Clemastine for Acute Optic Neuritis

Inclusion Criteria: * Patients diagnosed or suspected to have an acute demyelinating optic neuritis in at least one eye within 3 weeks from the onset of any visual symptom other than pain * Use of disease-modifying therapies is not a contraindication * Use of appropriate contraception during the period of trial (women) * Understand and sign the informed consent Exclusion Criteria: * Other major ophthalmologic diseases / concomitant ophthalmologic disorders (e.g. diabetes, macular degeneration, glaucoma, severe myopia, etc) * Disc hemorrhages in the qualifying eye * No light perception in qualifying eye * Simultaneous bilateral optic neuritis * Cotton wool spots in the qualifying eye * Macular star in the qualifying eye * History of significant cardiac conduction block * History of cancer * Suicidal ideation or behavior in 6 months prior to baseline * Pregnancy, breastfeeding or planning to become pregnant * Involved with other study protocols simultaneously without prior approval * Concomitant use of any other putative remyelinating therapy as determined by the investigator * Serum creatinine \> 1.5 mg/dL; aspartate transaminase (AST), alanine transaminase (ALT), or alkaline phosphatase \> 2 times the upper limit of normal * History of drug or alcohol abuse within the past year * Untreated B12 deficiency (as determined by B12 serological assessments and metabolites including methylmalonic acid (MMA) and homocysteine) or untreated hypothyroidism * Clinically significant cardiac, metabolic, hematologic, hepatic, immunologic, urologic, endocrinologic, neurologic, pulmonary, psychiatric, dermatologic, allergic, renal, or other major diseases that, in the PI's judgment, may affect the interpretation of study results or patient safety * History or presence of clinically significant medical illness or laboratory abnormality that, in the opinion of the investigator would preclude participation in the study. * Positive for NMO antibody discovered within the first 2 weeks after randomization.