The impact of different lenses on visual and musculoskeletal complaints in VDU workers with work-related neck complaints: a randomized controlled trial
Cagnie et al. Environmental Health and Preventive Medicine
The impact of different lenses on visual and musculoskeletal complaints in VDU workers with work-related neck complaints: a randomized controlled trial
Barbara Cagnie 0
Kayleigh De Meulemeester 0
Lieselotte Saeys 0
Lieven Danneels 0
Liesbet Vandenbulcke 0
Birgit Castelein 0
0 Department of Rehabilitation Sciences and Physiotherapy, Ghent University , De Pintelaan 185 3B3, 9000 Ghent , Belgium
Objectives: The impact of wearing lenses on visual and musculoskeletal complaints in VDU workers is currently unknown. The goal of this study was 1) to evaluate the impact of wearing VDU lenses on visual fatigue and self-reported neck pain and disability, compared to progressive lenses, and 2) to measure the effect of both lenses on head inclination and pressure pain thresholds during the performance of a VDU task. Methods: Thirty-five eligible subjects were randomly assigned to wear progressive VDU lenses (VDU group) (n = 18) or progressive lenses (P group) (n = 17). They were enquired about visual complaints (VFQ), self-perceived pain (NRS) and disability (NDI) at baseline (with old lenses), and 1 week, 3 months and 6 months after wearing their new lenses. In addition, Forward Head Angle (FHA) and PPTs were assessed during and after a VDU task before and 6 months after wearing the new lenses. A short questionnaire concerning the satisfaction about the study lenses was completed at the end of the study. Results: In both groups, visual fatigue and neck pain was decreased at 3 and 6 months follow up, compared to baseline. All PPTs were higher during the second VDU task, independent of the type of lenses. The VDU group reported a significantly higher suitability of the lenses for VDU work. Conclusion: It can be concluded that there is little difference in effect of the different lenses on visual and musculoskeletal comfort. Lenses should be adjusted to the task-specific needs and habits of the participant.
Lenses; VDU; Musculoskeletal complaints; Visual fatigue; Neck pain
Over the past years, the use of computers and other
digital electronic devices has increased dramatically. The
use of these visual display units (VDU) is often
accompanied by physical complaints of the neck, shoulder,
forearm and hand, with incidence and prevalence rates
ranging from 21 to 36% [1–3].
Many VDU workers not only experience
musculoskeletal complaints, but also eye discomfort and vision
problems when working with the computer for a long
period . This phenomenon is called Computer Vision
Syndrome (CVS) and may be caused by poor lighting,
glare on a digital screen, poor seating posture,
uncorrected vision problems, improper viewing distances, or a
combination of these factors.
Few studies have investigated the impact of
inappropriate vision on neck pain in VDU workers. Myopia, or
nearsightedness, is a condition in which objects on a far
distance appear blurred. This condition generally starts
during childhood and progresses until the age of 20.
Hyperopia (farsightedness) and astigmatism are two
other conditions that frequently contribute to the
development of visual symptoms when using a computer or
digital screen device. All these conditions can co-occur
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with presbyopia, the normal age-related loss of near
Today, a large variety of lenses exists to correct several
kinds of vision problems. Single-vision lenses are
prescribed if one of the above mentioned conditions occur
solitarily. When two or more conditions are present at
the same time, bifocals or progressive lenses can be
prescribed. However, most of these lenses are not suitable
for computer work as their intermediate zone is not
large enough to enable VDU work comfortable. As these
lenses are not perfect for computer work, VDU workers
might compensate their blurred vision by leaning
forward, or by tipping their head to look through the
bottom portion of their lenses, which can result in neck
With the increase of computer use, lenses designed
specifically for computer use have been developed.
These lenses provide a clear vision of the intermediate
zone at a distance of approximately 70 cm, which allows
a clear view of the computer screen. Table 1 gives a clear
overview of the main differences between progressive
lenses and office lenses.
Only a few studies have evaluated the impact of
wearing single- or progressive lenses on body posture, muscle
overload and pain during VDU work [5–9]. Becker et al.
 compared progressive lenses with single-vision lenses
and found that wearing progressive lenses leads to
greater degrees of change in forward head posture
and occipital extension. In an observational study of
Jaschinski et al. , a significantly larger head
inclination was found while wearing progressive lenses,
compared to wearing single-vision lenses for far or near vision.
