; Lovie-Kitchin
& Woo, 1987) have shown that character size
must exceed threshold size for optimal visual
performance. The amount by which the charac-
ter size must exceed threshold size has been
termed the acuity reserve (Whittaker & Lovie-
Kitchin, 1993) and is usually represented as
Recommendations for the amount of the acuity
reserve are wide ranging. Cheong, Lovie-Kitchin,
and Bowers (2002) determined that reading rate
leveled off with an acuity reserve of 2:1 for low
vision patients, whereas Yager, Aquilante, and
Plass (1998) determined an acuity reserve of 4:1
for normally sighted young adults. These acuity
reserves would require character sizes of 10 and
20 arcmin, respectively, for a person with 20/20
vision, or15 and 30 arcmin for a person with acuity
reduced by one line to 20/25. The BSR/HFES
100 draft standard (Human Factors and Ergonom-
ics Society, 2002) recommends character sizes of
16 to 18 arcmin for the design distance. Jaschinski-
Kruza (1991) found that a group of participants
adjusted a screen with 5-mm characters to a
Figure 3. Vergence test results following 2-hr task with computer display set to three different viewing distances.
Significant (Tukey test) differences between distances are marked (----*----). N = 24. Error bars indicate standard
VISUAL DISPLAY DISTANCE
preferred distance of 74 cm. This results in char-
acter sizes of 23 arcmin.
The Arial capital letters used in the editing
task of our study subtended 21.6, 15.5, and 13.3
arcmin, respectively, at the reference posture
viewing distances for the near, middle, and far view-
ing conditions. The angular size of the characters
at the near viewing distance (21.6 arcmin) exceeds
the acuity reserves reviewed previously, where-
as the angular size at the far viewing distance
(13.3 arcmin) results in a smaller acuity reserve
than desired for optimal viewing. This is the like-
ly explanation for the result that the participants
moved toward the display more with the farther
viewing distances, as compared with the shorter
one; it is also the likely reason for the result that
symptom measures were significantly higher at
the two longer viewing distances.
Thus, with the present fixed character size,
which was chosen to resemble many practical
conditions, the text on the screen can be easily
resolved only at a rather short viewing distance.
As a consequence, this means a certain load on
the oculomotor systems of accommodation and
vergence. In order to reduce this oculomotor load
and to adapt the preferred viewing distance to the
individual oculomotor functions of vergence and
accommodation (see the Introduction), longer
viewing distances and, accordingly, larger char-
acters would be required. Because such large
characters are not commonly used in the work-
place, they were not used in the present study.
It is likely that a balance occurs between visual
efficiency and postural adjustments. At the far-
ther viewing distances the gains in visual effi-
ciency by moving closer are greater, and hence
more postural adjustment occurs. At the near
viewing distance the gains in visual efficiency by
moving closer to the display are less, and hence
less postural adjustment occurs. Greater postural
adjustments may lead to greater joint moments
and increased muscle loads and fatigue. At the far
viewing distance, the participants’ postural ad-
justments were done by moving both the head
and torso toward the monitor. During the task, the
increase in torso flexion angle and the lowering
of the height of the torso (i.e., slumped posture)
suggest that the torso motion was done by flex-
ion at the thoracic and lumbar spine, not by flexion
of the torso at the hips.
At the far viewing distance, the head forward
movement was done by moving the head for-
ward of the torso without changing the head flex-
ion angle. This forward head gliding motion
maintains the same up-down gaze angle of the
eyes in the orbit across the three distances. This
forward head motion also maintains the head in
the same location relative to the C1 vertebra and,
therefore, should not alter the moment and mus-
cle load about that joint. However, the forward
head motion is done by increasing the moment of
the head about the C7 vertebra and, therefore,
increases the muscle load about that joint. This
increased moment would be balanced by an
increased load of the upper trapezius and splenius
Several limitations of the study should be con-
sidered. The assumption that the initial, upright
reference posture represented an “optimal” torso
and head posture may not be valid. However, the
initial posture measured at the beginning of each
of the three tasks was very similar within partic-
ipants; therefore, it provides a common reference
from which to evaluate the effects of the three
screen positions on posture. Another limitation is
that participants were allowed to freely move
their upper bodies during the task. This movement
led participants to alter their viewing distance to
the monitor. Therefore, the study is not a test of
a fixed viewing distance. A fixed posture and
viewing distance may have been difficult for par-
ticipants to maintain for 2 hr. A final limitation
was that the protocol of testing all three viewing
distances on the same day likely led to an order
effect associated with fatigue; however, this
should have been mitigated by the randomized
In conclusion, the viewing distance to a com-
puter monitor over the range of 50 to 85 cm, if the
screen character sizes are held constant, can affect
visual and head symptoms, convergence recovery,
and head posture. The near distance was associ-
ated with less blurred vision, less dry or irritated
eyes, less headache, and improved convergence
recovery when compared with the middle and far
distances. Participants moved their torsos and
headscloser to the monitor when it was set to the
far distance. These findings are likely to be medi-
ated by the reduction in visual angle of the char-
acters with the far viewing distance.
It is important to note that this study does not
address the independent effects of character an-
gle and viewing distance. In workplace condi-
tions in which the character size is fixed to about
838October 2007 – Human Factors Download full-text
3.3 mm, as in the present study, it is recommend-
ed that the computer monitor be positioned
between the near (52 cm) and middle (73 cm) dis-
tances from the eyes. However, the physiological
evidence reviewed in this paper suggests that a
viewing distance of about 50 cm may lead to
visual strain, particularly in participants with
problems in near convergence (independent of
accommodative problems in presbyopia). These
participants may benefit from using a longer
viewing distance, provided the character size is
increased accordingly with an appropriate soft-
This study was supported in part by the Office
Ergonomics Research Committee. The authors
would like to thank Linda Kincaid, Alan Barr,
and Betsy Llosa for their assistance with the
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David Rempel is director of the ergonomics program
and a professor of bioengineering at the University of
California, Berkeley. He is also a professor of medicine
at the University of California, San Francisco, where he
received his M.D. in 1982.
Kirsten Willms is a consultant in ergonomics in Calgary,
Alberta, Canada. She received her M.S. degree in ergo-
nomics from the University of Waterloo in Ontario,
Canada, in 2006.
Jeffery Anshel is an independent practitioner of oph-
thalmology and a consultant with Corporate Vision
Consulting in Encinitas, California. He received his
O.D. in 1975 from the Illinois College of Optometry.
Wolfgang Jaschinski is the head of the Individual Visual
Performance research group at the Leibniz Research
Centre for Working Environment and Human Factors in
Dortmund, Germany. He received his Ph.D. in ergo-
nomics from the Technical University of Darmstadt,
Germany, in 1988.
James Sheedy is a professor and dean at the College of
Optometry at Pacific University, Forest Grove, Oregon.
He received his O.D. in 1974 and his Ph.D. in physio-
logical optics in 1977 from Ohio State University.
Date received: August 10, 2006
Date accepted: February 10, 2007