Reading Disorders In Children
Introduction
Reading is the foundation of education. Books, papers, articles
and lecture notes all depend on reading to convey the ideas and
thoughts used in the educational process. Therefore, it is understandable
why reading difficulties have been the subject of considerable
thought and study as their cause and treatment have been explored.
At times parents, teachers and physicians all feel the frustration
when dealing with this important and complex issue. Unfortunately,
"quick fix" remedies all too often help to add to this
frustration. This chapter will explore how we read, current theories
on what causes some people to have difficulty reading and the
treatment of reading disorders. Evaluation of treatment methods
based upon the erroneous belief that reading difficulties are
due to a dysfunction of visual processing will be critically evaluated.
Finally, the role of the ophthalmologist when faced with these
issues will be discussed.
History
In 1896 Hinshelwood gave a detailed description of a forty-five
year old man with dyslexia.26 He credited the term
"dyslexia" to Berlin.2 Samuel Orton, a neurophychiatrist,
provided the first insight into the etiology and treatment of
dyslexia in 1925. He theorized that dyslexia was due to a dysfunction
in visual perception and vision memory which was caused by a maturational
lag. Treatment, he felt, should be educationally based through
the use of tutorials.42 Unfortunately, a full century
after its initial description, the etiology and treatment of dyslexia
is still an issue of considerable controversy.
Definitions
The terms reading disability and dyslexia are often used interchangeably. Dyslexia refers to the inability to develop the capability to read, at an expected level, despite an otherwise normal intellect. Most dyslexics also display poor writing ability as well. Dyslexia is a primary reading disorder and should be separated from other, secondary, forms of reading difficulties. Secondary reading disorders include: mental retardation, environmental deprivation, educational deprivation and physical, or organic, diseases. Because there is no one standard test for dyslexia, the diagnosis is usually made by comparing reading ability with intelligence and standard reading expectations.
Incidence:
Due to the lack of a universal definition of dyslexia, it
is difficult to arrive at a consensus of the incidence of the
disorder from the literature. Most studies suggest an incidence
of 5-10% of the school aged population in the United States.
In the past it had been thought that boys outnumbered girls by
a ratio of 2:1 to 5:1.7,15 There is evidence that
this prevalence may actually be a reflection of school referral
bias. In a study of students from the Connecticut Longitudinal
Study, Shaywitz et al found a research-identified incidence of
reading disability of 8.7% of boys and 6.9% of girls. However,
a teacher-identified incidence of the same population identified
13.6% of boys and only 3.2% of girls. The authors suggested that
greater reports of behavioral difficulties among boys in the classroom
may have lead to this bias.49 Until a universally
agreed upon definition is found, the exact incidence of dyslexia
will be difficult to determine.
How we read
Eye movements:
In 1879, the French ophthalmologist Javal provided the first
description of the eye movements during reading. He noted that
the eyes moved in small steps, saccades, from left to right with
moments of steady fixation between these saccades. A small percentage
of saccades were also made from right to left.
Visual information is perceived during periods of fixation.
This accounts for 90% of our time reading. Approximately 85%
of fixations take place after forward saccades and 15% after backward
saccades.38,45 Backward saccades are thought to play
a role in comprehension of previously read text. Short words are
read with one fixation and longer words are read with two, one
at the beginning and the end of the word.10,45 The
duration of a fixation varies with the difficulty of the test
being read. Fixations may last from 45 ms to 450 ms, with the
mean being approximately 180 ms.38 Because it takes
about 90 ms to generate a saccade following a neural impulse derived
from the retina, some fixations are so short that the text is
not perceived before a new saccade is initiated. It is therefore
thought that some saccades generated during reading are controlled
by a reflex not associated with fixation.
Saccades during reading bring a new area of text onto the
fovea. Unlike the fixation period, it is felt that visual perception
is suppressed during saccades. The average distance of a saccade
is two degrees, or about eight letters of average size text.38
The length of saccades varies between readers and affects the
speed of reading.34 Saccade length is dependent on
the individual's ability to recognize letters and combinations
of letters outside the central visual field, the difficulty of
the text being read and the length of the word prior to the saccade.
A longer word to the right of the new area of regard gives rise
to a shorter saccade. 10,34,47
The average backward saccade, or regression, is one half
the length of a forward saccade and covers about four letters.
