Assessment of nystagmus.

The assessment of a child with nystagmus involves first of all ensuring that the observed eye movement disturbance is genuine nystagmus rather than one of the stimulating disorders, particularly opsoclonus. Rather than a rhythmic to and fro oscillation as seen in nystagmus, children with opsoclonus demonstrate bursts of rapid (saccadic) eye movements that are multidirectional (horizontal, oblique, and vertical) and often distressing to the child. While such a disturbance of eye movements may be entirely normal in the first two to three months of life,' and should settle spontaneously, its persistence or appearance in an older child may denote the presence of an otherwise occult neuroblastoma2 and requires appropriate investigation. Childhood nystagmus has been the subject of intensive investigation and the underlying pathophysiology has recently been reviewed.3 However, using a simple clinical paradigm it is possible to arrive at an accurate assessment in most cases without recourse to detailed eye movement recording. It is traditionally divided into 'congenital' and 'acquired' forms, with the term congenital being somewhat loosely applied to nystagmus appearing in the first two to three months of life. Because of this imprecise usage, a recent review has recommended abandonment of the term congenital in favour of 'early onset nystagmus'.4 As yet this is not established in our literature, and will not, therefore, be used in this annotation. The congenital form of nystagmus (incidence 1/6550 live births) may in turn be subdivided into sensory deprivation nystagmus in which a disturbance of vision is the primary defect, and congenital idiopathic nystagmus in which there is no underlying disturbance ofthe afferent visual pathways. Of those children presenting to a department of paediatric ophthalmology with nystagmus, the great majority will have sensory deprivation nystagmus.5