Treatment of Pendular Nystagmus in OPT

Inclusion Criteria: * Patients with a diagnosis of oculopalatal tremor (OPT), following a focal brainstem lesion. * All patients may present a chronic acquired pendular nystagmus due to OPT, observed over a period of 6 months. * All patients will be informed about the design and purpose of the study, and all will give their informed, written consent to the protocol, which may have been approved by the local ethics committee. * Age: above 18 * Able to understand the instructions * Having a health coverage * Able to sit down for 1 hour * Stable dosage of previous medications (beginning 3 weeks previously and terminating at the end of the trial duration), except gabapentin or memantine. * For women: efficient contraception during the experimental time and in the two month following treatment withdrawal. Exclusion Criteria: * Ophthalmological * Other ophthalmological disorder that could impair corrected visual acuity (Maculopathy, Retinopathy…) * Neurological * Ongoing seizure * Severe handicap that does not allow sitting down position for 1 hour * Suicidal behavior or risk * Treatment * Under memantine or gabapentin medication (these medications should have been stopped for at least 1 week for gabapentin and 3 weeks for memantine) * Under morphine, N-methyl-D-aspartate such as amantadine, ketamine or dextromethorphan * Steroid medication for a current relapse (beginning 3 weeks previously and terminating at the end of the trial duration * Known hypersensitivity to memantine or gabapentin * General * Unstable medical state * Patient with a galactose intolerance, a lapp lactase deficiency or glucose-galactose malabsorption * Moderate renal failure (creatinine clearance \< 50 mL/min on bioassay dated from less than one month) * Recent heart infarction (\<3months) * Unstable congestive heart insufficiency * Unstable arterial hypertension * Leucopenia (\<2500/mm3) * Transaminase increase (\>5 time normal values) * Pregnancy (on questioning) * Tutelage or any legal protection measure