Réponses évoquées par le nystagmus spontané

A digital programme of wave form recognition was applied to a nystagmogram so as to pave the way for an average chronotopographic study of the occipital EEG activity triggered by the start of the rapid stage of the nystagmus. The programme was used in a clinical case of congenital nystagmus associated with a visual deficiency (coloboma of the optic nerve), with the following results: (i) in the patient examined, no average evoked response was observed either with eyes closed or with eyes open in the dark; (ii) an average response of small amplitude was observed with eyes open centred on a homogeneous illuminated field; this response was reinforced (greater amplitude and more complex structure) by a patterned field (checkerboard); (iii) the response to nystagmus showed characteristics similar to those of lambda response in the same subject.

These results appear to confirm the conclusions of Bender and Shanzer (1964) according to which the calcarine activity in monkeys in response to experimental nystagmus is “light and vision dependent and correlates with the visual input and not with the oculomotor output”.

Differences in amplitude, latency, and structure between the various responses recorded in the patient examined (response to nystagmus, to appearance of lighted checkerboard, and lambda response) and the same responses in normal subjects are considered and discussed in relation to factors associated with visual deficiency.