Opsomyoclonus is encountered as C/F of -
"At least 50% of children with opsoclonus-myoclonus have an underlying neuroblastoma." - Harrison
Opsoclonus-Myoclonus Syndrome 

Opsoclonus is a disorder of eye movement characterized by involuntary, chaotic saccades that occur in all directions of gaze; it is frequently associated with myoclonus and ataxia.

Causes of Opsoclonus-myoclonus 

Idiopathic
Cancer-related (paraneoplastic)


Cancers associated with opsoclonus-myoclonus are usually lung and breast cancers in adults and neuroblastoma in children.
Meningioma
Neuroblastoma
Neurofibromatosis
Excision