['acute optic neuritis']
['placebo', 'biib033 100mg/kg']

        Key Inclusion Criteria:

          -  Must have participated in Study NCT01721161 and received at least 1 dose of BIIB033 or
             placebo, as per protocol, within 2 years (+ 4 months) from Day 1 of this study (2
             years from Week 32 or projected Week 32 visit, if the subject did not complete all
             visits in Study NCT01721161).

        Key Exclusion Criteria:

          -  Not previously enrolled in Study NCT01721161

          -  Subjects with recent kidney function, such as serum creatinine above upper limit of
             normal range, will not be allowed to receive administration of Gd but will otherwise
             be allowed to participate in the study, including magnetic resonance imaging (MRI)
             assessments not requiring the use of Gd.

          -  Female subjects must have had a recent pregnancy test and must not be breastfeeding
             prior to MRI assessments with Gd.

        NOTE: Other protocol defined Inclusion/Exclusion criteria may apply.
      