Electronystagmographic studies with an attempt to quantify various parameters of congenital nystagmus are interesting although not conclusive clinically. This is due to the spontaneous variability of congenital nystagmus. A qualitative study (position and velocity) may be sufficient for clinical examination and treatment of congenital nystagmus. The quantification of the optokinetic response is also clinically difficult. This comes from the fact that various factors can affect the response; even healthy patients can have variable gain. However the optokinetic test, which compares the response to a nasotemporal and temporonasal stimulation, is useful. It enables us to identify patients who never had a visual binocular experience in their first year of life and who keep a directional asymmetry of the monocular optokinetic response.