In another study of Jaschinski et al. , a significantly
lower head inclination and better vision of the computer
screen was found while wearing VDU lenses, compared to
progressive lenses. Horgen et al.  compared 3 types of
progressive VDU lenses and single-vision lenses during a
VDU task and found no significant differences in muscle
load between the different lenses by using
electromyography. Later, Horgen et al.  set up a randomized
controlled trial (RCT) and compared the effect of wearing
different lenses for 1 year: 3 types of progressive VDU
lenses and single-vision lenses were compared. A
significant reduction of neck pain was found with one type of
the VDU lenses as well as high rates of satisfaction with
two types of the VDU lenses and the single-vision lenses.
However, the above mentioned studies have some
limitations, including limited follow-up and lack of more
objective measurements. In order to fulfill the need for
more objective measurements and larger follow-up
periods, an RCT was set up with the following research
1. What is the impact of wearing progressive VDU lenses, compared to progressive lenses, on self-reported neck pain and disability, and visual fatigue?
2. What is the impact of wearing progressive VDU lenses compared to progressive lenses, during a VDU task, on head inclination and pressure pain thresholds?
Male and female VDU workers working in a financial
holding in Ghent were recruited for this study. The
supervising physician of the study screened all subjects
for eligibility to participate in the study. The subjects
were included if they met the following criteria: (1) aged
between 45 and 65 years, (2) performing VDU work for
at least 4 h a day and 20 h a week (3) experiencing
work-related neck/shoulder pain or discomfort of more
than 30 days during the last year and (4) having a
difference in spectacle correction for presbyopia and myopia
of minimum 1.5 dioptres. Subjects were excluded in case
of (1) wearing VDU lenses before the study, (2) having
active eye diseases that could not be corrected with
eyelenses and (3) using medication that strongly influences
eye or muscle function.
All subjects signed an informed consent and the study
was approved by the Local Ethics Committee of Ghent
Table 1 Overview of the difference in function between progressive lenses and office lenses
Intermediate and near zone
Small intermediate and near zone to offer large
distance zone for uninterrupted far vision and
Gaze stabilization may take longer due to difficulties
finding the areas of optimal focus
Unlimited maximum viewing distance > 6 m
Full change in addition power needed
Large near and intermediate zones
Superior balance of optics because lens design has a
larger available lens area - no distance zone necessary
Limited viewing distance to 1 m, 2 m or 4 m
No full change in addition power needed
The study was conducted from April 2015 till December
2015. Eligible subjects were asked to fill out a
questionnaire concerning visual complaints (visual fatigue
questionnaire - VFQ) and self-perceived pain (numeric rating
scale - NRS) and disability (neck disability index - NDI).
First, subjects were tested with their current (old) lenses
in a landscape office while performing a 20-minute
VDU task (task 1). A 2D video analysis was performed
during the task to measure the Forward Head Angle
(FHA) . The PPT of the trapezius, levator scapulae
and infraspinatus muscles was measured after the VDU
task. After these first investigations, subjects were
randomly assigned to the treatment or control group using
a block randomization in order to obtain an equal size
and sex distribution in each group. The treatment group
was given progressive VDU lenses (ZEISS Officelens
Plus), specially designed for VDU work, whereas the
control group was given progressive lenses (ZEISS
Precision Plus). Spectacle frames of Silhouette® were
used and an eye examination was performed by an
experienced optician optometrist.
Within 1 month after the first test moment, the
participants received their new lenses and were asked to wear
these for 6 months during VDU work. The VFQ and
NRS were inquired 1 week (post1), 3 (post2) and 6
(post3) months after wearing their new lenses.
Selfperceived disability was enquired after 6 months wearing
the new lenses (post3). At 6 months follow up, the test
procedure was repeated while wearing the new lenses
(task 2). A short questionnaire concerning the
satisfaction about the study lenses was completed at the end of
the study. An overview of the study procedure is given
in Fig. 1.
All participants were tested in the morning and were
asked not to use alcohol, nicotine and caffeine 24 h and
painkillers 48 h before this VDU task. They were also
asked not to perform intensive physical activity 24 h
before the task. Participants were tested with the line of
sight parallel to the window. Glare was reduced by the
use of sun blinds and sufficient light was provided.
