Добавил:
Sekretar
kiopkiopkiop18@yandex.ru
t.me/Prokururor I Вовсе не секретарь, но почту проверяю
Опубликованный материал нарушает ваши авторские права? Сообщите нам.
Вуз:
Предмет:
Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_5253_Библиотеки_им_академика_М_И_Перельмана.pdf
potentially confounding variables (e.g., accommodation, refractive
error, medication, IQ, ADHD). If visual stress results from cortical
hyperexcitability (see Chapter 8) it is possible the resulting perceptual
distortions interfere with the blur feedback pathway that controls
accommodation. Therefore, poor performance at a clinical test of
accommodation might be the consequence (rather than a cause) of
visual stress and this would be an interesting topic for further research.
The Delphi method surveys a panel of experts and feeds back their
opinion to arrive at a collective consensus. A Delphi study has
suggested preliminary diagnostic criteria for visual stress (Table 12.1).21
It would be useful to investigate the effectiveness of these criteria in
predicting cases that would go on to benefit from coloured glasses or
tinted screens.
Table 12.1. Preliminary diagnostic indicators for visual stress from the
research by Evans, Allen, Wilkins (2017).21
As noted above, one stage in the diagnosis of visual stress is the
exclusion of other potential causes. As discussed in Chapter 10, the
difficulty with such a diagnosis of exclusion is that it depends on the
depth of investigations and the practitioner’s criteria in considering
Chapter 12 Research priorities and practice
343
when a test finding is abnormal. Additionally, if binocular co-ordination
and accommodation can be adversely affected by visual stress, as
seems possible, the current approach of treating these problems
before treating visual stress may be inappropriate in some cases.
Further research is required to investigate the influence of visual stress
on the performance of optometric tests.
Symptoms are part of the diagnosis of visual stress, as is the case
with many other healthcare conditions. It is noted below that a
checklist of symptoms has been produced by an organisation called
the Specific Learning Difficulties (SpLD) Assessment Standards
Committee (SASC). The validity of this checklist should be tested in
research.
Recommendations for research methodology
Most research in this field relates to three questions:
1. What optometric findings are particularly common in people
with reading difficulties or in people with visual stress?
2. Do these optometric factors contribute causally to reading
difficulties or visual stress?
3. What is the effect of optometric interventions on symptoms
and/or reading?
The first question is typically addressed by two types of research
study: case control studies and correlational studies.
Case control studies
In case control studies a group of individuals with a condition is
compared with a group which does not have the condition.22 This is
Vision, Reading Difficulties and Visual Stress
344
usually a matched group study: the two groups are matched for
potential confounding variables.
13 23-25
The most important point to
make about this type of research, is that a control group is essential.
The simpler approach of comparing, for example, the performance of
a group of children with dyslexia at optometric tests with normative
values for these tests is unlikely to produce meaningful results. This is
because the normative results are unlikely to have been obtained
under exactly the same conditions and the examiners are likely to
know that they are assessing a group with dyslexia, so their
expectations or beliefs are likely to influence the results.
Recommendations and suggestions for case control studies in this
field are included in Table 12.2. One challenge with this research design
is in deciding which confounding variables to control for, and the
results will only apply to the type of population that is studied. If groups
are matched on only two or even three variables, the results will be
distorted by the contribution of other covariates that are not matched.
These problems can be overcome in a correlation study, as discussed
later. Although the ideal is for researchers to be masked as to the
group to which a participant belongs, in reality there may be occasions
when a researcher becomes aware of this. For example, a dyslexic child
may inadvertently tell the researcher, or may read letter chart lines
backward. Such cases should be reported together with the study
findings (e.g., reference24). The examiners can be asked to give their
best estimate as to the group a patient belongs to, and these estimates
can be used in the analysis of the study findings
Chapter 12 Research priorities and practice
345
Table 12.2. Considerations for case control studies
Issue
Relevance to reading
difficulties (RD)
Relevance to visual stress
(VS)
Select
participants who
have the target
condition,
explicitly
defining
diagnostic
criteria.22
Specify the diagnostic
criteria used for RD or
dyslexia
Most people with RD do
not have VS, so it is not
appropriate to attempt to
research VS in subjects who
have been selected as
having RD. Participants
with VS should be selected
and the diagnostic criteria
should be specified.