These regressions are thought to aid in text comprehension by
validating previously read words. Regressions account for approximately
15% of all saccades but increase with the difficulty of the text.
31,38,47
Because eye movements of dyslexic readers are similar to those of beginning readers, it is helpful to understand the eye movements seen in early readers. A beginning reader reads slower than an experienced reader. This increased time is due to: longer fixations, increased number of fixations, shorter saccade length and a greater number of regressions. The early reader averages almost twice the number of fixations and regressions, fixates
twice as long, and travels only half as far with each saccade as a better reader.5,35,46 As the child's reading improves with age, he/she decreases fixation number and time and
lengthens saccade distance. A child approaches almost two-thirds
of an adult reading speed by ten years of age. Further improvement
is obtained by decreasing the number of regressions.46
Dyslexics show many of the same type of eye moments as the
beginning reader. Furthermore, good readers show the same type
of movements when asked to read text in which the letters have
been reversed or otherwise changed in position.34
Because dyslexics show normal sequential saccade tracking in other
areas of oculomotor functioning, it is believed that the abnormalities
seen in dyslexics during reading are a result, and not the cause,
of their reading disability.
Higher Cortical Processing
Vellutino presented a library model to understand the role of memory in reading.57 In this model, the processing of information occurs in three stages. The first stage takes place in a sensory storage system where a replica of the given stimulus is briefly held. The second stage takes place in a short-term working memory. This short-term memory has a limited capacity. Here, a transformed, encoded, version of the stimulus is held for up to thirty seconds. This transformation produces an abstract representation of the stimulus to
be placed into long-term memory. The third and final stage allows
the stimulus to be categorized and stored in long-term memory
or discarded.
Printed words are able to be identified through either "whole-word" or "part-whole"
processing. Whole-word processing is based on the visual features
of a word, its meaning and its context. Part-whole processing
is performed by breaking words down into letter sounds and is
based upon alphabetic mapping..
The beginning reader uses both the whole-word and part-whole
form of processing to identify words. If the child relies too
heavily on either strategy, reading difficulties arise. If
the whole-word strategy is used excessively, visual memory is
overutilized and letter reversals may occur. However, if alphabetic
mapping is overused, the reader will miss the salient features
of words and have difficulty reading fluently and comprehending
the text being read.
Spoken and written words are broken into individual phonemes and stored with a phonological code in memory. This code is analogous to a file card in Vellutino's library model. Proper coding of these cards is necessary for later retrieval. Poor phoneme segmentation would not allow enough "clues" to be stored on the file card to enable the correct recall of a word that has been read or heard.
Using experiments based upon his model, Vellutino was able to
explain many of the behavior patterns seen in dyslexic readers.
The common etiology of these behaviors were linguistic deficiencies
and not visual or perceptual disorders. In one experiment, dyslexic
children were able to name the letters of most words in the correct
order even though they often named them incorrectly. Furthermore,
when they were asked to reproduce words from an unfamiliar writing
system, Hebrew, dyslexics did as well as normal readers. Both
groups manifested identical tendencies to process the Hebrew letters
from left to right. Therefore, when wordlike symbols lacked linguistic
associates, visual recall was no different between these two groups.
. The conclusion was that memory for visual symbols representing
words is mediated by the linguistic properties of those words
and that difficulties in maintaining proper directionality is
a symptom, not a cause, of a reading disorder.
Mirror writing, or reversal errors, is common in dyslexia and may reflect an imbalance between whole-part and part-whole word processing. Children who were taught to identify meaningless words, pseudowords, by a whole-part method made many more reversal errors than those children taught to use alphabetic mapping. However, there was no difference in the number of reversal errors between normal and poor readers. The claim that spatial-confusion causes these types of errors is not supported by this evidence.
Auditory processing of spoken words is also abnormal in children
with reading difficulties. Poor readers demonstrated more trouble
recalling lists of recently heard words than normal readers.
However, they showed no difference in auditory sensory memory.
Like their visual traces, the auditory traces dissipated no faster
from a dyslexic's sensory memory than that of a normal reader.
This combined difficulty in both visual and aural recall, coupled
with normal sensory memory, would indicate that it is the linguistic,
not visual, processing of written text that is the cause of reading
difficulties.
