Early onset nystagmus is seen in three main clinical situations. Firstly, in children with neurological disorders; secondly in children with afferent visual failure; and finally in congenital idiopathic motor nystagmus (CIMN). The main diagnostic dilemma is in differentiating CIMN from sensory forms of nystagmus in a child with nystagmus and a normal fundus . Sensory nystagmus may be associated with a number of disorders including CSNB (Sect. 9.3.2), retinal dystrophies, cone-system dysfunction syndromes, albinism and optic nerve abnormalities. Full-field ERGs can identify a retinal aetiology and, when combined with VEP recordings, may localise dysfunction to the level of the retina or optic pathways or exclude a sensory cause. Equally, exclusion of afferent visual pathway dysfunction may be an important contribution to management.
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