Visual Dyslexia: Towards an Operational Definition from a Correlational Study


Carlo Aleci, Elena Belcastro


Annals of Eye Science, 2020 |


Background: Aim of the study is to provide an operational definition of “visual dyslexia” referred to a particular subgroup of dyslexics characterized by x,y anisotropic perception of the visual space, or unstable ocular dominance, or abnormal binocular interaction, and who benefit from increased interletter spacing. The working hypothesis of this investigation is that in dyslexic children who show the abovementioned alterations the correlation between reading rate and interletter spacing is a marker of visual involvement, and supports a causal role of these visual-perceptive alterations in their reading problems.

Methods: based on the results obtained by three psychophysical tests devised on purpose, a group of 193 school-age disabled readers with normal visual acuity and no significant co-morbidities has been classified into four different classes: no visual-perceptive sample, anisotropic sample, abnormal binocular interaction sample and unstable dominance sample. To test for the working hypothesis, the absence of the visual marker has been verified in the no visual-perceptive sample and its presence has then been investigated in the remaining classes.

Results: The non visual-perceptive class was negative to the visual marker. In the other classes the average reading rate of words and non-words improved as a function of the distance between characters (anisotropic sample: r2=0.51 and 0.43, p=.01 and .02 respectively; abnormal binocular interaction sample: r2=0.47 and r2=0.57, p= .02 and .007 respectively; unstable dominance: r2=0.43, p= .02 at non-words). Yet, individual analysis revealed that the marker was present no more than 23% of subjects with increased anisotropy, in 50% of unstable dominants, and in only 12% of patients with abnormal interocular inhibition.

Conclusions: even if on a population scale this line of investigation seems able to provide an operational definition of “visual dyslexia”, the individual detection of the “visual dyslexics” requires methodological improvement.


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