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Evaluation of visual stress symptoms in age-matched
dyslexic, Meares-Irlen syndrome and normal adults
Mana A. Alanazi1,
Saud A. Alanazi1, Uchechukwu
L. Osuagwu2
1Department of Optometry & Vision Science, King Saud
University, Riyadh 11433, Saudi Arabia
2Ophthalmic and Visual Optics Laboratory
Group, Institute of Health and Biomedical Innovation, Department of Optometry
& Vision Sciences, Faculty of Health, Queensland University of Technology,
Brisbane 4059, Queensland,
Australia
Correspondence
to: Uchechukwu L. Osuagwu. Ophthalmic and
Visual Optics Laboratory Group, Institute of Health and Biomedical Innovation,
Department of Optometry & Vision Sciences, Faculty of Health, Queensland
University of Technology, Q Block, Room 5WS36 60 Musk Avenue Kelvin Grove,
Brisbane 4059, Queensland, Australia. u.osuagwu@qut.edu.au;
uosuagoul@ksu.edu.sa
Received:
2015-04-18
Accepted: 2015-07-27
Abstract
AIM: To examine the prevalence of dyslexia and
Meares-Irlen
syndrome (MIS) among female students and determine their level of
visual stress in comparison with normal subjects.
METHODS: A random
sample of 450 female medical students of King Saud University Riyadh (age
range, 18-30y) responded to a wide range of questions designed to accomplish
the aims of this study. The detailed
questionnaire consisted of 54 questions with 12 questions enquiring on ocular history and
demography of participants while 42 questions were on visual symptoms. Items were categorized into critical and
non-critical questions (CQ and NCQ) and were
rated on four point Likert scale. Based on the responses obtained, the
subjects were grouped into normal (control), dyslexic with or without MIS
(Group 1) and subjects with MIS only (Group 2). Responses were analysed as
averages and mean scores were calculated and compared between groups using one way
analysis of variance to evaluate total visual stress score (TVSS=NCQ+CQ), critical and non-critical visual stress
scores. The relationship between categorical variables such as age, handedness
and condition were assessed with Chi-square test.
RESULTS: The
completion rate was 97.6% and majority of the respondents (92%) were normal readers, 2%
dyslexic and 6% had MIS. They were age-matched. More than half of the
participants had visited an eye care practitioner in the last 2y. About 13%
were recommended eye exercises and one participant experienced pattern glare.
Hand preference was not associated with any condition but Group 1 subjects
(3/9, 33%) were significantly more likely to be diagnosed of lazy eye than
Group 2 (2/27, 7%) and control (27/414, 7%) subjects. The mean±SD of TVSS responses
were 63±14 and it was 44±9 for CQ
and 19±5 for NCQ. Responses
from all three variables were normally distributed but the CQ responses were on the average more positive
(82%) in Group 2 and less positive (46%) in Group 1 than control. With NCQ, the
responses were equally less positive in Group 1 and 2 than control. Group 2 subjects
showed significantly higher TVSS
(P=0.002), NCQ (P=0.006) and CQ (P=0.008)
visual stress scores than control but no difference between Group 1 and control
subjects, was observed for all scores (P>0.05,
for all comparisons).
CONCLUSION: The prevalence of dyslexia and MIS
among Saudi female students was 2% and 6%, respectively. Critical questions performed
best for assessing visual stress symptoms in dyslexic and MIS subjects.
Generally, students with MIS were more sensitive to visual stress than normal
students but dyslexics were more likely to present with a lazy eye than MIS and
normal readers.
KEYWORDS:
dyslexia; visual stress symptoms; critical questions; non-critical questions;
Meares-Irlen
syndrome; questionnaire
DOI:10.18240/ijo.2016.04.24
Citation: Alanazi
MA, Alanazi SA, Osuagwu UL. Evaluation of visual
stress symptoms in age-matched dyslexic, Meares-Irlen syndrome and normal
adults. Int J Ophthalmol 2016;9(4):617-624
INTRODUCTION
Dyslexia describes a specific disability in learning to read despite
normal intelligence and opportunity[1]. An unequivocal definition of
dyslexia is difficult and can vary according to the discipline[2].
