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In the UK, the College of Optometrists guidance recommends that
Chapter 10 Clinical protocol
271
when examining patients with specific learning difficulties,
optometrists “should explore visual problems by means of a thorough
eye examination”.10 As always, it is recommended that clinicians keep
adequate clinical records.
Lightstone and Evans outlined the clinical routine for a special
investigation,
6 7
and this is discussed further in Chapters 2-4 and below.
The usual recommendation is for visual stress only to be diagnosed if
other potential optometric correlates of dyslexia have been excluded.
This means that visual stress is a “diagnosis of exclusion”. There are
some difficulties with this diagnosis of exclusion, and these difficulties
will now be summarised.
Limitations of a diagnosis of exclusion
The conventional problems that should be excluded before
coloured filters are prescribed are summarised in Figure 10.2 in three
categories: ocular health, refractive error, and orthoptic anomalies. For
each of these categories, there is a variety of opinions as to the range
of tests that are appropriate and when treatment is necessary. There
are many prescribing philosophies concerning refractive error
an even greater diversity of opinions as to when binocular vision and
accommodative problems exist and should be treated.
Practitioners often react to uncertainty about the diagnosis of
orthoptic conditions by applying a battery of tests. It needs to be borne
in mind that when more tests are carried out there is a greater chance
of a patient failing at least one of these tests. In other words, ‘a normal
patient is just one who has not been tested enough’! A scoring system
is suggested in the algorithm in Chapter 3 (Table 3.2) which addresses
this issue,14 and which has been used in several research studies.
13 14
11 12
and
15-17
excluded before a diagnosis of visual stress is reached and this gives
the diagnostic process a hierarchical nature which, in some cases,
might be inappropriate. Clearly, if a person has a serious ocular disease
or a large uncorrected refractive error, the priority should be to
manage these conditions. But low degrees of long-sightedness or
astigmatism are commonplace and might only be considered to
require correction if the person reports an appropriate symptom, such
as blurring.
11 12 18 19
If the blurring results from visual stress, this means
patients have to go through a stage in which glasses are prescribed
unnecessarily before the appropriate intervention in prescribed.
Similarly, if a patient has eyestrain or double vision resulting from
visual stress but also happens to have a subtle binocular vision
anomaly, then they might have to go through a time-consuming course
of eye exercises before they are allowed to have coloured filters. The
CITT-ART trial is, to date, the most thorough randomised controlled of
eye exercises (vision therapy) for a binocular vision anomaly.
20 21
This
study showed that prolonged and thorough exercises were no more
effective than a placebo at improving symptoms20 or reading.21 Nearly
40% of the group receiving vision therapy still had significant
symptoms or minimal improvement in symptoms after treatment.20
Some clinicians have questioned the hierarchical nature of Figure
10.2, arguing that subtle orthoptic anomalies may only be diagnosed
safely once visual stress has been excluded. The reasoning is that if
visual stress is causing a patient to have an unstable perception of text,
this will make it harder for the visual system to control the eye
alignment. In some cases, orthoptic function improves once the visual
stress has been treated. So, insisting on perfect orthoptic function
before prescribing Precision Tinted Lenses may be ‘the cart leading the
horse’. This may explain why some orthoptic (ocular motor) conditions
are correlated with visual stress.
22-24
Another difficulty is that the conditions in Figure 10.2 need to be
Vision, Reading Difficulties and Visual Stress
272
One approach, suitable for adults and older children whose
responses are reliable, is to investigate the effect of possible
interventions on symptoms. For example, if a patient reports text
moving, blurring, and flickering and they have a low refractive error
and signs of visual stress, the practitioner could ask the patient to view
text while comparing the effect of a refractive correction with the effect
of the optimal coloured filter. What effect, if any, do the interventions
have on their symptoms? This approach is only appropriate for subtle
(borderline) binocular and accommodative test results, which might be
considered by some clinicians to be within acceptable limits. In
contrast, if there is a definite anomaly (e.g., a decompensated
heterophoria at risk of breaking down into a strabismus), then the
management of this condition must take priority.
Symptoms to look for
There is evidence that children with dyslexia are more likely to have
symptoms than their peers.
25-27
There are many symptoms that can
lead a practitioner to suspect their patient may be susceptible to one
of the two main correlates of SpLD (visual stress and binocular
instability). Some of the most common symptoms include those listed
in Table 10.1.
It would be helpful if practitioners could predict what type of visual
problem a person has from their symptoms. Unfortunately, most of
the visual symptoms that are common in reading difficulties can have
several causes.28 Nonetheless, some symptoms do suggest the
possibility of the conditions indicated in Table 10.1.
Chapter 10 Clinical protocol
273
deficit/hyperactivity disorder.
Symptom or
history
Comment
Is the SpLD mainly
with reading,
spelling, writing, or
mathematics?
Sometimes reading may be adequate, but
nonetheless capable of improvement.
Is there a history of
spectacle wear?
Evans and colleagues6 found, children with SpLD are
more likely to have been prescribed spectacles, but
often are not using them. This may indicate an
enthusiasm for practitioners to try borderline
refractive errors, even though there is no evidence
they are more likely to help children with SpLD
compared with good readers (Chapter 2).
