OMA, also known as infantile-onset saccade initiation delay, is characterized by an inability to initiate volitional horizontal eye movements.[1,2] American ophthalmologist David Cogan first described the condition in 1952 when he published an account of four children who used horizontal head thrusts in order to shift their gaze. He called this clinical sign ocular motor apraxia because of its similarity to the ocular and head movements observed in adults with lesions in the frontal or parietal eye fields. Several individuals in the field have raised objections to the current terminology because the term "apraxia" refers to a wide spectrum of disorders that include the inability to perform a skilled or learned act rather than a primary motor or sensory deficit.[3,4,5] For example, it has been shown that acquired ocular motor apraxia can occur after bilateral frontoparietal infarcts. Nonetheless, it should be noted that pediatric OMA is a congenital neurologic condition with an absence of volitional horizontal saccades while reflexive saccades, smooth pursuit, and vertical saccades are often preserved.
Presenting Symptoms and Differential Diagnosis
Infants with this condition may often present with concerns that they do not have vision because they don't seem to follow objects with their eyes. The presence of compensatory head thrusts becomes obvious after head control develops. In order to compensate for oculomotor abnormalities, children may blink in order to break fixation and then overrotate their head beyond their focal target. Because of the preserved vestibulo-ocular reflex, the eyes deviate in the opposite direction and align toward the target.[2,7] In addition, the patients display an irregular fast phase during optokinetic nystagmus.[8,9]
Other conditions that have been described with OMA include developmental delay, hypotonia, incoordination, ataxia, and ataxia telangiectasia. The blinking and head thrusts often improve with age but do not completely disappear, and they can become more obvious in adults in stressful situations.[2,10] OMA is most often described as idiopathic, although examples of both recessive and dominant phenotypes have been described in the literature.[11,12,13] In one study, OMA was associated with deletions in the NPHP1 gene, resulting in juvenile nephronophthisis type 1, an autosomal recessive kidney disease.
The pathophysiology of OMA is unclear. MRI imaging studies may be completely normal or involve a range of abnormalities that most often include the cerebellum. The molar tooth sign is the appearance of elongated superior cerebellar peduncles in an axial section of the brain, giving the midbrain the look of a molar tooth. The molar tooth sign was initially described in Joubert syndrome, a developmental midbrain/hindbrain malformation that clinically presents with the impairment of both horizontal and vertical saccades. This radiologic phenomenon is not only associated with OMA but also with a number of other disorders, such as nephronophthisis and hepatic fibrosis.
Management, Follow-up, and Prognosis
The abnormal eye movements and head movements improve over time, although they do not completely resolve. Initial management of children with OMA should include radiologic studies with MRI to rule out Joubert syndrome or other congenital neurologic abnormalities.
Presently, no specific treatment or cure for OMA exists. Close follow-up with an ophthalmologist is recommended to help screen for potential associated symptoms. Because of the association with developmental delay, ataxia, hypotonia, and other brain abnormalities, MRI imaging is recommended. Referral and follow-up with a pediatric neurologist may be appropriate. If patients begin to have symptoms of renal involvement, such as excessive thirst and urination, referral to a nephrologist may be warranted. Although a number of cases are idiopathic, a family history of OMA may indicate being seen by a geneticist. Referral for occupational therapy, physical therapy, speech therapy, and early interventional services may be appropriate depending on the extent of the associated symptoms.
Medscape Ophthalmology © 2015
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Cite this: Jessica L. Hauser, Kimberly G. Yen. The Child With Abnormal Head Movements - Medscape - Oct 27, 2015.