Among practitioners, the diagnosis of dyslexia depends on showing that an
individual’s phonological, reading and spelling skills are well below what one
would expect for their age and other aspects of basic intelligence[3-4]. However, dyslexia is much more than this.
It is considered a neurological “syndrome” that involves much more than just reading
and writing[5]. Dyslexic individuals may experience significant
visual symptoms while reading. These symptoms may or may not be consistent with
binocular visual anomalies but they may impede the desire to read and write,
and perhaps ultimately handicap the learning process. The visual stress
symptoms include perceptual distortion, asthenopia and headache, diplopia,
blurred vision, visual confusion[2,6] (suggested to be as a result of
poor binocular control causing reading and spelling errors)[7]. Although
dyslexia is a lifelong condition[8-10], most dyslexic persons are
able to adapt to their condition by developing coping strategies (e.g. try to avoid reading) that help
them to overcome their reading difficulties.
There are no specific causes of dyslexia, but it is widely believed
that about 10%
to 15% percent of the population with dyslexia are due to a subtle
neuro-developmental syndrome[11-13] or disorder thought to have a
hereditary component[2,14]. Dyslexia with such
hereditary, neurodevelopmental aspects has been described as developmental dyslexia. Individuals with
developmental dyslexia present difficulties with decoding while comprehension
is more intact[13].
The connection between visual processes and dyslexia has gained much
publicity through the claims made by Irlen[15-17], who reported that many
children with dyslexia suffer from a perceptual dysfunction she called Scotopic
Sensitivity Syndrome. This condition is currently referred to as Meares-Irlen syndrome (MIS)[15,18].
MIS is often seen in children with dyslexia[19] but no clear definition has been
given[3]. It is characterized by visual perceptual distortion
such as illusion of images, colour and motion effects, and symptoms of visual
stress such as asthenopia in the form of eye strain, tired eyes, headache and
photophobia. Treatment of this condition involves the use of proprietary
coloured[17] and precision[20] overlays.
The involvement of visual stress in MIS is
quite obvious but the nature of the relationship between visual stress and
dyslexia is still unclear. Among children and adults with and without dyslexia,
evidence of a link between MIS and reading difficulties has been established[21-22]. Singleton and Henderson[21] investigated visual stress in
dyslexic and non-dyslexic children using a bespoke, computerized visual stress
screening test and found that the incidence of high level visual stress in
dyslexic children was almost twice that in control children. They observed that
dyslexic children who showed high visual stress scores reported more than 20%
improvement in reading speed with colour overlay in Wilkins Rate Reading Test
as compared with control children with high visual stress who showed between 5% and 10% improvement.
For children with lower visual stress scores, those with dyslexia showed at
least 5% improvement compared with <5% in controls when using coloured
overlays[21]. This indicates that predominance or incidence of
visual stress in dyslexics is higher than non-dyslexics.
Till date, many studies on dyslexia and its visual correlates have
focused on children with only a few studies in adults[22-24] even with
the identification of an urgent need to support dyslexic adults in higher
education[25]. Also, because the symptoms of MIS and visual stress
are non-specific, the need for a differentially diagnosis of the condition from
other ophthalmology
conditions, such as refractive error, binocular vision anomalies, and
accommodative anomalies has been identified[26]. Adults particularly students
are constantly involved in tasks that require a lot of reading and writing.
These increases their risk of experiencing visual stress symptoms and in the
presence of dyslexia, affects their workplace or studies[27]. In a
literate society, it becomes more disadvantageous and is compounded by racism[5].
