Simultaneous pattern electroretinogram and visual evoked potential recordings in dyslexic children.

To help clarify the conflicting evidence of neurophysiologic abnormalities in children with reading problems (dyslexia), we examined pattern electroretinograms and visual evoked potentials to stimulation with checks of 24', 49' and 180', each at 5%, 42% and 100% contrast, in a group of dyslexic children and a group of normal (i.e., normally reading) children. Neurophysiologic difference between the groups was restricted to the visual evoked potential, which showed a significant prolongation of the P100 wave in dyslexic children at the highest contrast (100%) and the smallest checks (24'). There was no significant difference between normal and dyslexic children in the P50 and N95 pattern electroretinogram waves. These results support the assumption of a visual deficit in dyslexic children. However, they are not consistent with the evidence of an isolated deficit of the magnocellular function, which, theoretically, would cause more prominent visual evoked potential changes to lower contrast and the largest check stimuli.

Do visual neurophysiological tests reflect magnocellular deficit in dyslexic children?

To address the question of a possible magnocellular visual deficit in children with reading problems (dyslexia), we examined pattern ERG and VEP responses to stimulation with checks of 24', 49' and 180' in size and of 5%, 42% and 100% contrast level. Neurophysiological difference between children with reading problems and those without them was found confined to VEP which showed a significant prolongation of P100 wave in dyslexic children at highest contrast (100%) and smallest checks (24'). Pattern ERG was normal. These results support the assumption of a visual deficit in dyslexic children. However, they are not consistent with an isolated deficit of the magnocellular function, which, theoretically, would cause VEP changes to lower contrast and largest check stimuli.