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Author(s): |
Marshall Keys M.D. |
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Reprinted with Permission From: |
International Dyslexia Association (info) |
Printed Date: Summer 2002
Date Posted on this Website: October 03 2002
When a child is first discovered to have difficulties reading, it seems logical for parents and teachers to assume that there must be something wrong with the child's eyes. Indeed, early researchers measured eye movements of individuals with reading disabilities and found that irregular motions and hesitations would frequently interrupt their eye movements across a page of text. Conclusions from these eye movement studies spawned a whole era of ocular and eye movement treatments for reading disabilities. I believe that practitioners of vision training ignored the fact that the eye movements of even skilled readers will become irregular or hesitate when the reader is stumped by a challenging word (e.g., dysdiadochokinesia). Concepts like "controlled clinical study" or "statistics" were ignored and overwhelmed by anecdotal reports and the raves of excited parents. Unfortunately, in spite of the lack of research findings and statistical support, vision training is still popular.
The role of the eyes in reading is to focus and to transmit retinal images along visual pathways to the brain. It is the brain that interprets or decodes visual stimuli (Helveston et al., 1985). Eye defects do not cause letter reversals, transpositions, or defective phonemic analysis. Although eye defects do not cause dyslexia, it is worth reviewing eye disorders that may contribute to reading difficulties. If these disorders are identified, they should be treated.
The visual system should routinely be evaluated to assure that the eyes are not contributing to a child's learning difficulties. Evaluation may reveal treatable conditions such as an inflammatory disease (iritis, keratitis, uveitis), congenital or acquired structural defects (cataracts, glaucoma, tumors), and other problems to be discussed below. Children with untreatable disorders (optic atrophy, retinal disease) may benefit from the use of optical aids and special placement in the classroom.
Many readers of this paper have experienced difficulties focusing on near print after the age of 40. Accommodation, the eye process of near focusing, is more difficult with age and can be assisted with reading glasses or bifocals. Weakness of accommodation in childhood is rather rare, but can occur and requires optical treatment. Refractive errors (myopia, hyperopia, and astigmatism) are common in childhood and require optical correction with glasses or contact lenses in approximately 10 percent of children in the one-to-twelve year age group.
Eye movement disorders can interfere with efficient reading. While focusing at near, the eyes also converge towards the nose so that both eyes are simultaneously pointed toward the text. An abnormal mechanism may cause double or blurred vision while viewing close objects. A very small percentage of the school age population has true convergence difficulties and few of the patients with convergence problems complain of reading difficulties. Nevertheless, children with reading disabilities that demonstrate convergence problems should have appropriate treatment to alleviate any problems that the convergence mechanism may be contributing towards reading discomfort. Treatment may consist of special glasses or convergence eye exercises.
It must be emphasized that convergence exercises are a very specific form of treatment directed toward a specific disorder involving a very minor percentage of children who mayor may not have reading problems. It is not a panacea for reading disorders. Generally, youngsters with a wide variety of ocular motor disorders compensate quite well without intervention and have no reading difficulties. Pediatric ophthalmologists routinely see children with significant eye movement syndromes such as strabismus, nystagmus, and muscle palsies that have no reading delays. Also, it must be understood that a significant percentage of the population does not have 100 percent eye muscle coordination, yet still fit within the bell shaped distribution of the normal range of eye control. Conditions that are less than perfect do not necessarily require treatment. Statistical analysis of large populations reveals no increased incidence of ocular problems in children with learning disabilities. Yet, optometric visual training continues to be strongly promoted.
The American Academy of pediatrics, the American Academy of Ophthalmology, and the American Association for Pediatric Ophthalmology and Strabismus issued a joint organizational statement on this topic (1998). It recommends:
References
Helveston, E.M., Weber, J.C., Miller, K., et al., (1985). Visual function and academic performance. Am. J. Ophthalmol.99:346-355.
Committee on Children with Disabilities, American Academy of Pediatrics, American Academy of Ophthalmology, American Association for pediatric Ophthalmology and Strabismus, (1998). Dyslexia and Vision: A Subject Review. Pediatrics 102:1217-1219.