This study aims to examine the prevalence of dyslexia and MIS in a population
of literate individuals[28] and whose field of study demand
a high level of study time. The strict admission policy of the prestigious medical
schools is sufficient guarantee of a generally high level of knowledge. Given
that a common support strategy at undergraduate university level is the
provision of extra time in examinations, this study will also subjectively
evaluate visual stress levels that are inferred from reading associated
symptoms scores among these students, determine the appropriateness of
questions to be used in identifying higher levels of visual stress associated
with reading, and compare visual stress levels among dyslexic, MIS and normal
subjects in order to identify which group of adults are more sensitive to
visual stress.
SUBJECTS AND METHODS
Subjects A total of 450 female
medical students of King Saud University aged between 18 to 30y were recruited
over a 2-month
period. All participants gave consent to participate in the study after the
protocol has been fully explained. Ethical approval was obtained from King Saud
University Ethical Committee and all procedures followed the tenets of the
Declaration of Helsinki and the participants were required to complete an
extended set of survey questions. Contact details for investigators were
available on the survey.
Questionnaire Design
A paper version of a validated
questionnaire with a wide range of questions was randomly distributed among
medical students of the university who were recruited by oral invitation from
the investigators. The survey was designed to subjectively identify the type
and the degree of symptoms associated with reading, and whether those symptoms
hinder the learning process or are associated with a specific reading and/ or
spelling difficulty. The detailed
questionnaire consisted of 54 questions with 12 questions enquiring on participants’ ocular history
and demography while 42 questions were on visual symptoms including: symptoms related to visual distortion at
near and distance, binocular visual dysfunction and reading or writing errors experienced by the
participants. Survey items were derived from previous studies on dyslexia, MIS
and visual discomfort[21,26,29-31]. Students who responded positively to previous diagnoses of dyslexia
and MIS were contacted at the end of data collection and the diagnosis was
confirmed in all subjects.
Statistical Analysis The results were entered into a Microsoft Excel
spreadsheet (Microsoft, Redmond, WA, USA), overlaid to
eliminate data errors and corrected. Data was analysed using SPSS version 16 (SPSS Inc. Chicago, Illinois,
USA). Besides the questions on demography and ocular history which were close
end questions (requiring yes/no answer), all other items in the questionnaire were rated on four point Likert scales from 1
(never) to 4 (always) and a neutral response was scored as zero.
Differences were considered
significance at P<0.05. Analysis
was to assess the construct validity by studying the correlation between the
final subjects’ questionnaire scoring with the case condition for all subjects
using Tukey’s post hoc analysis of one way ANOVA. Questionnaire items were divided
into two classes of questions: critical and non-critical questions.
Critical questions (CQ) were those that purely relate to the reading and/or
writing errors and to the visual stress symptom associated with reading while
the non-critical questions (NCQ) describe visual symptoms that are attributed
to binocular vision dysfunctions rather than the underlying issue or topic.
Total visual stress score (TVSS) is the sum of both CQ and NCQ scores. Based on
the responses obtained from the categorical questions, the subjects were
grouped into normal (control), dyslexic with or without MIS (Group 1) and
subjects with MIS only (Group 2). Chi-square test were conducted with
continuity correction to relate independent categorical items such as age,
handedness, presence of refractive error, sensitivity to the light, history of
eye exercises and sensitivity to pattern glare to case condition (dyslexia or
MIS). The average responses for each group of participant were also presented
graphically. To evaluate total, critical and non-critical visual stress scores
amongst the subject, ANOVA and post hoc test were conducted.
RESULTS
Subjects’ Characteristics Initially, 461 students agreed to participate. Six
students withdrew from the study due to the length of the survey and 5 failed
to respond to most of the questions. Only data from 450 participants (97.6%) who responded to
majority of the survey questions were included in the analysis. Of these
students, 92% (414/450) were normal subjects (age range, 18-30y) and 8% (36/450;
age range 18-26y)
had previously been diagnosed with reading difficulties. Of these subjects, 2% were dyslexic with or
without MIS (9/450) and 6% (27/450) had MIS only and were using colour
filters for reading. The subjects were matched in age. Percentage analysis of
the responses elicited by questions on demography and characteristics of the
subjects is shown in Table 1. More than half of the participants had visited an
eye care practitioner in the last 2y and about 47% and 34% use prescription
glasses and contact lenses, respectively. About 13% had been recommended eye
exercises and only one participant responded positively to experiencing pattern
glare.
