Behaviour of the alpha rhythm in electroencephalograms of visually impaired children.

One hundred and thirty-eight electroencephalograms (EEGs) of 104 children with ocular visual loss were studied and the findings correlated with clinical information. Records of blind children without other neurological deficits did not contain posterior slowing or occipital spikes. The frequency, reactivity and regulation of alpha rhythm were affected only when vision was at the level of finger-counting. Therefore the EEGs of the majority of 'normal' visually impaired children showed normal alpha behaviour. Although most totally blind children's records lacked alpha, five had spontaneously appearing and disappearing alpha rhythm. The EEG is a valuable tool in the evaluation of visually impaired children, provided the findings are interpreted appropriately. The earlier theory that visual deprivation can cause electrical abnormalities over the visual cortex was not supported by these data.