Control for
confounding
variables.
Rather than comparing an experimental group with
norms (which may have been acquired using different
tests or a non-equivalent population), a comparison
should be made with a control group.
The two groups may be matched for age, IQ,
26 27
sex,
and preferably ADHD (but see note in the text).
Use a masked
design, when
possible.
Ideally, the researchers should be unaware whether
participants are in the reading disabled or the control
group.
Use continuous
variables
whenever
possible.
Some variables are truly categorical (e.g., the number
of eyes a person has). Most variables are not (e.g.,
refractive error, convergence) and it is preferable to
treat these data as continuous rather than categorical
variables. Reducing these variables to categories or
worse still dichotomizing into normal/abnormal,
28 29
reduces power and introduces an arbitrary cut-off (e.g.
reference 30)
Research on the
mechanism
should be
relevant.
RD and dyslexia are
likely to be multi-
factorial, so the research
design should not
assume a single cause.
Research on VS shows the
required tint should be
prescribed individually and
with precision. Research on
potential mechanisms for
VS should allow for this.
Vision, Reading Difficulties and Visual Stress
346
Correlational studies
In a correlational study the researchers measure the type and
strength of relationships among variables that are not under the
researchers’ control. For example, a range of optometric variables and
reading skills might be measured in an unselected cross-section of
children to look for correlations between reading skills and optometric
variables.
A correlational design can be combined with a matched group
design and a good example of this is the study by White and
colleagues.31 These researchers tested 23 dyslexic and 22 control
children and measured a very wide range of variables (e.g., reading
skills, phonological skills, IQ, visual stress, magnocellular-dorsal
function). In addition to comparing the group averages at each test in
a matched group analysis, the researchers used data from their
control group to define the range of normal performance at each test,
under the exact conditions used in the research study. From this, they
determined which dyslexic participants performed poorly at each task,
resulting in the useful summary diagram in Figure 12.1
Chapter 12 Research priorities and practice
347
Figure 12.1. Results of multiple case control study by White and colleagues,
reproduced with permission.31
The value of correlational studies depends on the variables that are
selected and on the sample size. Potentially confounding variables can
be controlled for in the statistical analysis of correlational studies.
A correlational design cannot indicate causality but can provide data
on the strength of relationships between variables. This allows limited
inferences to be drawn about the likelihood of relationships being
causal. In visual stress, evidence suggestive of causality can be
obtained by having participants carry out reading or visual search
tasks32 with and without coloured filters, and comparing performance
under conditions that have been designed to exacerbate or minimise
visual stress.
33 34
The strongest evidence for causality comes from a
special type of cohort study, called a double-masked randomised
controlled trial.
Double-masked randomised controlled trials (RCTs)
For establishing cause-and-effect relationships, no study design is
Vision, Reading Difficulties and Visual Stress
348
more highly regarded than a randomised controlled trial (RCT).35 If
systematic reviews reveal several RCTs that provide consistent results
Consideration
Relevance to reading
difficulties (RD)
Relevance to visual
stress (VS)
Subject inclusion
criteria.
Specify the diagnostic
criteria that are used for
RD or dyslexia.
Most people with RD do
not have VS, so it is not
appropriate to attempt to
research VS in subjects
who have been selected
as having RD. Participants
should be selected who
have VS and the
diagnostic criteria should
be specified.
