Download - Reading Disorders In Child
Reading disorders in children
Scott E. Olitsky, MDa,*, Leonard B. Nelson, MDb,c
aDepartment of Ophthalmology, Children’s Mercy Hospital, 2401 Gillham Road,
Kansas City, Missouri 64108, USAbPediatric Ophthalmology Services, Wills Eye Hospital, 9th and Walnut Streets,
Philadelphia, Pennsylvania 19107, USAcDepartments of Ophthalmology and Pediatrics, Jefferson Medical College,
Philadelphia, Pennsylvania, USA
Reading is the foundation of education. Books, papers, and lecture notes all
require reading to convey the ideas and thoughts that are so important in the
educational process. Therefore, it is understandable why the cause of reading
difficulties and their treatment has been the subject of considerable thought and
study. At times children, parents, teachers, and physicians all feel frustration
when dealing with this important and complex issue. Unfortunately, quick-fix
remedies all too often add to this frustration. This article explores the process of
reading, current theories on what causes some children to have difficulty
reading, and the treatment of reading disorders. Treatment methods based on
the erroneous belief that reading difficulties result from a dysfunction of vision
are evaluated. Finally, the role of the pediatrician when faced with these issues
is discussed.
History
In 1896, Hinshelwood gave a detailed description of a 45-year-old man with
dyslexia [1]. He credited the term dyslexia to Berlin [2]. Samuel Orton, a
neuropsychiatrist, provided the first insight into the cause and treatment of
dyslexia in 1925. He theorized that dyslexia resulted from a dysfunction in
visual perception and vision memory caused by a maturational lag. Treatment, he
felt, should be educationally based through the use of tutorials [3]. Unfortunately,
0031-3955/03/$ – see front matter D 2003, Elsevier Science (USA). All rights reserved.
PII: S0031 -3955 (02 )00104 -9
Adapted from Olitsky SE, Nelson LB, editors. Reading disorders in childhood. Ophthalmology
Clinics of North America 1996;309-15; with permission.
* Corresponding author.
E-mail address: [email protected] (S.E. Olitsky).
Pediatr Clin N Am 50 (2003) 213–224
more than a century after its initial description, the etiology and treatment of
dyslexia is still an issue of considerable controversy.
Definitions
Although the term dyslexia is often used to describe a specific subtype of
reading disability, 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. 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
Because of 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% to 10% of the school-aged population in the United
States. In the past dyslexic boys were thought to outnumber dyslexic girls by a
ratio of 2:1 to 5:1 [4,5]. There is evidence that this prevalence may actually
reflect school referral bias. In a study of students from the Connecticut
Longitudinal Study, Shaywitz et al [6] found a research-identified incidence of
reading disability of 8.7% of boys and 6.9% of girls. A teacher-identified
incidence of the same population, however, identified 13.6% of boys and only
3.2% of girls as dyslexic. Greater reports of behavioral difficulties among boys in
the classroom may have led to this bias [6]. Until a universally agreed-upon
definition is found, the exact incidence of dyslexia will be difficult to determine.
Eye movements in reading
In 1879, the French ophthalmologist Javal provided the first description of the
eye movements during reading. He noted that the eyes moved in quick, small
steps, saccades, from left to right with moments of steady fixation between
saccades. A small percentage of saccades were also made from right to left. These
eye movements are reversed when reading languages written from right to left.
Visual information is perceived during periods of fixation. These periods
account for 90% of the time spent reading. Approximately 85% of fixations take
place after a forward eye movement (ie, from left to right), and 15% take place
after a backward movement [7,8]. Backward saccades are thought to play a role
in comprehension of previously read text. Short words are read with one fixation,
S.E. Olitsky, L.B. Nelson / Pediatr Clin N Am 50 (2003) 213–224214
and longer words are read with two, one at the beginning and one at the end of
the word [8,9]. The duration of a fixation varies with the difficulty of the text
being read. Fixations may last from 45 milliseconds to 450 milliseconds, with the
mean being approximately 180 milliseconds [7]. Slow eye movements, called
pursuits, play no role in reading.
The movement of the eyes during reading brings a new area of text onto the
fovea, the portion of the retina used for reading vision. Visual perception is
thought to be suppressed during saccades, unlike the fixation period. The
average distance of a saccade is 2�, or about eight letters of average-size print
text [7]. The length of saccades varies among readers and affects the speed of
reading [10]. Saccade length depends 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 before the saccade. A longer
word to the right of the new area of regard gives rise to a shorter saccade
[9–11].
A backward saccade is also called a regression. The average 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 be read [7,11,12].
A beginning reader reads more slowly than an experienced reader. The
increased time is caused by longer fixations, increased number of fixations,
shorter saccade length, and a greater number of regressions. A child who is
beginning to read 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 [13,14]. As the child’s reading improves with age, the fixation number and
time decreases, and the saccade distance lengthens. A child approaches almost
two thirds of an adult’s reading speed by 10 years of age. Further improvement is
obtained by decreasing the number of regressions [14].
