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      Magnocellular visual function in developmental dyslexia: deficit in frequency-doubling perimetry and ocular motor skills Translated title: Função visual magnocelular na dislexia do desenvolvimento: déficit na perimetria de frequência duplicada e nas habilidades motoras oculares

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          Abstract

          Purpose

          This study aimed to verify if patients with developmental dyslexia present deficits coherent with visual magnocellular dysfunction.

          Methods

          Participants with confirmed diagnosis of developmental dyslexia ( n=62; age range=8-25 years; mean age=13.8 years, standard deviation=3.9; 77% male) were compared to a control group with normal development, matched for age, sex, ocular dominance, visual acuity, and text comprehension. The frequency-doubling technology perimetry was used to evaluate the peripheral visual field contrast sensitivity threshold. The Visagraph III Eye-Movement Recording System was used to evaluate ocular motor skills during text reading.

          Results

          The developmental dyslexia group had significantly worse contrast sensitivity in the frequency-doubling technology, with strong effect size, than the matched control group. The developmental dyslexia group had more eyes classified in the impaired range of sensitivity threshold to detect frequency-doubling illusion than the control group. Moreover, the developmental dyslexia group had poorer ocular motor skills and reading performance, revealed by a difference in ocular fixations, regressions, span recognition, reading rate, and relative efficiency between groups. A significant correlation was found between contrast sensitivity and ocular motor skills. Participants with good relative efficiency had significantly better contrast sensitivity than participants with poor relative efficiency.

          Conclusions

          The developmental dyslexia group presented a markedly worse performance in visual variables related to visual magnocellular function ( i.e., frequency-doubling technology perimetry and ocular motor skills) compared with a matched control group. Professionals need to be aware of the importance of evaluating vision of individuals with developmental dyslexia beyond visual acuity and including in their assessments instruments to evaluate temporal processing, with contrast sensitivity threshold.

          Translated abstract

          Objetivo

          Verificar se pacientes com dislexia do de senvolvimento (DD) apresentam déficits coerentes com uma disfunção magnocelular visual.

          Métodos

          Participantes com diagnóstico confirmado de dislexia do desenvolvimento ( n=62; faixa etária=8 a 25 anos; Média da idade=13.8 anos, desvio padrão=3.9; 77% homens) foram comparados a um grupo controle com desenvolvimento típico, pareado por idade, sexo, dominância ocular, acuidade visual e compreensão de texto. A perimetria Frequency-Doubling Technology avaliou o limiar de sensibilidade ao contraste do campo visual periférico. O rastreador ocular Visagraph-III registrou os movimentos dos olhos durante leitura de texto.

          Resultados

          O grupo com dislexia do desenvolvimento apresentou piores limiares de sensibilidade no Frequency-Doubling Technology, com tamanho de efeito forte, do que o grupo controle. O grupo com dislexia do desenvolvimento apresentou mais olhos classificados com déficits na sensibilidade à ilusão de frequência duplicada do que o grupo controle. O grupo com dislexia do desenvolvimento apresentou pior habilidade motora ocular e no desempenho de leitura, revelado pela diferença entre os grupos em relação às fixações oculares, regressões, alcance de reconhecimento, taxa de leitura e eficiência relativa. Foi encontrada correlação significativa entre a sensibilidade ao contraste e as habilidades motoras oculares. Os participantes com boa eficiência relativa apresentaram uma sensibilidade ao contraste significativamente melhor do que os participantes com baixa eficiência relativa.

          Conclusões

          O grupo com dislexia do desenvolvimento apresentou desempenho inferior nas variáveis visuais relacionadas à função visual magnocelular ( i.e., perimetria de frequência duplicada e habilidades motoras oculares), quando comparado ao grupo controle pareado. Os profissionais precisam estar cientes da importância de investigar a visão dos pacientes com dislexia do desenvolvimento além da acuidade visual e incluir nos seus procedimentos diagnósticos instrumentos para avaliar o processamento temporal, com limiar de sensibilidade ao contraste.