Table 1 Result of analysis of responses on participants’
characteristics
n (%)
|
Responses of questions
enquiring about oneself |
Counts
of responses |
Total |
||
|
Yes |
No |
Not response |
||
|
Use prescription
glasses |
211 (46.9) |
237 (52.7) |
2 (0.4) |
450 (100) |
|
Use prescription
contact lenses |
153 (34.0) |
296 (65.8) |
1 (0.2) |
450 (100) |
|
Handedness |
||||
|
Right-handed |
409 (90.9) |
- |
- |
450 (100) |
|
Left-handed |
41 (9.1) |
- |
- |
|
|
Visited optometrists in
the last 2a |
263 (58.4) |
187 (41.6) |
- |
450 (100) |
|
Previously diagnosed of
lazy eye |
32 (7.1) |
418 (92.9) |
- |
450 (100) |
|
Previously wore eye
patch |
56 (12.4) |
394 (87.6) |
- |
450 (100) |
|
Eye exercises
previously recommended |
57 (12.7) |
393 (87.3) |
- |
450 (100) |
|
Previously diagnosed
with dyslexia |
9 (2.0) |
441 (98.0) |
- |
450 (100) |
|
Sensitivity to light |
3 (0.7) |
447 (99.3) |
- |
450 (100) |
|
Used coloured
overlays/tinted glasses for reading |
30 (6.7) |
420 (93.3) |
- |
450 (100) |
|
Sensitivity to pattern
glare |
1 (0.2) |
449 (99.8) |
- |
450 (100) |
Cross tabulation on Chi-square
analysis showed no significant association (P>0.05) between all categorical measures
(age, handedness, history of eye exercises etc.)
and case condition (dyslexia with/without MIS or MIS) except previous diagnosis
of lazy eye which was significant associated (Chi-square, χ2=9.6, P=0.008)
with dyslexia (Group 1). The subjects in Group 1 (3/9, 33%) were
more likely to receive a diagnosis of lazy eye than Group 2 (2/27, 7%) and
control (27/414, 7%)
subjects.
Result of Analysis on Responses from Critical and
Non-critical Questions The visual stress
scores from all three variables were normally distributed. The mean±SD of
responses for TVSS was 63±14 and it was 44±9 for CQ and 19±5 for NCQ. The average responses from CQ and NCQ are
shown in Figures 1 and 2 respectively for control, Group 1 and Group 2 subjects. With respect to the use of CQ, the response was
on the average more positive (82%) for group 2 subjects and less positive (46%)
for Group 1 subjects compared with the response from the control. Group 2 subjects (i.e. MIS subjects who did not receive a diagnosis of dyslexia but
used coloured filters while reading) scored the highest when CQ was used to
assess visual stress followed by Group 1 (dyslexic with MIS or without MIS) and
control subjects (Figure 3).
Figure 1 Analysis of average responses on
visual stress symptoms using critical questions in dyslexics with or without Meares-Irlen
syndrome MIS (Group 1) and Meares-Irlen
syndrome subjects (Group 2).
Figure 2 Analysis of average responses on
visual stress symptoms using non-critical
questions (NCQ) in dyslexics with or without Meares-Irlen
syndrome (Group 1) and Meares-Irlen
syndrome subjects (Group 2).
Figure 3 Mean visual stress scores with 95%
limits of confidence intervals (CI) for critical questions in control, dyslexic
with or without MIS and MIS subjects The subjects with MIS are those who did not
receive a diagnosis of dyslexia but use coloured filters to help in reading;
dyslexic without MIS are subjects who have been diagnosed as dyslexic but do
not use coloured filters to help in reading while dyslexics with MIS are
subjects who have been diagnosed as dyslexic and use coloured filters to help
in reading.