Eye movements in dyslexia
Dyslexics show many of the same type of eye moments as a beginning reader,
with longer fixations, smaller saccades, and a greater number of regressions.
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 [10].
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.
Abnormal eye tracking has also been mistakenly implicated as having a
causative role in reading problems. Frequent backward saccades, irregular
saccadic movement, and other abnormalities of eye movements have been
blamed as a cause for poor reading by some observers. Patients with an almost
complete inability to move their eyes show normal reading ability, however [15].
S.E. Olitsky, L.B. Nelson / Pediatr Clin N Am 50 (2003) 213–224 215
The abnormal eye movements seen in poor readers and dyslexics may also be a
sign of the disorder, not a cause.
Higher cortical processing
Vellutino presented a library model to understand the role of memory in
reading [16]. 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 30 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 can 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 on alphabetic mapping.
The beginning reader uses both the whole-word and the part-whole forms 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. If alphabetic mapping is
overused, the reader will miss the salient features of words and will have
difficulty reading fluently and comprehending the text being read.
Spoken and written words are broken into individual sounds (phonemes) and
stored with a phonologic 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 patterns seen in dyslexic readers. The common origins of these patterns
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 the words or letters 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, there was no
difference in visual recall between these two groups. The investigators concluded
that memory for visual symbols representing words is mediated by the linguistic
properties of those words, and that difficulties in maintaining proper direction-
ality 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
S.E. Olitsky, L.B. Nelson / Pediatr Clin N Am 50 (2003) 213–224216
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. There was no difference, however, 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. Mirror writing may
indicate a reading problem but is not the cause.
Neurobiologic changes in dyslexia
Neuroanatomic 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 [17]. The first
abnormality is the absence of the normal asymmetry in the language regions of
the brain. Normally, the left planum temporale is larger than the right. This lack
of asymmetry has also been observed in other studies and in living dyslexics
through the use of MR imaging [18]. This abnormal symmetry seems to be
associated with the linguistic difficulties typical of some dyslexics [19–22].
Another abnormality observed in dyslexics was also found in language-related
areas. Goldman-Rakic and Rakic [23] demonstrated distortion of neuronal
microarchitectural arrangement in these areas. This distortion seems to originate
from misdirected migration of these neurons during embryonic brain devel-
opment [23].
Neurophysiologic studies have shown differences between dyslexics and
normal readers in the language areas of the parietal and temporal lobes. They
have also found differences in the regions of the brain that are important in the
planning and sequential transformation of information processed during reading
[24,25]. These abnormalities of cortical organization include a smaller size and
atypical locations of language areas. These abnormalities have been demonstrated
in abnormal readers undergoing studies of language functions during neurosur-
gical operations performed under local anesthesia [26]. Mapping abnormal brain
electrical activity of dyslexics during tests of language and nonlanguage
functions may reflect these differences in language localization that are caused
by the small ectopic developmental anomalies in the brains of dyslexics. The
current neurobiologic evidence further supports the theory that dyslexia is caused
by abnormalities in language anatomy and processing and is not caused by
visuospacial or oculomotor dysfunction.
Recently, an abnormality of the magnocellular system has been implicated as
causing the problems seen in people with dyslexia [27–31]. The visual magno-
cellular system is responsible for timing visual events during reading. This theory
suggests that an underdeveloped magnocellular system in dyslexic brains causes
motion sensitivity to be impaired, so that images move off of the fovea during
reading. Letters seem to move around the page, making the acquisition of good
reading skills more difficult. There has been considerable debate over the
plausibility of this theory and the results of studies supporting it [32–34].
S.E. Olitsky, L.B. Nelson / Pediatr Clin N Am 50 (2003) 213–224 217
Treatment
Because dyslexia is a language-based disorder, treatment should be directed at
this cause. Early remediation of reading difficulties should involve intensive
individualized tutoring by an education specialist. 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 devel-
opment [35].
Because the supposed association between ocular dysfunction and poor
reading is so intuitively logical, and because it is easy to accept a visual or
oculomotor deficit as the cause for reading difficulties, parents and teachers are
easily led 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, such as vision therapy, further escalates the
temptation to believe in these scientifically unproven modalities.
Vision therapy
Vision therapy has been proposed as a therapeutic intervention for the alleged
visual abnormalities responsible for reading disorders. A careful reading of the
research supporting vision therapy shows several major flaws in the investiga-
tional 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 placebo treatment
given to a control group in a masked manner. The foundation of many studies is
an initial preconception that an isolated visual factor is responsible for reading
disabilities. These preconceptions rely too heavily on anecdotal or superficially
logical evidence. Reports of the efficacy of vision therapy fail to control for
nonspecific gains, which may result simply from the increased time and attention
given to poor readers during the course of these investigations or from the
conventional education remediation that many of the children studied are also
undergoing [36–39]. Finally, the claims that show the benefits of vision therapy
generally are reported by groups that have a vested interest, usually financial, in
proving the validity of these benefits. Groups without a potential vested interest
have not been able to duplicate these findings in a scientifically based manner.