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          Most cited references27

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          The current status of the magnocellular theory of developmental dyslexia

          John Stein (2018)
          Some people doubt that the concept of developmental dyslexia (DD) is useful at all because the phonological weaknesses seen in DD cannot be distinguished from those found in every person with poor reading skills, whatever their cause. Here I argue that true DD is characterised by poor temporal processing, hence impaired visual and auditory sequencing, that is caused by impaired development of transient/magnocellular (M-) systems throughout the brain. These deficits can be measured in order to distinguish the causes of the phonological weaknesses in DD from those causing similar deficits in other types of poor reading. Importantly this knowledge can be exploited to develop effective improvements in treatment. The evidence for impaired visual magnocellular function in many, if not all, people with dyslexia is now overwhelming; it is supported not only by psychophysical tests of M- function, but also by electrophysiological, eye movement, attentional, imaging, interventional and genetic findings. Analogously, auditory temporal processing is mediated by auditory transient, 'magnocellular', processing systems, and evidence is accumulating persuasively that this system is also impaired in dyslexics. I briefly introduce the idea that 'motor magnocellular systems' may also be impaired in dyslexia, then consider genetic, immunological and nutritional factors that interact to cause the impaired magnocellular phenotype. I then discuss why the dyslexic phenotype is so common by speculating about what strengths it might confer that would maintain the responsible genes in the human genome.
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            Are dyslexics' visual deficits limited to measures of dorsal stream function?

            We tested the hypothesis that the differences in performance between developmental dyslexics and controls on visual tasks are specific for the detection of dynamic stimuli. We found that dyslexics were less sensitive than controls to coherent motion in dynamic random dot displays. However, their sensitivity to control measures of static visual form coherence was not significantly different from that of controls. This dissociation of dyslexics' performance on measures that are suggested to tap the sensitivity of different extrastriate visual areas provides evidence for an impairment specific to the detection of dynamic properties of global stimuli, perhaps resulting from selective deficits in dorsal stream functions.
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              • Article: not found

              Explaining the sex difference in dyslexia.

              Males are diagnosed with dyslexia more frequently than females, even in epidemiological samples. This may be explained by greater variance in males' reading performance.
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                Author and article information

                Journal
                Arq Bras Oftalmol
                Arq Bras Oftalmol
                abo
                Arquivos Brasileiros de Oftalmologia
                Conselho Brasileiro de Oftalmologia
                0004-2749
                1678-2925
                Sep-Oct 2021
                Sep-Oct 2021
                : 84
                : 5
                : 442-448
                Affiliations
                [1 ] Laboratory of Applied Research in Neuroscience of Vision, Hospital de Olhos de Minas Gerais-Dr. Ricardo Guimarães, Belo Horizonte, MG, Brazil
                [2 ] Laboratory of Cognitive Processes, Graduate Program on Psychology: Cognition and Behavior, Universidade Federal de Minas Gerais, Belo Horizonte, MG, Brazil
                [3 ] Faculty of Psychology and Education Science, Universidade do Porto, Porto, Portugal
                Author notes
                [Corresponding author: ] Douglas de Araújo Vilhena. E-mail: douglasvilhena@ 123456ufmg.br
                Author information
                http://orcid.org/0000-0003-2670-7963
                http://orcid.org/0000-0002-5475-5375
                http://orcid.org/0000-0001-7600-855X
                http://orcid.org/0000-0002-5852-4320
                Article
                10.5935/0004-2749.20210069
                11878433
                34320103
                11264654-ea52-4955-b1ab-7ee231a50ee3

                This is an Open Access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

                History
                : 30 January 2020
                : 03 July 2020
                Funding
                Funded by: Capes
                Award ID: 001
                Categories
                Original Article

                dyslexia,reading,visual perception,vision disorders,oculomotor muscles,eye movements,dislexia,leitura,percepção visual,transtornos da visão,músculos oculomotores,movimentos oculares

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