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1.  Pharmacological tests of hypotheses for acquired pendular nystagmus 
Acquired pendular nystagmus (APN) occurs with multiple sclerosis (MS) and oculopalatal tremor (OPT); distinct features of the nystagmus have led to the development of separate models for the pathogenesis. APN in MS has been attributed to instability in the neural integrator, which normally ensures steady gaze. APN in OPT may result from electrotonic coupling between neurons in the hypertrophied inferior olivary nucleus, which induces maladaptive learning in cerebellar cortex. We tested these two hypotheses by analyzing the effects of gabapentin, memantine, and baclofen on both forms of nystagmus. No drug changed the dominant frequency of either form of APN, but the variability of frequency was affected with gabapentin and memantine in patients with OPT. The amplitude of APN in both MS and OPT was reduced with gabapentin and memantine, but not baclofen. Analyzing the effects of drug therapies on ocular oscillations provides a novel approach to test models of nystagmus.
PMCID: PMC3187918  PMID: 21951011
cerebellum; inferior olive; plasticity; learning; Guillain–Mollaret triangle; multiple sclerosis
2.  Changes in Dynamic and Kinematic Properties of Saccades in Ocular Myasthenia following Intravenous Immunoglobulin Treatment 
We studied the dynamics and kinematics of saccades in a patient with severe ocular myasthenia before and after treatment with intravenous immunoglobulin (IVIG). Before therapy, horizontal saccades were hypometric, but faster than similar-sized saccades made by normal subjects. During a 5-minute test period, saccades decreased in size (fatigue effect), but remained faster than those of controls. Listing’s plane of the eye with greater ophthalmoplegia was increased in thickness. After IVIG treatment, the range of eye movements improved, but saccades remained faster than those of controls. Also, no fatigue was observed and the thickness of Listing’s plane was reduced towards the normal range. Increased peak velocity, despite progressive hypometria due to fatigue, supports the hypothesis that the pale global extraocular muscle fibers are relatively spared in myasthenia. Involvement of other extraocular muscle fiber types leads to limited range of eye movements and an increase in the thickness of Listing’s plane.
PMCID: PMC3166887  PMID: 19645950
saccades; fatigue; pale extraocular muscle fibers; Listing’s plane
3.  Upbeat-torsional nystagmus and contralateral fourth nerve palsy due to unilateral dorsal ponto-mesencephalic lesion 
The central projections of the anterior semicircular canals are thought to be conveyed from the vestibular nuclei to the ocular motor nuclei in the midbrain by three distinct brainstem pathways: the medial longitudinal fasciculus, crossing ventral tegmental tract, and brachium conjunctivum. There is controversy as to whether upbeat nystagmus could result from lesions involving each of these pathways. We report a 52-year-old man who presented with a contralesional fourth nerve palsy and primary position upbeat-torsional nystagmus due to a small unilateral dorsal ponto-mesencephalic lymphomatous deposit. We postulate that the upbeat-torsional nystagmus was caused by involvement of the brachium conjunctivum, which lies adjacent to the fourth nerve fascicles at the dorsal ponto-mesencephalic junction, but we cannot exclude involvement of the crossing ventral tegmental tract. Our observations suggest that, in humans, excitatory upward-torsional eye movement signals from the anterior semicircular canals could be partly conveyed to the midbrain by the brachium conjunctivum.
PMCID: PMC2866066  PMID: 19645952
Upbeat Nystagmus; Torsional Nystagmus; Fourth Nerve Palsy; Pons; Mesencephalon; Brachium Conjunctivum

Results 1-3 (3)