Transient pattern visual evoked potentials in children with Down's syndrome

Visual acuity and contrast sensitivity are lower in children with Down's syndrome than in those developing normally. In many cases, this difference might be accounted for by the relatively high incidence of ocular abnormalities (including refractive error and strabismus) in Down's syndrome. However, abnormal spatial vision persists in children with Down's syndrome in the absence of ocular abnormality, suggesting that abnormal retino-cortical visual processing explains reduced visual function in this group. The aim of the present study was to assess retino-cortical function in children with Down's syndrome by recording transient visual evoked potentials (VEPs) in response to pattern stimuli. Responses from children with Down's syndrome were compared with those recorded from children developing normally. Response latency is similar in the two groups, but morphology differs, with the N75 component being clearly present in the normal responses, but diminished or undetectable in responses from children with Down's syndrome. Our findings may suggest a cortical abnormality specific to the source of the N75 component of pattern-reversal achromatic VEPs.