Is there a history of
eye exercises or
patching?
Children may have received eye exercises or vision
therapy as treatment for binocular vision anomalies,
or for other reasons (Chapter 4). Patching might
indicate amblyopia.
Is there a history of
coloured filter use?
The required colour may change. Discontinued use
of coloured filters in the past does not necessarily
mean that filters are no longer required.
Is there a history of
epilepsy, “fits, faints
or funny turns”?
Some people with photosensitive epilepsy can be
helped by using coloured filters (Chapter 11).
29
Are there headaches
(if so, frequency,
type, severity,
location, associated
factors, triggers)?
Headaches when reading or from lights or patterns
can be a sign of visual stress, particularly if the
headaches have the characteristics of migraine.
Migraine is sometimes alleviated by using precision
tinted lenses.30
Headaches can also be triggered by binocular vision
anomalies
15 31
or uncorrected refractive errors,
32-34
although most headaches are non-ocular in origin.35
Is reading usually
clear; does it ever go
blurred?
Blurring can be a sign of refractive errors,
accommodative defects, orthoptic anomalies, dry
eye, or visual stress.
Table 10.1. Examples of some symptoms than can be useful in assessing
Vision, Reading Difficulties and Visual Stress
274
people with SpLD. N.B., this list is not exhaustive. ADHD, attention
For some children, text is initially clear and then
blurs. Some children answer questions literally.
Therefore, questioning needs to ask not just
whether text is clear, but also whether text blurs.
Do letters or words
stay still, or do they
move?
Moving text is a common symptom of visual stress
but can also be a sign of binocular vision
anomalies.14 Again, the movement may only happen
after reading for a while, so the questioning should
reflect this.
Do letters or words
change size or fade
or disappear?
These symptoms can indicate anomalies of
binocular co-ordination or accommodation, latent
hypermetropia; or visual stress.
Do you have trouble
changing your focus
from viewing the
board to a book?
This could be a sign of accommodative dysfunction
or poor binocular co-ordination. Alternatively, there
may be no visual cause since people with dyslexia
often have poor short-term memory and copying
from the board requires the person to hold
information in short-term memory.
Do you ever
experience double
vision?
Double vision is a classic sign of a binocular vision
anomaly but can also be a sign of visual stress.
Double vision can be demonstrated (e.g., with an
insuperable vertical prism) so that the child knows
what the term means. If double vision is eliminated
by covering one eye, it probably results from a
binocular vision anomaly.
Do you ever
experience sore or
tired eyes (e.g.,
when reading)?
Can be a sign of refractive, binocular,
accommodative and anterior segment anomalies
(e.g., dry eye), visual stress, or just tiredness. If
linked specifically with reading (e.g., ‘Reading hurts
my eyes and I have to stop’) rather than, for example
drawing or gaming on a smartphone, suggestive of
visual stress.
Do you hold reading
unusually close or
far away?
May be a sign of refractive, binocular, or
accommodative anomalies, visual stress, or just a
habit.
Do you ever close or
cover one eye?
This symptom is strongly suggestive of a binocular
anomaly. Occasionally, can be a sign of visual stress
Chapter 10 Clinical protocol
275
(closing one eye reduces the input to the visual
cortex)
Do you tend to skip
or omit words or
lines?
Can be a sign of visual stress, ADHD, a binocular
anomaly, or just late reading development (“top
down”). Rarely, it might be a sign of an eye
movement anomaly.
Does the page seem
too bright?
Can be a sign of visual stress (e.g., ‘the page is so
bright that it stops me seeing the words properly’).
Are you particularly
sensitive to light?
Can be a sign of visual stress, a binocular vision
anomaly, or other ocular conditions. Photophobia
and frequent headaches seems to be a strong
indicator that precision tinted lenses may help.36
However, a sudden increase in photophobia can be
sign of various ocular pathologies (e.g., uveitis, angle
closure glaucoma, corneal ulcer) or systemic
pathology.
Is there a family
history of learning
problems?
SpLD tends to run in families.
Is there a family
history of orthoptic
problems?
Orthoptic problems tend to run in families.
Is there a family
history of migraine?
Migraine headaches tend to run in families and can
sometimes be helped with precision tinted lenses.
Is there a family
history of visual
stress?
Visual stress seems to run in families.
37 38
Many of
the neurological disorders with which visual stress
and photophobia are associated have a hereditary
component.
The term visual perceptual distortion is sometimes used to describe
generically several symptoms that can occur when viewing text (e.g.,
blurring, doubling, movement, patterns, fading, colours).
Children may fail to describe any symptoms for a visual condition
Vision, Reading Difficulties and Visual Stress
276
that would, in an adult, cause complaints. Yet, once the condition has
been corrected the child may then comment on the initial symptom
that has now been alleviated. If the symptom has been perceived for a
long time, the child may be so habituated that the symptom appears
to them as “normal”.
Teachers need to be made aware that it is not safe for them to
conclude that a child does not need an eye examination simply
because they do not report visual symptoms. Even when children do
describe visual symptoms, their reports are often difficult to interpret.