Computer screen, chair and table height were adjusted
individually with the top of the screen at or just below eye
level and 90° of flexion in the elbows, hips and knees.
The subjects performed a typing task during 20 min.
This task consisted of copying a predefined, unknown
text that was given on the left side of the screen. The
subjects were asked to type this text in a blank
document at the right side of the screen, using the computer
mouse only to scroll down in both documents.
Primary outcome measures
Self-reported visual fatigue The Visual Fatigue
Questionnaire (VFQ) was enquired at four different time
points (pre-post1-post2-post3). This questionnaire
consists of 15 questions, which have to be answered on a
VAS ranging from zero to ten . It enquires eye
strain, impaired vision, impaired eye surface and
problems apart from the eyes, e.g. headache. The content
validity index is 0.75 and the correlation between the
results of the questionnaire and the Visual Fatigue Meter,
a device that measures the eye fatigue changes, is −0.87
. Scores below 0.65 indicate ‘no fatigue’, between
0.66 and 2.36 ‘low fatigue’, between 2.37 and 3.88
‘moderate fatigue’ and scores above 3.89 ‘severe fatigue’.
Self-perceived pain General neck pain was assessed on
a 11-point Numeric Rating Scale (NRS) (0, no pain; 10,
worst possible pain) at four different time points
(prepost1-post2-post3). At these time points, subjects were
asked to rate the pain that they experienced in the
Self-reported disability The Neck Disability Index
(NDI) was completed at the beginning (pre) and at the
Fig. 1 Overview of the general study procedure
end (post3) of the study . The NDI consists of ten
questions concerning pain and daily living activities such
as lifting, reading and driving, and each item is scored
from 0 to 5. The maximum score is therefore 50. A
score between 5 and 14 represents a mild disability
whereas a score between 15 and 24 is interpreted as a
moderate disability. NDI scores higher than 25 reflect a
Secondary outcome measures
Head posture A 2D video analysis of the head posture
was performed during the task using a Logitech® webcam
with a ZEISS® Tessar HD 1080p lens and MaxTRAQ and
MaxMATE software. FHA was measured by placing
markers on C7 and the tragus and calculating the angle
between the vertical and the line connecting the tragus
and the C7 marker . The webcam was positioned on a
tripod, perfectly horizontal with a level meter and at a
standardized distance from the participant. The
participant was recorded for 15 s during the 5th, 10th and 15th
minute of the VDU task (45 s in total). The mean of the
three measurements was used for further analysis.
Pressure pain threshold The Wagner™ FDX 50
handheld pressure algometer is a digital device that measures
the level at which pressure (N) becomes unpleasant, also
known as the Pressure Pain Threshold (PPT). The
subject had to sit down relaxed with the hands on the
thighs. The investigator applied an increasing pressure
on a predetermined point of the muscle at a rate of
approximately 1 N/s with a 1 cm2 round rubber tip. The
subject was instructed to say “yes” when the comfortable
pressure changed into an unpleasant pressure. The
algometer was applied on the trapezius muscle (the middle
between C7 and the posterior part of the acromion), the
levator scapulae muscle (superior and medial of the
superior angle of the scapula) and the infraspinatus muscle
(the angle between the spina scapulae and the lateral
margin of the scapula), each time on both sides of the
body. Measurements were performed twice after the
Walton et al.  demonstrated substantial to near
perfect reliability (ICC = 0.76 –0.97) of the PPT of the
trapezius in people with and without acute neck pain. In
the current study all measurements were performed by
the same rater.
Satisfaction A short questionnaire concerning the
satisfaction about the study lenses was completed at the end
of the study. First, the overall satisfaction was
questioned. Second, participants had to indicate to which
extent the study lenses were appropriate to use for VDU
work, for near (e.g. reading) and far vision (e.g. looking
at colleagues in the same working area). A score had to
be given on a five-point likert scale ranging from ‘not at
all’ to ‘extremely satisfied’.
Data were analysed using IBM® SPSS® Statistics version
23.0. An Independent Samples T Test was applied to
reveal significant group differences and to assess
In order to investigate the impact of wearing
progressive VDU lenses, compared to progressive lenses on
selfreported visual fatigue, neck pain and disability, analyses
of variance with repeated measures was applied. For all
outcome measures, the between factor was group with
two levels (VDU lenses and progressive lenses) and the
within factor was time with four levels (pre, post1, post2
and post3), except for the NDI (pre and post3).
