Dyslexia and vision
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A learning disability is a disorder in one or more of the basic cognitive and psychological processes involved in understanding or using written or spoken language; it may be manifested in age-related impairment in the ability to read, write, spell, speak, or perform mathematical calculations.1 Dyslexia is a language based learning disability that affects the ability to read. It is the most common learning disability. Dyslexia is variable in severity across a spectrum from mild reading delay to severe inability to interpret written words. Persons with dyslexia have deficits in brain word analysis pathways that make it difficult to convert written text to spoken text units called phonemes. 2 A phoneme is the smallest phonetic unit in a language that is capable of conveying a distinction in meaning, as the "m" of mat and the "b" of bat. The English language is phonemically complex; 26 letters combine to produce 44 sounds or phonemes. Dyslexic persons struggle with accurate and/or fluent sight word recognition, have trouble decoding written text into appropriate phonemes and are often poor spellers.
The etiology of dyslexia is multifactorial. Most persons with dyslexia have a variety of problems with language that stem from altered brain function. Dyslexia has a strong genetic component.2 Approximately 40% of siblings, children or parents of an affected individual will have dyslexia. It affects more boys than girls. In the United States, 40% of early elementary students have some difficulty learning how to read. About 5% of early elementary students are referred for reading remediation. Children with dyslexia often have other learning disabilities.3
Attention Deficit Hyperactivity Disorder (ADHD) is a risk factor for coexisting dyslexia. A family history of ADHD places children at increased risk for the development of dyslexia.2,3
Functional MRI has demonstrated areas in the left occipital-temporal region of the brain that are necessary for skilled reading. Persons with dyslexia are less able to activate these regions than persons with normal reading skills and develop compensatory mechanisms in the right and front parts of the brain. 4,5
Persons with dyslexia often have a history of phonologically based language difficulties (e.g., mispronouncing words, speech punctuated by hesitations and dysfluencies), of trouble reading new or unfamiliar words, of spelling difficulties, and of requiring additional time for reading and taking tests relative to the level of education achieved.2,7 In most schools, an educational diagnostician, an educator trained as a reading specialist, and a school psychologist are the professionals charged with evaluating and diagnosing reading disabilities. Outside the school environment, a child psychologist, an educational diagnostic specialist, or a child neuropsychologist is usually best able to examine a child with a reading disability. A formal assessment for learning disabilities should include evaluation of cognition, memory functions, attention, intellectual ability, information processing, psycholinguistic processing, expressive and receptive language function, academic skills, social and emotional development, and adaptive behavioral functioning.2
A history of delay or difficulty in developing speech and language, learning rhymes, or recognizing letters and sound/symbol connections may be an early indication of dyslexia.
The child with reading problems should be assessed by the general practitioner for the presence of medical problems that could affect the child’s ability to learn.7 Screening eye and hearing examinations are an essential part of the evaluation. Children with suspected learning disabilities in whom a vision problem is suspected by the child, parents, physicians, or educators should be seen by an ophthalmologist with experience in the assessment and treatment of children. Some of these children may also have a treatable visual problem that accompanies or contributes to their primary reading or learning dysfunction. Treatable ocular conditions can include strabismus, amblyopia, convergence and/or accommodative deficiencies, and refractive errors.7 Small or subtle deficits in visual function do not contribute to the development of dyslexia.
ADHD associated with dyslexia should be treated with appropriate stimulant therapy. Medical treatment is not indicated in remediation of learning disabilities. The affected individual should be referred to the appropriate education services. Families should be referred to state and local support groups. Caregivers should be discouraged from pursing unproven and alternative treatments such as behavioral vision therapy, eye muscle exercises (except for the treatment of convergence insufficiency) and tinted glasses or overlays, as these treatments have not been found in controlled clinical trials to have benefit.8,9
Persistently poor readers (ie, children identified in the early grades by their poor phonemic processing) continue to read more poorly than their nondisabled peers.2,3,7 Although these children learn to read, they continue to lag significantly behind peers throughout high school in decoding, reading rate, and accuracy. There is a smaller gap in overall reading comprehension. With persistent intervention and considerable personal effort, dyslexic children can achieve adequate literacy to function in society.
2. Shaywitz SE. Dyslexia. N Engl J Med. 1998;338(5):307–312
3. Tynan, WD. Learning Disorder, Reading. 2008. emedicine.medscape.com/article/1835801-overview
4. Shaywitz BA, Shaywitz SE, Pugh KR, et al. Disruption of posterior brain systems for reading in children with developmental dyslexia. Biol Psychiatry. 2002;52(2):101–110
5. Temple E, Deutsch GK, Poldrack RA, et al. Neural deficits in children with dyslexia ameliorated by behavioral remediation: evidence from functional MRI. Proc Natl Acad Sci U S A. 2003;100(5):2860 –2865
6. Learning Disabilities, Dyslexia, and Vision Pediatrics 2009;124;837-844; originally published online Jul 27, 2009; American Academy of Pediatrics, Section on Ophthalmology, Council on Children with Disabilities, American Academy of Ophthalmology, American Association for Pediatric Ophthalmology and Strabismus and American Association of Certified Orthoptists.
7. Sheryl M. Handler. Evidence shows vision therapy does not benefit children with dyslexia. AAP News 2010;31;19 DOI: 10.1542/aapnews.2010315-19 8. Helveston EM. Scotopic sensitivity syndrome. Arch Ophthalmol. 1990;108(9):1232–1233
9. Menacker SJ, Breton ME, Breton ML, Radcliffe J, Gole GA. Do tinted lenses improve the reading performance of dyslexic children? A cohort study. Arch Ophthalmol. 1993;111(2):213–218