Visual and ocular effects from the use of
flat-panel displays
Esteban
Porcar 1, Alvaro
M. Pons1, Amalia Lorente2
1Department of Optics, Optometry and Vision Science
Unit, Physics College, University of Valencia, Burjassot, Valencia 46100, Spain
2Department of
Optics II, Optometry College, Complutense University of Madrid, Madrid 28040,
Spain
Correspondence
to: Esteban Porcar.
Faculty of Physics, Department of Optics, Dr. Moliner 50, Burjassot, Valencia 46100, Spain. esteban.porcar@uv.es
Received: 2014-08-06 Accepted: 2015-06-11
Abstract
AIM: To evaluate the prevalence of eye symptoms
in a non-presbyopic population of video display unit (VDU) users with
flat-panel displays.
METHODS: One hundred and sixteen VDU users with
flat-panel display from an urban population participated in the study; their
ages ranging from 20 to 34y. There were 60 females and 56 males. An eye
examination to rule out the presence of significant uncorrected refractive
errors, general binocular dysfunctions and eye conditions was carried out. In
order to determine and quantify the type and nature of eye symptoms,
participants were asked to answer written questionnaire and the results were
grouped by gender, age and number of hours a day spent using a VDU.
RESULTS: Seventy-two percent of participants
reported eye symptoms related to VDU use. Eye symptoms from moderate-to-severe
were found in 23% of participants. The main symptom was moderate-to-severe
tired eyes (14%); followed by sensitivity to bright lights (12%), blurred
vision at far distances (10%), eyestrain or dry eye or irritated or burning
eyes (9%), difficulty in refocusing from one distance to another or headache
(8%) and blurred vision at near or intermediate distances (<4%). Eye symptoms
were greater among females (P=0.005)
and increased with VDU use, markedly above 6h spent using a VDU in a typical
day (P=0.01).
CONCLUSION: Significant eye symptoms
relate to VDU use often occur and should not be underestimated. The increasing
use of electronic devices with flat-panel display should prompt users to take
appropriate measures to prevent or to relieve the eye symptoms arising from
their use.
KEYWORDS: asthenopia; eye symptoms; computer
terminals; computer vision syndrome
DOI:10.18240/ijo.2016.06.16
Citation: Porcar E, Pons AM, Lorente A. Visual and ocular effects from the use of
flat-panel displays. Int J Ophthalmol 2016;9(6):881-885
INTRODUCTION
The
use of video
display units (VDU) has become an
essential element in everyday life for work,
study and leisure purposes, with an increasing preference for
smaller-screen devices (laptops, tablets and smartphones)[1-2]. Its use has been boosted by the
development and wide availability of Internet (email, text messaging, social networking…).
The increasing use of computers has brought about a much higher
incidence of various health problems:
visual complaints, ocular and extraocular discomfort (headache and
musculoskeletal problems)[2-4].
Eyestrain or/and tired eyes are the most common complaints in VDU users and
have a significant relationship with VDU use[5-17].
It should be noted that a wide range of prevalence rates ranging 19.6%[16] to 83.7%[6]
were found in office workers. It is difficult to provide an exact value since
it depends on several factors, such as the criteria to define the study
population or the methods employed to assess it[18].
For example, surveys are a very common method[5,17].
However, refractive errors, as well as eye health and general binocular
dysfunctions have not been previously evaluated and could have influenced the
final results. In addition, dry eye is more common in the population of females
increasing with age[19], therefore
a higher proportion of them in studies will also show a higher result for dry
eye.
Previous studies[12-13,15,20] have determined risk factors such as the
characteristics of cathode ray tube (CRT) screen
(flashes, low resolution, poor image and others), environmental conditions (e.g. illumination, relative humidity and others), visual problems
(refractive errors and general binocular dysfunctions), ocular problems (dry
eye or disease), age, gender, number of hours spent on a VDU and/or the
conditions of their use (stressful eye conditions).