Neurobiological changes in dyslexia
Neuroanatomical changes that have been observed in the brains
of dyslexic patients are located in language related areas. Galaburda
described two forms of anomalies during postmortem analysis of
dyslexic subjects.18 The first abnormality was the
absence of the normal asymmetry in the language regions of the
brain. Normally, the left planum temporale is larger than the
right. The subjects studied showed no difference in the volume
between the right and left planum. This lack of asymmetry has
also been observed in living dyslexics through the use of magnetic
resonance imaging.8 This abnormal symmetry appears
to be associated with the linguistic difficulties typical of some
dyslexics.36
The second brain abnormality observed in dyslexics was also
found in language related areas. Goldman-Rakic and Rakic demonstrated
distortion of neuronal microarchitectural arrangement in these
areas. This distortion appears to originate from misdirected
migration of these neurons during embryonic brain development.19
Neurophysiological studies have shown differences between
dyslexics and normals in the language areas of the parietal and
temporal lobes. They have also found differences in the region
of the frontal lobes that are important in the planning and sequential
transformation of information processed during reading.9
These abnormalities of cortical organization include a smaller
size and atypical locations of language areas. This has been
demonstrated in abnormal readers undergoing studies of language
functions during neurosurgical operations performed under local
anesthesia.41 Abnormal brain electrical activity
mapping of dyslexics during tests of language and non-language
functions may reflect these differences in language localization
which are caused by the small ectopic developmental anomalies
in the brains of dyslexics. The current neurobiological evidence
further supports the theory that dyslexia is caused by abnormalities
in language anatomy and processing and is not due to visuo-spacial
dysfunction.
Treatment
Because dyslexia is a language based disorder, treatment
should be directed at this etiology. Early remediation of reading
difficulties should involve intensive individualized tutoring.
A balanced reading program that includes both the holistic/meaning
and the analytic/phonetic approaches to reading should be combined
with other activities to improve language development.57
Because the supposed association between visual dysfunction and
poor reading is so intuitively logical and because it is easy
to accept a visual deficit as the cause for reading difficulties,
parents and teachers are easily lead to believe that therapies
aimed at treating visuo-perceptual dysfunction will offer an effective
intervention. The proliferation of so called "evidence"
of the efficacy of these treatments further escalates the temptation
to believe in these scientifically unproven modalities.
Vision therapy has been proposed as a therapeutic intervention for the alleged visual abnormalities responsible for reading disorders. Research supporting vision therapy shows several major flaws in their investigational and interpretative designs. Such research fails to differentiate between normal variation, association and cause-and-effect. Most studies involving vision therapy lack matched comparison groups and fail to provide a sham or placebo treatment given to a control group in a masked manner. The foundation of many studies are based on an initial preconception that an isolated visual factor is responsible for reading disabilities. These preconceptions rely too heavily on anecdotal or superficially
logical evidence. The efficacy of vision therapy in these reports
fail to control for nonspecific gains which may be derived by
the product of simply increasing the time and attention given
to poor readers during the course of these investigation.1,33,37,40
Finally, the claims that show the benefits of vision therapy
by and large are reported by groups that have a vested interest,
usually financial, in proving the validity of these benefits.
