Ocular motor apraxia (OMA) is the absence of, or a defect in, the control of voluntary purposeful eye movement. Children with this condition have difficulty moving their eyes in a desired direction. In other words, their saccades (the normal, quick, simultaneous movement of both eyes in the same direction) are abnormal. Because of this, most patients with OMA have to turn their head in order to follow objects in side gaze. They must utilize a head thrust to compensate for this inability to initiate horizontal eye movements away from the straight-ahead gaze position. Typically, vertical eye movements are unaffected.
The source of OMA is in the brain. The process of initiating eye movements is a complicated neural pathway involving many different structures. Neuroimaging with magnetic resonance imaging (MRI) is commonly performed when evaluating OMA. Findings may be normal or may reveal poor development of regions of the brain, in particular the corpus callosum, cerebellum, and/or fourth ventricle.
Extensive investigations sometimes reveal no associated developmental issues. However, children with OMA often have developmental delays and can possess low muscle tone (hypotonia). Speech, reading, and motor delays are common even when neuroimaging studies are normal.
The etiology of OMA is usually not known. However, the condition is sometimes attributed to insults occurring either during the perinatal period or the first 6 months of life. Such central nervous system insults may include perinatal hypoxia, meningitis, periventricular leukomalacia, cerebral palsy, septicemia, anemia, herpes encephalitis, and seizure disorder.
Sometimes OMA can be seen in patients with underlying conditions. A wide range of clinical entities have been reported in children with OMA. These include agenesis of the corpus callosum, Joubert syndrome, Dandy-Walker malformation, microcephaly, hydrocephalus, vermis hypoplasia, porencephalic cyst, megalocephaly, Krabbe’s leucodystrophy, Pelizaeus Merzbacher disease, Infantile Gaucher disease, GM1 gangliosidosis, Infantile Refsum’s disease, propionic acidemia., ataxia telangiectasia, Bardet-Biedl syndrome, vermis astrocytoma, vermis cyst, carotid fibromuscular hypoplasia, Cornelia de Lange syndrome, and microphthalmos.
The genetics of OMA are not well understood and may be multifactorial. Isolated OMA is generally considered non-hereditary and would not be associated with an increased risk of siblings or other family members developing this condition. However, a number of genetic mutations have been identified which cause OMA in addition to other clinical features. Siblings would be at increased risk of developing the condition in these cases, but the inheritance patterns can be variable.
There is no specific treatment for OMA. However, if a child has OMA, parents should be cognizant of potential developmental delays that can be associated with this condition, so that if present, therapies may be started sooner rather than later. Serial ophthalmologic examinations are recommended to monitor for other eye problems that can be associated with OMA.
There are few reports of the long-term prognosis of children born with OMA. The head thrusts associated with OMA typically diminish over time, but tend not to completely disappear. This may represent a true improvement in the disorder or be an adaptive compensatory mechanism to mask the head thrust.
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