In order to evaluate differences in head inclination and
PPTs during a VDU task between wearing progressive
VDU lenses and progressive lenses, a similar analysis of
covariance with repeated measures was performed. For
all outcome parameters, the between factor was group
(VDU lenses vs. progressive lenses), and the within
factor was time (task 1 and task 2). A post-hoc pairwise
comparison was performed using a Bonferroni
correction. An alpha level of 0.05 was applied to all the data in
determining significant differences.
Sixty-five participants were screened for eligibility in
February and March 2015 and 35 participants (14
females and 21 males) met the eligibility criteria. Eligible
participants were randomized into the VDU lenses group
(n = 17; mean age ± SD, 51.09 ± 4.19 years) or the
progressive lenses group (n = 18; mean age ± SD, 53.67 ±
3.97 years). No significant differences in demographic
characteristics were found between both groups. Seven
participants dropped out during the course of the study,
resulting in a total of 15 subjects in de VDU lenses
group and 13 subjects in the progressive lenses group,
who completed the study. The two dropouts from the
VDU lenses group noted that the lenses were
appropriate to see the computer screen clearly, but one could
not see his colleagues clearly and the other could not
see his second computer screen appropriately. All five
dropouts from the progressive lenses group stated that
the lenses were not suitable for VDU work.
Primary outcome measures
Mean ± SD of all primary outcomes measures are
described in Table 2. No significant time x group
interaction effects were found for all primary outcome
measures (P > 0,05).
Table 2 Descriptive statistics of VFQ, NRS and NDI of the VDU and P group at different time points
Self-reported visual fatigue There was a main effect for
time (F = 7.947; p = 0.001), but not for group (F = 2.362;
p = 0.136). Post hoc analysis revealed no significant
differences between pre and post 1 and between post2 and
post3, but demonstrated significantly lower values in
post2 and post3 compared to pre and post1 (Fig. 2).
Self-perceived neck pain There was a main effect for
time (F = 3.561; p = 0.034), and for group (F = 6.031;
p = 0.021). Post hoc analysis revealed significantly lower
scores at post2 and post3 compared to post1, independent
of the type of lenses and a significantly lower score in the
VDU group, independent of time (Fig. 3).
Self-reported disability No significant main effects
for time (F = 0.021; p = 0.887) and group (F = 0.193;
p = 0.664) were identified for self-reported disability.
Secondary outcome measures
Mean ± SD of all secondary outcomes measures are
described in Table 3. No significant time x group
interaction effects were found for all secondary outcome
measures (P > 0,05).
Head posture No significant main effects for time
(F = 0.921; p = 0.347) and group (F = 2.210; p = 0.150)
were found for FHA.
Pain pressure threshold There was a significant main
effect for time for all PPTs (p < 0.004) (Fig. 4) but not for
group (p > 0.05). All PPTs were significantly higher when
using the new lenses (task 2), independent of the type of
Satisfaction No significant difference in overall
satisfaction between the two types of lenses was found
(p = 0.072) (Table 4). The VDU lenses group reported a
significantly higher suitability of the lenses for VDU work
(p = 0.001) while the progressive lenses group reported a
significantly higher suitability for far vision (p < 0.001). For
the satisfaction for close vision no significant difference
was found between the two types of lenses (p = 0.115).
The aim of this RCT was to investigate the influence of
wearing progressive VDU lenses, compared to
progressive lenses on self-reported pain, disability and visual
Fig. 2 Mean ± SE based on estimated marginal means of the VFQ at the different time points
Fig. 3 Mean ± SE based on estimated marginal means of the NRS at the different time points in the VDU and P group
fatigue and to investigate the impact of these lenses on
pain sensitivity and head inclination during a VDU task.
It can be concluded that both lenses have a significant
impact on different outcome measures but that there is
little difference in visual and musculoskeletal comfort
between wearing progressive and VDU lenses.
In both groups there was a significant decrease in
selfreported visual fatigue and neck pain at 3 and
6 months follow up compared to baseline (for visual
fatigue only) and 1 week after wearing the new lenses
(for both outcome measures).
