Using infra-red oculography, electro-oculography and fundus video-recordings, waveform characteristics (amplitude, frequency, waveform shape and foveation) were examined in over 150 individuals with congenital nystagmus. For many of the subjects the nystagmus exhibited marked variability in both space and time. The sources of this variability were explored and the state of attention of the observer was found to be a dominant factor. The waveform and precision of foveation were not found to be related to any one classification group (eg. albino or idiopathic).