A Proof-of-Concept Study to Correlate Retinal Nerve Fiber Layer Changes in Patients With Multiple Sclerosis Treated With Natalizumab or Interferon Beta 1-a

Inclusion Criteria: * Diagnosis of RRMS. * Patients with unilateral AON consistent with Multiple Sclerosis (MS). * Treatment with intravenous methylprednisolone (IVMP) at 1gm daily for three days after the onset of AON, without a taper, and completed within 14 days of the AON symptom onset. * Age 18-55 years. * Expanded Disability Status Scale (EDSS) 0 to 5.0. * Understand and sign informed consent. Exclusion Criteria: * History or presence of progressive multifocal leukoencephalopathy (PML). * Diagnosis of Primary Progressive Multiple Sclerosis (PPMS) or Secondary Progressive Multiple Sclerosis (SPMS). * Immune-compromised in the judgment of the Investigator. * History of or presence of clinically significant medical illness or laboratory abnormality that, in the opinion of the investigator or Sponsor, would preclude participation in the study. * Concomitant ophthalmologic disorders (e.g. diabetes, macular degeneration, etc). * Previous history of severe disc edema, hemorrhage, or \> 1 confirmed optic neuritis (ON) with the most recent ON symptom onset being less than 12 months ago. * Previous treatment with \> 1 Disease Modifying Therapy (DMT). * Previous treatment with investigational products for MS, immunosuppressant or cytotoxic therapy. * Previous treatment with TYSABRI® * Women who are not postmenopausal, surgically sterile, or willing to practice contraception. * Women pregnant, breast feeding, or planning to become pregnant. * Involved with other study protocol simultaneously without prior approval. * Determined not suitable for study participation by Investigator and/or Sponsor.