Abstract
Developmental dyslexia affects around 5-15% of the population and has a heterogeneous aetiology. Optometric disorders are more prevalent in dyslexic populations but the relationship be- tween eye movement control and dyslexia is not well established. In this study, we investigated whether children with dyslexia show saccadic or fixation deficits and whether these deficits are related to deficits in visual acuity and/or accommodation. Thirty-four children with and without dyslexia were recruited for the project. All participants had an optometric examination and performed a saccade and fixation experiment. We used two eye movement paradigms: the step and the gap task. Eye movements were recorded by an infrared eye-tracker and saccade and fixation parameters were analysed separately. Saccadic latencies, premature saccades, and directional errors were similar between children with dyslexia and typically developing children. In contrast, fixations were significantly less stable in the dyslexic group. Neither saccades nor fixations were associated with deficits in accommodation or visual acuity. Children with dyslexia showed no difficulties in saccadic performance, but their fixation stability was reduced compared to the control group. The reduced fixation stability can be explained by general deficits in the cognitive processes that underpin eye movement control, that have also been found in other neuro-developmental disorders.
Highlights
Developmental dyslexia is a prevalent condition affecting about 5-15% of the population (Heim et al, 2008; Helland et al, 2011; Schulte-Korne, 2010; Shaywitz et al, 2006)
There was an increased prevalence of hyperopia and accommodation insufficiency in the developmental dyslexia (DD) group compared to the typically developing children (TD) group, no single optometric measure was significantly different between groups, for details see (Vikesdal et al, 2020)
This study found no difference in saccadic parameters between children with and without dyslexia
Summary
Developmental dyslexia is a prevalent condition affecting about 5-15% of the population (Heim et al, 2008; Helland et al, 2011; Schulte-Korne, 2010; Shaywitz et al, 2006). A child with developmental dyslexia (hereafter dyslexia) struggles with word recognition, spelling and word decoding, and finds reading demanding (Bishop & Snowling, 2004). It is important that children with dyslexia are identified quickly and provided with effective interventions to prevent disruption to academic development (Bishop & Snowling, 2004). In Norway, dyslexia is commonly diagnosed around the age of 10–11 years, which is when the importance of learning through text increases (Morken & Helland, 2013). While efforts have been made to identify children at an earlier age, there is currently no program for early detection or intervention for at-risk children (Helland et al, 2011). There is no consensus on how to assess dyslexia and there is a lack of valid screening tools as well as a “gold standard” for diagnosis (Nergård-Nilssen & Eklund, 2018)
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