The emergence of
new technologies, has rapidly introduced the use of flat-panel displays, due to better visual recognition and
higher subjective preference in relation to the CRT displays[15]. However, there is limited
published data regarding eye symptoms related to flat-panel displays.
It should be noted
that eye symptoms from moderate-to-severe could limit personal activities[5], therefore we thought it would be
interesting to determine an accurate prevalence so as to understand the
repercussions arising from VDU use, in particular flat-panel displays.
The purpose of this
study is to make an assessment of eye symptoms affecting VDU users with
flat-panel displays within a well-defined study population: young,
non-presbyopic subjects, with no significant uncorrected refractive error, no
eye conditions and no general binocular dysfunctions.
SUBJECTS
AND METHODS
Subjects They were recruited through advertisements in job and
public information boards. VDU users with eye symptoms were not
specifically targeted. We looked for subjects aged 20 to 34y using a VDU for at least 2h per day. The upper limit of 34
years old in the inclusion criteria was meant to exclude subjects that could
potentially have pre-presbyopia. Candidates who were contact-lens wearers, who
had undergone refractive surgery or who had any given systemic or ocular
disease were excluded from the study.
The study followed the tenets of the
Declaration of Helsinki, and informed consent was obtained from all subjects
after an explanation of the nature and possible consequences of the study. It
also complied with the ethical requirements set by the University of Valencia.
This study was conducted at the Lluís Alcanyís
Foundation’s Optometry Clinic (University of Valencia).
Methods
All participants underwent a thorough eye examination,
carried out in all cases by the same examiner, who was in charge only of this
task. A different examiner analysed the data collected from the participants.
Those subjects with significant uncorrected refractive error (those that
exceeded a spherical equivalent of -0.5 D or +0.75 D in their correction),
general binocular dysfunctions, ocular motility disorders, vertical deviation,
strabismus or any other ocular health problem were excluded of the present
study. Then, in order to determine and quantify the type and nature of eye
symptoms, a questionnaire based on Hayes et
al's[5] was used.
Questionnaire A case history included a
10-question questionnaire developed by Hayes et al[5] to
determine the type and nature of eye symptoms in VDU users. This questionnaire
has been already used in previous studies[17,21-23] and
it is shown to be reliable. Table 1 shows the classification of the eye
symptoms considered, following the one proposed by Hayes et al[5] .
Table 1 Classification of eye symptoms related to VDU
use
Classification |
Symptoms |
Visual (blur) |
Experience blurred vision at near distances |
|
Blurred vision at intermediate distances |
|
Blurred vision at far distances |
|
Difficulty in refocusing eyes from one distance to
another |
Ocular surface
(dry eye) |
Irritated or burning eyes |
|
Dry eye |
Asthenopic (eye
strain) |
Eyestrain |
|
Headache |
|
Tired eyes |
|
Sensitivity to bright lights |
The questionnaire
is from Hayes et al[5].
The
symptoms assessed in this questionnaire (blurred
vision at far, intermediate and near distances, difficulty in refocusing eyes
from one distance to another, irritated or burning eyes, dry
eye, eyestrain, headache, tired eyes and sensitivity to bright
lights) were graded according to their intensity as: 4 (severe), 3 (moderate), 2 (mild), 1 (slight) or 0 (none).
This allowed us to obtain each symptom’s mean impact (in a 0-to-4 scale) within
the study population. Subjects were fully informed on how to complete the
questionnaire and they understood the significance of questions.
Statistical Analysis The data collected from the questionnaire were
analysed using SPSS software (version 15.0 for Windows, SPSS
Inc., Chicago, IL,
USA). The Mann-Whitney U test or Kruskal-Wallis
tests were used to differences between demographic data (gender, age and number
of hours a day using a VDU). A P-value
<0.05 was regarded as statistically significant.
RESULTS
One
hundred and sixteen VDU users, aged 20 to 34y and living in an urban
environment participated in this study. All subjects participating in the study
were Caucasians and had a corrected monocular visual acuity of 20/20 or better
in both eyes. They used flat-panel displays (liquid-crystal displays or light-emitting diodes backlights, that are equivalent in visual results[24]) on devices 49% desktop and 51% laptop. Table 2 shows
socio-demographic characteristics of VDU user participants.
