• Patients with a history of MS with anterior visual pathway involvement and longer than 6 months after presentation with ON or an acute demyelinating event/relapse

• Age 10 year to 25 years and 11 months

• Latency delay \> 115 milliseconds on baseline full-field transient pattern reversal VEP in at least one eye (electrophysiological evidence of demyelination) or \> 10 milliseconds difference between eyes, or Retinal Nerve Fiber Layer (RNFL) thickness on OCT of \< 90 µm in at least one eye or an inter-eye difference in the RNFL of 10 µm or more

• Retinal Nerve Fiber Layer (RNFL) Thickness on baseline OCT ≥60 µm

• If on an MS disease-modifying therapy, no changes in the therapeutic agent or dosing in the 6 months prior to study initiation

• No significant renal or liver abnormalities

• Expanded Disability Status Scale (EDSS) 0-6.0 (inclusive)

• Has either English as his or her native language or English comprehension needed to complete the neuropsychological testing

• Meet criteria for adequate organ function requirements as described below:

⁃ Adequate renal function defined as:

⁃ Creatinine clearance or radioisotope glomerular filtration rate (GFR) \> 70 mL/min/1.73 m2 or serum creatinine based on age/gender as follows:

⁃ Range Serum Creatinine Level (µmol/L): Age 5 to \<12 years (male)=25-50, Age 5 to \<12 years (female)=25-50; Age 12 to \<15 years (male)=37-67, Age 12 to \<15 years (female)=37-67; Age 15 to \<19 years (male)=51-89, Age 15 to \<19 years (female)=40-69; Age ≥19 years (male)=58-110; Age ≥19 years (female)=46-92

⁃ Adequate liver function defined as:

⁃ Total bilirubin \< 1.5 x upper limit of normal (ULN) for age SGOT (AST) or SGPT (ALT) \< 1.5 x upper limit of normal (ULN) for age