Chapter 12 Research priorities and practice
349
with narrow confidence intervals the evidence is even stronger.36
However, even systematic reviews of RCTs involve an element of
subjective judgement.37 The design of RCTs requires a knowledge of
the likely effect of the variables and for this reason is usually
undertaken as a late stage in the gathering of evidence. Participants
with the target condition are randomly allocated to two groups: one
receiving the real treatment and the other receiving a control
treatment. If reading is improved by the experimental intervention
more than by the control intervention this is strong evidence that the
treatment is helpful. It is also evidence that the condition that was
treated contributes causally to poor reading. Issues pertinent to this
type of research are summarised in Table 12.3. Crossover RCTs are
particularly useful because they reduce the effect of variability
between participants.
Table 12.3. Considerations for double-masked randomised placebo-
controlled trials of treatments for reading difficulties and visual stress
Subject exclusion
criteria.
Any exclusion criteria
should be specified.
If participants are
excluded for any
optometric (or other)
reasons this should be
stated, together with the
number excluded.
Active & control
treatment.
It is essential to have a
control treatment,
otherwise any
improvement could be
attributable to factors
other than the
intervention (e.g., placebo
effect,38 regression to the
mean).
39 40
The control treatment
should give participants
the same time, attention,
and an equally convincing
explanation as the active
treatment.
For the active treatment,
coloured filters should be
individually & precisely
prescribed.
Spectral data on the tints
should be provided.
Ideally, the control tint
should be inert, but a
‘sub-optimal’ colour may
be required for the
masking to be credible.
For RCTs on vision
therapy, it is particularly
important that there is a
convincing control
treatment.
Random
allocation.
Participants should be randomly allocated to receive
the active or control interventions.
Masking
(blinding).
Participants, parents, teachers, and researchers should
all be masked as to which is the active and control
intervention.
Minimise
attrition (drop-
outs).41
Bias may occur if participants receiving a particular
treatment are more likely to drop out. Make every
effort to reduce attrition and minimise attrition bias;
consider the pros and cons of an intention to treat
approach.
42-45
Vision, Reading Difficulties and Visual Stress
350
Some of the points in Table 12.3 may seem self-evident but are
often not considered. For example, coloured filters are an intervention
for visual stress and most people with dyslexia do not have visual
stress.
32 46 47
It is therefore surprising that some researchers investigate
the effect of coloured filters on populations selected solely because
they have a diagnosis of dyslexia or reading difficulties. Several studies
are not included in sections of this book (e.g.,
48-57
) because one of the
factors in the tables in this chapter means their results are difficult to
interpret.
Randomised controlled trials (RCTs) can provide strong evidence,
but the strict experimental conditions they use may limit applicability
in the real world.58 In particular, the criteria by which participants are
selected in RCTs determine how the findings can be applied. Other
research designs can also provide important evidence.59 This is an
important point and means that RCTs, although essential, are
insufficient on their own, and observational studies of interventions in
everyday clinical practice are also required.
Some suggestions for eye care practitioners
In common with most healthcare sciences, a great many everyday
activities of optometrists lack a strong evidence-base.36 Particularly in
these cases, but even when there is a good evidence from research,
the practitioner should integrate the best available research evidence
with the clinical findings, practitioner’s clinical expertise, and patient’s
preferences (Figure 12.2).
60 61
Chapter 12 Research priorities and practice
351
Figure 12.2. Satterfield's summary of the evidence-based approach (After
Satterfield et al.61
Increasingly, reading takes place with electronic devices, such as
personal computers, tablets, electronic readers, and smartphones.
Whilst these devices can introduce eye strain,
62 63
particularly if they
flicker, they also have the potential to reduce it. For example, font type,
letter size, letter spacing, line spacing and the font and background
colour can all be adjusted and many users find this beneficial.64 This is
discussed in Chapter 9.
The Specific Learning Difficulties (SpLD) Assessment Standards
Committee (SASC) guidance (see next section)65 noted the need for a
protocol for optometrists to follow in eye examinations of children who
struggle at school. A protocol is detailed in Chapter 10, which builds on
earlier work,66 updated with the Delphi study described above.21
Vision, Reading Difficulties and Visual Stress
352