Concerning NCQ visual
stress measure, the responses were on average equally positive in Group 1 and 2
but more positive than control (Figure 2). On analysis,
the mean score was highest for Group 1 followed by Group 2 and control (Figure 4) and the TVSS was
highest for Group 2 subjects than Group 1 and control (Figure 5). Tukey’s
homogenous test showed that the sample size in each group did not influence the
results of statistical analysis when total TVSS (P=0.085), CQ (P=0.148), NCQ (P=0.080) were used
as measure variables. Analysis using one way ANOVA showed no statistical significant differences in
mean score of subjects within
groups for TVSS, CQ and NCQ
(P>0.05, for all) but between groups, the TVSS score (P=0.003),
the CQs (P=0.012) and NCQs (P=0.002) visual stress scores were
statistically significantly different.
Figure 4 Mean visual stress scores with 95%
limits of CI for non-critical questions in control, dyslexic with or without
MIS and MIS subjects. The
subjects with MIS are those who did not receive a diagnosis of dyslexia but use
coloured filters to help in reading; dyslexic without MIS are subjects who have
been diagnosed as dyslexic but do not use coloured filters to help in reading
while dyslexics with MIS are subjects who have been diagnosed as dyslexic and
use coloured filters to help in reading.
Figure 5 Mean visual stress scores with 95%
limits of CI for TVSS in control, dyslexic with or without MIS and MIS
subjects. The subjects
with MIS are those who did not receive a diagnosis of dyslexia but use coloured
filters to help in reading; dyslexic without MIS are subjects who have been
diagnosed as dyslexic but do not use coloured filters to help in reading while
dyslexics with MIS are subjects who have been diagnosed as dyslexic and use
coloured filters to help in reading.
The breakdown of post hoc analysis showing the mean difference in TVSS, CQ and NCQ visual stress
scores and the limits of confidence intervals (CI) are shown in Table 2. From the table, Group 2 subjects showed
significantly higher TVSS (P=0.002), NCQ visual stress scores (P=0.006) and CQ visual stress scores (P=0.008) than control. In contrast, the
TVSS, NCQ and CQ visual stress scores were similar between control and Group 1
subjects (P>0.05, for all
comparisons). However, when this analysis was performed with Group 1 being
split into dyslexic only and dyslexics with MIS, the TVSS (mean difference: -22; 95% CI: -42 to -2; P=0.024) and NCQ visual stress scores (mean
difference: -11, 95% CI: -18 to -4;
P=0.001) became significantly higher
for dyslexics with MIS than control.
Table 2 Mean
differences in mean scores between groups and 95% confidence intervals for
critical question (CQ), non-critical question (NCQ) and total visual stress
symptoms (TVSS)
|
Dependent variable |
Group
1 |
Group
2 |
Mean difference |
SE |
P |
95% confidence interval |
|
CQ |
Control |
Dyslexic with/without MIS |
-0.217 |
3.723 |
0.998 |
-8.973,
8.538 |
|
MIS |
-6.551 |
2.195 |
0.008 |
-11.712,
-1.389 |
||
|
Dyslexic with/without MIS |
Control |
0.217 |
3.723 |
0.998 |
-8.538,
8.973 |
|
|
MIS |
-6.333 |
4.253 |
0.297 |
-16.335,
3.669 |
||
|
MIS |
Control |
6.551 |
2.195 |
0.008 |
1.389,
11.712 |
|
|
Dyslexic with/without MIS |
6.333 |
4.253 |
0.297 |
-3.668,
16.335 |
||
|
NCQ |
Control |
Dyslexic with/without MIS |
-4.210 |
2.077 |
0.107 |
-9.094,
0.674 |
|
MIS |
-3.766 |
1.224 |
0.006 |
-6.645,
-0.887 |
||
|
Dyslexic with/without MIS |
Control |
4.210 |
2.077 |
0.107 |
-0.674,
9.094 |
|
|
MIS |
0.444 |
2.373 |
0.981 |
-5.135,
6.023 |
||
|
MIS |
Control |
3.766 |
1.224 |
0.006 |
0.887, 6.645 |
|
|
Dyslexic with/without MIS |
-0.444 |
2.372 |
0.981 |
-6.023,
5.135 |
||
|
TVSS |
Control |
Dyslexic with/without MIS |
-4.428 |
5.156 |
0.667 |
-16.554,
7.699 |
|
MIS |
-10.316 |
3.040 |
0.002 |
-17.465,
-3.168 |
||
|
Dyslexic with/without MIS |
Control |
4.428 |
5.157 |
0.667 |
-7.699,
16.554 |
|
|
MIS |
-5.889 |
5.891 |
0.577 |
-19.741,
7.963 |
||
|
MIS |
Control |
10.316 |
3.040 |
0.002 |
3.168,
17.465 |
|
|
Dyslexic with/without MIS |
5.889 |
5.891 |
0.577 |
-7.963, 19.741 |
P values are results of post hoc analysis using Tukey’s HSD. The mean difference is significant at the 0.05 level.
