Unusual Eye Movements
Nystagmus in children often accompanies strabismus or is found in association with selected syndromes. Nystagmus is most often horizontal and comitant. A few unusual disturbances of ocular motility deserve increased notice.
Downbeat nystagmus is unusual in children. It is typically worse on lateral gaze and can reflect pathology at the cervicomedullary junction. The Chiari I malformation, increasingly recognized as a source of headache in children, involves herniation of the cerebellar tonsils into the foramen magnum. Eye movement disorders arise from cerebellar ectopia and lower brainstem distortion. Eye findings are frequently intermittent and include acquired esotropia and oscillopsia, typically associated with downbeat nystagmus. Associated features include occipital headache that worsens with Valsalva, ataxia, vertigo, disequilibrium, or dysphagia. Posterior fossa decompression can result in improvement in symptoms.
"Setting Sun" Sign
An infant with "setting sun" sign demonstrates lid retraction and a tonically downward deviation of the eyes. Mid-dilated pupils that constrict to light but not to accommodation to a near target and convergence retraction nystagmus are associated findings.
This exaggerated form of dorsal midbrain syndrome occurs in infantile hydrocephalus because the posterior commissure is stretched by an enlarged third ventricle or suprapineal recess. An enlarged head size, dilated scalp veins, and tense and bulging fontanelle are additional signs of hydrocephalus and/or shunt failure. Urgent neuroimaging is recommended. Other entities in the differential diagnosis include Marcus Gunn jaw-winking ptosis, neonatal thyroid eye disease, and cranial nerve III palsy with aberrant regeneration. Occasionally the "setting sun" sign in infants is benign without associated hydrocephalus. In these infants, versions are full and lid retraction is absent. Benign tonic downgaze often dissipates by 6 months of age.
Opsoclonus and Opsoclonus-Myoclonus-Ataxia Syndrome
Opsoclonus is a striking ocular motility disorder characterized by bursts of multidirectional high amplitude saccades.
Opsoclonus-myoclonus-ataxia syndrome (OMAS) is a constellation of opsoclonus, tonic muscle spasm, and inability to control trunk and limb movement. OMAS often presents in the second year of life. Speech problems, irritability, vomiting, sleep disturbance, and lethargy are also features of OMAS. Importantly, neuroblastoma is present in 50% of children with OMAS. The syndrome is a manifestation of the paraneoplastic syndrome that can occur with neuroblastoma. Neuroblastomas associated with OMAS tend to be more mature, with favorable histology, and prognosis for treatment is excellent. OMAS symptoms respond to steroids, immunosuppressants, and biologic agents, although a relapsing and remitting course is common. Despite control of OMAS manifestations with medications, affected children have long-term sequelae with delay in the areas of motor function, sleep, behavior, and speech.
Infant With Opsoclonus
Congenital Ocular Motor Apraxia
Infants with congenital ocular motor apraxia (COMA) seem blind for the first several months of life. Horizontal (but not vertical) voluntary saccade initiation is impaired and saccadic amplitude is decreased. Because pursuit in young infants is actually a series of hypometric saccades, young infants with COMA cannot follow an object of interest. Once head control is mastered, infants use a bizarre head thrusting behavior to redirect their gaze. Head thrusts recruit the vestibulo-ocular reflex to drive the eyes opposite to the direction of the head thrust, allowing the gaze to fall on the object of regard. Parents describe their child as looking out the sides of the eyes. With time, the head thrusts become more subtle and act to initiate saccades rather than recruit the vestibulo-ocular reflex. Most children with congenital COMA show some degree of delayed motor, speech, or cognitive development. COMA may be a feature of several neurometabolic diseases, most notably ataxia telangiectasia (Louis-Bar syndrome) and Joubert syndrome.
Child With Ocular Motor Apraxia Using Head Thrusts to Change Gaze Position
The child with voluntary nystagmus should not mislead the savvy ophthalmologist. Actually, the entity is saccadic oscillation rather than true nystagmus. Voluntary nystagmus is horizontal and comitant, often associated with convergence, and cannot be sustained for greater than 30 seconds. The patient experiences oscillopsia and decreased vision during the episodes. The only treatment necessary is reassurance as to the benign nature of the child's unique trick.
Child With Voluntary Nystagmus