Whilst many adults can clearly differentiate between blurring,
doubling, and words moving; children may not.
Many of the visual symptoms in Table 10.1 do not occur
immediately, but rather after the child has been reading for a while. As
indicated in the table, questioning of the patient needs to detect this.
For example, some children who would say “no” to the question “Are
words in a book blurred?” would say “yes” if asked “Do words in a book
ever go blurred?”
Although the absence of symptoms does not imply that an eye
examination is unnecessary, the presence of visual symptoms does
indicate the need for an eye examination. Nonetheless, the presence
of symptoms does not necessarily mean that a visual problem is
present. Just asking about a symptom will be enough to convince some
children that they suffer the symptom, even when they do not!
It is recommended in this book that eye care practitioners
specialising in this field should carry out a detailed investigation of
visual function in people with reading difficulties. It is useful to send
out a questionnaire in advance of these appointments and this might
include, as a starting point, the questions listed in Table 10.1. A link to
such a questionnaire that can be downloaded and modified by
practitioners for their own use is included in the Appendices.
Chapter 10 Clinical protocol
277
The eye examination
The several visual problems that can be associated with reading
difficulties have been described. These conditions can cause similar
symptoms, so the eye care practitioner is faced with a challenge of
differential diagnosis, requiring a comprehensive eye examination.14
The eye examination would typically include the components listed in
Table 10.2.
Table 10.2. Components of the eye examination for people with SpLD. Not
all tests may be appropriate in every case.
General description
Details
Refractive error & visual acuity
Presenting vision at distance & near
Retinoscopy
Subjective refraction
Corrected visual acuity
Health assessment
Pupil reactions
Ophthalmoscopy
Visual fields (if old enough)
Colour vision (Ishihara)
Ocular motor assessment
Cover-uncover test at distance and
near
Dissociation test at distance & near
(e.g., alternating cover test, Maddox
rod, Maddox wing)
Aligning prism at distance & near
(Mallett fixation disparity test)
Ocular motility
Near point of convergence
Fusional reserves at near (possibly
distance)
Vergence facility
Stereoacuity
Amplitude of accommodation
Vision, Reading Difficulties and Visual Stress
278
Accommodative lag (MEM
retinoscopy)
Facility of accommodation
Visual stress screening
Intuitive Overlays
Wilkins Rate of Reading Test
Pattern Glare Test
Coloured lens prescribing
Intuitive Colorimeter
Precision tinted lenses
Most of the tests in Table 10.2 will be familiar to optometrists, but
the less common ones are described below and in more detail
elsewhere.14 One additional test is appropriate in some cases.
Neurologists and other practitioners sometimes refer patients with
headaches associated with near vision to clinicians with an Intuitive
Colorimeter, to see if precision tinted lenses will be helpful. For adults,
particularly if there is significant hypermetropia or Asian ethnicity, it is
a sensible precaution to check anterior chamber angles with the Van
Herick test.39 This is relevant because anterior chamber angle-closure
can be sub-acute and intermittent and can cause symptoms, including
blur and photophobia when reading. Rarely, this condition can affect
patients under the age of 40 years40 and very rarely under 20 years.41
What refractive correction should be worn during ocular
motor tests?
The main purpose of ocular motor tests is to detect visual problems
that may be affecting the child in the classroom. So, if the child wears
glasses more than 50% of the time when doing schoolwork at the
appropriate distance, the child should wear these glasses during ocular
motor tests at the same distance.14 An exception is ocular motility,
when spectacles are not usually worn unless there is a very high
refractive error, in which case the test should be done with and without
Chapter 10 Clinical protocol
279
glasses.14
It is sometimes useful to repeat some binocular vision tests when a
practitioner is proposing making a significant change to the refractive
correction (e.g., prescribing glasses for the first time), to check that the
new refractive correction is not going to worsen the situation. This can
also be sensible if there is a significant chance that the patient may
“change” their refractive status, by stopping wearing their glasses. For
example, if a hypermetropic child rapidly breaks down to a convergent
strabismus without their glasses, then parents should be warned to
have a spare pair and to avoid periods without spectacle wear.
Binocular stability assessment, fusional reserves, and vergence
facility
Binocular instability (Chapter 3) describes a subtle weakness in the
co-ordination of the two eyes. The eyes appear to be straight to the
casual observer and may even be orthophoric on cover testing.
However, if a clinician uses a dissociation test (e.g., the Maddox wing),
they will detect an excessive degree of instability (e.g., the arrow in the
Maddox wing test moves over a large range, such as from 0 to 6) and
low fusional reserves. Binocular instability can cause symptoms
including double vision, blur, visual perceptual distortions (e.g., words
appearing to move) and headaches.
One method of investigating binocular stability is to use the fixation
disparity test on the near Mallett Unit (Figure 10.3). An advantage of
this test is that it mimics the everyday situation when a person is
reading. This is different from many orthoptic tests that create artificial
conditions, such as dissociation tests that present completely different
images to each eye. With the Mallett test, the test itself (O X O in Figure
10.3) and the surrounding text is seen normally by both eyes together,
so the eyes have the usual stimulus to align. Only the two green strips
Vision, Reading Difficulties and Visual Stress
280