DISCUSSION
Learning and reading disorders are common
presentations in the primary care setting[29] and can have serious consequences on educational achievement of
subjects. The need for increased awareness of symptoms and identification of
patients has been identified[30]. In this study we assessed for the first time the frequency of
occurrence of dyslexic and MIS among a Saudi literate population. The results
show that about 8% of female medical students have reading difficulties. One in
every 50 student (2%) is dyslexic and one in every 16 student (6%) has MIS.
Although it has been difficult to assess the true prevalence of dyslexia mainly
due to the differences in the definition of the condition, prevalence studies
estimate that it affects between 4% and 10% of children[31-33] and higher rate of dyslexia has been reported among creative students
than non-creative students[34]. In another study the prevalence of MIS in adult population was
reported to be as common as in children[35]. Irlen[15]
inferred that MIS affects 12% of the general population and the condition
coexists in 65% of dyslexic people. In this study, we observed that a smaller
proportion of dyslexic subjects (33%) also had MIS. Irlen’s observation were
not backed up by actual data and as such cannot be compared with the current
results. In addition to the subjective confirmation of MIS by the persistent
benefit of coloured filters used during reading, or from immediate benefit that
is indicated by increased reading rate[19,35], the respondents in this study also self-confirmed the diagnosis of
the conditions, at the end of data collection. We included a large number of
items to ensure content validity[36] as the study was designed to measure a particular trait in a given
group of subjects (dyslexics).
Considering the very high completion rate
recorded, it appears that the use of this questionnaire as a measure of visual
stress level in dyslexic and MIS subjects was well received by the respondents
in this study. It is possible that the high response rate was a reflection of the
relevance of the subject being assessed to the respondents’ occupation (medical
students faced with greater writing and reading task). Whether this survey will
perform equally well in adults particularly with lesser education or of
different occupation is subject to future research. Of the questions asked,
enquiring on the respondents’ history of “pattern glare”
(a symptom well known to be attributed to MIS condition) may not have been
understood because only one positive response was received even though 27
respondents had MIS. Perhaps, the respondents were not familiar with the term
although opportunity was made available for them during data collection to ask
questions in order to clear any ambiguous issue, or those with MIS were unaware
of this symptom. Pattern glare
refers to the description of visual perceptual distortions, e.g. motion of the reading material,
change in the spacing between letters and coloured halos, which in turn can
cause visual discomfort, and asthenopic symptoms, by viewing certain “striped” pattern stimuli with
spatial characteristics such as lines of the text on a page[19]. A revision
of this term into a more familiar term in future studies may improve the
respondents’ understanding of the symptom.
Visual stress which is the subjective experience of unpleasant visual symptoms when reading
(especially for prolonged duration) and in response to some other visual stimuli[37] affects both dyslexics and non-dyslexic individuals[21].