Table 2 Demographic data of VDU user participants n=116 (%)
Parameters |
No.
of subjects |
Gender |
|
F |
60 (52) |
M |
56 (48) |
Age (a) |
|
20-24 |
47 (41) |
25-29 |
41 (35) |
30-34 |
28 (24) |
No. of hours a day using a VDU |
|
At least 2h |
10 (9) |
2-4h |
35 (30) |
4-6h |
30 (26) |
6-8h |
26 (22) |
More than 8h |
15 (13) |
VDU: Video display units.
Table 3 summarizes
the results of the questionnaire derived from Hayes et al[5]; which is,
the frequency of occurrence of each eye symptom, grouped by its intensity
level. The questionnaire’s internal consistency was verified by means of the
Cronbach’s alpha test (0.82).
Table 3 Percentage of subjects reporting eye symptoms related to VDU use
in a typical day
n=116
Questions |
Eye symptoms (%) |
||||
None |
Slight |
Mild |
Moderate |
Severe |
|
Experience
blurred vision at near distances |
70 |
18 |
9 |
3 |
0 |
Blurred vision
at intermediate distances |
64 |
25 |
9 |
2 |
0 |
Blurred vision
at far distances |
66 |
15 |
9 |
9 |
1 |
Difficulty in
refocusing eyes from one distance to another |
53 |
24 |
15 |
7 |
1 |
Irritated or
burning eyes |
47 |
23 |
21 |
9 |
0 |
Dry eye |
49 |
25 |
17 |
9 |
0 |
Eyestrain |
59 |
22 |
10 |
7 |
2 |
Headache |
50 |
25 |
17 |
8 |
0 |
Tired eyes |
28 |
30 |
28 |
12 |
2 |
Sensitivity to
bright lights |
48 |
21 |
19 |
9 |
3 |
The questionnaire
is derived from Hayes et al[5].
Seventy-two percent of subjects (n=83)
showed some eye symptom (confidence level at 95%±8.17;
range 63.83% to 80.17%). Slight or mild eye symptoms were commonly found,
however 23% (27 subjects) showed moderate-to-severe eye symptoms (confidence level
at 95%±7.66; range 15.34% to 30.66%).
The median total
score of eye symptoms was 7 [interquartile range (IQR) =7; overall range 0-27].
Figure 1 shows the data grouped by the 116 participants’ socio-demographic
characteristics. Data have
been grouped by gender, age and hours per day of VDU use. The differences in
eye symptoms by gender, age and by number of hours a day of VDU use are
analysed below.
Figure 1 The median total score of eye symptoms
obtained by the participants (n=116)
in relation to socio-demographic factors.
Gender Statistically significant differences were observed
between two genders (U=1168.5; P=0.005). When it came to individual symptoms between the two
genders, tired eyes (U=1130; P=0.002), headache (U=1349.5; P=0.048) and
blurred vision at near distances (U=1190;
P=0.001) were the ones showing
statistically significant differences.
Age The median age of participants was 25y
(IQR=8; age range 20-34y). For the purposes of this analysis, three age
subgroups at five-year intervals were established. Statistically significant
differences were not observed across the three age subgroups (H=2.87; P=0.24). In regard to individual symptoms, statistically
significant differences was observed in blurred vision at near distances (H=8.99; P=0.011).
Number of Hours a Day of Video Display Units Use Subjects were classified into five different
subgroups, according to the number of hours spent each day using a VDU.
Statistically significant differences were observed between the five different
subgroups (H=13.27; P=0.01). Regarding individual symptoms,
tired eyes (H=12.39; P=0.015) and blurred vision at far
distances (H=16.65; P=0.002) were the ones for which
statistically significant differences across subgroups were found.