Because current available evidence has failed to implicate visual
disorders as a cause of reading problems and there remains no
scientific evidence that validates vision therapy as a way of
treating these problems, the Academy of Pediatrics, the American
Academy of Ophthalmology and the American Association for Pediatric
Ophthalmology and Strabismus do not recognize vision therapy as
a treatment option for reading disorders.44
Vision Therapy
Many authors in the optometric literature proclaim the usefulness of vision therapy for reading and learning disabilities.16,17,54,55,58 The basic tenant of their hypotheses is that children with reading disorders have an increased incidence of vision abnormalities.28 Treatment of these abnormalities will therefore help to correct reading deficiencies. However, there is no evidence that there is an increased incidence of visual abnormalities in this population. Helveston could not find a statistical relationship between visual function and academic performance in a masked study of a large group of first, second and
third grade students.25 Vision therapy has also been
suggested to reduce visual stress and better integrate the right
and left hemisphere. Improved integration would then supposedly
help to settle the conflict between the conscious and subconscious
state and ultimately lead to positive changes in personality traits.4
The ophthalmologist is often consulted after a recommendation
for vision therapy has been made. To properly counsel patients
with reading disorders, it is useful to understand the common
types of vision therapy prescribed, the theory behind their usefulness
and the flaws in the methodology showing their benefits
Binocular Dysfunction
Various forms of ocular motility disturbances have been associated with reading disabilities. These disorders include: exophoria, esophoria, excessive fixation disparity, amblyopia and "minimum binocular dysfunction". Most of these studies claim that patients with these binocular dysfunctions experience visual symptoms which lead to degradation in reading performance.50,51,52,53,59 The link between binocular dysfunction and reading symptoms is assumed and the small degree of heterophoria in the normal population is not taken into account. In a retrospective study, Grisham, et al reported an increased incidence of various symptoms in slower readers. They could not show a
significant difference in reading ability between readers with
normal and abnormal binocular function. Also, there was no proof
of cause-and-effect between decreased binocular function and symptoms
or between symptoms and poor reading.22 Other studies
have also been unable to find an increase in the incidence binocular
disorders in children with reading difficulties or an association
between motility disorders and reading ability.3,23,25
Low Plus Lenses
There are a number of accommodative disorders that are said to give rise to reading disorders. Accommodative spasm, accommodative insufficiency, ill-sustained accommodation and accommodative inertia have all been implicated.21,52,53,55 Accommodative inertia describes the sluggishness that has been reported to occur in some individuals when changing from one level of accommodation to another. Problems said to be caused by these disorders include: print blurring, day dreaming, decreased attention span, increased heart and respiratory rate and poor posture.20,27,43,56 It is the symptoms caused by these problems that supposedly lead to poor reading. It is argued that treatment of accommodative dysfunctions with low plus lenses will therefore eliminate these secondary problems and their associated symptoms thereby improving reading efficacy. However, there is no proof that there is a difference in accommodation between normal and abnormal readers or that there is a correlation between reading performance and any specific type of refractive error, including hyperopia. 11,13,60
Perceptual Training
There exists an extensive amount of literature supporting
the use of perceptual-motor training in the treatment of reading
disabilities.6,16,24,48,54,55 Perceptual-motor training
has not been demonstrated to be useful for reading disorders in
other studies and reviews of the scientific merit of studies supporting
their efficacy have shown them to be unfounded.14,32
Tinted Lenses
In 1983, Irlen reported using tinted lenses to successfully treat a group of adults with a long history of reading disorders.29 The author described a new disorder called "scotopic sensitivity syndrome and claimed that it affected half of all dyslexic readers. People with this syndrome are thought to suffer from perceptual dysfunctions caused by sensitivities to particular frequencies and wavelengths of light. When subjected to these wavelengths, fatigue and trauma to the visual system occurs leading to poor coordination, decreased depth perception, sore eyes and fatigue. Reduction of the offending wavelengths through
the use of tinted overlays or lenses correct these secondary dysfunctions and improve reading ability.30 How scotopic sensitivity relates to reading has not been explained. Retinal rods function under scotopic conditions and are not present in the fovea where
printed text is processed during reading. In a double-blind study
of dyslexic children, tinted lens therapy was not shown to improve
reading ability subjectively or objectively.39 Studies
claiming the efficacy of these lenses have not held up to scientific
review.12
Role of the ophthalmologist in children with reading
disorders
Although the ophthalmologist does not treat reading disorders, he/she is often asked to comment on their etiology and proper treatment. Commonly, these questions arise after various forms of treatment have been suggested and the parent has become increasingly frustrated. The ophthalmologist plays an important role in dealing with this frustration. The known facts about reading disorders, including their cause and treatment, should be given to the parent. Equally important, the myths surrounding these disorders should be addressed and dispelled. Any underlying visual disorder should be identified and treated even though it rarely is the cause for the initial consultation. It should be stressed that treatment requires a multidisciplinary approach involving educators, psychologists and physicians. Parents need to be warned that this is a complex disorder and there are no
quick cures. By dealing with these problems in a logical and
straightforward manner, frustration can be minimized and effective
intervention can be implemented.
Summary
Reading difficulties are a complex set of disorders. Current
research indicates that these disorders are not due to vision
abnormalities. Treatment of these disorders requires a multidisciplinary
approach involving educators, psychologists and physicians. Treatment
of ophthalmologic disorders are important but do not treat reading
problems. Parents, physicians and school officials should understand
that there are no quick cures for these children.
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