Chapter 8

Introduction

The most common forms of nystagmus in infancy and childhood differ clinically and pathophysiologically from adultonset nystagmus. Acquired nystagmus in both childhood and adulthood may often be associated with neurological lesions involving the vestibular and ocular motor pathways in the brainstem and/or cerebellum. On the basis of the clinical and electrophysiological characteristics of the nystagmus and any associated neurological signs or symptoms, neurotopical localization can often be inferred and then confirmed by neuroimaging.

The initial evaluation of pediatric nystagmus is simplified by the fact that most affected children have either infantile nystagmus or latent nystagmus. The clinical appearance of infantile nystagmus usually distinguishes it from the rarer forms of pediatric nystagmus caused by neurologic lesions. Children with this condition frequently present with a head turn, which is used to maintain the eyes in the position of gaze of the null point (position of minimum nystagmus). Oscillopsia is almost never spontaneously reported in infantile nystagmus, but can sometimes be evoked by having patients look away from their null position. Head oscillations, which can also be part of the infantile nystagmus syndrome, are not used as the strategy to improve vision except in those rare patients with abnormal gain of their vestibuloocular reflex.

Infantile nystagmus can occur in association with congenital or acquired defects in the visual sensory system (e.g., albinism, achromatopsia, congenital cataracts, optic nerve hypoplasia). Accurate, repeatable classification and diagnosis of nystagmus in infancy are best accomplished through a combination of clinical and motility findings; in some cases, the latter are indispensable for diagnosis. Infantile nystagmus may result from abnormal “cross-talk” from a defective sensory system to the developing motor system at any time during the sensitive period of the motor system. The primary ocular motor instability underlying infantile nystagmus is the same, but its clinical and oculographic expression is modified by both initial and final developmental integrity of

all parallel afferent visual system processes. The cause and precise mechanism of infantile nystagmus have not been elucidated.

Visual loss should be highly suspected in any infant or toddler with the onset of nystagmus after early infancy because mild-to-moderate visual loss may not be readily apparent in the preverbal years. If a child with nystagmus has suspected visual loss but a normal ocular examination, an afferent system and a neurological evaluation are necessary because retinal dysfunction may be detected even in the absence of pigmentary degeneration. Optic nerve dysfunction is usually recognizable ophthalmoscopically by the presence of optic atrophy or hypoplasia. In contrast, underlying retinal disorders are often clinically occult and may be identifiable only through electrophysiological testing. Because infantile nystagmus is often an epiphenomenon of bilaterally decreased visual acuity, the identification of infantile nystagmus should be viewed as the initial step in the diagnostic evaluation. Determination of the presence or absence of an associated underlying sensory system visual disturbance is important, as it may be present in at least 50% of patients with infantile nystagmus.279

An inherent problem that vexes the diagnostic interpretation of pediatric nystagmus is that infantile nystagmus cannot be definitively distinguished from the manifest form of latent nystagmus without eye movement recordings. This problem renders the clinician less able to categorically establish the diagnosis of infantile nystagmus unless the patient has a clinical picture of latent nystagmus and fixes with the preferred eye in adduction (i.e., a patient with a right head turn fixes with the right eye and has a “latent” component to the nystagmus). Most examiners necessarily rely on time-honored clinical parameters, despite the inherent uncertainty that the clinical examination provides.279

The most common diagnostic error in the evaluation of infantile nystagmus is the acquisition of neuroimaging studies in the child who is otherwise neurologically normal. We continue to be impressed by the fact that parents of the child with infantile nystagmus so often arrive for neuro-ophthalmologic consultation with negative neuroimaging studies in hand.