Twenty-eight patients (14 females and 14 males aged between four and 34 years) with myelomeningocele and Chiari malformations were examined neuro-ophthalmologically at the Karolinska Institute, Huddinge University Hospital, Huddinge, Sweden. The Chiari malformation, determined with MRI, was type I in three patients and type II in 25. All had hydrocephalus; mild in 12, moderate in 13, and marked in three. Shunt procedures had been performed in 20. Spontaneous or gaze related nystagmus and abnormal optokinetic nystagmus were the most common disturbances of ocular motility. Horizontal gaze paresis occurred in 14 patients and vertical gaze limitations in nine, all in upward gaze. Horizontal nystagmus occurred in 17 whereas vertical nystagmus was uncommon and downbeat nystagmus was not observed. Strabismus occurred in 11 patients and esotropia was more common than exotropia. No signs of optic atrophy or other changes in the visual pathways were found. [1]

COMMENT. Downbeat nystagmus has been considered almost pathognomonic of the Chiari malformation but was absent in the cases in this study. A girl aged ten referred to me recently because of migraine headaches had downbeat nystagmus and a refractive error; the MRI was negative for Chiari malformation and brain stem auditory evoked responses were normal. Lennerstrand G et al have used the MRI to determine the correlation between disturbances of ocular motility and the degree of hydrocephalus, tactile plate deformity, and dislocation of the cerebellum and medulla oblongata in 28 patients with myelomeningocele 2. All patients had Chiari malformations. Strabismus and spontaneous nystagmus were related to the degree of hydrocephalus and to the amount of lower brain stem deformities. Convergence defects correlated with upper brain stem deformities.