Many authors in the optometric literature, as opposed to the ophthalmologic
literature, proclaim the usefulness of vision therapy for reading and learning
disabilities [40–44]. A basic tenant of their hypotheses is that children with
reading disorders have an increased incidence of vision abnormalities [45] and
that treatment of these abnormalities will therefore help correct reading deficien-
cies. There is, however, no evidence that there is an increased incidence of visual
abnormalities in children who are experiencing difficulty reading. Helveston [26]
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
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students. Vision therapy has also been suggested to reduce visual stress and better
integrate the right and left hemisphere. Improved integration would then
supposedly help settle the conflict between the conscious and subconscious state
and ultimately lead to positive changes in personality traits [46].
The medical establishment’s response
Because current available evidence has failed to implicate visual disorders as a
cause of reading problems, and because no scientific evidence 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 [47].
The pediatrician is often consulted when a child is doing poorly in school. In
addition, the pediatrician’s opinion may be sought after a recommendation for
vision therapy has been made. To counsel patients with reading disorders
properly, 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. Most of these studies claim that patients with these binocular
dysfunctions experience visual symptoms that lead to degradation in reading
performance [35,48–50]. The link between binocular dysfunction and reading
symptoms is assumed, however, and asymptomatic, latent strabismus in the
normal population is not taken into account. In support of vision therapy,
Grisham et al [51], in a retrospective study, 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 [51]. Other
studies have also been unable to find an increase in the incidence of binocular
disorders in children with reading difficulties or an association between motility
disorders and reading ability [52–55].
Low-power reading glasses and bifocals
There are a number of accommodative, or focusing, disorders that are said to
give rise to reading disorders. Accommodative spasm, accommodative insuf-
ficiency, ill-sustained accommodation, and accommodative inertia have all been
implicated [43,49,50,55]. Problems said to be caused by these disorders include
S.E. Olitsky, L.B. Nelson / Pediatr Clin N Am 50 (2003) 213–224 219
print blurring, daydreaming, decreased attention span, increased heart and
respiratory rate, and poor posture [56–59]. The symptoms caused by these
problems supposedly lead to poor reading. For example, poor focusing may lead
to poor posture when reading. Poor posture then leads to lower back discomfort
which then leads to a dislike of reading. It is argued that treatment of
accommodative dysfunctions with low-power reading lenses will eliminate these
secondary problems and their associated symptoms, thereby improving reading
efficacy. There is, however, no proof that there is a difference in focusing ability
between normal and abnormal readers or that there is a correlation between
reading performance and a need for glasses [60–62]. The very low power of the
reading glasses or bifocals that are often prescribed throws further doubt on their
usefulness in a child who will often show large amplitudes of focusing ability.
Perceptual training
An extensive amount of literature supports the use of perceptual-motor
training in the treatment of reading disabilities [40,42,43,63,64]. 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 [65,66].
Tinted lenses
In 1983, Irlen reported using tinted lenses to treat successfully a group of
adults with a long history of reading disorders [67]. 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 occur, leading to poor coordination, decreased depth
perception, sore eyes, and fatigue. Reduction of the offending wavelengths
through the use of tinted overlays or lenses corrects these secondary dysfunctions
and improves reading ability [68]. How scotopic sensitivity relates to reading has
not been explained. Rod cells, the scotopic receptors in the retina, function under
dark conditions and are not present in the fovea where text is processed during
reading. Unbiased studies of tinted lenses have been unable to document their
effectiveness [29,69,70].
Role of the pediatrician in treating children with reading disorders
Although pediatricians do not treat reading disorders, they are often asked to
comment on their cause and proper treatment. These questions may arise after
various forms of treatment have been suggested, and the parent has become
S.E. Olitsky, L.B. Nelson / Pediatr Clin N Am 50 (2003) 213–224220
increasingly frustrated. The pediatrician plays an important role in dealing with
this frustration. Parents will often hear conflicting advice from various eye care
professionals regarding the role of vision in children who are struggling with
reading. The pediatrician often represents a familiar, unbiased voice that is not
viewed as having any vested interest. 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. If there is a question regarding a possible vision problem, a referral
to an ophthalmologist should be made, even though the eyes are rarely a cause for
poor performance in school. It should be stressed that treatment requires a
multidisciplinary approach involving educators, psychologists, and physicians.
Vision therapy should be discouraged as an ineffective and unproven treatment
for reading disorders. Parents need to be warned that dyslexia is a complex
disorder, and there are no quick cures. By dealing with these problems in a logical
and straightforward manner, the pediatrician can help minimize frustration and
implement effective intervention.
Summary
Reading difficulties are a complex set of disorders. Current research indicates
that these disorders are not caused by vision abnormalities. Treatment of these
disorders requires a multidisciplinary approach involving educators, psycholo-
gists, and physicians. Parents, physicians, and school officials should understand
that there are no quick cures for these children.
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