Repeatability of Questionnaire A study about the repeatability of the
questionnaire according to the ranking method established (in a 0-to-4 scale)
was carried out. Two sessions at a time separated by at least 48 to 72h were
performed on 38 VDU users. The repeatability was analysed using the
Bland-Altman method. In concordance with the current guidelines from the
British and International Standards, that recommend the expression of
repeatability in term of standard deviation (Sw), the repeatability was Sw=1.53
and the limits of agreement at the 95% level were -0.24±2.99 (Figure 2).
Figure 2 Bland-Altman plot of repeatability between
two sessions (A and B) in 38 participants.
DISCUSSION
The findings of
present study have shown that a large number of VDU users experienced eye
symptoms related to VDU use (72%). A high percentage of
these symptoms were insignificant or mild in nature (49%) in concordance with
previous studies[5-6]. However, it should be noted that despite
the fact that subjects with significant uncorrected refractive errors, eye
health problems or general binocular dysfunctions were excluded, significant
eye complaints from moderate-to-severe in 23% of subjects (n=27)
were found. These subjects could have less productivity due decreased visual
efficiency. Therefore, these findings show that appropriate ergonomic measures
should be taken to minimize eye symptoms in VDU users.
The median total
score of eye symptoms in our study, was similar to a previous study[17]. Portello et al[17] used the
same ranking method (in a 0-to-4 scale), but evaluated the frequency of eye
symptoms, therefore our results, which are based on the intensity of eye
symptoms, cannot be compared directly with their findings. On the other hand, the determination of
the repeatability of the questionnaire derived of Hayes et al[5] according
to the ranking method established (in a 0-to-4 scale) is another contribution
from the present study. The repeatability of this test can be considered
appropriate, since the findings have shown little variability between the two
measures so it is reliable in the evaluation of eye symptoms in VDU users.
Socio-demographic
findings (Figure 1) have reported more eye symptoms among females than males,
which is in good agreement with previous studies[6,12].
However, the findings of this study have determined that in particular females
had more complaints of tired eyes, headache and problems of blurred vision at
near distances than males. In addition, increasing age also had impact on eye
symptoms, although no statistically significant differences were found. The
oldest-age subgroup (30 to 34y) had more eye symptoms than the other two
subgroups. In particular, blurred vision at near distances increased with age.
Finally, previous studies[6,10,20] have
also shown that the intensity of eye symptoms increased with the amount of time
spent daily using a VDU. The findings of this present study showed that there
was a significant increase of eye symptoms above 6h spent using a VDU in
concordance with previous studies[10,20]. This
factor seems to be one of the main triggers of eye symptoms, particularly tired
eyes and blurred vision at far distances were the main symptoms that showed a
statistically significant correlation with the number of hours a day of VDU
use.
Dry eye is another
very common symptom in VDU users[9], however
values of prevalence should be taken with caution due to the influence of
multiple factors, the different methodologies applied and the study population[17]. It may result from many factors
such as: environmental factors, reduced blink rate, incomplete blinking,
increased corneal exposure, age and gender, systemic diseases and medications,
contact lens wear, ocular conditions and cosmetics[3].
In our study, 34% of participants showed insignificant or mild dry eye and only
moderate in 9%. These results are difficult to compare with other studies, it
should be noted that our population study were young and non-presbyopic
subjects, in addition, contact lens wearers were excluded.
In conclusion, the
participants of this study used flat-panel displays, therefore our findings
have determined their current influence upon the eye symptoms of these VDU
users. Twenty-three percent of subjects showed both moderate-to-severe visual
and ocular symptoms. Symptoms were higher in females and markedly more than 6h
spent using a VDU. These conditions are likely to have a significant
detrimental impact on both productivity and quality of life. In addition,
despite the better quality and characteristics of flat-panel displays against
CRTs, the findings of this study should prompt users to take appropriate
measures to prevent or to relieve eye symptoms arising from their use.
ACKNOWLEDGEMENTS
Conflicts of Interest: Porcar E, None; Pons
AM, None; Lorente A, None.
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