To be eligible, patients must have a history of one or more episodes of previous demyelinating optic neuritis occurring in the setting of classic, adult-onset definite MS (clinically definite or laboratory-supported definite MS, or cranial MRI changes consistent with MS). In most cases, onset of MS will have occurred between the ages of 18 and 45. Patients must be younger than 50 years and must have apparently irreversible loss of visual acuity that meets the following criteria: