Page 64 - CJO_F18

C CLINICAL RESEARCH

Several hypotheses involving visual impairments have been put forth regarding the cause of dyslexia and other
learning disabilities. Although some differences of opinion persist, the most widely accepted hypothesis to date is
that there is a “deficit in the phonologic component of language that makes it difficult to use the alphabetic code to
decode the written word.” The visual difficulties that are sometimes encountered are in fact attributable to a lack of
4
reading experience. A recent study has shown that training in phonology-based reading improves not only read-
9-12
ing skills, but also visual functions. Thus, the visual abnormalities sometimes evoked would be a consequence of the
9
learning disability, not its cause. 3,4,6,8-10,13
Since dyslexia is considered to be a phonological language disorder and not a visual impairment, publications by the
American Academy of Pediatrics as well as the Canadian Paediatric Society recommend treatment based on decod-
ing, fluidity, vocabulary and comprehension, and phonemic awareness and its application. 3-5,7,9,14,15 Since this learning
disability is chronic in nature, it will not disappear with age. However, for the establishment of an intervention plan
that focuses on the specific needs of each child and maximizes their learning, early science-based management is
encouraged. 7

TREATMENT OF LEARNING DISABILITIES USING VISUAL THERAPIES: STATE OF KNOWLEDGE
Certain vision problems can interfere with the reading process, and thus some learning difficulties can be overcome
by correction of the visual impairment in question. Therefore, it is critical that a child with a learning disability
undergo a comprehensive visual examination at the first indication of a problem to assess vision and eye health. 3,6,16

However, children with dyslexia or learning disabilities have not been shown to have any more abnormalities
in their visual function and eye health than children without these conditions. 4,6,8,14,17-19 While they may struggle
to learn subjects such as mathematics and English, they often succeed very well in other areas of development
that require the same level of visual skills. There is currently no scientific evidence-based support for the
notion that subtle refractive errors or mild visual problems can cause or increase the severity of learning dis-
abilities, decrease visual effectiveness, or lessen the response to various educational treatments. 3,4,17,20 Thus, the
hypothesis that children participating in visual therapy would be more receptive to various learning programs
is not valid. 2,4,6,15,20-23

VISUAL ACUITY, REFRACTION AND TRAINING GLASSES
Children who start learning to read and write use texts with a large font size. As the level of education increases,
the font size decreases and the visual demand increases. While good vision is important, optimal resolution is not
essential to discern the traits used in early school learning. There is no evidence that novice readers with myopia,
hypermetropy and/or mild to moderate astigmatism have more difficulty learning to read than other children.
4
Small degrees of hypermetropia are considered normal in young children and generally have no pathological signifi-
cance. They are in fact a normal stage of eye development. Children have unique visual needs based on their visual
demands and the development of their optical system. 24-28 Children’s refractive needs cannot be extrapolated to the
needs of adults. Currently, there are no absolute rules specifying the exact levels of the various ametropia that would
require optical correction. In fact, the recommendations are based on clinical experience and different consensuses
of recognized optometry and paediatric ophthalmology professionals. 4,24-29
Children have a much greater accommodative capacity than adults. Children aged 6 to 10 years have an average ac-
commodative function of 12.00 dioptres (D) or more. 4,25,30 Therefore, they can generally compensate for moderate
hypermetropia without having visual difficulties. The average refraction among White children in the United States
is about 2.00 D of hypermetropia in the first 5 years of life. This hypermetropia tends to gradually decrease during
4
adolescence. This is why mild to moderate hypermetropia often does not need to be corrected, since it has little
impact on eye-visual function. 24,25,27

There does not appear to be an increased likelihood of dyslexia in children with uncorrected hypermetropia. In
the absence of a decrease in visual acuity, there is no correlation between reading skills, academic performance,
and the degree of hypermetropia. Six-year-olds generally have no significant reduction in visual acuity if the hy-
31
permetropia does not exceed 4.00 D; fewer than 1% of children have a stronger hypermetropia. A high refractive
25
error, hypermetropic in nature, can cause considerable visual discomfort. As a result, these children can lose inter-
est in tasks requiring prolonged visual effort and may develop consecutive learning difficulties. However, these are
reversible with correction of the visual problem. Conversely, a child with uncorrected elevated hypermetropia who
has dyslexia or a real learning disability could notice an improvement in comfort, visual acuity and even academic

64 CANADIAN JOURNAL of OPTOMETRY | REVUE CANADIENNE D’OPTOMÉTRIE VOL. 80 NO. 3

38668_CJO_F18_ONLINE_ONLY_ARTICLES August 13, 2018 12:32 PM APPROVAL: ___________________ DATE: ___________________