It can be evaluated using objective and subjective techniques. Subjective
assessment of visual stress level requires the use of appropriateness questions and
in this study, significantly
higher visual stress scores were observed in MIS subjects than control
regardless of the questions implored as measurement tools. But, between the
control and dyslexic subjects, we found no significant differences in mean
scores when NCQ, CQ and TVSS were implored for assessment of visual stress.
Additionally, we found that subjects with MIS were more sensitive to
visual stress than normal subjects. More dyslexic adults (22%) than MIS (19%) and normal (11%) adults
experienced transient blurring of near vision and about 56% of dyslexics, 18%
of MIS and 24% of controls experienced double vision during prolonged reading
(none of these symptoms differed between groups). von Károlyi and Winner[23] did not find any difference in the
performance of perceptual and spatial tasks between dyslexic and non-dyslexic
young adults. It has been reported that about 5% of all children and half of
all dyslexic children complain of visual problems when they try to read and in
these children, letters appear blurred or move around and go double while
reading, making the children unable to see them properly[38]. Obviously, these symptoms will interfere with reading in these
subjects[4] and may cause eyestrain and headaches. However, these may be reduced, in some cases, by wearing tinted lenses[39].
Various
questionnaires have been used to
assess visual stress in dyslexics[34,40-42]. Some have assessed the effects of
coloured overlays on symptoms and reading rate[35] or measured the distribution of visual discomfort symptoms in
dyslexics during reading[43]. While none of these studies have compared the level of visual stress
in both groups (dyslexics and MIS subjects) in relation to controls, the
responses from studies on children may have under-reported the symptoms due to
a lack of understanding[44]. Children who constantly experience symptoms of visual stress during
reading may not identify the symptom as unusual and therefore might accept it
as normal, except perhaps if these symptoms are relieved by use of coloured
overlays[35,45].
Scientists have searched for connections between hand preference and
the presence of disorders that affect reading and language development.
However, until now, no convincing evidence has been found. Recently, a genetic
variant was discovered that appears to link handedness and reading ability.
Children with a particular version of the gene, called PCSK6, have a right hand
that is unusually dominant and are also poor at reading[46]. Most of the participants (90.9%) in this study were right handed (90.6% normal,
77.8% dyslexics and all MIS subjects) but this preference for hand and the other categorical variables like age and
history of eye exercises were not significantly
associated with either dyslexia or MIS. However, dyslexic subjects with or without MIS were
significantly more likely to be diagnosed with lazy eyes than other subjects in
this study. This is in agreement with a previous report that
reduced amplitudes of
convergence and accommodation were significantly correlated with dyslexia[47].
The authors also suggested that the binocular instability they observed in
dyslexic subjects was due to the decreased amplitude of accommodation.
As a general drawback to all questionnaires, we could not expand the
questions beyond the ones already asked and although we did not clinically
examine these subjects in order to confirm actual diagnosis, the participants
were contacted at the end of data collection and their self-reported diagnosis
were confirmed. The decision to recruit only females in this study was
pre-intended due to the high preponderance
of visual stress symptom scores in women[48-49]. Although this may limit the generalization of the current results, the study highlights
the importance of developing a standard set of questions for use in assessing
visual stress among dyslexic and MIS adults as this will aid proper
intervention in this group of subjects.
In conclusion, we observed that dyslexia (with or without MIS) and MIS
alone were present in 2% and 6% of adult female students in Saudi Arabia,
respectively. Subjects with MIS were significantly more sensitive to visual
stress than normal subjects but between dyslexic and normal subjects, the
sensitivity to visual stress was similar. On the other hand, the dyslexic
subjects were more likely to present with lazy eyes than other subjects and the
use of critical questions was more appropriate for assessing visual stress
levels in adult university students with reading difficulties.
ACKNOWLEDGEMENTS
Foundation:
Supported by the Research
Centre, College of Applied Medical Sciences and the Deanship of Scientific
Research at King Saud University.
Conflicts of
Interest: Alanazi MA,
None; Alanazi SA, None; Osuagwu UL, None.
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