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There is an emphasis on recognition, matching, and recall. Periods of sustained near work are infrequent, and visual stimuli (i.e., letters) are relatively large and widely spaced. Visual efficiency and visual processing speed become relatively more significant later in the educational process. Reading demands increase with the need to achieve grade-appropriate rates of reading with comprehension (fluency) over more extended periods of time, when letters and text become smaller and more closely spaced. Equally, this increase in sustained periods of near work becomes a significant risk factor for the development of visual efficiency problems. Demands for reading and writing fluency create a requirement for efficient and well-timed visual information processing.B. EPIDEMIOLOGYEstimates of the prevalence of learning problems among school -aged children range from 2 to 10 percent, depending on the nature of the diagnostic process and the definitions applied by individual school districts.^60,61 The prevalence of learning disabilities is subject to some dispute because of the lack of an agreed upon definition with identification criteria. Nationally, nominally 5 percent of all school children are diagnosed with learning disabilities; a greater number have milder learning problems. Learning disabilities account for nearly half of all children receiving special educational services. Of that number, as many as 75 percent have particular difficulty with reading. While it was previously thought that males were more affected than females, evidence now indicates that an equal number of male and females are affected.^62-64 Learning disabilities are both familial and heritable.⁶⁵Appraisals of the prevalence of learning related vision problems vary considerably, depending on the definitions, sample selection criteria, and the examination methods used. At least 20 percent of individuals with learning disabilities are thought to have a prominent visual information processing deficit.^68-72 The prevalence of clinically significant visual8 Learning Related Vision Problemsefficiency problems is thought to be in the 15 to 20 percent range.^73-78 Accommodative dysfunctions have been reported to occur in 60 to 80 percent of individuals with vision efficiency problems; with accommodative insufficiency the most prevalent subtype and convergence insufficiency the most common vergence anomaly.²¹Convergence insufficiency is of particular interest because it has been shown to have an impressive prevalence rate among school-aged children, with accommodative insufficiency an important co-morbid condition.⁷⁹ The Convergence Insufficiency and Reading Study Group (CIRS) found that a considerable number of children with convergence and/or accommodative insufficiency report symptoms of blurred or double vision. ⁸⁰ These learning related vision problems, when present, represent risk factors for delayed reading progress.

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