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


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].


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


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


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


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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