Visual fatigue has been assessed in previous studies
using mainly one dimensional measurements, but none
of these studies have used the VFQ, as this is a rather
new measurement tool. Similar to the results of the
general neck pain, the VFQ at 3 and 6 months follow up
showed only small, but significant changes in both
The baseline NRS value for neck pain intensity and
the decrease in intensity is similar to a previous study of
Horgen et al.  who followed VDU-workers during a
12-month period wearing different types of lenses.
Despite this significant difference, the decrease in NRS
was lower than the MCID of 1.5 points, which is
required to obtain a small detectable patient-perceived
change . These small changes could amongst others
be attributed to the fact that the general level of pain
was relatively low at baseline.
Neither of the groups’ results showed significant
changes in self-reported neck disability. All participants
Fig. 4 Mean ± SE based on estimated marginal means of the PPT of the left and right UT, LT and LS after task 1 and task 2
Pain pressure threshold
Levator scapulae left (N/s)
Levator scapulae right (N/s) VDU
Infraspinatus left (N/s)
Infraspinatus right (N/s)
Table 3 Descriptive statistics (mean ± SD) of head posture and
PPT of the VDU and P group at different time points
had a mild limitation (NDI scores between 5 and 14) at
the start of the experiment which may explain why no
significant changes in NDI scores were found. On the other
hand, NDI scores indicating mild limitation are rather
common in patients with work related neck pain.
There were no changes in FHA during the VDU tasks.
Past research included only one study that compared
VDU lenses with progressive lenses. Jaschinski et al. 
found a significantly lower head inclination when
wearing VDU lenses which is conflicting with the results of
All PPTs were higher during the second VDU task,
independent of the type of lenses. This increase in PPT
could be attributed to the decrease in general neck pain
and visual fatigue
The VDU group reported a significantly higher
suitability of the lenses for VDU work while the P
group reported a significantly higher suitability of the
lenses for far vision. According to Jaschinski et al. ,
vision of the computer screen was judged significantly
Table 4 Descriptive statistics (mean ± SD) of the satisfaction
questionnaire (five point scale) of the VDU and P group
better with VDU lenses and far vision was judged better
with progressive lenses which is comparable with the
results of this study.
Besides the quantitative analyses, some subjects in the
VDU lenses group reported that the lenses were not
suitable for far vision and that social contact with colleagues
in the same working area was strongly reduced. Others
reported that the lenses were not suitable to walk with in
the working area because of dizziness and reduced depth
perception. In the VDU lenses group there was still a need
to use progressive lenses for other tasks then VDU work.
Some subjects reported that it was difficult to switch
between both types of lenses during the day.
In the progressive lenses group several subjects
reported that the lenses were not suitable for VDU work
and that the computer screen had to be placed in
another position or that the head had to be positioned
in an unnatural posture.
The present results should be viewed within the
limitations of the study. There was no blinding possible for
the intervention because of the nature of the study.
VDU lenses can only be used during VDU work,
whereas progressive lenses can be used all day long, so
the participants couldn’t be blinded.
Another limitation of this RCT was that the kind of
lenses that participants used at the beginning of the
study was not taken into account into the analysis.
When entering the study, sixteen participants used
progressive lenses, 13 used reading lenses, 2 used lenses for
far vision and 4 didn’t use any lenses at all during VDU
work. In the two groups a comparable number of
subjects already used similar kinds of lenses at the
beginning of the study.
In future studies, a more in depth qualitative analysis
of comparing different lenses is needed. Bigger sample
sizes, in order to meet a high dropout rate, is needed. In
addition, the kind of lenses that are used at the
beginning of the study should be taken into account as well in
order to have a more homogeneous population.
It can be concluded that there is little difference in
effect of the different lenses on visual and musculoskeletal
comfort. Lenses should be adjusted to the task-specific
needs and habits of the participant.
BC participated in the design of the study and coordination, KDM and LS
carried out the study and performed the data analysis, LD participated in the
design of the study, LV carried ou the medical screening, BCa participated in
the design of the study and performed the statistical analysis. All authors
read and approved the final manuscript.
Ethics approval and consent to participate
All subjects signed an informed consent and the study was approved by the
Local Ethics Committee of Ghent University Hospital.
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